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Form of mercury in stream fish exposed to high concentrations of dissolved inorganic mercury
Cheraosphere, Vol. 30, No. 4, pp. 779-787, 1995
Pergamon
0045-6535(94)00407-2
Elsevier Science Ltd Printed in Great Britain
FORM OF MERCURY IN SWREAM FISH EXPOSED TO HIGH O3N~TIONS
OF DISSOLVED INORGANIC MERCURY
G. R. Southworth', R. R. Turner, M. J. Peterson, and M. A. Bogle Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, Bldg. 1505, MS 6036, Oak Ridge, Tennessee 37831-6036. (Received in USA 3 August 1994; accepted 8 September 1994)
Abstract The form of mercury predominating in mercury-contaminated fish from both pristine and industrialized waters in North America and Europe has almost universally been methylmercury. Sunfish (Lepom/s aur/tus) living in a stream contaminated with 0.5 -1 t~g/L dissolved inorganic mercury accumulated greater concentrations of total mercury at headwater sites, where the dissolved mercury concentrations were greatest, than they did at downstream sites.
However, despite evidence from laboratory studies that dissolved
inorganic mercury is rapidly accumulated by fish without transformation to methylmercury, methylmercury constituted 85% or more of the total mercury concentration in fish at all sites. Introduction Although methylmercury occurs at small concentrations relative to inorganic mercury in natural waters, the mercury content of axial muscle of fish from both pristine and contaminated freshwater generally is greater than 90% methylmercury (Bloom 1992, Huckabee et al. 1979).
The toxicological hazard of eating fish contaminated with
methylmercury is much greater than that of ingesting similar quantities of inorganic mercury (Clarkson and Marsh 1982). Laboratory studies have demonstrated that dissolved inorganic mercury, in both elemental and oxidized forms, is readily taken up directly from water, and is excreted slowly (Oison et al. 1973, Schoper 1974, Kramer and Neidhart 1975, Ribeyre and Boudou 1984, Neuman and Doubet 1989, Kindon 1993). Inorganic mercury accumulated in this manner is not converted to methylmercury within the fish. Fish exposed to high (>0.1/~g/L) concentrations of 779
780
dissolved inorganic mercury would be expected to accumulate detectable concentrations of inorganic mercury.
East Fork Poplar Creek originates as ground water and single-pass cooling water discharges within the U.S. Department of Energy Y-12 Plant in Oak Ridge, Tennessee (Fig. 1). It emerges from a complex underground storm sewer network, and flows for approximately 1.8 lan through the industrial facility as a straight, shallow, rock and gravel bottomed ditch. It then flows through a concrete dispersion channel from which it is discharged at several points to a plastic lined, 1.1 ha. settling pond. Below an overflow discharge from the pond, the creek flows through a mixture of urban and rural landscapes for 23.5 km before emptying into an embayment of Watts Bar Reservoir (Fig. 1).
Aqueous mercury concentrations have averaged 1.3 #g/L in East Fork Poplar Creek at the Y-12 Plant over the 1991/1992 period (Kornegay et al. 1992, 1993). Concentrations of total aqueous mercury decline rapidly with distance downstream from the Y-12 Plant, dropping to about 0.1 ~g/L 16 km downstream. Studies of the aqueous speciation of mercury in EFPC have demonstrated that total aqueous mercury is predominantly particle-associated inorganic mercury at all sites from the settling pond at kilometer 23.5 downstream (Southworth, Turner, and Nourse 1993). Methylmercury concentrations are far lower than inorganic mercury concentrations; typically about 5 x 10"~ ~g/L.
Total mercury
concentrations above and below the settling pond at km 23.5 differ little; however, speciation of inorganic mercury is markedly different between the headwater reach above the pond and downstream reaches. In the headwaters, dissolved inorganic mercury is the predominant form, accounting for approximately 50% or more of the waterborne mercury. Below the settling pond, dissolved mercury only accounts for about 15% of the total aqueous mercmy (Southworth et al. 1993).
