Bioaccumulation and Biomagnification

Bioaccumulation occurs when an organism absorbs a contaminant faster than it can eliminate it, causing concentrations to increase in tissues over its lifetime. Lipophilic (fat-soluble) and persistent chemicals are most prone to bioaccumulation because they dissolve into fat stores rather than being excreted in urine. Mercury, for example, is converted by bacteria in aquatic sediments to methylmercury, which is absorbed through fish gills and gut walls and stored in muscle tissue. A large tuna may bioaccumulate methylmercury to concentrations one million times higher than the surrounding water. The bioconcentration factor (BCF)—the ratio of chemical concentration in the organism to concentration in water—quantifies this process.