Mercury and Selenium in Marine‐ and Freshwater Fish

Mercury, methylmercury and selenium concentrations were determined in fillets and livers of various marine‐ and freshwater fish species. About 90% of the mercury in the fillets was found to be present as methylmercury. The concentration of mercury in some freshwater fish samples exceeded the FDA guideline of 1.0 mg/kg, whilst the mercury concentration in marine fish was below this level. In nearly all marine fish samples the stoichiometric Hg:Se ratio was smaller than one. Accumulation of mercury in freshwater fish took place in such a way that the stoichiometric Hg:Se ratio was larger than one. A linear relationship was observed between the methylmercury and selenium concentration in the livers of eight perch samples.