Of all the pollutants released into the environment every year by human activity, persistent organic pollutants (POPs) are among the most dangerous. POPs are either used as pesticides, in industry, or generated unintentionally as by-products of various industrial/combustion processes.
POPs are toxic, causing an array of adverse effects, including death, disease, and birth defects among humans and animals. Effects may include cancer, allergies and hypersensitivity, damage to the central and peripheral nervous systems, reproductive disorders, and disruption of the immune system. Some POPs are also considered to be endocrine disrupters, which, by altering the hormonal system, can damage the reproductive and immune systems of exposed individuals as well as their offspring; endocrine disrupters can also have developmental and carcinogenic effects.
These stable compounds can persist for years or decades before breaking down. They circulate globally through a process known as the 'grasshopper effect'. POPs released in one part of the world can, through a repeated (and often seasonal) process of evaporation and deposition, be transported through the atmosphere to regions far away from the original source.
POPs are also problematic because they concentrate in living organisms through bioaccumulation. Though not soluble in water, POPs are readily absorbed in fatty tissue where concentrations can become magnified by up to 70,000 times the background levels. Fish, predatory birds, mammals, and humans are high up the food chain and so absorb the greatest concentrations. When they travel, POPs travel with them. As a result of these two processes, POPs can be found in people and animals living in remote regions such as the Arctic, thousands of kilometers from any major POPs source.
Adapted from Persistent Organic Pollutants: what are POPs? - World Bank. 2008.