Thus, East Fork Poplar Creek differs from most aquatic systems in which mercury accumulation in fish is a concern in that dissolved inorganic mercury concentrations in the headwaters of the stream are substantial, often exceeding 1.0 ~g/L. Prior to December 1992, fish populations in the reach of the stream where dissolved mercury was highest were small and transitory because of the presence of near toxic concentrations of total residual chlorine (TRC) in the water (Peterson et aL 1994).
In November 1992 a system was
installed to add roughly stoichiometric concentrations of sodium bisulfite to the discharges respons~le for most of the TRC in the creek. This action, eliminated toxic concentrations of TRC in the creek and allowed the rapid colonization of the upper reaches of the creek with fish. As a result, the large numbers of fish were exposed to substantial concentrations of dissolved inorganic mercury.
Fig. 1.
2
I
I
3km I i 1 mile
v
RM,IDOK
J
24.8
Sampling sites for redbreast sunfish in East Fork Poplar Creek in Oak Ridge, Tennessee. Sites are designated by distance (kin) upstream from the mouth of East Fork Poplar Creek.
0.5
I
1
•
I~PIARCR~x
ORNL-DWG 93M-9316R
oo
782
The objective of the study described in this paper was to ascertain whether measurements of total mercury in fish, previously monitored as an estimate of methyimercury concentration in fish, would continue to be an accurate indicator of methyimercury contamination in those fish that were exposed to high concentrations of dissolved inorganic mercury. Methods Redbreast sunfish (Lepom/s aw/tus) were collected by backpack electrofishing and angling from sites in East Fork Poplar Creek above, within, and below the settling basin at the boundary of the Y-12 Plant (Fig 1) at six month intervals between November/December 1991 and May/Jane 1993. The fish were placed on ice immediately, and filleted and skinned within 24 h of capture. A 2-3 g sample of the anterior dorsal portion of the axial muscle was excised, wrapped in heavy duty aluminum foil, and frozen at -15" C until analyzed. Samples were analyzed for total mercury by acid digestion, reduction with stannons chloride, and cold vapor atomic absorption spectroscopy (EPA 1991, procedure 245.6) by the analytical chemistry division at Oak Ridge National Laboratory. Mercury speciation analyses were conducted by Brooks Rand, LTD. using a modification of the procedure developed by Bloom (1989). In this procedure homogenized tissue samples were subjected to KOI-I/methanol digestion, aqueous phase ethylation, gas chromatographic separation of derivatives of methylmercury and inorganic mercury and detection by cold vapor atomic fluorescence spectroscopy. Comparison of total mercury concentrations in split samples of the same fish analyzed by ORNL using EPA 245.6 and total mercury concentrations (E inorganic and methylmercury) determined by Brooks Rand agreed well, averaging 1.16 and 1.08 ~g/g, respectively (nffi20). The mean difference (± SE) between individual split samples analyzed by the two labs was 0.08 ± 0.02 #g/g, which, although small, was statistically significant (two tailed t-test on paired comparisons, p < 0.05). Results and Discussion
In November/December 1991 and May/June 1992, prior to dechlorination of upper East Fork Poplar Creek, mean total mercury concentrations in the muscle of redbreast sunfish, the most abundant sport/food fish in the creek, were <1/~g/g at all sites (Fig. 2). When fish were collected in December 1992 and May 1993 from the previously uusampled TRCimpacted reach (kin 24.8) following dechlorination, mercury concentrations in sunfish at that site were substantially higher than those found at the downstream sites (Fig 2), averaging
783
nearly twice the concentration found at the next most contaminated site. The higher concentrations of dissolved inorganic mercury at the headwater site, coupled with the observed rapid rates of accumulation of inorganic mercury in laboratory studies (Shoper 1974, Kindon 1993, Ribeyre and Boudou 1984, Newman and Doubet 1989), su88ested that much of the difference in mercury concentrations in fish between the headwater and downstream sites might be a result of the accumulation of inorganic mercury.
Before dechlorination 1.2
0. ;;=,,.,, 0. 0.
0.
1.6 1.4 1.2 ]
,..,= == L.
