Marine Environmental Research 18 (1986) 185-202 Rock Phosphate: The Source of Mercury Pollution in a Marine Ecosystem at Albany, Western Australia Michael Jackson," Donald Hancock, b Roger Schulz5 Victor Talbot a & David Williams e Health Department of Western Australia, 60 Beaufort St, Perth. Western Australia, Australia b Fisheries Department, 108 Adelaide Tce, Perth, Western Australia, Australia '' Government Chemical Laboratories, 125 Hay St, Perth, Western Australia, Australia a Department of Conservation and Environment, [ Mount St, Perth, Western Australia, Australia (Received: 30 July, 1985) 5, ~,- ABSTRACT Mercury (Hg) is present in rock phosphate as a trace element (< 0"6mgkg-l). It has been established that some of this Hg was liberated, during fertilizer manufacture, into scrubber fluids. These were subsequently discharged to Princess Royal Harbour, Albany, at a rate oJ" about 14 kg Hg per annum between 1970 and 1983. This resulted in Hg pollution of sediments (< 1.7 mg k g- L ), molhlscs ( < 50 mg kg- l wet weight) anddemersalandpelagicfish ( < 7.6 mg kg- l wet weight). Corrective action has been taken to stop the discharge and to protect consumers offish from the area. INTRODUCTION During November 1983 routine sampling of fish caught in Princess Royal Harbour (PRH), Albany, Western Australia (Fig. l), showed mercury (Hg) levels exceeding the National Health and Medical Research Council (NHMRC) guidelines (0.5 mg kg- 1 wet weight). On confirmation of the abnormally high Hg levels, an ad hoc working group was formed to 185 Marine Environ. Res. 0141-1136/86/$03.50 ~ Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain
Transcript
Marine Environmental Research 18 (1986) 185-202
Rock Phosphate: The Source of Mercury Pollution in a Marine Ecosystem at Albany, Western Australia
Michael Jackson," Donald Hancock, b Roger Schulz5 Victor Talbot a & David Williams e
Health Department of Western Australia, 60 Beaufort St, Perth. Western Australia, Australia
b Fisheries Department, 108 Adelaide Tce, Perth, Western Australia, Australia ' ' Government Chemical Laboratories, 125 Hay St, Perth, Western Australia, Australia
a Department of Conservation and Environment, [ Mount St, Perth, Western Australia, Australia
(Received: 30 July, 1985)
5, ~,- A B S T R A C T
Mercury (Hg) is present in rock phosphate as a trace element (< 0"6mgkg- l ) . It has been established that some of this Hg was liberated, during fertilizer manufacture, into scrubber fluids. These were subsequently discharged to Princess Royal Harbour, Albany, at a rate oJ" about 14 kg Hg per annum between 1970 and 1983.
This resulted in Hg pollution of sediments (< 1.7 mg k g - L ), molhlscs ( < 50 mg k g - l wet weight) anddemersalandpelagicfish ( < 7.6 mg kg - l wet weight). Corrective action has been taken to stop the discharge and to protect consumers offish from the area.
INTRODUCTION
During November 1983 routine sampling of fish caught in Princess Royal Harbour (PRH), Albany, Western Australia (Fig. l), showed mercury (Hg) levels exceeding the National Health and Medical Research Council (NHMRC) guidelines (0.5 mg kg- 1 wet weight). On confirmation of the abnormally high Hg levels, an ad hoc working group was formed to
185 Marine Environ. Res. 0141-1136/86/$03.50 ~ Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain
130. ~l Jackson, D Hancock, R. Schuiz, ~ Talbot, D. ~#tlltams
investigate and resolve the problem. This study was undertaken to assist the working group in its task.
The main aspects of the study were tackled simultaneously, namely the identification of the source, the establishment of the pathway of Hg to PRH and examination of options to eliminate the pollution. Detailed surveys of sediments, molluscs and fish were carried out to define the area and severity of the pollution.
