Dichlorvos
Pesticide Fact Sheet
Prepared for the U.S. Department of Agriculture, Forest Service by Information
Ventures, Inc.
This fact sheet is one of a series issued by the Forest Service for their workers and the
general public. It provides information on forest and land management uses,
environmental and human health effects, and safety precautions for the insecticide,
dichlorvos and its formulations. Unless otherwise stated, the toxicity data presented in
this fact sheet refer to the active ingredient, dichlorvos (DDVP). When included, data
on formulated products will be specifically identified.
In 1988 the U.S. Environmental Protection agency began a Special Review of DDVP
based on evidence that exposure to the registered uses could pose unreasonable risks
of cancer as well as adverse effects on the central nervous system as a result of the
pesticide’s cholinesterase-inhibiting effects. During the course of this Special Review,
EPA determined that DDVP poses a cancer risk only as a result of dietary
exposure, and not from dermal or inhalation exposure. On September 28, 1995,
the EPA published a Notice of Preliminary Determination (Position Document 2/3) in
the Federal Register that proposes to cancel most uses of DDVP and to restrict the
retained uses to specially trained certified applicators. The use of DDVP impregnated
strips (such as Vaportape II) in outdoor insect traps was excluded from the proposed
cancellations and restrictions because this use does not result in significant human
exposure
V. Toxicology Data
Acute toxicity:
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Acute oral toxicity: In tests in rats, the acute oral LD50 was 56 mg/kg for
females and 80 mg/kg for males. (Toxicity Category II, Table I, Oral)
Acute dermal toxicity: In rats, the acute dermal LD50 was 75 mg/kg for
females and 107 mg/kg for males. (Toxicity Category II, Table I, Dermal)
Primary irritation score: In laboratory tests inrabbits, dichlorvos was a mild
skin irritant. (Toxicity Category IV, Table I, Skin Irritation)
Primary eye irritation: In laboratory tests in rabbits, dichlorvos was a mild
eye irritant. (Toxicity Category III, Table I, Eye Irritation)
Acute inhalation: In tests in rats, the acute inhalation LC50 was greater than
198 milligrams/cubic meter. (Toxicity Category II, Table I, Inhalation)
Chronic toxicity:
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Carcinogenicity: Studies were conducted in mice and rats given dichlorvos at
10 to 40 mg/kg per day (mice) or 4 to 8 mg/kg per day (rats) for up to 2 years.
There was an increase in the number of tumors in female mice and female and
male rats.
Developmental: Laboratory studies in rats and rabbits indicated that
dichlorvos did not cause birth defects.
Reproduction: In a three generation study in rats, dichlorvos at up to 500
mg/kg of diet (highest dose tested) had no effect on fertility or offspring. In
male mice given dichlorvos at a dose of 40 mg/kg body weight, there was a
decrease in the weight of the testes, and an increase in atrophy or wasting of
the testes.
Mutagenicity: In laboratory tests, dichlorvos was found to be a mutagen.
HAZARD: Based on the results of animal studies, dichlorvos is classified as a
mutagen and a possible human carcinogen (Class C). Dichlorvos is not classified as a
teratogen. Laboratory tests have shown that dichlorvos may affect the immune
system.
A Special Review of dichlorvos was initiated in February 1988 because EPA
determined that the registered uses of dichlorvos may pose a risk of cancer as well as
inadequate margins of safety for cholinesterase inhibition and liver effects to exposed
persons. As a result of the Special Review, the EPA published a Notice of Preliminary
Determination (Position Document 2/3) in the Federal Register on September 28,
1995. While the EPA proposed that most dichlorvos uses be cancelled and that most
retained uses be restriced to specially trained certified pesticide applicators, no action
was proposed for dichlorvos impregnated strips used in outdoor insect traps. The EPA
concluded that this use does not result in significant human exposure.
