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Chlorpyrifos


Chlorpyrifos is a crystalline organophosphate insecticide that inhibits acetylcholinesterase and is used to control insect pests. Trade names include Brodan, Detmol UA, Dowco 179, Dursban, Empire, Eradex, Lorsban, Paqeant, Piridane, Scout, and Stipend. Chlorpyrifos is moderately toxic and chronic exposure has been linked to neurological effects, developmental disorders, and autoimmune disorders

Manufacture and use

Chlorpyrifos is manufactured by reacting 3,5,6-trichloro-2-pyridinol with diethylthiophosphoryl chloride.[1] In the US, chlorpyrifos is registered only for agricultural use, where it is "one of the most widely used organophosphate insecticides", according to the United States Environmental Protection Agency (EPA).[3] The crops with the most intense chlorpyrifos use are cotton, corn, almonds, and fruit trees including oranges and apples.[4] It is produced via a multistep synthesis from 3-methylpyridine

History

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.[6] It is still widely used in agriculture, and Dow continues to market Dursban for home use in developing countries. In Iran, Dow claims Dursban is safe for people,[7] and its sales literature claimed Dursban has "an established record of safety regarding humans and pets."[8]

In 1995, Dow was fined US$732,000 for not sending the EPA reports it had received on 249 Dursban poisoning incidents, and in 2003, Dow agreed to pay US$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".[9] On July 31, 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.[10]

In August 2007, Dow's Indian offices were raided by Indian authorities for allegedly bribing officials to allow chlorpyrifos to be sold in the country.[11]

In 2008, the National Marine Fisheries Service (NMFS) imposed 1000 ft buffer zones around salmon habitat to protect endangered salmon and steelhead species. Aerial applications of chlorpyrifos will be prohibited within these zones.[12]

Health effects

Chlorpyrifos is a neurotoxin and suspected endocrine disruptor, and it has been associated with asthma,[13] 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.[14]

An earlier study demonstrated a correlation between prenatal chlorpyrifos exposure and lower weight and smaller head circumference at birth.[15] A 2010 study found that each 10-fold increase in urinary concentration of organophosphate metabolites was associated with a 55% to 72% increase in the odds of ADHD in children.[16]

Chlorpyrifos is highly toxic to amphibians, and a recent study by the United States Geological Survey found that its main breakdown product in the environment, chlorpyrifos oxon, is even more toxic to these animals.[17] The substance is very toxic for aquaculture (fish) and bees[citation needed].


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