Organochlorines are chemicals in which carbon and chlorine are combined. Some organochlorines are found in nature and some are byproducts of combustion and industrial processes, but the vast majority may have been specifically manufactured for a wide range of uses, including pharmaceuticals, pesticides, plastics, and solvents. Most of organochlorines are Persistent Organic Pollutants (POPs).
The organochlorine pesticides being studied are aldrin, dieldrin, endrin, endosulfon, heptachlor, DDT, hexachlorobenzene (HCB), mirex, technical hexachlorocyclohexane (HCH), lindane, and toxaphene.
Canada was the first country to ratify the 1998 Protocol on Persistent Organic Pollutants (POPs) under the UN Economic Commission for Europe's 1997 Convention on Long Range Transboundary Air Pollution. This Protocol lists 16 POPs substances, 11 of which are pesticides. The 16 POPs now subject to international action are:
are the common names of two insecticides that are closely related chemically. Aldrin is readily converted to dieldrin in the environment, so these two closely related compounds are considered together by regulatory bodies. Their toxicities do not differ significantly.
Aldrin and dieldrin were widely used from the 1950s to the early 1970s, and their primary use was for control of corn pest. Aldrin has been used as a soil insecticide to control rootworms, beetles, and termites. Dieldrin has been used in agriculture for soil and seed treatment and in public health to control disease vectors such as mosquitoes and tsetse flies. Dieldrin has also had veterinary use as a sheep dip and, along with chlordane, was used in the timber processing industry. Persons could be occupationally exposed to aldrin and dieldrin from inhalation and by absorption through the skin.
is an insecticide. It was first introduced in the 1950s. Although it may also be used as a wood preservative, endosulfan is used primarily on a wide variety of food crops including tea, coffee, fruits, and vegetables, as well as on rice, cereals, maize, sorghum, or other grains. Endosulfan is a highly toxic substance. The World Health Organisation (WHO) classifies endosulfan as moderately hazardous, and the US Environmental Protection Agency (US EPA) classifies it as highly hazardous pesticide. Short-term toxicity is high, and influenced by the solvents and emulsifiers used to dissolve it. Endosulfan is easily absorbed by the stomach, by the lungs and through the skin, meaning that all routes of exposure can pose a hazard.
is a rodenticide used to control mice and voles, and an insecticide used on cotton, rice, and maize. Closely related to aldrin and dieldrin, endrin is the most toxic of the three in the aquatic environment and its metabolites are more toxic than endrin itself. In soils endrin is extremely persistent, with a half-life as long as twelve years.
is a broad-spectrum insecticide that has been used since 1947. It was applied on corn, citrus, deciduous fruits and nuts, and vegetables. Its use has recently been increasingly restricted in many countries, and it is now used mainly to destroy termites by subsurface injection into soil, and for fire ant control in power transformers.
Chlordane is very resistant to degradation. In experimental animals, prolonged exposure in the diet causes liver damage. Chlordane produces liver tumours in mice, but the weight of evidence indicates that it is not genotoxic. Chlordane can interfere with cell communication in vitro, a characteristic of many tumour promoters.
is a broad-spectrum insecticide, the use of which has been banned or restricted in many countries. At present, the major use of heptachlor is for termite control by subsurface injection into soil.
Heptachlor is quite persistent in soil, where it is mainly transformed to its epoxide. Heptachlor epoxide is very resistant to further degradation. Heptachlor and heptachlor epoxide bind to soil particles and migrate very slowly. Heptachlor and heptachlor epoxide have been found in drinking-water at levels of nanograms per litre. Diet is considered to represent the major source of exposure to heptachlor, although intake is decreasing.
Prolonged exposure to heptachlor has been associated with damage to the liver and central nervous system toxicity.
is an inexpensive, persistent, broad-spectrum, nonsystemic ingested and contact insecticide. From 1946-1972 DDT was the most widely used agricultural insecticide in the world. DDT was commonly used to control insect pests in gardens, orchards, agricultural crops and forests and to control bloodsucking insects and disease vectors. It is still widely used in tropical countries for disease vector control (malaria, yellow fever, trypanosomiasis and typhus) because of its efficiency as a broad-spectrum insecticide and low manufacturing costs.
