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Methylmercury Contamination in Fish and Shellfish
(Released February 2007)

 
  by Laura Griesbauer  

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  1. Bioaccumulation and Trophic Transfer of Methylmercury in Long Island Sound

    Chad R. Hammerschmidt and William F. Fitzgerald.

    Archives of Environmental Contamination and Toxicology, Vol. 51, No. 3, Oct 2006, pp. 416-424.

    Humans are exposed to methylmercury (MeHg) principally by consumption of marine fish. The coastal zone supports the majority of marine fish production, and may therefore be an important source of MeHg to humans; however, little is known about the bioaccumulation of MeHg in near-shore marine ecosystems. We examined MeHg in microseston, zooplankton, a decapod crustacean, and four representative species of finfish that differ in trophic status and/or prey selection in Long Island Sound (LIS), a large coastal embayment in the northeastern United States. MeHg biomagnifies in LIS; levels in microseston were 10 super(4.2) greater than those in water and 2.3-fold less than zooplankton. MeHg concentrations were related positively to fish length for each species, but often varied considerably among larger individuals. This may be due to differences in the past dietary MeHg exposure of these fish, some of which are migratory. Sedimentary production and mobilization can account for most of the MeHg in microseston of LIS, and by extension, other near-shore locations. Hence, much of the MeHg in higher trophic levels of coastal marine ecosystems, including fishes destined for human consumption, may be attributed to net sedimentary production and dietary bioaccumulation.

  2. Daily intake of arsenic, cadmium, mercury, and lead by consumption of edible marine species

    Gemma Falcó, Juan M. Llobet, Ana Bocio and José L. Domingo.

    Journal of agricultural and food chemistry, Vol. 54, No. 16, Aug 9 2006, pp. 6106-6112.

    The daily intake of arsenic (As), cadmium (Cd), mercury (Hg), and lead (Pb) through the consumption of 14 edible marine species by the general population of Catalonia, Spain, was estimated. Health risks derived from this intake were also assessed. In March-April 2005, samples of sardine, tuna, anchovy, mackerel, swordfish, salmon, hake, red mullet, sole, cuttlefish, squid, clam, mussel, and shrimp were randomly acquired in six cities of Catalonia. Concentrations of As, Cd, Hg, and Pb were determined by ICP-MS. On the basis of recent fish and seafood consumption data, the daily intake of these elements was calculated for eight age/sex groups of the population. The highest As concentrations were found in red mullet, 16.6 microg/g of fresh weight, whereas clam and mussel (0.14 and 0.13 microg/g of fresh weight, respectively) were the species with the highest Cd levels. In turn, swordfish (1.93 microg/g of fresh weight) and mussel and salmon (0.15 and 0.10 microg/g of fresh weight) showed the highest concentrations of Hg and Pb, respectively. The highest metal intake through fish and seafood consumption corresponded to As (217.7 microg/day), Cd (1.34 microg/day), and Pb (2.48 microg/day) for male seniors, whereas that of Hg was observed in male adults (9.89 microg/day). The daily intake through fish and seafood consumption of these elements was compared with the provisional tolerable weekly intakes (PTWI). The intakes of As, Cd, Pb, and total Hg by the population of Catalonia were below the respective PTWI values. However, the estimated intake of methylmercury for boys, 1.96 microg/kg/week, was over the PTWI.

  3. The effect of fish consumption on blood mercury levels of pregnant women

    Euy Hyuk Kim, In Kyu Kim, Ja Young Kwon, Sang Wun Kim and Yong Won Park.

    Yonsei medical journal, Vol. 47, No. 5, Oct 31 2006, pp. 626-633.

