How Do Chemical Contaminants Move Through Food Webs?
Food webs can also be a pathway for harmful chemical contaminants. Mercury and PCBs can pass to higher trophic levels in a process called bioaccumulation. • Small bottom-dwelling organisms take up contaminants that are in bottom sediments while feeding or through skin contact. • Larger fish accumulate toxins in their tissues when they eat contaminated smaller organisms. • In turn, birds, other wildlife and even humans may eat contaminated fish, allowing the contaminants to continue to move through the food web. The severe decline of bald eagles and osprey in the 1950s through the 1970s was the result of bioaccumulation of DDT, a pesticide used to control insects and agricultural pests. DDT caused eagles to lay extremely thin-shelled eggs that would break in the nest.
