In or near the sediments, a crucial transformation occurs; bacteria change some of the inorganic mercury (Hg) into the orgainic, more toxic, methylmercury (CH3 Hg). Methylmercury is then accumulated by organisms all along the food chain--from tiny plants (algae) and animals (invertebrates), to smaller fish such as kokanee and perch, to larger fish such as adult walleye that eat other fish, and to fish-eating birds and mammals, including humans. Methylmercury is stored in the muscle tissue (the fillet) of the fish where it bioaccumulates and biomagnifies. Because humans eat from the top of the aquatic food chain, we can be exposed to high concntrations of methylmercury.
(USGS FS-102-97, August 1997) |