MeHg is stable in the body compared to other species. It is slowly demethylated to mercuric Hg in tissue macrophages, intestinal flora, and the fetal liver. Although these sites of demethylation are known, the enzymes in mammalian tissues responsible for the biotransformation have not yet been identified. It is metabolized to ionic mercury at a rate of around 1% of the body burden per day. The mercuric Hg resides for long periods of time in the CNS, probably in an inert form.