The physical features of the study area (Fig. 1) have been described in studies by Platell (1978) and Atkins et al. (1980), who determined the effects of industrial discharges with respect to nutrient and bacteriological parameters of harbour waters. A heavy metal study (Talbot, 1983) indicated lead pollution at the western end of PRH, as evidenced by the contamination of the edible molluscs Katelysia scalarina and Mytilus edulis. The cause of that pollution was traced to a fertilizer plant whose acidic discharges contained lead compounds, and entered PRH via drainage channels and to a lesser degree an effluent pipe discharge. Because of the documented Pb pollution caused by the fertilizer plant and the knowledge of the presence of trace Hg concentrations in rock phosphates (Langmyhr et al., 1977), waters in the vicinity of the plant and discharges from it were examined for Hg.
MATERIALS AND METHODS
Sampling and storage
Water samples were collected from selected drains and effluents at and near the fertilizer plant, in acid-washed pyrex glass bottles. The samples were preserved by acidification with concentrated AR grade HNO 3 to p H I . Additional samples were taken of scrubber effluents from the fertilizer works at Albany on five consecutive operating days. Scrubber effluent samples were also collected from three fertilizer plants located in Western Australia (WA).
Samples of rock phosphate, superphosphate, sulphur and H2SO ~ were obtained from the fertilizer manufacturer as well as rock phosphate from the archives of the WA Government Chemical Laboratories.
Surface sediment samples (79) were collected from PRH from the top 20 mm of sediment, and core samples (27) were taken to a depth of up to 290 mm by the methods described by Talbot (1983). Prior to analysis all samples were stored below 0°C in polyethylene bags.
1 ~ tl. d,.ickso,r. D. Hancock. R. Schu/-_, [ T,~/hor.. D IfE/:~m~
Molluscs (Katelysia scalarina) were colt~ted from 16 sites (Fig. 2). All samples were stored below 0-~C in polyethylene bags.
Fish were collected by seining and netting at night. An initial survey of t'our pristine areas (Wilson Inlet, Bald Head. Frenchman's Bay and Oyster Harbour) and one suspected polluted area in PRH as shown in Fig. 1, was followed by regular monitoring of the western part of the eastern end of PRH. All samples were stored frozen in polyethylene bags.
Analysis
Analysis followed the methods described by APHA (1980) for inorganic Hg and total Hg in waters and effluents, Collett et al. (1981) for total Hg in all other samples, and Collett et al. (1980, 1981) ['or alkyl Hg, The sample treatment for molluscs, not given above (Collett et al., 1981) was: 10 cockles were drained, the mean drained weight of flesh per cockle was recorded and all of the meat was homogenized. A portion was taken for the Hg determination.
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Mercury pollution in a marine ecosystem 189
Hg losses during fertilizer manufacture were established by:
(1) Heating rock phosphate for 2 h at 140°C in a laboratory oven and determining Hg on the cooled material.
(2) Grinding rock phosphate and allowing it to react with a stoichiometric amount of H_,SO4 to form superphosphate. Hg content was determined on the ground rock and the product.
Scrubber effluents were treated chemically to remove Hg from the solutions following the method described by Schulz (1984).
Quality control
All glassware was stored in 0.5M HNO 3 and rinsed in deionised water immediately before use. Samples were handled with polyethylene gloves and any dissections were carried out with acid-washed surgical knives.
About 5 % of samples were blanks or standards (inorganic and alkyl Hg). In addition several samples of each type were spiked with alkyl Hg prior to digestive treatments. Recoveries were between 90-100 %.
~RESULTS AND DISCUSSION
Source investigation
Hg levels of effluents and waters from the vicinity of the fertilizer plant are given in Table 1.
The scrubber effluent was the only significant source of Hg entering PRH. The mean Hg level of this effluent was some 6000-fold above the water quality criterion of 0.14 ~g litre- ~ for marine and estuarine waters for the 6-month median (Dept. Conservation and Environment, 1981).
T A B L E ! Mercury Content of Waters and Effluents in Vicinity of Fertilizer Plant
Location Total mercury (l~g litre- t )
Swamp drains and main drain upstream from plant Contributory drains and main drain downstream from plant Effluent-holding pond for recycling within plant Scrubber effluent pit for discharge to PRH
<0"2 <0"2-0"3
0"4 600--920
t90 M. J~zckson+ D. Hancock, R. Schu/z, V Talbot, D. ~Vi//iczms
The Hg content of scrubber effluents from other fertilizer plants in WA was analysed and was found to vary with scrubber design between 250 ug litre- x and 15 600 ~g litre - t. It was apparent therefore that Hg in scrubber effluents was common to all fertilizer works in WA, and probably the world, since the technology of fertilizer manufacture and the scrubber systems to remove fluorides are similar.
