Page 1
Evaluation of gamma activities of naturally occurring radioactivematerials in uncontaminated surface soils of Jamaica
Maurice Miller • Mitko Voutchkov
Received: 28 September 2013
� Akademiai Kiado, Budapest, Hungary 2014
Abstract In this study a geological, lithological or ped-
ogenesis analysis is used to explain the values and distri-
bution of the primordial specific gamma activities in the
Jamaican soil environment. A random systematic sampling
method resulted in Jamaica being divided into 50 square
grids with a maximum sampling density of 225 square
meters per sample. The resulting sixty-eight (68) samples
were measured on a Canberra HPGe detector for 24 h and
the photopeaks for the primordial gammas of 238U, 232Th
and 40K analyzed. Spearman’s correlation was used to
investigate the relationships between the primordial spe-
cific activities and the geological features of the soil
samples collected and the geographic information system,
ArcGIS v10.1 used to graphically depict the gamma profile
of the primordials across the island. The Kruskal–Wallis
test indicated that in general the variations of the primor-
dial gamma specific activities over the underlying soil
geologies were statistically significant. However, the pair-
wise Post-Hoc test results did not suggest a significant
variation in mean specific for any of the primordial with all
the underlying geology even when the unadjusted p value
was used. This result along with the Spearman’s coefficient
correlation values suggested a moderate to weak relation-
ship between the gamma profile of the top soil and its
underlying geology. With the exception of a weak corre-
lation with 232Th (-0.295) no other primordial radionu-
clide correlated with the UNESCO/FAO soil categories for
the island. The most significant correlations for soil char-
acteristics and gamma activities were organic matters
which were positive for 232Th (0.518), 238U (0.481) but
negative for 40K (-0.284).
Keywords Primordial radionuclides � Soil � Geology
Introduction
Objective of the research
This research has two main objectives. The first is to
investigate the hypothesis that the characteristics of the soil
location in Jamaica impact the gamma signature of natu-
rally occurring radioactive material (NORM) in uncon-
taminated soils. The characteristic of the soil location was
restricted to the following parameters; organic matter,
bauxicity, pH, geology, elevation, latitude, and longitude.
Areas where the soil environment may be affected by
anthropogenic activities are excluded from this investiga-
tion. The second objective is to establish a baseline data for
primordial activities in Jamaica in order to quantify the
impact of any nuclear accident worldwide, on the terrestrial
environment; in this exercise the distribution of the pri-
mordial will be characterized. This study assumed that the
soil and its underlying geology are related.
Review of related studies
Numerous studies have been done all over the world on the
analysis of primordial radionuclides in both contaminated
and uncontaminated soils. The main purposes of these
studies are usually (a) to determine the activity of these
primordial sources and quantify the health/exposure radio-
logical indices that indicate the levels of risk faced by the
populations in these areas, (b) establish a baseline data for
M. Miller (&) � M. Voutchkov
Department of Physics, Faculty of Science and Technology,
University of the West Indies, Mona Campus, Kingston 6,
Jamaica
e-mail: [email protected]
123
J Radioanal Nucl Chem
DOI 10.1007/s10967-014-3000-x
Page 2
the level of normal background radiation levels, (c) deter-
mine the variability of particular radionuclide concentration
across the area, (d) quantify the impact of industrial oper-
ations such as cement manufacturing, bauxite, and petro-
leum and electricity generation on the normally occurring
radioactivity materials in the environment, and (e) deter-
mine the levels of specific artificial radionuclides, espe-
cially those produced in nuclear reactors [1–16]. The
NORM of interest in soil varies between countries and
between radionuclides; in almost all cases examined the
activity of 40K outpaces by sometimes a factor of ten the
activities of 238U, 226Ra, and 232Th. The carcinogenic
impact of primordial radiation is of particular interest
worldwide and has been examined in a number of publi-
cations. The excess lifetime risks of cancer, and the annual
effective gamma doses in western Mazandaran Province of
Iran, were found higher than the global average when
gamma analysis of 54 soil samples were performed [1]. In
Nigeria, incidence of cancer from soil radioactivity found
that cancer cases attributable to radiation exposure due to
soil radioactivity was low, constituting between 1.3 and
9.2 % of the total reported cases [17]. In Kirklareli, Turkey,
the excess lifetime cancer risks and outdoor gamma dose
rates were determined from 230 sampling stations and soil
samples taken from 177 locations. The annual effective
gamma dose of Kirklareli was 144 [mu]Sv and the excess
lifetime cancer risk of 5.0 9 10-4 [18].
