What is being sprayed?

Permethrin is the main chemical agent in Biomistthe pesticide being used to kill adult mosquitos throughout the country including Northeast Ohio. It has been registered with the EPA since 1977. It resembles pyrethrins chemically, but is chlorinated to increase its stability. Although the acute toxicity of the mixture is less than that of natural pyrethrins, the cis-isomer is considerably more toxic. Compared to other pyrethroids, permethrin is very stable, even when exposed to ultraviolet light.

Permethrin is strongly absorbed in soil and other organic particles, with half-lives in soil of up to 43 days. When used as a termiticide, permethrin can persist up to 5 years.

Permethrin received an EPA toxicity rating of II (I= most toxic, IV= least toxic), and carries either the word WARNING OR CAUTION on its label, depending on the formulation. While it is not extremely toxic to humans, there are numerous reports of transient skin, eye and respiratory irritation. Like all pyrethroids, permethrin is a central nervous system poison. Workers and researchers report tingling in face and hands, and some report allergic reactions.

Based on studies demonstrating carcinogenicity, EPA ranks permethrin as a class C, or possible human carcinogen (U.S. EPA, 1997). Other studies have shown effects on the immune system, enlarged livers and at high doses, decreased female fertility and endocrine disruption. Permethrin is extremely toxic to aquatic life, bees and other insects. It should not be applied in crops or weeds where foraging may occur (ETN, Permethrin, 1996)

  • Soil microorganismsPermethrin may suppress populations of soil microorganisms.
  • PlantsAlthough permethrin is not toxic to most plants, it may injure some sensitive plants.
  • Aquatic animalsPermethrin is highly toxic to fish, and highly toxic to many aquatic invertebrates (bugs and shelfish)
  • Permethrin is practically non-toxic to birds, and slightly toxic to practically non-toxic to mammals. It is highly toxic to bees.

Source: Shaker Heights West Nile Task Force, "Summary Report"

Other Resources:

  • Environmental Defense maintains a web site called Scorecard, at which you can find information on the Toxic Release Inventory (TRI) about chemicals and pollutants. [type Permethrin in the search box]
  • Pesticide Action Network Pesticide Database
    Identifying information, including synonyms, ID numbers, use type, chemical classification, and a link to a list of all products containing this chemical, toxicity to humans, regulatory status in the U.S., physical properties affecting water contamination potential and more.
  • The Cuyahoga County Board of Health's West Nile Virus Web page including information on West Nile Virus, the board's surveillance data, spraying policy and schedule.
  • The U.S. Environmental Protection Agency's Office of Pesticide Programs data sheet on pesticide and mosquito control
  • The Consumers Union Guide to Environmental Labels


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2841 Scarborough Road Cleveland Heights OH 44118
Cuyahoga Bioregion
(216) 932-3007
Copyright 2002-2003

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