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Persistent organic pollutants

Persistent organic pollutants, known as POPs, are toxic substances released into the environment by human activities. They are either used as pesticides, consumed by industry, or generated as byproducts of various industrial and combustion processes.

Of all the pollutants released into the environment every year by human activity, POPs are among the most dangerous. They are highly toxic, causing death, disease, and birth defects among humans and animals. Specific effects can 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; they can also have developmental and carcinogenic effects.

These highly stable compounds can last 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 deposit, be transported through the atmosphere to regions far away from the original source.

POPs are a group of twelve particularly hazardous chemicals that have been singled out by the recent Stockholm Convention for urgent action to eliminate them from the world. They include polychlorinated biphenyls (PCBs), mainly found in electricity transformers, and several pesticides that are very persistent and toxic to the environment.

In addition, POPs concentrate in living organisms through another process called 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, the POPs travel with them. As a result of these two processes, POPs can be found in people and animals living in regions such as the Arctic, thousands of kilometers from any major POPs source. Even Brazilian pygmies deep in the Amazon have minute traces in their body fat and higher concentrations are disrupting the breeding patterns of seals in the Antarctic. These chemicals can also seep into the ground water and contaminate wells and water tables.

See also:

• World Bank Group "Persistent organic pollutants"