DDT is highly persistent on solid surfaces and readily partitions into animal fats where it has been demonstrated to bioaccumulate and biomagnify. It has been reported in humans at levels which are of potential concern to health.
Human exposure can result directly from spraying or through skin contact, inhalation or from ingestion of contaminated foods. DDT and its metabolites display acute and chronic aquatic toxicity, and mammalian chronic toxicity and there is strong evidence of teratogenicity, mutagenicity, and carcinogenicity.
was introduced in the 1940s as a seed-dressing to prevent fungal disease into several crops. HCB is also formed as a waste product in the production of several chlorinated hydrocarbons and is found as a contaminant in some pesticides. HCB has been detected in all environmental compartments. HGB persists in the environment and has been shown to bioaccumulate and biomagnify in the food chain.
In humans, HCB is easily absorbed to accumulate in fat tissues, and persists for many years since it is highly lipophilic and resistant to metabolic breakdown. Tissue residue surveys showed that HCB concentrations have not declined since 1975 in some regions such as the Great Lakes and suggest that concentrations may be increasing. HCB produces a spectrum of biological and toxic conditions that are characteristic of polyhalogenated compounds and is capable of enzyme induction and disruption of endocrine control. HCB is toxic by all routes of exposure: inhalation, ingestion and dermal contact. Nursing infants ingest 200 to 300 times the adult intake on a body-weight basis.
is a stomach insecticide that was used against fire ants, leaf cutters, harvester termites, Western harvester ants, and pineapple mealybugs. Also been used as a fire retardant in plastics, rubber, paint, paper and electrical goods. Recently, the use of mirex has become increasingly restricted or prohibited in many countries. Mirex is carcinogenic.
HCH, a pesticide introduced during the 1940s, has two technical grades: technical HCH and lindane. Technical HCH contains only 10 - 12% of the active ingredient, gamma-HCH, and is predominantly made up of the non-insecticidal isomers alpha-HCH (60-70%), beta-HCH (5-12%) and other minor components. Lindane is almost pure gamma-HCH, and is used as an insecticide in agriculture for the control of lice on cattle and grass grub in pasture, and for insect control on vegetables and in orchards.
HCH enters the environment through direct application and through non-point sources during manufacturing and disposal. Once in the environment HCHs persist and have been show to bioaccumulate. HCHs is the most abundant pesticide in the Arctic Ocean.
Dietary exposure is the primary route of human exposure where HCH is used on plants and animals, since it is adsorbed from the gastrointestinal tract. The estrogen effects of HCH and its adverse effects upon the male reproductive system have been reported in a variety of animal studies. Because of concentrations of this pesticide in human breast milk, nursing infants are at special risk.
is a complex mixture composed of many congeners with different chemical properties. Toxaphene has been used against insect pests on cotton, tobacco, forests, grains, ornamental plants and livestock. Toxaphene is very persistent in the environment and is transported long distances in the atmosphere.
Toxaphene is both acutely and chronically toxic to aquatic species and wildlife. It has also been identified as a potential carcinogen. Human exposure to toxaphene can induce neurological and respiratory dysfunctions, heart dilations, brain haemorrhages and death.
Organochlorine pesticides have entered the environment through industrial discharges, the manufacture and use of organochlorine pesticides in agriculture and industry, and disposal of organochlorine pesticides.
These organochlorine pesticides are chemically very stable, which means they break down only very slowly and can remain in the environment for a long time. Organochlorines which are stable and vapour-forming can be carried by air currents for long distances. Eventually they condense and are deposited on land and water, particularly in cold climatic regions.
Organochlorine residues have been detected in air, water, soil, sediment, fish, and birds global wide. They have also been found in remote areas, such as open oceans and polar regions.
If they contaminate the food supply of animals, the organochlorines become more concentrated as they move up through the food chain. For this reason the highest levels of organochlorines are found in species at the top of the food chain: human beings, fish-eating birds and marine mammals. They build up in the fatty tissue and stay in the body for a long time because they are only slowly metabolised and excreted.
The organochlorine pesticides which have all four properties of persistence, toxic, vapour-forming, and concentrating up the food chain (bio-accumulative), are among the chemicals now referred to internationally as persistent organic pollutants (POPs). These chemicals are a focus of international concern.
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