    In the present study, we examined the relationship between average fish consumption, as well as the type of fish consumed and levels of mercury in the blood of pregnant women. We also performed follow-up studies to determine if blood mercury levels were decreased after counseling and prenatal education. To examine these potential relationships, pregnant women were divided into two groups: a study group was educated to restrict fish intake, whereas a control group did not receive any prenatal education regarding fish consumption. We measured blood mercury level and performed follow-up studies during the third trimester to examine any differences between the two groups. Out of the 63 pregnant women who participated in our study, we performed follow- up studies with 19 pregnant women from the study group and 12 pregnant women from control group. The average initial blood mercury level of both groups was 2.94 microg/L, with a range of 0.14 to 10.75 microg/L. Blood mercury level in the group who ate fish more than four times per month was significantly higher than that of the group who did not consume fish (p = 0.02). In follow-up studies, blood mercury levels were decreased in the study group but slightly increased in the control group (p = 0.014). The maternal blood mercury level in late pregnancy was positively correlated with mercury levels of cord blood (r = 0.58, p = 0.047), which was almost twice the level found in maternal blood. Pregnant women who consume a large amount of fish may have high blood mercury levels. Further, cord blood mercury levels were much higher than that of maternal blood. Because the level of fish intake appears to influence blood mercury level, preconceptual education might be necessary in order decrease fish consumption.

  4. Environmental controls on the speciation and distribution of mercury in coastal sediments

    E. M. Sunderland, F. A. P. C. Gobas, B. A. Branfireun and A. Heyes.

    Marine Chemistry, Vol. 102, No. 1-2, Nov 2006, pp. 111-123.

    Methylmercury production by sulfate reducing bacteria in coastal sediments leads to bioaccumulation of mercury in fish, shellfish, and ultimately humans. Sulfur, organic carbon, and sediment structure and composition can all affect methylmercury production by changing the amount of bioavailable inorganic mercury and by stimulating the activity of methylating microbes. This study investigates total and methylmercury in solids and porewaters relative to total sulfide concentration, redox potential, sediment grain size, and total organic carbon in a range of sediment types from the Bay of Fundy region of Canada. Using these data, we construct a conceptual model of the biogeochemical environment surrounding methylating microbes in high sulfide, organically enriched sediments. Whereas other studies of methylmercury dynamics measured porewater sulfide concentrations in relatively low-sulfide systems (~20-300 mu M), we measured total sulfide levels using a method developed to indicate organic enrichment across a much wider range of sulfidic sediments (10-4000 mu M). We observed that higher sulfide concentrations correspond to an elevated fraction of mercury in methylated form suggesting higher net methylation rates in these sediments. This relationship is strongest in sediments that are moderately impacted by organic enrichment, but weak in less impacted, aerobic sediments. Higher sulfide concentrations in porewaters containing dissolved organic matter appear to yield a geochemical environment that is conducive to uptake of Hg(II) by methylating bacteria. Data collected in this study imply that moderate levels of organic enrichment through fish farming may enhance methylmercury production in the Bay of Fundy.

  5. An examination of the factors influencing the flux of mercury, methylmercury and other constituents from estuarine sediment

    R. P. Mason, E. H. Kim, J. Cornwell and D. Heyes.

    Marine Chemistry, Vol. 102, No. 1-2, Nov 2006, pp. 96-110.

    The flux of mercury (Hg), methylmercury (MeHg), other metals (zinc (Zn), cadmium (Cd) and lead (Pb)), arsenic (As), nutrients, dissolved organic carbon (DOC) and sulfide from sediments collected in Baltimore Harbor, Maryland, USA were measured over the period of approximately 5 days. Fluxes of the various constituents changed over time and the magnitude and direction of the fluxes of the major metals (Fe and Mn) correlated with the extent of oxygen depletion and the presence or absence of sulfide in the water column. It appeared that the heavy metals, Zn, Cd, Pb, and Hg, were taken up into the sediment under hypoxic/anoxic conditions but were released under more oxic conditions. The fluxes of As and phosphate followed that of Fe. Overall, the fluxes of these constituents confirmed expectation based on thermodynamic considerations. For Hg and MeHg, there appeared to be little relationship between their flux and that of the major metals, or sulfide, or DOC. For MeHg, there is a suggestion that processes occurring at the sediment /water interface, including methylation, may play a major role in determining the extent of the MeHg flux to the water column.

  6. Japan remembers Minamata

    Justin McCurry.

    Lancet, Vol. 367, No. 9505, 2006 Jan 14 2006, pp. 99-100.

