Dichlorvos

Full Profile

General Information

Dichlorvos is a synthetic organic chemical used as a pesticide.^[2] It is a dense, sweet smelling colourless liquid which evaporates easily into air and reacts readily with water.^[2] Dichlorvos is a member of the organophosphate group of pesticides.^[2] It may also be referred to as DDVP, and trade names include Vapona®, Atgard®, Nuvan®, and Task®.^[2,3] There are numerous other synonyms and product names; see HSDB for more information.^[3]

Dichlorvos has been classified by IARC as Group 2B, possibly carcinogenic to humans, based on animal studies that showed increased rates of leukemia and forestomach and pancreatic tumours in rats, and increased esophageal and forestomach tumours in mice following exposure.^[4] A recent analysis of the Agricultural Health Study cohort data in the US did not find elevated cancer rates in pesticide applicators exposed to dichlorvos.^[5]

Dichlorvos is highly toxic to the nervous system through its inhibition of acetylcholinesterase.^[2] Acute exposure to dichlorvos may cause nausea, fatigue, drowsiness and headache. Coma, respiratory arrest and death may result from high exposures (≥ 5 ounces of a 5% dichlorvos solution).^[2]

Dichlorvos has been ranked by CAREX Canada as Group A (immediate high priority) for environmental settings and as Group B (possible high priority) for occupational settings. Prioritization was based on the carcinogenicity and other toxic properties of dichlorvos, the prevalence of exposure in Canada, and the feasibility of assessing exposure.

Regulations and Guidelines

Occupational Exposure Limits (OEL)

Canadian Jurisdictions	OEL (mg/m3)
Canada Labour Code	0.1 (IFV) [sk, sen]
AB	0.1 [sk]
SK	0.1 (IFV) [sk, sen] 0.3 [stel]
BC, MB, ON, NL, PE, NS, NB	0.1 (IFV) [sk, sen]
QC	0.9 [sk]
YT	1 [sk] 3 [stel]
NT, NU	0.9 [sk] 2.7 [stel]
Other Jurisdiction	OEL (mg/m3)
ACGIH 2011 TLV	0.1 (IFV) [sk, sen]

Canadian Environmental Guidelines

Jurisdiction	Limit	Year
Veterinary New Drug List, Sec. 2: Food and Drug Act	Included	2001[8]

Canadian Maximum Residue Level (MRL) Limits^[9]

Food Item(s)	MRL (ppm)
Tomatoes	0.25
Non-perishable packaged foods of low fat content (<6%)	0.5
Non-perishable packaged foods of high fat content (>6%)	2.0

Canadian Agencies/Organizations

Agency	Designation/Position	Year
Health Canada	DSL – high priority substance with lowest potential for exposure	2006[10]
PMRA	Re-evaluation of dichlorvos – ongoing	2008[12]

Main Uses

Dichlorvos has been widely used as an insecticide since 1961.^[4] It is mainly used for insect control in food storage areas, greenhouses and barns, and for parasite control in livestock and domestic animals.^[2] It is also used to control insects in workplaces.^[13]In general, dichlorvos is not used on outdoor crops.^[2]

Dichlorvos may be used in the form of dust, granules, pellets, impregnated resin strips or concentrates.^[4] It can also be diluted with other liquids and used as a spray, or incorporated into slow releasing plastics.^[2]

Canadian Production and Trade

No evidence was located on Canadian production or trade of dichlorvos.

Occupational Exposures

Workers with the highest potential for exposure are involved in its production and use.^[4] These occupations include chemical plant workers, transport workers, and pesticide applicators. Workers are mainly exposed through inhalation; dermal exposure can also occur.^[2]

Environmental Exposures

The general public is most likely to be exposed to dichlorvos via inhalation of contaminated air. Skin contact may occur via contaminated soil, and small amounts of dichlorvos residue has been detected in food.^[2,18] However, it is expected that the general population is minimally exposed to dichlorvos through the food and drinking water routes.^[13] The majority of exposure to dichlorvos occurs from its use in pest strips or sprays for insect control in the home and in public.^[4,18] Dichlorvos is not known to be accumulated in plants or animals.^[2]

Dichlorvos evaporates easily into the air and can react with water vapour to be broken down (this reaction is faster under conditions of high heat and humidity).^[2] Dichlorvos may enter the environment through landfill waste contamination, accidental spills during transport, and leaks from storage containers.^[2] Dichlorvos does not bind easily to soil and moves through it quickly, however its breakdown in this medium is slower than in air or water.^[2] On dry hard surfaces it can persist longer; on wood, 39% of dichlorvos may remain for up to 33 days.^[13]

Exposure may occur in populations living near hazardous waste sites containing dichlorvos (usually in the form of liquid solution or as solid plastic pellets or strips) or sites where it is manufactured, processed, or stored.^[2]

The World Health Organisation (WHO) and the Food and the Agriculture Organization of the United Nations have designated 0–0.004 mg/kg of body weight as an acceptable daily intake (ADI) of dichlorvos.^[13] WHO recently concluded that a formal guideline value for dichlorvos in drinking water was unnecessary since it is not normally found in drinking water, although a guideline value would be useful in the case of water contamination following accidental spills.^[13]

Dichlorvos is not reportable to the NPRI.^[19] A search in the Household Products Database yielded two products, both were pest control strips.^[20]

Sources

1. Wikimedia Commons Photo: Dichlorvos
2. ATSDR Toxicological Profile for Dichlorvos (1997) (PDF)
3. Hazardous Substances Database entry for Dichlorvos (Search term: ‘dichlorvos’)
4. IARC monograph summary, Volume 53 (1991) (PDF)
5. Koutros S, Mahajan et al - Dichlorvos exposure and human cancer risk: results from the Agricultural Health Study Cancer Causes Control (2008) 19:59–65
6. Health Canada (2010) Guidelines for Canadian Drinking Water
7. Exposure Guidelines for Residential Indoor Air Quality (1987)
8. Health Canada, Veterinary New Drugs List – Section 2 of the Food and Drugs Act (2001)
9. Health Canada, Consumer Product Safety, Maximum Residue Limits for Pesticides (2011)
10. Health Canada’s Prioritization of the DSL (2006)
11. CEPA List of Toxic Substances (1999)
12. Health Canada Consumer Product Safety Re-evaluation Note: Dichlorvos Interim Measures (2008)
13. WHO Background document for development of Guidelines for Drinking-water Quality (2007) (PDF)
14. BC Ministry of the Environment, Survey of Pesticide Use in BC (2003) (PDF)
15. Ontario Ministry of Agriculture and Food, Survey of Pesticide Use in Ontario, 2003 (2004)
16. Canadian Food Inspection Agency, Livestock Feed, Dichlorvos (2009)
17. Government of Canada (2010) Chemicals Management Plan – List of all Challenge Substances
18. EPA: Dichlorvos (2007)
19. The National Pollutant Release Inventory
20. Household Products Database (US)

Other Resources

1. ATSDR Toxicological Profile for Dichlorvos (1997) (PDF)
2. World Health Organization, International Programme on Chemical Safety – Environmental Health Criteria 79: Dichlorvos
3. INCHEM Document: Evaluation of some Pesticide residues on food (1967)