ALDRIN - A pesticide applied to soils to kill termites, grasshoppers and other insect pests. It can also kill birds, fish and humans. In one incident, aldrin-treated rice is thought to have killed hundreds of shorebirds along Texas's Gulf Coast.

CHLORDANE - Used extensively to control termites and as a broad-spectrum insecticide on a range of crops. Tests show it can kill birds and fish and may affect the human immune system and may be a carcinogen. It is already banned or severely restricted in several countries.

DDT - Perhaps the most infamous of the POPs, DDT was widely used during World War Two to protect soldiers and civilians from malaria, typhus and other diseases spread by insects. It has since been widely employed to control disease and some nations have an opt-out to continue to use it to combat malaria. More than 30 countries have banned DDT and more than 30 have severely restricted its use. Long-term exposure has been associated with chronic ailments in humans while its best known toxic effect is to thin the shells of birds' eggs.

DIELDRIN - Used mainly to control termites and textile pests, its half-life in soil is around five years. It is highly toxic to fish and other aquatic animals, especially frogs. In a U.S. survey, dieldrin was the second most common pesticide found in pasteurized milk.

DIOXINS - These chemicals are produced unintentionally due to incomplete combustion, as well as the manufacture of pesticides and other chlorinated substances. They are emitted mostly from the burning of hospital waste, municipal waste and hazardous waste and have been linked to a number of adverse effects in humans, including immune and enzyme disorders. Food, especially from animals, is the major source of exposure for humans.

ENDRIN - An insecticide sprayed on the leaves of crops such as cotton and grains. It is also used to control mice and other rodents. It can persist in the soil for up to 12 years and find its way to water, where it is highly toxic to fish.

FURANS - These compounds are produced unintentionally from many of the same processes that produce dioxins and have been found in emissions from waste incinerators and automobiles. They are similar to dioxins and produce many of the same toxic effects.

HEPTACHLOR - Mostly used to kill soil insects and termites, it is believed to be responsible for the decline of many wild bird populations, including Canada geese and American kestrels in the Columbia River basin of the United States. High doses are also fatal to mink, rats and rabbits. It is classified as a possible human carcinogen.

HEXACHLOROBENZENE (HCB) - Introduced in 1945 to treat weeds, it kills fungi that affect food crops. When people in eastern Turkey ate HCB-treated seed grain between 1954 and 1959, they developed a variety of symptoms including colic. Several thousand developed a metabolic disorder called porphyria turcica and 14 percent died. HCB is found in food of all types.

MIREX - This insecticide is mainly used to combat fire ants and has also been used as a fire retardant in plastics, rubber and electrical goods. Direct exposure does not seem to cause injury to humans but it has been classified as a possible human carcinogen.

POLYCHLORINATED BIPHENYLS (PCBs) - These compounds are used in industry as heat exchange fluids, in electric transformers and as additives in paint and plastics. They are toxic to fish and have been linked to reproductive failure and immune system suppression in a number of wild animals including seals and mink. Large numbers of people have been exposed to PCBs through food contamination. Consumption of PCB-contaminated rice oil in Japan in 1968 and Taiwan in 1979 caused pigmentation of nails and fatigue, nausea and vomiting. Children born up to seven years after the Taiwan incident in infected mothers showed developmental delays and behavioural problems.