  7. Methylmercury Concentrations in Fish from Tidal Waters of The Chesapeake Bay

    Robert P. Mason, Deborah Heyes and Auja Sveinsdottir.

    Archives of Environmental Contamination and Toxicology, Vol. 51, No. 3, Oct 2006, pp. 425-437.

    Striped bass (Morone saxatilis), white perch (Morone Americana), and largemouth bass (Micropterus salmoides) were collected in the Chesapeake Bay mainstem and tributaries and analyzed for total mercury (Hg) and methylmercury (MeHg) content. Striped bass are anadromous, whereas white perch and largemouth bass are resident species, and the largemouth bass are also restricted to the tidal fresh portion of the Bay. Total Hg and MeHg concentrations in striped bass increased with fish size, and large fish (>7.5 kg wet weight) tended to have MeHg concentrations of 300 ng g super(-1) or greater. On average, the striped bass MeHg concentration was 120 plus or minus 100 ng g super(-1) and the fraction of the total Hg as MeHg was 65 plus or minus 22%. Reasons for the lower relative MeHg content are discussed. Otolith strontium/calcium ratios were also determined to examine whether migration had a significant impact on MeHg content in striped bass. Resident fish did appear to have a higher MeHg burden than the more migratory fish of similar size. Largemouth bass and white perch tended to have low MeHg content (respectively, 14 plus or minus 7 and 13 plus or minus 11 ng g super(-1); all fish <1 kg wet weight), and the white perch also had a low %MeHg (28 plus or minus 14%), reflecting their mostly planktivorous lifestyle. A comparison of largemouth bass and striped bass MeHg concentrations for the estuarine fish with those of fish in Maryland reservoirs of similar size showed that the estuarine fish have much lower MeHg burdens. Differences in MeHg concentration in the estuarine waters compared to the reservoir waters likely account for much of this difference, although the importance of other factors is also discussed.

  8. Recent Advances in Evaluation of Health Effects on Mercury with Special Reference to Methylmercury: A Minireview

    Shun'ichi Honda, Lars Hylander and Mineshi Sakamoto.

    Environmental Health and Preventive Medicine, Vol. 11, No. 4, 2006, pp. 171-176.

    Mercury is a metal that has long been used because of its many advantages from the physical and chemical points of view. However, mercury is very toxic to many life forms, including humans, and mercury poisoning has repeatedly been reported. The main chemical forms of mercury are elemental mercury (Hg super(0)), divalent mercury (Hg super(2+)) and methylmercury (CH sub(3)-Hg super(+)), the toxicities and metabolisms of which differ from each other. Methylmercury is converted from divalent mercury and is a well-known neurotoxicant, having been identified as the cause of Minamata disease. It bioaccumulates in the environment and is biomagnified in the food web. Human exposure to methylmercury is mainly through fish and seafood consumption. Methylmercury easily penetrates the blood-brain barrier and causes damage to the central nervous system, particularly in fetuses. In this paper, we summarize the global mercury cycle and mercury metabolism, toxicity and exposure evaluation, and the thresholds for the onset of symptoms after exposure to different chemical forms of mercury, particularly methylmercury.

  9. The Toxicology of Mercury and Its Chemical Compounds

    Thomas W. Clarkson and Laszlo Magos.

    Critical Reviews in Toxicology, Vol. 36, No. 8, 2006 Sep. 2006, pp. 609-662.

  10. Bioaccumulation Factors for Mercury in Stream Fish

    G. R. Southworth, M. J. Peterson and M. A. Bogle.

    Environmental Practice, Vol. 6, No. 2, Jun 2004, pp. 135-143.

