IAEA-TECDOC-368
BEHAVIOUR OF LONG-LIVED RADIONUCLIDESASSOCIATED WITH DEEP-SEA DISPOSAL
OF RADIOACTIVE WASTESREPORT OF A CO-ORDINATED RESEARCH PROGRAMME
ORGANIZED BY THEINTERNATIONAL ATOMIC ENERGY AGENCY
1982-1984
A TECHNICAL DOCUMENT ISSUED BY THEINTERNATIONAL ATOMIC ENERGY AGENCY, VIENNA, 1986
BEHAVIOUR OF LONG-LIVED RADIONUCLIDESASSOCIATED WITH DEEP-SEA DISPOSAL OF RADIOACTIVE WASTES
IAEA, VIENNA, 1986IAEA-TEC DOC-368
Printed by the IAEA in AustriaApril 1986
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FOREWORD
The Agency sponsored this Coordinated Research Programme to improveknowledge of various long-lived radionuclides likely to be dumped in the deepsea. During 1981 the first steps were taken to organise the programme, and theprecise objects were;
1. To identify and quantify the factors which control the migration andchemical forms of long-lived radionuclldes in deep-ocean sediments.
2. To quantify the rate and degree of transport of the radionuclides fromsediments to overlying waters.
3. To improve knowledge of the dispersion of dumped waste from thedeep-sea to surface and other water bodies.
4. To determine the redistribution of radioactivity by burrowing organisms(bioturbation).
5. To develop quantitative estimates of radionuclide uptake by benthicorganisms and transfer through the marine food-chain.
During the period of the programme, meetings were held in Lisbon (8-12November 1982), Hamburg (24-28 October 1983) and Monaco (29 October -2November 1984).
If radionuclides can diffuse from a point where they are dumped in thedeep ocean to man, it is necessary to accumulate knowledge of the paths andtheir relative importance. This must be done for many isotopes, and the amountof research involved is therefore large. It necessarily involves prediction,since actual transfer to man from such dumpsites has not yet been demonstrated.
Because of the international character of such potential pollution,international investigation is appropriate.
The isotopes studied were mainly 238Pu, 239,240pUj 24lAm, 226Ra> 210pOj90Sr, 137Cs, 60Co, and 99Tc.
With sediments a knowledge of the way these isotopes distribute themselvesbetween the water and solid phase helps in predicting diffusion. This isusually considered in terms of a parameter known as "K ". However, there hasbeen some controversy whether that parameter is applicable when thesolid/liquid ratio is very high. One study in this TECDOC considers this andthe great importance of good phase separation in experimental studies. Someauthors describe the actual distributions and inventories of isotopes found insediments and in waters, while others describe work on how bioturbation hasprobably influenced those concentrations. Bioturbation seems to be rather moreimportant than previously emphasized, and more work will therefore benecessary.
When radionuclides enter the water phase, at least two obvious pathways toman exist; through material ingested by fish which are then caught, or throughthe water carrying the radionuclides to the coast where exposure could arisethrough other paths. Two authors describe concentrations of various isotopesin fish, one in various trophic levels of an ecosystem which is in relativelyshallow water, but contains high quantities of such radionuclides (weapontesting grounds in the Pacific) and another in a deepwater fish, which maylive relatively near a dumpsite.
As regards speciation much work remains to be done, but some useful dataare supplied which describe amounts of various forms of isotopes includingthose attached to particles in the oceans.
Investigations on areas even closer to man are described by some workers,who analysed littoral biota, such as mussels, for various radionuclides, andfinally a paper gives a perspective on likely levels of ultimate transfer toman, or risk.
During the three years of this coordinated research programme the state ofknowledge has advanced significantly in this area, and this document providesa review of the progress.
The authors discussed each others' contributions at the last meeting heldin Monaco, but this should not be construed as meaning they have all reviewedin detail the final form of contributions as presented here.
CONTENTS
Actinide sorption on marine sédiments ............................................................................ 7J.J.W. Higgo, L. V.C. Rees, D.S. Cronan
Fallout plutonium in Western North Pacific sédiments .................................................... 27H.D. Livingston
Plutonium distribution in marine and riverine sediments from La Spezia area(Ligurian Sea) ................................................................................................................ 35R. Delfanti, C.D. Jennings, C. Papucci
The chemical behavior of long-lived radionuclides in the marine environment ................ 41D.N. Edgington, D.M. Nelson
Studies on behavior of long-lived actinides plutonium and americium in the Baltic Sea;effect of season, distribution coefficients in particulate matter and surface sediment .... 61S. Leskinen, T. Jaakkola, J.K. Mietfinen
Marine behaviour of long-lived radionuclides (fall-out) at the proposed disposal site ofradioactive wastes in Western North Pacific ................................................................ 73T. Miyamoto, M. Hishida, N. Shibayama, M. Shiozaki
Nordostatlantisches monitoring programm (NOAMP). An environmental study of thedeep layers of the North-East Atlantic ........................................................................ 81G.A. Becker, R. Berger, I. Bork, H. Heinrich, E. Mittelstaedt, H. Nies, U. Schauer
The behaviour of certain long-lived radionuclides in the marine environment .................... 101R.J. Pentreath, P.J. Kershaw, B.R. Harvey, M.B. Lovett
Biological mixing and radionuclide redistribution in marine sediments ............................ 115E.H. Schulte
Biogeochemical studies of long-lived radionuclides in marine environments .................... 119V.E. Noshkin, K.M. Wong, R.J. Eagle, T.A. Jokela
Intercomparison studies of transuranics in North Atlantic deep sea sediments from theNEAdumpsite ............................................................................................................ 129A. Aarkrog, H. Dahlgaard
Technetium distribution and accumulation in marine sediments and biota ........................ 133E.H. Schulte
Measurement of long-lived radionuclides in the Atlantic related to radioactive wastesdeep-sea disposal ............................................................................................................ 137A.O. Bettencourt, M.M. Bordalo Costa, P.P. Carvalho, G. Ferrador, G. Alberto
Studies on the bioaccumulation of radionuclides of long half-life in mussels in North-East of Spain ................................................................................................................ 145M. Montesinos del Valle
Long-lived radionuclides important in marine waste disposal ............................................ 149A. Aarkrog
ACriNIDE SORPTION ON MARINE SEDIMENTS
J.J.W. HIGGO, L.V.C. REES, D.S. CRONANImperial College of Science and Technology,London, United Kingdom
Abstract
Sorption experiments with Pu, Am and Np were carried out using deep sea sedimentscollected from near the North-east Atlantic dump site. Experiment times were aslong as 100 days and sediment concentrations ranged from a few tens of milligramsto a few tens of grams per litre because the aim was to model diffusion within thesediments. If R, has the same units as K but with no assumption of equilibriumthen the Am R was 10 , but that for Np only 600 for red clay and about 1000 forcarbonate sediment. For Pu (R, normally 1000) there was a decrease in R, with
-1sediment concentrations of greater than 10 mg 1 ascribed to carbonate complexation.Calculations showed that if R, is high, imperfect phase separation may easilyproduce artificially low apparent R, values. The effect of changing the oxidationstate of Pu was important. The results showed that if such isotopes in the form ofwaste were emplaced 20 m or more below the sediment surface, the amount ultimatelyreaching the surface would be negligible, at least for this clay and carbonatesediment .
1-. INTRODUCTION
The disposal of high-level nuclear waste in subseafloorsediments is under investigation in several countries as analternative to disposal on land. If cannisters containing thevitrified waste are buried in the sediments the main barrier tothe final emergence of the radioactive nuclides to the marineecosystem will be the near-surface sediments. How effective thesediments will be as a barrier will depend upon the extent towhich they interact with any nuclides that escape from the wastepackages. This paper is a brief summary of a series ofexperiments designed to study the interaction between theactinides amencium neptunium and plutonium and deep-seasediments. The work has been described in more detail inreferences 1-5.
The sea water/sediment system is extremely complex and inorder to assess the suitability of marine sediments as a barrierto radionuclide migration it was decided to adopt an empiricalapproach. Thus, a set of thirteen carefully selected sedimentswas contacted with sea water which had been spiked with thenuclide of interest under conditions as close as possible tonatural conditions and their sorption behaviour studied. Thesediments were never allowed to dry out after recovery from theseabed, the temperature was maintained at ^ C througnout theexperiments and natural sea water was used. No attempt was made,
however, to control the E and it was assumed that the effect ofpressure would be small. Because the actinides may exist inseveral oxidation states the oxidation state distribution wasdetermined at each stage of the experiments.
The samples were chosen to represent a wide variety ofsediments occurring in the deep sea. The calcium carbonatecontent varied from less than 21 to 89Z and X-ray diffraction wasused to identify the other components present. In addition tothe sediments containing calcium carbonate and various types ofclays, two manganese nodules were crushed and studied in the sameway as the other samples.
The reason for including these nodules in the study is thathydrous oxides of manganese and iron occur in virtually allsediments, both as discrete oxide particules and as partialcoatings on other minerals and it is likely that they exert aninfluence on the sorptive properties of the sediments which isout of all proportion to their concentration. The ion exchangecapacities of these oxides is large, but possibly more important isthe fact that they themselves participants in oxidation reductioncycles and evidence is accumulating that retention of actinidesin sediments is frequently the result of precipitation duringredox reactions rather than by ion exchange. All the sampleswere characterized as fully as possible to assess whether anyparticular property had an effect on the sorptive properities.Thus in addition to the mineralogical analysis, chemicalcomposition, surface areas and cation exchange capacities weredetermined.
The results of the sorption experiments are given in terms ofthe distribution ratio R defined asd
Concentration of a species on the solid aï time of measurementR u — "~—•—rr""1-'—"—- -~~~"—————™————————— " - —"——•—™———•————————--—.—————————-———-..- ——Concentration of the species in the liquid at time of measurement
the unit used being ml/g. This is an empirical ratio and unlikethe distribution coefficient, Kd, does not imply reversibility orequilibrium and no attempt is made to relate it to a specificsorption mechanism .
2. EXPERIMENTAL2.1 Sample Characterization
The mineralogy of the sediments was determined by X-raydiffraction and the elemental composition by inductively coupledplasma spectroscopy after fusing with LiÖO (ma^or elements) andby atomic absorption spectroscopy after digestion inHF/HNO /HC10 (minor elements). Surface areas were determinedby the simplified ethylene glycol monoethyl ether (EGME)procedure ' and cation exchange capacities were determined bythe caesium exchange procedure described by Beetem. The sodiumacetate method was also used on some samples and agreementbetween the two methods was found to be good.2.2 Determination of Distribution Coefficients
The batch partitioning exeriments were carried out as -far aspossible according to the method prescribed by Relaya in the'Task 4' Status Report. K values reported by differentlaboratories for similar or even the same materials tend todiffer widely and Relaya has emphasized the need forstandardization.
The temperature was kept at 4 C at all times and the seawater was filtered through 0.22u filters before use. In orderto ensure that representative samples were obtained sedimentswere mixed with sea water to form a slurry and samples weighingbetween 50 and 100 mg (dry weight) were transferred by pipettingwhile agitating into 50 ml Oakridge-type polycarbonate centrifugetubes. After an initial prewash in sea water they werecentrifuged for 90 minutes at 7000 rpm and the supernatediscarded.
Spiked sea water solutions were prepared by adding 1-2 ml ofthe tracer in acid solution to 500 ml sea water. The pH wasreadjusted to 8.2 with NaOH and the solutions left to equilibratefor several weeks. Immediately before use they were filteredthrough 0.22u filters and analyzed for tracer concentration. Thefinal concentrations in these spiked solutions were 1.8 x 10 Mor 1.8 a210~ M for Am = 2 X 10~ M for Pu and 3 X 10~ or1 X 1 0 M for Np. Even at these low concentrations the Am was not intrue solution. Thus, filtration of the more concentratedsolution through successive pairs of millipore filter papersshowed that about M of the total activity was in the size rangeO . J M to Dc22u and another 1Z was in the size range 0.025y-0 . 1 u .
Am, Np, Np and Pu were the isotopes used in thesorption experiment. Np concentrations were determined bycounting 5g portions of liquid in a Nal well-type scintillationcounter. Am, Np and Pu were determined by alphaspectrometry after extraction into TTÂ (2-thenoyltrifluroacetgne) dissolved in cyclohexane or benzene. Am,
Np and Pu were used as yield monitors. The oxidation statedistribution was determined before and after sorption using acombination of lanthanide fluoride precipitations and solventextraction with TTA. ' ' '
In the first set of experiments the solid/solution ratio waskept constant at 3.3g sediment/1 (on a dry weight basis). Laterit was found that this was a critical parameter and the resultsof a thorough investigation into the effect of varying solid/solution ratio are given in section 4.
3. RESULTS AND DISCUSSION3.1 Sediment Characterization
The results of the mineralogical and chemical analyses andof the surface area and cation exchange determinations are givenin Tables I and II. It can be seen that the samples fall intoseveral categories, viz:
1. Those high in calcium carbonate and containing minor"amounts of montmorillonite, quartz, and clay minerals. Thecalcium carbonate content of these samples ranges from 45Z to 802and, as many of the other variables show a direct relationship tothis value, the samples have been arranged in order of decreasingCaCO content.
2. Red clays. These were obtained from the mid-Atlantic ata depth of about 6000m. they are almost completely carbonatefree and contain quartz and various clay minerals. Although notdetected by X-ray diffraction, the chemical analysis suggests thepresence of 5Z-10Z amorphous iron oxy-hydroxides. Although thesurface area of these sediments is high the cation exchangecafccity is low.
IÜ4ÜO»K
IOS l
MV 65 l
626(J Nu 2
TAULI: iMiiKT.ilügy ot Sediments
Couijioïitioii
Sample Nu Major
10S3 Ukiu
M77 2Ü f .kilt
103W:r7k C ilun.
IUS d C ikiK
IOS4 (aluu
IOS 3 Cakiu
IOS2 Cik i iL
S7U2 Cjiuie.Qujn/
SU 1578 Srncunc (30 AQ'.i)
Minor
Qu ni/
K.iulllUk, llllli.'
SjllcCIHC elltuJIU
Qum/ K.iolmitcllllli, MotiliiUHilloimt.
MunimonllointcllliicK loliniic
Qiuiu, KaüliuiiL'lllue
Quail/, lllnuMumnioi illoimc
Illuo
Tr.ice
Illiu, k Minute
H iLMuclaM. !^.ld^pai
Qujru
Mi\cil |j>cr uilonte
Fc Ox)liyJroxidcj(« lu'.')SIÛT as .miurpliuui M!U.J
Quai u
kaolmiu
Sir fKiiilcTodorokiiL
AmuiphuUiMil mil I c
K.iolimteS l l K v . t l l C
f L u.\)li)dru\uli.i
QUJU/
Pô uxyli) dioxuloï
QuarU
A - MiiO)
Table 2- Chemical Composition of the Sediments.SampleHoIOS-3
M77-20
10399=7K
IOS-6IOS-4
IOS-5IDS 2
S 702
SH 1576
10400'8t!
IOS-1
MV 65 1
6269 Ho 2
CaCO Si: J l69 07
88 22
85 9 3
73 1 9
69 27
59 33
50 3 6
45 524 12 0
3 246
<? 7 7
_
Ft2
0 6
1 7
i a1 .6
i a2.3
2 5
3 114 6
5 0
5 3
2 2
13 7
HnZ
0
0
0
0
0
0
0
04
0
D
32
16
05
12
10
09
07
13
03
14
3
32
3l
9
B
AlZ
0 85
1 4
3 4
2 4
3 0
3 64 6
5 0
2 0
8 8
5 E
2 2
1 7
Mg1
0 18
-
0 73
D 5
0 57
0 76
1 0
-
-1 68
1 E
-
Na2
0
0
0
0
0
0
0
0
0
0
0
-
55
20
88
38
55
4044
44
70
63
85
Kl
0
11
2
0
01
1
1
0
2
2
--
31
32
4
66
96
10
30
13
34
5
S
Hlppm
20
2t
-
35
32
4950
165
555
-109
1800
4E80
Cuppm
68
297
-
90
90
92
6963665
-167
1200
1560
Znppm
44
109
E5
75
87
10169
435
-
137
1340
680
Tlppm
150
680
1800
1200
1500
2200230025001100
5500
-
--
Pppm140GO
250
310
190
330
500
430340
E80
690
--
Pbppm
10
8
-
<5
<5
2020
9
75
-30
22
760
CECHEq/tOOg
7
7
17
19
17
43
31
20124
43
45
100
82
m /g24
30
85
54
G3
S8
131
97396
190
199
95
340
10
3. Manganese nodules, 6269 No.2 is high in amorphous ironand manganese hydroxides whereas MV 651 is composed mainly of theminerals oirnessite and todorokite.
4. SH 1578, a smectite rich sediment containing amorphoussilica and iron oxy-hydroxides.
3.2. Distribution Ratios3.2.1 Americium and Neptunium.
Figures 1-4 show how the distribution ratios varied with time.For all the sediments studied they were > 10 for americium. Neptuniumdistribution coefficients were more variable, red clay givingthe lowest values and the iron and manganese rich samples thehighest. Apart from one red clay, all the neptunium distributioncoefficients were > 10 . Conditions used were relativelyoxidizing and under more reducing conditons R are likely to beeven higher. This means therefore that if transport is mainly bydiffusion it would take Np about 10 years (50 Np-237 half lives)and Am about 10 years (10 Am-241 half lives) to pass through30m of sediment. Americium would therefore certainly neverreach the sediment/water interface and neptunium is unlikely topose a significant hazard. Provided, therefore, that the otherproperties are satisfactory, all the sediments studied (with thepossible exception of the red clays for neptunium) should formexcellent barriers to the migration of both these nuclides.
It was found that both before and after sorption theneptunium was in the V oxidation state. Americium waspresumably in the III state.
The reactions for Np appeared to be reversible [with thepossible exception of the Fe-Np reaction) but desorption R forAm are an order of magnitude higher than adsorption R . Thisapparent difference between sorption and desorption R may meanthat the sorption/desorption reaction is irreversible or it may bedue to the presence of a poorly sorbed species in the sorptionexperiments.
3.2.2 Plutonium: Figure 5 shows how the distribution ratio fortotal plutonium changed with time and it can be seen thatalthough sediments absorbed plutonium at different rates thefinal overall R was > 10 for all sediments after 12 days.
Figure 6 snows how the concentration of the variousoxidation states changed with time. At the beginning of theexperiment approximately 722 of the Pu in the initial spiked seawater was in the oxidised Pu(V + VI) forms. This agrees wellwith the values found by Nelson and Lovett for surface waters inthe Irish Sea. Thus, although the Pu concentration in this spikedsea water was roughly three orders of magnitude higher than inthe Irish Sea (3.1 x 10~ M as compared with 6.7 x 10~ M) theoxidation state distributions were similar. When sediment wasadded to this sea water the concentration of reduced P u ( 1 1 1 + IV)dropped much more rapidly than the concentration of Pu(V + VI).Thus for sample (10400 8K) the concentration of Pu ( 1 1 1 + IV)dropped by more than a factor of ten during the first hour,whereas after that time the Pu(V + VI) was still more than twothirds of its original value. It is fairly meaningless tocalculate distribution ratios for individual oxidation statesbecause there may be interchange between them but it isinteresting to compare R after one hour and to note that forPuUII + IV) it was 3000 as compared with 50 for Pu (V + VI).
11
With time the oxidised Pu(V + VI) was also very efficientlyremoved from solution. In fact after 102 days there was morereduced than oxidised Pu in solution for all the samples. It isimpossible to tell whether the Pu-V is adsorbed as Pu-V orwhether it is reduced during or before sorption but it is clearthat it is the rate of sorption of Pu-V which governs the rate atwhich the overall R increases with time. It is probablysignificant that there is a strong correlation between the rateat which Pu-V is removed from solution and the Np distributioncoefficient. This is illustrated in Figure 6 where the Np Rare written next to the corresponding graphs showing the rate atwhich the Pu-V concentration decreases during 22 hours. Thisfigure also illustrates the dramatic difference in the rates ofsorption.
If one assumes that removal from solution is accompanied byreduction then one can rank the sediments in order of reducingability, the order being SH 1578 > 10399 7K > 10400 8K. So,although the range in final distribution coefficients was notlarge, the rate at which Pu was adsorbed by the differentsediments varied significantly Thus the smectite, SH 1578,adsorbed 982 of the total Pu within the first 22 hours whereasthe red clay and the carbonate-rich sediment adsorbed 602 and 802,respectively, during the same period. This rate appears to berelated to the ability of the sediments to reduce plutonium fromthe Pu-V to the Pu-IV form.
Desorption distribution ratios were five to ten timesgreater than sorption distribution ratios and the proportion orreduced plutonium in solution was much the same as at the end ofthe sorption period. To a certain extent the high desorptiondistribution ratios may be explained by the presence of some non-sorbable spieces (e.g. organic complexes or micro-plarticulatesthat were not removed during phase separation) which lowers theobserved sorption Rd more than the desorption Rd. However,differences of this magnitude probably indicate that thesorption-desorption reaction is, at least to some extent,irreversible.
Edgington, ' by comparing the K values reported in theliterature has ranked the actinides in order of decreasingdistribution coefficient as follows:
Th(_IV) = Pu(IV) = Am(III) > U(VI) » Np(V)This ranking was based on the results from a number of differentsediments studied under different conditions. As a result of thepresent work we now have a complete set of R values for Pu, Amand Np all determined under identical conditions and on the samesediments and these values for both sorption and desorption aregiven in Table 3. Included in Table 3, on the assumption thatTable 3 Relationship between distribution ratios and the rate at which Pu V is removed from
solution by the different sediments.
S ample
SH 1570
0393 IK
t O t O O O K
"Reducing Poweras indicated bypercent Pu Vremaining inSolution after
Ihr 2hr 30d
1 1 1 0 1
55 27 07
89 17 37
Distribution Ratio ml/g
Np
sorptionanddesorption
7 x ID3
3 x Id3
0 3 x ID3
Pu
Sorption desorption102 d
9 x 10* 1 x ID5
6 X 10* 2 x 1C5
5 X 10* 2 x I05
Am
sorption desorption58 d
t x 10 2 6 x 1 0
2 x 1C5 - 6 x 105
1 x ID5 - 6 x 105
12
this is a measure of the ability of the sediments to reduce theactinides, is the percent of Pu-V remaining in solution after thedifferent time intervals. Of course, this may not be a validassumption and thse figures may simply be an indication of therelative ability of the different sediments to adsorb pentavalentactinides.4. The Effect of Solid/Solution Ratio on the MeasuredDistribution Coefficient
In all the work described so far a solid/solution ratio of3.3 g/1 was used. However, in the disposal situation this ratiowill, of course, be much higher and it was decided to investigatethe effect of increasing this ratio. The results showed twoimportant effects. One, specific to plutonium on high-carbonatesediments has important implications from the waste managementpoint of view and the other which applies to all high Rd specieshighlights some of the problems associated with the determinationof distribution coefficients by the batch method.4.1 Plutonium on high-carbonate sediments.
Two sets of samples of the high-carbonate sediment, 1039 7Kwere shaken with sea water Which had an initial concentration of35000 Bq/1 (2.33 x 10~ M) Pu. The solid/solution ratioranged from about 0.002 to 0.2 (2g/1 - 200/1) and a series ofexperiments were carried out on them. Phase separation wasalways carried out by centrifuging for 90 mins at 7000 rpm.(5280g) followed by filtration through 0.22u nulipore filters.
The first set of sediments was 1} analysed after 24 daysand the distribution ratios calculated. 11) the supernateremaining after the first sorption was transferred to tubescontaining 0.1g quantities of fresh sediment and a seconddistribution ratio determined. 111) Fresh unspiked sea waterwas added to the loaded sediment and the desorption distributionratio was measured.
The second set of sediments was d) analysed after 29 days(exactly 5g of the solution phase removed) for reduced Pu(III +IV) and oxidised Pu(V + VI) as well as total Pu, (11) after 128days the solution phase was again analysed but this time theexcess solution was added to fresh sediment keeping the solid/solution ratio the same as in the original sorption experiments.
Table 4 shows the three sets of distribution ratios togetherwith the percent reduced Pu in solution after phase separation.It can be seen that for solid/solution ratios greater than about0.04 (40g/1) the distribution ratios were remarkably low {100 to200 ml/g instead of the usual >10 ml/g) and there was nosignificant increase in Rd as the contact time increased from 24to 128 days. Furthermore, at these high solid/solution ratiosthe plutonium in solution was virtually all in the oxidised (V +VI) forms. At low solid/solution ratios, on the other hand, theplutonium was mostly in the reduced (III + IV) forms anddistribution ratios were greater than 10 . For the two samplescontaining the least sediment the distribution ratio after 129days did seem to be significantly greater than after 29 days.
We thus have the situation that in carbonate sedimentsPlutonium behaves quite differently at high and lowsolid/solution ratios. The obvious explanation is that at highsolid/solution ratios carbonate complexes are formed which aresorbed less strongly than are Pu 0 * and Pu(OH)+ which are theforms in wgic|jgpl^onium exists in sea water in the absence ofsediment. ' ' No attempt was made to determine whether the
13
TabU 4 Pu Oxidation State Distribution During Sorption
InitialSea-water
3 1 x 10"nM
COin
Ii/i
ztr^
<J*en0
î£
0«•o
1 h22 h30 d
102 d
1 h22 h30 d
102 d
1 h22 h30 d
102 d
Pu-238 Concentration (Bq/1) during Sorption
Total
4356 ± 1421
1026 * 17188 ± 824 ± 224 i 2
2416 i 98855 ± 41
34 ± 320 i 1
2982 ± 8951724 ± 35
122 ± 1526 i 2
(III + IV)
1242 ± 120
103 i 336 ± 219 ± 217 ± 1
107 ± 1149 ± 219 ± 213 ± 1
128 ± 668 ± 417 ± 114 ± 1
3366 ± 144
1053 ± 31644 ï 3
2 4 ± 0 74 8 i 1 4
1983 ± 88897 ± 51
22 ± 26 ± 2
3011 i 1091589 ± 180
126 ± 68 ± 1
(II1+IV+V)
4656 ± 185
1022 ± 12989 i 221 ± 124 ± 2
2364 ± 709766 i 42
44 * 2520 i 2
2909 ± 1461345 ± 61
98 ± 924 ± 1
IV
1200 ± 138
90 ± 1046 * 220 ± 119 ± 1
80 ± 543 ± 218 ± 114 ± 2
64 ± 1465 ± 621 ± 217 ± 1
III
42 i 183
1 3 * 1 1-10 * 3- 1 ± 2- 2± 2
28 ±125± 31 ± 2
-li 2
64± 154± 7
-4i 2-3± 2
VI
.
--
1 5 i 0 60 3 i 0 3
-
1 4 * 0 50 9 * 0 3
-12 * 21 * 1
Rat io
V + VIIII + IV
2 7 * 0 3
10 2 i 3 11 2 * 0 10 1 t 0 040 3 i 0 1
19 i 218 ± 1
1 ±0 20 5 to 2
24 i 123 l 3
7 i 10 6 0 1
plutonium was in the V or the VI form but the fact thatneptunium did not behave in the same way indicates that we wereprobably dealing with Pu(VI) complexes, since neptunium has beenshown to be in the V form in sea water and in our laboratoryexperiments. ?This is in agreement with the predictions ofSkytte Jensen which give PU (CO ) and PUO (CO ) as the mostlikely carbonate species at PR 8 and Eh about îOO mv. Thebicarbonate Pu(0 )(OH) (HCO ) may also be present. Sullivanand Woods22 have studied the interaction of Pu(IV) with bicarbon-ate and concluded that in sea water soluble Pu(VI) would exist inroughly equal amounts as PuO (OH) and Pu(OH) (HCO )~ with about 152a s P u 0 2 (C03)2- 2 2 2 3
When the solution phase remaining after the first Rddetermination was contacted with fresh sediment the resultsdepended on whether the solid/solution ratio was kept high orwhether it was lowered for the second Rd determination. If thesolid/solution ratio was high for both the first and secondsorptions the distribution ratio was the same both times andvirtually all the plutonium was in the oxidised (V + VI) formsafter both sorptions. This must mean either that only oneplutonium species was present in solution or that equilibriumbetween different species was rapidly re-established as onespecies was removed from solution.
If the solid/solution ratio in the second sorption was lowthe distribution ratio rose to >10 and the percentage ofoxidised Pu(V + VI) dropped. Clearly, therefore, in the absenceof large quantities of sediment some of the plutonium carbonateshave reverted to more readily sorbable species.
4.2 Effect of the presence of some "low-Rd" species.
It was found experimentally that in many cases the observedRd decreased as the solid/solution ratio was increased. Thiseffect has been observed by other workers and variousexplanations offered. We considered that the most likely
14
explanation was that some "low-Rd" species was present. Itwould remain with the solution phase and lower the observedoverall Rd. This low-Rd species could be in the form ofcomplexes with organic matter or anions such as carbonates or itcould simply be micro-particulates which remained with the liquidphase during phase separation. These micro-particulates could betrue colloids but are more likely to be fine particles ofsediment or iron and manganese oxy-hydroxides to which thenuclides have sorbed.
In order to assess the effect that the presence of such low-Rd species would have on the measured Rd a series of theoreticalcalculations were carried out and graphs showing the effect thatsmall amounts of a low-Rd species will have on the observed Rdare given in Figures 7 and 8. It is frequently convenient toplot log (Co - C)/C rather than log Rd against Log m/v (where Coand C are the initial and final concentration in solution,respectively, and both sets of graphs are given.It can be seen from Fig 7 that if the Rd of the high-Rd speciesis as high as 10 then very small amounts of a low-Rd specieshave a marked effect on the measured Rd. Figure 8 shows thatthe effect of a small amount of low-Rd species decreases withdecreasing Rd. Thus 0.052 of a species with Rd = 0.1 will have nodetectable effect if the Rd of the high-Rd species is 10 or less.
Figures 1 1 - 1 3 show the effect of varying the solid/solutionratio on the experimentally determined Rd for Am, Np and Pu ondifferent sediments. Superimposed on the experimental curves aretheoretical graphs that best fit the observed graphs. For Am andPu it is possible to fit the experimental graphs very closely totheoretical ones assuming the presence of between 0.12 and 0.32of a low-Rd species. Similar amounts of low-Rd Np species mayalso be present but the lower Np Rd means that these samll amountswould not be detected.
The experiments in which "second Rd" were determinedconfirmed our conclusion that the presence of some low-Rd specieswas causing the drop in measured Rd for Am and Pu (apart from Puon high-carbonate sediments). Distribution ratios obtained whenthe solution removed after the first Rd determination wascontacted with fresh sediment were several orders of magnitudelower than values obtained for the same solid/solution ratio whenthe fresh spiked sea water was used. Second Rd for Np were thesame as the first Rd, presumably because the amount of low-Rdspecies was too low for detection.Summary and Conclusions
From the waste disposal point of view we are now in aposition to assess much more accurately the likely mobilities ofthe three nuclides studied and to make reccommendations asregards future research. Modellers must bear in mind the possi-bility that R obtained using the batch method might have beenaffected by the presence of micro-particulate or complexedmaterial. In general the effect of such materials will be tolower the observed R of the main species and hence predictionsbased on such results will be conservative. However, themobilities of the micro-particulates and complexes themselves(assuming that some of them, at least, are not simply generatedduring shaking) must also be considered. They are likely to beneutral or negatively charged and could travel a considerabledistance before being converted to a more readily sorbedform.
15
Looking at each element individually we can conclude that -(1) Americium is the least likely of the three elements studiedto escape from the sediments. On both sediments more than 99.952was sorbed with a R of 10 and the small amount of nuclide thatdid not appear J^p be sorbed was almost certainly colloidal. Thereis evidence ' ^ that carbonate complexes of americium arepresent in natural waters. However, these are likely to be inequilibrium with the main positively charged trivalent species andwill therefore be sorbed soon after the bulk of the americium isremoved from solution. Sandia have developed computer codesfor use in sensitivity studies of radionuclide migration in deep-sea sediments and, using risk methodologies developed for the USEnvironmental protection Agency, have calculated the minimumpermissable Kd as a function of burial depth for a number ofradionuclides. These "critical Kd" are listed in Table 5 and itcan be seen that the critical Kd for americium, even at a burialdepth of 2m, is two to three orders of magnitude lower than ourmeasured R
It is recommended, therefore, that investigations into thebehaviour of americium be given a low priority in futureresearch except where its tendancy to remain in the III oxidationstate makes comparisons with the other actinides of interest.The readiness with which it forms colloids could also be exploitedin colloidal studies.
Table 5 Critical K for isotopes of Am, Np and Pu inml/g (from Sandia. 19B3 Status Report27).
Burial Depth (m)
10 20 30
Am -
Am -
Pu -
Pu -
Pu -
Pu -
Np -
241
243
238
239
240
242
237
103
to4
210
103
103
0
,o3
103
103
10
102
102
0
103
,o2
102
0
io2
102
0210
10
102
0
10
10
0
10
10
10
0
110
0
10
(2) Plutonium : Because of its complex chemistry plutonium isalways likely to provide surprises and investigations into itsbehaviour should continue. The fact that the R for high-carbonate sediments dropped so dramatically with increasingsolid/solution ratio emphasises the fact that site-specificstudies are necessary, that experimental results cannot beextrapolated from one sediment type to another and that it is notpossible to predict the behaviour of one actinide from that of the
16
others (or from chemical analogues such as the rare earths).Although at first sight this low R is disconcerting, it is notnecessarily diasasterous. The main plutonium isotopes havereasonably short half lives and it can be seen from Table 5 thatthe critical K for a burial depth of 20m is only 10 ml/g whichmeans that an R of 100 ml/g gives a satisfactory safety marginprovided that the waste is placed 20m or more below the sedimentsurface.
From the waste management point of view it is clear that Puoxidation state is not important. Plutonium, whether originallypresent in reduced or oxidised form was strongly sorbed by allthree types of sediment studied, final overall distributioncoefficients being > 10 in all cases.
(3) Neptunium: Neptunium R did not decrease with increasingsolid/solution ratio probably because Np has a relatively low Rand small amounts of a low-R species would not have beendetected. Because 237Np has such a long half-life and becauseit is poorly sorbed to many geological materials it is generallyconsidered to be the actinide most likely to find its way backinto the environment. However, we have consistently found thatthe R for carbonate sediment is >10 ml/g wich means that even a2m burial depth would be satisfactory in this sediment type(Table 5). The R. for the red clay was only 600 and even lower
Q O Dvalues have been reported by others e.g. Fowler et.al. Aburial depth of at least 20m would be necessary in this type ofsediment. Under the relatively oxidising conditions used inthese experiments the Np in solution was in the V state. Undermore reducing conditions it may be reduced to Np-IV and thedistribution ratio would almost certainly rise.
Tablet Effect of Solid/Solution Ratio - Summary of Results.
Am
Np
Pu
RED CLAY - 10040ft6K
Sorption
Rj Increased withdecreasing solid/solnratio. Levelled offat 10° ml/g. % non-separable ^0.03,(0.22 u filters)•v. 0.02% (0.10 vfilters).
RH constant at about480 ml/g for solid/soin, ratio > 0.016.Increase for twolowest solid/soln.ratios (580* 750ml/g) X non-separable< 0.2Ï (O.lOu filters).
R(J Increased withdecreasing solid/soln.ratios. Levelled offat 7.9xl04 ml/g.t non-separable•v 0.05Ï (0.22u filters)
Desorption R.
> Sorption R.
> Sorption R(jDifferencegreater forlower solid/soin, ratios.
> Sorption R^
Second Sorption Rd
« 1st Rd
Same as firstRd for highsolid/soln.ratios.
« 1st RdDifferencegreatest athigh solid/soln.ratios.
CARBONATE SEDIMENT 10399#7K
Sorption
Rd increased withdecreasing solid/soin, ratioLevelled off^atIxlO6 - 2xl06
X non-separable•v^.055! (0.22 ufilters). 0.02 -0.03% (0.10 vfilters).RH constant forall solid/soln.ratios. % non-separable <0.5%(0.10 u filters).
Desorption Rrf
> SorptionRd
^ SorptionRd
High Solid/Solution Ratios
R<j low i.e. 100-300 ml/g All inPu(VtVI ) form.
