Chlorpyrifos (a.k.a Dursban) - the facts
0,0-diethyl-0-(3,5,6-trichloro-2-pyridyl) phosphorothioate


* Chlorpyrifos is an organophosphate pesticide that kills animals by attacking their nervous system (a "neurotoxin"). Organophosphates were first developed by Nazi scientists as chemical warfare agents in the 1930s. They all inhibit the action of cholinesterase, a natural enzyme produced by both insects and mammals that turns off signals sent by the nervous system. When cholinesterase is blocked by chlorpyrifos, the body cannot turn off these signals, which essentially locks the nervous system in an "on" position. The greater and more frequent the exposure--whether via inhalation, ingestion or skin contact--the more severe and long-lasting the effects on the central nervous system and especially the sensory nerves.

* Chlorpyrifos was first marketed in the USA in 1965 by the Dow Chemical Company and is now one of the top five insecticides with annual sales over $2 billion. It is made by Dow AgroSciences, a Dow subsidiary that was set up in 1997 after the Eli Lilly Co. exercised its option to sell Dow back its 50% share in DowElanco, the manufacturer since 1989.

* Chlorpyrifos is registered for use in over 900 different pesticide formulations. The best selling consumer brand is Dursban, which is used for killing termites, cockroaches, ants, fleas and mosquitoes by over 17% of U.S. households, who apply 10 to 14 million pounds per year. The best selling agricultural brand is Lorsban. Approximately 9 to 13 million pounds of chlorpyrifos are sold annually under this and other names for use on food crops.

* Chlorpyrifos poisoning usually affects many if not all organs of the body. Among the most commonly affected are the central and peripheral nervous system, eyes, respiratory system, and the digestive tract. Symptoms of acute and chronic chlorpyrifos exposure documented in humans include headache, dizziness, mental confusion, mood swings, vomiting, muscle weakness and/or twitching, sweating, chest tightness, stomach cramps, hypertension, salivation, uncontrolled urination, nausea, diarrhea, blurred vision, seizures and--at sufficiently high doses--unconsciousness, coma, and even death due to respiratory failure as the breathing muscles stop working. According to a 1997 review by U.S. EPA, the most commonly reported chronic effects are multiple chemical sensitivity, followed by neurobehavioral problems and peripheral neuropathy (characterized by pain and/or numbness and tingling in arms and/or legs), which may not appear until weeks or even months after exposure but can then last for years. Exposure to chlorpyrifos during the first trimester of pregnancy has been associated with a unique pattern of birth defects affecting the head, face, ears, eyes, digestive tract and genitals.

* Like most pesticides, chlorpyrifos is sold in formulations that include more than just the "active" ingredient. The U.S. EPA allows these other ingredients to labeled as "inert," which suggests they have no effect on human health or the environment. In fact, many inert ingredients such as emulsifiers and propellants are quite toxic. Among the "inerts" reportedly detected in commercial formulations of chlorpyrifos are phenols, alcohols, glycols and solvents--usually xylene, toluene and/or kerosene. One of the main ingredients, contaminants and unique metabolites of chlorpyrifos is trichloropyridinol (TCP), which is known to be teratogenic in animals.

* For 10 years, from 1984 to 1994, both Dow and DowElanco hid hundreds of medical reports about adverse health effects associated with chlorpyrifos exposure that they were required by law to report to the U.S. Environmental Protection Agency within 30 days (FIFRA, Sec.6(a)(2)). These reports show that MCS complaints are second only to those of "cholinergic symptoms." They also show that even when applied according to the label or by licensed pesticide applicators, chronic chlorpyrifos poisoning may occur, although most cases were associated with gross negligence on the part of applicators.

* In January 1997, EPA announced a voluntary agreement with DowElanco to discontinue many uses of chlorpyrifos (including all broadcast sprays and foggers) and require changes in the education of both applicators and the general public. EPA also selected chlorpyrifos as the first pesticide whose re-registration review was expanded to consider health effects on more sensitive populations (like children, who eat more pesticide-treated foods), effects from multiple routes of exposure, and the combined effects of exposure to other organophosphates, as now required by the Food Quality Protection Act.
A 5-year phase out of most indoor uses of chlorpyrifos was announced by EPA in 2000 due to concern for birth defects.

* Recent exposure to chlorpyrifos can be assessed with a urine test for TCP, which is much more sensitive than the standard but non-specific test for cholinesterase in blood. Although both abnormalities usually can be detected for only 72 hours after exposure, a government study done in 1994 found over 80% of Americans with detectable levels of TCP (greater that 1microgram/liter) and 31% with over 5 micrograms/liter -- a six-fold increase over the last 20 years! These data suggest that most Americans are now chronically exposed to chlorpyrifos; they also provide a well-validated population curve against which individual TCP levels can be compared.

* Depending on the pesticide formulation and type of application (liquid, aerosol, solid or powder), chlorpyrifos residues may be detectable in water, soil, fabrics and on surfaces for months to years. The manufacturer claims chlorpyrifos residues are active for up to 18 years.

For more information on chlorpyrifos, contact the Dursban Information Group, c/o MCS Referral & Resources, 508 Westgate Road , Baltimore MD 21229-2343, 410-362-6400, fax 362-6401.

Fact sheet compiled by Albert Donnay, 9/00 edition.

Source: DowElanco. 1994. DowElanco Submission to the United States Environmental Protection Agency on Claims Related Notifications to the Agency from October 13, 1994 to November 4, 1994.