Dichlorodiphenyl-Trichloroethane

views updated

Dichlorodiphenyl-trichloroethane

Dichlorodiphenyl-trichloroethane (DDT) can be degraded to several stable breakdown products, such as DDE and DDD. Usually DDT refers to the sum of all the DDT-related components.

DDT was first developed for use as an insecticide in Switzerland in 1939, and it was first used on a large scale on the Allied troops in World War II. Commercial, non-military use began in the United States in 1945. The discovery of its insecticidal properties was considered to be one of the great moments in public health disease control, as it was found to be effective on the carriers of many leading causes of death throughout the world including malaria , dysentery, dengue fever, yellow fever, filariasis, encephalitis, typhus, cholera , and scabies. It could be sprayed to control mosquitoes and flies or applied directly in powder form to control lice and ticks. It was considered the "atomic bomb" of pesticides, as it benefited public health by direct control of more than 50 diseases and enhanced the world's food supply by agricultural pest control. It had eliminated mosquito transmission of malaria in the United States by 1953. In the first 10 years of its use, it was estimated to have saved five million lives and prevented 100 million illnesses worldwide.

Use of DDT declined in the mid-1960s due to increased resistance of different species of mosquitos and flies and other pests, and to increasing concerns regarding the potential harm to ecosystems and human health. Although the potential hazard from dermal absorption is small when the compound is in dry or powdered form, if the compound is in oil or an organic solvent it is readily absorbed through the skin and represents a considerable hazard.

Primarily DDT affects the central nervous system, causing dizziness, hyperexcitability, nausea, headaches, tremors, and seizures from acute exposure. Death can result from respiratory failure. It also is a liver toxin, activating microsomal enzyme systems and causing liver tumors. DDE is of similar toxicity. It became the focus of much public debate in the United States after the publication of Silent Spring by Rachel Carson, who effectively dramatized the harm to birds, wildlife , and possibly humans from the widespread use of DDT. Extensive spraying programs to eradicate Dutch elm disease and the gypsy moth (Porthetria dispar ) also caused widespread songbird mortality . Its accumulation in the food chain/web also led to chronic exposures to certain wildlife populations. Fish-eating birds were subject to reproductive failure, due to egg shell thinning and sterility. DDT is resistant to breakdown and is transported long distances, making it ubiquitous in the world environment today. It was banned in the United States in 1972 after extensive government hearings, but is still in use in other parts of the world, mostly in developing countries, where it continues to be useful in the control of carrier-borne diseases.