The amount of Hg in the effluent was unexpected since it was known that the raw materials contained only traces thought to remain in the product. Analysis of the sulphur used in the manufacture of H 2 S O ~ and the acid itself indicated negligible amounts of Hg (< 0.01 mgkg- 1 and < 0.01 mg litre- t, respectively). The rock phosphate results are shown in Table 2.
The Hg content of the locally used rock phosphate (Nauru and Christmas Islands) has remained essentially constant over the last 50 years. Hg levels of all sources analysed in the Government Chemical Laboratories were of the same order as data available from the literature and confirmed the expected trace level of Hg in the rock.
Mercury liberation in the Jertilizer manufacture Laboratory experiments showed that negligible amounts of Hg were liberated from rock pl'losphate when exposed to dry heat of I40°C, a
TABLE 2 Mercury Content of Rock Phosphates
Source Year mg k g - t ReJ~'rcnce
Nauru 1927 053 1955 0-45 1974 0.41 1984 0.56
Christmas Island 1930 0.08 1955 0.24 This study 1974 0-10 t978 0.29
Casablanca, Morocco t929 0+05 Makutea 1932 t. 1 Florida, USA 1984 0+20 Florida, USA Unknown 0.14 "1 Kola, USSR Unknown 0.30 j~ Langmyhr et al., 1977 Morocco Unknown 0-094 Phosphate rock No. 32 Unknown 0-025 Dumarey et al., 1980
Mercury pollution in a marine ecosystem 191
temperature which may be attained in the den after treatment with sulphuric acid. In an attempt to prove and quantify Hg liberation during the manufacturing process, superphosphate was produced in our laboratory. Results are recorded in Table 3 and compared with those obtained in the plant at Albany.
Table 3 shows that up to 67 ~o of Hg is lost (liberated) during fertilizer manufacture since only about 33 O/¢o of the original Hg content ends up in the superphosphate product. The losses of Hg occur during crushing/ grinding operations and during the rock phosphate-HzSO 4 reaction in the den-associated processes.
Since efficient dust and fume extraction is common in fertilizer plants, liberated Hg is exhausted into the scrubber system where a proportion is dissolved in the liquor.
Mercury discharge loads At a superphosphate production rate of 169 000 t per annum and a 53/47 blend of the rock phosphate, some 45.6 kg of Hg are introduced into the plant per annum, calculated from Table 3. Of this, 15.2 kg of Hg leave the plant in the superphosphate product. The remainder is exhausted to the scrubber system.
Scrubber effluenfdis~harge to PRH was measured over several days. At a mean discharge volume of 5.63 m 3 h - t and a mean Hg concentration of 860 ~g litre- t, the annual Hg discharge to PRH was calculated at 14.2 kg. Hence about 65 ~o of the original Hg, as derived from the raw material, was accounted for. It is assumed that the remainder (16.2 kg per annum)
T A B L E 3
Mercury Contents During Superphosphate Manufacture
Albany plant Laboratory (mgkg- l) (mgkg- l)
Rock phosphate ° Rock phosphate after fine grinding Superphosphate Rock phosphate equivalent calculated from
superphosphate value b
0.43 0.53 - - 0.31
0-09 0. I1
0.14 0.18
a The laboratory trial used Nauru material while the plant at Albany used a 53/47 blend of Nauru/Christmas Island materials. b Calculation based on 5 parts of rock phosphate yielding 8 parts of superphosphate.
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M e r c u r y po l lu t ion in a mar ine ecosys tem 193
was discharged to the atmosphere. Using simple dilution calculations for chimney gases (Bosanquet, 1957), this Hg concentration was calculated to be 2-3 orders of magnitude below the threshold limit value for continuous gaseous Hg exposure (0.05mgm3), and hence this discharge was considered to pose no environmental risk.
