Mercury in fish

Exposure. The exposure of humans and animals to mercury from the general environment occurs mainly by inhalation and ingestion of terrestrial and aquatic food chain items. Pish generally rank the highest (10—300 ng/g) in food chain concentrations of mercury. Swordfish and pike may frequently exceed 1 p.g/g (27). Most of the mercury in fish is methyl mercury [593-74-8]. Worldwide, the estimated average intake of total dietary mercury is 5—10 p-g/d in Europe, Russia, and Canada, 20 pg/d in the United States, and 40—80 pg/d in Japan (27). 

Mercury in fish has been found in waters in the United States and Canada. Mercury in the waters is converted into methyl mercury by aquatic vegetation. Small fish consume such vegetation and in turn are eaten by larger fish and eventually by humans food with more than 0.5 ppm of mercury (0.5 mg/kg) cannot be sold in the United States for human consumption. 

Fig. 15-8 The mercury cycle, demonstrating the bioaccumulation of mercury in fish and shellfish. Reprinted with permission from An Assessment of Mercury in the Environment" (1978) by the National Academy of Sciences, National Academy Press, Washington, DC.

In a report from the U.S. EPA (1980), fish contained between 10,000 and 100,000 times the concentration of methyl mercury present in ambient water. In a study of methyl mercury in fish from different oceans, higher levels were reported in predators than in nonpredators (see Table 8.2). Taken overall, these data suggest that predators have some four- to eightfold higher levels of methyl mercury than do nonpredators, and it appears that there is marked bioaccumulation with transfer from prey to predator. 

Knowledge of intrinsic co-variables. Concentrations of mercury in fish are typically correlated with age or body size. An understanding of, and ability to account for, the effects of such intrinsic variables is essential for evaluating contaminant trends. 

Andersson P, Borg H, Kaerrhage P. 1995. Mercury in fish muscle in acidified and limed lakes. Water Air Soil Pollut 80 889-892. 

Baker RF, Blanchfield PJ, Paterson MJ, Flett RJ, Wesson L. 2004. Evaluation of non-lethal methods for the analysis of mercury in fish tissue. Trans Am Fish Soc 133 568-576. 

Tremblay G, Legendre P, Doyon J-F, Verdon R, Schetagne R. 1998. The use of polynomial regression analysis with indicator variables for interpretation of mercury in fish data. Biogeochemistry 40 189-201. 

Fimreite N, Holsworth WN, Keith JA, Pearce PA, Qruchy IM. 1971. Methyl mercury in fish and fish-eating birds from sites of industrial contamination in Canada. Can Field Natural 85 2211-2220. 

Four courses of action now seem warranted. First, toxic mercurials in agriculture and industry should be replaced by less toxic substitutes. Second, controls should be applied at the point of origin to prevent the discharge of potentially harmful mercury wastes. Third, continued periodic monitoring of mercury in fish and wildlife is needed for identification of potential problem areas, and for evaluation of ongoing mercury curtailment programs. And fourth, additional research is merited on mechanisms of mercury accumulation and detoxification in comparatively pristine ecosystems. 

Anderson, M.R., D.A. Scruton, U.P. Williams, and J.F. Payne. 1995. Mercury in fish in the Smallwood Reservoir, Labrador, twenty one years after impoundment. Water Air Soil Pollut. 80 927-930. Andersson, P., H. Borg, and P. Karrhage. 1995. Mercury in fish muscle in acidified and limed lakes. Water Air Soil Pollut. 80 889-892. 

Cooper, J.J. 1983. Total mercury in fishes and selected biota in Lahontan Reservoir, Nevada 1981. Bull. Environ. Contam. Toxicol. 31 9-17. 

Hakanson, L., T. Andersson, and A. Nilsson. 1990. Mercury in fish in Swedish lakes — linkages to domestic and European sources of emission. Water Air Soil Pollut. 50 171-191. 

Holden, A.V. 1973. Mercury in fish and shellfish, a review. Jour. Food Technol. 8 1-25. 

Lodenius, M., A. Seppanen, and M. Herrnanen. 1983. Accumulation of mercury in fish and man from reservoirs in northern Finland. Water Air Soil Pollut. 19 237-246. 

Paulsson, K. and K. Lundbergh. 1989. The selenium method for treatment of lakes for elevated levels of mercury in fish. Sci. Total Environ. 87/88 495-507. 

Swain, E.B. and D.D. Helwig. 1989. Mercury in fish from northeastern Minnesota lakes historical trends, environmental correlates, and potential sources. Jour. Minnesota Acad. Sci. 55 103-109. 

Leonzio, C., S. Focardi, and E. Bacci. 1982. Complementary accumulation of selenium and mercury in fish muscle. Sci. Total Environ. 24 249-254. 

MMHg is UpophiUc, causing it to bioaccumulate and biomagnify through the marine food web. About 85 to 95% of the total mercury in fish is MMHg, most of which is the result of biomagnification. Marine fish consumption accoimts far most of the mercury burden in... 

The primary concern with organic mercury is methyl mercury in fish. Children and women of childbearing age should be cautious about consuming fish known to accumulate mercury such as tuna, shark, swordfish, and pike. Local fish consumption advisories should be followed. 

The primary human exposure to methyl mercury is from consumption of contaminated fish. The most sensitive population is the developing fetus or infant due to the effects of methyl mercury on the nervous system (neurotoxic) and developmental effects. Exposure limits and fish consumption advisories are directed at pregnant women, women of childbearing age, and children. All agencies also recognize that fish consumption has many nutritional benefits and is an important part of many people s diet. Nevertheless, the widespread distribution of mercury and subsequent bioaccumulation of methyl mercury requires that many agencies have developed recommendation for levels of mercury in fish. Below is a list of some of these recommendations, but it is very important to consult the local fish consumption advisories. 

Ancient Worldwide Mercury Mine workers poisoned 1930s hat industry (the Mad Hatters) 1950s Japan, mercury in fish 1970s mercury in seed grain acceptance of mercury as a developmental neurotoxicant released from coal-fired electrical plants ongoing contamination of fish... 

Figure 6.6. Cause-and-effect diagram for the analysis of mercury in fish showing the introduction of factors associated with the digestion process.

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