Geological and soil characterization of Jamaica
The island of Jamaica is located at coordinates 18�150N77�300W with an area of 10,911 square kilometers. The
geology of Jamaica may be classified by rock types
belonging to the groups Cretaceous, Wagwater and John
Crow Rift deposits, Limestone (yellow and white), Coastal
Groups and Alluvium as shown in Fig. 1. The yellow lime-
stone group in Jamaica overlay tectonically stable blocks
during the mid-Eocene period and along with the white
limestone, these Cenozoic limestone constitute 70 % of the
island and dominate the central regions of Jamaica [19]. This
central section of the island has a blanket of terra rossa and
bauxite covering the Cenozoic limestone and the large
majority of bauxite plants and productions occur here. The
soils in Jamaica have a wide range in classification mainly
due to the variability in the parent material, topography and
rainfall. These soils cover two major regions; a highland
interior and an almost flat coastal region in Jamaica. The red
limestone occurs mainly in St. Ann, Manchester and St.
Elizabeth and constitutes the bauxitic soils with red color due
to oxidation of iron. The black limestone, exposed over
yellow limestone rock, do not exhibit the red bauxite color
due to their high calcium and water component which
inhibits ferric oxidation.
The Alluvial Plain and Valley soils, deposited by rivers,
are mostly found on the southern and eastern end of the
island and in small areas in the central regions. They are
known to consist of loam, sand and gravel and gave rise to
good agricultural lands. The soil environment is described
by a 1984 study which developed 206 Jamaican soil names
which characterized the soils in Jamaica according to
features such as the texture, slope, root limiting layer,
internal drainage, moisture supplying capacity, erosion
hazard, and the levels of pH, potassium, phosphorus, and
nitrogen. The soil names were developed from the areas
where they were first found and is appended by the soil
texture; the same name was then applied anywhere else the
soil was found. Except for the St. Ann clay loam which
constitutes 5.3 % of the island, all the other soils are less
that 5 % in island wide distribution {Rural Physical Plan-
ning Department-Ministry of Agriculture, 1982 #2581}. A
more international naming convention of the soil environ-
ment in Jamaica is based on the United Nations Economic,
Scientific and Cultural Organization/Food and Agricultural
Organization (UNESCO/FAO) soil type published in the
World Harmonized Soil Database. The soils types in
Jamaica are listed as Ferralsols, Leptosols, Cambisols, and
Vertisols. The Jamaican soil has a Soil Mapping Unit ID of
17312. Other studies have been done examining terrestrial
gamma rays in the geological environment. Ramli et al.
[20] reported a valid statistical relationship between pre-
dicted terrestrial gamma dose rate based on geological
features and soil types in Kota Tinggi district, Malaysia. A
study in the Levos island of Greece using gamma-ray
scintillation spectrometry attempted to correlate radioac-
tive isotopes levels among various igneous rock types
formations exposed on the island. They noted high levels of40K, 232Th and 238U in several geological formations [21].
A study done in Jamaica resulted in a publication ‘‘A
Geochemical Atlas of Jamaica’’ detailing soils and heavy
metal analysis [22].
The soil metadata
The soil samples were distributed as follows: (a) underly-
ing geology—alluvium deposits (25.8 %), coastal group
(15.2 %), cretaceous (15.2 %),Wagwater (4.5 %), White
Limestone (36.4 %), and yellow limestone (3 %) (b) FAO
soil category—Canbisols (13.6 %), Ferralsols (66.7 %),
Leptosols (12.1 %), and Vertisols (7.6 %) (c) pH level—
acidic (15.2 %), alkaline (57.6 %), neutral (6.1 %), slightly
acidic (18.2 %), and unreported (3.0 %) (d) Soil texture—
clay (12.1 %), clay loam (10.6 %), gravelly loam (3 %),
gravelly sandy loam (3 %), loam (6.1 %), sand (3 %),
sandy loam (1.5 %), stony loam (59.1 %), and swamp
(1.5 %) (e) elevation levels—range 5–1,237 m with
50th percentile of 110 m (f) organic matter—range
J Radioanal Nucl Chem
123
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2.65–28.30 % with 50th percentile of 11.8 %. The soil
environment is dominated by soils categorized by the FAO
as Ferralsols (66.7 %) with a dominant texture of stony
loam (59.1 %). These factors are analyzed further to see if
they impact the gamma profile of the terrestrial environ-
ment in Jamaica.