The Hg in the effluent was determined to be completely inorganic. When the effluent was mixed with seawater, at dilutions up to 1:1000, no visible or non-filterable precipitate was formed within 48 h. Hence, in the absence of sorption sites such as sediment particles, it may be assumed that the mercury is relatively mobile in solution.
Effluent treatment investigations Recent literature reviews (Nagy & Olson, 1980, 1982) on treatment options were found to list either processes that had a low removal rate or processes that appeared to be too expensive and/or complex for a simple fertilizer production plant. In Table 4 some of these options are listed and compared with our recent laboratory and plant trials.
With commercial lime treatment, removal rates in excess of 99 ~ were obtained. It is a cheap treatment that requires little expertise or supervision. The effluent is neutralised under constant agitation with an excess of lime (added a's solid or slurry) to a pH of about 10. The resultant slurry is pumped into a settling pond.
Actual mixing time was found to be unrelated to the Hg removal efficiency; however, the settling time was related (Table 5). Longer settling times increased the removal efficiency, with about 24 h being required for 99 7o removal.
TABLE 5 Typical Mercury Removal Efficiency Variation with Settling Time
Se t t l i ng t ime
(h) M e r c u r y concentra t ion
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M e r c u r y remot 'al
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0.5 530 446 16 2.0 530 393 26 4.0 530 319 40
20 530 39-6 92 28 530 5-6 99
194 3 I Jackson, D. Hancock. R. Schulz. ~ . Talbot, D. ~¢d/iam,s
This relationship was not due to the physical settling of suspended matter since filtration of the treated effluent through a 0.45 :~m membrane filter gave similar removal rates to those shown in Table 5. The chemistry of this process is complex and no attempt was made to identify the Hg species at different stages in the process, but it is thought that Hg is precipitated as the slowly forming oxide or an oxy-carbonate complex.
The Hg removal efficiency improved for more concentrated effluent both in terms of per cent removal and residual concentration in the final liquor. In the field and in the laboratory residual levels of < 0.2 l~g litre- i of Hg were achieved in the supernatant liquor.
This residual liquor, after evaporation losses, may be included in the granulator feed water requirements and can be completely recycled.
All precipitated Hg is retained in the sludge, which when drained and dried may be used as filler in fertilizers.
Sediment investigation
The results of nearly 80 sites, from the comprehensive survey, were plotted as contours tbr PRH (Fig. I).
The extent of the coBtamination of the sediments is shown with heavier pollution being in the vicinity of the outfall. The shape of the pollution- affected area approximately follows the shelf bed contours. Core sample analyses showed that most of the Hg is located in the top 20 mm of the sediments with only the more heavily polluted sites showing significant levels below 60 ram. For environmental consideration the top 20 mm of sediment are most important since the Hg in only this layer is available to the marine biota (Rudd et al., 1983). Hg bound to sediment at a greater depth than 20 mm can be considered as permanently lost to the ecosystem unless a major storm causes a physical reworking of the sediment in which instance the whole surface sediment can be regarded as being diluted with less contaminated materials. Minor rework due to tidal and ionic strength variations (Millward & Herbert, 1981) is expected to gradually reduce the Hg content of the sediments.
Mercury speciation Speciation analysis on sediment samples with an elevated Hg level showed the Hg to be present essentially ira the inorganic form (alkyl Hg < 0-01 mgkg- l ) . This is in agreement with the results reported by Collett eta/. ( 198 I) on sediment investigation in Cockburn Sound. This is
Mercury pollution in a marine ecosystem 195
considered to be advantageous as it is an indication of the occurrence of little or no methylation reactions in the sediment. Hence at Albany, bioaccumulation of alkyl Hg must occur higher in the food chain, particularly as nutrient studies (Platell, 1978; Atkins et al., 1980) have shown that PRH is still a relatively clean waterbody where possible phytoplankton and sediment interaction, causing alkyl Hg con- tamination in the algae, should be minimal.
Mercury load estimation in the sediments Based on the surface sediment data presented in Fig. 1, it would appear that the natural background level in the sediment is less than 0-10 mg kg- 1 ( < 0.01-0.06 mg kg- 1). Such an assumption is compatible with a number of background mercury levels given in the literature: Irish Sea 0.1-0-4mgkg-1 (Rae & Aston, 1981), Plym Estuary 0.02-0.11mgkg -1 (Millward & Herbert, 1981), Bay of Naples 0.1-0-2mgkg -1 (Baldi et al., 1983), Gulf of Venice 0.13mgkg - l (Donazzolo et al., 1981), Baffin Bay, Greenland 0.02-0.08mgkg -1 (Campbell & Loring, 1980).