    The bioaccumulation of methylmercury in fish is a complex process affected by many site-specific environmental factors. The US Environmental Protection Agency (USEPA) recently recommended changing the basis for expressing the ambient water quality criterion for mercury from an aqueous concentration to a measure of the methylmercury concentration in fish. This change would make the regulation of mercury in surface waters a site-specific exercise in which fish-based bioaccumulation factors (BAF; the ratio of mercury concentration in fish to the concentration of mercury in water) are used to calculate aqueous concentration limits for total mercury. These limits would then be used to allocate mercury loading among various point and nonpoint sources and guide regulatory actions. In order for this approach to succeed, it is critical that the sitespecific BAFs and methylmercury:total mercury conversion factors be independent of aqueous total mercury concentration (Hg sub(T)). We investigated this relationship by measuring aqueous methylmercury and Hg sub(T)s and mercury in fish in ecologically similar warm-water streams in the southeastern United States. Bioaccumulation factors based on Hg sub(T) in water were found to decrease with increasing Hg sub(T), primarily as a consequence of the reduction in the ratio of aqueous methylmercury to total mercury with increasing Hg sub(T). Methylmercury-based BAFs did not vary as a function of Hg sub(T). The implication of this relationship is that site-specific determination of aqueous Hg sub(T) limits at contaminated sites may use BAFs that would be underestimates of the appropriate BAFs to describe mercury bioaccumulation in the system after mercury inputs have been reduced. In such cases, regulatory limits set using site-specific BAFs might not achieve their intended purpose of reducing mercury contamination in fish to acceptable concentrations.

  11. Environmental mercury exposure in children: South China's experience

    Patrick Ip, Virginia Wong, Marco Ho, Joseph Lee and Wilfred Wong.

    Pediatrics International, Vol. 46, No. 6, Dec 2004, pp. 715-721.

    Background: Environmental mercury levels significantly increased in the past decades following its increase in industrial applications. In spite of an increasing concern on the potential harmful effects of mercury on children, there is no reported data for the Chinese population. The relationship between dietary habit and environmental mercury exposure in Chinese children was studied. Methods: The hair and blood mercury levels of Chinese children aged above 3 years in 2000 March to September, were studied. Sociodemographic data, dietary habits of the past 6 months, and other risk factors for environmental mercury exposure were collected. Those children with blood mercury levels above the toxic range (i.e. > 45 nmol-L) and their family members were further evaluated and their blood and hair mercury levels were monitored before and after Fishing-Moratorium period (June to August 2000) in South China Sea. Results: Altogether, 137 Chinese children (mean age, 7.2 years) were recruited. The mean hair mercury level was 2.2 p.p.m and the mean blood mercury level was 17.6 nmol-L. There was a strong correlation (r = 0.88) between hair and blood mercury levels in our cohort. Frequency of fish consumption correlated with hair (r = 0.51) and blood (r = 0.54) mercury levels. For those children who consumed fish more than 3 times-week, hair and blood mercury levels were twice as high as those who consumed fish l-3 times-week and threefold of those who never consumed fish. Five children and 12 family members had toxic blood mercury levels. Their blood (P < 0.0001) and hair (P = 0.02) mercury levels dropped significantly after reducing fish consumption during Fishing-Moratorium period. Conclusion: Both blood and hair (i.e. Tissue) mercury levels of children in Hong Kong was elevated and correlated with the frequency of fish consumption.

  12. Fear of Fish: The Contaminant Controversy

    S. Senkowsky.

    Bioscience, Vol. 54, No. 11, Nov 2004, pp. 986-988.

  13. Health Effects of Methylmercury

    Katherine M. Shea, Karen L. Perry and Mona Shah.

    Physicians for Social Responsibility, 2004, pp. .

  14. Maternal and Fetal Mercury and n-3 Polyunsaturated Fatty Acids as a Risk and Benefit of Fish Consumption to Fetus

    M. Sakamoto, M. Kubota, X. J. Liu, K. Murata, K. Nakai and H. Satoh.

    Environmental science & technology, Vol. 38, No. 14, 15 Jul 2004, pp. 3860-3863.

