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IUPAC name O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate
Molecular formula C9H11Cl3NO3PS
CAS number 2921-88-2
SMILES CCOP(=S)(OCC)Oc1nc(Cl)c(Cl)cc1Cl
Molar mass 350.59
Density 1.398 @ °43.5 C
Solubility in water 1.398 mg/L
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references

Chlorpyrifos is a toxic crystalline organophosphate insecticide that inhibits acetylcholinesterase and is used to control insect pests. Trade names include Dursban (home and garden uses), Empire, and Lorsban (agricultural uses).



In the US, chlorpyrifos is registered only for agricultural use (and ant and roach baits for domestic use in concentrations not exceeding 0.5%), where it is "one of the most widely used organophosphate insecticides," according to the EPA.[1] The crops with the most intense chlorpyrifos use are cotton, corn, almonds, and fruit trees including oranges and apples.[2]


First registered in 1965 and marketed by Dow Chemical Company under the tradenames Dursban and Lorsban, chlorpyrifos was a well known home and garden insecticide, and at one time it was one of the most widely used household pesticides in the US. Facing impending regulatory action by the EPA, Dow agreed to withdraw registration of chlorpyrifos for use in homes and other places where children could be exposed, and severely restricted its use on crops. These changes took effect on Dec. 31, 2001.[3] It is still widely used in agriculture, and Dow continues to market Dursban for home use in developing countries. In India, Dow claims Dursban is safe for people,[4] and its sales literature claimed Dursban has "an established record of safety regarding humans and pets."[5]

In 1995, Dow was fined $732,000 for not sending the EPA reports it had received on 249 Dursban poisoning incidents, and in 2003, Dow agreed to pay $2 million - the largest penalty ever in a pesticide case - to the state of New York, in response to a lawsuit filed by the Attorney General to end Dow's illegal advertising of Dursban as "safe".[6]

On July 31st, 2007, a coalition of farmworker and advocacy groups filed a lawsuit against the EPA seeking to end agricultural use of the chlorpyrifos. The suit claims that the continued use of chlorpyrifos poses an unnecessary risk to farmworkers and their families.[7]

In August of 2007, Dow's Indian offices were raided by Indian authorities for allegedly bribing officials to allow chlorpyrifos to be sold in the country.[8]

Health Effects

Chlorpyrifos is a neurotoxin and suspected endocrine disruptor, and it has been associated with asthma,[9] reproductive and developmental toxicity, and acute toxicity. For acute effects, the EPA classifies chlorpyrifos as Class II: moderately toxic. Recent research indicates that children exposed to chlorpyrifos while in the womb have an increased risk of delays in mental and motor development at age 3 and an increased occurrence of pervasive developmental disorders such as ADHD.[10] An earlier study demonstrated a correlation between prenatal chlorpyrifos exposure and lower weight and smaller head circumference at birth.[11]

Chlorpyrifos is highly toxic to amphibians, and a recent study by the USGS found that it's the main breakdown product in the environment, chlorpyrifos oxon, is even more toxic to these animals. [12]


A body burden study conducted by the CDC found TCPy—a metabolite specific to chlorpyrifos—in the urine of 91% of people tested.[13] An independent analysis of the CDC data claims that Dow has contributed 80% of the chlorpyrifos body burden of people living in the US.[14]

Air monitoring studies conducted by the California Air Resources Board (CARB) have documented chlorpyrifos in the air of California communities.[15] Analyses of the CARB data indicate that children living in areas of high chlorpyrifos use are often exposed to levels of the insecticide that exceed levels considered acceptable by the EPA.[16][17] Recent air monitoring studies in Washington and Lindsay, CA have yielded comparable results.[18][19] Grower and pesticide industry groups have argued that the air levels documented in these studies are not high enough to cause significant exposure or adverse effects,[20] but a follow-up biomonitoring study in Lindsay, CA has shown that people there have higher than normal chlorpyrifos levels in their bodies. [21][22]


  1. ^ Reregistration Eligibility Decision for Chlorpyrifos
  2. ^ NASS Agricultural Chemical Database
  3. ^ EPA's Chlorpyrifos Page
  4. ^ Islamic Republic News Agency, Feb 17th, 2007
  5. ^
  6. ^
  7. ^ Press Release: Lawsuit Challenges EPA on Deadly Pesticide, EarthJustice, July 31st, 2007.
  8. ^ CBI raids Dow Chemical's Indian subsidiary for graft. Monsters and Critics, August 21st, 2007.
  9. ^ AOEC Exposure Codes
  10. ^ Wyatt RM et al, Pediatrics, 2006, 118, e1845-e1859
  11. ^ Wyatt RM, et al., Environmental Health Perspectives, 2004, 112, 1125-32
  12. ^ Breakdown Products Of Widely Used Pesticides Are Acutely Lethal To Amphibians, Study Finds, Science Daily, June 25, 2007, accessed July 2, 2006.
  13. ^ CDC Third National Exposure Report
  14. ^ "Chemical Trepass," Pesticide Action Network North America, 2004
  15. ^ CARB Chlorpyrifos Monitoring Studies
  16. ^ Lee et al., Environmental Health Perspectives, 2002, 110, 1175-1184
  17. ^ S Kegley et al., "Secondhand Pesticides," Pesticide Action Network North America, 2003
  18. ^ C Dansereau et al., "Poisons on the Wind," Farm Worker Pesticide Project, 2006
  19. ^ S Kegley et al., "Drift Catching In Lindsay, California," Pesticide Action Network North America, 2006
  20. ^ Heather Hansen, "Proper Pest Management Keeps Washington Fruit Crop Healthy," Seattle Post Intellegencer, Jan 19, 2007.
  21. ^ Douglas Fischer, "Toxins permeate Central Valley town," Tri-Valley Herald, May 15th, 2007.
  22. ^ Californians For Pesticide Reform, Airborne Poisons: Pesticides in Our Air, and in Our Bodies, May 16th, 2007.
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Chlorpyrifos". A list of authors is available in Wikipedia.
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