Based on the contours in Fig. 1, the area with a Hg content exceeding 0-1 mg kg- 1 has been estimated at 3 280 000 m 2 or 11.4 ~ of PRH. Other estimated areas for different Hg levels are given in Table 6.
The weight of Hg stored in the surface sediments (0-20mm) was estimated from the average of all surface sediment data in the affected area and amounted to 70 kg. Because of variable results from inconsistent depth intervals within the affected area, it was not possible to accurately quantify the Hg stored in the profile below 20 mm, but it is estimated to be of a similar order to that stored in the 0-20 mm region.
T A B L E 6 Area E s t i m a t i o n s o f Po l lu ted S e d i m e n t s
Mercury content Total area Comparison to PRH (mg kg- ' ) (m 2) (%)
> O. I 3 280 000 I 1 O-I-0.2 1 4 4 0 0 0 0 5-0
> 0-2 I 840 000 6.4 0-2-1.0 I 6 3 0 0 0 0 5-7
> I.O 2 1 0 0 0 0 0-7
196 .~1 Jackson, D. Hancock, R. Schul:. [" Ta!bor, D ;¢iH:amv
Mollusc investigation
It has been shown that molluscs accumulate heavy metals to the extent that they are useful as indicator organisms for pollution (Manly & George, 1977; Riisgard, t984). Results for the cockle Katelvsia scalarina (contours in Fig. 2) are mostly above the National Health and Medical Research Council (NH MRC) value. While cockles from the whole sample area are contaminated, the heaviest area of contamination is near the old diffuser site.
Results of a subsequent study of selected sites are given in Table 7. This study is part of a continuing assessment and evaluation programme, and the extracted data cover the 4-month time span from March to July 1984.
Sites from Table 7 are shown in Fig. 2. The relatively high results for the new diffuser site are of particular interest since the new diffuser has been in use for tess than 2 years. The Hg contamination has apparently increased rapidly to about half of that at the previous diffuser location.
Mercury speciation in cockles Speciation analysis of cockles (total Hg content 3.1 mg kg- L) indicated the presence of only 0-23 mg kg- 1 of alkyl Hg. Hence 92-6 °J' o of the Hg content of the edible 19ortion of the cockle was in the inorganic form. It appears that the biotransformation of inorganic Hg to the more toxic alkyl Hg in cockles is either a very slow process or relatively inefficient. In the literature there appears to be little data on Hg speciation in molluscs. Although other workers (Cunningham & Tripp, 1975: Wrench, 1975: Roesijadi, 1982) found that dissolved inorganic Hg is rapidly taken up in the gills of the mussel Mytilus edulis and concentrated in the inorganic form in the gills prior to gradual transport to other organs, nothing is
TABLE 7 Cockles from Selected Sites
Site Nuntber o f Mean drained Mercury samples weigh t
n (g) Range Mean ( m g k g - l ) ( m g k g l)
20m west of old diffuser 9 1.5 3.2-9-2 4.9 Old diffuser 8 I, 1 2.2-26 10-8 Ne~v diffuser 4 1-8 3.5-9.3 5.3
Mercury pollution m a marine ecosystem 197
mentioned about the final speciation of the Hg. From our data it can be implied that long term Hg storage is also mainly in the inorganic form. Results of the analysis of the shell of cockles indicated that 0.3 ~o of the total Hg load of the edible meat is either adsorbed on external surfaces or deposited by the cockle into the shell.
Fish inves t iga t ion
Location o f the general pollution area The results of the initial survey of pristine and suspected waters are shown in Table 8.
Elevated Hg levels were recorded only in PRH; at all other locations background values were recorded (Dept. of Primary Industry, 1980).
Detailed fish stud)" o f P R H In Table 9 all fish data were grouped according to species and area of catch in PRH (the western or eastern end).
