Although there is some uncertainty regarding the toxicity of inorganic Hg derived from demethylation, a detoxification mechanism for MeHg in seabirds and marine mammals has been proposed that entails demethylation by reactive oxygen species and subsequent formation of high molecular weight Hg-selenium (Se)-protein compounds, which subsequently undergo degradation in lysosomes, creating an insoluble Hg-Se compound (35, 37).