ORGANOCHLORINE INSECTICIDES

Chemical properties

The organochlorine insecticides are persistent organic pollutants that are highly resistant to biological, photolytic, or chemical degradation due to the stable carbon–chlorine bond. These compounds are characterized by low water solubility, high lipid solubility, and semi-volatility. Large molecular weight compounds with cyclic, aromatic, and cyclodienetype structures include the organochlorine insecticides such as DDT, chlordane, lindane, heptachlor, dieldrin, aldrin, toxaphene, mirex, and chlordecone (IPCS, 1995).

The Uses of ORGANOCHLORINE INSECTICIDES

The organochlorine insecticides are important historically as a major class of synthetic insecticides. During World War 2, European supplies of traditional botanical insecticides used for crop protection, such as pyrethrum extract and nicotine, were limited by blockades and shortages. The critical need to protect crops from insect pests and to protect personnel in tropical areas from malaria and other insect-borne diseases stimulated the search for synthetic replacements. The organochlorine insecticides were one of the first major classes of synthetic chemicals to meet the needs of public health and agriculture. Despite their great utility and the low costs of manufacture, the production and use of many organochlorine insecticides has now been discontinued or restricted because they are not readily biodegradable and have become ubiquitous environmental contaminants. They may accumulate or bioconcentrate through the food chain and directly or indirectly they show potential for adverse effects in man and the environment.

The Uses of ORGANOCHLORINE INSECTICIDES

Organochlorine compounds were widely used in agriculture and malaria control programs for decades, beginning in the mid-1940s. They declined in use in the 1960s and now have been nearly completely banned in the United States. This action was taken in response to evidence that these insecticides have a high potential for persistence and bio-magnification in food chains. Organochlorine insecticides are still used in many other countries for malaria control because of their low cost and high efficacy (IPCS, 1995). Aldrin, dieldrin, and chlordane were used extensively to control termites around buildings until the early 1970s when their use was canceled (ATSDR, 2002a).

Environmental Fate

The organochlorines strongly adsorb to soils and do not readily leach into groundwater due to low water solubility. However, the presence of organic solvents at hazardous waste sites may promote leaching. Limited biodegradation by microorganisms may occur in soils and water. Photodegradation and hydrolysis are not important pathways for degradation of these compounds. Volatilization and adsorption to atmospheric particulates results in global transport and deposition. Bioconcentration has been measured throughout the food chain from plants to domestic livestock and fish (IPCS, 1995).
Chemical properties resulting in limited environmental degradation mean these compounds are persistent pollutants. While aldrin is rapidly converted to dieldrin, the half-life of dieldrin on temperate soils is about 5 years. As much as 50% of applied DDT and related compounds can remain on soils for >10 years (IPCS, 1995; ATSDR, 2002a,b).