Organochlorines

Organochlorines are composed primarily of carbon, hydrogen, and chlorine. These chlorine-containing compounds are found in the environment as a result of human activities. Organochlorines such as chlorinated pesticides and polychlorinated biphenyls represent an important group of persistent organic pollutants that have caused worldwide concern as toxic environmental contaminants. The large-scale manufacture and distribution of organochlorines took place after the accidental discovery of dichlorodiphenyltrichloroethane (DDT) as an insecticide by Paul Hermann Müller in 1946. Uses of organochlorine pesticides (OCPs) take a wide range of forms, ranging from pellet application in field crops to sprays for seed coating and grain storage. Some organochlorines are applied to surfaces to kill insects.

The persistence of OCPs; their tendency to accumulate in soil, sediment, and biota; their harmful effects on wildlife; their widespread ecological damage; and global contamination and resistance by target insects resulted in their ban and restrictions in most countries, especially in the United States. Banned OCPs include DDT, aldrin, dieldrin, toxaphene, chlordane, and heptachlor. Despite the restrictions, these compounds are still detected in the environment and tissue samples. Biomonitoring studies continue to find them in food, blood, adipose tissue, and breast milk of humans. Body burdens have declined since these organochlorines were banned, yet virtually the entire population still carries detectable levels of the toxic chemicals. Chronic exposure to low levels of OCPs can cause a wide range of serious harmful effects in animals and humans. Those that are still being used include lindane, endosulfan, dicofol, methoxychlor, and pentachlorophenol. They are known animal carcinogens and potential human carcinogens. Examples of organochlorines are DDT, chlordane, lindane, aldrin, dieldrin, toxaphene, heptachlor, endosulfan, dicofol, methoxychlor, hexachloro benzene, mirex, pentachlorophenol, beta-hexachlorocyclo hexane, trans-nonachlor, heptachlor epoxide and pentachlorophenol, 2,3,5-trichloro phenol.

Organochlorines generally have low volatility, chemical stability, lipid solubility, and slow biotransformation and degradation. They are persistent and bio-concentrate and bio-magnify. They are hydrophobic compounds that tend to adsorb to suspended particulate [Page 341]matter and bottom sediments in aquatic ecosystems. These qualities are not environmentally desirable. The lipophilic nature, hydrophobicity, and low chemical and biological degradation rates of OCPs have led to their accumulation in biological tissues and the subsequent magnification of concentrations in organisms, progressing to the food chain. Polychlorinated biphenyls are very persistent in the environment and are among the industrial chemicals banned and included in the list of priority contaminants to be monitored regularly. They cause a variety of carcinogenic effects and neurological problems in organisms.

Soils can be contaminated in many ways by organochlorines. The most common ways include

• using more organochlorine pesticide than is recommended,
• spills during mixing and loading,
• tank overflows, and
• improper disposal of containers or surplus spray mixtures.

The capacity of the soil to filter, buffer, degrade, immobilize, and detoxify organochlorines is a function of the quality of the soil. Their presence and bio-availability in soil can adversely affect humans, animals, plants, and soil organisms. Spills on sand or sandy loam soils can lead to serious contamination of groundwater through leaching. Spills on clay soils remain on the soil surface longer and are more likely to spread to other areas because of surface runoff. Many pesticides degrade in the soil, but some persist for long periods of time. Organochlorines can enter surface and groundwater in several

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