Materials and methods
Sample collection
The application of a random systematic sampling technique
resulted in Jamaica being divided into 50 square grids with
a maximum sampling density of 225 square meters per
sample. A location within the grid was selected using a
random generator which generated two numbers corre-
sponding to a location within the grid. At least one repre-
sentative soil sample (of minimum five sub-samples taken
from an area 20 9 20 m) was then collected from each
location resulting in a total of sixty-eight (68) soil samples.
The samples taken were restricted to the 0–10 cm section
of the soil after all living vegetation was removed. The
collected soils samples were sieved using a 2 mm sieve,
dried at 60 degrees for approximately 18 h and stored in a
sealed cylindrical container in a cool dark area for a min-
imum of thirty days prior to gamma measurement to ensure
secular equilibrium between 238U and its progenies.
Spectrometry
The detector used in this research was a Canberra 3825
HPGe detector (absolute efficiency = 27.61 %, measured
and 28.15 %, ISOCS value. This detector has an active area
of 38 cm2 and active diameter of 71 mm, [100] and was
cryogenically cooled by liquid nitrogen in a vertical dip-
stick type 7500SL 30 litre Dewar throughout the mea-
surement process. The detector and samples were enclosed
in a 950-kg Model 747E 10-cm thick lead shield with
graded 1 mm tin and 1.6 mm copper liner to reduce
interference from lead x-rays, cosmic and background
radiation during counting, reduce counting time and
improve the lower levels of detection. The floor of the
shield had a 12.1 cm hole to facilitate the cryostat and the
shield itself had a 9.5 mm thick low carbon steel. Soil and
background samples were counted in lead enclosure for
approximately 24 h using Genie 2000 software for spec-
trum acquisition. The entire detector and samples were
enclosed in a lead shield to reduce the background radia-
tion. Soil and background samples were counted in lead
enclosure for approximately 24 h using Genie 2000 soft-
ware for spectrum acquisition. The data for each sample
were entered into a Microsoft Excel spreadsheet for further
analysis. SPECTRW software was used for gamma ana-
lysis of the spectrum for each sample. For counting and
activity analysis the following photopeaks were used
(a) 40K, peak at 1,460.83 keV, (b) 235U, weighted average
of photopeak at 143.76 and 185.71 keV after correcting for
interference from 226Ra at 186.21 keV. (c) 238U, from the
weighted average of the daughters 214Pb (351.9 keV), 214Bi
(609.32 keV), and (d) 232Th, the weighted average of the
daughters 208Tl (583.19 keV), 228Ac (911.16), and 212Pb
(238.63 keV).
Minimum detection limits
Genie 2000 Nuclide MDA Report was run to generate the
minimum detectable activity for the radionuclides under
investigation in this study. This report was found to be
quite useful as it showed nuclides identified during the
nuclide identification process, the energy at which it was
found in the spectrum, nuclides that required/did not
required coincidence correction, and nuclides whose
energy were not found in the spectrum. The MDA (in
brackets in Bq/kg), for the radionuclides of interest were as
follows: 40K (6.24), 208Tl (0.889), 212Bi (7.20), 214Bi
(1.59), 214Pb (1.49), 226Ra (1.16), 234Pa (2.4), 234Th (5.8),
and 235U (0.706).
