Dichlorovos

Dichlorvos is an insecticide used on crops, animals, and in pest-strips. Acute (short-term) and chronic (long-term) exposures of humans to dichlorvos results in the inhibition of an enzyme, acetylcholinesterase, with neurotoxic effects including perspiration, vomiting, diarrhea, drowsiness, fatigue, headache, and at high concentrations, convulsions, and coma. No information is available on the reproductive, developmental, or carcinogenic effects of dichlorvos on humans. A study by the National Toxicology Program (NTP) reported an increased incidence of tumors of the pancreas, mammary glands, and forestomach in animals.

Uses

Dichlorvos is used as an agricultural insecticide on crops, stored products, and animals. It is also used as an insecticide for slow release on pest-strips for pest control in homes. Dichlorvos is used as an anthelmintic (worming agent) for dogs, swine, and horses, as a botacide (agent that kills fly larvae) for horses, and in flea collars for dogs.

Sources and Potential Exposure

Individuals involved in the manufacture, formulation, and application of dichlorvos in agricultural, household, and public health uses are most likely to be exposed to this insecticide. Individuals may be exposed to dichlorvos from indoor air in buildings where it is used in pest strips or sprays for insect control. Small amounts of residues of dichlorvos have been detected in food.

Assessing Personal Exposure

Tests are available that measure the activity of two enzymes, serum cholinesterase and erythrocyte acetylcholinesterase, that are affected by dichlorvos.

Acute Effect

Health Hazard Informations:

Dichlorvos exerts its toxic effects in humans and animals by inhibiting the enzyme, acetylcholinesterase. Effects from acute exposure include perspiration, nausea, vomiting, diarrhea, drowsiness, fatigue, headache, and at very high concentrations, convulsions, and coma.

Tests involving acute exposure of rats, mice, and rabbits have demonstrated dichlorvos to have high to extreme acute toxicity from oral or dermal exposure and extreme acute toxicity from inhalation.

Chronic Effects (Noncancer):

Acetylcholinesterase inhibition may also occur in humans from chronic exposure to dichlorvos.

Symptoms in animals orally exposed to dichlorvos include ataxia, salivation, dyspnea, tremors, and diarrhea.

The Reference Concentration (RfC) for dichlorvos is 0.0005 milligrams per cubic meter (mg/m3) based on decreased brain cholinesterase activity in rats. The RfC is an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the

human population (including sensitive subgroups), that is likely to be without appreciable risk of deleterious noncancer effects during a lifetime. It is not a direct estimator of risk but rather a reference point to gauge the potential effects. At exposures increasingly greater than the RfC, the potential for adverse health effects increases. Lifetime exposure above the RfC does not imply that an adverse health effect would necessarily occur.

Reproductive/Developmental Effects:

No information is available on the reproductive or developmental effects of dichlorvos in humans. In one study, birth defects in fetuses were observed in rats exposed to dichlorvos by injection; however, in several other animal studies, birth defects were not observed. Sperm abnormalities were observed in mice injected with dichlorvos.

Cancer Risk:

No information is available on the carcinogenic effects of dichlorvos in humans. In a gavage study by the NTP, there was an increased incidence of tumors of the pancreas and leukemia in male rats, tumors of the pancreas and mammary gland in female rats, and tumors of the fore stomach in both sexes of mice. Dichlorvos was not found to be carcinogenic in an animal study by the National Cancer Institute (NCI) in which the compound was administered in the diet.