VI. Human Health Effects
Acute toxicity (poisoning):
Reported effects: Several fatal and nonfatal poisonings from dichlorvos have been
reported after concentrated formulations of dichlorvos splashed onworkers. There
have been several reported suicides using dichlorvos. There have been reported
incidents in which children have been poisoned by pest strips containing dichlorvos;
none of these have been fatal. Dichlorvos is an organophosphate insecticide. Like
other organophosphate insecticides, it inhibits the enzyme acetylcholinesterase, which
normally prevents the accumulation of acetylcholine at nerve synapses (junction
between nerve cells). Acetylcholine then accumulates, interfering with the function of
the nervous system. Symptoms of overexposure to dichlorvos include vision
problems, nausea, headache, and shortness of breath.
Chronic toxicity:
Reported effects: Symptoms of chronic exposure are similar to those of acute
exposure, plus tension, insomnia, loss of appetite, apathy, trembling and confusion.
Potential for adverse health effects from contacting or consuming treated
vegetation, water or animals: Because the dichlorvos is embedded in slow release
plastic strips, there is only limited contact with vegetation, water and animals. Under
normal handling and use conditions, strips containing dichlorvos are not likely to be a
significant hazard to workers or the public. There might be a potential for adverse
effects if children or other persons tamper with traps, and remove the strips.
Potential for adverse health effects from inert ingredients contained in the
formulated product: Because of concern for human health and the environment, the
U.S. Environmental Protection Agency (EPA) announced its policy on inerts of
toxicological concern (Lists 1 and 2) in the Federal Register on April 22, 1987 (52 FR
13305). The intent of this policy is to encourage the use in pesticide products of the
least toxic inert ingredients available. EPA's strategy for the implementation of this
policy included the development of lists of inert ingredients according to toxicity. The
toxicity categories for the lists of inert ingredients are:
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List 1 - Inerts of toxicological concern
List 2 - Potentially toxic inerts/high priority for testing
List 3 - Inerts of unknown toxicity for which there is little concern that they
will be shown to be toxic
List 4A - Minimal risk inert ingredients
List 4B - Inert ingredients for which the EPA has sufficient information to
conclude that their current use patterns in pesticide products will not adversely
affect public health and the environment
For pesticides containing List 1 inerts, the EPA has given the pesticide registrant the
opportunity to reformulate theproduct to remove the List 1 inerts. If the registrant
chooses not to reformulate the product, then the List 1 inerts must be identified on the
product label. For List 2 inerts, the EPA is monitoring ongoing testing and gathering
existing information on the potential adverse effects of these chemicals to determine if
further regulatory action is required. The EPA has no particular regulatory plans for
List 3 and List 4 inerts. The Forest Service will incorporate new data on inerts into
updated fact sheets as it becomes available.
No inerts cited on EPA List 1 are included in the Vaportape® II formulation. None of
the inerts in these formulations have been publicly identified by the manufacturer.
Health effects of exposure to formulated products: Under condition of normal
handling and use, it is unlikely that dichlorvos impregnated strips will present a
significant hazard to workers or the general public. However, if the strips are not
handled properly during trap assembly or transport, or if traps are tampered with,
significant exposure may occur. Oral, dermal, and inhalation exposure to dichlorvos
strips may result in signs of organophosphate poisoning.
Health effects associated with other formulations: Some formulations of
dichlorvos also contain other active ingredients, such as propoxur or phosalone. The
information in this fact sheet only applies to formulations in which dichlorvos is
the only active ingredient. Consult other fact sheets for information on the other
active ingredients.
Health effects associated with contaminants: Contaminants in dichlorvos include
the related compounds dipterex, O,O-dimethyl 2-chlorovinyl phosphate, O,Odimethyl methylphosphonate, O,O,O-trimethyl phosphate, and trichloroacetaldehyde.
These compounds are known to be or are likely to be toxic. In Vaportape® II, these
compounds together account for 0.75% of the contents.
Health risk management procedures: The Forest Service has evaluated health
effects data in the development of both pesticide background statement documents
and environmental impact statements for pesticide use on forest lands. These health
effects evaluations have taken into consideration the potential for both worker and
public exposure from Forest Service operations. This information has been used in
assessing health risks and consequently in formulating protective measures to reduce
risk to forest workers and to the public. Section VII of this fact sheet, Safety
Precautions, provides guidance for the safe handling and use of dichlorvos.
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