^Sorption R(jAll in Pu<;+Vlform
Second Sorption R,
« 1st Rd
"- lst Rd
% 1st Rd
Low Solid/Solution Rat ios.
Rd > 104 ml/q.Mostly inPu(IIt + IV)form.
> Sorption R,jMostly inPu(III + IV)fom.
« 1st Rd
17
ACKNOWLEDGMENT
The work described in this report has been carried out for theDepartment o-f the Environment as part of its radioactive wastemanagement research program. The results will be used in theformulation of Government policy but at this stage do notnecessarily represent that policy.
REFERENCES
1. Higgo 3.J.W., Rees L.V.C., and Cronan D.S. 1983a "Sorption ofamericium and neptunium by deep-sea sediments".Radioactive Waste Management and the nuclear fuel cycle. A.,pp. 73-102.
2. Higgo J.J.W.. Rees L.V.C., and Cronan D.S., 1302." Radionuclide sorption by marine sediments: Part 2, Neptuniumand americium". DOE Report No: DOE/83/130.
3. Higgo J.J.W., Rees L.V.C., and Cronan D.S. 1983b."Radionuclide sorption by marine sedimets: Part 3,Plutonium, americium and neptunium". DOE Report/RW/131.
4. Higgo J.J.W., Rees L.V.C., and Cronan D.S. 198Aa "Radio-nuclide sorption by marine sediments: Part A, Effect ofsolid/solution ratio on the observed distribution ratio"DOE/RW/8WOA
5. Higgo J.J.W., Rees, L.V.C., and Cronan D.S. 1984b. "Sorptionof plutonium by deep-sea sediments" Submitted to Radio-active waste management and the Nuclear Fuel Cycle.
6. NEA: 1983. "Sorptio..: Modelling and measurement for nuclearwaste disposal studies". Summary of an NEA workshop held 6-7June in Paris.
7. L.J. Cihacek and J.M. Bremner. Soil Sei. Soc. Am. J.A3 821-822 ( 1979) .
8. M.D. Heilman. D.L. Carter and C.L. Gonzalez.Soil SciencelODA 0 9 - A 1 3 (1965).
9. W.A. Beetem, V.J. Janzer and J.S. Ulahlberg. Geological surveyBulletin 1 1 A O - B B1-B5 (1962).
10. H.D. Chapman. Methods of Soil Analysis Agronomy 9, pp. 891-901 , (1965) .
11. J.F. Relaya, R.J. Seme and D. Rai, Pacific NorthwestLaboratories. PNL-33A9. (1980).
12. S.C. Foti and E.C. Freiling.Talantal1 385-392, (196A).
13. C.N. Murray and D.A. Stanners. Radioactive Waste Management2 (1982).
1A. H.E. Nuttall, A.K. Ray and E.J. Davis.Nuclear Technology52260-272, (1981).
18
15. A.K. Ray, E.J. Davis and H.E. Nuttall. Annals of NuclearEnergy 8 415-442, (1981 ) .
16. G.R. Heath. Geological disposal of nuclear waste. 19thAnnual Symposium, Albuquerque, New Mexico. March 15, 1979.
17. Edgington, D.N. 1980a "Characterisation of transuranicelements at environmental levels", in Techniques forIdentifying Transuranic Speciation in Aquatic Environments.Proc. of a technical committee meeting. Ispra, 24-28 March,1980. IAEA, Vienna, pp. 3-25.
18. Edgington, D.N. 1980b "A review of the persistence of long-lived radionuclides in the marine environment - sediment/water interactions" in Impacts of Radionuclide Releases intothe environment. Proc. Symp. Vienna, 6-10 Oct. 1980, IAEA,Vienna, pp. G7-91.
19. Allard, B. 1982b. "Solubilities of actinides in neutral orbasic solutions", in Actinidesin Perspective ed. Edelstein,N.M. (Pergamon Press).
20. Cleveland J.M., Rees T.F. and Nash K.L. 1983. "Plutoniumspeciation in water from Mono Lake, California." Science 22.pp. 221-223.
21. Skytte Jensen, B. 1982. Migration phenomena of radionuclidesinto the geosphere. (Harwood Academic Publishers).
22. Sullivan J.C. and Woods M. 1982. "Thermodynamics ofplutonium (IV) interaction with bicarbonate".Radiochim Acta. 31. pp. 45-50.
23. Eicholz G.G., Wahlig E.G., Powell G.F. and Craft T.f."Subsurface migration of radioactive waste materials byparticulate transport." Nucl. Tech. . 58, pp. 511-520.
24. Harderman J. 1981. "The influence of speciation on thegeospheric migration of radionuclides." Nucl. Tech. 56 pp102-105. —'
25. Murray C.N. and Avogadro A. 1980. "Effect of a long termrelease of plutonium and americium into an esturine andcoastal ecosystem". inTechniques for Identifying TransuranicSpeciation in Aquatic Environments." Proc. Tech. Comm.Meeting. Ispra 24-28 March 1980. IAEA, Vienna, pp. 103-114.
26. Avogadro A., Bidoglio G. and Murray C.N. 1980. "Theimportance of complexes of plutonium and americium withinorganic anions present in natural waters." Presented atXXVII Congress of International Commission for ScientificExploration of the Mediterranean Sea. 9-18 October 1980.Cagliari Italy.
27. Sandia: 1983, Sandia 1983 Status Report, Sandia Laboratories.Albuquerque. New Mexico, U.S.A.
23528. Fowler S.W. and Aston S.R. 1981. "Applications of Np inexperimental aquatic radioecology : Preliminary observationsof neptunium behaviour in sea water, sediments andZooplankton". Health Physics, 42, pp. 515-520.
19
10 20 30 40 iU 50 la 80
10
m l / g
10
&-&
o-a
l O S - 6l O S - 5I O S - 4I O S - 2I O S - 3M77-20
O—o S702
10 20 30 «0 SO 60T i M E D I T S
l K ÎURC \ Amcnuuin Distribution C FIGURC 2. Anicncnitn Distribution Coetfiui.nt'i Hijjli-Cjrbonaie Sediments
2 0
ml /9
10
A 6 2 6 9 NO 2o SK 15!Bt MV SS lo i o s - 1 S O R P T I O N
M O D U L E
SHECTIIE
N O O U L E
20 i 0 50T U E O S T S
l REDJ CUT
ï l ) T o o !2cT~
BESORPTIOII
ml/9~^T10
«77-20l OS-5IOS-3
» IOS-«o 10 S-»« s 702a. IOS-2
SORPTION
20 40
IGLKi- J \ , I J M ' i b i i i i i n i i i . l l im.ni i LUA Cirbonalo Sedimente
20 40 SO ai 100 I2l>
T IME 0 » T S
IJESOI1PTIO«
2 l 4 0
FlGURT 4 Np Distribution Coclficicnts Ili^h-Cjrbonatc Sediments-
20
100 - 0 1
T I M E . D A Y S
njULüLJL • P L U T O N I U M D I S T R I B U T I O N
C O E F F I C I E N T S
3000
2000 -
1000zujC3
10 15 20
100
TIME, H O U R S
F I G U H E 6 , C O N C E N T R A T I O N OF O X I D I S E D & R E D U C E D P L U T O N I U M - 238
I N S O L U T I O N D U R I N G T H E F I R S T 2 2 H O U R S
21
to(O
Fig 7 The ef fect of a f ixed proportion of a second species which is not adsorbedby the sediment on the relationship between loq m/v and {a) loq Rd (b)
log(C0 - C ) / C for di f ferent percentages of lew Pd species (RH = 10", RL = 0 .1) .
Fig 8 Tne effect of a fixed proportion of a second species with Rd = 100 onrelationship between log m/v and (a) log Rd {b) Log[Co-c)/c for differentpercentages of low Rd species. (R„ = 10° , R, = loZ).
•-a'
---- - - 9 9 9 5 V . RH - 10
-fx"
9 9 - 9 8 V. RH = 10 ; 0-02 V.
9 9 - 9 7 7 . R = 106 -^ 0-03 7.
6 O .OSV,
- t- -i
I 0-22 )j 34 days
^ 0-1O fJ 24 d a y s
0 0.10 ^j 74 d a y s
0-1
0 - 1
0-1
I-5
1
-4
2. 9
- 3 log m/v - 23 log mg/l 4
-15
Effect of solid/soln ratio on the value of log (Co-c)/c for amencium on the high-carbonate sediment10399#7K
,-« rX
19 '•-* xT •"
J 0-22
X 0-10
e 0-10
- -0-
" ' I ' 3
0
-- X"
9 „ -
Theore t ica l
99-98 % RH =2 \ 1O ; 0 027. RL = O.I
99-97 X RH - 1 X 1O ; 0 O3% RL = O.I
24 days
27 days
54 days
mo
-51
-4
2
-3 log m/v -2 -10 1 2 3 log mg/l 4 5F) -|Q Effect of solid/soln ratio on the value of log (Co-c)/c **for americium on the red clay, 10400#8K.
06
23
. oo r.
- D-OS y0-1 '/
0-2 l
. 0-4 '/
-2 -3 -2 -1 0 log m/v1 2 3 4 S e l o q mq/lFiq 11 Effect of solid/soln ratio on the value of log (Co-c)/c for the sorption of neptunium onto the*
hig-carbonate sediment 10399$7K. Dotted lines represent theoretical curves for different percentagesof a non-separable species. (RH = 3980, RL = 0.1)
I J_
0
l loul0»0
-s1Fig.
-4 -3 -2 -1 02 3 4 5 6
•(2 Effect of solid/soln ratio on the value of log (Co-c)/c for sorption of neptunium on red clay, 10400 $: 8K.Dotted lines represent theoretical curves for different percentages of a non-separable species(RH = 500, RL = 0.1).
24
T t~i e o r f t i cal
4• 9 9 - 9 5 ' ^ RH = 7 - 9 4 X 1 0 . 0 0 5 7 . R^O!
.ï
T E x p e r i m e n c a l^- points
ero
i__________i_________u-6 -5 -4 -3 log m/v -2 -1 0
O 1 2 3 l a g mq/l 4 5 6Fl9. 13 Effect of solid/soln ratio on the value of log(Co-c)/c for the sorption of plutonium onred clay, 10400 8K
25
FALLOUT PLUTONIUM IN WESTERN NORTH PACIFIC SEDIMENTS*
H.D. LIVINGSTONWoods Hole Océanographie Institution,Woods Hole, Massachusetts,United States of America
Abstract
The study compared sediment samples from the Mid-Pacific Gyre area north of Hawaiiand from the Western North Pacific. The latter had from 2 7-5.5 the concentrations ofPu isotopes compared with the former, but the profiles wj th depth were similar.The increased levels were probably due to close-in fall-out from the Marshall Islands
-2weapons tests. The inventories for water column plus sediment were 4 0-4.3 mCi kmfor NW Pacific and 2.9 for the Mid Pacific area. The proportions in the sediments arerespectively 8% and 2%. Evidence is presented that close-in fallout was more availableto scavenging For NW Pacific, significant bioturbation effects were seen, redistr-ibuting Pu as deep as 46 cm, even though these sediments are abyssal. This impliessubsurface waste disposal may be more vulnerable to the effects of bioturbatiDn thanpreviously supposed
1. IntroductionThe results of transuranic analyses of water samples collected
as part of the GEOSECS program in the North Pacific revealed two featuresfound at stations throughout much of this ocean area.A. A subsurface maximum in Pu concentration centered at about 500 m.B. A near bottom maximum in Pu concentration — especially in Western, Central
and Northern locations. No sediment samples were collected in theGEOSECS program so there were no observations about the delivery oftransuranics to Pacific sediments.
This report describes subsequent studies of the contrast between thesediment distributions of transuranics in Western N. Pacific sediments com-pared to that found at the HPG-1 (Mid-Pacific Gyre) study site north ofHawaii. The latter site has received study in connection with the U.S. Sub-seabed Disposal Program which has been assessing the technical feasibilityof the use of deep ocean sediments for the disposal of high level radioactivewastes. Some of the results of fallout nuclide analyses of sediment cores
[21from the HPG-1 site were discussed in an early CRP technical report.This report also included some discussion of the fallout profiles in thesediments in the context of bioturbational mixing in the sediments at thesite.
* IAEA CRP Research Agreement No 3246/RI/CF
27
2. Sample Collection and AnalysisIn Hay 1980, a series of large diameter (21 cm) gravity cores were
collected on a cruise of R/V HAKUHO HARU from Tokyo-Honolulu. The corer wasmounted on a tripod assembly permitting slow penetration of the sediments[3]with the corer maintained in a vertical position. The locations atwhich core samples were collected are indicated in Figure 1—as cores num-bered 1-4. Also shown in this figure is the general location of the HPG-1site, where earlier studies were carried out, and one coring station occu-pied by R/V KNORR in July 1978.
The methods used for extruding and sectioning the cores and performing239 240the radiochemical analyses for ' Pu have all been summarized or refer-[4]enced in a recent publication. Some discussion of data quality assurance
also appears, or is referenced, in this publication, both in terms of generalphilosophy and specific examples. This laboratory has continued to partici-pate in both national and international intercalibration exercises of radio-chemical quality assurance, including recent exercises organized by the IAEAMonaco laboratory. Our performance in these exercises continues to give usconfidence that our data are of high quality.3. Results
The results of the radiochemical analyses of these Western N. Pacificsediment cores are tabulated in Tables 1 and 2—together with the positions
238and depths of sampling. Pu was also measured when detectable, together238with several other fallout nuclides. The ratios Pu to ' Pu in the
cores fell in the range 0.02-0.06. In core #3, there appeared to be a trend
TABLE 1 PU IN WESTERN PACIFIC SEDIMENTS(R/V HAKUHO HARU - HAY 1980)
Core No. :LatitudeLongitude :Water Depth:
139°58'
156°01'5530 TO
SedimentSection (cm)0-12-34-58-9
13-1519-21Bottom=29 cm
NE
239,240pu*
857f38162+1580+8
6.71-3.30.7f0.70.8+0.7
239°01'166°02'5600 m
SedimentSection (cm)0-11-22-34-56-79-10
13-1517-1921-2331-33Bottom=60 cm
NE
239,240pu*
863+28657*23343+15262+1575+7731-10128+921 + 221 + 31+1
* 239,240Pu mBq/Kß (dry weight)
28
TABLE 2 PU IN WESTERN PACIFIC SEDIMENTS(R/V HAKUHO MARU - HAY 1980)
Core No, :Latitude :Longitude :Water Depth:
338°00179°455520 m
SédimentSection (cm)0-11-22-33-44-55-67-89-10
10-1214-1618-2024-2630-3236-3842-4444-4646-48Bottom=60 cm
•N'W
239,240pu*
1378+43802+25430+32380+13218+20180 + 787+1141+834+311 + 210 + 312+20.7+0.50 + 1
6.3+2.74.3+1.0-0.7il.8
430°00UO'OO'
S432 m
SédimentSection (cm)0-22-33-45-67-89-10
13-1519-2131+_33Bottom=68 cm
'NU
239,240pu*
164 + 875+ 691 + 7115+1090 + 758^2240 + 45 + 21 + 0.5
* 239 240' Pu mBq/Kg (dry weight).of decreasing ratios from the sediment/water interface—the upper two centi-meter sections lying in the range 0.04-0.06, whereas the sections from 3 to6 centimeters lay in the range 0.02-0.03.
239 240The total inventory of ' Pu found in each core was calculatedby summing the amounts found in each section on a unit area basis. The re-sults of these calculations are plotted in Figure 1 for each core besidesits location.4. Discussion4.1 Concentrations and Inventories in Northwest and Northeast Pacific
SedimentsFigures 1-2 contrast the differences in Pu concentrations and inven-
tories at the Western Pacific stations with those from the HPG-1 area. Itis clear that the inventories and, especially, the concentrations of Pu aremuch higher in the sediments from the Western Pacific stations. The inven-tories range from 2.7-5.5 times the mean HPG-1 value (excepting core 4 whichis closer in all respects to those from MPG-1), while the concentrations ofPu in the 0-1 cm sediment section range 6-10 times higher. The depth distri-bution pattern of the nuclides in these Western Pacific sediments is notmarkedly different from those found in the MPG-1 region.
29
60'
so-
SEDIMENT Pu INVENTORIES (mCi/kmz)140' 150* 160' 170' ISO* 170' 160* 150* 140' 130' 120*
30
20'
10
10*
20*
30'
0.95o
ENEWET1K8IKINI
.XS A
0.33
MPG-10,12
0.06
JOHNSTON 1$
• CHRISTMAS IS
O KHOtf 73 Jllll 1971
• HAKUHO HAKU SMTlOf/S UM 1910
\
100
80
60
40
20
0
08
0.6
*i\ 04
0.2
0
FIGURE 1
SEDIMENT CONCENTRATIONIN 0-1 cm CORE SECTION
NORTHWEST BASIN NORTHEAST BASIN
0
119)
r SEDIMENT INVENTORIES
NORTHWEST BASIH NORTHEAST BASIN
(16)
Pu IN NORTH PACIFIC SEDIMENTS
FIGURE 2
30
It seems necessary, in looking for an explanation of the elevatedtransuranics in these Western Pacific sediments relative to those from HPG-1,to invoke an extra source of supply associated with input via close-in fall-out of debris from tests conducted at the U.S. Pacific test site in theMarshall Islands in the 1950s. This source was necessary to explain thedistribution and inventories of Pu in N. Pacific water columns at GEOSECSstations. In the water columns of the Western Pacific in the 30-40°latitude range, Pu inventories exceeded those of the Eastern end of the sec-tion by about a factor of 2—the excess Pu being attributed to a close-infallout source.
Such an input would be expected to be recorded in sediments underlyingthe input area. Although the necessary data are not available, it seemshighly probable that surface seawater concentrations of Pu in the areasaffected by close-in fallout from the 1950's test series must have been muchhigher than those subsequently resulting from fallout from global debris fromthe stratosphere from the 1960's testing. Euphotic zone scavenging in turnwould have supplied underlying sediments with particles transporting substan-tially elevated concentrations of Pu.
Comparisons of these Pacific sediment Pu inventories with those mea-sured during GEOSECS in the overlying water offers an opportunity tocompare, at least qualitatively, the rate of Pu transfer to the deep oceanas a function of whether its source was from close-in or global fallout. Itis clear from both the sediment data shown here and the GEOSECS water inven-tories, that Western N. Pacific stations between 30"N and 40°N must have re-ceived proportionately more "close-in" fallout that did those in the EasternN. Pacific. Specifically the locations represented by the Hakahu Maru cores
22 and 3 have water column plus sediment Pu inventories in the 4.0-4.3 mCi/kmrange. At the MPG-1 location, the corresponding total is close to 2.9
2mCi/km . At this latitude, the stratospheric Pu input could well be taken2to be about 2 mCi/km —as represented by the stations at the eastern end
of the GEOSECS E/W section between 30°N and 40°N. When this is sub-tracted from the total inventories, there is left an estimated inventory of
2"close-in" fallout of about 2.2 and 0.9 mCi/kra at the Hakuho Maru core2/3 positions and the MPG-1 location respectively. At the former location,Pu is distributed between the ocean water column and the underlying sedimentssuch that about 921 is in the water and about 8% is in the sediments. Thecorresponding figures for the HPG-1 location are 98% and 21. If the parti-tion of "close-in" fallout between 160°E and 180°E is put at 2.2 mCi/km2 in2the water and 0.26 mCi/km in the sediments (subtracting the MPG-1 averagesediment inventory as being a measure of the stratospheric fallout component),
31
the water/sediments proportions become 111 and 891. The implicationof these comparisons would seem to suggest that the "close-in" fallout Puwas delivered in a form which made it more available to scavenging and part-icle sinking processes than was stratospherically delivered fallout Pu. Analternative explanation for the higher proportion of fallout Pu found in the160°E-180°E region sediments compared to the MPG-1 site, would be possibleif there were significant differences in the biogenic large particle fluxesbetween the two areas. Bacon et al. have shown that these fluxes arethe major controls on the fluxes of both natural radionuclides and Pu to thedeep Sargasso Sea. No comparable particle flux data exist for the twoPacific areas in question, but it is very unlikely that primary productivitydifferences, and hence biogenic particle fluxes, are sufficiently differentto account for the higher proportion of Pu found in 160QE-180°E region sedi-ments compared to that at the MPG-1 site. For these reasons it may be morelikely that the observed difference is related to the more reactive characterof "close-in" fallout Pu with respect to particle association and sinking.4.2 Relevance to Radioactive Waste Disposal
There are at least two facets to these data which have relevance toquestions associated with the consequences of disposal of radioactive wastesin the oceans.4.2.1. The elevated Pu concentrations in near surface sediments in areas of
the Western N. Pacific means that benthic organisms including infaunahave been exposed to levels of transuranics ranging up to an order ofmagnitude higher than in the MPG-1 study area. This is a favorable sit-uation in respect to determination of benthic organism concentrationfactors for Pu. These are often hard to measure because of the low levelof the fallout signal available. Here, in contrast, levels of organismPu concentrations should be more rapidly measurable.
4.2.2. Any waste disposal operations which might be planned for the futurein the Western Pacific would have to be monitored against the higherfallout background likely to be found there. It makes abundantly clearthe necessity of there being an extensive high quality data set on theexisting patterns and concentrations of fallout isotopes against whichto assess the effects of additional input associated with waste disposalsources.
4.3 Bioturbation Implications of Sediment Plutonium Distributions210The fallout radionuclides and unsupported Pb are often used to in-
fer the depth and nature of organism mixing processes in sediments with slowrates of accumulation. In contrast to the relatively deep bioturbationalmixing of coastal or shelf sediments, ' deep sea sediment bioturbation is
32
generally thought to be restricted to sediment close to the sediment/waterinterface. At the MPG-1 site in the North Pacific, for example, falloutnuclide penetration is seldom detectable at depths greater than 10 to 12 cmwithin the sediment. '
From the data tabulated in Tables 1 and 2 it is possible to draw someconclusions about the nature and extent of bioturbation in the sediments ofthe Western North Pacific at the core sites occupied in 1980—Figure 1. Atcore locations 1-3, the Pu concentration fell below 10% of the upper layervalue at a depth 10 cm below the interface. The slope of the concentrationcurves were generally similar to those seen at the MPG-1 site—implying sim-ilar rates of biological mixing. At core location 4, a more intensive mixingrate is implied by the steeper slope of the Pu distribution curve. Also, thePu concentration at depth does not drop below 10% of the top section concen-tration until a point somewhere between 15 and 19 cm. This location is char-acterized by a Pu distribution indicating both greater mixing intensity andto a greater depth within the sediment.
The higher concentrations of Pu found in these sediments compared withthose which occur in most other deep ocean sediments, including those at theMPG-1 site, results in the effects of low intensity deep mixing processesbecoming detectable if they are active. At locations where ambient concen-trations are low, deep section concentrations may fall below the availableanalytical sensitivity. This point is clearly illustrated in the two highinventory cores (2 and 3). In both cores, Pu is readily measurable in the20-25 cm depth range—albeit at concentrations 1-2% of their surficialvalues. Even more striking, in core 3, is the sediment zone between 42 cmand 46 cm where a distinct Pu signal was detectable over that in the over-lying and underlying sediment. When this core was extruded, organism burrowswere noted as penetrating to this depth.
The surprising conclusion is drawn from these sediment mixing profilesthat abyssal sediment mixing activities are not as slow or as shallow as isgenerally believed. The evidence in these patterns points to the ability ofdeep ocean organisms to move surficial sediment to considerable depth withinthe sediment in a relatively short period of time.
References
1) Bowen, V. T., V. E. Noshkin, H. D. Livingston and H. L. Volchok. Falloutradionuclides in the Pacific: vertical and horizontal distributions,
33
largely from GEOSECS statons. Earth Planet. Sei. Lett. 49: 411 (1980).2) Bowen, V. T. Transuranic behavior in the marine environment. In "Trans-
uranic Cycling Behavior in the Marine Environment." IAEA-TECDOC-265, p.129 (1982).
3) Burke, J. C,, R. E. Hamblin and S. A. Casso. Tripod modification ofsphincter corer: construction, operation, core extrusion and samplingefficiency. Woods Hole Océanographie Institution Technical Report,WHOI-83-36 (1983).
4) Livingston, H. D. and V. T. Bowen. Pu and Cs in coastal sediments.Earth Planet. Sei. Lett. 43: 29 (1979).
5) Bacon, H. P., C.-A. Huh, A. P. Fleer and W. G. Deuser. Seasonality inthe flux of natural radionuclides and plutonium in the deep Sargasso Sea.Deep Sea Res., in press (1985).
6) Kershaw, P. J., D. J. Swift, R. J. Pentreath and H. B. Lovett. Plutoniumredistribution by biological activity in Irish Sea sediments. Nature306: 774 (1983) .
7) Druffel, E. R. M., P. H. Williams, H. D. Livingston and M. Koide. Vari-ability of natural and bomb produced nuclide distributions in abyssalred clay sediments. Earth Planet. Sei. Lett. 71: 205 (1984).
34
PLUTONIUM DISTRIBUTION IN MARINE ANDRIVERINE SEDIMENTS FROMLA SPEZIA AREA (LIGURIAN SEA)
R. DELFANTI, C.D. JENNINGS, C. PAPUCCICEC, c/o ENEA,La Spezia, Italy
Abstract
The inventory was 3.5 mCi km , much higher than for abyssal sediments. The plutoniumconcentrations in marine samples (15-71 dpm kg ) were about ten times higher thanfor the riverine samples (1.7-4.9 dpm kg ). Calculations from plutonium distributionin a core suggested a sedimentation rate of 0.56+0.06 cm y
1. Study areaThe study area is under the influence of the Magra riverwhich supplies to the sea a limited amount of both waterand suspended matter (1) from the drainage of two diffe-rent basins: above its confluence with the Vara, theMagra flows through a region dominated by marble anddolomite, while the Vara drains a region of sandstone,quartzite and schist. The suspended material coming fromthe river is transported by the prevailing currents toNorth West into the La Spezia Gulf(2,3). Riverine surfacesediments from the two different basins and marine sedi-ments (6 grab and 1 core samples) (Fig.l) were analyzedfor plutonium determination.
Fig.l - Study area and sampling points
35
2. Methods2.1 Sampling
The marine surface sediments were collected with a Shipeckgrab, while the riverine sediments were collected by handfrom protected areas. For the evaluation of the verticaldistribution of plutonium, a sampling and extruding appa-ratus was built for the collection of as much as possibleundisturbed sediment cores and for the sectioning of thecore in slices 1cm high directly in the field.With this pro-cedure it is also possible to discard the outer ring of1 cm, that can be disturbed by core penetration into thesediment, from each slice.(4)
2.2 Analytical procedureAmong the several published procedures for plutoniumseparation and purification from the matrix and interfer-ring radionuclides, an extraction procedure much similarto that published by Wong (5) was chosen, but the samples(aliquots of about 15 grams) were totally dissolved bysequential treatment with HN03-HF, HC1-H3B03, HN03-HC104.At the end of the dissolution step Pu was isolated fromthe mixture of acids by coprecipitation with CaCzO^, thatalso provided a preseparation of Pu from the matrix andfacilitated the subsequent double anion exchange procedure.The accuracy of the method was tested by analyzing threestandard sediment samples from NBS and IAEA. The resultsare shown in table 1.
239,240T A B . 1: R E S U L T S OF A N A L Y S I S OF Pu IN S T A N D A R D I Z E D S EDI H E N T SAMPLES
S A M P L E A C C E P T E D A C T I V I T Y M E A S U R E D A C T I V I T Y( d p m / K g ) (dp m/K g )
R i v e r s e d i m e n t 30.5 ! l.8 2 9 . 4 + 1 . 4NBS SRM 4350B266 î 67*I A E A SD-B-2 ^ 351 27422 î 44'
I A E A SD-B-3 1265 ! 155§ 1063 ! 19
* M e a s u r e d a t t h e I n t e r n a t i o n a l L a b o r a t o r y o f M a r i n e R a d i o a c t i v i t y( I L M R ) by l e a c h i n g w i t h h ydr oc h l o r i c a n d n i t r i c a c i d .
1 M e a s u r e d a t I L M R b y t o t a l d i s s o l u t i o n w i t h h y d r o f l u o r i c , p e r c h l o r i ca n d n i t r i c a c i d s .
§ A v e r a g e r e s u l t f r o m 8 l a b o r a t o r i e s p a r t i c i p a t i n g i n I L M R i n t e r c a l i -b r a t i o n e x e r c i s e .
36
3. Discussion3.1 Surface sediments
239,240Each sample was measured for porosity and Pu concen-tration (Tab.2). The porosities of the river sediments werehigh (0.62 - 0.79) and representative of the smallest particle
239,240 137TAB. 2: C O N C E N T R A T I O N S OF P L U T O N I U M , POROSITIES AND Pu/ CsR A T I O S I N S U R F A C E S E D I M E N T S O F T H E L I G U R I A N S E A N E A R L A SPEZIA A N DI N A D J A C E N T R I V E R S E D I M E N T S C O L L E C T E D I N J U L Y , 1984. U N C E R T A I N T I E SA R E 1 - S I G N A P R O P A G A T E D E R R O R S .
L o c a t i o n
S P A ACD neor o bpp r por ouSP PVSP 03SP 04SP 05V a r a R i v e rMagr a RiverMa gr a River
* not leas», 239,240
239,;(dpn/k;
56 î26 i25 ±7L i38 î60 î15 î
(VI) 4. 6 î(Ml) 1.7 +(M2) 4.9 î
ur edP,,/137CS.
>40Pu Pu/Cs) d r y )
3 _ _ - _ -2 _-.-_24 0.082 0.064 0.071 0.110.6 0.010.5 0.010.5 0.03
The r.s. H â t a is frnm
Por
0.0.0.0.0.0.nu0.0.0.
An*P !
o s i ty
629476484701586646*621790663
m î P t a
Depth(•)
100472412459318111
1 . M O.R71 anit is not fro» the sane s a n p l e s as the Pu data, but from s a m p l e sl e c t e d at the sane s t a t i o n s .
TAB. 3: C O N C E N T R A T I O N S OF P L U T O N I U M AND P O R O S I T I E S IN A S E D I M E N T CO-RE R A I S E D AT PV S T A T I O N IN THE G U L F OF LA S P E Z I A , L I G U R I A N SEA, INO C T O B E R , 1983. U N C E R T A I N T I E S A R E 1-SIGHA P R O P A G A T E D E R R O R S .
Depthin
core(ci)
0-12-34-56-77-88-9
10-1112-1314-1516-1719-2022-2325-2630-31
(c
0.2.5.7.9.10.13.15.16.21.25.29.33.39.
*z 1
«0
518281417411118
239,240„Pu
( dpn/kg dry )
51 i51 152 !66 t62 +75 ±59 ±24 ±20 -15 i
0.9 î0.8 t0.5 înd*»
24332322110.20.20.2
P o r o s i t y
0.0.0.0.0.0.0.0.0.0.0.0.0.0.
709669655656645641612626644637636639626627
* z 1 • s e d i i e n t d e p t h c o r r e c t e d for c o i p a c t i o n by the o v e r b u r d e n ofs e d i n e n t .** not d e t e c t e d
37
sizes exported by the Magra river. Plutonium concentrationsin marine sediments were about ten times higher than in riversediments. From literature data on 137Cs concentration in thesame study area 239,240pu/137cs ratios were calculated in thetwo cases. The average ratio in the river stations was 0.016,while the average from the marine stations was 0.08, indicatinga change in Pu adsorption onto the particles as they contactsea water. Plutonium concentration is highly correlated toporosity, which in turn is related to grain size (6).Porosity and Pu concentration in the range of this studyare accurately described by a linear relationship (fig.2).
239+240r
70 -
60 -
50 -
O-o
30-
20-
J P u ( d p m / k g )
0 10 20 30 40 50 60 70 80
y=mx+bCoefficients :m=198.7b=-72.46RMS ERROR=3.980
.{.000 .6000 .8000.5000 .7000
P o r o s i t y o f s e d i m e n t
.9000
/Fig.2 - Relationship between porosity and "b+'4Upconcentration in surface sediments of theLigurian Sea.
Fig.3 - Vertical profile of 239+24Opuin sediment core PV c o l l e c t e din October 1983.
3.2 Vertical distribution of Pu - Sedimentation rateThe results of the analyses on the vertical distribution ofPu in the core raised at PV station are shown in Tab.2.The vertical profile (fig.3) shows a well preserved andclearly defined subsurface maximum which suggests that themixing rate at this station is low as also would be expec-ted from low tidal and wave energy environments.On the basis of the depth of Pu subsurface maximum, correc-ted for compaction (7), the average sedimentation rate atthis point has been calculated to be 0.56-n 0.06 cm/yr.
3.3 Plutonium inventoryThe inventory of 239,240pu in sediments at the coring sitewas calculated to be 3.5 mCi/km2, a value which is substan-tially higher than the cumulative fallout deposition at
38
this latitude, but in good agreement with other publishedvalues on coastal Mediterranean (8,9,10) and Pacific sedi-ments (11). These results contrast those in deep water sedi-ments (12,13,14) in which the inventories are only a fractionof that delivered by fallout. The inventory differencesbetween shallow and deep water marine environments may beexplaned by the fact that Pu is removed from seawater inprimarily hydrous Fe and Mn oxide coatings on particles,both inorganic and biogenic. In the open sea, low particlepopulation and sedimentation regime result in low inventoriesof Pu in deep water sediments. Zooplankton fecal pelletsprovide an important transport pathway in this environment.In shallow water, on the other hand, higher primary producti-vity, greater runoff from land and resuspension of sedimentsnear the sea floor provide greater concentrations of particlesand thus enhanced removal of Pu from the water column.
References
1) PIERCE,J.W,TUCCI,S.,and FIERRO.G. (1981).Assessing variations insuspensates,Ligurian Sea (Northwest Mediterranean). Geo-MarineLetters,!., 149-154.
2) ANSELMI.B.,BRONDI,A.,FERRETTI,0.,and PAPUCCI.C. (1982).Connessionitra geomorfologia costiera.granulometria dei sedimenti e distribu-zione dei radionuclidi in zone marine subcostiere. Annali di radio-protezione,109-130.
3) ESPOSITO.A.,and MANZELLA.G. (1982).Current circulation in theLigurian Sea . Hydrodynamics of semi-enclosed seas,ed.by J.C.J.Nihoul,187-204,Elsevier,Amsterdam.
4) PAPUCCI.C.,JENNIGS,C.D.,LAVARELLO,0.(1985).A modified box-corerand extruder for marine pollution studies.In preparation.
5) WONG,K.M.(1971).Radiochemical determination of Plutonium in seawater ,sediments and marine organisms.Anal.Chim.Acta,56,355-364.
6) HETHERINGTON.J.A.,JEFFERIES.D.F.,LOVETT.M.B.(1975).Some investi-gations into the behaviour of plutonium in the marine environment.In Impacts of nuclear releases into the aquatic environment,IAEA-SM-198,193-212,Vienna.
7) MATSUMOTO.E.,and WONG.C.S.(1977).Heavy metal sedimentation inSaanich Inlet measured with 210pb technique. J. Geophys. Res.,82, 5477-5482.
39
8) TRIULZI, C., DELLE SITE,A.,and MARCHIONNI,V. (1982). 239,240puÇf O Qand Pu in sea water, marine organisms and sediments of
Taranto Gulf (Ionian Sea). Estuarine coastal shelf Sei., 15,109-114.
9) DELLE SITE,A., FERRETTI,0.,MARCHIONNI,V. and PAPUCCI.C. (1984)Measurements of 137Cs, 239+240pu and 238pu j_n some coastalsediments of Tyrrhenian Sea. In International symposium on thebehaviour of long-lived radionuclides in the marine environment,ed.by A.Cigna and C.Myttenaere.CEC,Luxembourg,233-243.
10) JENNINGS,C.D., DELFANTI,R.,and PAPUCCI.C. (1985). The distributionand inventory of fallout plutonium in sediments of the LigurianSea near La Spezia, Italy. J. Environ. Radioactivity, in press.
11) BEASLEY,T.M., CARPENTER,R.,and JENNINGS,C.D. (1982). Plutonium,Am, Cs ratios, inventories and vertical profiles in
Washington and Oregon continental shelf sediments.Geochim.Cosmochim. Acta, 46, 1931-1946.
