   EPA Restricts Use of Chlorpyrifos - November 22, 2000 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Home gardeners are about to lose one of their most effective pest control tools. Some of you will remember hearing about it in the media. On June 8, 2000, the Environmental Protection Agency (EPA) announced an agreement to eliminate most household uses of the organophoshate insecticide chlorpyrifos (Dursban and Lorsban). Chlorpyrifos was first registered for use in 1965 and is one of the most commonly used insecticides. This pesticide has been used by homeowners to treat a host of insect pests including: ants, borers, beetles, cockroaches, crickets, fleas, mosquitoes, termites, and ticks. Under the new restrictions, some industrial and agricultural uses will still be allowed, but at lower application rates. Don't misunderstand; I am not saying that the EPA's action is right or wrong. It simply means that many gardeners are going to look at other pest control alternatives and that in itself will be good. We should always assess our need to apply a pesticide before reaching for the sprayer and mixing up a batch. Anyhow, let's look at the reasoning for the chlorpyrifos restriction. This action was precipitated by a 1993 National Academy of Sciences study: Pesticides in the Diets of Infants and Children. The study found that infants and children are more susceptible to the toxic effects of pesticides than adults and "exposure to neurotoxic compounds at levels believed to be safe for adults could result in permanent loss of brain function if it occurred during prenatal and early childhood period of brain development". This created a sticky situation for food producers because some products, such as apple juice, already contained the maximum safe allowance of these compounds in some cases. As a result of the NAS study, President Clinton signed the Food Quality Protection Act in 1996, which created new standards for pesticide chemical residue in foods. New tests were run on chlorpyrifos in early 2000 and the new data showed that the brains of young rats were more severely affected than previous studies had shown. This led the EPA to take action to mitigate these risks. Action taken: chlorpyrifos will not be manufactured for consumer (homeowner) use after December 31, 2000; retailers will continue to sell chlorpyrifos until December 31, 2001; chlorpyrifos will be banned for use in termiticides; and the use of chlorpyrifos in homes, parks, and schools will stop on December 31, 2001. Part of the risk of chlorpyrifos (and other organophosphates) is caused by the mode of action of the pesticide. The specific mode of action of organophosphates is called "Cholinesterase Inhibition". Nervous systems of animals and insects send messages from one nerve cell to the next by way of synapses. These systems control muscles, glands, and other functions by firing signals across the synapses. A compound called acetylcholine is used to stimulate the connection. An enzyme called cholinesterase is secreted to stop the signal. The nervous system functions by close regulation of acetylcholine and cholinesterase in the synapses. When organophosphate insecticides are applied, insects absorb them and are unable to stop synapses from communicating because acetylcholine builds up and cholinesterase is deactivated. The result is constant nervous stimulation. This can be seen by the constant twitching in an insect exposed to this family of pesticides. The potential danger to human health becomes obvious and in fact, one of the signs of acute exposure to organophosphates is twitching muscles along with headache, sweating, tearing, drooling, vomiting, and tunnel vision. Many pesticide applicators are routinely tested for cholinesterase to monitor exposure levels. Homeowners are losing one of their valuable insect control tools in the near future and other insecticides will likely follow. The good news: researchers are identifying new and safer methods to control insect populations that have a reduced risk to non-target organisms (humans and other vertebrates). The University of Arizona Cooperative Extension has publications and information on pesticides and their use. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. The Yavapai County Cooperative Extension web site is http://ag.arizona.edu/yavapai/. |