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Chemical Toxicity
Organophosphorus Pesticides

Toxic Effects

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Organophosphorus Pesticides ¹

The word "organophosphates" refers to a group of insecticides or nerve agents acting on the enzyme acetylcholinesterase. The toxic effects of organophosphates were first used by the Germans to develop nerve gas such as Sarin, Toban, and Soman. Then the British experimented with the cholinergic orthophosphate, disaproppyfluorophosphate DFP to produce VX nerve agent. Afterwards the Americans used orthophosphates to synthesize the pesticides parathion, malathion and azinphosphomethyl, followed by DDT, dieldrin, and heptachlor ².
About 70% of the insecticides in current use in the United States are organophosphorous (OP) pesticides. They work by interfering with the nervous system of insects, a mechanism that also affects the human nervous system when people are exposed. Other health effects of individual OP pesticides vary; some are highly acutely toxic, some cause development or reproductive harm, and some are known or suspected endocrine disruptors.

Since the banning of most organochlorine pesticides in the 1970ís, industry now use the less persistent, but more acutely toxic organophosphate (OP) and carbamate compounds to control insect pests.
These chemicals are applied to crops, buildings, ornamental plants and lawns. Agricultural uses include field applications on corn, cotton, canola, alfalfa, produce and nuts. Exterminators use OP pesticides in residential and commercial structures, and certain pest control products for cats and dogs contain organophosphorus compounds.

Products containing OPs include Dursban and Lorsban (containing the OP chlorpyrifos), Spectracide (containing the OP diazinon), and Sevin (containing the carbamate carbaryl). Residential uses of chlorpyrifos and diazinon were recently banned by the U.S. EPA.
Organophosphate insecticides, which include diazinon, azinphos methyl, and malathion, are very commonly used in agriculture.
The insectide carbaryl is widely used in Washington on apple and grape crops and on lawns and gardens.
People are commonly exposed to OP pesticides through eating fresh and processed vegetables, contacting pesticide-contaminated surfaces, breathing air near pesticide applications (both indoors and outdoors), and drinking pesticide-contaminated water.

Health Effects

OPs are chemically similar to the chemical warfare agents originally produced during World War II, and they work by interfering with the nervous system of insects, as well as mammals, birds, and fish. Organophosphorus compounds block production of an enzyme called cholinesterase (ChE), which ensures that the chemical signal that causes a nerve impulse is halted at the appropriate time. Symptoms of exposure include nausea, headaches, twitching, trembling, excessive salivation and tearing, inability to breathe because of paralysis of the diaphragm, convulsions, and at higher doses, death.

OPs are among the most acutely toxic pesticides, with most of these chemicals classified by the U.S. Environmental Protection Agency as toxicity class I (highly toxic) or toxicity class II (moderately toxic). In addition, some OP pesticides cause developmental or reproductive harm, some are carcinogenic, and some are known or suspected endocrine disruptors.

Organophosphate pesticides and carbaryl can have immediate effects on the nervous system, with symptoms including weakness, cramps, breathing trouble, nausea, and vomiting.
Animal studies suggest that organophosphates may impair children's brain development.
Studies on farmworkers find that people with greater exposure have poorer motor function and shorter attention spans.
Carbaryl is listed as a likely human carcinogen (EPA), linked to a higher incidence of childhood brain cancer in homes where carbaryl is used. Farmers using carbaryl have a higher risk of non-Hodgkins lymphoma.

1. Pesticide Action Network North America -
2. Wikipedia - Organophosphates