12) LIVINGSTON,H.D.,CASSO,S.A.,BOWEN,V.T., and BURKE,J.C.(1979).Soluble and particle-associated fallout radionuclides inMediterranean water and sediments. Rapp.Comm.Int.Mar Medit.,25/26,5,71-75.
13) BOWEN.W.T.,LIVINGSTON,H.D.(1981). Radionuclide distributionsin sediment cores retrieved from marine radioactive wastedump sites. In IAEA SM-248, 33-63, Vienna.
14) NOSHKIN.V.E.,BOWEN,V.T.(1973). Concentrations and distributionsof long-lived fallout radionuclides in open ocean sediments.In IAEA-SM-158, 671-686, Vienna.
40
THE CHEMICAL BEHAVIOR OF LONG-LIVEDRADIONUCLIDES IN THE MARINE ENVIRONMENT
D.N. EDGINGTONCenter for Great Lakes Studies,University of Wisconsin-Milwaukee,Milwaukee, Wisconsin
D.M. NELSONEnvironmental Research Division,Argonne National Laboratory,Argonne, Illinois
United States of America
Abstract
Measurements of long-lived radlonucl1des 1n the marine environment have provideda wealth of Information regarding the physical/ biological, and chemicalprocesses which control the behavior of these and many other pollutants 1n theoceans. Their value as tracers for the dispersion» transport» and fate ofpollutants 1n the oceans 1s largely dependent on the chemical properties of eachIndividual radioélément. Differences 1n these properties, particularly 1nrelation to their Interaction with blotic or abiotic partlculate matter, resultin the separation of parent-daughter radloisotopes in the natural radioélémentseries or in changes in the ratios of fission and activation products. Suchdifferences have provided the means to provide time scales for a variety oftransport processes and to determine sedimentation rates. The properties ofthese radlonuclides in the oceans can, in general, be predicted from thechemical properties of the stable elements.For those elements such a plutonium, for which there are no naturally-occurringstable isotopes, studies of their distribution 1n the oceans have provided a newImportant understanding of their chemical behavior. This behavior has notalways agreed with what would have been predicted from laboratory studiescarried out at far higher concentrations. Differences between observeddistributions and laboratory predictions have highlighted the importance ofcorrect experimental conditions in order to avoid confusing experimentalartifacts. The Interaction of radlonuclides with particles 1n the oceans andmarine sediments can be described 1n terms of simple 1on exchange or adsorptionequilibria. The magnitude of the effective equilibrium constant for eachradionuclide 1s dependent on the redox properties and complex forming capabilityof the element 1n question, the concentration of the stable element, if any,the composition of the water—particularly 1n relation to the concentrations ofcomplex-forming ligands—and the surface and chemical properties of theparticles.
1. INTRODUCTIONLong-lived radlonuclides, both natural and artificial, have provided geo-
chemlsts and oceanographers with a series of extremely valuable tracers. Wfththe advent of nuclear fission several more extremely Important radlonucl1deshave become available. Improvements 1n nuclear radiation measurement technologyhave provided radlochemlsts with the capability to measure radlonuclides in the
41
marine environment at extremely low concentrations. There are now essentiallythree sources of long-lived radlonucHdes 1n the oceans: (1) natural elementsof cosmic origin, e.g. Be, Be, C, 2 Al, and 3^S1; (2) natural elements ofterrigenous origin, e.g. 40K, 129I, and uranium and thorium toaether with theirradioactive progenies and (3) artificial radlonucHdes, e.g. 50Sr, 137Cs, pluto-(Z30pu> 239-Z40pu) ancjf 241^m<Cl)
Measurements of these radlonucHdes 1n the marine environment have provideda wealth of Information regarding the physical, chemical and biological proces-ses which control the behavior of these and other pollutants 1n the oceans. Therange of these Interactive processes 1s Illustrated In F1g. 1. The value ofthese radlonucHdes as tracers for processes 1n the oceans 1s based largely ondifferences 1n their chemical properties, particularly 1n relation to theirapparent solubility or Interaction with particles - blotlc or abiotic. Thesedifferences result 1n the separation of parent-daughter radlonucHdes from theuranium or thorium series, or changes 1n the ratios of fission or activationproducts for the artificial radlonucHdes. Since the ratios of Introduction ofthe natural radlonucHdes to the marine environment (deposition of those ofcosmic origin, and in situ production of progeny from uranium and thorium decay)are constant and the deposition of artificial radlonucHdes, while being ex-tremely variable, 1s well known^2 , both artificial and natural radlonucHdesmay be used, depending on their half-life, as tracers for rate studies of par-ticle movement - vertical or horizontal^ , sedimentation and bloturbation.The differences 1n the chemical properties of the different daughter products ofuranium and thorium provide an effective means to disturb the radioactiveéquilibra chain and therefore oermlt the determination of sedimentation rates231Pa, 226Ra and zl°Pb(4), and particle
The cosmogenlc radlonucHdes *4C and iUBe have.alsosediment dating and 7Be to determine particle settling rates.and
settling rates using 23been used
Thfor
In addition, because the Inputs of the artificial racHonucHdes have beenextremely variable and effectively occurred over a very few years, they can alsobe used as tracers for rate studies of the mixing of water masses for periods of
heir radioactive half-life and mixing times of the oceans.time governed by theli
Short -termef fect«
Ufrtdke by porlldcs- orgonic- autochthonous- ollochthonous
Chemical »ptciotion— ionic slot*- oxidation «tot«
n-low transport processesRetention time
4 NN^^ f oemmc ot
timVÄtf BiagenK^^^"^• ^ inter-sfitiol J \^'
Sediments
Chemicol exchonge
Tvfejssstfssrwater
F1g. 1. The physical, chemical and biological Interactions of radlonucl tdes1n the aquatic environment.
42
Since thermonuclear testina has also Increased the flux of 14C to the oceans,this Isotope.as well as 137Cs, Sr and 239-240Pu may also be used ^n similarstudies.
The effectiveness of any radlonucUde as a tracer of particles 1n theoceans will depend on the chemical Interactions of the Ions or species 1nsolution with a heterogeneous phase - be 1t a sediment particle or living ordead organisms. It 1s clear then that a knowledge of the solution chemistry ofthe Ions Involved and the surface chemistry of the particles w i l l be critical tothe overall understanding of the adsorption process at the water/particleInterface.
2. SOLUTION CHEMISTRYThe chemical behavior of ^Cs ancj 90<;r -fn solution w i l l be typical oftheir stable cogeners 1n Groups I and II. Therefore they will act as tracers
for stable Cs and Sr 1n the water column» will be present» at the pH of sea-water, as simple Ions, and will participate 1n exchange reactions with clays.In addition, 90Sr will be Intimately Involved 1n carbonate equilibria and sub-stitute for other alkaline earth elements 1n corals and carbonate shell-materials. Because of the large concentrations of both alkali and alkalineearth elements 1n the ocean, these two rad1onucl1des will be essentially conser-vative 1n the water. However, the decrease 1n the residence times for the GroupI elements 1n the ocean from 6.8 x 10° years for K , to 4.5 x 10° for Rb , andto 560,000 years for Cs+ Indicates that there 1s a preferential removalmechanism for Cs+ Ions onto particles/"' The residence times for the alkalineearth elements decrease significantly. This 1s predominantly due to the de-crease 1n the solubility of their sulfates with Increasing atomic number.
Of particular Importance 1n this discussion 1s the behavior of the trans-uranlc elements Np, Pu, Am, and Cm. Since these elements have a far areatertendency to hydrolyze than those in Groups I and II, e.g. "'Cs and Sr, theyhave considerably smaller residence times 1n the oceans because of their inter-action with particles. In addition, several of these elements have more thanone oxidation state that can coexist in the environment, and variations 1n theratios of oxidation states can exert a major effect on their behavior. Whilethorium and uranium each occur 1n the marine environment 1n a single oxidationstate as Th4+ - or more Hkely as hydrolysed species Th(OH) (4~n7+, andUVI02++> which tends to act more like a simple divalent 1on, both Np and Pu canhave several different oxidation states coexisting 1n solution. However thenext two members of the series Am, and Cm apparently occur only in a singleoxidation state, Am3+ or Cm3"*".
Both Np and Pu can coexist under certain circumstances in four oxidationstates in acid solution because of the complex relationships involved betweenthe equilibria and the kinetics of conversion from one oxidation state toanother. In general, the reactions between M3+ and M4+, and NrU2+ an^ ^ ^2are rapid and those between Mn+ and MO?"1* are slow. The .latter two reactionsare clearly dependent on the hydrogen fon concentration. Very different eau1l1-brla and kinetics probably pertain at the near-neutral pH of seawater 9'- ' than1n add solution where most of the oxidation-state studies have been conducted.
In neutral or basic media the relationships between the oxidation statesare less certain because of the difficulties in measuring sensible redox couplesat metal concentrations where hydrolysis or precipitation may occur. However,estimates have been made for the formal potentials for plutonium 1n neutralsol-t1on(ll)
0.63 . Pu(OH)4yH2n - 1.11 PuQ2+ -0.77 PuOo_______ -0.94v ______________
43
Under these conditions PiH 1s unstable and Pu would appear to be more readilyoxidized to Pu(VI) than Pu(V).(10)
Several years ago Nelson and Lovett developed a simple technique to dis-tinguish between Pu(IV) and Pu(V) + Pu(VI) 1n natural water^125 based on theseparation of different oxidation states by co-predp1tat1 ng with rare earthfluorides as developed by Seaborg. ^' These experiments showed that a largebut variable proportion of the plutonium 1n ocean water 1s present 1n the higheroxidation state.
Nelson and Lovett(12:) and Nelson et al.(14) have shown that 1n watersamples collected from relatively shallow basins, and near the bottom of thedeep ocean» where relatively high suspended particle concentrations are present»the (Pu(V) + Pu(VI)/Pu(IV) ratio 1s large - 5, but 1n the open ocean the ratio1s closer to 1.0. In fresh waters with high dissolved organic carbon concentra-tions the plutonium 1s almost exclusively 1n the Pu(IV) state. -^
Further experiments by Nelson and Orlandini^6^ demonstrated that a labora-tory technique developed to separate Np(V5 from Np(IV) or (VI) 1n neutral solu-tion on silica gel where Np(VI) and Np(IV) are strongly» and N (V) 1s weaklyadsorbed» ' could be adapted for use with the very large vol urnes of waterneeded to measure the oxidation states of plutonium at environmental concentra-tions. They have also shown that 1f a solution of PU(VI) 1s added to a sampleof a natural water» the plutonium 1s reduced rapidly to Pu(V) unless a holdingoxldant like MnU4~ 1s present. With no oxldant present the reduction Is >90%complete 1n -2 hours. Furthermore» using a combination of the techniques out-lined above» they have shown that the higher oxidation state of plutonium 1nnatural waters 1s Pu(V) and not Pu(VI). Measurements by Harvey have shown thatneptunium In the Irish Sea 1s» not unexpectedly, 1n the Np(V) oxidationst ate «
The variability 1n the values of the ratios of Pu(V)/Pu(IV) 1n differentnatural waters or 1n different parts of the oceans raises questions regardingthe processes controlling the reactions between Pu(IV) and Pu(V) and the speciesInvolved.'1™ However, the reaction does appear to be catalyzed or otherwiseInvolve a reaction with particles.
The chemical concentrations of Pu(IV) 1n ocean waters (-0.2 - 0.5 x ICClZ M1n the open ocean and up to 3 orders of magnitude greater in the Irish Seaare far greater than one would oredict for the solubility of Pu4+ 1n equilibriumwith solid Pu(OH)/ at pH8 (=10-3%, «So = 1056)(21) In contrast, since Puv02behaves essentially as a univalent ion» it is very soluble in water with asolubility product Kc-, = 10"°* , and its maximum concentration at pH 8 could beas high as 2.5 x -10 M before precipitation is likely to occur. Since up to20% of the Pu is present as Pu(IV), the observed concentrations of Pu(IV) mustbe a result of complexlng by ligands which are readily available in naturalwaters. Pu(IV) forms strong complexes with a variety of inorganic and organicligands which are known to stabilize this oxidation state in solution. In par-ticular it has been shown that 5 x lO"4 M citrate ion solution prevented theformation of Pu(IV) hydroxide polymer in a solution with CPu]t = 10" M at pHvalues as high as ll.11;i;
3. INTERACTION WITH SEDIMENTS
It is foolhardy to believe that it will be possible to understand thebehavior of radionuclides in the oceans solely in terms of their solution chem-istry. The interaction of ions with particles in the water and in the sedimentsw i l l modify their behavior and perhaps exert the major control on theirtransport and fate in the environment.
44
Detailed studies of the behavior of plutonium* and other radionucl1des 1nrestricted bodies of water have provided a great deal of Information on theirassociation with particles and transfer to the sediments. 22*23) Measurementsof the distribution of radioactivity associated with different geochemlcallydefined phases - such as specific minerals or surface coatings - have providedInformation on the chemical nature of the Interaction at the particle-waterinterface. ' Changes 1n these distributions within the sediment column canprovide Insight into possible differences in behavior due to dlagenetic reac-tions Involving changes in the concentration of ligands or redox condi-tions/19'24^ A great variety of chemical techniques have been utilized todevelop a sensible scheme to assess the geochemlcal association of elements withparticles (1n particular* that part not found 1n sediments deposited in pre-development times). The different schemes have been reviewed elsewhere/"'The basic classification of Gibbs Identified four types of association - ion-exchange, adsorption with iron» manganese and other hydrous oxides» complexatlonby surface organic molecules, and incorporation into a crystalline or residualfraction/2 However» Edginqton has shown that such a simple classificationapparently breaks down for 2^Upb, since a large fraction of the total loading isapparently in the residual fraction - an observation that 1s difficult toreconcile since almost all of the 210Pb is of very recent origin (via the atmos-phere) and readily removed from sediment by dilute add/2''
While clay minerals are generally the major component of the fine grainsediments which may adsorb trace metals or organics in the ocean, their residualsurface charge permits the formation of organic or hydrous oxide surface layerswhich can drastically modify these adsorption properties at the surface. Thehydrous oxides and in particular, hydrous ferric oxide surface layers areubiquitous, adsorb many trace metals and have been the subject of intensestudy/28' Thus it is not surprising to find that the extraction results forplutonium and americium on sediments from the Great Lakes and Buzzards Bay showthat these elements are associated almost entirely with the reducible hydrousoxides, and that this association does not change with depth, and presumableredox conditions, 1n the sediments/23»2™ Aston has found a similar result forsediments from the Irish Sea/3 '
At this point 1t is clear that the behavior of the radionucl1des in theoceans is very dependent on not only their solution chemistry, but also thesurface chemical properties of the adsorbing solids. Using plutonium as anexample, because of its importance and occurrence 1n multiple oxidation states,a simple equilibrium model can be proposed to describe the interaction of thiselement with particles 1n the ocean. This is Illustrated 1n Fig. 2. The modelInvolves five different chemical reactions or equilibria:
(1) The oxidation/reduction couple
Pu4+ + 2H2o 5Ä Pu02+ + 4H+ + e (3.1)K™ v = CPuo2+] CH+]————————— (3.2)
CPu4+]The studies of Nelson and Lovett(12^ and Nelson and Orland1n1^165 have
shown that there are great differences in the values of the ratio ofPu(V)/Pu(IV) in ocean water. In the Irish Sea the ratio is strongly 1n favor ofthe oxidized state, = 0.8, but 1n the Pacific Ocean the ratio decreases to ~0.5» but 1n water Just above the sediment/water interface rises to ~ 0.8.Unpublished data from Nelson shows that the ratio also decreases with Increasingdistance north from the Irish Sea and around the north of Scotland/31'. Labora-tory studies have shown that 1n separate samples of carefully filtered LakeMichigan water, Pu(V) and Pu(IV) are stable, but in the presence of ~ 1 mg'1"1of sediment particles the Pu(IV) 1s rapidly oxidized and the Pu(V) 1s rapidly
45
0UJto
E P u ( I V )i
Pu(IV)S/
IV,,, iK
S Z Pu(IV)1
E u
tv.v
Pu(V)S
EPu(V)'
Hg. 2. The role of hydrolysis and complex formation reactions 1n theInteraction of plutonium or other ac t f r t des w i th sediments and theirrelation to measured values of KQ,
reduced to the extent that the Pu(Y)/Pu(IV) ratio - 0.8, the ambient ratiomeasured 1n Lake Michigan water/10' Thus 1t appears that the redox reaction 1scatalyzed by the presence of terrigenous particles.
(2) The Hydrolysis of Pu4+ and Pu02+
The study of the hydrolysis of Pu4+ has been hampered by the formation of4+colloidal species at fairly low pH values, and the maximum concentration of PuIons 1n solution is limited by the solubility of Pu(OH)4:
KSo = [Pu4+][OH~]4 = 10'56 (3.3)
The hydrolysis of Pu4+ however proceeds 1n a stepwlse manner:
Pu4+ + H20 *Ä Pu(OH)3+ + H+
PuOH3+ + H20 ÇA Pu(OH)2+ + H+ etc
(3.4)
(3.5)
with the possible formation of anionic hydroxyl complexes with formation con-stants:
Pu(OH)4 + OH" Pu(OH),
H =[PuOH3+][H+]
[Pu4+](3.6)
H _[Pu(OH)2+][H+]
when = 9,K9 , 1H i/ H (3.7)
H =
[Pu(OH)F]CH+]
CPu(OH)4]
46
where * = *K 1H«*K2
H> • . . '*i<5H
The values of the formation constants for the hydroxyl complexes of Pu4+ aresubject to some speculation. The values reported for log *K^ for Pu arealmost Identical to those for U , log #Ki" - 1.6. More recently» Allardhas critically examined the solubilities of the actlnlde elements 1n neutral orbasic solutions and quotes values for log H (n = 1 to 5) based on thesolubility of U4+.(9) The ratios of [Pu(OH)n
(4"n)+ * nH and the maximum
[Pu4+] CH+]n
[Pu(OH)n(4~nH] concentrations 1n equilibrium with Pu(OH)4 at pH 8 and thus
[Pu44"] (~ 10"32) at pH 8 are shown 1n Table I.
Table I. Hydrolysis of Pu4+. Stability Constants and Relative Concentrationsof the Principal Monomeric Hydrolysis Products.
n 1 2 3 4 5
log «BnH
CPu(OH) nC 4~ n H ]
-0.5 -2.5 -6.0 -11.5 -20.0
3.2 x 107 3.2 x 1013 1.0 x 1018 3.2 x 1020 1.0 x 1020
[Pu(OH) n( 4 ~ n H ] a 3.2 x lO" 2 5 3.2 x 10"19 1.0 x 10'16 3.1 x 10~12 1.0 x lO"12 M
Calculated maximum concentrations in equilibrium with Pu(OH)^, log Kgo = -56.0
Values of log * nH taken from ref (9) .
If the estimates of these formation constants are correct then concentra-tions of plutonium up to ~4 x 10~^ M 1n natural water at pH 8 1n equilibriumwith Pu(OH>4 can be explained completely 1n terms of complexlng by the hydroxyl1on.
In contrast» at the concentrations of plutonium (V) Hkely to be en-countered In.the ocean» the dominant species will be Pu^U2+> since univalentIons do not readily hydrolyse or form complexes.
(3) Complex Formation (Inorganic HX, or Organic HP» Ligands
Pu(IV) and Pu(VI) hydroxides will also dissolve 1n carbonate solutions toform complexes/3^»33) jne estimates of the stability-constant for the Pu(IV)-carbonate complex, based on solubility measurements» K ~ 10 » appears to be
z. 10" or oxalic add K-, = lO8''/ 1 It has been suggested that carbonaterather high 1n comparison with values for comparable Ugands such as citrate *K
or oxalic add K-, = lO8''/ 1anlonlc complexes could De the major species 1n solution. Such a hypothesis wasattractive before 1t was discovered that the predominant upper oxidation state1n solution was Pu(V) rather than Pu(VI), since U(VI), the analogue for Pu(VI)1s present in seawater as an anlonlc carbonate complex,
Even though Pu4"1" forms relatively strong complexes with S0|~ ion, e.g.
47
Pu4* + HS04~ =£ PuS042+ + H+ *Ki = __ _______ (3.8)^ [Pu4+3CHS04-]
where *KI = 740,(22) the CS04=] 1n seawater 1s only 3 x 10~2M, which 1s notgreat enough to contribute a significant fraction of the total Pu™ 1n solution1n the oceans.
In a discussion of complexlng In solution, the formation of organic com-plexes cannot be Ignored. The Importance of humlc acids as principal complexlngagents 1n natural waters and sediments 1s well established. While 1t ap-pears that complexatlon by the hydroxyl 1on could account for the observed con-centration of Pu(IV) 1n water, the potential role of complexlng by humlc addsshould be addressed. Unfortunately there are no directly measured values of astability constant of Pu(IV) (or any similar element) with humlc adds.
However, Nelson et al. have shown that additions of humlc add (solubleorganic carbon) to natural waters significantly depress the adsorption ofplutonium onto autosedlments suggesting the formation of complexes and thispermits the calculation of conditional stability constants^'.
(4) Interaction with Sediment.The Interactions of metal Ions with sediments that have been discussed
earlier 1n this paper can be expressed 1n terms of a simple heterogeneous chemi-cal reaction analogous to reactions with complexlng Ugands. For simplicity 1tw i l l be assumed that the only 1on1c species Interacting with the hydrous Iron
sLangmu1oxides 1s Pu (however this could be a hydroxo complex, see Hs1 and
r(37>:Pu4+ + HSsed ^ puIVssed + H+ <3'9)
and IVKS = {Pu(IV)S}[H+]—————————— (3.10)[Pu4+] {HS)
where C ] = moles'!"-*- and { } = moles'kgThere are two major problems 1n using this equilibrium reaction. The first
1s the parameterization of (HS), which is essentially the concentration of ac-tive exchangeable sites on the sediment particles. However, several techniqueshave been developed to estimate {HS}. ") The second problem 1s that the reac-tion with sediment particles may be more complex than Illustrated here. Jamesand Healy have suggested that metal hydroxo species are more strongly adsorbedthan free metal Ions since the adsorption of metals 1s strongly pH-dependent. Other models have been developed which explain the pH-dependence1n terms of the activity of the E Fe - 0~ groups/28'
(5) The Distribution Coefficient. KpSince it 1s impossible to measure the concentration of each plutonium spe-
cies 1n solution the association of plutonium with sediments 1s expressed 1nterms of a distribution coefficient/ (a parameter commonly used 1n describingheterogeneous equilibrium in solvent extraction and 1on exchange).
Total Pirg"^ sedimentKD = ————————————————— (3.11)
Total Pu'ml'1 1n solution l
48
[Pu(IV)] + CPu(V)]where
(3.12)
[PudVn = CPu4+l + n [Pu(OH)n(4n )+ + nt;puXa](4-n)+ + „[PuLn
(4~n)] (3.13)and also lvKp = {Pu lVS>/[Pu(iv)] and VKD = {PuvS>APu(V)3.* The definition ofthese equilibrium constants KQ and *KQ for the Interaction of plutonium withsediments presumes that these reactions are reversible. A large proportion ofthe measured values of KQ, which .Ip.s.Q facto are assumed to be the equil ibriumconstants, have only been measured for the uptake reaction. Edgington et al.have studied the uptake and descrption of plutonium on sediment and have shownthat the same Kn values for Pu(IV) and Pu(V) 'can be obtained from uptake anddesorptlon studies when approaching the equilibrium from either side. ij Theoxidation states of plutonium on sediment particles have been determined using amild leaching technique. The results show that the plutonium on particles 1salmost entirely in the Pu(IV) oxidation state, and that very little Pu(V) 1sfound. ^' However, the value of VKD estimated from these experiments, <. 10001s 1n close agreement with the value measured by Harvey for Np(V), -250, in thelaboratory/"" The value of the KD measured for Np in the Irish Sea is greaterthan that for Np(V) measured in the laboratory, but far less than the value ofeither K^ (Np) measured also 1n the laboratory or the value of the overall KDfor plutonium measured in the Irish Sea.(18) These data suggest that there Isless reduction of Np(Y) than Pu(V) in the Irish Sea and that K j y^y (Np) « K jy j V(PuMsee equa. 3.2).
A large number of KQ values have been measured for the transuranlc ele-ments: representative values for these, as well as for Th, and U for comparison,are summarized 1n Table II. The magnitude of the measured K^IS vary in theorder:
KD[Th(IV)] 5 KDpPu(IV)3 = KD[Am(III)] » KD [U(VD] > KD [Np(V)] = KQ [pu(V>]
Table II. Comparison of the Values of the Distribution Coefficients (log Kß)for the Act1n1de Elements from Field and Laboratory Measurements
Element F1 eld Laboratory
Th( IV) 6.9 (49) - > 7.0 (42)a
U ( V I > 3.0 ( 43 ) - 3.90<42)a
Np(IV) —— 4.30(18)
Np(V) 3.70 (18)b 2.40(18)
Pu(IV) 6.40t l4'19) 5.70 - 6.40
Pu(V) <3.00(14)
AM(III) 6.08(44) 5.40 - 5.70(45)
GmCIII) 6.09 (44)
aThese values may not reflect a true KQ since no attempt was made to determinewhether all of the Th or U 1n the bulk sediment was Involved 1n the surfaceexchange reaction.bS1nce no separation of Np(V) and Np(IV) was made for the sediment this valueprobably reflects a contribution from Np(IV) adsorbed to the surface.
*A similar parameterization Involving complexatlon has been suggested recentlyto account for varia tlons 1n the distribution coefficients for hydrophoblcorganic molecules between natural waters and sediments. The authors suggestorganic-organic Interactions in the aqueous
49
Considering the wide variety of sediment types Involved, possible differences inthe particle-size distribution of the sediments examined» and the variation inthe ratio of oxidation states» it was encouraging to find that the reportedvalues for Kn(Pu) for oceanic sediments have a relatively small range.Duursma and Bosch have shown that variations of a factor of 5-10 1n the value ofKQ can be explained solely by differences 1n the particle-size distribution innatural sediments/46' In those cases where the values of KQ are the greatest,the sampling technique favored the collection of extremely fine-grained sedi-ments, as has been discussed elsewhere.
There are some differences- between the values of KQ measured 1n the fieldand the laboratory. These differences can arise from perhaps two major causeswhich are related to experimental* conditions. First and foremost there 1s thequestion of particle size alluded to above. Values of KQ measured on bulksediment in the laboratory would be expected to be lower than those valuescalculated from the analysis of suspended sediments. Secondly, a factor»particularly Important when discussing the behavior of plutonium» 1s thequestion of the ratio of oxidation states and the chemical form of therad1onucl1de used for the measurements. As the [Pu(Y)]/[Pu(IV)] ratiodecreases, the value of the measured KQ will Increase. Secondary factors couldbe related to the effect of variations in the composition of the water orsediment used, related to changes in the concentration of potential complexlngagents in the water, sediment» or sediment/water ratio. The depression 1n thevalue of KQ for plutonium in the interstitial water of Irish Sea sediments 1spresumably due to an Increased concentration of organic complexlng agents due tothe diagenesls of natural organic material 1n the interstitial water*4''' as arethe observations by Santschl et al. that the KQ for amerlclum 1s depressedconsiderably when the sediment/water ratio 1s Increased. 4-^
The definition of KQ Implies that the total concentration of metal adsorbed1s a linear function of the concentration 1n solution. This definition is onlytrue as long as the fraction of the exchanageable sites occupied by metalsremains relatively small. When the surface coverage becomes significant» devia-tions from linearity are common and the Langmulr or Freundlich Isotherms must beemployed. However» for the transuranic elements, the probability of havingtotal concentrations present in the oceans» such that KQ ceases to be constant,1s unlikely.
Care must be taken that KQ values are reported for conditions that closelyapproximate natural conditions, or that both the solid and solution phases arewell characterized so that extrapolations are valid. Recently Webber fit al>have shown that the decrease in KQ of hydrophobic organic compound with In-creasing solid/water ratio 1s accompanied by a change in turbidity in theaqueous phase^4"' and this can be interpreted in terms of the formation oforganic-organic association. 4^
4. EFFECT OF ELEVATED CONCENTRATIONS OF PLUTONIUM
The problem of the hydrolysis of Pu4+ 1n even moderately strong add hasplagued chemists since this element was first produced by man. Plutonium poly-mers appear as soon as a solution of Pu4+ in add was diluted by adding water.Even though the overall acidity in solution was ~1 M» local areas of very highpH are formed causing the colloid to form. Nelson et al.» as part of a study todetermine the true solubility of plutonium in water» have developed techniquesto prepare stable, relatively concentrated solutions of Pu4+ and Pu(>2+ for use1n this and other environmental studies/4^) Solutions containing PuC>2+ aremade simply by adding solutions of Pu^* in dilute nitric add to the lake orocean water - reduction of PiA* to Pu^ is rapid and complete. Solutions con-taining Pu4"1" are prepared by evaporating a solution of Pu4+ in 8m HNO^ to dry-ness and dissolving the residue in a l M NaHCOg solution.
50
Using solutions prepared 1n this manner Nelson et al. have shown» by addingsuccessively higher concentrations of plutonium to Lake Michigan water con-taining suspended sediment» that the apparent constants established at 1n thefield at 10"17 -- ID"18 M for the Pu(V)/PU(IV) ratio - 5 and the IVKD ~ 5 x 10bdo not change over a concentration range of a factor of -10. At a totalplutonium concentration 1n solution between 10~° and 10"' M> the value of IV«QIncreased dramatically Indicating the formation of an Insoluble hydroxide re-sulting from the exhaustion of the complexlng capacity of the llgands 1n thewater and/or the saturation of adsorption sites on the sediments.5. EVALUATION EQUILIBRIUM CONSTANTS FOR A MODEL SYSTEM
The observation by Nelson et al. that there 1s a linear Increase In CPuIV]1n solution with Increasing total concentration of plutonium over -10 orders ofmagnitude» Indicating a constant value of Kp, and a constant ratio ofCPu(V)]/CPu(IY)] states provides a means to evaluate a 11m1t1ng-value for {HS},the concentration of active exchangeable sites on sediments.
Synthetically prepared goethlte and FeOOH have been shown to have a totalnumber of exchange sites - 1 - 135 moles'kg , but ocean surface sediments have1n excess of 2.7 moles'kg"1 as determined by tritium exchange. 38) In thissediment the exchange sites Included all hydrous oxides and not Iron oxides 1nparticular. Numerous workers have shown that transition metals, unlike p1u,tA"rnlum or americlum, are not solely associated with reducible hydrous oxides ",and that the value of Kp starts to decrease when the ratio of {MS)/{HS}, thefractional surface coverage, exceeds 0.1 - 0.2/38' jn fac-t, Edgington hasshown that only ~ 30% of *10Pb 1s associated with this phase.(27T In the caseof the Lake Michigan sediment» a direct determination of the number of exchangesites has not been determined, and a value based on the measured concentrationof readily extractable Iron will be used» because plutonium and amerlcium doappear to be specifically bound to reducible oxides/") The fine-grained LakeMichigan sediments contain ~ 3-4% total Iron, and the concentration of Iron that1s released with other hydrous oxides by reduction and extraction using thec1trate-dith1on1te method 1s ~ 15 mg g"1 or - 0.25 moles>kg~1.(27)
Provided that the required surface sites are available 1n excess and the Kp1s Independent of the total metal concentration» an adsorption equilibriumconstant may be calculated for the reaction, eqn (3.9)
Pu4+ + HS 5^ PuIVS + H+where» from eqn (3.10)
IV«S[H+] = {PuIVS}/CPu4+3{HS}Other workers express the constant in terms of the total metal concentration insolution and
e.g. *'KS = '______ (5.1){HS}
Now 1f the maximum concentration of Pu(IV) that can be held 1n solution 1na natural water, e.g. Lake Michigan, can be increased to ~ 10~° M without anyapparent change in the value of Kp, the fractional surface coverage can have avalue where {MS}/{HS} <. 0.01 - 0.02. Thus for a Kp = 5 x 10s, at CPu IV] = 10"0 M» the maximum value of {Pu(IV)S} is 0.005. If the value of {Pu(IV)S}/{HS} 1snot to exceed 0.01 - 0.02, and the minimum value of {HS} 0.25 Ü* assuming allof the citrate-d1th1onite extractable iron must be on surface as exchange sites.While It 1s now possible to calculate a value of IVKS, having establishedreasonable values of CPu4+], {Pu(IV)S}, and {HS}, there still remains a questionas to whether a single species 1s adsorbed e.g. Pu4+, or whether other speciesare adsorbed as well, Pu(OH)3+, Pu(OH)22+ etc. Under such conditions IVKS maybe def1ned e.g.
51
IV, (PuIVS}[H+][Pu4+]{HSJ
{Pu(OH)2S}[H+3
CPu(OH)92 + ] {HS}
etc.
Bal1str1er1 and Murray avoid the problem of defining the exact species 1nsolution by defining the constant In terms of the total metal concentration 1nwater (37)
(MS}[H+]K< (5.2)
EM]T{HS}For plutonium a value of IVKS may be defined 1n this manner as
IV K< = (5 x 10s) x (10~8) = 2 x 10'2 or log IVKS = -1.7.The definition of the constants 1n this manner normalizes the observed values ofKn for sediments with widely differing concentrations of exchange sites, andallows a direct method of comparison for the complexlng strength of metals withother sediments. Bal1strier1 and Murray report values of log Kg for Cd, Cu andzinc 1n geothlte of 0, -13 and -3.2, respectively, and for zinc onto a fine-grain sediment, a value of -0.6.(38) The KD value for Am(IV) on the samesediment 1s ~ 10e "6.
log Ks = -1.4.COMPLEXING BY NATURAL ORGANIC COLLOIDSIn an elegant series of experiments Nelson et al. have Investigated the
complexlng effects of natural organic macromolecules (humic acids) on the ad-sorption of plutonium and amerldum to sediment particles. °\ The complexlngability appears to be a function of the source of natural dissolved organiccarbon (D.O.C.). The effect on the value of ^ of readdlng Increasing concen-trations of D.O.C. (concentrated from Lake Michigan water by dialysis, M.W. cutoff 1000) Into depleted Lake Michigan 1s shown 1n F1g. 3. Up to the normalconcentration of D.O.C. 1n Lake Michigan water (^ 1 mg-1"1) the value of IVKpremains essentially constant. As the concentration is Increased to values >3.0mg-T1 the value of IVKD decreases markedly, the slope of the plot of log 1/KDvs log D.O.C. Increasing rapidly to a value approaching 2, suggesting that amixture of PuL and PuL2 complexes are formed.
CONC DISSOLVED ORGANIC CARBON (mg L'1)ICT1 I 10 ICO 1000
icr««T
10 ' 10 '[HL] ESUIV L'1 (x 12)
Fig. 3. Comparison of the observed and calculated effect of Increasingconcentration of colloidal D.O.C. on the value of IVKQ for plu-1n natural waters,
(a)
theplutonium
Observed data for Lake Michigan water and best fit calculatedf rom eqn. 6.6 w i th «log «K^ = 20.7 and log ,K2
L = 0.7,
(b)(c)(d)
concentration of PuL3
concentration of PuL2calculated change 1n Kg for ocean water from the Bay of Fundyusing the constants given by Nelson et al.
52
Starting with the definition of KD given above, 1t 1s clear that sinceconcentrations of D.O.C. less than the present concentration in Lake Michigan donot change the measured value of **KQ significantly, then at D.O.C. concentra-tions 12-3 mg*l~ > using the same form as 1n equ (3.16)> but for Pu(IY) only,
IVL{PuIVSJ
(6.1)n CPu(OH)n] n [PuXn3
where X represents any Inorganic complexes present,
orn*Kn
H[OH3n + n*Knx[X3n/CH+3n
(6.2)
where Ks* = IVKs{HS)/CH+3.