0.8 0.6 0.4 0.2 0 T
SITE (km upstream from mouth)
Fig. 2-
Mean mercury concentrations in axial muscle tissue of redbreast sunfish collected in the year before (Nov 1991/May 1992) vs the year after (Dec 1992/May 1993) de.chlorination of upper East Fork Poplar Creek. N = 16 samples per site for each period, error bars are SE.
Inorganic mercury concentrations were indeed greater in fish from the headwater site than they were in fish from lower reaches of the stream. However, the predominant form of mercury remained methylmercury, even at the uppermost site where it averaged 84 ± 4% (± SD, n--8) of the total mercury content (Fig 3). Fish collected from the headwater site
784
shortly after dechiorination was initiated had a higher average concentration of total mercury than fish collected from the same site six months later, but the fraction of the mercury that was methylmercury (83 + 5, 84 ± 4%) was the same on both dates (Fig 3).
At the
downstream sites (ian 23.4 and 18.2), the methylmercury fraction of the total mercury in fish was nearly 100% (Fig 3), averaging 96.5 + 2.6% (mean + SO, nffi8).
The direct accumulation of inorganic mercury from water by fish is both rapid and considerable. Inorganic mercury has a bioconcentration factor of approximately 500 -1000 in laboratory studies, and steady state is likely to be attained within 1 -2 weeks (Schoper 1974, Kramer and Neidhart 1975, Ribeyre and Boudou 1984, Newman and Doubet 1989, Kindon 1993). If a dissolved inorganic mercury concentration of 2 ~g/L is assumed typical of the headwaters of East Fork Poplar Creek, inorganic mercury concentrations of 1.0 ~g/g or greater would be expected in fish. However, mean concentrations of inorganic mercury in sunfish at that site were only 0.2 - 0.3 ~g/g. 2.5
2.0
,,•
1.5
1.0
0.5
0.0 EFK24.8, Dec 92
Fig. 3.
EFK24.8 ~
EFK23.5 EFK23.4 May93
EFKI8.2
Forms of mercury in muscle tissue of redbreast sunfish from upper East Fork Poplar Creek. Values are means of four fish.
Our results suggest that the presence of dissolved inorganic mercury at I - 2 ~g/L is unlikely to result in substantial accumulation of inorganic mercury in fish, relative to the accumulation of methylmercury expected to occur in a mercury-contaminated system. While the assumption that all mercury accumulated by fish in such a system is methylmercury may
785
be incorrect, the magnitude of the error associated with that assumption is likely to be small. Fish from reaches of stream containing high dissolved inorganic mercury accumulated higher concentrations of methylmercury than fish at the next site downstream, where total aqueous mercury concentrations were similar but most mercury was particle-associated rather than dissolved.
This observation suggests that dissolved inorganic mercury is more readily
converted to methylmercuzy by microorganisms than panicle associated mercury, and that natural processes that act to sequester mercury in sediments and suspended particulates may act to lessen the production of methylmercury in contaminated waters. If that is the case, remedial efforts that eliminate inputs of dissolved inorganic mercury may be effective at reducing mercury concentrations in fish in the upper reaches of the stream. Ac$mowiedgeme~ts We thank W. R. Hill and A. J. Stewart, ORNL Environmental Sciences Division, for reviewing the manuscript. This work was sponsored by the Oak Ridge Y-12 Plant, Health, Safety and Environment Division. ORNL and the Y-12 Plant are managed by Martin Marietta Energy Systems, Inc., under contract DE-AC05-840R21400 with the U.S. Department of Energy. Publication No. 4342, Environmental Sciences Division, ORNL References
Bloom, N.S. 1989. Determination of Picogram Levels of Methylmercury by Aqueous Phase Ethylation, followed by Cryogenic Gas Chromatography with Cold Vapour Atomic Fluorescence Detection. Can. J. Fish Aquat. Sci. 46:1131-1140. Bloom, N.S.
1992. On the Chemical Form of Mercury in Edible Fish and Marine
Invertebrate Tissue. Can J. Fish. Aquat. Sci. 49:1010-1017. Burrows, W. D. and P. A. Krenkel.
