Bioaccumulation

Bioaccumulation is the gradual buildup of substances, such as pesticides or other chemicals, inside an organism, occurring whenever the rate a substance is taken in exceeds the rate it is broken down or excreted. Organisms absorb these substances through respiration, through the skin, and through ingestion, and the longer a toxic compound persists in the body the greater the risk of chronic poisoning even where the surrounding environment holds only low concentrations. A related but narrower process, bioconcentration, occurs specifically when a chemical reaches a higher concentration inside an organism than in the surrounding environment. Bioaccumulation is distinct from biomagnification, in which the concentration of a chemical or metal increases as it passes from one trophic level to the next, so that top predators end up carrying the highest concentrations because they consume already-contaminated prey. Coastal fish and seabirds are routinely monitored for accumulated heavy metals, and methylmercury entering freshwater systems is a well documented example of a toxin that escalates through the food web, threatening aquatic life and the people who rely on fish for food.