© Stuart M Bennett 2001

Dichlorvos is an organophosphate compound used to control household, public health, and stored product insects. It is effective against mushroom flies, aphids, spider mites, caterpillars, thrips, and white flies in greenhouse, outdoor fruit, and vegetable crops. Dichlorvos is used to treat a variety of parasitic worm infections in dogs, livestock, and humans. Dichlorvos can be fed to livestock to control botfly larvae in the manure. It acts against insects as both a contact and a stomach poison. It has been used to make pet collars and pest strips. It is available as an aerosol and soluble concentrate.

IUPAC name: 2,2-dichlorovinyl dimethyl phosphate

Chemical Formula: C4H7Cl2O4P

LD50/LC50: The oral LD50 for dichlorvos is 61 to 175 mg/kg in mice, 100 to 1090 mg/kg in dogs, 15 mg/kg in chickens, 25 to 80 mg/kg in rats, 157 mg/kg in pigs, and 11 to 12.5 mg/kg in rabbits. The dermal LD50 for dichlorvos is 70.4 to 250 mg/kg in rats, 206 mg/kg in mice, and 107 mg/kg in rabbits. The 4-hour LC50 for dichlorvos is greater than 0.2 mg/L in rats.

Dichlorvos is highly toxic by inhalation, dermal absorption, and ingestion. Because dichlorvos is volatile, inhalation is the most common route of exposure. As with all organophosphates, dichlorvos is readily absorbed through the skin. Acute illness from dichlorvos is limited to the effects of cholinesterase inhibition. Compared to poisoning by other organophosphates, dichlorvos causes a more rapid onset of symptoms, which is often followed by a similarly rapid recovery. This occurs because dichlorvos is rapidly metabolized and eliminated from the body. Persons with reduced lung function, convulsive disorders, liver disorders, or recent exposure to cholinesterase inhibitors will be at increased risk from exposure to dichlorvos. Alcoholic beverages may enhance the toxic effects of dichlorvos. High environmental temperatures or exposure of dichlorvos to light may enhance its toxicity. Dichlorvos is mildly irritating to skin. Concentrates of dichlorvos may cause burning sensations, or actual burns.

Symptoms of acute exposure to organophosphate or cholinesterase-inhibiting compounds may include the following: numbness, tingling sensations, incoordination, headache, dizziness, tremor, nausea, abdominal cramps, sweating, blurred vision, difficulty breathing or respiratory depression, slow heartbeat. Very high doses may result in unconsciousness, incontinence, and convulsions or fatality. Some organophosphates may cause delayed symptoms beginning 1 to 4 weeks after an acute exposure that may or may not have produced immediate symptoms. In such cases, numbness, tingling, weakness, and cramping may appear in the lower limbs and progress to incoordination and paralysis. Improvement may occur over months or years, but some residual impairment may remain.

Effects on birds: Dichlorvos is highly toxic to birds, including ducks and pheasants; the LD50 in wild birds fed dichlorvos is 12 mg/kg.

Effects on aquatic organisms: UV light makes dichlorvos 5 to 150 times more toxic to aquatic life. Dichlorvos does not significantly bioaccumulate in fish.

Effects on other organisms: ***Dichlorvos is toxic to bees***.

Breakdown in soil and groundwater: Dichlorvos has low persistence in soil. Half-lives of 7 days were measured on clay, sandy clay, and loose sandy soil. In soil, dichlorvos is subject to hydrolysis and biodegradation. Volatilization from moist soils is expected to be slow. The pH of the media determines the rate of breakdown. Breakdown is rapid in alkaline soils and water, but it is slow in acidic media. For instance, at pH 9.1 the half-life of dichlorvos is about 4.5 hours. At pH 1 (very acidic), the half-life is 50 hours. Dichlorvos does not adsorb to soil particles and it is likely to contaminate groundwater. When spilled on soil, dichlorvos leached into the ground with 18 to 20% penetrating to a depth of 12 inches within 5 days.

Breakdown in water: In water, dichlorvos remains in solution and does not adsorb to sediments. It degrades primarily by hydrolysis, with a half-life of approximately 4 days in lakes and rivers. This half-life will vary from 20 to 80 hours between pH 4 and pH 9. Hydrolysis is slow at pH 4 and rapid at pH 9. Biodegradation may occur under acidic conditions, which slow hydrolysis, or where populations of acclimated microorganisms exist, as in polluted waters. Volatilization from water is slow. It has been estimated at 57 days from river water and over 400 days from ponds.

Breakdown in vegetation: Except for cucumbers, roses, and some chrysanthemums, plants tolerate dichlorvos very well.

Physical Properties:

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