    Maternal fish consumption brings both risks and benefits to the fetus from the standpoint of methylmercury (MeHg) and n-3 PUFA (polyunsaturated fatty acids). MeHg is one of the most risky substances to come through fish consumption, and mercury concentrations in red blood cells (RBC-Hg) are the best biomarker of MeHg exposure. Docosahexaenoic acid (DHA, C22:6n-3), which is one of the most important fatty acids for normal brain development and function, is also derived from fish consumption. Our objective in this study was to examine the relationships between RBC-Hg and plasma fatty acid composition in mother and fetus at parturition. Venous blood samples were collected from 63 pairs of mothers and fetuses (umbilical cord blood) at delivery. In all cases, fetal RBC-Hg levels were higher than maternal RBC-Hg levels. The geometric mean of fetal RBC-Hg was 13.4 ng/g, which was significantly (p < 0.01) higher than that of maternal RBC-Hg (8.41 ng/g). While the average fetal/maternal RBC-Hg ratio was 1.6, the individual ratios varied from 1.08 to 2.19, suggesting considerable individual differences in MeHg concentrations between maternal and fetal circulations at delivery. A significant correlation was observed between maternal and fetal DHA concentrations (r = 0.37, p < 0.01). Further, a significant correlation was observed between RBC-Hg and plasma DHA in fetus (r = 0.35, p < 0.01). These results confirm that both MeHg and DHA which originated from fish consumption transferred from maternal to fetal circulation and existed in the fetal circulation with a positive correlation. Pregnant women in particular need not give up eating fish to obtain such benefits. However, they would do well to at least consume smaller fish, which contains less MeHg, thereby balancing the risks and benefits from fish consumption.

  15. Speciation and bioavailability of mercury in well-mixed estuarine sediments

    E. M. Sunderland, F. A. P. C. Gobas and A. Heyes, et al.

    Marine Chemistry, Vol. 90, No. 1-4, 1 Nov 2004, pp. 91-105.

    Despite regulations controlling anthropogenic mercury sources in North America, high levels of mercury in coastal fish and shellfish are an ongoing problem in Maritime Canada and the Northeastern United States. This study presents sediment core data from a macrotidal estuary located at the mouth of the Bay of Fundy showing stratigraphic profiles of total and methylmercury concentrations and potential methylation rates measured using stable mercury isotopes. The results show that in contrast to the expected methylmercury profile typically observed in unmixed sediments, methylmercury production occurs throughout the estimated 15-cm-thick active surface layer of these well-mixed sediments. The resulting large reservoir of methylmercury in these sediments helps to explain why mercury concentrations in organisms in this system remain high despite emissions reductions. Current management policies should take into account the expected delay in the response time of well-mixed estuarine systems to declines in mercury loading, considering the greater reservoir of historic mercury available in these sediments that can potentially be converted to methylmercury and biomagnify in coastal food chains.

  16. Distribution of mercury over the Atlantic Ocean in 1996 and 1999-2001

    C. Temme, F. Slemr, R. Ebinghaus and J. W. Einax.

    Atmospheric Environment, Vol. 37, No. 14, May 2003, pp. 1889-1897.

    A series of measurements of total gaseous mercury (TGM) made over the Atlantic Ocean in 1977-1980, 1990, and 1994 has been continued by measurements made on board the research vessel (RV) Polarstern during three cruises: from Bremerhaven to Punta Quilla (October-November 1996), Bremerhaven-Cape Town- Antarctica-Cape Town (December 1999-March 2000), and Antarctica-Punta Arenas (February 2001). The data from these cruises are presented and compared with the data from previous cruises. In both hemispheres the average and median TGM concentrations in 1996 and 2000 were comparable to those measured in 1977-1980 but substantially lower than those observed in 1990. TGM measurements on board ships proved to provide a valuable complementary information to measurements by a ground based monitoring network since they show a large-scale distribution and can provide information about sources of mercury and its long-range transport in areas not covered by the present monitoring network.

  17. Potential for Increased Mercury Accumulation in the Estuary Food Web

    J. A. Davis, D. Yee, J. N. Collins, S. E. Schwarzbach and S. N. Luoma.

    San Francisco Estuary and Watershed Science, Vol. 1, No. 1, 2003, pp. .

