An increase in the concentration of chemicals, such as pesticides, in organisms that live in environments contaminated by a wide variety of organic compounds. These compounds are not usually decomposed in the environment (i.e. they are not biodegradable) or metabolized by the organisms, so that their rate of absorption and storage is greater than their rate of excretion. The chemicals are normally stored in fatty tissues. DDT is known as a persistent pesticide, as it is not easily broken down and bioaccumulates along food chains, so that increasing concentrations occur in individual organisms at each trophic level.