Contaminants: Information on the chemical structure and properties of organochlorine pesticides and PCBs

This page provides an overview of the significance of various organochlorine contaminant groups that we have looked at in our contaminant analysis. Where possible 3D structures are provided. It is STRONGLY recommended that you download MDL's CHIME plugin for your browser--this will allow you to view the structures we have provided below.

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    Heptachlor, Chlordane, Nonachlor

    Heptachlor and chlordane are pesticides commonly used for termite control. Heptachlor has also been used to protect the seeds or bulbs of plants.

    Nonachlor is a by-product of the manufacturing of chlordane and heptachlor. Chlordane can be transformed in the environment into a more toxic compound called oxychlordane. In the environment heptachlor is transformed into heptachlor epoxide. Heptachlor and chlordane continue to be used in small amounts in the southern US.

    Chlordane can promote cancer and is an endocrine disrupter. Heptachlor can produce tumors in mammals.

Heptachlor epoxide

(C10H5OCl7)

Heptachlor

(C10H5Cl7)

Chlordane

(C10H6Cl8)

Nonachlor

(C10H5Cl9)


Hexachlorobenzene (C6Cl6)

Hexachlorobenzene (HCB)

Hexachlorobenzene (HCB) is produced during the synthesis of chlorinated rubber and plastics products, and is used as a fungicide for seed grain. Although it is no longer used as a fungicide in most countries, it does occur as a contaminant in other chlorinated pesticides.

HCB is persistant and lipophillic, although less so than with many other OCs and PCBs. Toxicological effects include dermatological and neurological disturbances, effects on bone marrow, reproductive problems in some mammals, potential carcinogen, and porphyria.

Hexachlorocyclohexane (C6H6Cl6)

Hexachlorocyclohexane (HCH) or benzene hexachloride (BHC or lindane)

There are four types of HCHs, alpha (a), beta (b), gamma (g), and delta (d). Gamma-HCH is commonly known as "lindane," an insecticide that is used in large amounts in India and China and is in controlled use in North America. The other three forms of HCH are products of the breakdown of lindane in the environment.

These compounds disrupt immune function by affecting white blood cells, adversely affecting kidneys, affecting calcium metabolism, and are carcinogenic to some animals.

Methoxychlor (C16H15O2Cl3)

Methoxychlor

Methoxychlor is an insecticide with similar properties to those of DDT, though it is less persistent in the environment and less toxic to animals. Methoxychlor is presently used in both western and developing countries, but is more expensive and harder to produce than DDT.

Methoxychlor is an environmental estrogen and therefore decreases reproductive success, has been shown to hinderfetal development, and adversely affects development of the gonads of bird embryos.

Mirex (C10Cl12)

The Pentacyclodecane group (Mirex)

Mirex was used as an insecticide in the southern US and as an industrial flame- and fire-retardant in plastics in North America. The use of mirex has been prohibited in Canada and the US for over 10 years but it is in limited use elsewhere in the world. Mirex is highly persistent and accumulates in organisms to high concentrations.

Hooker Chemicals and Plastics Corp., along the Niagara River, was the manufacturer of mirex. The chemical made its way into Lake Ontario, and eventually into the Gulf of St. Lawrence, largely as a result of accidental discharges made by Hooker Chemicals.

Mirex's toxic effects include interference with the liver - including its ability to deal with PCBs, is considered carcinogenic, and it has been associated with retarded rates of growth in mammals.


    Aldrin, Dieldrin, Endrin, and Endrin aldehyde

    Aldrin and dieldrin are agricultural pesticides. Aldrin is converted to dieldrin in both in the environment and in the liver. The use of aldrin and dieldrin has been banned in most western countries, but they are still being used in Mexico, Caribbean countries and in Central and South America.

    Toxic Effects: dieldrin produces liver cancer in some mammals. Dieldrin suppresses the immune system and as a result decreases natural resistance to bacterial and viral infections. Even very low concentrations of dieldrin can have biological effects.

Aldrin

(C12H8Cl6)

Dieldrin

(C12H8OCl6)

Endrin

(C12H8OCl6)

Endrin Aldehyde

(C12H10OCl6)


DDT and related compounds
DDT - Dichlorodiphenyl-trichloroethane (C14H9Cl5)

DDT is considered one of the most effective and economical insecticides ever manufactured. While banned in North America in 1972, DDT is still in wide usage in third-world nations and China. Commercially, DDT is a complex mixture where the p,p'-isomer (the only isomer with insecticidal properties) contributes to about 75% of the product. DDT is persistent and lipophillic, and has been linked to reproductive failure, egg shell thinning, and a variety of other effects in various species.

DDD - Dichlorodiphenyl-dichloroethane (C14H10Cl4)

    Both DDD and DDE and generally metabolites of DDT - that is, when an organism ingests DDT its 'detoxifing system' tries to make it less harmful by converting it into DDD or DDE. DDE also exists in the environment, as it makes up ~1% of the commercial mixture of DDT.

DDE - Dichlorodiphenyl-dichloroethylene (C14H8Cl4)

     See above. DDD has also been used by itself as an insecticide.

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by Geoff Wild and
Jason de Koning