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Organochlorines PDF Print E-mail

These are organic chemicals containing chlorine. They include polyvinylchloride (PVC), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), many solvents, dioxins, polychlorinated biphenyls (PCBs), and many pesticides such as DDT, dicofol and the cyclodienes, aldrin, dieldrin and chlordane/heptachlor. Many are named in the Stockholm Convention on persistent organic pollutants.

Most organochlorines (OCs) are chemically stable compounds which are readily soluble in oils but only slightly soluble in water.

Health effects
After ingestion, OCs are only very slowly eliminated from the body and they accumulate in fatty tissue and in the fatty membranes of cells and nerves. The cyclodienes are designed to interfere with the nerve function of insects and, at sufficiently high concentration, they have the same effect on humans. They are slowly broken down by enzymes in the liver and some of them form products which are more toxic than the original compound and which damage the liver.

Due to their fat solubility, OCs are often found in human milk and can affect babies. They are also passed on from one organism to another in the food chain, becoming more concentrated in the fatty tissues at each step, for example plankton---fish---humans.

All OCs should be treated as toxic and hazardous. Acute effects of poisoning include nausea, vomiting, weakness, numbness in extremities, respiratory problems and chloracne. The cumulative effects of chronic, sub-acute exposure are less predictable but may include reduced liver and nerve function and a range of sub-clinical problems. Some OCs have been recognised as carcinogens and/or cancer promoters and as interfering with normal cell function. Many OCs and their breakdown products are now recognised as endocrine disrupters which interfere with the immune and hormone system (see Introduction).

Environmental effects
Many OCs are so stable and chemically inert that they have long-lasting effects on the environment. Cyclodiene pesticides can remain active in soil for up to 20 years; CFCs remain in the atmosphere for up to 100 years, giving them time to diffuse into the stratosphere (see Ozone); and the purely synthetic PCBs are found in nearly every living thing on earth. PVC plastic lasts for years as agricultural drains but has no biological effect.

All chlorine-containing compounds form highly toxic combustion products when they are burned, for example, in a waste incinerator. Special emission controls are required to prevent these from reaching the environment. Some chemical methods have been developed to dispose of PCBs, OC pesticides and other very stable organochlorine compounds which do not involve burning.


 

 
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