Similarly if the concentration of dissolved organic carabon Is CHL3» and1:1 and 1:2 complexes are formed, the value of the distribution coefficient wi l ldecrease to:
IVLKS*
*K x [X3 n CH + 3 nn * n tT1 + #K1L#K2
L[HL32EH+3"7
Inverting this expression and substituting fori i
1 1_
leads to
-2
'K DIV
D KS*I Vu
(6.4)
Nelson et al. have studied the effects of Increasing the concentration of D.O.C.on *^KQ for several different natural waters - both fresh and marine - and havefound that while most waters collected 1n the northern United States behavesomewhat similarly to Lake Michigan (Fig. 4) in that they form both 1:1 and 1:2complexes, fresh and marine waters from the southern states form 1:1 complexesonly.(36) They found that the values of *KjL/Ks* giving the best fit to datavaried by a factor of 100 - from 9.7 x 10"5" in a southern swamp to 7.5 x 10~7 inLake Michigan. Ocean waters from the Gulf of Mexico (1:1 complex only) and Bayof Fundy (1:1 and 1:2 complexes) had val ues of 4.0 x 10~6 and 8.8 x 10~6respectively.
-K> -9 -• -T -S -5 -4 -3 -tTOTAL PLUTONIUM ADDED (M)
F1g. 4.
Schematic representation of the predicted variation 1n theconcentration of plutonium 1n solution, [Pu(IV)D, as a function oftotal plutonium added to the system.
(a) No sediment» complexlng by hydroxl Ion only;
<b) effect of additional complexlng by naturally occurring Ugands;
(c) - 0.1 g.sediment T1, IVKD = S x 10s;
(d) the effect of exceeding the adsorption capacity of thesediment, KQ decreases by factor of 100;
(e) same as (c) with IVKQ = S x 1C3;
(f) the effect of exceeding the complexlng capacity of the naturalUgands;
(g) the effect of exceeding both the adsorption and llgandcomplexlng capacities of the system;
(h) the variation 1n [Pu(V)] under same conditions as 'c!).
53
From the data shown in Fig. 3 it is possible to estimate values of #Ki and*B2L. The total CPu(IV)] in solution in Lake Michigan (which is 1/IVKD is givenby the denominator of equation (63)1/(IVKD) [Pu (IV)] (1 + n*BnHCH+]-n + *K1L[HL][H+]-l + B2L[HL]2[K^]-2) (6.5)
From the experimental data shown in Fig. 3 it is evident that complexing by acomponent of the dissolved carbon contributes a measurable fraction (~ 25%) ofthe total CPu(IV)] found in the water. The data also indicate that the changein KQ is due to the formation of 1:1 and 2:1 complexes. Since the only changemade to the system in these experiments is to increase the concentration of [HL3+ [L~], then
1/(IVKD) (1/(IVKD) = aK^CHLHH+r1 + »B2LCHL]2CH+]-2 (6.6)The ratio of the value of the ratio of *K}L/*B2L giving the best fit to the datawas found to be - 5.0. Using the same assumptions made earlier *K^ = 5 x lO^Oand *B2 - 1 * 10 or *K2L = 0.2. The variations in the concentrations ofthe PuL and PuL? complexes alone are also shown in Fia. 3. At the concentrationof colloidal D.O.C. in Lake Michigan water (~ 1 mg-l"1), the increase inconcentration of Pu(IV) 1s solely due to the formation of PuL. Theconcentration of D.O.C. would have to increase by a factor of ~ 10 before theconcentration of the [PuL2] became significant.
The conditional stability constants (*KiL) for the humic acid complexes inthe marine environment vary between 2.7 x ICF^ for the Gulf of Mexico and 5.8 xlO2-^ for the Bay of Fundy. Considering that the concentration of D.O.C. inocean water is 1 03 of the concentration in Lake Michigan, it is still apparentthat complexing by humic acids could be very important at certain locations inthe marine environment. Also shown in F1g. 3 is the calculated change inconcentration of Pu(IV) for water in the Bay of Fundy based on the constantsgiven by Nelson et al. 36) If the concentration of D.O.C. is ~ 1 mg'l"1, thenCPuL3+] + CPuL22+] account for ~ 90% of the total [Pu(IV)] in solution. If theconcentration of D.O.C. is 0.1 mg'l~l the complexes account for ~ 50% of thetotal CPu(IV)] in solution.
The effect of Increasing ligand concentrations» presumably D.O.C. on the[Pu(IV)] 1n solution is also apparent from studies of interstitial water. Nel-son and Lovett have shown that the values of ™Kp calculated from measuredconcentrations of Pu(IV) on sediments and in interstitial water taken from theIrish Sea are an order of magnitude lower than the value of KQ in the overlyingo e r o m a g n u e ower a n v e Qwater 4" The ratio of CPuV]/[Pu(IV)] decreases from - 5.0 in the overlyingwater to - 0.1 in the interstitial water. Presumably the decrease in the valueof Kn for Am(III) with increasing sediment/water ratio is also due to a similarcomplexing reaction. 5) Clayton et al. have shown that concentrations of EDTAgreater than 10" M depress the value of KQ for Am(III) the formation of acomplex in solution. However, part of the decrease in the value of KQ maybe due to the destruction of the hydrous oxide layer as a result of the com-plexing of iron etc. It must be stressed that the values of these stabilityconstants are based on the assumption that the stability constants calculated byAllard for the hydroxyl complexes are correct » but this has no effect onrelative concentrations.
Provided that the formation constants for the hydrolysis of Pu4"1" are cor-rect, there is no need to invoke complexing by ligands other than OH" and humicacids. In fact» it can be shown that» even if all the low molecular weightcomponent of D.O.C. in the water is assumed to be present as ligands such as4citrate and oxalate - known to form strong complexes with Pu i o n s ' andwithout considering competitive equilibria with major cations, the complexesformed wou ld not significantly change the concentration of Pu(IV) in solution.
54
The interplay between the various factors: (1) solubility product» (2)complexing by hydroxyl Ions, (3) complexing by humic add» and (4) thedistribution coefficient, is simply illustrated. Each of these factors in theirown way limit the total and maximum concentration of plutonium that can remainin solution. Thts 1s best Illustrated as 1n Fig. 4 by showing the change 1nconcentration 1n solution as a function of the total concentration of plutoniumin the system (water and sediment).
In the absence of complexing by hydroxyl Ions the maximum concentration ofPu(IV) that can exist 1n solution as Pu4+ before a precipitate forms would be10~32 M- Calculations using the stability constants reported by Allard Indicatethat complexing by hydroxyl ions increases by a factor of 10 , but theexperimental data of Nelson et al/49) suggests that this factor should be 1024with [Pu(IV)3 =. 10" - 10. Complexing of further plutonium by organic carbonwill increase this concentration by a further factor of ~ 3.0. This 1sillustrated in Fig. 4, curves (a) and (b). In the presence of sediment, thetotal amount of plutonium that can be added to the system before precipitationof Pu(OH)4 occurs will Increase by a factor equal to KD, larger curves (c) and(d). A complication arises when the fraction of adsorption sites occupied byplutonium on the sediment increases beyond - 1% and the value of the KQ de-creases. In this example 1t is assumed that the decrease is a factor of 100between 1% and 100% coverage, a value that appears to be typical for othermetals.^8' This is illustrated in curve (d). As the surface coverage is In-creased the KQ decreases and the concentration in solution moves towards a valuelimited by a KQ value of 5 x 103 rather than the original KQ = 5 x 105.
A further complication will be Introduced when the total concentration ofcomplexing Ugand CHL] + CL~] ~ [Pul_nL If the total concentration of plutoniumadded approaches this value, the concentration 1n solution will move towards thevalue governed by Just the hydroxyl 1on concentration, curves (f) and (e).Finally if exhaustion of ligand occurs before the saturation of surface ad-sorption sites on the sediment a behavior approximated by the curve (d) - (g)might occur. The behavior of Pu(V) under similar conditions is also show, curve(h).
7. CONCLUSIONS
1. The behavior of the long-Hved radionucl ides in the oceans 1s con-trolled by the formation of complexes and the Interaction of specific specieswith sediments.
2. The maximum concentration of plutonium that can exist in neutral orslightly basic natural waters is influenced by the ratio of CPuV]/[PuIV3. As anunivalent ion, the solubility of Pu(V) 1s large and in equilibrium with Pu02OHat pH 8, the maximum [Pu02+] s. 2.5 x 10~3 M. The maximum [Pu(IV)] at pH 8approaches 10 M» a concentration which is several orders of magnitude higherthan would be predicted from published values of Kg0 and hydroxyl 1on com-plexing.
3. Under normal environmental conditions, these radlonuclides are underadsorption/desorptlon control, thus confirming Goldberg's hypothesis of equilib-rium distribution,^!) but 1n situations where extremely large concentrationsare discharged precipitation/dissolution could become the major controlling fac-tor.
55
4. At environmental concentrations of plutonium or americium their ef-fective solubility is controlled by the total concentration of solids present 1nthe system. However» if the total concentrations of Pu or Am added is doubled»the final concentration in solution w i l l be doubled also. Thus expressing solu-bilities as a percentage of total radionuclide added is meaningless.
ACKNOWLEDGEMENTSThe authors would like to acknowledge the generous support of the U.S.Department of Energy, Office of Health and Environmental Research and the U.S.E.P.A., Office of Exploratory Research during the many years of effort devotedto understanding the behavior of long-lived radionuclides in the environment.They appreciated the fruitful discussions with R.P. Larsen and J. Pentreathduring the course of this work.
REFERENCES(1) National Research Council. Radioactivity in the Marine Environment.
National Academy of Sciences, Washington, D.C. (1971).(2) Health and Safety Laboratory. Final Tabulation of Monthly 90Sr Fallout
Data, 1954-1976. Environmental Quarterly, U.S. Dept. of Energy H.A.S.L.- 329 (1977).
(3) Guinasso, N.L., Schink, D.R. Quantitative estimates of biological mixingrates in abyssal sediments. J. Geophys. Res. 8_0_ (1975) 3032-3038.
(4) Goldberg, E.D., Bruland, K. Radioactive Geochronologles. The Sea. Vol.V (Goldberg, E.D., Ed.) (1974) 451-490.
(5) Bacon, M.P., Anderson, R.F. Distribution of Thorium Isotopes BetweenDissolved and Particulate Forms in the Deep Sea. J. Geophys. Res. 87(1982) 2045-2056.
(6) Turekian, K.K., Volchok, H.L. The Natural Radioactive Isotopes ofBeryllium in the Environment. Abstracts of Meeting sponsored by YaleUniversity and U.S. Dept. of Energy (1979).
(7) Bowen, V.T., Noshkin, V.E., L1v1ngton, H.D., Volchok, H.L. FalloutRadionuclides in the Pacific Ocean. Earth and Planetary Science Letters4_8_ (1980) 411-434.
(8) Bowen, H.J.M. Environmental Chemistry of the Elements. Academic Press,London (1979).
(9) Allard, B. Solubilities of Act1n1des 1n Neutral or Basic Solutions. In"Actinides in Perspective" (Edelstein N.M., Ed.) Pergamon Press (1981)553-580.
(10) Ray, D., Serne, R.J. Plutonium Activities 1n Soil Solutions and theStability and Formation of Selected Plutonium Minerals. J. Environ.Quai. É. (1977) 89-95.
(11) Cleveland, J.M. The Chemistry of Plutonium. Gordon and Beach, New York,N.Y. (1970).
(12) Nelson, D.M., Lovett, M.B. Oxidation State of Plutonium 1n the IrishSea. Nature 276 (1978) 599-601.
(13) Katz, JJ. and Seaborg, G.T. The Chemistry of the Actinide Elements.Methuen & Co., London (1957).
56
(14) Nelson, D.M., Metta, D.M., Larsen, R.P. Oxidation state distribution ofplutonium 1n marine waters. Radiological and Environmental ResearchDivision Annual Report, ANL-80-115, Part III (I960) 26-28.
(15) Nelson, D.M., Karttunen, J.O., Orland1n1, K.A., Larsen, R.P. Influenceof Dissolved Organic Carbon on the Sorption of Plutonium to NaturalSediments, Ibid. 19-25.
(16) Nelson, D.M., Orland1n1, K.A. Identification of Pu(V) 1n natural waters.Radiological and Environmental Research Division Annual Report, ANL-79-65, Part III (1979) 57-59.
(17) Inone, Y., Tochlyama, 0. Determination of the oxidation state ofneptunium at tracer concentrations by adsorption on silica gel and bariumsulfate. J. Inorg. Nucl. Chem. 3_2 (1977) 1443-1447.
(18) Harvey, B.R. Potential for post-depos1t1onal migration of neptunium 1nthe Irish Sea sediments. Impacts of Radlonuclide Releases 1n the MarineEnvironment (Proc. Symp. Vienna, 1980), I.A.E.A. Vienna (1981) 93-104.
(19) Edglngton, D.N. A review of the persistence of Iong-I1v1ed radionucl1des1n the marine environment - sediment/water Interactions. Ibid. 67-92.
(20) Hetherlngton, J.A. The Behavior of Plutonium 1n the Irish Sea.Environmental Toxldty of Aquatic Rad1onucl1des - Models and Mechanisms.(Miller, M.W., Stannard, J.N., Eds.) Ann Arbor Science, Ann Arbor, MI(1976) 81-106.
(21) SUlen, LG., Martel l, E.A. Stability Constants. Chem. Soc. (London)Special Pub. No. 17 (1964).
(22) Edglngton, D.N., Robblns, J.A. The behavior of plutonium and the long-lived radlonucHdes 1n Lake Michigan. II. Patterns of deposition in thesediments. Impacts of Nuclear Releases Into the Aquatic Environment(Proc. Symp. Otan1em1, 1975) I.A.E.A. V ienna (1975) 245 -
(235 Edglngton, D.N., Alberts, J.A., Wahlgren, M.A., Karttunen, J.O., Reeve,J.A. Plutonium and amer1c1um In Lake Michigan sediments. TransuranlcNuclldes 1n the Environment (Proc. Symp. San Francisco, 1975) I.A.E.A.Vienna (1976) 493 -
(24) Sholkovltz, E.R., Cochran, T.M., Carey, A.E. Laboratory studies of thedlagenesls and mobility of 239,240pu anc| 1370S ^n nearshore sediments.Geochlm. Cosmochlm. Acta. 41 (1983) 1369-1380.
(25) Forstner, U., Wlttmann, G.T.W. Metal Pollution 1n the AquaticEnvironment. Springer-Verlag* Berlin (1979).
(26) G1bbs, R.J. Mechanisms of trace metal transport In rivers. Science ISO.(1973) 71 -
(27) Edglngton, D.N. Unpublished data (1983).
(28) Schlndler, P.W. Surface complexes at oxide-water Interfaces. Adsorptionof Inorganics at Solid-Liquid Interfaces (Anderson, M.A., Rubin, A.J.,Eds.) Ann Arbor Science, Ann Arbor, MI (1981) 1-49.
(29) Alberts, J.J., Müller, R.N., Orland1n1, K.A. Particle size and chemicalphase distribution of plutonium 1n an esturalne sediment. Radiologicaland Environmental Research Division Annual Report. ANL-76-88, Part III(1976) 34-36.
57
(30) Aston/ S.R.» Stanners, D.A. Observations on the deposition, mobility andchemical associations of plutonium 1n 1ntert1dal sediments. Techniquesfor Identifying Transuranlc Spedatlon 1n Aquatic Environments (Proc.Tech. Meeting, Yspra , 1980) I.A.E.A. V ienna (1981) 209-218.
(31) Nealson, D.M., Lovet, M.D. Unpublished data.
(32) Moskvln, A,I.» Gel'man, A.D. Determination of the composition andInstability constants of oxalate and carbonate complexes of plutonium(IV). Zhur. Neor. Kh1m11 III (1958) 962-974.
(33) B1dogl1o, G, Characterization of Am(III) complexes with bicarbonate andcarbonate Ions at groundwater concentration levels. Radlochem.Radloanal. Letters 5_3_ (1982) 45-60.
(34) Stumm, W., Brauner, P.A. Chemical Spedatlon, Chemical OceanographyVo lume I (2nd Ed.). (Ri ley, J.P., Sk l r row, G., Eds.) Academic , New York,N.Y. (1975) 173-239.
(35) Reuter, J.H., Perdue, E.M. Importance of heavy metal - organic matterInteractions in natural waters. Geochlm. Cosmochlm. Acta 41 (1977) 325-334.
(36) Nelson, D.M., Penrose, W.P., Karttunen, J.O., Mehlhaf f , P. Effects ofDissolved Organic Carbon on the Adsorption Properties of Plutonium 1nNatural Waters. Submitted to Envlr. Sc1. Tech. (1983).
(37) Hsl, C.D. and D. Langmulr. Adsorption of uranyl ferric oxyhydroxides;application of surface complexatlon site-binding model. Geochlm.Cosmochlm. Acta (1985) 45:1931-1942.
(38) Ba11str1er1, US., Murray, J.W. Metal solid interactions In the marineenvironment: estimating apparent binding constants. Geochlm. Cosmochlm.Acta 4J. (1983) 1091-1098.
(39) James, R.O., Healy, T.W. Adsorption of hydrolysable metal ions at theoxide-water Interface. J. Colloid Interface Sei. 4. (1972) 42-81.
(40) Voice, T.C. and W.J. Weber. Sorbent Concentration Effects inLiquid/Solid Partitioning. Environ. Sei. Techno!, 19_, (1985) 789-796.
(41) Edgington, D.N., Karttunen, J.O., Nelson, D.M., Larsen, R.P. Plutoniumconcentration in natural waters - its relationship to sedimentadsorption. Radiological and Environmental Research Division AnnualReport. ANL-79-65, Part III (1979) 54-56.
(42) Wahlgren, M.A., Orlandlni, K.A. Comparison of the geochemical behaviorof plutonium, thorium, and uranium in selected North American lakes.Environmental Migration of Long-lived Radionuclides (Symp. Knoxville,1981) I.A.E.A. V ienna (1982) 757-774.
(43) Burton, J.D. Radioactive nuclides in the marine environment. ChemicalOceanography, Vol. 3 (Riley, J.p., Sk l r row, G., Eds.) Academic Press,London (1975), 91.
(44) Pentreath, R.J., Jefferies, D.F., Lovett, M.S., Nelson, D.M. Thebehavior of transuranic and other long-lived radionuclides in the IrishSea and its relevance to the deep sea disposal of radioactive waters.Marine Ecology (Proc. 3rd NEA Sem. Tokyo, 1979) Û.E.C.D. Paris (1980)203-201.
58
(45) Santschi, A.L, Schell, W.R.» Sibley, T.H. Distribution coefficients forradionuclides in aquatic environments: Adsorption and desorptlon studiesof plutonium and amer1c1um. U.S. Nuclear Regulatory Commission REportNUREG/CR-1852, Vol. 5 (1981).
(46) Duursma, K.E., and Bosch, C.J. Theoretical, experimental and fieldstudies concerning the diffusion of radlolsotopes In sediments andsuspended solid particles of the sea. Part B, Methods and Experiments.Neth. J. Sea Res. 4(1970) 395-469.
(47) Nelson, D.M., Lovett, M.B. Measurements of the oxidation state andconcentration of plutonium in Interstitial waters of the Irish Sea.Impacts of Radionuclides into the Marine Environment (Symp. Vienna, 1980)I.A.E.A. (1981) 105-118.
(48) Voice, T.C., Rice, C.P. and Webber, W.J. Effect of Sol Ids Concentrationon the Sorptlve Partitioning of Hydrophobie Pollutants in AquaticSystems. Environ. Sei. Techno!., H, (1983) 573-578.
(49) Nelson, D.M., Larsen, R.P., Karttunen, 0.0. Plutonium solubility 1nnatural waters. Radiological and Environmental Research Division AnnualReport. ANL-82- (1983)
(50) Clayton, J.R., Slbley, T.H., Schell, W.R, Distribution coefficients forradionuclides in aquatic environments. Effects of dissolved organiccompounds on the distribution coefficients of 5'Co, 10°Ru, 137cs, anc(241Am. U.S. Nuclear Regulatory Commission Report NUREG/CR-1853, Vol. 1(1981).
(51) Goldberg, E.D. Marine Geochemistry I. Chemical Scavengers of the Sea.J. Geol. 62 (1956) 249-255.
59
STUDIES ON BEHAVIOR OF LONG-LIVED ACTINIDES PLUTONIUM ANDAMERICIUM IN THE BALTIC SEA;EFFECT OF SEASON, DISTRIBUTION COEFFICIENTS INPARTICULATE MATTER AND SURFACE SEDIMENT
S. LESKINEN, T. JAAKKOLA, J.K. MIETTINENDepartment of Radiochemistry,University of Helsinki,Helsinki, Finland
Abstract
Concentrations found are similar to other seas at the same latitude and probablyoriginate from fallout. Both elements increased in concentration in surface waters insummer. Americium was more closely associated with particulate matter than Pu.Analysis of particulates showed similar concentrations to those in surface layers ofsediments. K values for both were 10 -10 , very similar to results reported elsewhere.In contrast to deep sea regions, 2% of Pu and Am were in the water column and 98% inthe sediments. A method for separating Pu ' and Pu ' in water was developedwhich relies on NdF coprecipitation.
1. INTRODUCTION
The behaviour of trarisuranic elements plutonium and americium in thewater of the Baltic Sea and its Gulfs have been studied since 1979[1,2]. The first phase of the investigations was to determine the239 240 241' Pu and Am concentrations in the water and especially toinvestigate the distribution of plutonium and americium betweenfiltered seawater and the particulate fraction.
The Baltic Sea and its Gulfs is a shallow brackish water area. Thesalinity of water samples collected varied between 3 - 8 %, in surfacewaters and 7 - 13 %0 in bottom waters. The highest sampling depth ofour study has been 235 m. In the Baltic Sea there is also a largeseasonal variation in temperature. Thus, the conditions in the BalticSea are very different from those existing in the locations studied aspossible deap-sea dumping sites. This gives an opportunity to considerthe effect of some factors on behavior of transuranic elements inmarine environment.
61
During the project period of 1982 - 1984 the effect of seasonal239 240 241variation and salinity on the distribution of ' Pu and Am in
the Baltic Sea was studied. In addition the distribution coefficientsfor these radionuclides in particulate matter of water and surfacesediments have been calculated.
To understand the interaction of transuranic elements between waterphase and particulate fraction (or sediment) information aboutchemical form and oxidation states are needed. In present study amethod for determination the oxidation states of plutonium as afunction of sampling depth in the large volume samples was developed.
2. mTERTAI-S AND METHODS
2.1. Samples
Water and sediment samples have been collected in the Baltic Seaduring the years 1979 - 1984. Figure 1 indicates the locations of thesampling stations. Collection of water and particulate samples havebeen described earlier [1,2].
Figure 1. Sampling sites in the Baltic Sea and its gulfs.
62
The water samples was filtered through Millipore cartridge filter,pore size 0,30 .Mm. No effect of pore size, m the range of 0.22 - 0.50fim, on the concentrations and distribution coefficients of Pu andand Am was found. The sediment samples have been takenwith a gravity corer having an inner diameter of 21 cm [ 3] . Thecores were split into transverse sections of 1.5 - 5 cm.
2.2. Determination of 239'240Pu and 241 "Am
Tne water and air dried particulate samples were analyzed for239 240 241' Pu and Am by procedures reported earlier[ 1,2]. To improve
241the chemical yield and separation of Am a method reported byBojanovsky et al [4] and modified at our institute[ 5] was introduced.
This method is based only on anion- and cation-exchange and it is
especially suitable for sediment samples. The alpha-activity of
samples were measured with Si-surface barrier semiconductor detectorfor 3 - 1 0 days.
2.3. Validity of the results
To check the reliability of the plutonium and americium results theintercalibration samples SW-N-I (seawater) and SD-N-I (sediment)obtained from the IAEA were analyzed.
The reagent background was regularly controlled. The background countrate for alpha-spectrometer used for determination of low ' Pu
241and Am concentrations was 0-3 and 2-5 counts per 10 000 mm for239,240^ , 241.' Pu and Am energy regions , respectively.
2.4. Separation method for determination of plutonium oxidationstates
63
400 1 SEA WATERFILTERED OR UNFILTERED
FILTRATE (PU (V t VI)
0.70 dpm Pu(IV)-TRACER0.70 dpm 236 Pu(IV)-TRACER
2.5 1 8 M HN03
2.5 1 5 M H2S04 - 0.02 M K Cr Oy
200 ML Nd-CARRIER (100 mg/ml Nd)ALLOW TO STAND ABOUT 30 MINUTES
200 ml 4O % HFSTIR AND ALLOW TO STAND FOR 30 MINUTESFILTER ON 0.22 H m CARTRIDGE FILTER
FILTER (Pu (III + IV) I
80 g (NH4)2 Fe (S04)2 6 HjO200 ml NdALLOW TO STAND ABOUT 30 MINUTESFILTER ON 0.22-1 m CARTRIDGE FILTER
DETERMINE Pu BYSTANDARD PROCEDURE (6)
| FILTER (Pu (III + IV)) I
DETERMINE Pu BY
•STANDARD PROCEDURE (6)
* IF UNFILTERED IT IS ALLOWED TO STAND 24 HOURS
Figure 2. Determination of the oxidation states of plutonium.
Ine analytical scheme to separate the lower oxidation states ofplutonium (III, IV) from the higher oxidation states (V, VI) is indicatedin Figure 2. The method is based on the method suggested by Lovett andNelson [6 . Pu(IV) will coprecipitate quantitatively on lanthanumfluoride whereas Pu(VI) stays in solution. The holding oxidant,K_Cr_O7, was added to prevent reduction of Pu (VI) by any reducingagent and also to oxidize Pu(V) to Pu(VI) as well as Pu(III) toPu(IV). Both filtered (pore size 0.22Hm) and unfiltered seawatersamples were analyzed. Also the particulate matter was analyzed fortotal Pu.
3. RESULTS AND DISCUSSICN
The results for water samples collected in 1981 in the Baltic SeaProper are given in Table 1. These results will complete our earlierdata [l,2].
64
Table 1. 739 ?40~ -, *.•*>•"•• upu and "xAm in water of the Gulf of Finland andthe Baltic Sea in 1981. The filter pore size used was0.30«m. The standard deviation of the radioassay (1 o) isindicated.
Station
LL-7"
F81"""
IL-3A
"
Us-7
"
Date ofcollection1981
14.7"
15.7""K
16.12
"
17.12
"
Depth
m
surface60
surface40130220
surface
50
surface
50
Plutonium -239,240Filtered watermBq/m
6.3 +_ 0.74.1 +_ 1.1
4.4 + 0.73.0 + 0.72.2 + 1.14.8 + 1.1
6.0 i- 2.2
3.4 +_ 0.7
5.0 + 1.5
3.8 + 1.3
ParticlesmBq/m(mBq/g dry wt)
O.48 + 0.070.26 + 0.07
0.18 +_ O.O70.059 +_ 0.0220.18 + 0.070.30 +_0.07
3.29 +0.36(3.70 + 0.40)1.46 +_ 0.18
(1.42 +0.17)
1.98 +_ 0.46(2.26 +_ 0.53)0.97 +_ O.22(0.73 +_ 0.17)
Anericium -241Filtered watermBq/m
1.5 <- O.71.1 <- 0.4
_0.7 _+ 0.40.7 + 0.70.4 + 0.4
0.6 + 0.6
0.5 ± 0.5
0.8 +_ 1.0
1.1 +_ 0.8
Particles3mBq/m(mBq/g dry wt)
0.15 + 0.070.11 +_ 0.04
„< 0.10.18 +_ 0.150.15 +_ 0.07
0.60 _+ 0.15(0.67 +_ 0.17}0.44 + O.O9(0.43 +_ 0.09
0.44 t 0.11(0.51 + 0.13)0.67 + 0.16(O.51 +_ 0.12)
The average concentrations of ' Pu and Am in the Baltic andits Gulfs during 1980 - 1981 were 5.9 + 2.5 mBq/m3 and 1.8 +_ 0.8mBq/m respectively. These results are in good agreement with thosefound in Danish and Swedish waters [? - S~\.
239 240 241The integrated total concentrations of ' Pu and Am in the 2entire water column at the station F81 (depth 235m) were 0.68 Bq/moand 0.17 Bq/m respectively. Comparing these values with the totalcumulative fallout in the water column and sediment core it was foundthat in 1981 only 2 % of plutonium and americium is present in thewater column.
3.1. Vertical distribution of Pu and Am in water column
The variations at different depth are rather small especially for Am.239 240The vertical profile of ' Pu content, water temperature and salinity
at the deepest sampling site of the Baltic in July is shown in Fig. 3.It can be seen that the vertical distribution of plutonium in filteredwater and water particulate has a minimum in water under a sharp
65
thermocline and halocline. The water mass at the depth of theminimum plutonium concentration is surface water originating fromprevious winter. Similar distribution of plutonium as a function ofdepth was found in the water columns of the other sampling sites, too.
A: ZRÄI
a" PARTICUUTES
"W 200DEPTH (M)
B:
SALINITY •/„TEMPERATURE *C
239 240Figure 3. A) ' Pu concentration in filtered water andparti culate matter as a function of depth.
B.) Salinity and water temperature as a function of depth.The determinations were carried out at 'the station F 81 inJuly 1981.
3.2. Seasonal variations
No effect of season on total concentrations of 'Pu andsea water samples of the Baltic Sea was found (Table 1).
in
239 240 241The concentrations of ' Pu and Am in particulate fraction ofsea water samples collected at different time of year showedsignificant differences (Table 1.) [2]. In Fig. 4. the concentra-tions of ' Pu and Am in particulate matter of water at thestation LL-7 as a function of season are presented. A significantdecrease in concentrations of Pu and Am occured in July. These resultsindicate that plutonium and americium are depleted from the surfacewater but do not reach bottom water during the summer months. Inwinter the concentrations of particulate Pu and Am in surface water
66
increased to the concentrations existing in the spring. This is due tothe winter mixing period, which can be seen in Fig. 5. In May and Julythere are a sharp thermocline and halocline at a depth about 50 m. InDecember the differences of the water temperature and salinity aremuch smaller because the water bulks are mixed. Similar behavior of Puand Am as a function of season as at the station LL-7 was found at theother sampling sites, too. The transfer of plutonium and americium tothe surface sediment was delayed by the seasonal circulation.
mBqrrf.-3
1
SURF/>CE BOTTOM W^TER
239.2«o Pu241
4 Am
MONTH
239 240 241Figure 4. The concentrations of ' Pu and Am in theparticulate matter in spring (May 1980), summer(July 1981) and winter (December 1981)."Water sampleswere collected at the station LL-7.
SALINITY •/«• v„ •/„TEMPERATUrtE t *C
' &'
50 70 0MAY
DEPTH M
SOJULY
0 SO 70DECEMBER
Figure 5. Salinity and water temperature as a function of depth at thestation LL-7 in spring (May 1980), summer (July 1981) andwinter (December 1981).
67
3.3 The K,-values of 239'240pu and241Ama
3.3.1. Particulates of water
The particulate mass (> 0.30rtm) in water of the Gulf of Finland inDecember 1981 varied from 0.9 to 1.3 mg/1. Using the concentrationsof plutonium and americium in filtered sea water and particulatematter and the total mass of particulates in the water the K,-factors?QQ -MO 241for - ' UPU and Am were calculated (Table 2.) The K,-valuesaobtained for 239'240pu were the same order of magnitude (105 ml/g).For Am the K^-values varied from 10 to 10 ml/g. These resultsare in good agreement with those reported in literature [10, 111.
The higher K,-values of Am compared to those of 239'240pu agreealso with the data presented in Figure 6. The percentages of
241particulate bounded Am are consistently higher than those of239 240 241 239 240Pu. The average Am/ ' Pu activity ratio in particulatematter seems to be higher (0.5 -f 0.3) than in filtered water (0.3 -f 0 2)These observations may suggest that americium tends to be moreefficiently associated with particulate matter than plutonium.
Table 2. Distribution coefficients (K. , 239,240^ . 241for Pu and Am inparticulates of water ( 0.30*m) and in surface layer ofsediments.
Station
LL-3A
LL-7
EB-I
F81
Sample
Particles, surface water50 m
Particles, surface water50 m
Sediment, 0 - 5 on
Sediment, 0 - 1.5 cm1.5 - 3 cm
Date ofcollection
16.12.1981M
17.12.1981It
04.08.1980
15.07.1981
Kd (ml/g)Pu
6.2 x 1054.2 x 105
4.5 x 1051.9 x 105
6.0 x 105
5.0 x 10S0.8 x 105
Am
11 x 1058.6 x 105
6.4 x 1054.6 x 105
2.5 x 105
24 x 1052.3 x 105
68
Figure 6. The percentage of particulate bounded Pu and Am fromtotal concentrations in water. The samples were collectedat the station LL-7.
3.3.2. Surface layer of sediments239 240The total integrated ' Pu in sediment cores at the
2sampling sites of EB-I and F81 were 38 and 26 Bg/m , respectively.O A "} OFor Am 6.3 Bg/m at the EB-I was obtained. The average activity
ratio Am to 239'240pu j_n these sediment cores was 0.27.
239 240 241The distribution coefficients of ' Pu and Am in surfacelayer of sediments are given in Table 2 . The K,-values for Pu
5and Am are the same as in particulates of water being 10 ml/g forPu and from 10 to 10 ml/g for Am. The K,-values of Pu and Am forsurface bottom sediments (0 - 3 cm) in Danish water are slightly
5 5 r ~ llower, 1.1 x 10 and 3.3 x 10 for Pu and Am, respectively L7J .This is probably due to the higher salinity (30 - 34 %c ) in Danishbottom waters than in bottom water of the Baltic Sea (7 - 13 %c ).
4. SUMMARY
*? *3 Q *5 /ï fï OyITThe concentrations of ' Pu and Am found in the Baltic Seaare very similar to those reported for sea areas located in thesame latitude band and where the plutonium present in waterpredominantly originates from global atmospheric fallout.
A seasonal variation in concentrations of particulate boundedplutonium and americium in surface water was found. There was asignificant decrease of Pu and Am concentrations in summer. During the
69
winter mixing period the concentrations increased back to the springvalues. Amencium seems to be more efficiently associated withparticulate matter than plutonium.
239 240 241The concentrations of ' Pu and Am, expressed as mBq/g dry wt,are the same as those of surface layer sediments. The K, -factors of239 240 241Pu and Am in particulate matter of water and in surfacesediments are the same, too. The average K , -values for Pu and Am
r r fwere 10 and 10 - 10 ml/g, resp.. Thesewith K, -values reported for other regions.
r r fwere 10 and 10 - 10 ml/g, resp.. These values are in agreement
In contrast with the deep-sea regions only about 2 % of totalintegrated concentrations of plutonium and americium in the BalticSea was in water and 98 % in sediment [12].
For the determination of oxidation states of plutonium inseawater a method for separation Pu (III, IV) and Pu(V,VI) fromlarge volume water samples was developed. This method is based ontne NdF3-coprecipitation. The oxidation states of plutonium willbe studied especially at deep sampling sites (e.g. Gotland deep,F 81) where the hydro-chemical observations indicate practicallyoxygen-free conditions and high H_S-concentrations in bottom water.
ACKNOWLEDGEMENT
This investigation was financially supported by the Finnish Ministryof Trade and Industry.
We gratefully acknowledge the collaboration with the Institute ofMarine Research, Helsinki.
REFERENCES
239 240 2141. Lax, Marianne, ' Pu and Am in brakish water, Communicationpresented at the IAEA Coordination meeting in Cadarache France,March 1980.
2. Miettinen, J.K., Leskinen, S., Jaakkola, T., Studies ondistribution of actinides between seawater and particulate
70
fractions in the Baltic Sea and its Gulfs in: Transuranic cyclingbehaviour in the marine environment, IAEA-TECDOC, Vienna 1982,33-34.
3. Niemisto, L., A gravity corer for studies of soft sediments,Merentutkimuslait-/Havsforskningsinst. Skr. 238: 33 - 38, 1974.
4. Bojanowsky, R., Livingstone, H.D., Schenider, D.L., Mann, D.R.,Procedure for analysis of americium in Marine EnvironmentalSamples in: Reference Methods for Marine Radioactivity, StudiesII, IAEA, Vienna 1975.
5. Hakanen, M., Jaakkola, T., and Rajamäki, S., Determination of Am insediment samples in: Radioactive foodchains in the subarcticenvironment, contract EY-76-C-02-3011. A 003 of US ERDA, FinalReport September 1979.
6. Lovett, M.B. and Nelson,, D.M., Determination of some oxidationstates of plutonium in sea water and associated particulate matterin: Techniques for identifying transuranic speciation in aquaticenvironments, IAEA, Vienna, 1981.