1973. Studies on the Uptake and Loss of
Methylmercury-203 by Bluegills (Lepom/.vmacrochin~ Raf.). Environ. Sci. TechnoL 7:11271130. Clarkson, T. W. and D. O. Marsh. 1982. Mercury Toxicity in Man. in A. S. Prasad (ed.). Clinical, Biochemical, and Nutritional Aspects of Trace Elements, Vol. 6. Alan R. Liss, Inc., New York.
786
Elwood, J. W., R. R. Turner, R. B. Cook, and M. A. Bogle. 1988. Behavior and Fish Uptake of Mercury in a Contaminated Stream. Proceedings, 6th International Conference on Heavy Metals in the Environment, New Orleans, La., Sept. 15-18, 1987, CEP Consultants Ltd., Edinburgh, U.K. Huckabee, J. W., J. W. Elwood, and S. G. Hildebrand. 1979. The Biogeochemistry of Mercury in the Environment. Elsevier/North Holland Biomedical Press, NY. p 277. Kindon, S.R. 1993. Uptake, Bioaccumulation, and Elimination of Elemental Mercury by Blacknose Dace (Rh/mc'hthys atraadus).
M.S. Thesis, University of Tennessee,
Knoxville, TN. Kornegay, F. C., D. C. West, R. A. Evans, M. F. Tardiff, F. D. Adams, and P.C. Mucke. 1992. Oak Ridge Reservation Environmental Report for 1991 ES/ESH-22/V1. Environmental, Safety, and Health Compliance and Environmental Management Staffs, Oak Ridge Y-12 Plant, Oak Ridge National Laboratory, and Oak Ridge K-25 Site, Martin Marietta Energy Systems, Inc., Oak Ridge, Tennessee. Kornegay, F. C., D. C. West, L G. Scipe, J. B. Murphy, L W. Macmahon, and W. S. Koncinski. 1993. Oak Ridge Reservation Environmental Report for 1992 ES/ESH-31N1. Environmental, Safety, and Health Compliance and Environmental Management Staffs, Oak Ridge Y-12 Plant, Oak Ridge National Laboratory, and Oak Ridge K-25 Site, Martin Marietta Energy Systems, Inc., Oak Ridge, Tennessee. Kramer, H. J. and B. Neidhart. 1975. The Behaviour of Mercury in the System Water-Fish. Bull. Environ. Contam. Toxicol. 14, 699-704. Newman, M. C. and D. K. Doubet. 1989. Size-dependence of Mercury (II) Accumulation Kinetics in the mosquitofish, Gambusia affmb (Baird and Girard). Arch. Environ. Contain. Tox/col. 18:819 - 825. Olson, K. R., H. L Bergman, and P. O. Fromm. 1973. Uptake of Methylmercuric Chloride and Mercuric Chloride by Trout: A Study of Uptake Pathways into the Whole Animal and Uptake by Erythrocytes in vitro. J. Fish. Res. Board Can. 30:1293 - 1299. Peterson, M. J., G. R. Southworth, and IL D. Ham. 1994. Effect of sublethal chlorinated discharges on PCB accumulation in transplanted asiatic clams. Water, Air, and Soil Pollution. 73:169-178.
787
Ri'beyre, F. and A. Boudou. 1984. Bioaccumulation et Repartition Tisslaire du Mercure HgCI2 et CH3HgCI -Chez Sa/mo ga/rdned Apres Contamination Par Voie Directe. Water, Air, and Soil Pollution. 23, 169-186. Schoper, N. J.
1974. The Uptake, Biotransformation, and Elimination of Elemental
Mercury by Fish. M.S. Thesis, University of Georgia, Athens,Ga. Southworth, G. R., Turner, R. R., and B. D. Nour~. 1993. Site-Specific Water Quality Criterion for Total Mercury in East Fork Poplar Creek Downstream from the Oak Ridge Y-12 Plant. Y/ER-126. U. S. Dept. of Energy Y-12 Plant, Oak Ridge, Tennessee. 19 pp.