Nuclear analytical technique
A special gamma analytical method was used throughout
the research to ensure that the reported values were as
accurate as possible. This method involved the use of
several software applications including Canberra’s Lab-
SOCs and Genie 2000 for absolute efficiency measure-
ments and spectra counting respectively, SPECTRW
(courtesy of Costas Kalfas, Greece, for gamma analysis),
EFTRAN (courtesy of Tim Vidmar, Belgium, for cascade
summing correction), and Sigma Plot 10.0 (curve fitting
algorithm and generation of fitting parameters). In ana-
lyzing the photopeaks at 241 keV, the analysis program
used in this study firstly assigned the counts to both 224Ra
and 214Pb, since the corresponding peaks at 241.00 and
241.92 respectively cannot be separately resolved since as
it falls outside the resolution capability of the detector. The
observed peak is the sum of the two individual radionuc-
lides and is then apportioned by examining the activity of214Pb at 351 keV to determine the counts at 241 keV which
would give this activity. Since 214Pb has peaks (at
295 keV, BR = 18.5 %, and 351 keV with BR = 35.8 %),
an average activity can be assigned to this isotope based on
these intense peaks. A similar case, but a different
approach, was adopted for the 186 keV spectral line with
the unresolved composite of the 185.715 keV (235U) and
186.21 keV (226Ra).
J Radioanal Nucl Chem
123
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Quality assurance
The method suggested by the equipment manufacturer
(Canberra) was adopted for Quality Assurance during the
counting process. Specific counting parameters were
monitored and documented following the analysis of the
radioactive source Model EU-NA-S installed in the Model
ISOXSRCE Check Source Fixture which ensured a con-
sistent geometry. This source contains 155Eu (86.5 and
105.3 keV), 22Na (511 and 1,275 keV); each nuclide has a
1 microcurie initial activity. On the front and side orien-
tation position, the source is located at 10 cm above and
beside the detector’s end-cap. Because it was deemed
impractical to move the detector from the lead shield each
time the QA measurements were being done, the 86.5 keV155Eu peak was discarded from the analysis due to possible
interference from lead X-rays at 87.15 keV. A counting
time of 5 min was employed to ensure a 1–2 % relative
precision in the 1,275 keV energy peak [23].
Other analytical technique
The soil type, pH, geographic information systems (GIS)
shapefiles, geological parameters, and the underlying geo-
logical formation related to the soil sampling locations in
Jamaica were obtained from both the Rural Physical Plan-
ning Division of the Ministry of Agriculture and Fisheries,
and the Department of Geology and Geography at the Uni-
versity of the West Indies in Jamaica. The GIS shapefiles
were analyzed using ArcGIS 10.1 state-of-the-art geo-
graphic information systems software to develop an under-
standing of the geographic distribution of the general soil
texture characteristics and the levels of calcium, potassium,
and nitrogen from which the samples originated. Additional
soil geological properties related to aluminum and pH were
obtained from the publication ‘‘A Geochemical Atlas of
Jamaica’’. The bauxiticy levels of the soils were inferred
from the levels of aluminum (Al) reported for the sample
locations. The adopted convention used was that soils with
less than 10 % concentration of aluminum are considered
non-bauxitic. The underlying geological formation was
provided by maps supplied by the Geology and Geography
Department of the University of the West Indies and the
1:250,000 geological map of Jamaica published by the Mines
and Geology Department of the Ministry of Energy and
Mining. Another useful source of information was the 1984
Comprehensive Resource Inventory and Evaluation System
Report that characterized the soil environment in Jamaica.
The geological related parameters of interest examined in
this research were the soil levels of potassium, phosphorus,
nitrogen, pH and bauxiticy. Sample point parameters col-
lected were the UNESCO/FAO soil type, elevation, latitude,
longitude, organic matter, soil texture and the underlying
geology. ArcMAP (a component of ArcGIS) was used to
overlay the various shapefiles and relate each sample point to
its geological characteristics. The Inverse Distance
Weighting interpolation technique was used to develop
various maps showing the distribution of the primordial ra-
dionuclides and gamma activity in Jamaica. The soil samples
were described by the following metadata (a) underlying
geology (b) FAO soil category (c) pH level (d) soil texture
(e) sample elevation levels, (f) organic matter (g) primordial
specific gamma activity, and (h) geographic location. A
number of statistical approaches,including the One-Sample
T-Tests, Kruskal–Wallis Test, Spearman’s Correlation,
Percentile Ranks, Box-and-Whisker plots, and parametric
and non-parametric Post-Hoc tests for variability of means
were used to analyze and report the data. For the Post-Hoc
analysis of the samples within the geologies for the specific
radionuclide, the adjusted p value was used as it gives a better
representation of the data set, incorporates all the processes
which contribute to the characteristics of the data, and is a
conservative method [24]. The statistical software SPSS
version 22.0 and GraphPad Prism version 6.00 for Windows
were used to perform the statistical analysis reported in this
paper.