7. A arkrog ; A . , Dahlgaard, H . and Nilsson, K., Studies on thedistribution of transuranics in the Baltic Sea, the Danish Belts,the Kattegat and the North Sea in: Transuranic cycling behaviourin the marine environment, IAEA-TECDOC-265, Vienna, 1982, 23 - 32.
8. Kautsky, H. and Eicke, H.-F., Distribution of transuranic isotopesin the water of the North Sea and adjacent regions in: Transuraniccycling behavior in the marine environment, IAEA-TECDOC-265, Vienna,1982, 47-54.
9. Holm, E. , Persson, B.R. and Mattsson, S., Studies of concentration andtransfer factors of natural and artificial actinide elements in amarine environment, 5th International congress of the InternationalRadiation Protection Association, Volume III, Jerusalem, Israel,March 9-14, 1980, 311 - 314.
71
10. Pentreath, R.J. , Jeffériés, D .F . , TaUbot, J .W. , Lovett, M.B. andHarvey, B.R., Transuranic cycling behaviour in the marine environment,IAEA-TECDOC, vienna 1982, pp. 121 - 128.
11. Pillai, K .C . , Mathew, E., Plutonium in the aquatic environment, itsbehaviour, distribution and significance, IAEA, Vienna 1976, PaperNo IAEA-SM-199/27.
12. Fukai, R., Holm, E. , Ballestra, S., A note on vertical distributionof plutonium and americium in the Mediterranean Sea, CceanologicaActa 1979, Vol. 2(1979), No. 2.
72
MARINE BEHAVIOUR OF LONG-LIVED RADIONUCLIDES (FALL-OUT)AT THE PROPOSED DISPOSAL SITE OF RADIOACTIVE WASTES INWESTERN NORTH PACIFIC*
T. MIYAMOTO, M. HISHIDA, N. SHIBAYAMA, M. SHIOZAKIHydrographie Department,Maritime Safety Agency,Tokyo, Japan
Abstract
Water and marine sediment was sampled Analysis was for Sr, Cs, 60, ' Pu,and ' Th. The integrated values of Sr and Cs were 78 and 120 reCi km ,similar to GEOSECS figures. All isotopes were detected in sediment, which indicatesfast sinking particulate material transport, since water depth is 6000m. Cores showedbioturbation effects surprisingly often. Pu penetrates to about 15 cm, Cs to 20cmInventory values for 1980-1983 for water and sediments gave the following ranges,-
Sr (water) 78-89 mCi km , (sediment) 0.03-0.09; Cs 115-151 and 0.53-0.91239respectively; Pu (sediment) 0.09-0.12. These are smaller than for the Atlantic.
1. IntroductionIn Japan, land disposal and deep sea disposalhave been discussed as the
disposal methods of solidified low level radioactive waste.As for the latter, a proposed disposal area was chosen in the western
north Pacific, and now we are conducting environmental research such as bottomtopography, geology, deep current, diffusion, marine organisms and radioactivitiesof marine environments. Among them,the measurements of radioactivity of seawater and seabed sediments have been carried out by the Hydrographie Departmentof Maritime Safety Agency at the proposed disposal site.
At this site, the solidified low level radioactive wastes have not yet beendisposed, therefore, all radioactive materials which we are measuring areglobal fallout radionuclides derived from the atomic bomb tests.
Research about the radioactivity level and the behavior of fall outradioactive nuclides at this area are very important to assess the effects ofocean disposal of solidified low level radioactive wastes on the marine environ-ment in the western north Pacific in advance of disposal operations.
In this report, the results of radiological researches conducted from1980 through 1983 by the Hydrographie Department at the proposed disposal sitefor test disposal of solidified low level radioactive wastes are described.
2. Research areaThe research area (named as B area) is 900 km south east of Tokyo and 100
km square centered at 30 N, 147 E (Fig.l). The bottom in this area is mostlyflat and covered with soft red clay (1). Manganese nodules have beenscarcely found. The mean depth is approximately 6200 m.
* Part of IAEA-coordinated research programme on the "Marine Behaviour of Long-Lived Radionuclides Associated with the Deep-Ocean Disposal of Radioactive Wastes".
73
Fig. 1. Proposed ocean disposal site for radioactive solid wastes
3. Sampling and pretreatmentsSampling of sea water and marine sediments for the radiochemical analysis
were carried out on board the Hydrographie Department surveying ship "Syoyo"(1842 tons). Sampling locations were determined by a combination of rolan Cand NNSS. Sampling locations of sea water and marine sediments are shownin Fig. 2. Sea water samples were collected at several stations in eachyear. At one station among them, sea water samples were collected fromabout 12 layers from a 10 m layer to near a bottom layer. At other stations,only two water samples were collected from 10 m and 100 m above the bottomrespectively. The ampler used is made of polypropyrene and 100 litersvolume. The distance of the sampling layer from the bottom was determinedby a pinger at the bottom water sampling. Sea water samples were acidifiedby adding hydrochloric acid immediately after the sampling and brought to Tokyowhere the radiochemical analyses were performed.
Marine sediment samples were collected at several stations in every yearby using a Smith-Mclntyre grab sampler. Sediments from top to 2 cm depthwere taken. At some stations among them, three more sediment samples deeperthan 2 cm were taken. These deeper slices were 3 cm thick. 2-5 cm, 5-8 cm,8-11 cm.
At the center of the proposed area, a core sediment sample of about 85 cmlength was taken by using a gravity corer with a 9 cm diameter. The samplewas divided on board into 17 segments of 5 cm thickness except for the top onewhich was 2.5 cm thick.
4. Radiochemical analysisRadionuclides analysed were Sr-90, Cs-137 and Co-60. They were selected
taking into account the contents of low level radioactive wastes which are tobe disposed and the half lives of the radionuclides.
74
sediments Q sea waterI_______i______i
• 1
o.1 40.5
© 5
3O4
t)
30'
20
10'
•30-00 N
50'
JO'
30'
20' 30 40' 50' 30'147-00'E 10' 20'
Fig.2. Sampling locations of sea water and marine sediments
Although the plutonium content of low level radioactive4wastes is verysmall, the half life of plutonium-239 is very long (2.44 x 10 years).Plutonium analysis was also made on the marine sediment sample.
Core sediment samples collected at St. 1 by gravity corer were analysed forTh-230,232 in addition to Pu-239,240, to discuss the possibility of bioturvationeffects.
Outlines of analytical procedures are as follows.4.1 Sea water4.1.1 Cs-137
Sea water sample was acidified by adding hydrochloric acid and cesium wasadsorbed to ammonium phospbomolybdate and precipitated. After the precipitatewas dissolved in alkali media, cesium was separated from rubidium by cationexchange column chromatography with Duolite C-3 resin. The radioactivity ofcesium-137 was measured by low-background gas-flow counter as cesium chloro-platinate which hadi been previously filtered on filter paper, was dried andweighed.4.1.2 Sr-90
Strontium was precipitated as carbonate with calcium from the water samplein which cesium-137 was previously separated off. The carbonate precipitate •was dissolved in acid and left for a period of more than 2 weeks after additionof yttrium carrier. Yttrium was precipitated as hydroxide with magnesiumhydroxide precipitates and was purified by cation exchange column chromatography(2) and solvent extraction method using HDEHP (3). The radioactivity of Y-90was measured by low background gas flowcounter as yttrium oxalate which waspreviously filtered on filter paper, dried and weighed.4.1.3 Cot-60
Cobalt which was precipitated together with carbonate precipitates ofcalcium and strontium was separated from alkaline-earth metals as hydroxideprecipitates and then purified by anion exchange column chromatography withhydrochloric acid and then cation exchange column chromatography with tetrahydro-furan (THF)-hydrochloric acid mixture (4). Cobalt was at last electroplatedon copper plate. The radioactivity of Co-60 was measured by low back groundbeta-ray spectrometer.
75
4.2 Marine sediments4.2.1 Co-60
Cobalt was leached from sediment sample by hot 8N hydrochloric acid andseparated from large amounts of iron, aluminium and manganese by anion exchangecolumn chromatography by Kraus method and cation exchange column chromatographyby using the tetrahydrofuran (THF)-hydrochloric acid mixture as eluent.The purified cobalt was electroplated on copper plate. The radioactivity ofradiocobalt was measured by low back ground beta ray spectrometer.4.2.2 Cs-137
The effluent of the anion-exchange column operation of cobalt analyses wasused for cesium and strontium analysis. Cesium was adsorbed on ammoniumphosphomolybdate precipitate and precipitated and thereafter procedures werethe same as procedures of sea water analysis.4.2.3 Sr-90
The solution from which ammonium phosphomolybdate precipitates werefiltered was used for the determination of strontium-90. Strontium wasconcentrated by precipitation as carbonate and Lhen treated by the sameprocedures as sea water analysis.4.2.4 Pu-239,240
Known amount of Pu-242 ( for the samples collected in 1982, Pu-236)which was calibrated by NBS was added to the marine sediment sample andthen leached by hot 8N nitric acid. After the Pu was oxidized, the leachedsolution was passed through an anion exchange column. Pu was purified bywashing the column with nitric acid and then hydrochloric acid. Pu waseluted by hydrochloric acid containing ammonium iodide. Purified Pu waselectroplated on stainless steel plate. The radioactivity was measured byalpha ray spectrometer.4.2.5 Th-230,232
Thorium was leached by acid solution from the sediment sample andpurified by anion exchange column chronatography in nitric acid medium.Purified thorium was electroplated on stainless steel plate and radio-activity was measured by alpha ray spectrometer.
5. Results and discussion5.1 Sea water
The vertical distributions of Sr-90 and Cs-137 from near surface to 10 mabove the bottom are shown in Fig. 3 together with those of water temperatureand salinity. Sr-90 and Cs-137 are almost identical throughout the surfacelayer (0-500 m) and the concentrations of these nuclides decrease abruptlyfrom 500 m with depth. At deeper than 1500 m, we could hardly detect theseradionuclides by using 100 liter sea water samples.
These features of vertical distribution have been almost the same since1980 when the vertical observations were begun. The only exception is thedecrease of radioactivities of these nuclides in the surface layer.
The integrated values of Sr-90 and Cs-137 are 78 and 120 mCi/km2 respec-tively and they are slightly decreasing. These values are fairly equal tothe values obtained during GEOSECS observations (5) and the values in theNorth Atlantic (6) taking into consideration of latitudinal variation ofinventory.5.2 Marine sediments
The concentrations of Pu-239,240, Cs-137, Sr-90 and Co-60 in the uppermost2 cm layer are 1.6-4.2, 7.1-32.6, 0-3.9 and 0.1-2.5 pCi/kg-dry respectively.
There is remarkable difference between the results of the radioactivitiesof sea water and those of sediments: Cs-137 and Co-60 are concentrated insediments compared with Sr-90. Co-60 was detected in sediments which hasnot been detected in sea water samples. The detection of these artificialradionuclides in deep sea bottom over 6000 m depth may indicate the presenceof particulate materials which concentrate some artificial radionuclidesconsiderably and sink fast to sea bottom.
As for the temporal variations of these nuclides, any variation was notobserved since 1977 except the gradual decrease of Co-60 by its short half life.
The vertical distributions' of Pu-239,240 and Cs-137 in marine sedimentssince 1981 are shown in Fig. 4. These vertical distributions are classifiedinto two types. The first types are those concentrations of radionuclideswhich decrease with depth, the second type are those concentrations of radio-
76
5.1 -u 0T"v 0« Ar* p
0
}• S10so
35 0!0
100'———
XHOl
,-•-0-"-o-
S.U.,1t,
• C« 137 pCl/ IOOO Itr
o t, -m pci/iooo ifi
90 137Fig. 3 Vertical distributions of Sr, Cs, temperature and salinity
nuclides which do not decrease conspicuously with depth. The former dis-tribution indicate that the sediments are not so disturbed by biomaterials insediments while the latter indicates that the sediments are considerabllydisturbed by bioturbation.
77
Pu-239,240pCi/kg-dry
Cs-137pCi/kg-dry
10—I———i——
20 30i
198329-34.0 'N
146-48 .3 'E
0
2
4
6 -
198230-05.6'N
1 4 6 - 5 9 . 8 ' E
6
8
10 -
198129-58 6 'N
146-55 7 ' E
Fig. 4. Vertical distributions of Pu-239 and Cs-137 in sediments
To determine whether this bioturbation reaches a depth of more than 10 cmor not, a 90 cm depth core sample was taken by using a 9 cm diameter gravitycorer. Ionium and Th-232 were also analysed, as well as Pu-239,240 and Cs-137. The results are shown in Fig. 5 and 6. As apparent from thesefigures, Pu-239,240 penetrate to about 15 cm depth. Though it was difficultto say clearly owing to the large counting error, Cs-137 reached about 20 cmdepth. The vertical distribution of the ratio of Th-230/Th-232 indicatedexponential decrease down to 40 cm depth which corresponds to an age of 10.6 x1Q4 years. Mean sedimentation rate is calculated as 3.75 mm/10J y.Below the 40 cm depth, ratios are disturbed down to 65 cm depth. As thisdisturbance is observed at other part of the ocean (7), it may be due to othercauses than bioturbation. Below 65 cm, ratios exponentially decrease again.These results considerably agree with other investigator's results (7).
In the present core,the remarkable effects of bioturbation are notobserved in the vertical distribution ratio of Th isotopes in the sedimentcolumn from surface layer through 40 cm depth. The concentrations of Pu-239 , 240 and Cs-137 also decrease abruptly with depth.
In Fig. 6, two more vertical distributions are shown, which illustrateratios that juffered the effects of considerable bioturbations.
On the other hand, in the sediment samples collected by Smith Mclntiregrab sampler, we found 1 cm diameter and several cm long green burrowing worm.
78
In conclusion, in some part of this area, marine sediments are not sodisturbed by biornaterials, but in other part, they are considerably disturbed.
10i
o
10-
20
30
40- •
50"
60"depHi
70on00-
90
20 Cs-137 pCt/kg-dry
2 Pu-239,?40l I___________
• Pu-239,240O Cs-137
30-27 O'N
6?00 m
Fig. 5. Vertical distributions of Pu-239 and Cs-137 in core sample
Io/Th
50
30
10
30
20
50
30
10
30-27.O'N
146-39 5'E
6200 m
i * t
30-08.6'N147-09.1'E6255 m
29-34.O'N146-48.3'E6010 m
0 10 20 30 40 50 60 70 80 90
depth (cm)
Fig. 6. Vertical distributions of Th-230/Th-232 in core sample
79
'Integrated radioactivity from surface to core bottom was calculated andthe results are shown in Table 1. Temporal and horizontal variation of theintegrated values was not observed but these values are relatively smallerthan those in deep sea sediments of the Atlantic Ocean. These differencemay be due to the latitudinal variations of plutonium inventory in the PacificOcean.
90 137 239 240Table 1. Inventory values of Sr. Cs. ',2 >1980 1981
Pu in sea water and sediments
1982 1983
Sea water Sr-90Cs-137
89151
82115
78120
Marinesediments Sr-90
Cs-137Pu-239
0.070.910.12
0.090.770.09
0.030.530.09
References
1) HYDROGRAPHIC DEPARTMENT OF MARITIME SAFETY AGENCY, Marine environmentalresearches for deep sea disposal of solidif:ed radioactive wastes (inJapanese), 7 (1975)
2) SHIOZAKI, M., ODA, K., KIMURA, T. and SETO, T., The artificial radio-activity in sea water. Researches in Hydrography and Oceanography, Tokyo,205 (1972)
3) BRITT, R.D. Jr. The radiochemical determination of promethium-147 infission products. Anal. Chem., 33, 602 (1961)
4) KORKISCH, J. and AHLUWALIA, S.S.,Separation of large amounts of iron(III)from cobalt, nickel and aluminium by combined ion exchange-solventextraction. Anal. Chim. Acta, 34, 308 (1966)
5) BOWEN, B.T., NOSHKIN, V.E., LIVINGSTON, H.D. and VOLCHOK, H.L., Falloutradionuclides in the Pacific Ocean: Vertical and hol:zontal distributions,largely from GEOSECS stations. Earth and Planetary Science Letters, 49,411 (1980)
6) FELDT, W., KANISH, G. and LAUER, R., Radioactive contamination of theNEA dumping sites. IAEA SM-248/111
7) MIYAKE, Y. and SUGIMURA, Y., A study on the rate of deep sea depositionin the western North Pacific by means of ionium-thorium method. Jour.Geogr., 74, 95 (1965)
80
NORDOST ATLANTISCHES MONITORING PROGRAMM (NO AMP)
An environmental study of thedeep layers of the North-East Atlantic*
G.A. BECKER, R. BERGER, I. BORK, H. HEINRICH,E. MITTELSTAEDT, H. NIES, U. SCHAUERDeutsches Hydrographisches Institut,Hamburg, Federal Republic of Germany
Abstract
o o ' o oThe NOAMP area is 46 -48 30 N 18 -22 W. Topographic details are given anddistribution of sediments, with comments on sedimentation and geology. Eightvertical profiles for Cs were taken down to depths of about 5000 m. Down to -about 500 m the layer is well mixed and concentrations vary between 2.52 and 5.56mBq 1 . Within 100-200 m of the bottom a slight increase of Cs is observed,whichis assumed to be due to the nepheloid layer. The hydrography is variable and describedin detail. Bottom current measurement results are described and results of a modelfor dispersion based on the above findings.
1 . IntroductionThe NOAMP area extends from 46° to 48° 30' North and 18° to22° West (Fig. 1).The field work of NOAMP covers the period from 1983 to 1985.During spring and fall there is a MOAMP-cruise with the re-search vessel METEOR to study the regional- bathymetry and geology- radiochemistry and marine chemistry- water masses and nepheloid layers- water transports, especially within the near-bottom layer.Additionally, the research vessels POLARSTERN and SONNE under-took bathymetrical, geophysical and geological surveys in theframework of NOAMP.The primary aim of these investigations is the descriptionof the regional water transports at great depths. Of specialimportance are dispersion and the pathways of suspendedmatter within the near-bottom layer as well as the possibletransports from the sea floor upwards into the interior ofthe ocean.
* Supported by the Bundesminister für Forschung und Technologie and performed bythe Deutsches Hydrographisches Institut, Hamburg.
81
Besides the observational work theoretical studies are go-ing on within the framework of NOAMP. Models simulating thecirculation and dispersion in the North Atlantic are used tocomplement and to improve the final conclusions provided bythe field measurements.The following brief descriptions are intended to give animpression of preliminary observational results from thefirst cruise (NOAMP I) during Sept./Oct. 1983 as well assome examples of the current modelling effort.
2. Geology and BathymetryFor NOAMP the following geological issues are of interest:- the topographical features of the ocean floor,- the compositions of the sea bed materials and their
regional distribution,- the thickness and the spatial structure of the
sedimentary cover lying upon the basaltic ocean crust,- the processes of sedimentation and redeposition of
particulate matter.The results presented here are qualitative observationsrather than quantitative results, except the seismic andtopographic mapping performed with the SEA BEAM Systems ofR/V POLARSTERN and RV SONNE.A literature review of the surrounding area is given byR. B. KIDD ( 1983) .Topographic mapping during two cruises in 1983 (centralNOAMP box, N 47° - 47° 30', W 19° 30' - 21°) and in 1984(easterly extension, N 47° - 48°, W 18° 40' - 19° 30')yielded a high quality map of the ocean floor. The depthsrange between 3600 m and 4600 m. Maximum slope angles areabout 15°. The main feature is a system of valleys extend-ing in a North-South direction which are separated bychains of hills and ridges. Seismic reflection records withthe Pneuflex-Airgun revealed basaltic basement ridges asthe internal cores of the hill chains, which strike parallelto the Mid-Atlantic Ridge (MAR). The sediment cover of theseridges is rather thin, whereas the valleys contain a sedi-ment filling of up to several hundreds of meters (Fig. 2).The microphysiography of parts of the sea floor proved tobe unfavourable for structural investigations of the upper-most sediment with an acoustic sub-bottom profiling system(3.5 kHz - SBP) due to the physical properties of the systememployed. A noisy and hyperbolic reflection record resultedapparently due to rough surfaces of the hills. Areas with athicker sediment cover reveal a set of distinct reflectorsparallel to the sediment surface, but of unknown origin.For their identification and for stratigraphie purposes longpiston cores were taken (11.5 m recovery).Box grab samples were taken from the crest of a hill(height: 700 m) along a transect extending 4 nautical miles
82
away from the hill foot. The surface sediment is a toughand sandy lime mud produced by coccolith shields and fora-miniferal tests (mainly G. inflata). On the hill and at thesite furthest from it one observes buried and uncoveredglacial marine remains of continental origin. The regionimmediately at the foot of the hill is free of theseclastites.There are also differences in the uppermost 50 cm as can beseen from the box grabs: On the hill crest and at the deepplain positions the lime mud is underlain by a tough clayeymarl, rich in glacial sand and gravel. The transitionbetween these two layers is relatively sharp, but there isa continuous increase of clay content in the samples fromthe hill foot without any coarse glacial remains (Fig. 3).The sediment is pasty and exhibits intense bioturbationphenomena.A 5 m long piston core from the deep plain showed at itsbase sharp glassy volcanoclastites mixed with angular quartz,plagioclase and sandstone remains, as well as shell relictsof shallow water mollusks.Depending on the topographic features, the NOAMP area ispart of the abyssal hill region. The relief is formed byridges of oceanic basement rocks which strike parallel tothe MAR. The ridges have a thin sediment cover whereas thesediment thickness in the valleys is considerably larger.The recovered surface sediments consist of calcareous mudabove a clayey marl, both with various amounts of glacialmarine remains. At first sight two sedimentary processesseem to be of great importance: the primary supply ofpelagic and glacial marine material through the watercolumn from the sea surface down toa subsequent transport of very finecrests down to their immediate foot
the ocean floor, andgrains fromregions.
the hill
9.3. Radiochemistry 137Cs:Within the framework of NOAMP (North East Atlantic Moni-toring programme) eight verticaT profiles of the J/Csactivity concentration were obtained. The positions anddepths of these eight stations are given below in table
StationStationStationStationStationStationStationStation
12345315459
41°42°42°46°45°47°47°47°
0314300259251821
,3',8',2',7',0',8',5',6'
NNNNNNNN
13°14°14°16°17°20°20°19°
04,0'15,4«29,6'13,7'15,7'55,0'06,0'35,5'
WWWWWWWW
52705240525541754710447044904420
m
1«J'1mjra 'mm-
previousdumpsite
1actualdumpsite
NOAMPi area
Table 1 : Positions and water deuths of the eieht radio-chemical stations on METEOR-cruise 65 inSept./Oct. 1983
83
Samples at up to 16 different depths were taken at eachstation. Due to the decreasing concentration of artificialradionuclides with depth (Kautsky et al., 1977, Feldt et al.,1981), the sample volume had to increase with depth: from50 1 at the surface to 400 1 below 2000 m and 500 1 closeto the bottom below 4000 m.
1 37The Cs activity concentrations of the NEA dumpsites andreference locations are shown in Figs. 4 and 5,respectively. A well-mixed surface layer was found down to500 m depth with some peak values.The values of this layer vary between 2,52 (-0,17) and 5,56(-0,23) mBq/1. From 500 m depth to about 4000 m the valuesdecrease by 50 % approximately every 550 m. Some values arebelow detection limits (about 0,1 mBq/1). Within 100 to200 m above the bottom, a slight increase of 'Cs concentra-tion is observed. As the water was not filtered, it is con-ceivable, that this slight increase is due to the particleconcentration of the nepheloid layer. It is not the resultof locally dumped radioactive waste, because in the MOAMParea (where no dumping takes place) similar trends are foundThere is no significant difference between the profiles ob-tained at the dumpsites (Fig. 4) and those obtained at thereference locations (Fig. 5). The values are consistentwith fallout levels.
9.4. HydrographyDuring NOAMP I a grid of 80 stations were surveyed by meansof a Neil-Brown-CTD-System including a nephelometer to-gether with a rosette sampler. The CTD work was cooperativebetween DHI, Hamburg, and PROSPER, Neuchâtel. The spacing ofthe grid was 10 n.mi. and 20 n.mi. respectively (Fig. 6).The CTD-casts all reached to within 5 - 20 m of the seafloor. Water samples were taken to calibrate salinity andto determine oxygen content, phosphate and silica at1 3 depths.All parameters show a distinct variability throughout thewhole water column, suggesting that in the NOAMP boxdifferent water masses exist side by side down to greatdepths. The 6-S diagrams show large differences in thesurface layer down to about 125 m, uniformity in the 9-Sdomain of the North-East Atlantic Central water below thesurface layer, and again large variations around the coreof the Mediterranean Water between 650 m and 1250 m(Fig. 7). The salinity minimum of the Middle NorthAtlantic Deep Water (MDW) originating in the Labrador Sea(Lee and Ellett, 1965) is clearly visible at most of thestations below the Mediterranean Water.Whether the observed relative salinity maximum below theMDW is due to eastern Overflow Water coming from the Northor whether it is caused by Mediterranean water, which hasbeen mixed down to about 2000 m far away from the NOAMP
84
area and is then laterally transported to the NOAMP siteis uncertain. The water below 3000 m fits well in thecharacteristic 6-S relationship found to be valid at manysites in the North-East Atlantic (Saunders, priv. comm.).The profiles of oxygen and phosphate show considerablescatter as well (Figs. 8 and 9). Maximum variationsare within the layer of the Mediterranean water around1000 m depth and in the layer of the relative salinitymaximum in about 2500 m. Also in the layer close to thebottom the differences of oxygen and phosphate betweenthe stations clearly exceed the accuracy of the determination
5 . Near-Bottom CurrentsAbout 7 long-term moorings with 40 to 50 current metresare in operation for the period from fall 1983 until fall1985. They are to be replaced every half-year. Five mooringswith 5 to 6 current metres each cover the 300 m thick layerabove the deep sea bottom (water depths between 3600 and4300 m). Two moorings cover the water column up to 400 mbelow the sea surface (12 current metres each). The twolowest instruments at 10 and 30 m above the bottom areacoustic vector averaging current metres (Neil Brown).The other current metres are Aanderaa (RCM5).Additionally use is made of 3 moorings of the CentreOcéanologique de Bretagne, Brest, which have been deployedin the framework of 'Topogulf. These moorings within ornear the NOAMP-area, respectively, have been out deployedfor one year and have been replaced by a single one-yearmooring during summer 1984. All French moorings have beenand are equipped with a NOAMP current metre close above thebottom.Moreover a joint field project will be carried out betweenthe Centre Océanologique de Bretagne and the DeutschesHydrographisches Institut, Hamburg, using deep sea neutral-ly buoyant floats in the NOAMP-area. The float experimentis scheduled for one year starting in spring 1985 withMETEOR. The 14 floats are supposed to move at a prescribeddepth of 3500 m. There will be 4 listening stations mooredin the NOAMP-area.During some cruises short-term current measurements with ahigher sampling interval of 5 to 10 minutes during periodsof I to 3 weeks are carried out by means of deployed currentmetres.One example is short current measurements of about 1? daysduration during NOAMP I by means of deployed current metres.Fig. 10 represents the vector velocities averaged over thewhole observation period at 5 positions. The topography dis-played in Fig. 10 is the result of an echo sounder surveyof R.V. POLARSTERN in May 1983 of the central MOAMP-box.The moorings are 10 to 20 n.mi. apart. The current recordsreveal remarkable differences of the mean flow within the
85
r.ear-bottom layer at the various mooring positions (Figs.10 and 1 1 ) . This apparently has to do with the roughness
of the local topography. Among points of special interest isthe obvious large deviation of the mean flow direction 10 mabove the bottom relative to the flow direction at 30, 70,15C, 200, and 250 m height above the sea floor (Stat. K1,K2, K5) .The r.ear. speeds within the layer close to the bottom rangebetween " and 6 en s . The rr.cst important short-termcurrent variations (not shown here) are caused by the semi-diurnal tidal currents. The semi-diurnal speeds are about5 cm s-"1. Occasionally topographically induced inertiacurrents seem to occur. The maximum speed of the overallcurrent reaches about 14 cm s~'1.
9.6. .Modell ingThe field work of NOAMP is supplemented by numericalsimulations on the transport by an annual mean flow andnixing of radionuclides in the North Atlantic Ocean.The underlying current field is computed using a modeldeveloped by Bryan (1969) and Semtner (1974). The resultsof this calculations are to some extent questionableespecially at great depth. (For a detailed discussionsee Bork, Schulte, Mittelstaedt, 1983.)The model itself is, at present, the standard model forthree-dimensional circulation calculations of the oceanand therefore the best and most reliable model, which canbe handled with a reasonable effort.The reason for including the transport by the meancirculation in a dispersion model, at all, is that thedistribution of activity concentration due to a radio-active source in the ocean is assumed to be primarilydetermined by advection and only secondarily by mixing.That is, the resulting distribution will be inhomogenousin space, even if a temporarily steady state will bereached.The present application of the model covers the Atlanticfrom 30° S to 70 N. It has a horizontal resolution ofone degree and 17 layers of different thickness.From the three-dimensional mean annual current field ofthe model, particle paths have been derived. As an examplea particle source is assumed in the NOAMP area at a depthof 4700 m (Fig. 12).The released particle moves slowly northward at depthduring the first 30 years. After 90 years it emerges nearthe continental slope at a depth of about 1000 m andcontinues its way until it approaches the continental slopeoff Morocco at depths of about 1400 m after 100 years.For comparison the trajectory of a particle startingat 3200 m depth is described in Fig. 13. The particleremains in the NOAMP area for about 10 years. After the
86
first decade it ascends and noves, in general, towards theSouth and later towards the West. During a period ofabout 65 years it crosses the North Atlantic and turnswith the Gulf stream back eastward. The return transportfrom the east coast of the United States to the regionbetween Iceland and Europe takes less t bar. about 15 years.Other series of numerical experiments deal with Euleriancalculations simulating a continuous radioactivity sourceof 1COO TBq per year in the NOAMP area at a depth of 4500 n(T3q = Tera Bq = 1012 Bq).Examples of these experiments are shown in Figs. 14 and
15. The figures represent model results on the con-centration of activity at 3000 m and 500 m depth, 100 yearsafter the first release. For these simulations_a half lifeofA
30 years and diffusion coefficients Au = 10? cm2 s~1 andV cm 2 s"1 are assumed. H
Figure 16 indicates the temporal adjustment of the maximumactivity concentration at various depths. The diagramsuggests an equilibrium of the concentration throughoutthe water column after about 100 years. At the source depth(4500 m) the equilibrium sets in already after about 10 to20 years of a continuous release of radionuclides with ahalf life of 30 years.A vertical profile of the maximum equilibrium activityconcentration composed of the maximum concentration at eachmodel depth is shown in Fig. 17. The maximum indicatesthe source depth of 4500 m.
ReferencesBork, I., D. Schulte, E Mittelstaedt ( 1983):
Dispersion Of RadioactiveIn The Ocean.Unpublished report, 56 pp,Deutsches HydrographischesHamburg.
Substances30 Figs.Institut,
Bryan, K. ( 1969) :
Feldt, W., Kanisch, G
A numerical method for the study ofthe circulation of the world ocean.J. Comp. Phys. , 4, 347-376.
and Lauer, R. , ( 1981 )Radioactive contamination of the MEADumping Sites.In: Impacts of Radionuclide Releasesinto the Marine Environment,IAEA-SM-248/1•1.Vienna, 465-480.
Kautsky, H., Koltermann, K. P., and Prahm, G., (197?)Iberische Tiefsee: Hydrographischeund radiologische Untersuchungen.Meereskur.dliche Beobachtunger, undErgebnisse Nr. -5, FS XETEOR, DHI,HamburE.
87
Kidd, P. B.: Sediment d istr ibut ior. and sedimentaryprocesses at the dumpsite.Interim Océanographie Descriptionof the North-East Atlantic Sitefor the Disposal of Low-level Radio-active Waste.NEA: p. 16-29, Paris, 1983.
Lee, A. , and D. Ellett ( 1965):On the contribution of overflow
water from the Norwegian Sea.Deep Sea Res., Vol. 12, pp. 129-142.
Sentner, A. J. (1974): An oceanic general circulation modelwith bottom topography. Numericalsimulation of weather and climate.Tech, Rep., 9, Dept. Meteorol.,University of California.
88
MO)13•oüü•z.Q
.
"O50)<yD-9!PtXI
89
Fig. 2 Oceanic basement ridpes (lieavy lines) and vfillev:; (shaded) in t.he cetitral NOAMP box
90
pelagic contribution( l ime & debris)
4.0
OJ-f
i-O.tm
! \\\\\\\ l ime mud
clayey marl
{*.«-«] glaciomarine debris
Fig. 3 Schematic model of the sedimentation and sediment transport at adeep sea hill.A possible mechanism for down-slope transport might be winnowingby currents.
_C-Pa.CDa
Meteor cruise 65 Sept./Oct. 1983
st»t.Stmt. 3 (l«2
x St.t. k (k6m Stat. J (1»J
2 (l»2° 11».8' M 1110
30.2' N 14
02.7
13.4'29.6'
K 16° 13 .7«
v)v)v)
59.0« H 17° 1 5 . 7 « v)
6880l.M 2.BB 3. M 4.98 5.00
Cs-137 CmBcj/13T 37,Fig. 4 Vertical profiles of the '~"Cs activity concentration in the
water column of the previous (Stat. 2 and 3) and the actual(Stat. A and 5) NEA dumpsites in the North-East Atlantic.
Meteor0
cruise 65 Sept. /Oct. 1983
*)QaaCOOC-
3080._c-p
Q_<D
Q
6080
..-*
•*&.
/:/•////:•/
./*''
0 Stat. 1 (1*1° 0 3 . 3 « N 13° 03 .0« V)* Stat. 31 (1*7° 25.8' K 20° 55 .0« W)•f Stat. 5!* (1»7° 18 .5« N 20° 06.0» V)
« Stat. 59 (1*7° 21 .6« N 19° 35.5' V)
0.00
Fig.
I.I 2.00 3.00 4.00Cs-137 CmBc,/!]
5.00
5 Vertical profiles of the 'Cs activity concentration inthe water column at reference locations
92
NOAMP I
I D1
70
--47« OO
•-4*'00'
45*30'2TOO' 22*00' 21*00' 20-00'
1 ' | ' I ' I ' I ' I ' ' ' | I ' * • ' | • I ' I
iroo' i«*oo' 17*00
Fig. 6 Station grid during NOAMP Io CTD-Stations• Current metre moorings; D1, D2, D3 are COB'(Brest)-moorings
Fig.
35.6 S 35.8
7 Potential terperature/salinity-diagramfrom NOAMP I(uncorrected raw data)
93
45 5.0 5.5 6.0 6.5
Tie feCkm3
0.5 H
1.0-
1.5-
2.0-
2.5-
3.0-
3.5-
4.0-
4.5 -
5 4708 J00825.435 « 0.177
5^92 t 0.2875.042* 0.356
4.731 l 0.319
5.040 » 0.437
5.413 t 0.308
5.987 t 0.220
6.232 t 0.111
6.087 i 0.209
5.92 8 i 0.170
5 74 3 i 0.137
5.609 t 0.093
5.546 t 0.073
Fig. 8 Scatter range of the vertical Op-profileComposite of all Op-determinations during KOAMP IBars indicate standard deviation.
94
Tiefe
M0,5
1,0
1.5 •
2.0 -
2.5-
3.0 -
4,0-
PO, ]0.5 1,0 1,5 2,0
I-H
Fig. 9 Vertical profile of PO, with scatter barsComposite of all PO,-determinations duringNOAMP IBars indicate standard deviation.
95
0\
\lalKl.,I, I _T,i>iii NOXMP Pion O'
Fig 70 Mean current vectors, averaged over about 17 days duririp NOAMP TObservation depths: 10, 30, 70, 150, POO, arid ?50 m above the bottomSampling interval: 5 minutesIsobaths in meters
" tss t i r r t H i HO n -f M IM» n +flNFRNG Ifi 9 I9H3 2l M 'IS. 0MESSDnucn JTI. oil
•fl,-n n -t
K3
M f S S T I E f C H?so M + 'u')') M 4-'HNFRNG 16 9 1983 IH H SO. 0MESSDflUER Hl I. 0 H
'IM t() M 4-
K5
K2
H?<iS n + K t ' . s t i r r E H-ÎHS n +IG IB T I9R3 17 II .?S. 0
MCSSO-RUER H04. OH
w s s n r f E H;")H n -f- « I ' M I C I E HM;M n +RNFRNG 16 9 19«^ t 7 H 7S. 0HI SSOnil fR H?e. 0 M
Fip. 11 Unfiltered oropressive vector diagrammeswithin a 300 m thick layer above the bottomduring NOAMP IDifferent trajectories in one diagramneindicate different observation depthsCrosses indicate 24 h-intervalsDuration: about 17 daysLocation of the position K1, ... K5, see Fig. 9.
