Chlorinated hydrocarbons:

Two of the earliest chlorinated hydrocarbons were DDT and DDE. Banned in the late 70's in the US, their presence is still felt worldwide today.

DDT, is a colorless chemical pesticide, [dichlorodiphenyltrichloroethane], used even today to eradicate disease-carrying and crop-eating insects. It was first isolated in Germany in 1874, but not until 1939 did the Swiss Nobel Prize-winning chemist Paul Müller recognize it as a potent nerve poison to insects.

First used heavily in World War II for preinvasion spraying, DDT was disseminated in great quantities thereafter throughout the world to combat yellow fever, typhus, elephantiasis, and other insect-vectored diseases. In India, DDT reduced malaria from 75 million cases to fewer than 5 million cases in a decade. Crops and livestock sprayed with DDT sometimes as much as doubled their yields.

However one problem with these compounds is due to their ability to persist in the environment. Compare the turnover times for the following compounds:

Mode of action: most are neurotoxins, affecting the CNS with symptoms of tremor, jerking of eyes, changes in personality and loss of memeory.




They are absorbed through the lungs, GI tract, skin.

Till not too long ago, they were used for scabies treatment - topical treatment containing 10%

Aldrin LD = (rat) 39 mg/kg Dieldrin LD = 46 mg/kg

Still now, you can find these same compounds in the news.... some how they just don't disappear... recycled one to many times throughout the globe as the 2 abstracts below describe.....

World to discuss persistent organic pollutants ////

DDT drastically affected peregrine falcon populations in Utah's Zion National Park.Persistant organic pollutants will be the subject of debate at a conference in Montreal, Canada,

"In addition to producing death and sickness through direct contact, many highly toxic chemicals and pesticides persist for years in the environment, where they cause long-term damage to human health and to nature", said Klaus Toepfer, executive director of the United Nations Environment Program, which is sponsoring the negotiations. "These substances travel readily across international borders to even the most remote region, making this a global problem that requires a global solution", he said.

A growing body of scientific evidence indicates that exposure to very low doses of certain POPs -- which are among the most toxic substances ever created -- can lead to cancer, damage to the central and peripheral nervous systems, diseases of the immune system, reproductive disorders and interference with normal infant and child development.

Another concern behind the treaty negotiations is the growing accumulation of unwanted and obsolete stockpiles of pesticides and toxic chemicals, particularly in developing countries. Dump sites and toxic drums from the 1950s, 1960s and 1970s are now decaying and leaching chemicals into the soil and poisoning water resources, wildlife and people.

These highly stable compounds can last for years or decades before breaking down. They circulate globally through a process known as the "grasshopper effect". POPs released in one part of the world can, through a repeated (and often seasonal) process of evaporation, deposit, evaporation, deposit, be transported through the atmosphere to regions far away from the original source.

In addition, POPs concentrate in living organisms through another process called bioaccumulation. Though not soluble in water, POPs are readily absorbed in fatty tissue, where concentrations can become magnified up to 70,000 times the background levels. Fish, predatory birds, mammals and humans are high up the food chain and so absorb the greatest concentrations. When they travel, the POPs travel with them. As a result of these two processes, POPs can be found in people and animals living in regions such as the Arctic, thousands of kilometers from any major POP source.

POPs are either used as pesticides, consumed by industry or generated unintentionally as by-products of various industrial processes.

The Montreal talks will focus on a list of 12 persistent organic pollutants -- aldrin, chlordane, DDT, dieldrin, dioxins, endrin, furans, heptachlor, hexachlorobenzene, mirex, PCBs and toxaphene. Scientific criteria will be developed for identifying other POPs that may be added to the list later.

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