A toxic substance that is not biodegradable and persists in the environment. POPs can concentrate as they move up the food chain and are generally deleterious to health. In 2001, an international conference in Sweden resulted in an agreement (the Stockholm Convention) to reduce or eliminate the 12 POPs of greatest concern, and to add other chemicals to the list in the future. The 12 chemicals were the pesticides aldrin, chlordane, DDT, dieldrin, endrin, heptachlor, mirex, and toxaphene, together with the industrial chemical hexachlorobenzene and the groups polychlorinated biphenyls, dioxins, and furans.

http://chm.pops.int/default.aspx Official Stockholm Convention site