Results and discussions
Minimizing uncertainty in the nuclear analytical
process
All analyzed samples were associated with an error from
which the mean activities were reported. The errors and
standard deviations in the mean specific activities of the
radionuclides in this study were detailed in the ‘‘Results
and discussion’’ section of this paper. The nuclear analysis
technique employed a dual efficiency curve for the cylin-
drical container in contact with the face of the Canberra
3825 HPGe detector; the expressions are shown in Eq. (1).
The resulting equations below (for the range before and
after 100 keV respectively) increased the accuracy of the
spectrometry results.
Equation (1)—Dual efficiency curve for the analytical
process.
ln Effð Þ ¼ �38:01 � þ22:38lnðE Þ � 4:642lnðEÞ2
þ 0:3185lnðEÞ3
¼ �110:8 � þ76:3lnðEÞ � 20:35lnðEÞ2
þ 2:56lnðEÞ3 � 0:15 ln Eð Þ4þ3:214 � 10�3lnðEÞ5
ð1Þ
Additional uncertainties were reduced by employing
coincidence correction to the photopeaks, interference
corrections (see ‘‘Nuclear analytical technique’’ section),
J Radioanal Nucl Chem
123
Page 5
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J Radioanal Nucl Chem
123
Page 6
the type of background shielding employed (see ‘‘Spec-
trometry’’ section), and the quality assurance employed
during the counting process (see ‘‘Quality assurance’’
section). Photopeaks below 100 keV were avoided to
eliminate interference from fluorescence x-rays in the
experimental setup, and reduce errors due to attenuation
and self-absorption of low energy gamma [25]. The 208Tl
photopeak at 510.7 keV was omitted from the weighted
activity for 232Th as it difficult to resolve from the 511 keV
annihilation peak. Errors due to disequilibrium in the post
radium nuclides of 238U, were reduced by keeping the
samples in a sealed container in a cool dark section of the
lab for a minimum of 30 days before counting. The door to
the lab was kept closed (as long as practical) to reduce
fluctuations in the background due to radon, and the entire
counting system was kept on a rubber mat to reduce
microphonics interference. Finally, the background used in
the peaked background correction process, was counted for
approximately three days.
Correlation data
The Spearman’s non-parametric statistic was used to
deduce the correlation among the variables investigated in
this report since the D’Agostino and Pearson Onibus
Normality tests indicated that with the exception of the
gamma total specific activity, all other variables were from
a non-Gaussian distribution. The correlation results are
shown in Table 1 and their implications are discussed in
the subsequent sections.
Potassium-40 distribution characteristics in Jamaica
Figure 2 showed that the distribution of potassium-40 (K-
40) in Jamaica ranged from 19.67 to 654.25 Bq/kg with the
eastern section of the island showing higher in comparison
to the mid central regions. The One-Sample T-Test results
[t(67) = -17.636, p \ 0.01] indicated that the sample dis-
tribution (M = 200.7601 ± 21.50431, SD = 177.32912)
Bq/kg was statistically significantly lower than the world
mean of 640 Bq/kg. The Jamaican mean specific activity of
200 Bq/kg is the vicinity of values reported for Indonesia
(197 Bq/kg), Philippines (212 Bq/kg), and Mexico
(244 Bq/kg) [26].The percentile rank of the world mean
(0.97) suggested that 97 % of the island is below the world
mean for K-40; a similar test showed that 62 % of the
island was below the local mean value of 200 Bq/kg.The
most significant correlations were with thorium (-0.596)
and uranium (-0.704). The higher levels of potassium-40
activity in the eastern end of the island are indicative of
higher levels of potassium salts and potassium–feldspar
present in the soil. The lower levels of potassium (in the
bauxitic areas) are probably due to the process of frac-
tionation which dominates the process of accumulation of
Fig. 1 Simplified geology map of Jamaica: courtesy of the Department of geology and Geography, University of the West Indies
J Radioanal Nucl Chem
123
Page 7
these radionuclides in the presence of thorium. Addition-
ally, the correlation relationship is probably indicative of
the differences in (a) how they were accumulated in rocks
during the formation period, the different chemical prop-
erties which provided different migration rates, and (b) the
formation patterns of the soils. This low level of correlation
between 40K and 232Th has been reported in a previous
study with value of 0.32 over metamorphic rocks [7].
