Toxicologic Information About Insecticides
Used for Eradicating Mosquitoes
(West Nile Virus Control)
April 2005
The Division of Toxicology of the Agency for Toxic Substances and Disease Registry (ATSDR) prepared this document in response to queries to the Centers for Disease Control and Prevention and ATSDR about environmental health issues associated with insecticide applications that have been or may be used for eradicating mosquitoes, particularly the mosquito vector of West Nile Virus transmission. These insecticides are malathion, naled, permethrin, phenothrin, and resmethrin. In addition, the Division of Toxicology has included summaries for fenthion, methoprene, and temephos because they also have been used for mosquito control.
The purpose of the document is to provide health assessors within ATSDR and other public health officials with one source of summaries of toxicologic issues of the insecticides of interest. The individual summaries present brief background information about the insecticide use, environmental factors, potential for human exposure, health effects/toxicity in humans and animals, toxicokinetics, and standards and guidelines for protecting human health. Toxicity data are summarized in tables that provide no-observed-adverse-effect levels (NOAELs) and lowest-observed-adverse-effect levels (LOAELs) for endpoints for each study. Developmental and reproductive NOAELs and LOAELs also are presented. The tables are arranged by duration of exposure, route of exposure, and species.
Because of time constraints and the relative unavailability of unpublished studies submitted to the Environmental Protection Agency (EPA) under the Federal Insecticide, Fungicide and Rodenticide Act, the summaries presented in this document were compiled primarily from secondary sources. These sources included EPA’s registration documents and other EPA documents, the World Health Organization’s (WHO’s) International Programme on Chemical Safety (IPCS) data sheets, the Hazardous Substances Data Bank and others. The summaries for malathion, and the pyrethroids (resmethrin, phenothrin, and permethrin) were compiled from information in ATSDR’s Toxicological Profiles for these insecticides.
Fenthion, malathion, naled, and temephos are organophosphate insecticides that act by inhibiting the activity of cholinesterase. They have varying degrees of toxicity. Organophosphates also inhibit cholinesterase activity of animals and humans and at high enough levels can produce symptoms of cholinergic poisoning ranging from mild (headache, drowsiness) to moderate (difficulty breathing, cardiac arrhythmias, confusion) to life-threatening (coma, seizures, paralysis) effects. The pyrethroids (resmethrin, phenothrin, and permethrin) are synthetic analogues of original pyrethrins, which are natural extracts in the flowers of the chrysanthemum plant and act by rapidly paralyzing flying insects. Methroprene is an insect growth regulator and is used as a larvicide. It is a synthetic analogue of the insect juvenile hormone that has very low toxicity for animals and humans.
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