The build-up of a toxin as it moves up the food chain. For example, pesticides wash into waterways, are eaten by aquatic organisms which are in turn eaten by large birds, animals, or humans, and become concentrated in tissues or internal organs. Since aquatic food chains have more links, biological magnification is greater; see, for example, Sutherland et al. (2000) Arch. Env. Contam. & Toxic. 38, 4.