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The Dangers of Pesticides
Natural Resources Defense Council

Organophosphate and Carbamate Insecticides

Americans, especially children, are widely exposed to these hazardous pesticides. Of nearly 900 pesticides registered for use in the United States, 37 belonging to a class of insecticides known as organophosphates and 22 known as carbamates are among those posing the highest risks to human health, according to 1997 findings of the Environmental Protection Agency. The chemicals in these two classes are designed to kill insects by disrupting their brains and nervous systems. Specifically, they inhibit the function of a key enzyme in the nervous system called cholinesterase.

Cholinesterase, however, is not unique to insects -- it is also a component of the human nervous system. Nevertheless, 17 organophosphate insecticides, as well as additional carbamates, are registered by the EPA for "residential" use, which includes use in and around homes and schools and on playgrounds, lawns, and gardens. (Dursban, the most heavily used insecticide in the country, is an organophosphate.)

Organophosphates are considered the most likely pesticides to cause acute poisoning. From 1993 to 1996, nearly 63,000 reports were made to U.S. poison control centers about unintentional residential exposures to organophosphates. Almost 25,000 of these incidents involved children under 6, who are particularly vulnerable to organophosphate poisoning, and at least 482 resulted in hospitalization.

More alarming, studies in animals now show that even a single, low-level exposure to certain organophosphates, during particular times of early brain development, can cause permanent changes in brain chemistry as well as changes in behavior, like hyperactivity. Chlorpyrifos (the chemical in the insecticide Dursban), for example, decreases the synthesis of DNA in the developing brain, leading to drops in the number of brain cells. If these findings pertain to humans, it may mean that early childhood exposures to chlorpyrifos can lead to lasting effects on learning, attention, and behavior -- just as were seen with another environmental neurotoxin, lead.

Even with these factors in mind, many people may not consider organophosphate poisoning a serious worry, assuming they can avoid exposing their children to these chemicals by keeping them away from the lawn and garden after insecticides have been applied. But in addition to outdoor exposure, people, children included, also receive exposure to organophosphate and carbamate insecticides indoors and through food.

Indoor Exposure to Organophosphates

Many organophosphates are used indoors, by homeowners and professionals. Out of the sunlight, insecticide residues can persist. Residues are also tracked into the home on clothes or shoes, or drift indoors from adjacent lawns or fields.

A study in Jacksonville, Florida, estimated that in the spring, summer and fall there are detectable levels of three organophosphates, malathion, diazinon, and chlorpyrifos, in indoor air in the homes of at least 17, 83, and 88 percent of the population, respectively. Carpets, furniture, and house dust all collect pesticides; some pesticide residues persist in carpets for up to a year. In the Jacksonville study, Dursban and diazinon residues were each found in carpet dust of at least 82 percent of sampled homes. Another study of 362 homes found Dursban in the carpet dust of 67 percent.

Exposures to Organophosphates Through Food

The majority of insecticides used in homes and schools, as well as on playgrounds and household lawns, are also used on food crops, including many foods that are favorites with children (see the chart below). Which means that even intermittent residential exposure to organophosphate and carbamate insecticides are piled on top of a daily burden of residues in food.

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