Pergamon
0045-6535(94)00407-2
Elsevier Science Ltd Printed in Great Britain
FORM OF MERCURY IN SWREAM FISH EXPOSED TO HIGH O3N~TIONS
OF DISSOLVED INORGANIC MERCURY
G. R. Southworth', R. R. Turner, M. J. Peterson, and M. A. Bogle Environmental Sciences Division, Oak Ridge National Laboratory, P. O. Box 2008, Bldg. 1505, MS 6036, Oak Ridge, Tennessee 37831-6036. (Received in USA 3 August 1994; accepted 8 September 1994)
Abstract The form of mercury predominating in mercury-contaminated fish from both pristine and industrialized waters in North America and Europe has almost universally been methylmercury. Sunfish (Lepom/s aur/tus) living in a stream contaminated with 0.5 -1 t~g/L dissolved inorganic mercury accumulated greater concentrations of total mercury at headwater sites, where the dissolved mercury concentrations were greatest, than they did at downstream sites.
However, despite evidence from laboratory studies that dissolved
inorganic mercury is rapidly accumulated by fish without transformation to methylmercury, methylmercury constituted 85% or more of the total mercury concentration in fish at all sites. Introduction Although methylmercury occurs at small concentrations relative to inorganic mercury in natural waters, the mercury content of axial muscle of fish from both pristine and contaminated freshwater generally is greater than 90% methylmercury (Bloom 1992, Huckabee et al. 1979).
The toxicological hazard of eating fish contaminated with
methylmercury is much greater than that of ingesting similar quantities of inorganic mercury (Clarkson and Marsh 1982). Laboratory studies have demonstrated that dissolved inorganic mercury, in both elemental and oxidized forms, is readily taken up directly from water, and is excreted slowly (Oison et al. 1973, Schoper 1974, Kramer and Neidhart 1975, Ribeyre and Boudou 1984, Neuman and Doubet 1989, Kindon 1993). Inorganic mercury accumulated in this manner is not converted to methylmercury within the fish. Fish exposed to high (>0.1/~g/L) concentrations of 779
780
dissolved inorganic mercury would be expected to accumulate detectable concentrations of inorganic mercury.
East Fork Poplar Creek originates as ground water and single-pass cooling water discharges within the U.S. Department of Energy Y-12 Plant in Oak Ridge, Tennessee (Fig. 1). It emerges from a complex underground storm sewer network, and flows for approximately 1.8 lan through the industrial facility as a straight, shallow, rock and gravel bottomed ditch. It then flows through a concrete dispersion channel from which it is discharged at several points to a plastic lined, 1.1 ha. settling pond. Below an overflow discharge from the pond, the creek flows through a mixture of urban and rural landscapes for 23.5 km before emptying into an embayment of Watts Bar Reservoir (Fig. 1).
Aqueous mercury concentrations have averaged 1.3 #g/L in East Fork Poplar Creek at the Y-12 Plant over the 1991/1992 period (Kornegay et al. 1992, 1993). Concentrations of total aqueous mercury decline rapidly with distance downstream from the Y-12 Plant, dropping to about 0.1 ~g/L 16 km downstream. Studies of the aqueous speciation of mercury in EFPC have demonstrated that total aqueous mercury is predominantly particle-associated inorganic mercury at all sites from the settling pond at kilometer 23.5 downstream (Southworth, Turner, and Nourse 1993). Methylmercury concentrations are far lower than inorganic mercury concentrations; typically about 5 x 10"~ ~g/L.
Total mercury
concentrations above and below the settling pond at km 23.5 differ little; however, speciation of inorganic mercury is markedly different between the headwater reach above the pond and downstream reaches. In the headwaters, dissolved inorganic mercury is the predominant form, accounting for approximately 50% or more of the waterborne mercury. Below the settling pond, dissolved mercury only accounts for about 15% of the total aqueous mercmy (Southworth et al. 1993).
