Methylmercury bioavailability

Watersheds are sinks for atmospheric Hg deposition (Grigal 2002). However, they are highly variable in their ability to retain inputs of total Hg (THg), convert ionic Hg (Hg(ll)) to bioavailable methylmercury (MeHg), and snpply Hg(II) and MeHg to downstream aqnatic ecosystems, ultimately influencing exposure to sensitive biota and hnmans. 

Choi, M.H., J.J. Cech, Jr., and M.C. Lagunas-Solar. 1998. Bioavailability of methylmercury to Sacramento blackfish (Orthodon microlepidotus) dissolved organic carbon effects. Environ. Toxicol. Chem. 17 695-701. 

McCloskey, J.T., I.R. Schultz, and M.C. Newman. 1998. Estimating the oral bioavailability of methylmercury... 

Leaner, J. J. and Mason, R. P. (2002). Factors controlling the bioavailability of ingested methylmercury to channel catfish and atlantic sturgeon, Environ. Sci. Technol., 36, 5124-5129. 

R. P. Mason, A. L. Lawrence, Concentration, distribution, and bioavailability of mercury and methylmercury in sediments of Baltimore Harbor and Chesapeake Bay, Maryland, USA, Environ. Toxicol. Chem., 18 (1999), 2438-2447. 

Bioavailabilitv of methvlmercurv in food. Measurements of absorption and toxicity have generally been made using aqueous solutions of methylmercury. The absorption and bioavailability of methylmercury in food, specifically fish and bread, may be affected by dietary components. Potential confounders that may affect bioavailability of methylmercury are dietary phytate and other dietary fibrous materials found in bread and the complexation of methylmercury with selenium in fish. 

Dietary fiber and phytate. Dietary fiber and phytate are known as potential inhibitors of the absorption of divalent cations however, the literature regarding the effect of dietary fiber and phytate on the bioavailability of minerals is contradictory. Data by Yannai and Sachs (1993) indicate that phytate does not affect methylmercury absorption. Yannai and Sachs (1993) compared the absorption by rats of mercury found intrinsically in experimental fish meal with and without added phytate and found no significant differences in the absorption of Hg (93 5%) between 2 experimental fish meal diets (containing 1.4 mol Hg/kg diet), with or without added sodium phytate. The authors speculated that phytate might be preferentially bound to zinc, iron, and copper, which were present at much higher concentrations in the diet. 

Regarding the bioavailability of methylmercury in fish, the available data indicate that methylmercury uptake is not affected by its presence in fish. Experimental studies on the metabolism of methylmercury in humans following the ingestion of contaminated fish (using methylmercury bound to fish muscle protein) have shown that absorption is almost complete (95% absorbed) (Miettinen 1973). Animal studies also support this absorption value. Data on cats given fish homogenates indicate absorptions of 90% of methylmercury, whether added to the homogenate, accumulated by fish in vivo, or from methyl-... 

The food web that exists primarily in the water column may be impacted by methyla-tion of reactive mercury species. Concentrations of methylmercury in predatory piscivorous marine fishes that inhabit coastal waters (such as sharks) may exceed 1 mg kg Most of this methylmercury is thought to be transferred through and accumulated in the food web, as methylmer-cuty is very bioavailable. Almost 100% of the mercury found in fish muscle tissue is... 

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