About DICHLORVOS

Please Note: The main sources of information for this fact sheet are EPA's Integrated Risk Information System (IRIS), which contains information on inhalation chronic toxicity of dichlorvos and the RfC, oral chronic toxicity and the RfD, and the carcinogenic effects of dichlorvos including the unit cancer risk for oral exposure; and the International Agency for Research on Cancer (IARC) monographs on chemicals carcinogenic to man. Other secondary sources include the Hazardous Substances Data Bank (HSDB), a database of summaries of peer-reviewed literature, and the Registry of Toxic Effects of Chemical Substances (RTECS), a database of toxic effects that are not peer reviewed.

 Environmental/Occupational 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. (1)

* Individuals may be exposed to dichlorvos from indoor air in buildings where it is used in pest strips or sprays for insect control. (2)

* Small amounts of residues of dichlorvos have been detected in food. (3)

Assessing Personal Exposure   

* No information was located concerning the measurement of personal exposure to dichlorvos.

Health Hazard Information   

Acute Effects:

* Acute (short-term) exposure to dichlorvos by inhalation has resulted in the reduction of cholinesterase levels in the blood of some humans. (2,3)

* Symptoms of acute inhalation exposure observed in humans include: tightness of chest, wheezing, pupil constriction, blurred vision, tearing, and headaches. Acute oral exposure results in nausea, vomiting, cramps, and diarrhea. Sweating and twitching have been observed in humans acutely exposed to dichlorvos dermally. Paralysis and respiratory failure are severe reactions that may occur in humans by any route of exposure to dichlorvos. (1,2,4)

* Tests involving acute exposure of animals, such as the LC50 and LD50 tests in 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. (5)

Chronic Effects (Noncancer):

* Decreased plasma and red blood cell cholinesterase levels have been observed in animals and humans chronically (long-term) exposed to dichlorvos by ingestion or inhalation. (3)

* The RfC for dichlorvos is 0.0005 mg/m3 based on decreased brain cholinesterase activity in rats. (4)

* EPA has medium confidence in the study on which the RfC was based because the principal study was well-conducted for its time; medium confidence in the database because an inhalation-based assessment of its multigeneration reproductive toxicity was not found; and consequently the confidence in the RfC is medium.

* The RfD for dichlorvos is 0.0005 mg/kg/d based on plasma and red blood cell cholinesterase inhibition in male and female dogs and brain cholinesterase inhibition in male dogs. (4)

* EPA has medium to high confidence in the study on which the RfD was based because, although the principal study is of good quality, there was a change in the dosing regime; medium confidence in the database because it lacks a rabbit developmental toxicity study and adequate studies to fully address chronic and reproductive toxicity in the rat; and, consequently, medium confidence in the RfD.

Reproductive/Developmental Effects:

* No information is available on the reproductive or developmental effects of dichlorvos in humans.

* In one study, birth defects in 3 of 41 fetuses were observed in rats exposed to dichlorvos by injection; however, in other animal studies, birth defects were not observed. (2,3)

Cancer Risk:

* No information is available on the carcinogenic effects of dichlorvos in humans.

* Significant increases in forestomach tumors in mice and leukemia and pancreatic adenomas in rats have been observed in animals exposed to dichlorvos by gavage (experimentally placing the chemical in the stomach). Also, lung tumors in male rats and mammary tumors in female rats have been reported. (4)

* EPA has classified dichlorvos as a Group B2, probable human carcinogen. (4)

* EPA uses mathematical models, based on human and animal studies, to estimate the probability of a person developing cancer from drinking water containing a specified concentration of a chemical. EPA calculated an oral unit risk estimate of 8.3 H 10-6 (m g/L)-1. EPA estimates that, if an individual were to drink water containing dichlorvos at 0.1 m g/L* over his or her entire lifetime, that person would theoretically have no more than a one-in-a-million increased chance of developing cancer as a direct result of drinking water containing this chemical. Similarly, EPA estimates that drinking water containing 1.0 m g/L would result in not greater than a one-in-a-hundred thousand increased chance of developing cancer, and water containing 10.0 m g/L would result in not greater than a one-in-ten thousand increased chance of developing cancer. (4)

* EPA's Office of Air Quality Planning and Standards, for a hazard ranking under Section 112(g) of the Clean Air Act Amendments, has ranked dichlorvos in the nonthreshold category. The 1/ED10 value is 1.7 per (mg/kg)/d and this would place it in the medium category under Superfund's ranking for carcinogenic hazard. (6)

Physical Properties

* The chemical formula for dichlorvos is C4H7Cl2O4P, and its molecular weight is 220.98 g/mol. (3,7)

* Dichlorvos occurs as an oily colorless to amber liquid that is slightly soluble in water. (1,3,4)

* Dichlorvos has an aromatic chemical odor; the odor threshold has not been established. (1,4)

* The vapor pressure for dichlorvos is 0.012 mm Hg at 20 EC. (3,7)

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. (4)

References

1. M. Sittig. Handbook of Toxic and Hazardous Chemicals and Carcinogens. 2nd ed. Noyes Publications. Park Ridge, NJ. 1985.

2. U.S. Department of Health and Human Services. Hazardous Substances Data Bank (HSDB, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.

3. International Agency for Research on Cancer (IARC). IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Humans: Some Halogenated Hydrocarbons. Volume 20. World Health Organization, Lyon. 1979.

4. U.S. Environmental Protection Agency. Integrated Risk Information System (IRIS) on Dichlorvos. Environmental Criteria and Assessment Office, Office of Health and Environmental Assessment, Office of Research and Development, Cincinnati, OH. 1994.

5. U.S. Department of Health and Human Services. Registry of Toxic Effects of Chemical Substances (RTECS, online database). National Toxicology Information Program, National Library of Medicine, Bethesda, MD. 1993.

6. U.S. Environmental Protection Agency. Technical Background Document to Support Rulemaking Pursuant to the Clean Air ActCSection 112(g). Ranking of Pollutants with Respect to Hazard to Human Health. EPAB450/3-92-010. Emissions Standards Division, Office of Air Quality Planning and Standards, Research Triangle Park, NC. 1994.

7. The Merck Index. An Encyclopedia of Chemicals, Drugs, and Biologicals. 11th ed. Ed. S. Budavari. Merck and Co. Inc., Rahway, NJ. 1989.

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