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CDC - Cancer Cluster archived website note

Historical Document

This document is provided by the National Center for Environmental Health ONLY as an historical reference for the public health community. It is no longer being maintained and the data it contains may no longer be current and/or accurate.

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What are organophosphates?

Organophosphates are a group of human-made chemicals that poison insects and mammals. Organophosphates are the most widely used insecticides today. They are used in agriculture, the home, gardens, and veterinary practice.

Organophosphate insecticides (such as diazinon) are one type of pesticide that works by damaging an enzyme in the body called acetylcholinesterase. This enzyme is critical for controlling nerve signals in the body. The damage to this enzyme kills pests and may cause unwanted side effects in exposed humans. All organophosphates have a common mechanism of toxicity and can cause similar symptoms in humans who have too much exposure.

Urine samples from participants in the Churchill County leukemia study were analyzed for organophosphate insecticides and their breakdown products (metabolites). The metabolites are not toxic, but show that exposure to organophosphates occurred in the few days before testing. Linking some of these metabolites to a specific, original organophosphate compound is not possible without additional information. Even though an organophosphate or its metabolites in a person indicates exposure, it does not necessarily show the person will become sick.

In our study of leukemia in children, levels of two organophosphate metabolites were high:

  • 3,5,6-Trichloro-2-pyridinol, a metabolite of chlorpyrifos
  • Diethylthiophosphate, a metabolite of numerous organophosphates such as diazinon

What happens to organophosphates when they enter the environment?

  • Because organophosphates are often sprayed on crops and plants, small particles of the chemical may be carried away from the field or yard before falling to the ground.
  • After organophosphates are applied, they may be present in the soil, surface waters, and on the surface of the plants. They can move through the soil and contaminate ground water.
  • Rain can wash organophosphates on soil and plant surfaces into surface waters.
  • Organophosphates are rapidly broken down into other chemicals so they do not build up in the environment.
  • Organophosphates are not likely to build up to high or dangerous levels in animal or plant foods that you might eat.

How can people be exposed to organophosphates?

  • By working for companies that make or apply organophosphates.
  • By ingesting (eating or drinking) or breathing them or by getting them in your eyes or on your skin.
  • By touching contaminated soils or contaminated runoff water or groundwater.
  • Eating contaminated food and skin contact during home application are the main sources of exposure.

Can exposure to organophosphates make people sick?

Yes. Symptoms of sudden poisoning by organophosphates start during or after exposure, depending on how the poison is contacted. Symptoms start fastest after organophosphates are breathed, and next by eating or drinking contaminated food or water or getting them on your skin. Some symptoms are headache, dizziness, weakness, diarrhea, nausea and vomiting, salivation, watery eyes, and small pupils. Severe symptoms are seizures, slow pulse, difficulty breathing, and coma. Long after exposure, people also can develop nervous system problems such as muscle weakness and numbness and tingling of the hands and feet (neuropathy).

Long-term exposure to organophosphates can cause confusion, anxiety, loss of memory, loss of appetite, disorientation, depression, and personality changes. Other symptoms such as weakness, headache, diarrhea, nausea and vomiting also may occur.

Can organophosphates cause any types of cancer, including leukemia?

We do not know for sure. Some studies in adults and children have linked organophosphate exposure to lymphoma and leukemia. Home pesticide use overall has been linked to childhood cancers such as soft tissue sarcomas, leukemias, and cancer of the brain. The results of these studies are controversial. No studies have definitively linked these exposures with cancer because the exposure is not measured and people usually are not exposed to just the one pesticide being studied.

In lab rats, studies of different organophosphates showed more adrenal, thyroid, and pancreatic tumors.

Can organophosphates cause reproductive or developmental problems?

There is no evidence to suggest that organophosphate exposure affects human reproduction or development.

Most organophosphates do not cause reproductive or developmental problems in animals, but some cause lower birth weights or more death in newborn animals.

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