Thus, East Fork Poplar Creek differs from most aquatic systems in which mercury accumulation in fish is a concern in that dissolved inorganic mercury concentrations in the headwaters of the stream are substantial, often exceeding 1.0 ~g/L. Prior to December 1992, fish populations in the reach of the stream where dissolved mercury was highest were small and transitory because of the presence of near toxic concentrations of total residual chlorine (TRC) in the water (Peterson et aL 1994).
In November 1992 a system was
installed to add roughly stoichiometric concentrations of sodium bisulfite to the discharges respons~le for most of the TRC in the creek. This action, eliminated toxic concentrations of TRC in the creek and allowed the rapid colonization of the upper reaches of the creek with fish. As a result, the large numbers of fish were exposed to substantial concentrations of dissolved inorganic mercury.
Fig. 1.
2
I
I
3km I i 1 mile
v
RM,IDOK
J
24.8
Sampling sites for redbreast sunfish in East Fork Poplar Creek in Oak Ridge, Tennessee. Sites are designated by distance (kin) upstream from the mouth of East Fork Poplar Creek.
0.5
I
1
•
I~PIARCR~x
ORNL-DWG 93M-9316R
oo
782
The objective of the study described in this paper was to ascertain whether measurements of total mercury in fish, previously monitored as an estimate of methyimercury concentration in fish, would continue to be an accurate indicator of methyimercury contamination in those fish that were exposed to high concentrations of dissolved inorganic mercury. Methods Redbreast sunfish (Lepom/s aw/tus) were collected by backpack electrofishing and angling from sites in East Fork Poplar Creek above, within, and below the settling basin at the boundary of the Y-12 Plant (Fig 1) at six month intervals between November/December 1991 and May/Jane 1993. The fish were placed on ice immediately, and filleted and skinned within 24 h of capture. A 2-3 g sample of the anterior dorsal portion of the axial muscle was excised, wrapped in heavy duty aluminum foil, and frozen at -15" C until analyzed. Samples were analyzed for total mercury by acid digestion, reduction with stannons chloride, and cold vapor atomic absorption spectroscopy (EPA 1991, procedure 245.6) by the analytical chemistry division at Oak Ridge National Laboratory. Mercury speciation analyses were conducted by Brooks Rand, LTD. using a modification of the procedure developed by Bloom (1989). In this procedure homogenized tissue samples were subjected to KOI-I/methanol digestion, aqueous phase ethylation, gas chromatographic separation of derivatives of methylmercury and inorganic mercury and detection by cold vapor atomic fluorescence spectroscopy. Comparison of total mercury concentrations in split samples of the same fish analyzed by ORNL using EPA 245.6 and total mercury concentrations (E inorganic and methylmercury) determined by Brooks Rand agreed well, averaging 1.16 and 1.08 ~g/g, respectively (nffi20). The mean difference (± SE) between individual split samples analyzed by the two labs was 0.08 ± 0.02 #g/g, which, although small, was statistically significant (two tailed t-test on paired comparisons, p < 0.05). Results and Discussion
In November/December 1991 and May/June 1992, prior to dechlorination of upper East Fork Poplar Creek, mean total mercury concentrations in the muscle of redbreast sunfish, the most abundant sport/food fish in the creek, were <1/~g/g at all sites (Fig. 2). When fish were collected in December 1992 and May 1993 from the previously uusampled TRCimpacted reach (kin 24.8) following dechlorination, mercury concentrations in sunfish at that site were substantially higher than those found at the downstream sites (Fig 2), averaging
783
nearly twice the concentration found at the next most contaminated site. The higher concentrations of dissolved inorganic mercury at the headwater site, coupled with the observed rapid rates of accumulation of inorganic mercury in laboratory studies (Shoper 1974, Kindon 1993, Ribeyre and Boudou 1984, Newman and Doubet 1989), su88ested that much of the difference in mercury concentrations in fish between the headwater and downstream sites might be a result of the accumulation of inorganic mercury.
Before dechlorination 1.2
0. ;;=,,.,, 0. 0.
0.
1.6 1.4 1.2 ]
,..,= == L.