    Present concentrations of mercury in large portions of San Francisco Bay (Bay), the Sacramento-San Joaquin Delta (Delta), and the Sacramento and San Joaquin rivers are high enough to warrant concern for the health of humans and wildlife. Large scale tidal wetland restoration is currently under consideration as a means of increasing populations of fish species of concern. Tidal wetland restoration activities may lead to increased concentrations of mercury in the estuarine food web and exacerbate the existing mercury problem. This paper evaluates our present ability to predict the local and regional effects of restoration actions on mercury accumulation in aquatic food webs. A sport fish consumption advisory is in place for the Bay, and an advisory is under consideration for the Delta and lower Sacramento and San Joaquin rivers. Mercury concentrations in eggs of several water bird species from the Bay have exceeded the lowest observed effect level. A variety of mercury sources, largely related to historic mercury and gold mining, is present in the watershed and has created a spatially heterogeneous distribution of mercury in the Bay-Delta Estuary. Mercury exists in the environment in a variety of forms and has a complex biogeochemical cycle. The most hazardous form, methylmercury, is produced at a relatively high rate in wetlands and newly flooded aquatic habitats. It is likely that distinct spatial variation on multiple spatial scales exists in net methylmercury production in Bay-Delta tidal wetlands, including variation within each tidal wetland, among tidal wetlands in the same region, and among tidal wetlands in different regions. Understanding this spatial variation and its underlying causes will allow environmental managers to minimize the negative effects of mercury bioaccumulation as a result of restoration activities. Actions needed to reduce the uncertainty associated with this issue include a long term, multifaceted research effort, long term monitoring on local and regional scales, and careful evaluation of individual restoration projects with regard to potential increase of food web mercury.

  18. Variations in the isotope composition of mercury in a freshwater sediment sequence and food web

    T. A. Jackson.

    Canadian Journal of Fisheries and Aquatic Sciences, Vol. 58, No. 1, Jan 2001, pp. 185-196.

    Analysis of a sediment core and food-web animals from the Niagara Basin of Lake Ontario yielded the first recorded evidence for systematic variations in the stable-isotope composition of mercury (Hg) in natural environments on Earth. The sediments comprised younger strata enriched in Hg by recent pollution overlying older strata containing background Hg only. Several Hg isotope ratios, including super(199)Hg/ super(201)Hg, super(201)Hg/ super(204)Hg, and super(202)Hg/ super(204)Hg, varied significantly with the Mn/Fe ratio of the extractable readily reduced oxyhydroxide fraction of the sediment and with the concentrations of extractable Mn or Fe fractions, or both, in the sediment, and the zone of recent Hg pollution gave strikingly different results than the zone of background Hg. Food-web animals displayed a progressive increase in the super(202)Hg/ super(204)Hg ratio from lower to higher trophic levels in the order crustaceans < forage fish < trout; but superimposed on this trend were secondary trends owing to systematic decreases in the ratio from planktonic to benthic crustaceans and, correspondingly, from plankton-eating to benthos-eating forage fish. The results of the research suggest fractionation of Hg isotopes by natural processes, including Hg methylation, with effects linked to temporal variations in the oxidation-reduction potential of the sediments. These findings show that Hg isotopes could provide valuable but as yet untapped information about the sources and biogeochemical cycling of natural and anthropogenic Hg.

  19. Understanding Minamata disease and strategies to prevent further environmental contamination by methylmercury

    Y. Takizawa.

    Pergamon, UK: Elsevier Science Ltd., 2000

    Minamata disease is a neurological disorder caused by methylmercury poisoning which originated from the discharge of wastewater containing methylmercury from chemical plants in Japan. Residents in the area who consumed large amounts of fish and other seafoods suffered from the disease. The main symptoms consist of sensory disturbance, ataxia, restriction of visual field and hearing impairment. Various measures have been taken to deal with Minamata disease, including environmental pollution control, treatment for patients, and promotion of research activities. Through the compensation law, 2,952 persons have been certified as Minamata disease patients, and a total of approximately 144 billion yen had been paid in compensation by the responsible companies as of March, 1999. Meanwhile, people who were not certified as patients have filed suits against the Japanese Government and local government challenging the diagnostic criteria. The Japanese Government, patients and their supporters reached an agreement in 1996, and Minamata disease legal issues were finally resolved, 40 years after the outbreak. The Minamata experience has left us with an invaluable understanding of the importance of taking thoroughgoing measures to prevent health damage from environmental pollution.

