Methylmercury percent

For Hg, the MLs apply only to fish and fishery products [11]. For most fish species the ML is 0.5 mg kg-1. In certain other species, mostly predatory such as pike and tuna, the ML is set at 1 mg kg-1. It is generally accepted that over 90 percent of Hg in fish and shellfish is present as methylmercury, that is, a much more toxic species. 

R. Wagemann, E. Trebacz, R. Hunt, G. Boila, Percent methylmercury and organic mercury in tissues of marine mammals and fish using different experimental and calculation methods, Environ. Toxicol. Chem., 16 (1997), 1859-1866. 

Methylmercury is produced by methylation of inorganic mercury present in both freshwater and saltwater sediments, and accumulates in aquatic food chains in which the top-level predators usually contain the highest concentrations. The percent of total mercury accounted for by methylmercury generally increases with higher trophic levels, confirming that methylmercury is more efficiently transferred to higher trophic levels than inorganic mercury compounds. 

Mercury in pinniped muscle, unlike fiver, was mostly methylmercury in both mothers and pups pups acquired most of their mercury during gestation. The percentage of methylmercury in any tissue from any marine mammal appears to be inversely correlated with total mercury content. For example, fiver of harbor seals from Maine contained a maximum of 7.8 mg total Hg/kg FW vs. 50.9 from those collected from New Brunswick, Canada methylmercury accounted for 13-37% of total mercury in Maine (U.S.) seal fivers but only 2-11% in Canadian seals. Among healthy California sea lions, Zalophus californianus, concentrations of total mercury in tissues in mg/kg FW and percent methylmercury were as follows fiver 74.0 and 3.7% kidney 7.0 and 17.2% muscle 1.2 and 88.6% and heart 0.59 and 88.1%. 

In sediment samples, methylmercury levels are typically only a few percent or less of the inorganic mercury level and even minor artificial methylmercury formation during sample preparation will result in significant overestimation of the actual methylmercury content. A correction can be carried out with a single measurement, when stable Hg isotopes are used, by measuring different isotopes to determine the artefact formation factor. 

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