0.8 0.6 0.4 0.2 0 T
SITE (km upstream from mouth)
Fig. 2-
Mean mercury concentrations in axial muscle tissue of redbreast sunfish collected in the year before (Nov 1991/May 1992) vs the year after (Dec 1992/May 1993) de.chlorination of upper East Fork Poplar Creek. N = 16 samples per site for each period, error bars are SE.
Inorganic mercury concentrations were indeed greater in fish from the headwater site than they were in fish from lower reaches of the stream. However, the predominant form of mercury remained methylmercury, even at the uppermost site where it averaged 84 ± 4% (± SD, n--8) of the total mercury content (Fig 3). Fish collected from the headwater site
784
shortly after dechiorination was initiated had a higher average concentration of total mercury than fish collected from the same site six months later, but the fraction of the mercury that was methylmercury (83 + 5, 84 ± 4%) was the same on both dates (Fig 3).
At the
downstream sites (ian 23.4 and 18.2), the methylmercury fraction of the total mercury in fish was nearly 100% (Fig 3), averaging 96.5 + 2.6% (mean + SO, nffi8).
The direct accumulation of inorganic mercury from water by fish is both rapid and considerable. Inorganic mercury has a bioconcentration factor of approximately 500 -1000 in laboratory studies, and steady state is likely to be attained within 1 -2 weeks (Schoper 1974, Kramer and Neidhart 1975, Ribeyre and Boudou 1984, Newman and Doubet 1989, Kindon 1993). If a dissolved inorganic mercury concentration of 2 ~g/L is assumed typical of the headwaters of East Fork Poplar Creek, inorganic mercury concentrations of 1.0 ~g/g or greater would be expected in fish. However, mean concentrations of inorganic mercury in sunfish at that site were only 0.2 - 0.3 ~g/g. 2.5
2.0
,,•
1.5
1.0
0.5
0.0 EFK24.8, Dec 92
Fig. 3.
EFK24.8 ~
EFK23.5 EFK23.4 May93
EFKI8.2
Forms of mercury in muscle tissue of redbreast sunfish from upper East Fork Poplar Creek. Values are means of four fish.
Our results suggest that the presence of dissolved inorganic mercury at I - 2 ~g/L is unlikely to result in substantial accumulation of inorganic mercury in fish, relative to the accumulation of methylmercury expected to occur in a mercury-contaminated system. While the assumption that all mercury accumulated by fish in such a system is methylmercury may
785
be incorrect, the magnitude of the error associated with that assumption is likely to be small. Fish from reaches of stream containing high dissolved inorganic mercury accumulated higher concentrations of methylmercury than fish at the next site downstream, where total aqueous mercury concentrations were similar but most mercury was particle-associated rather than dissolved.
This observation suggests that dissolved inorganic mercury is more readily
converted to methylmercuzy by microorganisms than panicle associated mercury, and that natural processes that act to sequester mercury in sediments and suspended particulates may act to lessen the production of methylmercury in contaminated waters. If that is the case, remedial efforts that eliminate inputs of dissolved inorganic mercury may be effective at reducing mercury concentrations in fish in the upper reaches of the stream. Ac$mowiedgeme~ts We thank W. R. Hill and A. J. Stewart, ORNL Environmental Sciences Division, for reviewing the manuscript. This work was sponsored by the Oak Ridge Y-12 Plant, Health, Safety and Environment Division. ORNL and the Y-12 Plant are managed by Martin Marietta Energy Systems, Inc., under contract DE-AC05-840R21400 with the U.S. Department of Energy. Publication No. 4342, Environmental Sciences Division, ORNL References
Bloom, N.S. 1989. Determination of Picogram Levels of Methylmercury by Aqueous Phase Ethylation, followed by Cryogenic Gas Chromatography with Cold Vapour Atomic Fluorescence Detection. Can. J. Fish Aquat. Sci. 46:1131-1140. Bloom, N.S.
1992. On the Chemical Form of Mercury in Edible Fish and Marine
Invertebrate Tissue. Can J. Fish. Aquat. Sci. 49:1010-1017. Burrows, W. D. and P. A. Krenkel.