The table shows that fish caught in the eastern end of PRH, with the exception of the flathead species, had mean Hg levels below the N H M R C guideline. But of the fish caught in the western end of PRH, only sea garfish and the two-species of mullet had mean Hg values below the N H M R C guideline.
WI = Wilson Inlet; PRH = Princess Royal Harbour; FB = Frenchman's Bay: OH = Oyster Harbour; BH = Bald Head (for location see Fig. I).
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Mercury pollution in a marine ecosystem 199
Speciation of mercury in fish Cobbler, being a bottom feeder and an economically important species, was analysed for Hg speciation. From a total Hg content of 0.60 mg kg- 1, 0 .56mgkg- I (93 ~o) of rig was in the alkyl Hg form. This proportion of alkyl Hg in the fish flesh is of the same order as published data for many fish species (Schreiber, 1983).
Management strategy
I. Effluent It has been shown that effluent from the fertilizer plant was responsible for the pollution of PRH.
Any rehabilitation of the harbour required the reduction or preferably the cessation of the input of Hg to the aquatic ecosystem. Since it was shown that the effluent could be successfully treated and most Hg removed from it by batch treatment at relatively small cost, the company was requested to install treatment facilities, namely a reaction (mixing) pit and settling lagoons, the required lime dosing and storage facilities and the necessary pumping facilities. Fortuitously, due to long-range planning by the company and a future anticipated change in raw materials, the compafiy c~mmissioned a new scrubber plant in December 1983.
The new plant, utilising recycling scrubber liquor, has a greatly reduced effluent discharge volume. This has allowed lime treatment of the effluent in convenient sized batches prior to discharge to the settling lagoons. These are large enough to allow effluent storage for evaporation and potential complete re-use of the liquor in the plant. Accordingly, in March 1984, all Hg contaminated effluent discharges to PRH were terminated some 4 months after the discovery of the pollution problem.
2. Sediment The complete removal of the Hg contaminated sediment would be the only certain way of removing potentially available Hg from the PRH. The costs of dredging options were estimated by the working group at up to $A8 000 000.
When the local pollution of sediments is compared with guidelines available from Japan (Koba, 1978) for the removal of Hg contaminated sediments, it appeared unwarranted to remove the sediment. The relatively small local area with a maximum level of 1.7 mg kg- t is well
20!) ~I. J~zcl,~,~,e. D. Hancock. R. Sctud-. i T~ltbor. D WHl,~am.,
below the national Japanese criteria for sediment removal and only marginally above a local Japanese government criterion. Although the tidal action has been calculated to cause a daily flushing of PRH by about 24 °, o (Platell, 1978). there is doubt as to the effectiveness of the flush with respect to the shallow western end. A systematic sediment monitoring programme has been instigated to assess changes to the Hg levels.
3. Molluscs and jTsh When the extent of the pollution of PRH became evident, the Fisheries Department. in conjunction with the Public Health Department, closed the western end of PRH (west of a line between points A and B on Fig. 1) to all public and professional fishing. Warning signs have been erected and the area is patrolled regularly.
Continuing monitoring, and a research programme covering fish and cockles, is being undertaken to study any changes in Hg levels in the ecosystem with a view to reopening the area to fishing once acceptable Hg levels are resumed.
A C K N O W L E D G E M E N T S
Michael Jackson'is F'6od and Nutrition Officer in the Health Department and is Chairman of the Working Group which was responsible for investigating and co-ordinating action on the mercury pollution.
Donald Hancock is Chief Research Otficer of the Fisheries Department and, as a member of the Working Group, initiated the fish sampling programme in Princess Royal Harbour and evaluated the data obtained from that survey.
Roger Schulz is a Chemist and Research Officer with the Government Chemical Laboratories and was responsible for analysis of water, and effluent samples, and for preparation of this paper.
Victor Talbot is a Research Scientist in the Department of Conservation and Environment and, as a member of the Working Group, was responsible for sediment, cockle and on-site investigations.
David Williams is a Chemist and Research Officer with the Government Chemical Laboratories and was responsible for analysis of fish, cockles and sediments.
The authors thank the management of the fertilizer plants for their co- operation and colleagues for analytical assistance and critical review of the manuscript.
Mercury pollution in a marine ecosystem 201
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