The wide dissemination of POPs in the environment is generating increasing international concern. POPs, long-lived organic compounds that become more concentrated as they move up the food chain, can travel thousands of kilometers from their point of release .
Although POPs include a wide range of chemicals, much of the research revolves around 12 chemicals (or chemical classes) that include the industrial PCBs, polychlorinated dioxins and furans (unwanted by-products of various industrial processes), and pesticides such as DDT, chlordane, and heptachlor . Although their use is restricted or banned in most developed countries, many POPs are still manufactured in the United States and other developed nations for export and remain widely used in developing countries . A recent survey of 60 countries found that the majority were still producing, importing, or exporting the nine POPs studied. In Africa, for instance, only two countries have banned the use of chlordane, dieldrin, or heptachlor . (See Toxic Chemicals are Widely Used Despite Known Risks.)