MOMO n -fifi s nni
'1030 " -»-q H Pr, n
Fig. 12 Three-dimensional trajectory of an advected particle 100 years afterbeing released at a depth of A?00 m in the NOAMP area.The trajectory is annotated at 10 year interval.The consecutive numbers at the trajectory indicate the position andthe depth of the particle every 10 years (see table on the left).The source is at 0.
10
Fig. 13 Three-dimensional trajectory of an advected particle 100 years afterbeing released at a depth of 3200 m in the NOAMP area.The trajectory is annotated at 10 year interval.The consecutive numbers at the trajectory indicate the position andthe depth of the particle every 10 years (see table on the left).The source is at 0.
98
Fig TA Concentration of activity (Eq/p) at 2000 m deoth, 100 years aftercontinuous release of 1000 TBq/year.The source is at a depth of 450C m in the t>OAMP areaDiffusion coefficients AH = 10' cnTs"1 and AV - 1 cn^s"1.The concentration refers to a half life of 30 yearsThe small squares denote the 3000 m depth contour
Fig.15 CorcentratiC" of activity <2o/m ) at a decth of 500 r,100 years after continuous release of COO ""Eq/year"he source is 4500 n depth in the OAÎ'P area. ,3iffusion coefficients: A0 = 107 cx2s~] and AV ; 1 CDS"The concentration refers to a half life or 30 yearsThe small souares denote the 500 m depth contour
99
-2
-4
-t -
-I -
(scjrce depth)——————— 4500m
3000m
SOYEARS
16 Teiicoral adjustment of the rraximum concentration of activityin loglQ C (Bq/m 3) at ^500, 3000, 500 ard 25 m Tiefe
dur ing a coritTruous release of 1000 TEo/year at ^500 m depth.Diffusion coefficients: A„ = 107 cir^s-1 ar.d A.. = 1 cnTs-1.n VThe concentration refers to a half life of 30 years.
.17
tooo
2000
MX» -
«000
5000 L-
Maximum concentration of activity in log^ Cas function of depth (m) after 100 years of co'nrelease of 1000 TBq/year at 4500 IP depth.
(Bq/m )inuous
Diffusion coefficients: A r }0!
The concentration refers to a half l i f e of 30 years.and AV = 1
100
THE BEHAVIOUR OF CERTAIN LONG-LIVEDRADIONUCLIDES IN THE MARINE ENVIRONMENT*
R.J. PENTREATH, P.J. KERSHAW, B.R. HARVEY, M.B. LOVETTMinistry of Agriculture, Fisheries and Food,Directorate of Fisheries Research,Fisheries Laboratory,Lowestoft, Suffolk, United Kingdom
Abstract
99 222 226 228 210Methods have been developed for analysis of Tc, Rn, Ra, Ra, Pb,Po, Th, Th, U nuclides in fish tissue and different oxidation statest
of Pu, Am and Np. Research, much in the Irish Sea has studied the latter elementsand Tc and provided information about distribution and speciation in water. Puisotope ratios give information on the source (Sellafield, Cap La Hague, or fall-out). The possibility of memory effects in shipboard sampling systems is pointed
239 240 241out. At least 240 TBq of ' Pu and 290 TBq of Am are associated with theupper 30 cm of the seabed within a 30 km belt of the Cumbrian coast. Bioturbationhas been studied using C, Pb, Th, Pu, Am, Cm and redistribution downto 140 cm demonstrated. Pu and Np isotopes were partially reduced in interstitialwater and the presence of artefacts due to subsequent exposure to oxidisingconditions was shown to be important, and to be avoided. Organic complexation isalso being studied. Concentration factors for many of the above isotopes in biotawere derived. A review of K, factors for deep sea environments was produced.
1. Introduction
Many of the long-lived radionuclides associated with thedeep-sea disposal of radioactive waste are released into UK coastalwaters, principally from the British Nuclear Fuels pic reprocessingplant at Sellafield bordering the Irish Sea. The environmentalbehaviour of these nuclides is being studied primarily to assess thelong-term consequences of coastal water discharges, but the Irish Seaalso provides unique opportunities to study certain aspects of insitu radionuclide behaviour which cannot be achieved in the deep seaenvironment. It also needs to be borne in mind that a large fraction
* Crown copyright.
101
of the dose to man resulting from any disposal of radionuclides intothe deep sea will arise via coastal water pathways. Direct studieson deep sea materials have also been made, however, plus research onphysical and chemical océanographie processes which may influence thebehaviour of radionuclides released in the deep ocean.
Much of the deep-sea programme has involved studies of processesat the Nuclear Energy Agency (NEA) low-level radioactive wastedumpsite in the NE Atlantic because of the UK's active involvement inpackaged-waste disposal at this site in recent years (1~19).
2. Methodology
A considerable effort has been spent on developing and improvingthe analytical methodology. A method suitable for the separation ofTc from water, sediments and biota has been developed andsuccessfully tested in an international intercomparison exerciseorganised by the US Dept. of Energy. (M. S. Feiner, 1984. A 99Tcvegetation reference material. Environ. Measurements Lab. US Dept.Energy, New York, 27 pp.) It consists of an initial ammoniacalashing at 450°C (where appropriate), a ferric hydroxide scavenge fromchloride solution to remove many contaminating radionuclides,followed by the uptake of pertechnetate on to an anion exchangecolumn from NaOH solution. Tc is removed from the column with NaClCLand finally co-precipitated with CuS prior to ß counting for 99Tc.Work is being carried out to investigate the suitability of 99mTc,95mTc and 97Tc as yield tracers. A discussion of the use of yieldtracers in the determination of alpha-emitting actinides has beenpublished(20) .
The techniques developed for the measurement of 222Rn, 226Ra,228Ra> 210pb) 210p0) 230Th and 23^ in sampies of seawater, sedimentand biological tissues have been described with some examples of thedata produced(2j- >22 ). Further refinements to the method ofdetection of 23LfTh in sediments are being made.
A technique for the analysis of uranium nuclides in fish tissueat environmental levels has been developed. Processing blanks of~ 0.1 mBq kg"1 (wet tissue) have been achieved by using non-glassapparatus and isolating U as U(IV). The latter precaution avoids theneed to use chemicals, for the separation of U as U(VI), whichinvariably contain U as a contaminant.
102
In order to differentiate between the two higher oxidationstates of Pu (V and VI) in seawater, a technique involvingco-precipitation on Ca-C03 at pH 9.0 by the addition of aNa2 C03/NaHCU3 mixture has been investigated. Approximately 80% ofPu V will co-precipitate under these conditions. Less than 10% ofPu VI co-precipitates, as can be demonstrated by carrying out areplicate co-precipitation having made the seawater 0.001M withrespect to KMn04, which maintains any 'oxidised1 Pu in the hexavalentstate. Preliminary results indicate that the Pu is predominantly inthe pentavalent form.
An investigation has also been made of Fe(OH)3 (0.1 mg Fe 1~*)as an alternative co-precipitant for reduced forms of the transuranicelements. Both this and the NdF3 method gave similar results for Pu.But some 20% of the environmental 2LflAm in seawater failed to followthe 21"Am(III) yield tracer in the hydroxide precipitation. Thisfigure increased to 70% in some waters with higher suspended loads(> 5 mg 1~ ). it appears that another form of Am is present whichsubsequently can be quantitatively scavenged on to Fe(OH)3, using21+2Cm(III) as a yield tracer, following the addition of a reducingagent (Na2S03 at pH 1.0). Work is continuing to identify the secondAm species or complex.
A reliable 23^Np tracer has been produced and used to study theco-precipitation of Np in different oxidation states, both by theNdF3 and Fe(OH)3 (0.1 mg I"1) methods, and with Ca as CaC03.Laboratory experiments in an ultra-violet irradiator indicate anequilibrium between the two oxidation states which is pH dependent(Fig. 1). ^
<0 100r
COC
JE 10aE(D
ü<Da05
T3<DO3
XJa>
1.0
O
0.2 1 . 0 10pH
Fig. l Oxidation of 235Np tracer in a U.V. irradiator^and NaOH added to 800 ml seawater to adjust pH,
HC1
103
Routine quality control is applied to all analytical procedures;for Pu and Am the vast range of concentrations in samples handled(> 107) creates potential problems of cross contamination, but blanklevels over the whole range are kept below 1%, and are typically0.1%, of the sample concentrations. The laboratory takes part inboth national and international intercomparison exercises; theresults of a recent one of U are given in Table 1. It should benoted, however, that 'concensus values' do not necessarily representthe 'true' concentrations. A number of certified reference materialsare now available, but even these offer little help in detectinganalytical bias at the lowest concentration levels. Ultimately,confidence arises from continued intercomparison of results. As anexample, Table 2 indicates the concentrations and Pu nuclidequotients of sea water samples collected in the Arctic Ocean.Differences in the quotients - from those of fallout to thoseassociated with coastal water discharges - indicate the ability todetect these nuclides to a high degree of accuracy and precision.
Table 1. Recent Intercalibration ExercisesNucllde JRL data
Bq.kg-1Mean value of Range of valuesall participants Bq.kgBq.kg.-1
(a) U r a n i u m nuclides in a marine sediment (acid leach)
238U234u234/238
15.2810.63 14.07+2.2216.10±0.62 1A.37+2.071.05 + 0.06 1.02±0.07
11.48-16.4211.43-16.100.94- 1.08
(b) 237Up in a marine sediment
FRL data
6.2510.12
Mean value ofall participantsBq.kg--1
6.22+0.29
Range of valuesBq.kg-1
5.92-6.60
Table 2. Americium and plutonium in filtered seawater CIROLANA cruise fromthe North Sea to the Arctic 1981
Station Lati tude Longitude 2L|1Amnumber LtBa.l-1
21032
106123140166181
54°N58°N67°N74°N80°N72°N64°N58°N
1°4°
10°10°
7°6°0°0°
EEEEEW
21111212
.29+0.
.4610.
.62+0.
.86+0.
.8910.
.46±0..5810..39+0.
1408111317181127
239- f -240p u
ußq.l-1
44 .9+19.4+16.3+13.7+15.4+12.6+
238 P U 2 3 9 + 2 4 0 p u
2 3 8 p u
2.10.80.80.60.70.6
4.7410.2249.1+ 2.1
9 . 2 2 + 0 . 4 62. 6810.131.7910.120.87+0.060.85+0.070.60+0.060.44+0.049.92+0.53
479
15182110
4
.9+0 .1
. 2 + 0 . 2
.1+0.5
.8+1.0
.2+1 .3
. 1t 1 . 8
.810.9
.9+0 .2
Errors quoted are ± la propogated counting errors only
104
3, Shelf aeas research
Measurements have been made of the chemical nature of theeffluent discharged from the BNFL reprocessing plant at Sellafield,UK(23>21+). The effluent arises both from water used to purge fuelelement ponds and miscellaneous sources routed through 'sea tanks'.The latter is the major source of transuranium elements (> 90% forPu(a)). A large proportion of the Pu(a), 241Am, 243/21+1+Cm and 237Npwas associated with particulate (> 0.22 um) material which alsocontained 'hot' particles, identified as discrete clusters of atracks by CR-39 a-track detection. Both Pu(a) and 21+1Am weresolubilised on dilution (lilO*4) in seawater and there werecorresponding changes in oxidation state(24).
The distribution and speciation of Te, Np, Pu and Am have beeninvestigated on a number of cruises throughout UK coastal waters. Noevidence has been found so far for a reduced form of Tc in the IrishSea. Most Np is present as Np(V) but a small proportion (0.2-0.3%)is present as Np(IV), consistent with the pH-dependent equilibriumreaction investigated experimentally with 235Np (Fig. 1).Measurements of Np have been made in all UK coastal waters. Thedischarge from the Cap de la Hague reprocessing plant is clearlysuperimposed on the distribution pattern of Sellafield-derived Np(Fig. 2). Kp values for Np between suspended particulate andseawater (1 E3-7 E4) were similar to those reported previously(25).Further data have been obtained on the distribution and speciation of238Pu, 239/2<tOpu and 241^ in fiitereci seawater and suspendedparticulate. The variation in Pu isotope ratios has been used toidentify the sources of Pu as Sellafield, Dounreay (N. Scotland), Capde la Hague or from fallout (Atlantic Ocean).
Seawater samples are usually collected using the ship'scontinuously-pumped seawater supply, which has an intake, 3 m belowthe surface, fitted with a zinc screen which acts as a sacrificialanode. It has been demonstrated, in the later part of 1984, thatthis sampling method results in a memory effect which becomesapparent when passing from waters with relatively high radionuclideconcentrations to waters with relatively low radionuclideconcentrations. This can result not only in anomalously high Np, Puand Am concentrations, but also in erroneous K., estimates. Themagnitude of the effect is dependent upon the ship's location, and
105
50 -
Fig. 2 Concentration of 237Np (uBq I"1) in filtered seawaterin UK coastal waters in 1982 and 1983.
the time spent at that location, in the period prior to sampling. Acomparative study is being undertaken using alternative samplingtechniques (e.g. Niskin bottles) and the results of this study,together with an assessment of the quality of previously collecteddata, will be reported in due course. Undoubtedly the mostsignificant effect will be on samples collected in Atlantic waters(i.e. fallout levels) immediately after the ship has spent aprolonged period (several weeks) in the NE Irish Sea. The higherthan expected 237Np concentrations of 3 p,Bq I"1 measured in the SWApproaches in 1982 and 1983 (Fig. 2) almost certainly result from
106
this memory effect. This case serves as a warning that problemsconcerning data quality may come from unexpected sources.
A considerable analytical effort has been expended to estimatethe quantities of Pu and Am residing in the sediments and water ofthe Irish Sea. An inventory of Pu and Am, as of 1977/1978, has beenpublished(23). At least 240 TBq of 239/240pu and 290 TBq of 241^were associated with the upper 30 cm of the seabed within a 30 kmwide belt along the Cumbrian coast. An extensive re-samplingprogramme has been carried out which will provide an improvedinventory estimate, as of 1983, taking account of the observedvertical distribution of Pu and Am in the seabed(3Lt).
The distribution of naturally-occurring radionuclides in IrishSea sediments has been used to assess the extent, and quantify therates of, physical processes which will influence the futurebehaviour of artificial radionuclides. ^C data fail to show activesedimentation but reveal deep, homogenous mixing of the seabed over aperiod of hundreds or thousands of years( ). Mixing processes havebeen further studied using 210Pb and 234Th. Rapid turnover of theupper few centimetres (months) and upper few tens of centimetres(years) is a widespread phenomenon. Direct evidence of thebiological control on Pu, Am and Cm redistribution at depths of up to140 cm by bioturbation has been published(2^>2^). An extensivesurvey of the distribution, density and behaviour of benthic faunahas been undertaken. The large echiuroid Maxirfulleria lankesteri andthe crustacean Callianassa subterranea are regarded as the mostimportant bioturbating organisms. [It is worth noting thatechiuroids are also known to occur in deep sea sediments.]
The radiochemistry of interstitial waters has been studied ontwo cruises to the Irish Sea. The results of the first cruise in1982 have been published(28). The data confirmed previouslypublished work(25»29) on the proportions of Pu in higher and loweroxidation states. Partial reduction of Np(V) to Np(IV) was observed.Considerable precautions were taken on the second cruise in 1984 toexclude oxygen at all stages of the sub-sampling, squeezing andanalysis procedure.
The necessity for the elaborate precautions used in 1984 wastested by comparing Pu data obtained using methods used previously in1979 (see 2 ). Changes in oxidation state in response topost-collection redox changes, and enhanced scavenging of reduced Pu(III+IV) by the oxidation of ferrous iron, could both arise from
107
processing samples in the normal atmosphere, resulting in changes inthe observed sediment-interstitial water distribution coefficientCKQ). There were no significant differences in Pu KQ values forparticular depth horizons obtained using the two methods. It appearsthat elaborate precautions to exclude oxygen may not be necessary forthese particular sediments but further work is required to confirmthis. The quality of the separation of Np(IV) using both NdF3 andTTA/xylene was monitored with 235Np as a tracer. The Np data fromthis cruise are still being worked up. Some measurements were made
241of Am which indicated a distribution coefficient between solid andliquid phases of about l E6.
The nature of sediment-radionuclide interactions in Irish Seasediments is under investigation. Alpha-emitting 'hot' particleshave been identified in surface and sub-surface sediments using theCR-39 (plastic) nuclear track detector technique. The spatialdistribution of 'hot' particles off the Cumbrian coast approximatesto that of Pu measured by conventional a-spectrometry.Experiments are underway to examine the partitioning of Pu and Ambetween different components of the sediment, such as carbonate andMn-oxide phases, by a sequential leaching procedure. Humicsubstances have been extracted from sediments and interstitial watersfrom the Irish Sea, and from 400 £ seawater samples from around theUK coast. They will be analysed for Th, U, Np, Pu, Am, Cm and Tc toassess the extent of organic complexation. A project has begun tostudy the relationship between suspended sediment load andradionuclide concentration, and the shorewards flux of sediment-boundradioactivity using rig-mounted current meter, transmissiometer andwater sampler arrays. This project will be developed over a numberof years.
Studies on the accumulation of long-lived radionuclides bybiological materials have continued with emphasis on food specieseaten directly by man( ). Measurements of Np, Pu and Am have beenmade in a variety of marine organisms and algae collected from StBees Head near the Sellafield discharge and at Balcary Point some 30miles distant on the southern Scottish coast. Concentration factorsfor each species are broadly similar at the two sites. Lobsters(Homarus gammarus) have been collected over a two-year period, fromlocations near to Sellafield, at three monthly intervals and analysedfor Pu, Am and Cm. Analyses are also being made for Np and Tc. Theresults to date confirm previous observations on the different
108
metabolism of Pu and Am, with the former being preferentiallyaccumulated by claw muscle and the latter by tail muscle. Observed2 Am/239+21*°Pu quotients in claw muscle ranged from 1.4 to 3.1, intail muscle from 7.4 to 19.2. In contrast, the quotients for theprincipal routes of entry into the animals, the gut and the gill,ranged from 0.7 to 1.3 and 0.6 to 1.4 respectively.
Other environmental studies have covered a number of subjectareas, including the species-specific affinity of 9 Tc for benthicalgae, the response of benthic algae to variations in time of pulsed
9 9discharges of Tc from Sellafield, concentrations of transuraniumnuclides in plankton collected off Sellafield, Dounreay and Cap de laHague, and the distribution of a number of radionuclides, includingU, in coastal water fish species. Laboratory accumulation
qu 9^7 9 '-î <îexperiments have been conducted with 3:>mTc, ^ Pu and * Np toassess their assimilation, retention and distribution in lobsters(Homarus gammarus) , Nephrops norvegicus , winkles (Littorina littorea)and plaice (Pleuronectes platessa). The effects of moulting on theaccumulation of Tc by juvenile losbters have been studied in detail;the results have been prepared for publication( ).
4. Deep sea research
A provisional assessment of radiation regimes in the deep oceanenvironment has been published( > ) . Measurements have been madeof 210Po, 238Pu, and 239/240pu ±n the deep-sea fish Coryphaenoidesarmatus .
Studies of sedimentary processes which may influenceradionuclide scavenging in the deep sea have been concentrated at theNEA Dumpsite. Discussions of sedimentation and bioturbationprocesses based on li4C and 210Pb data have been published(35~37) .
237The uptake of Pu by calcareous NE Atlantic sediments has beenfj o
studied( ). A review of Kß and CF values for use in genericmodels of deep sea radioactive disposal has been prepared( ). Thesorption properties of the NEA Dumpsite sediments and the K~ valuesused for the 1984 NEA Site Suitability Review have beendiscussed(39).
5r Conclusions
A considerable amount of data on the behaviour of long-livedradionuclides in UK coastal waters has been generated in the period1982-1984. An understanding of the environmental behaviour of such
109
radionuclides is required to allow accurate predictions to be made ofthe consequences of the deep sea disposal of radioactive wastes.Concomitantly, a knowledge is required of the physical and chemicalocéanographie processes which will influence the migration ofradionuclides released into the deep ocean.
Publications list, 1982-19841) DUTTON, J. W. R. Seawater radionuclide analyses. pp. 82-84 JLn
Interim Océanographie Description of the North-East AtlanticSite for the Disposal of Low-Level Radioactive Waste,(edited by P. A. Gurbutt and R. R. Dickson.) NEA/OCED,Paris, (1983).
2) HILL, H. W. A physical oceanography program to examine thefeasibility of radioactive waste disposal in the deep ocean,pp. 123-131 In Wastes in the Ocean. Volume 3. RadioactiveWastes and the Ocean. (edited by P. K. Park et al.)Wiley-Interscience, New York and Chichester.
3) MITCHELL, N. T. Disposal of high-activity nuclear wastes.(Letter.) Mar. Pollut. Bull., _U, 358-361 (1983).
4) MITCHELL, N. T. History of dumping and description of waste,pp. 8-12 JLn Interim Océanographie Description of theNorth-East Atlantic Site for the Disposal of Low-levelRadioactive Waste. (edited by P. A. Gurbutt and R. R.Dickson.) NEA/OECD, Paris, (1983).
5) MITCHELL, N. T. and PENTREATH, R. J. Monitoring in thenorth-east Atlantic Ocean for the dumping of packagedradioactive waste, pp. 120-125 In Proceedings of the 3rdInternational Symposium on Radiological Protection - Advancesin Theory and Practice, Inverness, 6-11 June 1982. Vol. I.Society for Radiological Protection 1982.
6) PENTREATH, R. J. Principles, practice and problems in the moni-toring of radioactive wastes disposed of into the marineenvironment. Nucl. En., _21, 235-244 (1982).
7) PENTREATH, R. J. Future requirements in environmental research,J. Soc. Radiol. Prot., _3_ (4), 15-20 (1983).
8) PENTREATH, R. J. Biological studies, pp. 101-118 In InterimOcéanographie Description of the North-East Atlantic Site forthe Disposal of Low-Level Radioactive Waste. (edited byP. A. Gurbutt and R. R. Dickson.) NEA/OECD, Paris, (1983).
9) PENTREATH, R. J. Alpha-emitting nuclides in the marine environ-ment, Nucl. Instrum. Meth. Phys. Res., 223, 493-501 (1984).
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10) PENTREATH, R. J. The accumulation of long-lived radionuclidesby marine organisms: problems past, present and future,pp. 257-268 n The Behaviour of Long-Lived Radionuclides inthe Marine Environment. (edited by A. Cigna andC. Myttenaere). CEC, Luxembourg, (1984).
11) PENTREATH, R. J. (Editor). Comparative review of the behaviourof radionuclides released into coastal environments. IAEATec. Doc. 329 (1985).
12) PENTREATH, R. J., Radioactive discharges from Sellafield. IAEATec. Doc. 329, Vienna, 67-110. (1985)
13) PRESTON, A. Impact on the marine environment of coastally sitednuclear power installations. p!51 In Seminari InternazionaliSull1 Inquinamento Marino, Geneva, 1980. (edited by N. D.Croce). Instituto Scienze Ambintali Marine-Universita diGenova, 1982. (Summary only.) (1982).
14) PRESTON, A. Deep-sea disposal of radioactive wastes.pp. 107-122 _In Wastes in the Ocean. Volume 3. RadioactiveWastes and the Ocean. (edited by P. K. Park et al.)Wiley-Interscience, New York and Chichester, (1983).
15) PRESTON, A. Use of the oceans for waste disposal. The Siren,(21), 9-14 (1983).
16) PRESTON, A., The environmental behaviour of long-livedradionuclides: radiological protection requirements, pp.3-15 _In The Behaviour of Long-Lived Radionuclides in theMarine Environment. (edited by A. Cigna and C. Myttenaere).CEC, Luxembourg, (1984).
17) TEMPLETON, W. L. and PRESTON, A. Ocean disposal of radioactivewastes. Radioact. Waste Mgmt. _3(1), 75-113 (1982).
18) WOODHEAD, D. S. Contamination due to radioactive materials,Mar. Ecol. _5_ (3), 1111-1287 (1984).
19) WOODHEAD, D. S. Radioecology: rapporteur summary, ICRR 7thInternational Congress of Radiation Research (in press).
20) HARVEY, B. R., LOVETT, M. B. The use of yield tracers for thedetermination of alpha-emitting actinides in the marineenvironment, Nucl. Instrum. Meth. Phys. Res. 223, 224-234(1984).
21) BAKER, C. W. Radiochemical techniques for determining somenaturally-occurring radionuclides in marine environmentalmaterials, Nucl. Instrum. Meth. Phys. Res. 223, 218-223(1984).
Ill
22) BAKER, C. W. and YOUNG, A. K. The determination of radium andradon isotopes in marine environmental materials. I_nEnviron, and Biol. Materials, 4th Symp. on the Determ. ofRadionucl. N.P.L., Glazebrook Hall, Teddington, 18/19 April1983. Paper No. 8, 14 pp (1983).
23) PENTREATH, R. J., LOVETT, M. B., JEFFERIES, D. F., WOODHEAD, D.S., TALBOT, J. W., MITCHELL, N. T. The impact on publicradiation exposure of transuranium nuclides discharged inliquid wastes from fuel element reprocessing at Sellafield,U.K., pp. 315-329 I_n Radioactive Waste Management, Vol. 15,IAEA-CN-43/32, IAEA, Vienna, (1984).
24) PENTREATH, R. J., WOODHEAD, D. S., KERSHAW, P. J., JEFFERIES, D.F. and LOVETT, N. B. The behaviour of plutonium andamericium in the Irish Sea. ICES Symposium on ContaminantFluxes through the Coastal Zone. Contr. No. 21 (in press).
25) PENTREATH, R. J., JEFFERIES, D. F., TALBOT, J. W., LOVETT, M. B.and HARVEY, B. R. Transuranic Cycling Behaviour in theMarine Environment. IAEA Tec. Doc. 265, Vienna, pp. 121-128(1982).
26) KERSHAW, P. J., SWIFT, D. J., PENTREATH, R. J. and LOVETT, M. B.Plutonium redistribution by biological activity in Irish Seasediments. Nature, Lond. 306, 774-775 (1983).
27) KERSHAW, P. J., SWIFT, D. J., PENTREATH, R. J. and LOVETT, M. B.The incorporation of plutonium, americium and curium into theIrish Sea seabed by biological activity. Sei. TotalEnviron., 40, 61-81.
28) HARVEY, B. R. and KERSHAW, P. J. Physico-chemical interactionsof long-lived radionuclides in coastal marine sediments andsome comparisons with the deep-sea environment. pp. 131-141In The Behaviour of Long-Lived Radionuclides in the MarineEnvironment. (edited by A. Cigna and C. Myttenaere). CEC,Luxembourg, (1984).
29) HARVEY, B. R. The influence of pore-water chemistry on thebehaviour of transuranic elements in marine sediments. InProc. Conf. - 'Transfer Processes in Cohesive SedimentSystems', Windermere, 1981. (in press).
30) NEWTON, D., JOHNSON, P., LALLY, A. E., PENTREATH, R. J. andSWIFT, D. J. The uptake of cadmium ingested in crab meat.Human Toxicol. 3, 23-28 (1984).
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31) SWIFT, D. J., The accumulation of 95mTc from seawater byjuvenile lobsters (Homarus gammarus L.). J. Environ.Radioact. (in press).
32) WOODHEAD, D. S. The natural radiation environment of marineorganisms and aspects of the human food chain. J. Soc.Radiol. Prot., 2 (4), 18-25 (1982).
33) WOODHEAD, D. S.and PENTREATH, R. J. A provisional asessment ofradiation regimes in deep ocean environments, pp. 133-152I_n Wastes in the Ocean. Volume 3. Radioactive Wastes andthe Ocean, (edited by P. K. Park _et_ al.) • Wiley-Interscience,New York and Chichester, (1983).
34) KIRBY, R., PARKER, W. R., PENTREATH, R. J., LOVETT, M. B.Sedimentation studies relevant to low-level radioactiveeffluent dispersal in the Irish Sea, Part 3. IOS Report(1984).
35) KERSHAW, P. J. ll*C and 210Pb in NE Atlantic sediments: evidenceof biological reworking in the context of radioactive wastedisposal. J. Environ. Radioact. (in press).
36) KERSHAW, P. J. and RUTGERS VAN DER LOEFF, M. M. Sedimentaryprocesses 1: sedimentation. In Interim OcéanographieDescription of the North-East Atlantic Site for the Disposalof Low-Level Radioactive Waste. Vol. 2. (edited by R. R.Dickson, P. A. Gurbutt and P. J. Kershaw). NEA/OECD, Paris(in press).
37) KERSHAW, P. J., SMITH, J. N. and NOSHKIN, V. E. Sedimentaryprocesses 2: bioturbation. In Interim OcéanographieDescription of the North-East Atlantic Site for the Disposalof Low-Level Radioactive Waste. Vol. 2. (edited by R. R.Dickson, P. A. Gurbutt and P. J. Kershaw). NEA/OECD, Paris(in press).
38) IAEA. Sediments K_s and concentration factors forradionuclides in the marine environment. IAEA TECDOC Series,IAEA, Vienna (in press).
39) KERSHAW, P. J., RUTGERS VAN DER LOEFF, M. M., and WHITEHEAD, N.E. Sediment sorption properties. I_n_ Interim OcéanographieDescription of the North-East Atlantic Site for the Disposalof Low-Level Radioactive Waste. Vol. 2. (edited by R. R.Dickson, P. A. Gurbutt and P. K. Kershaw). NEA/OECD, Paris(in press).
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40) KERSHAW, P. J. Radiocarbon dating of Irish Sea sediments.Estuar. Cstl. Shelf Sei. (in press).
Al) KERSRAW, P. J. Marine waste disposal and MAFF. Brit. Geol., _U(2), 48-51 (1985).
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BIOLOGICAL MIXING AND RADIONUCLIDEREDISTRIBUTION IN MARINE SEDIMENTS*
E.H. SCHULTECEC,c/oENEA,La Spezia, Italy
Abstract
Literature survey indicates that bioturbation strongly affects the recycyling of239,240radionuclides through the benthic boundary layer, and nuclides such as Pu and
241Am may be resolubilized by anionic complexers released by fauna.Transfer of nuclidesto fauna which ingest particles is very low, whereas transfer from water ismuch more efficient. This suggests that interstitial water is probably the predominantsource of transuranics for benthic organisms in sediments.
Biological activities such as feeding, burrowing, and irrigationof benthic infaunal organisms clearly affect physical and chemical proper-ties and characteristics of the sediment-water interface.This process ofbiological mixing or bioturbation of surface sediments is widespread andconsidered to be a possible important mechanism for the migratory behavi-our of long-lived radionuclides in marine sediments (1).
In the geobiochemical cycling of many natural and man-made contami-nants sediments may be considered as a final sink and/or ultimate pollu-tant reservoir in the marine environment. In addition to physical proces-ses ,bioturbation, generated by biological activties of sediment-dwellingorganisms, seems to be a principle mechanism in transfers and recyclingof sediment-associated pollutants through benthic ecosystems.
Among the sediment infauna deposit- and detritus-feeders are the mostimportant and abundant groups that redistribute contaminants and radionucidesfrom sediments to the overlying water, where other benthic organisms ofthe benthic boundary layer (2) are responsible for their vertical trans-port from deep to surface waters.
The extensive biological reworking of the sediment column, generallyresults in the disruption of the sedimentary stability and composition evi-denced by a disturbance of the stratigraphy of the upper sediment layers,which normally are inhabited by more than 90 percent of meio- and macrofau-nal species (3, 4).
Population densities of the sediment infauna show great variabilitiesin relation to physical and chemical characteristics of the sediment likegrain size, organic matter content, oxygen content, compactness of the se-diment etc (5). Besides these, other parameters such as depth and distan-ce from the continent clearly influence benthic faunal densities, showing
* Contribution N 2197 of the CEC Radioprotection Programme.
115
a general decrease of population densities from about 10 in coastal en-vironments to some tens or hundreds of individuals per square meter in theabyssal sea (6). The most abundant species found were Polychaetes, Crusta-cea, Pelecopoda and Sipunculoidea which comprise 80 to 100 percent of thefauna. Generally, the importance of the meiofaunal taxa in this contextis clearly underestimated due to difficulties of quantitative sampling pro-cedures. Nevertheless, these groups may be found up to 4 times more abun-dant than the macrofaunal taxa with nematodes as the dominating group (7) .
In the process of biological reworking of sediment particles, biolo-gical mixing or turnover rates of sediments have been reported to reachvalues of 10 to 10" cm /1000 years for densely populated, coastal environ-ments, whereas these rates decreased with depth to 1 to 10^ cm /1000 yearsin the deep ocean reflecting reduced biological activities (8). Sedi-ment turnover rates induced by bioturbation may vary considerably fromonce every 15 years to once every 10 weeks according to species invol-ved and the population densities present. However, most rates fall inthe range of 1 to 5 years typical for populations of deposit-feeding po-lychaetes. The annual rate of sediment turnover for polychaetes from the*-)continental slope (250m) was reported to be about 10 Kg dry sediment/m /year. Assuming a medium sediment reworking depth of 5 cm (5 x 10 ml sedi-nent/m2), a steady state population of polychaetes could completely turn-over the sediment in 4 to 5 years (9). In shallow areas, however, it isnot surprising to find that the surface of the muddy sea floor is passedthrough the benthos at least once, and in some cases, several times a year(5).
The amount of organic matter in sediments can affect sediment turn-over rates, which, as a consequence, decrease with increasing food supply.Deposit- and suspension-feeders entrap biological particles from the wa-ter column and the sediment, aggregate the ingested material in the gut,and void the feces as discrete pelletés or fecal strings. This process ofbiodeposition is known to be important to biogeochemical cycles especial-ly in intertidal areas. Deposit-feeders probably play the quantitativelymost important role in "pelletizing" marine sediments by biodepositionof feces and pseudofeces. In some areas between 40 to 100 percent of theparticles of the sediment surface are in the form of pellets mainly pro-duced by polychaetes and bivalves, sometimes resulting in an upper, 1cm,thick surface layer of pellets (5).
The reworking of the sediment column by populations of deposit-fee-2ding bivalves may reach values of 60 to 120 Kg sediment/m /year. This pro-cess accelerates the remobilisation and vertical transport of organic de-tritus together with nutrient-rich bottom mud to the sediment-water inter-face severving, after resuspension into the water column, as a potentialsource of food for suspension-feeders, whereas the particles may act asscavengers for radionuclides with subsequent sedmentation and incorpora-tion into the sediment.
Recent field data confirm, that bioturbation strongly affects therecycling of radionuclides through the benthic boundary layer especial-ly in highly productive areas. The feeding activities of infaunal ben-thic organisms transfer radionuclides from the overlying water to the se-diment (10). Pu-239, Pu-240 and Am-241 fixed in sediments may be resolu-bilized in the presence of anionic organic complexes, released deep in
116
the sediment by metabolic activities of the infauna. In this form the ra-dionuclides may freely migrate upwards through the sediment via intersti-tial waters or through infaunal borrows and finally could be released in-to the overlying waters.
Benthic organisms may play an important role in the redistributionof transuranium nuclides in near shore and deep-ocean sediments. In thebenthic boundary layer Pu and Am, present in the water, will become readi-ly associated with a variety of benthic fauna living in or on the sediment.Accumulation of transuranium nuclides by benthic biota may occur by di-rect sediment ingestion (11). In tissues of various invertebrate infaunaconcentrations of plutonium of 5 to 10 times those in the sediment havebeen found.These findings suggest that sediment-associated transuranicsare available to biota (12). In laboratory experiments with polychaetesmore than 90 percent of the plutonium were derived from a source otherthan sediment, possibly from deposited material or interstitial pore wa-ter (11). Thus, the sediment pathway is responsible for only a few per-cents of the total body burden of plutonium in polychaetes (13). Conside-ring the high concentration factors in biota of 100 to 1000 reported inthe literature for direct uptake from water one may conclude that water,possibly interstitial water, is the predominant pathway for uptake oftransuranics by sediment infauna.