Potassium moderately correlated with geology (-0.355)
and further investigation using the Independent Samples
Kruskal–Wallis Test indicated that the distribution of the
activity by geology (shown in Fig. 3) was significant,
H(5) = 15.782, p \ 0.05. The Post-Hoc pairwise compar-
ison test within the samples however, indicated that only
the difference (in mean rank) between the White Limestone
and the Cretaceous rocks was statistically significant at the
p = 0.5 level when the adjusted p value (= 0.017) was
used. When the unadjusted p value was used, other sig-
nificant differences in the mean ranks were White Lime-
stone–Alluvium (p = 0.010), White Limestone—Coastal
Group (p = 0.021), and White Limestone Wagwater
(0.036). The largest standard deviation in the specific
activity occurred over the cretaceous rocks (241.73 Bq/kg)
may be probably due to a wide variation in the density of
the potassium–feldspar in the soils or variation in the
chemical processes which gave rise to the rocks in these
areas.
238U and 232Th distribution characteristics in Jamaica
The analysis of uranium-238 (238U) and thorium-232
( 232Th) distribution, shown in Figs. 4 and 5 respectively, is
presented together because of certain similarities in their
distribution in the Jamaican environment. Both radionuc-
lides were closely correlated (0.86) with increased gamma
activity over the central bauxite mining areas of the island.
Their ranges in the Jamaican soil are similar with uranium-
238 ranging from 4 to 400 Bq/kg and thorium ranging from
4 to 172 Bq/kg. The One-Sample T-Test results for ura-
nium [t(67) = -3.687, p \ 0.01] indicated that the local
sample’s mean specific activity (M = 87.0156 ± 12.751,
SD = 105.139) Bq/kg was statistically significantly higher
than the world mean of 40 Bq/kg and by as much as 200 %
in some areas. The Jamaica mean activity of 87 Bq/kg is
similar to Hong Kong (84 Bq/kg) but lower than Thailand
(114 Bq/kg) [26]. The percentile rank of the world mean
(0.54) suggested that 46 % of the island is above the world
mean of 40 Bq/kg for uranium-238. However, for thorium,
the local mean specific activity of 42.92 ± 4.98 Bq/kg was
not statistically different from the world mean value of
40 Bq/kg although 40 % of the island showed elevated
levels of this radionuclide. Locations with similar mean
activity for thorium 232 include India (42 Bq/kg), Iran
(39 Bq/kg), and China (41 Bq/kg) [26]. The Independent
Samples Kruskal–Wallis tests rejected the null hypothesis
that the gamma activity distribution of 238U
[H(5) = 121.018] and 232Th [H(5) = 20.052] were the
same at the a = 0.5 level. The Post-Hoc pairwise com-
parison analysis using the adjusted p value suggested sig-
nificance in the mean rank between the Cretaceous and
White Limestone regions for 238U and between the Coastal
Fig. 2 Map of 40K specific
activity (Bq/kg) distribution
across Jamaica
Fig. 3 -Distribution of 40K specific gamma activity (Bq/kg) over
underlying geology in Jamaica. Post-Hoc pairwise comparison
indicates that only Cretaceous and White Limestone distributions
were statistically significant
J Radioanal Nucl Chem
123
Page 8
Group and White Limestone regions for 232Th; the dis-
tributions are shown in Figs. 6 and 7.
A published survey of soils in Jamaica, indicated that238U correlated with aluminum (0.72), chromium (0.71),
iron (0.61) and the rare earth elements (0.60–0.76) [22].