1973. Studies on the Uptake and Loss of
Methylmercury-203 by Bluegills (Lepom/.vmacrochin~ Raf.). Environ. Sci. TechnoL 7:11271130. Clarkson, T. W. and D. O. Marsh. 1982. Mercury Toxicity in Man. in A. S. Prasad (ed.). Clinical, Biochemical, and Nutritional Aspects of Trace Elements, Vol. 6. Alan R. Liss, Inc., New York.
786
Elwood, J. W., R. R. Turner, R. B. Cook, and M. A. Bogle. 1988. Behavior and Fish Uptake of Mercury in a Contaminated Stream. Proceedings, 6th International Conference on Heavy Metals in the Environment, New Orleans, La., Sept. 15-18, 1987, CEP Consultants Ltd., Edinburgh, U.K. Huckabee, J. W., J. W. Elwood, and S. G. Hildebrand. 1979. The Biogeochemistry of Mercury in the Environment. Elsevier/North Holland Biomedical Press, NY. p 277. Kindon, S.R. 1993. Uptake, Bioaccumulation, and Elimination of Elemental Mercury by Blacknose Dace (Rh/mc'hthys atraadus).
M.S. Thesis, University of Tennessee,
Knoxville, TN. Kornegay, F. C., D. C. West, R. A. Evans, M. F. Tardiff, F. D. Adams, and P.C. Mucke. 1992. Oak Ridge Reservation Environmental Report for 1991 ES/ESH-22/V1. Environmental, Safety, and Health Compliance and Environmental Management Staffs, Oak Ridge Y-12 Plant, Oak Ridge National Laboratory, and Oak Ridge K-25 Site, Martin Marietta Energy Systems, Inc., Oak Ridge, Tennessee. Kornegay, F. C., D. C. West, L G. Scipe, J. B. Murphy, L W. Macmahon, and W. S. Koncinski. 1993. Oak Ridge Reservation Environmental Report for 1992 ES/ESH-31N1. Environmental, Safety, and Health Compliance and Environmental Management Staffs, Oak Ridge Y-12 Plant, Oak Ridge National Laboratory, and Oak Ridge K-25 Site, Martin Marietta Energy Systems, Inc., Oak Ridge, Tennessee. Kramer, H. J. and B. Neidhart. 1975. The Behaviour of Mercury in the System Water-Fish. Bull. Environ. Contam. Toxicol. 14, 699-704. Newman, M. C. and D. K. Doubet. 1989. Size-dependence of Mercury (II) Accumulation Kinetics in the mosquitofish, Gambusia affmb (Baird and Girard). Arch. Environ. Contain. Tox/col. 18:819 - 825. Olson, K. R., H. L Bergman, and P. O. Fromm. 1973. Uptake of Methylmercuric Chloride and Mercuric Chloride by Trout: A Study of Uptake Pathways into the Whole Animal and Uptake by Erythrocytes in vitro. J. Fish. Res. Board Can. 30:1293 - 1299. Peterson, M. J., G. R. Southworth, and IL D. Ham. 1994. Effect of sublethal chlorinated discharges on PCB accumulation in transplanted asiatic clams. Water, Air, and Soil Pollution. 73:169-178.
787
Ri'beyre, F. and A. Boudou. 1984. Bioaccumulation et Repartition Tisslaire du Mercure HgCI2 et CH3HgCI -Chez Sa/mo ga/rdned Apres Contamination Par Voie Directe. Water, Air, and Soil Pollution. 23, 169-186. Schoper, N. J.
1974. The Uptake, Biotransformation, and Elimination of Elemental
Mercury by Fish. M.S. Thesis, University of Georgia, Athens,Ga. Southworth, G. R., Turner, R. R., and B. D. Nour~. 1993. Site-Specific Water Quality Criterion for Total Mercury in East Fork Poplar Creek Downstream from the Oak Ridge Y-12 Plant. Y/ER-126. U. S. Dept. of Energy Y-12 Plant, Oak Ridge, Tennessee. 19 pp.