DDT

(Adil Alam, islamabad)

DDT is one of the most controversial chemical compounds in recent history. It has proven effectiveness as an insecticide, but its potent toxicity isn't limited to insects. Banned by many countries including the United States, DDT is nonetheless still used legally or illegally in some places.

DDT, also known as dichloro-diphenyl-trichloroethane, belongs to a class of pesticides known as organ chlorides. A synthetic chemical compound that must be made in a laboratory (it doesn't occur in nature), DDT is a colorless, crystalline solid. DDT can't be dissolved in water; it is, however, easily dissolved in organic solvents, fats or oils. As a result of its tendency to dissolve in fats, DDT can build up in the fatty tissues of animals that are exposed to it. This accumulated build-up is known as bio accumulation, and DDT is described by the EPA as a persistent, bio accumulative toxin. Because of this bio accumulation, DDT remains in the food chain, moving from crayfish, frogs, and fish into the bodies of animals that eat them. Therefore, DDT levels are often highest in the bodies of animals near the top of the food chain, notably in predatory birds like eagles, hawks, pelicans, condors and other meat-eating birds.

People are most likely to be exposed to DDT from foods, including meat, fish, and dairy products. DDT can be absorbed by eating, breathing, or touching products contaminated with DDT. In the body, DDT is converted into several breakdown products called metabolites, including the metabolite dichloro-diphenyl-trichloroethane (DDE). DDT and DDE are stored in the body’s fatty tissues. In pregnant women, DDT and DDE can be passed to the fetus. Both chemicals are found in breast milk, resulting in exposure to nursing infants. How DDT Affects People’s Health Human health effects from DDT at low environmental doses are unknown. Following exposure to high doses, human symptoms can include vomiting, tremors or shakiness, and seizures. Laboratory animal studies showed effects on the liver and reproduction.

The U.S. Department of Agriculture, the federal agency with responsibility for regulating pesticides before the formation of the U.S. Environmental Protection Agency in 1970, began regulatory actions in the late 1950s and 1960s to prohibit many of DDT's uses because of mounting evidence of the pesticide's declining benefits and environmental and toxicological effects. The publication in 1962 of Rachel Carson's Silent Spring stimulated widespread public concern over the dangers of improper pesticide use and the need for better pesticide controls.

In 1972, EPA issued a cancellation order for DDT based on its adverse environmental effects, such as those to wildlife, as well as its potential human health risks. Since then, studies have continued, and a relationship between DDT exposure and reproductive effects in humans is suspected, based on studies in animals. In addition, some animals exposed to DDT in studies developed liver tumors. As a result, today, DDT is classified as a probable human carcinogen by U.S. and international authorities. DDT is known to be very persistent in the environment, will accumulate in fatty tissues, and can travel long distances in the upper atmosphere.

In September 2006, the World Health Organization (WHO) declared its support for the indoor use of DDT in African countries where malaria remains a major health problem, citing that benefits of the pesticide outweigh the health and environmental risks. The WHO position is consistent with the Stockholm Convention on POPs, which bans DDT for all uses except for malaria control.


 

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