The results of this study validates the conclusion of a
previous local study which found higher uranium gamma
levels in bauxite areas of Jamaica [22]. 232Th mobility
during high-grade metamorphism or retrogression has been
suggested as the reason for its variation in metamorphic
rocks, with the highest concentration found in shales due to
absorption into clays. The higher levels of thorium found in
the St. Elizabeth and Trelawny areas of Jamaica were
consistent with previous studies [22]. A previous study
confirms this observation by noting that thorium correlates
well with Al (0.90) in Jamaican soil [22]. Other significant
correlations have been found with Cr (0.86), Sc (0.80), Fe
(0.75), and the rare earth elements (0.72–0.94) [22].The
observation from this study may be useful in using the
activity of Tl-208 to identify areas where bauxite produc-
tion may be useful, as well as areas where the correlated
heavy metals may be found. The negative correlation
Fig. 4 Map of 238U specific
activity (Bq/kg) distribution
across Jamaica
Fig. 5 Map of 232Th specific
activity (Bq/kg) distribution
across Jamaica
Fig. 6 Distribution of 232Th specific gamma activity (Bq/kg) over
underlying geology in Jamaica. Post-Hoc pairwise comparison
indicates that only Coastal Group and White Limestone distributions
were statistically significant
Fig. 7 Distribution of 238U specific gamma activity (Bq/kg) over
underlying geology in Jamaica Post-Hoc pairwise comparison
indicates that only Cretaceous and White Limestone distributions
were statistically significant
J Radioanal Nucl Chem
123
Page 9
between 232Th and 40K (-0.596) suggested that the
geochemical processes that gives rise to these soils, favors
fractionation over accumulation. The lowest activity of
thorium was noted as occurring over the Wagwater
deposits and Cretaceous rocks in Jamaica.
Total gamma from primordial sources
Figures 8 shows the two main hotspots for primordial
gamma radiation in Jamaican soils. Hot Spot A occur in
soils overlaying the Cretaceous and Wag Water geological
formation in the eastern end of the island, and Hot Spot B
is in the bauxitic soils overlaying predominantly White
Limestone in the central portion of the island. The radiation
map shows that the highest levels of radiation in Jamaica
occur over the non-bauxitic soil regions of the eastern end
of the island with the main contributor here being 40K.
This area is mainly in the St. Thomas and southern Port-
land region where the Wagwater and John Crow Rift
deposits occur in the island. In the analysis (shown in
Table 1), total gamma correlated moderately with 40K
(0.489). The total gamma specific activity was Gaussian in
distribution as shown in Fig. 9.
A One-Way Analysis of Variance Test (ANOVA)
however indicated that the variability in the means (of the
total specific gamma activity) over the geologies was not
statistically significant [H (5) = 1.753, p [ 0.05]. The
study therefore concludes that there is no relationship
between total gamma specific activities from primordial
sources and the underlying soil geologies in Jamaica.
The impact of soil characteristics
The general observations from Table 1 indicated that the
gamma activities of the primordials in Jamaica exhibited
weak to moderate correlation with the chemistry, location,
texture or FAO classification of the soil environment. The
correlation between soil texture and 232Th (0.44) and 238U
(0.50) were moderate but weak for 40K (-0.275). With the
exception of a weak correlation with 232Th (-0.295) no
other primordial radionuclide correlated with the UNE-
SCO/FAO soil categories for the island. The lack of cor-
relation between FAO/UNESCO soil type and primordial
gamma was initially expected, but is perhaps due to the
extensive underlying limestone geology which has varying
levels of primordial concentration. The most significant
correlations for soil characteristics and gamma activities
were organic matters which were positive for 232Th
(0.518), 238U (0.481) but negative for 40K (-0.284). A
possible explanation for this correlation result is that while238U and 232Th accumulate to reasonable concentrations in
soils with high organic matter constituent unlike 40K.The
accumulation of uranium in anaerobic soils and peats has
been noted by other researchers [27, 28]. Ashing of soil
samples could therefore assists in the analysis of 40K.
Ashing is recommended for samples originating from the
biosphere but generally not required for samples originat-
ing from the lithosphere [29].
Summary of major findings
(a) K-40 specific activity values falls below the world
mean (of 640 Bq/kg) in approximately 97 % of the
High : 702.033
Low : 82.8502
Hot Spot A –mainly due to 40K
Hot Spot B –mainly due to 238U
Fig. 8 Map of total gamma
from primordial sources in Bq/
kg in Jamaica showing the two
major radiation hotspots and
their main radionuclide
contributors
Fig. 9 Distribution of total gamma in the data set
J Radioanal Nucl Chem
123
Page 10
island with the bauxite soil exhibiting lower activity
than the local mean value of 200 Bq/kg. The highest
levels occur in soils overlaying the Cretaceous and
Wag Water geological formation in the eastern end of
the island. The most significant correlations were with
thorium (-0.596) and uranium (-0.704).