The processes involved in the transfer of radionuclides from sedi-ments to benthic infaunal organisms are still unclear and may depent onthe physico-chemical forms of the different isotopes present in the se-diment and interstitial water.
The transfer factors for contaminated sediments and whole bodies ofinfaunal organisms that ingest sediment particles continously were foundto be very low for plutonium, americium and technetium.The values obtainedrange from 0.1 to 0.001 for polychaetes, molluscs, and crustaceans(11,14,15).resulting in a relatively small net uptake of those radionuclides fromcontaminated sediments. In this process part of the radionuclides trans-ferred to infaunal species will come from the sediment's interstitial porewater while another part would be obtained by direct transfer from sedi-mentary particles to the organisms (14).
In conclusion, the literature data and experimental results show apotential remobilisation of transuranic elements from biodisturbed sedi-ment layers by benthic infaunal species. However, the relatively high con-centration factors of 1000 determined for the uptake from water and thevery low transfer factors of 0.001 for sediments indicate that intersti-tial or pore water and not the sediment particles will be the predominantsource of transuranics for benthic infaunal organisms.
References
1) GORDON, D.O.Jr., The effects of deposit-feeding polychaete Pectinariagouldii on the intertidal sediment of Barnstable Harbour, Limnol.Ocea-nogr. , 11., 327 (1966) .
2) GOMEZ, L.S., HESSLER, R.R., JACKSON, D.W., MARIETTA, M.G., SMITH,K.L.,TALBERT, D.M., YAYANOS, A.A., Biological studies of the United StatesSubseabed Disposal Program, Sandia Report N° SAND79-2073 (1980).
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3) PETR, T., Bioturbation and exchange of chemicals in the mud-water in-terface, In Interactions between sediments and fresh water, H.L. Gol-terman (Ed.), W.Junk B.V.Publishers, Wageningen (1977).
4) RUTGERS VAN DER LOEFF, M.M., LAVALEYE, M.S.S., Geochemical and biologi-cal research at the NEA dumpsite for low-level radioactive waste, Inter-im report Dutch DORA program, Netherlands Institute for Sea Research,27, (1984).
5) RHOADS, D.C., Organism-sediment relations on the muddy sea floor, Ocea-nogr. Mar. Biol. Ann. Rev., 12, 263 (1974).
6) SANDERS, H.L., HESSLER, R.R., HAMPSON, G.R., An introduction to thestudy of deep-sea benthic faunal assemblages along the Gay-Head-Ber-muda Transect, Deep Sea Res., 12, 845 (1965).
7) MULLIN, M.M., GOMEZ, L.S., Biological and related chemical researchconcerning subseabed disposal of high-level nuclear waste, JacksonHole, Jan. 12-16, 1981; Sandia report N° SAND81-0012 (1981).
8) GOMEZ, L.S., HESSLER, R.R., JACKSON, D.W., MARIETTA, M.B., SMITH, K.L.,YAYANOS, A.A., Environmental studies data base development and data syn-thesis activities of the US-Subseabed Disposal Program, In Impacts ofradionuclide releases into the marine environment, IAEA Vienna, N° IAEA-SM-248/142 (1980).
9) NICHOLS, F.H., Sediment turnover by a deposit-feeding polychaete, Limnol.Oceanogr. , IS), 945 (1974).
10) LIVINGSTON, H.D., BOWEN, V.T., Pu and Cs in coastal sediments, EarthPlanet. Sei. Lett., 43, 29 (1979).
11) BEASLEY, T.M., FOWLER, S.W., Plutonium and americium: uptake from con-taminated sediments by the polychaete Nereis diversicolor, Mar.Biol.,38, 95 (1976).
12) BOWEN, V.T., LIVINGSTON, H.D., BURKE, J.C., Distribution of transura-nium nuclides in sediment and biota of the North Atlantic Ocean, InTransuranium nuclides in the environment, IAEA Vienna, N° IAEA-SM-199/96, 107 (1976).
13) MURRAY, C.N., RENFRO, W., Uptake of plutonium from seawater and sedi-ment by a polychaete worm, J. Oceanogr. Soc. Japan, 32, 249 (1976).
14) MIRAMAND, P., GERMAIN, P., CAMUS, H., Uptake of americium and pluto-nium from contaminated sediments by three benthic species: Arenicolamarina, Corophium volutator, Scrobicularia plana, Mar.Ecol.Prog.Ser.7, 59 (1982).
15) MASSON,M.,APROSI,G.,LANIECE,P.,GUEGUEN1AT,P.,BELOT,Y., Approches expé-rimentales de l'etude des trasferts du technetium a des sédiments et ades espèces marines benthiques, In Impacts of radionuclide releases in-to the marine environment, IAEA Vienna, N° IAEA-SM-248/24 (1980).
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BIOGEOCHEMICAL STUDIES OF LONG-LIVEDRADIONUCLIDES IN MARINE ENVIRONMENTS
V.E. NOSHKIN, K.M. WONG, R.J. EAGLE, T.A. JOKELALawrence Livermore National Laboratory,University of California,Livermore, CaliforniaUnited States of America
239 240In Enewetak and Bikini lagoons, ' Pu is always present at levels higher thanfor fallout, in water samples, indicating remobilisation from sediments. The
-1 -1respective- water levels are 21 fCi 1 and 42 fCi 1 , and lagoon inventories2410.96 and 1.2 Ci, which are 0.08% of sediment inventories. Small amounts of Am
also solubilise. Pu attached to suspended particles is mostly Pu ' , and ifV.VI , 90r 137^ 239,240^ 241 207_.soluble is Pu . Concentrations of Sr, Cs, Pu, Am, Bi and
Pb. Bi and Po in fish showed some variation with trophic level. Values90 239 240 241 137increased between levels 2 and 5 for Sr, ' Pu, Am, but not Cs.
Concentration factors varied, and a single generic value for all fish species wasnot possible. Extrapolation of results from contaminated lagoons to lessercontaminated lagoons was not possible because in the former radionuclides werefused with CaCO~ and dissolve in the gut of fish to some extent. Speciation is
207different in lesser contaminated lagoons. 80% of Bi was in the muscle of goat-fish but less than 1% for surgeonfish and mullet. Evidence was obtained that theisotope is translocating. Similarly Bi formed in fish bone translocates toliver. In the North-east Atlantic dumpsite, only global fallout levels were foundfor radionuclides which could have potentially leached from the wastes.
1. IntroductionMany of_the questions regarding deep-sea disposal of transuranium
elements and other long-lived radionuclides can be partially answeredfrom studies at contaminated, more accessible locations — here some ofthe processes, reactions, and rates that influence the fate of theseradionuclides in the marine environment can be identified and evaluated.Reliable information on the environmental behavior of these radionuclidesin the ocean is required to improve our understanding of the pathwaysthat may lead back to man from any future practices involving dispos?. Ieither onto or into marine sediments.
For several years, we have conducted studies related to the cyclingof lonq-lived radionuclides at several locations in the Pacific whichinclude the Farallon Islands waste disposal site off the coast ofCalifornia, USA; Marshall Islands with the emphasis on B i k i n i andEnewetak Atolls; the previous United States proving grounds in thePacific; Johnston Atoll; and San Clémente Island off"the coast of
119
California, USA. In addition to the Pacific studies, a deep-sea programwas recently initiated in the 'vicinity of the Northeast Atlanticradioactive waste-disposal site. Many of the sites mentioned in thePacific are among the few in the world where long-lived radionucl ides,now found in solution or accumulated-by organisms, originate from bottomsedimentary deposits. Therefore, research results obtained from theseareas have relevance in assessing the use of the sea bottom forradioactive waste disposal. Results from a few studies, conducted duringthe tenure of- this research agreement and which are relevant to seabeddisposal of radioactive wastes, are briefly discussed in this report.2. Mobilization of Plutonium from Enewetak and B i k i n i Lagoon Sedimentsto Seawater.
One important question 'related to the long-term behavior of thetransuranium elements in the marine environment is whether theradionucl ides, after deposition in bottom sediments, can return to thewater column and eventually re-enter biological food chains remote fromthe point of origin. At some sites, contaminated by global fallout orsurface discharges, where high concentrations are maintained in theoverlying water column, mobilization of plutonium from sedimentarysources to solution is difficult to demonstrate' 1 >. However, at siteswhere plutonium was introduced directly onto sedimentary materials orwhere current inputs to sediments are small, mobilization of plutoniumcan be easily identified^"''. For example, the lagoon sediments atBikini and Enewetak, the sites previously known as the Pacific ProvingGrounds, were contaminated with fission and activation products fromnuclear devices tested there by the United States between 1946 and 1958.Following the last nuclear test at Enewetak in 1958, the residualradionucl ides deposited to the laaoon water either settled rapidly to thebottom sediments or remained as dissolved or particulate species in thewater and were eventually discharged to the ocean. If we accept the•thesis of no mobilization, we would observe a concentration of dissolvedplutonium (and americium) in the lagoon water mass during any timesubsequent to 1958 at a level equivalent to that from global fallout inthe north equatorial Pacific surface water, the replacement water for thelagoon. Table 1 shows the variation of the mean tjy+eWpu activity infiltered samples of seawater collected during the years indicated fromdifferent locations in the lagoons at Enewetak and Bikini. Falloutlevels of 239+240pu ^ ^g surface waters of the north equatorialPacific have averaged °4i°>,?,nfCi/l over the last 10Concentrations of <-3y+240pu greater than fallout backgroundconcentrations are found in the water samoled from all locationsthroughout the lagoons. This is a direct indication that 239+240pu hasbeen continuously mobilized over the years to solution from the solidphases in these enXiS°9/i'nn s' ^^e var"'a'tions between the average solubleconcentrations of 239+240pu determined from samples obtained during theperiods indicated are not, at this time, considered siqnificant and theassumption is made that the standing average amount of plutonium in thelagoon water mass at any time, is constant. -Stated differently, steadystate conditions have been established for 239+240pu partitioning fromthe sedimentary reservoirs at these atolls to solution. Since 1972 theaverage "soluble" 239+240pu at Enewetak has been 21 fCi/1. At Bikinithe mean value from 1972 to 1982 has been 42 fCi/1. With the appropriatedimensions for each lagoon, these concentrations convert to lagooninventories of 0.96 and 1.2 Ci at Enewetak and Bikini, respectively.Particulate concentrations are not included in these estimates. Thesequantities represent 0.08% of the sediment inventories determined to adepth of 16 cm at each atoll. The mean Quantity of 239+24Gpy mobilizedand found in solution at any time repres°nts a small fraction of the120
inventory associated with the major reservoir at the atolls.Mobilization of 239+240pu from marine deposits is a slow, butnevertheless real process.Small amounts of 24'Am are aiso capable of dissociating from thesemarine deposits, 241/\m ^s more f^rm]y bound to the sediments than239+240Pu> The amount Of 239+240Pu mobilized to solution at theatolls can be reasonably predicted using a K^ of approximately2.3x10^ and the mean sediment concentrations.
The mobilized 239+240pu a^ Enewetak and Bikini has solute-likecharacteristics and different valence states coexist in solution. Thelargest fraction of the soluble plutonium is in an oxidized form (+V orVI). Quantities associated with suspended particulate material andsediments are predominately in the reduced state (+III or IV). Thesorption-desorption process is not completely reversible because ofchanges that occur in the relative amounts of the mixed oxidation statesin solution with time. The oxidized forms of 239+240pu -jn solutionhave a lesser tendency to associate with sedimentary or particulatematerial than reduced plutonium. Complexation after mobilization alsoaffects the résorption rate. Therefore, any characteristics of239+240pu described at a point of reference may not necessarily berelevant to explain behavior after mobilization and migration insolution. Some small fraction of any 239+240pu p]acecj On the surfaceof the sea floor in oxygenated environments should, in time, disperse tothe overlying water mass and migrate from its original site. The 24'Amshould remain more firmly fixed to the sedimentary material near thepoint of introduction. The rate of disappearance of the tworadionuclides from marine deposits will depend on the physical,biological, and chemical characteristics of the sediments and the rate ofwater movement into and out of the contaminated region.
Table 1. The 239+240 pu Average Lagoon Water Concentrations. a
Enewetak Laaoon933 km^—Lagoon Area49 m—Average Depth
Month and Year and Number of Water Samples in Parenthesis10-12/72 (35) 7/74 (71) 5/76 (29) 5/82 (23)
Soluble (fCi/liter) 22 25 16 17Particulate (fCi/liter) 10 19 13 nd
TOTAL 37 "4T 79"Bik i n i Laooon
629 km2--Laaoon Area45 m--Averaae Depth
Month and Year and Dumber of Water Samples in Parenthesis12/72 (17) 1-2/77 (26) 9/82 (21)
Soluble (fCi/liter)Particulate (fCi/liter)
and
TOTAL
Arithmetic mean values.not determined
42 49 3413 nd nd•55
121
3. CoßCfiDtcatlfips of 9_2sr, IJZCs, 239+240Pl 24^ 207Rl-^Upb.2]0Bl-.210Po 1n fl-sh frnm +hp . .
Studies of the accumulation of lonq-lived radionuclides by marineorganisms and specifically by fish eaten by man, have been conducted indifferent Marshall Island Atolls where sediments play a role in determiningbody burdens of radionuclides jn some fi$h.Concentrations of 90Sr, 137Cs, 239+240pU) and 241Am weredetermined in tissues of fish, near-shore surface sediments, and seawaterfrom several atolls contaminated with close-in fallout debris generated atthe Pacific Proving Grounds in the late 1940s through the late 1950's. Theatolls were sorted with respect to present contamination levels detected inthe surface sediments from the lagoons. The "A" group of atolls, whichinclude Ailuk, Likiep, Taka, Ujelang, Uterik and Wotho, have the lowest meanlevel of contamination and Rongelap has the .highest. The "B" group ofatolls consists of Ailinginae, Bikar and Rongerik which have higher levelsof contamination in the surface sediments than the "A" group but less thanat Rongelap. Sediment-to-lagoon water concentration ratios for theseradionuclides (a measure of the sediment/ water distribution coefficient)increased proceeding from the lesser contaminated atolls to Rongelap.Fractions of the radionuclides still detected in the marine environment areirreversibly bound with the mineral matrix of the sediments, and equilibriumconditions do not exist at all atolls. Mean radionuclide concentrationfactors were computed for bone and muscle of the fish representing troohiclevels II-V from the groups of atolls by relating the measured tissueconcentrations to those in filtered lagoon seawater. Values of 90Srconcentration factors for bone and muscle of fish decrease between the 2ndand 5th trophic level. The concentration factor for bone of bottom feedingfish is the largest at atolls where "^Sr is more permanently fixed to thenear shore sedimentary material. There was no unique relationship betweentrophic levels of the fish and the 7cs muscie concentration factor.Some of the variability in the ^Cs concentration factors is best relatedto differences in diet, with concentration factors being lower for bottomfeeding fish than for pelagic species. Higher concentration factors arealso found for ^37Cs at atolls where the radionuclide is still detected inbottom sediments.Values of 239+240pu ancj 241Am concentration factors for bonefollowed the same trend noted for Sr, decreasing between II and Vtrophic level. Ratios of 24^Am to 239+240pu increased in bone andmuscle between 2nd and 5th troohic level species. ^ 'Am seems to be morebiologically available than 239+240pu to higher trophic level species fromthe lagoons, whereas at lower trophic levels the opposite seems to be thecase. Both 239+240pu anc( 241Am concentration factors are greater forbottom feeding species from the more contaminated atolls than found for thesame species at the lesser contaminated atolls. This feature is common forall the long-lived man-made radionuclides determined in this study. Thefollowing is a partial ranking of the radionuclide concentration factors inmuscle for some species from the different atolls.Surgeonfish muscle concentration factors (Trophic Level II)
A atolls 137Cs >_ 239+240Pu > 241Am > 90SrB atolls 137Cs > 239+240pu > 241Am > 90SrRongelap 239+240Pu > 137Cs > 241Am > 90Sr
122
Mullet muscle concentration factors, (Trophic Level II)A atolls 23M40>U > b7Cs > 24ÏAm ^ !)0SrGoatfish muscle concentration (Trophic Level III)A atolls T37Cs £ "9+240pu > 241Am > 90$rTrophic V species,,., „„ „„ „„„All atolls ?37Cs > 239+240Pu > 241Am > 90Sr
This ranking shows there is no precise ordering of the values ofconcentration factors for all fish, which negates the use of a singlegeneric value for all fish species. The ordering is altered byspecies, trophic level, and degree of bottom sediment contaminations.
Bottom-feeding fish have the ability to extract radionuclides thatare irreversibly bound to sedimentary deposits and attain tissueburdens that are larger than the concentrations found in the samespecies from environments where near-equilibrium conditions have beenestablished. The values for the concentration factors generated at thelesser contaminated atolls cannot be used with water concentrations togenerate reliable estimates of concentrations in tissues of speciesfrom the more contaminated lagoons. An explanation for this anomaly isthat some bottom-or coral-feeding fish with diets containing, in part,carbonate material have the ability to lower their gut pH duringfeeding, which results in dissolution within the gut of a fraction ofthe calcium carbonate ingested with food. Fractions of the ^3'Cs,90Sr, 239+240Pu, and 241Am previously fixed or fused within thecalcium carbonate matrix during the period of nuclear testing atEnewetak and Bikini are released by the digestive juices and can passacross the gut wall of the fish.
Contaminants irreversibly fixed to carbonate sediments are notisolated from biological cycles in the ocean. Hiaher trophic levelspecies that do not rely on sediments or coral for this source of foodshow no such increasing trend in the values for the concentrationfactors between differently contaminated atolls.
Another study conducted at Enewetak and Bi k i n i Atolls involved thedetermination of 20/Bi and natural à luPb-2 lüßi-2 luPo in tissuesof different fish. 20'Bi was produced during the series of nucleartests conducted by the United States at Bikini and Enewetak Atollsbetween 1946 and 1958, possibly by reactions such as 2^'Pb (p,n) or2^6pb (p,y), assuming stable lead was present during testing asshielding material p,ear the nuclear devices ( ). Table 2 showsconcentrations of 207Bi determined by gamma spectrometry in tissuesand organs of several species of fish collected from Bikini andEnewetak during different years.
Most striking is the range of concentrations in tissues and organsamong different species of fish collected simultaneously from the samelocation. Highest concentrations of 2^7Bi were consistently detectedin the muscle and other tissues of goatfish and some of the pelagiclagoon fish compared to those of other reef fish such as mullet,surgeonfish, and parrotfish. Over 80% of the whole-body activity of20'ßi in goatfish is associated with the muscle tissue, whereas lessthan 1% is found in the muscle of surgeonfish and mullet. Theconcentration factor for 2U'Bi is not single-valued for fish andvaries with the species.
Concentrations of 2^p0 were a]so determined in the muscle of afew goatfish, mullet and surgeonfish from Bikini Atoll. The averageconcentration in goatfish flesh (0.67 pCi/wet g) exceeded the level insurgeonfish (0.065 pCi/wet g) and mullet (0.38 pCi/wet g). These datacoupled with the observation of higher levels of 2^'Bi in goatfish,led us to speculate that similar enrichment might be expected for2'0ßi (t]/2 = 5.01 d), the precursor of 2'0po and direct daughterproduct from decay of 2^Pb. Any unsupported 2^Bi detected could
123
be a potential source for some fraction of excess 2'^Po detected inmarine organisms. A variety of fish representative of differenttrophic levels were caught at Bikini. Enewetak. Rongelap, and KwajaleinAtolls for the analysis of 210Bi, 210Po, and 210Pb. Separationsof these radionuclides were made onboard the research vessel within24 h of collection to minimize the unavoidable growth-decay corrections.
The 2'0ßi concentrations in liver and flesh from all speciesexceed those of its percursor 2^Pb measured in these tissues.Therefore, some account of excess 2^ßi in edible portions of freshlycaught and rapidly consumed fish should be made in radiological doseestimates from natural radionuclides in marine food pathways. Based onthe 2°'Bi results and the assumption that any unsupported ^1 OBiaccumulated by fish from food or water would relate to 207Biconcentrations, we anticipated levels of 2^Bi in the muscle ofgoatfish several orders of magnitude larger than the unsupportedconcentrations in surgeonfish, mullet, and parrotfish. Rather, wefound no significant differences in concentrations of 2'0ßi in themuscle among all the species. It is clear, therefore, that the excessof 210ß-j -jn the muscle and liver of surgeonfish, mullet, andparrotfish is not from its percursor in the tissue nor from theenvironmental sources from which 207ß-j -js derived. The data suggeststhat the excess 2 E!i may be translocated to muscle and liver tissuefollowing the decay of 2'Opb accumulated in the bone. Allunsupported 210p0 measured in fish, and possibly in other organisms,does not necessarily have to result directly from the food chain. Somefraction, which may vary with the species, of unsupported 2'°Po inspecific tissues such as muscle and liver may result fromredistribution and decay of 2^Bi generated from 210pb accumulatedin bone.
Concentration factors for 210Po in muscle to that in filteredseawater have been calculated using a mean value of 31±3 fCi/1 for2'0po measured in 12 lagoon and ocean surface-water samples. Valuesrange from 8x102 for surgeonfish muscle to 2.3xl04 for goatfish.4. Plutonium in Northeast Atlantic Sediments
Deep-sea disposal of packaged, low-level radioactive wastes hasoccurred at several sites in the Northeast Atlantic. However, since1977, disposal has been restricted to a single site, 4 x 103 km2 inarea, within 10 mi north and south of 46°N and between 16°W and17°30'W. A program of coordinated scientific studies was initiated in1980 by the Nuclear Energy Agency (NEA) of the Organization forEconomic Cooperation and Development to develop a site-specific modelfor predicting radiation exposures from the disposed wastes. Taskgroups on physical oceanography-geochemistry, biology, modeling, andradiological surveillance were established to provide scientific inputon the physical, geochemical, and biological processes controlling thebehavior of radionuclides in the deep ocean and specifically at thedisposal site. As part of this effort, various cooperative studies wereundertaken with other investigators to improve our understanding of thebehavior of long-lived radionuclides in pelagic sediments.The concentrations and inventories of 239+240pu ^ sediments fromwithin the boundaries of the low-level radioactive waste-disposal sitein the Northeast Atlantic are no different from global fallout levels indeep-sea sediments from this region of the Atlantic. No man-madegamma-emitting radionuclides were above detection limits in the sedimentsamples analyzed. There is no indication that past disposal practiceshave led to an area-wide contamination of the site with waste-relatedradionuclides. The 239+240pu Sediment-depth distributions indicate
124
Table 2. Concentrations of ^°^Bi in fish from Enewetak and B i k i n i A t o l l s
Atoll aisland
E-24
E-10
3-5
3-1
mdYear Common namexx
80 Mullet (Crenimuail)dDSurgeonfish (II)Goatfish (II)Snapper (Lethrinus) (V)Snapper (Lut ianus)(V)Bonito (V)
78 Hüllet (Cremn>uail)dl)Surgeonfish (II)Goatfish (III)Parrotfish (IV)
81 Nullet (Cremnuoil)dl)Surqeonfish (II)Goatfish (III)Parrotfish (IV)
78 nullet (Cremmuoil)dl)Mullet (NecHivxtisMlI)Surgeonfish (II)Goatfish (III)Jack (IV)
Muscle
11
6562631911(6<2<1
6530<2<2<456<44
<21360121
.1 (27)
.8 (29)(1)(2)(2)(3)
(2)
(1)
(20)
(2)(2)
Bone
<25 (30)
283 (2)102 (4)198 (2)60 (24)<5<6
1770 (11)0004«1122 (3)
<14<4
<8<25400 (4)19 (35)
?07B i (pCi/kg wet)fStomacnViscera
57891
661713
1130421
115020
9560024421145<49546849206120
(1)(2)(1)(2)(2)(3)(1)(18)(1)
(9)(35)(12)
(11)(6)(20)(2)(H)
content
1490 (2)--—92 (4)
124 (12)1420 (2)65 (16)
1220 (7)--
<40242 (13)51 (23)124 (11)100 (28)
<1901070 (11)<60
Skin
<14.5 (20)
«5 (2)266 (3)150 (2)90 (18)<2<S
-570 (1)«oo<K
37 (?5)<23<3<4
<30960 (2)--
L wer
30391
1190....
6620!89
7460
--<403650<5011643
0003020190
(20)(2)(1)
(7)
(10)
(2)
(24
(1C)1
(15)(25
(2)
\
(20)
E = Enewetak Atoll and B » B i k i n i A t o l l . Nunbers designate islands.The 1 o counting error expressed as the percentaoe of the l i s t e d v a l u e appears in parenthesis, 1 pCi = 37 mBq.
** Trophic l e v e l sho*vn in parenthesis
that downward transport of labelled surface material has occurred todepths greater than 15 cm in the sediment column. There arewell-defined maxima in the majority of the 239+240pu profj]es> ynisfeature is not consistent with one-dimensional vertical mixing models.Heterogenous bioturbation is the dominant mechanism moving 239+240pufrom the sediment surface downward and laterally in Northeast Atlanticpelagic sediments.5- puality-Assurance ,and Jntej;cj3mß.ar_tS£m .Program.
During the last 12 years we have participated in a large number ofnational and international intercalibration exercises and have conducteda continuing rigorous internal quality assurance program. In theGEOSECS program we provided quality control data of many kinds for themeasurements of radionuclides in seawater. These results are discussedin greater detail elsewh?re(9). some additional quality-control datawere generated during the northern Marshall Island survey and have beendiscussed!10). More recently, the sediments from the NortheastAtlantic were processed for the radiochemical separation of plutoniumradionuclides and 24^Am using modifications of published techniquesthat were tested on an IAEA intercalibration exercise performed inCDDJunction with the sample analysis. The results submitted for<ujy-WUpu and ^4iAm concentrations in sediment sample SD-N-1/1,distributed by the Monaco Laboratory of the IAEA, are shown in Table 3along with the median values chosen as the most reliable estimators ofthe true values^''. Agreement between our reported values and the
125
most reliable estimators of the true value may be consideredsatisfactory. The mean 239+240pu concentration of the "standard"sediment is comparable to the mean concentration in surface-sedimentincrements from within and outside the dump site.
We currently are conducting other intercalibration exercises withPortugal (deep sea fish); IAEA (seaweed and sediment); UK (sediment);and other LLNL divisions. We maintain a large number of National Bureauof Standard samples and IAEA standards that are continually used on ouranalytical program to validate detector calibration and separationprocedures.
Table 3. Results of intercomparison of artificial radionuclidemeasurements on marine sediment sample SD-N-1/1.
LLNL meana____ MOSt reliable estimatorRadionuclide f C i g ' 1 m ß q g " 1 o f true value m8qg~l
238DPu239+240pu241Am60Co137Cs
5.1±0.8 0.19±0.03 (21)15.2±1.1 0.56±0.04 (21)13.0±1.6 0.48±0.06 (11)
10.9±0.5 (3)15.2±0.8 (3)
0.180.560.49
11.814.0
a Number of samples analyzed shown in parentheses.
References(1) Nelson, D.M. and Lovett, M.B. Measurements of the Oxidation State and
Concentration of Plutonium in Interstitial Waters of the Irish Sea. ln_IAEA-SM-248, Vienna, 105 (1981).
(2) Noshkin, V.E., Wong, K.M., Jokela, T.A., Eagle, R.J. and ßrunk, J.L.Radionuclides in the Marine Environment Near the Farallon Islands.UCRL-52381, Lawrence Livermore National Laboratory, Livermore,California, 17pp. (1978).
(3) Noshkin, V.E. Transuranium Radionuclides in Components of the BenthicEnvironment of Enewetak Atoll. Ir\_ Transuranic Elements in theEnvironment (edited by W.C. Hanson) DQE/TIC-22800, U.S. Department ofEnergy, Washington, District of Columbia, 578 (1980).
(4) Schell, W.R., Lowman, F.G., and Marshall, E.P. Geochemistry ofTransuranic Elements at Bikini Atoll. In Transuranic Elements in theEnvironment (edited by W.C. Hanson) DOE7TIC-22800, U.S. Department ofEnergy, Washington, District of Columbia, 541 (1980).
(5) Noshkin, V.E. and Wong, K.M. Plutonium Mobilization from SedimentarySources to Solution in the Marine Environment. In Marine Radioecoloqy(Proc. 3rd NEA Sem., Tokyo, 1979), OECD, Paris, T£5 (1980).
126
(6) Noshkin, V.E., Brunk, J.L., Jokela, T.A. and Wong, K.M. 238PuConcentrations in the Marine Environment at San Clémente Island. HealthPhys. 40_, 643 (1981).
(7) Nelson, D.M. and Mett.a, D.N. The Flux of Plutonium from Sediments toWater in Lake Michigan. ]_n_ Radiological and Environmental ResearchDivision Annual Report, ANL-8R-65, Part 3. Argonne National Laboratory,Argonne, Illinois, 31 (1983).
(8) Beasley, T.M. Lead-210 Production by Nuclear Devices: 1946-1958.Nature, 224, 573 (1969).
(9) Bowen, V.T., Noshkin, V.E., Livingston, H.D. and Volchok, H.L. FalloutRadionuclides in the Pacific Ocean: Vertical and HorizontalDistributions, Largely from GEOSECS Stations. Earth Plant Sei. Ltr. 49,411 (1980). —
(10) Jennings, C.D. and Mount, M.E. The Northern Marshall IslandsRadiological Survey: A Quality Control Program for RadiochemicalAnalysis: UCRL-52353 Pt. 5. Lawrence Livermore National Laboratory,Livermore, California, 73 pp (1983).
(11) ßojanowski, R. Intercomparison of Artificial Radionuclide Measurementson Marine Sediment SD-N-1/1. Report No. 21, International Laboratory ofMarine Radioactivity, Monaco, 16 pp. (1984).
Acknowledgment
The work in the Pacific was performed under the auspices of the U.S.Department of Energy by the Lawrence Livermore National Laboratory undercontract W-7405-ENG-48 and the work in the Northeast Atlantic wassupported by the Office of Radiation Programs, United StatesEnvironmental Protection Agency (DOE-EPA Interagency AgreementA089F00070).
DISCLAIMER
This document was prepared as an account of work sponsored by an agency of the United States Government.Neither the United States Government nor the University of California nor any of their employees, makesany warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, com-pleteness, or usefulness of any information, apparatus, product, or process disclosed, or represents that itsuse would not infringe privately owned rights. Reference herein to any specific commercial products, process,or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply itsendorsement, recommendation, or favoring by the United States Government or the University of California.The views and opinions of authors expressed herein do not necessarily state or reflect those of the UnitedStates Government thereof, and shall not be used for advertising or product endorsement purposes.
127
INTERCOMPARISON STUDIES OF TRANSURANICS INNORTH ATLANTIC DEEP SEA SEDIMENTS FROM THENEA DUMPSITE
A. AARKROG, H. DAHLGAARDRis$ National Laboratory,Roskilde, Denmark
Abstract
Detailed intercomparison of two cores from the dumpsite showed that horizontal239 240activity distribution was not homogeneous for ' Pu. However the vertical
inventory remains the same. There was no systematic bias between the Pu analysisby the two laboratories. The Pu/ ' Pu mean ratio was 0.08+0.02 and for241 239 240Am/ ' Pu was 0.26-1-0.12, both compatible with global fallout.
1. THE SAMPLES
Two cores (Nos 4 and 11) taken on the Tyro 82 cruise to the NBAdumpsite (45°50'N to 46°10'N and between 16°W and 17°30'W)inAugust-September 1982 [l] were obtained from Dr. V. Noshkin,Lawrence Livermore National Laboratory. The cores had beensectioned into 1 cm depth increments and the surface area ofeach section is 28.2 cm2. The two cores were subcores from twodifferent 0.25 m2 Mark III boxcores, from each of which Dr.Noshkin had analysed another duplicate subcore.
2. RESULTS
Ten (or twenty for the weakest samples) grammes aliquots ofdried sediments were analysed for Pu and Am by the methods ofTalvitie [2] and Holm [ 3] .
Core 4 (Table 1) shows an exponentially decreasing 239/240puconcentration with a half depth of 2 cm. Core 11 (Table 2) showsa subsurface maximum at 2-4 cm depth. The 239,240pu inventoriesof the two cores down to 11 cm were 5.83 Bq m~2 (0.16 mCi km"2)and 7.01 Bq m~2 (0.19 mCi km~2), respectively. Noshkin [ijfound 0.16 and 0.22 mCi 239,240pu Km"2, respectively in hiscorresponding subcores. The mean ratio of the concentrations
129
Table 1. Plutonium and americium in core T 8204 B collected at
No.
PMSG
-
-
-
-
-
-
-
-
-
-
the NBA dumpsite in 1982
Segmentin cm
08889909192939495969798
The relativein brackets.
0-11-22-33-44-55-66-77-88-99-10
10-11
SD (in % )
Table 2. Plutonium and
No
the
•
PMSG 198---------_
199200201202203204205206207208
239,240Pu 239Pu 241Am
Bq kg"1 Bq m~2 Bq kg~l Bq kg"1
0.36 ( 7)0.164 (10)0.100 (10)0.067 (13)0.049 (16)lost0.0148(18)0.040 (17)0.0182(21)0.0092(27)0.0067(33)
2.431.170.710.500.34-
0.110.300.140.070.06
due to counting
0.023 (23) 0.093(100.0156(30) 0.018(320.0084(27)0.0047(33)
-----_
-
statistics are shown
americium in core T 8211 B collected atNEA dumpsite in 1982
Segmentin cm
0-11-22-33-44-55-66-77-88-99-10
10-11
239,240Pu
Bq kq~l Bq
0.23 ( 9)
0.093 (11)
0.172 ( 6)0.207 ( 7)
0.054 (17)0.074 (10)0.027 (16)
0.030 (17)0.035 (17)0.045 (14)0.0135(27)
m-2
1.410.661.221.630.400.550.210.220.280.330.10
239Pu 241Am
Bq kg~l Bq kq~l
0.0172(32) 0.098(12)-
0.0187(30) 0.054(14)0.038(18)
-0.0040(33)
-----
The relative SD (in %) due to counting statistics are shownin brackets.
130
in the various layers found by Ris0 and Livermore was 1.08 ± 0.70(N=18; ± 1SD). This shows that the horizontal activity distri-bution of the boxcores are inhomogeneous. However, the inven-tories of the 0-11 cm layers within a core are the same. Theresults, furthermore, show that there is no systematic biasbetween the Pu-analysis performed by Livermore and Ris0.
The 238Pu/239,240Pu mean ratio was 0.08 ± 0.02 (N=7; ± 1SD) andthe 241Am/239,240Pu mean ratio was 0.26 ± 0.12 (N=5; ± ISO) .These ratios are compatible with those expected from globalfallout. We can thus support the conclusion of Noshkin [l]who stated that no evidence of plutonium contamination in thesesamples from any other source than global fallout had beenfound.
3. INTERCALIBRATION
Throughout the years Ris0 National Laboratory has participatedin the intercalibration exercises organised by the IAEA MonacoLaboratory.
In the intercomparison of marine sediment SD-N-1/1 [4] we hadlaboratory code No. 3. The mean of the accented 239,240puresults was 0.57, we found 0.53 ( mBq g"1); our 238Pu an(3 241 m
results were also within the accepted range.
REFERENCES
[l] Noshkin, V.E., Wong, K.M., and Eagle, R.J. "Radionuclidesin sediments from the North-East Atlantic disposal site".UCID 199 24. Lawrence Livermore Laboratory (1983).
[2] Talvitie, N.A. "Radiochemical determination of plutonium inenvironmental and biological samples by ion exchange. Anal.Chem. 43, 1827 (1971).
131
[3] Holm, E., Ballestra, S. and Fukai, R. A method for ionexchange separation of low levels of americium in environ-mental samples, Talanta, 26, 791-794 (1979).
[ 4] IAEA, .Monaco Laboratory. "Intercomparison of artificialradionuclide measurements on marine sediment SD-N-1/1.Report No. 21 (1984) .