  20. Mercury in the Canadian Environment: Current Research Challenges

    L. M. Azzaria and R. G. Garrett.

    Geoscience Canada [Geosci.Can.], Vol. 25, No. 1, Mar 1998, pp. .

    Elevated methylmercury concentrations are common in fish and other wildlife in ecosystems remote from any industrial point sources. Concern about chronic exposure to methylmercury for people who depend on fish as a dietary staple has focused attention on mercury sources and cycling processes in rural and remote areas, and on the potential for airborne mercury to travel hundreds to thousands of kilometres. A number of other studies have demonstrated that elevated concentrations of mercury in fish may be attributable to local geological sources. Compared to the large body of literature that is emerging on anthropogenic sources, however, there is a relative lack of research aimed at quantifying the contribution of mercury from natural sources. This has resulted in a debate over the relative significance of anthropogenic and natural mercury inputs to rural and remote lakes. Geoscience research is needed to improve our understanding of the biogeochemical cycling of mercury species released from common sulphide minerals and other crustal sources into soil, sediments, air, water, vegetation and ultimately into the human food chain.

  21. Uptake, toxicity, and trophic transfer of mercury in a coastal diatom

    R. P. Mason, J. R. Reinfelder and F. M. M. Morel.

    Environmental science & technology, Vol. 30, No. 6, Jun 1996, pp. 1835-1845.

    The primary mechanisms controlling the accumulation of methylmercury and inorganic mercury in aquatic food chains are not sufficiently understood. Differences in lipid solubility alone cannot account for the predominance of methylmercury in fish because inorganic mercury complexes (e.g., HgCl sub(2)), which are not bioaccumulated in fish, are as lipid soluble as their methylmercury analogs (e.g., CH sub(3)HgCl). Mercury concentrations in fish are ultimately determined by methylmercury accumulation at the base of the food chain, which is governed by water chemistry, primarily pH and chloride concentration. Our studies of mercury speciation, toxicity, and phytoplankton uptake demonstrate that passive uptake of uncharged, lipophilic chloride complexes is the principal accumulation route of both methylmercury and inorganic mercury in phytoplankton. The predominance of methylmercury in fish, however, is a consequence of the greater trophic transfer efficiency of methylmercury than inorganic mercury. In particular, methylmercury in phytoplankton, which accumulates in the cell cytoplasm, is assimilated by zooplankton four times more efficiently than inorganic mercury, which is principally bound in phytoplankton membranes. On the basis of these results, we constructed a simple model of mercury accumulation in fish as a function of the overall octanol-water partition coefficient of methylmercury. Our model can explain the variability of mercury concentrations in fish within, but not among, different lake regions.

  22. Mercury in the Adriatic

    J. Ui and S. Kitamura.

    Marine Pollution Bulletin, Vol. 2, No. 4, 1971, pp. 56-58.

    Environmental pollution by organic mercury compounds in Japan and in Sweden is briefly discussed with particular regard to Minamata disease and sources of contamination. Investigations were carried out at the ANIC factory at Ravenna, Italy, which synthesises acetaldehyde using a mercury catalyst. Elevated mercury concs have been observed in fish in the large lagoon near the waste discharge of the factory as well as in the harbour channel and its mouth. Mercury pollution by factory waste is suspected. However there is no remarkable mercury pollution in samples of fish on sale in fishmarkets or caught in districts far from the mouth of the harbours. Typical symptoms of Minamata disease have never been recorded in the district. The much higher conc of organic substances in sea water in the Adriatic than in Japan or Sweden may be important since it is known that the more advanced the state of eutrophication of a water body, the less the accumulation of toxic material into fishes because of the dilution effect of organic sub stances in the water. The significance of a future ecological investigation of the lagoon on the north side of the factory is pointed out. Other possible mercury sources are discussed and the need for further investigation stressed.