(b) 238U and 232Th exhibit certain similarities in their
distribution in the Jamaican environment. Both radio-
nuclides were closely correlated (0.86) with increased
gamma activity over the central bauxite mining areas
of the island. Their ranges in the Jamaican soil are
similar with Uranium 238 ranging from 4 to 400 Bq/
kg and Thorium ranging from 4 to 172 Bq/kg.
(c) Two major radiation hotspots were identified. Hot
Spot A occur in soils overlaying the Cretaceous and
Wag Water geological formation in the eastern end of
the island, and Hot Spot B is in the bauxitic soils
overlaying predominantly White Limestone in the
central portion of the island.
(d) The radiation map shows that the highest levels of
radiation in Jamaica occur over the non-bauxitic soil
regions of the eastern end of the island with the main
contributor here being potassium-40.
(e) While the rank of the mean of specific primordial
activities were significant over the various geological
formations in Jamaica, Post-Hoc non parametric tests
showed that, with the exception of the White Lime-
stones, no other geology could be characterized by all
of the primordial radionuclides specific activities in
the soils in Jamaica. A conservative approach was
adopted to use the adjusted p value instead of the
usual unadjusted p value. This approach showed that
in general, the geology cannot be completely charac-
terized from the radiation signature of the surface
soils.
(f) The organic matter distribution of the Jamaican soil
environment was similar in distribution to 232Th and238U, indicating that bauxitic soils in Jamaica exhibit a
tendency for higher organic matter composition.
(g) The study therefore concludes that there is no
relationship between total gamma specific activities
from primordial sources and the underlying soil
geologies in Jamaica.
Application of research results
(a) The low values recorded for thorium over the Creta-
ceous inliers is typical due to the low bedrock con-
centration inherent in this lithology. Gamma
spectrometry of thorium activity may prove useful in
identifying and classifying lands for agricultural use
based on low or high concentrations of bedrocks
which may accommodate specific plant growth based
on root requirements.
(b) In the Jamaican environment, the gamma profile of
thorium is a minimum distribution over Wagwater
deposits and cretaceous rocks, and a maximum over the
limestone regions of Jamaica. This study suggest that
the wide variation over the limestone regions of
Jamaica is probably due to the existence of metamor-
phic rocks originating from the transformation of
various rock types and now containing various chem-
ical compositions from its prolith. From a geological
perspective, this information may be useful in classi-
fying metamorphic rocks characteristics in Jamaica by
measuring the activity of thallium-208 (208Tl) at
583 keV. Perhaps the gamma activity of the locations
that are similar, may be classified as either originating
in the same era or from the same prolith rocks.
(c) Geostatistical analysis suggested where 232Th spe-
cific activity exceeds approximately 45 Bq/kg, coin-
cided with the areas where the soil is mined for
bauxite and aluminum.
Conclusion
(a) This study recommends the development of a national
environmental specimen banking approach to aid in
the nuclear contamination monitoring by real-time
and retrospective analysis. These contaminants are
more likely to originate from local anthropogenic
sources such as in the manufacturing of cement and
bauxite and the production of electricity, the latter
which is still based on fossil fuels in Jamaica. A good
reference for prototyping a specimen bank has been
published [30]. Since the lungs, kidneys and bone in
humans receive the highest annual doses from ura-
nium [31], additional study in required to further
enhance our understanding of the impact of elevated
levels of soil-resident uranium and their impact on
cancers and related health issues in Jamaica.
(b) The main agricultural produce should be measured to
ascertain the transfer ratio of uranium since thorium is
relatively insoluble with low specific activity making
it available in biological materials in insignificant
amounts [31]. Also, since the human body does not
store excess potassium because of matters related to
homeostatic control and the relative low level of 40K
found in Jamaican soils, 40K radiation is not
considered critical.
Acknowledgments The authors wish to acknowledge the kind
cooperation of the following organizations: The Rural Physical
J Radioanal Nucl Chem
123
Page 11
Planning Authority, Ministry of Agriculture, Jamaica, The Depart-
ment of Geology and Geography, the University of the West Indies,
Mona Campus, and The Mona Geoinformatics Institute.
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