132
TECHNETIUM DISTRIBUTION AND ACCUMULATION INMARINE SEDIMENTS AND BIOTA*
E.H. SCHULTECEC c/o ENEA,La Spezia, Italy
Abstract
VIITechnetium normally exists in marine environments as pertechnetate Tc . Howeverwhen sediments are reduced and organic rich, it becomes fixed rapidly to them.Bacterial activity does not seem to be responsible. Concentration factors for Tcin biota are generally 10-20 but two exceptions are macrophytic algae (1100) andpolychaetes (300-800). Biological half lives are weeks or months. Retention wasgenerally about 20% of that in the food source, and 25% of that was retained inthe digestive gland or liver.
In the last years the principle objectives of radioecological stu-dies at this laboratory have been to gather information on and furtherunderstanding of the environmental behaviour of long-lived radionucli-des with special respect to technetium. The only recent introductionof technetium, an artificial radioélément which has no stable isotopes,into the environment has been of considerable concern regarding thecycling of its long-lived radioisotope Tc-99 in the geo- and biosphere(1). As other long-lived radionuclides,such as transuranics, technetiumis found in the three major compartments of the marine environment,!.e.in solution, in biota, and in sediments. During the period covered bythis report considerable effort has been expended on studying the beha-viour of technetium in these compartments under laboratory conditions.
In aqueous solutions technetium may occur in various physico-che-mical forms according to thermodynamic considerations, but in the ran-ges of pH and Eh values normally occurring in the marine environmentpertechnetate (VII) is clearly the most stable chemical form (2),whichhas been confirmed also experimentally. It has been shown that about90% of hydrazine-reduced technetium (IV) is rapidly reoxidized in welloxigenated sea water to pertechnetate within less than one hour, whilethe remaining 10% being oxidized slowly. Hence, in all further labora-tory studies only pertechnetate was used in order to ensure constantphysico-chemical behaviour of the radioisotope during the experiments.
A considerable effort has been expended in order to identify themechanisms by which technetium becomes incorporated into sediments(3).
* Contribution N° 2 196 of the CEC Radioprotection Programme.
133
In investigations using reducing sediments rich in organic carbon ra-pid disappearance of pertechnetate from the water column has been ob-served. The fixation rate of technetium in the sediment was found tobe dependend on several factors such as physico-chemical characteri-stics of the sediment bed, mass ratio between sediment and water,areaof the sediment/water interface etc. Investigations on the role of bac-terial activity in the fixation process of technetium within sedimentsrevealed only an indirect action of bacteria in that they contributein determining chemical and physical characteristics of the sedimentcolumn. Therefore, the principle factors responsible for the immobili-zation of technetium in sediments are most likely redox conditionswhile diffusion to deeper, anoxic layers in the sediment is most pro-bably the limiting factor in the fixation process of technetium.
Studies on the biological availability of technetium to marine or-ganisms were aimed at assessing and eventually better controlling theimpact of technetium releases on man and the environment. In laboratoryexperiments concentration factors, biological half-lives as well as as-similation edacities of a variety of marine organisms, including algae,invertebrates and fish have been determined (4). Generally concentra-tion factors were found to be quite low (10 - 20) with some exceptionslike macrophytic brown algae (Fucus; CF 1100) and polychaetes (OF 300-800). Rates of loss after accumulation of technetium from water or con-taminated food were high resulting in relative short biological half-lives of some weeks or months (5,6). Retention of technetium in marineorganisms was low and amounted about 20% of the radioactivity presentin the food stuff, of which about 25% was retained in the digestivegland or liver.
Despite the considerable amount of information recently gatheredon the environmental behaviour of technetium there are still require-ments for further studies in order to sufficiently assess the biogeo-chemical cycling and potential impact of technetium on man and the en-vironment.
ReferencesEN,K.M., GARLAND,T.R., Technetium sources and
behaviour in the environment. J.Environ. Qual.,8, 156 (1979).2) SCOPPA,P., SECONDINI,A., SCHULTE,E.H., Indagini sulla stabilité
dell'anione pertecnetato nell'ambiente marino. Atti del XXII Con-gresso dell'AIRP (Brescia 23-26/6/1981), 1, 503 (1983).
3) SCOPPA,P., SCHULTE,E.H., SECONDINI,A., Application of technetium-95m in experimental radioecology: chemical form and behaviour inthe marine environment. Ln Technetium in Chemistry and Nuclear Me-dicine (edited by E.Deutsch, M.Nicolini, H.N.Wagner,Jr.) CortinaInternational, Verona, 219 (1983).
4) SCHULTE,E.K., SECONDINI,A., SCOPPA.P., Trasferimento del tecnezioattraverso le catene alimentari marine. Atti del XXII Congresso-ell'AIRP (Brescia 23-26/5/1981), 1, 563 (1983).
134
5) FOWLER,S.W., BENAYOUN,G., PARSI.P., ESSA ,1-l.VJ. A . , SCHULTE,E .H. ,Experimental studies on the bioavailability of technetium in se-lected marine organisms. _Tn Impacts of Radionuclide Releases intothe Marine Environment, IAEA-SM-248/113, 319 (1982).
6) SCHULTE,E.H., SCOPPA,P., SECONDINI,A., Accumule e rilascio del tec-nezio da parte di alcuni organism! marini: Palaemon elegans. Boll.Soc. Ital. Biol. Sperim., LVII1 (21), 1361 (1982).
135
MEASUREMENT OF LONG-LIVED RADIONUCLIDES INTHE ATLANTIC RELATED TO RADIOACTIVE WASTESDEEP-SEA DISPOSAL*
A.O. BETTENCOURT, M.M. BORDALO COSTA,P.P. CARVALHO, G. FERRADOR, G. ALBERTOLNETI/DPSR,Sacavém, Portugal
Abstract
Deepsea fish, possibly potential links in a food chain to main from the N.E.Atlant ic, „ o 210 238,239,240 137dump-site were analysed for Cs , Pô, Pu. Cs is lower in such
fish than most other fish tissues. This was truealso for Po . Sediments from thesite gave similar results to those reported by other authors. Unfil tered water samples
239 240 -3were analysed for ' Pu and results were (in mBq m ) 12 for the Tagus es tuary ,
26 for 1500 m sample off Madeira , and 30 for one 3800 m sample NW of Portugal.
1. INTRODUCTION
The black scabbard (Aphanopus carbo) fishery is the only deepsea one known in the north-eastern Atlantic, representing a poten-tial pathway back to man for long-lived dumped radionuclides. So,a study of this fishery was implemented, including landing statis-tics, distribution, trophic relationships and radionuclide concen-trations .
Along this study, fishes from several species also caught atdifferent depths near Madeira island and south of Lisbon, wereidentified and analysed. Two shallow water fish species wereselected for comparing their radionuclide concentrations, thebarracuda (Sphyraena sphyraena) and the scabbard (Lepidopus cauda-tus) .
Fish, sea water and sediment samples were analysed for theircontents in transuranics. Cs and Po were also analysed infish muscle.
Research Contract 3091/RB.
137
2. METHODS
Fish muscle was prepared for analysis by drying and incinera-ting; isotopic tracers were added. The ashes were analysed bydirect gamma spectrometry for determining Cs. For plutoniumand americium radiochemical separation, samples were spiked with236,, 243, , 244„ m . ,..Pu, Am and Cm. Transuranic analysis involve ion exchangechromatography (AG 1x8), solvent extraction with HDEHP and electro-plating. The transuranic elements were measured by alpha spectro-metry, using silicon barrier surface detectors.
Some of the fish were dissected and the different organs wereanalysed for their content in Po by spontaneous plating fromHC1-HC1O solutions on silver disks followed by alpha spectrometry.
3. RESULTS
3.1. Black scabbard fisheryFish landing statistics obtained at Madeira, for the last ten
years, confirm the economic and social importance of black scabbardfishery for the region.
Some fishing cruises to south of Madeira (with sampling at dif-ferent depths) have been effected. They enable us to conclude thatscabbard lives mainly between 80O and 14OO m; besides, it has ne-ver been caught near the bottom.
Having never got young specimens, we can admit the possibilityof vertical migrations for this species.
Other ones were fished, identified and analysed as well.
3.2. TransuranicsO T ÖPu results were always below detection limit. So, Table 1
239+24Oonly presents Pu concentrations in fish muscle for some ofthe analysed samples. In black scabbard muscle they are about 0.1mBq/kg fresh. In other species, either from shallow waters or fromthe deep slope, higher values, around 1 mBq/kg, were found. Blackscabbard values were confirmed through an analysis performed byV. Noshkin at LLNL. Furthermore, the quality of our data in plutonium determinations is confirmed by the results obtained in theintercalibration exercises organized by ILMR, Monaco.
They can also be compared with those reported by Noshkin (1) ,Triulzi et al (2) and Bowen (3).
138
TABLE 1: 239+24°pu in Fish muscle3
REFERENCE12
1979 M1980 M1982 M1983 M1980 P1980 P198O P1982 M1981 M1983 P
SCIENTIFIC NAME
Aphanopus carboAphanopus carboAphanopus carboAphanopus carbocMalacocephalus laevisBeryx decadactylusDeania calceusHelicolenus dactylopterusSphyraena sphyraenaLepidopus caudatus
DEPTH (m)
12001200120012006OO40O
100O600
shal2OO
mBq/kg fresh
0,12*0.060.13*0.08
<0.30.1(35%)1.0*0.50.8 0.5
<11.2*0.21.0*0.31.1*0.4
fCi/g dry
0.017*0.0090.019*0.011
<O.O40.02(35%)0.13±O.O70.10±0.06<0,2
0.17*0.030.12*0.030.14*O.O5
Lower detection limit at 95% confidence level; error 1 sigma propagated°M: Madeira; P: west coast of Portugal3Analysed by V. Noshkin, LLNL
In some predatory fish, like tuna and squalidae, higher concentrations (3-4 mBq/kg fresh) were obtained, but they need furtherconfirmation.
Unfiltered water samples were also analysed for their plutonium239+240 3content. Pu concentrations found were 12 mBq/m for an estu_
arine water (Tagus river), 26 for a 1500 m depth water collectedoff Madeira island and 3O mBq/m for one 380O m depth sample fromthe north -west coast of Portugal. The statistic errors for thesedeterminations being about 1O%. These results can be compared withthose reported by Miettinen et al (4), Kautsky & Eicke (5) , Holm& Persson (6), Livingstone et al (7) and Ballestra et al (8), amongmany others.
Such values lead to a concentration factor of about 5 for theblack scabbard fish. For other species it would range from 4O to8O. However few results are yet available from the areas wherethese were caught.
Some sediment samples, from the deep sea, were also analysed1 3 V o o for plutonium, as well as for Cs and Ra by gamma spetrome-
try. The results correspond to a homogenized 10 cm surface layer.Results for plutonium (see Table 2) are within the range of valuesreported by Noshkin, for the northeast Atlantic (9) , and can alsobe compared to those reported by Triulzi et al (2) and Ballestraet al (8) .
139
TABLE 2: 238Pu, 239+24°Pu, 225Ra and 137Cs in deep-sea sedimentsa
YEAR
198019811982
DEPTH COORDINATES 238Pu 239+240pu(yBq/g) (mEq/g)C
1790 39°32' N 09°47' W < 3b 0.18 0.024200 39°35' N 10°20' W < 40 0.04-0.021465 32°35' N 17°05' W 9 3° 0.27 0.02
22Sa 137Cs(Bq/g)C (mEq/g)b
0.13 0.020.11-0.02o.oeio.04
<4<4<2
On dry weight basisLower detection limit at 95% confidence level'Errors given are 1 a
TABLE 3: 137Cs in fish muscle
REF
197919791979198019821983198419841984
1980198019801982198219831983
198219821983198319831984
a
MMMMMMMMM
APPMMPM
MMPMMP
SCIENTIFIC NAME
Aphanopus carboAphanopus carboAphanopus carboAphanopus carboAphanopus carboAphanopus carboAphanopus carboAphanopus carboAphanopus carbo
Epigonus telescopusMalacocephalus laevisDeania calceusHelicolenus dactylopterusFpigonus telescopusCentrophorus granulosusHelicolenus dactylopterus
Sphyraena sphyraenaSphyraena sphyraenaLepidopus caudatusThunnus thynnusSphyraena sphyraenaLepidopus caudatus
DEPTH(m)1200""""tiii"ii
60O1OOO1OOO60060O40060O
shalshal2OO
shalshal200
Bq/kg fresh
OOOOOO00
O
OOOO00
.25 0.
.38 0.
.40±0.
.47-0.
.11-0.
.21±0.
.51±0.i
.19-0.i:0.22
1.7±0.<0.5C1.1-0.1.7±0.1.1-0.<0.15.44-0.
.45-0.
.46 0.
.86-0.
.79-O.
.26-0.
.70 0.
0407070703Ol1712c
4
633c38
200404O51648
M: Madeira; A:Azores; P:west coast of Portugal"'Analysed by V.Noshkin, LLNL"Lower detection limit at 90% confidence level; errors givenare 1 o
140
3.3. Cesium-137
The results obtained for Cs concentration in fish muscleare presented in Table 3. The analysed fish are grouped as fol-lows: black scabbard; mid-depth species and shallow water fishes.
137It can be seen that the Cs concentrations are lower in theblack scabbard than in other fish tissues, except the Sphyraenasphyraena. They are of the same order of magnitude as the onesreported by Mitchell & Pentreath (10) for the Coryphaenoides ar-matus in the north east Atlantic deep waters.
3.4. Polonium-210
The highest doses for marine organisms and for man through food21Oconsumption being due to Po, their evaluation becomes important
for us to know background doses and compare them with those re-sulting from artificial radionuclides. It is also helpful to be
21Oaware of Po behaviour in the marine environment for understanding analog artificial radionuclides cycling.
210Some preliminary results on total Po concentration in dif-ferent fish tissues are presented in Table 4. These results are
21O 21Onot yet corjected for Po ingrowth from Pb present in thesample.
TABLE 4: 210Po (total) concentrations in Pish tissues (mBq/g dry)(Preliminary results not corrected for ingrowth from 210Pb)
SardinapilchardusTrachurustrachurusMerlucciusmerlucciusScomberscombrusRajaundulata
Aphanopuscar bo(Sesimbra)Aphanopuscarbo(Madeira)
MUSCLE
26(1)
19-4(2)
45-16(2)
6.1(1)
3.4(1)
0.5-0.1(3)
1.0±0.9(2)
GONADS
_
118(1)
295(1)
94(1)
86(1)
12(1)
48-57(3)
LIVER
1896(1)
1229 (1)
-
1074(1)
99(1)
16(1)
22-13(4)
SKELETON
43(1)
27(1)
3KD
12(1)
9.5(1)(cartilage)
4.2(1)
6.1(1)
Mean - 1 standard deviation (nr of analysed specimens)
141
It can be seen that Po concentrations in black scabbard fishtissues are significantly lower than those found in shallow waterfish as well as in other deep slope fish.
4. CONCLUSIONS
Being the black scabbard a species which lives at depths ofabout 8OO-14OO m, It can be considered a potential pathway back toman for dumped radionuclides. Furthermore, this fisheries is economically important for Madeira population.
Although being classified as a benthopelagic fish, no speci -mens were vere caught near the bottom: so, some doubts are arisingabout such classification.
Radionuclides concentrations in black scabbard tissues arelower than those found for other species from the same region,either from shallow waters or from deep slope. This seems toconfirm that this species is not a benthic one.
ACKNOWLEDGEMENTS
Grateful acknowledgements are due to the Hydrographie Institute(Portugal) and the Regional Fisheries Laboratory (Madeira) fortheir cooperation in sample collection.
BEFERENCE.S1) Noshkin V.E., Fallout concentrations in sediments and some biota
from regions of the northeast Atlantic, In_ Interim océanographiedescription of the northeast Atlantic site for the disposal oflow-level radioactive waste, 119, NEA/OECD, Paris (1983).
2) Triulzi C., Tassi Pelati L., Albertazzi S., Delle Site A. andMarchionni V. , Presence and distribution of plutonium isotopesin two typical marine systems I_n IAEA TECDOC 265, 83, IAEA, Vienna(1982).
3) Bowen V.T. Transuranic behaviour in marine environment, In IAEATECDOC 265, 129, Vienna (1982)
4) Miettinen J.K., Leskinen S., and Jakkola T,, Studies on distri-bution of actinides between sea water and particulate fractions inthe Baltic Sea and its gulfs, In IAEA TECDOC 265, 33, IAEA, Vienna(1982).
5) Kautsky H. and Eicke H.F., Distribution of transuranic isotopes inthe water of the North Sea and adjacent regions, In IAEA TECDOC265, 47, IAEA Vienna (1982).
6) Holm E. and Persson B., Transuranic cycling behaviour in marineenvironment, In IAEA TECDOC 265, 1O5, IAEA, Vienna (1982).
142
7) Livingstone H., Kuperman S., Moore R.M. and Bowen V.T., Verticalprofile of artificial radionuclide concentrations in the centralArtic Ocean, In IAEA TECDOC 265, 141 IAEA Vienna (1982).
8) Ballestra S., Thein M. and Fukai R., Distribution of transuranicnuclides in Mediterranean Ecosystems, I_n IAEA TECDOC 265, 163,IAEA, Vienna (1982).
9) Noshkin V.E., Plutonium in north-east Atlantic sediments, InInterim Océanographie description of the north-east Atlantic sitefor the disposal of low level radioactive waste, Vol 2, 95, NEA//OECD, Paris (1985).
1O) Mitchell N.T., Pentreath R.J., Monitoring in the north-eastAtlantic Ocean for the dumping of packaged radioactive waste,Third Int. Symp. of the Society for Radiological Protection,Inverness, Scotland, 6 pp (1982).
143
STUDIES ON THE BIOACCUMULATION OFRADIONUCLIDES OF LONG HALF-LIFE INMUSSELS IN THE NORTH EAST OF SPAIN
M. MONTESINOS DEL VALLEArea de proteccion radiologica y medio ambiente,Junta de Energia Nuclear,Madrid, Spain
Abstract
Water, sediments and mussels were analysed from areas in the NW of Spain, for ' 'Pu, Cs, Sr. Sea depths were 24-65 m. Ranges of activity for seawater (pCi 1 )were 0.138-0.335 for Sr, 0.150-0.480 for Cs, 0.140-0.190 for Co. Levels ofactivities noted in sediments compared closely with those in the Mediterranean byother workers. In pCi kg Pu figures were 5-96. Similarly for Mytilus edulis2T5 ?40 -1
' P u w a s 0.09-1.5 p C i k g w e t weight.
1. IntroductionSpain is a country with considerable coastline and there is so much
possibility of alteration of the marine ecosystem due to nuclear type ofincidents, that it is necessary to maintain a watch as far as possible on thelevels of activity in the ecosphere.
We have selected the zone to the northeast of Spain for study both becauseit is representative for mussel culture, and because of its situation withrespect to the Northeast Atlantic Trench.
2. Objectives in the first phase of the project2.1 Collection of mussel samples (which are consumed by humans) in theGallegas rivers as well as water and sediment samples/2.2 Radioanalysis of the samples for 238pU) 239pUj 240pu and 13?cs whichcan arise from radioactive fallout, from the production of nuclear energy andthe leaking of dumped radioactivity from the abyssal zone of the Atlantic.
3. Description of the investigation
3.1 Sampling areasFor the present study, the principal Gallegas rivers were selected;
Vigo, Pontevedra, Arosa, Muros, La Coruna, Vivero.3.2 Samples
The samples collected were water, sediment and Mytillus edulis
3.3 Methodology3.3.1 Sampling and pretreatment3.3.1.1 Water, Sediments
Sampling was done by the Boat B/0 Lura. The coordinates (determined byradar techniques) are given in Table 1. The samples of water were obtainedwith Nansen-type bottles, provided with inversion thermometers, were filteredthrough a 20 micron filter and acidified to pH 1.5 with concentrated nitricacid. The salinity was determined in the laboratory with a salinometer
145
calibrated against sea water of known conductivity. Oxygen concentrations weredetermined by a modified Winkler method. Sediment samples were taken eitherwith a Van-Veen drag or hydraulic box-corer. The upper part was dried at 100°for 24 hours.3.3.1.2 Mussels
At Vigo, Pontecedra, Arosa, La Coruna and Muros, sampling was done atvarious points, and three different depths. The Vivero mussels were collectedby a sailor. They were wrapped in polyurethane foam and rapidly frozen at -20°C.
3.3.2 Method and technique of analysisThe determination of radioactivity was done by analytical procedures
suited to detection of radionuclides at environmental levels, which includedevaporation, drying, ashing etc.3.3.2.1 Methods applied to the Mytillus edulis and sediment samples
-Gamma spectrometry. Gamma radioactivity was measured with coaxial Ge(Li)detectors with 25% eiffiency for 57co energies and resolution of 2.3 keV at1173 keV. Spectra were accumulated with a Canberra-80 4000 channelmultichannel analyser, and the SPECTRUM computer program was used foranalysis.
-Plutonium. The samples were ashed at 600° to eliminate organic matter.The transuranics were dissolved in nitric acid and hydrogen peroxide, thenprecipitated with calcium oxalate. The precipitate was dissolved with 8Mnitric acid and hydrogen peroxide. The solution was passed through a column ofAG 1x8 resin to retain Pu. Then the Pu was eluted with 1.2M HC1 containingH202.
The solution was evaporated and the eluted Pu electrodeposited in a NIfyOHmedium at pH 4 onto discs of stainless steel of 25 mm diameter.
The counting was done by an alpha spectrometer with a solid-state detectorof 300 mm2 area and effeciency of 20%.
-Cesium. Cesium was separated as phosphomolybdate and then purified as ahexachloroplatinate. It was determined in a gas-flow counter with about 45%efficiency by its beta emission.
-Intercomparison. Intercalibration exercises were undertaken inconjunction with the International Laboratory of Marine Radioactivity atMonaco.
4.Results
Standard statistical treatments of the counting data were employed.The values obtained in the samples analysed are reflected in tables 2 to 6.
5. ConclusionsOn viewing the results obtained in this first phase of the project, one is
able to conclude that:5.1 The methodology applied in collection, pretreatment and analysis of
samples appears to be adequate.5.2 The radiochemical methods applied for the obtaining of activities of
cesium gave good yields.5.3 The values obtained for water, sediments and mussels are similar to
those reported by other authors on the same type of sample.
146
Table 1. Sampling coordinates
LocationVigoPontevedraArosaMurosCorunaViveroVigoPontevedraArosaMurosCorunaVivero
Date11.07.8312.07.8314.07.8305.08.8302.08.8327.09.8314.11.8310.11.8310.11.8309.11.8307.11.8303.1 .83
Coordinates42°42042°42043043°42042042042°43°43°
13'23'33'45'22'42'13'23'33'45'22'42'
480330181818480330181818
"N"N"N"N"N"N"N"N"N"N"N"N
8°8°80908°7°808080908070
47'45'54'01'22'35'47'45'54'01'22'35'
480018000342480018000342
"W"W"W"W"W"W"W"W"W"W"W"W
Sea Depth35m25m46m35m29m27m43m32m65m35m24m24m
Table 2. levels of activity in sea water (pCi/1)
VIGO
POOTEVEDRA
AROSA
MUROS
LA. CORUflA
VIVERO
Sr-90
———
0.138 +_ 0.042
0.217 +_ 0.055
—— -
-——
0.335 +_ 0.063
Cs-137
0.170 +_ 0.030
0.150 +_ 0.020
0.170 + 0.020
0.170 + 0.020
———
0.480 + 0.050
Co-60
0.140
0.190
———
0.150
0.180
Table 3. Levela of activity In aedlaenta (pCi/kg dry velght)
VIGO
PGMTEVEDRA
AROSA
MUROS
LA CORUflA
VIVERO
Cs-137
38O + 10
440+10
240 + 10
28O +_ 10
1 6 + 2
15 +_ 2
Pu-239, 240
16 +_ 11
96 + 15
51 + 10
40+17
2 2 + 4
5 +_ 3
Cs/Pu
24
4.6
4.7
7
0.7
3
147
Table 4. Levels of activity In edible part of Hytlllus edulla (pCl/kg «et weight
VIGO
AROSA
LA CORUNA
VIVERO
Cs-137
6.0 + 2.2
6.5 + 2.4
6.7 -t_ 2.2
6.5
Pu-239, 24O
0.09 + 0.05
0.1 + 0.1
0.57 + O.O8~
1.50 + 0.03
Pu- 238
< 0.1
< 0.4
< 0.1
< 0 . 5
Table 5. Comparison _b_etycen the levels of activity of Cs and Pu foundI In aedlnents CpCi/kg dry weight
Location
Ligurian Sea
Ligurian Sea
Ligurian Sea
COSTAS GALLEGAS:Vigo
Pontevedra
Arosa
Muros
La Conjfia
Vlvero
Depth (m)
12
45
93
33
24
44
33
22
25
Pu
32
17
27
16
96
51
40
22
5
Cs/Pu
12.5
16.7
14.3
24
5
5
7
0.5
3
Worker
Jennings (1984)
•'
JEN (19B4)
'•
"
Table 6. Coaparlaon of levels of act ivi ty In Hytillua edulls In Mediterraneanand Atlantic (pCl/kg wet weight)
Location
MEDITERRANEANMonacoSaint HandrierMartigues PonteauPort de BoucPort Saint-Louis" " "
Gran du RoiSéte (Port)
11
" (étans)BanyulsVenez! a
ATLANTICVigoArosaLa CorvfiaVlvero
1
Sampling date
November 1976June 1976
n II
1« II
It M
May 1977June 1976o nMay 1977
u u
June 1976May 1977
June , Dec 1983I I I I I t
" " »
II M II
Pu-239, 240
0.39 + 0.040.15 + 0.020.20 * 0.030.06 + 0.010.09 + 0.010.23 1- 0.-G20.11 t 0.020.17 «• 0.020.11 t 0.020.12 + 0.040.61 + 0.070.11 *• 0.02
0.09 + 0.050.1 + 0.10.57 + 0.081.50 + 0.03
Worker
Ballestra"M
11
I I
"II
"11
II
"
"
JENH
It
II
148
LONG-LIVED RADIONUCLIDES IMPORTANT INMARINE WASTE DISPOSAL
A. AARKROGRis^ National Laboratory,Roskilde, Denmark
Abstract
The calculation starts with high level waste and tabulates results for time periods
of 0, 100,10,000 and a million years. The assumed relative activity figures are divided
by the Allowable Limit of Intake to give potential risk figures. The f igures are fur-
ther adjusted by a factor related to K which allows for the fact that most activity
for some radionuclides will be adsorbed onto sediments. Similarly a fur ther adjustment
is made to the figures to allow for the different concentration factors for radionu-
clides likely for the biota which are the probable route to man. In the period137 90100-10000 years the following radionuclides then predominate; Cs, Sr,
241 243 240 239 237 99m 93„ 244^ _ ^ , , n ,Am, Am, Pu, Pu, Np, Te, Zr, Cm. Future research projects should
therefore concentrate on these isotopes. Especially little information seems available
for Zr and Np.
1. _METHOD5 FOR IDENTIFICATION OF IMPORTANT NUCLIDES
1.1. Inventories
The disposal of high-level waste to the seabed presents the mostimportant potential source of radioactive marine pollution. Ourstudy shall be l imited to this source alone. Baxter [l] hasmade a list of those radionuclides which contribute over 97% ofthe total activity present at various timepoints after disposal.Table 1 shows the inventories in TBq (10 1 2 Bq) , assuming a meanlapse of 10 years prior to disposal.
The wastes aris ing in Table 1 are those to be expected from aglobal nuclear capacity of 2500 GW by the early to mid-21stcentury. However, the absolute amounts of waste are not im-portant in the present context. It is the relative levelsof the various radionuclides, which are of interest .
1.2. Potential impact
In order to estimate the potential radiological impact of thewaste we may divide the f igures in Table 1 with the ALIvalues [2] for the various radionuclides as given in Table 2.
149
Table 1. Hiqh activity waste arisinas and post-disposalactivities (TBq) (adonted froir Baxter .l].
TiTrteooint (vr)
30y29y
2y2.6y8.6y
18y90y
2.7y
0
137cs 1.3xl09
9°Sr S134Cs 1!47Pm 1154Eu 6244Qn 2151 ST. I
.9xlOB
.IxlO8
.OxlO8
.7xl07
.5xl07
.6xl07
.3xl06
30y29y90y
432y8.6y
8 By18y
7xl03y
102
137CS 1.9°Sr 7.
ISlsn. 7.24lftm 2.154Eu B.236pu 6.2440n 4.
243to 2'
104
3x108
4xl07
4xl06
2xlOE9xl05
7xl05
8x10=7xl05
2xl05y7xlo3y
7xl03v106y
2xl04y105y
7xl04y2xl06y
99Tc
243Am240pu
93Zr
PuSn
79Se
237TQQ
2x105
l.ixlO5
4.Bxl04
2.8xl04
l.SxlO4
7.8xl03
5.2xl03
5.9x103
106V
2x!05y
2xl06y3xl06y7xl06y
1.6xl07y2xl05y4xl09y
106
932r
99TC
237Np
135Cs
107pd129!2340
236-j
1.6xl04
7.8xl03
4.1xl03
S.lxlO3
l.SxlO3
5.2xl02
7.4x1014xlOl
Table. 2. Number of ALI values (divided by 10l2) in tne highactivity waste arisinqs in Table 1.
TimeDoint (yr)
0
90sr 9x102137cs 3x102244O 3x102134Cs 4xlOl154£u 3x100!47PTi 5x10-1125sb 1x10-1ISlSni 3x10-2
102
9°Sr 7x!0l241 Am 4xlOl!37cs 3xlQl244Cm 5x10°243Ain 5x10°238Pu 2x10°154Eu 4x10-2ISlsm 1x10-2
104
243Am 2x100237ND 2x100240pu 2x10-1239pu 9xlO-2
"TC 2x10-3l26Sn 8xlO"493zr 6xlO~479Se 3xlO~4
106
237Np ixioo129! 3x10-3932r 4xlO~4
234u 2xlO~4135Cs lxlO~4
99Tc 8x10-5238u 5x10-5l°7Pd 2x10-6
1.3. Radioecoloqical narine index
If the radionuclides escape from the waste containers to thethe sediments, the amount of activity entering the water isinfluenced by the magnitude of the K^ for pelagic sediments. Thetransfer from water to human marine food chains is determinedby the concentration factors (CF) from water to fish and
150
shellfish. The, International Atomic Energy Agency has recentlymade a review of sediment K,3 ' s and cocentration factors [3]. Wewill define a "Radioloqical Marine Index" for the radionuclidesin the waste as the ratio CF/Kd. As CF we shall use the con-sumption weighted CF for fish, crustaceans and molluses. Thetotal global catch of fish in 1980 was 56 M tons and of crus-taceans and molluscs 3.4 and 5 M tons, respectively [4]. InTable 3 the CF/K^ ratios are calculated for the radionuclidesmentioned in Table 1.
Table 3. Radioecological Marine Index (CF/K^) for elements inthe high-activity waste arisinqs in Table 1.
SeTcSnSbPdCsNpI
Sr
6x1002x1001x10°8x10-!6x10-25xlO-2
5xlO-2
5x10-21x10-2
UPuCmAïïiPmSmZrEu
8x10-33x10-32x10-31x10-39x10-49x10-48x10-42x10-4
1.4. Marine risk index
In order to calculate a "Marine Risk Index" we may multiplythe number of ALI values from Table 2 with the corresoondinqIndex values in Table 3 as shown in Table 4.
Inventory CFTable 4. "Marine Risk Index" values: ———————- x ——
ALI K
Timepoint (yr)
137CS90Sr134Cs244e™125Sb154Eu147151Sm
0
2xlOl9x10°2x1006x10-18x10-26x10-45x10-43x10-5
137CS90Sr24lAm244Q,238Pu243A!n151Sm154Eu
102
2x1007x10-14xlO-21x10-26x10-35x10-39x10-68x10-6
237ND"Tc243^79Se126Sn240Pu239Pu93Zr
10*
IxlOl4x10-32x10-32x10-38x10-46x10-43x10-45x10-7
106
237Np 5x10-2"Tc 2x10-4
129l 2x10-4135cs 5x10-6234u 2x10-6238u 4xlO"793zr 3x10-7l°7Pd 1x10-7
151
1.5. Marine CF.risk index
If we disreqard the absorption on sediments we may calculatea so-called "Marine CF Risk Index", as shown in Table 5.
I n v e n t o r yTable 5. " M a r i n e CF Risk Index" va lues : ———————— x CF
ALI
137Cs134Cs154Eu9°Sr147Pm125Sb15 Ism
0
9x1053x1044x1033xl032xl035x1024xlQl3x10°
Timepoint (yr)
102 104
24lAin 8xl04 243am 4X103 2244Q,,243^137Cs238Pu90Sr154Eu151STO
2xl04IxlO43xl036xl02IxlO24xlQl9x10-1
237Np Ixl02240Pu 6xl0l 1126Sn 4xlQl239pu 3xiol 179Se 2x10° :
99Tc 4x10"! -93Zr 2x10-1 :
106
93Zr 2x10-129i 3x10-299Tc 2x10-2-35Cs 9x10-3J34D 8x10-4^7Pd 6x10-4Î36u 2x10-4
2. DISCUSSION
The tables in the previous chapter may be used to identify thoselong-lived radionuclides, which are most important in thecontext of marine waste disposal.
If we base our indentif ication on inventories alone weuse Table 1. It is unlikelv that any waste disoosed in thedeep ocean will reach man before several years have elaosedafter the disposal. We may further argue that if the wastefirst enters the human food chain after one million years thedoses received at that time should have much less weight thanthose received now, and we may therefore neglect them. Thisleaves us with the time span from 10^ to 10^ years. Theimportant nuclides then becomes ^-^"^Cs, 9C)Sr (for the Ifl2 yearcase) and 99Tc, 243Am, 240Puf 93Zr, and 239Pu (for the 104year case) .
If we include the ALI values in our evaluation as shownTable 2, the important nuclides in the two cases become 90
and 137Cs and for 104 year: 243Am and 237Np.
in
152
If we include, furthermore, the environmental behaviour of theradionucl ides as shown in Table 4, we get for the Id2 yearcase: 137 Cs and 90sr as the important nuclides and for the104 year case: 237Np.
If we disregard the absorption on sediments, Table 5 showsthat 24lAm, 244Cm, and 243 become the important radionuclidesfor the 102 year case and 243 m anij 237^p for the 10^ year case.
If we combine the various methods of identification thefollowing radionuclides seem to be important: 137cs, 90gr^24lAm, 243 240pUf 239Pu, 237Npf 99Tc, 93Zr/ and 244 .
The importance of some of these radionuclides are influencedby the ALI, Kd and CF values. As regards the ALI values,Harrison [ 5] has recently shown that the ALI value for 23?NDmay be a factor of ten too low, while that of 239,240pu mavbe 5 times too high. This will not change the importance of237^p in Table 4, but it will make 237Np less important than239,240pu ^n fable 5, where the influence of Kd has beenneglected.
The Kcj and CF values are encumbered with considerable un-certainties. The range of the values for a given elementwill typically be 2 orders of magnitude [3]. Two of theradionuclides in our list: 237^p an^ ^^zr have a KJ range3 orders of magnitude, and in the case of 237Np the range of CFfor fish is the same.
3. CONCLUSION
Future research projects on radionuclides associated withdeep sea disposal of high-level radioactive waste should dealwith the following radionuclides: 90Sr, 93zr, 99-pc, 137Cs,237Np, 239,240PUf 241^, 243Am and 244^.
As the information on the environmental behaviour of ^^Zr,and in particular, 237Np is low, the research activity shouldfocus on these radionuclides.
153
REFERENCES
[l] Baxter, M.S.: The Disposal of High-activity NuclearWastes in the Oceans. Marine Pollution Bulletin 14,126-132 (1983).
[2] ICRP publication 30 parts 1, 2, 3. Limits for intakesof radionuclides by workers (1979-1983).
[3] IAEA. Sediment K^ 's and Concentration Factors forRadionuclides in the Marine Environment. (1984-08-31)to be published in the IAEA Technical Reports Series.
[4] FAO Yearbook of Fishery Statistics (1980) cited inStatistical Yearbook Danmarks Statistik, Copenhagen1982.
[5] Harrison, J.D. & David A.J. The qastrointestinalabsorption of transuranic elements in animals and theimplications for man. IRPA proceedings p. 427-430.IRPA Congress, Berlin 1984.
154
