Carbaryl

Spraying carbaryl on pine trees

Carbaryl (1-naphthyl methylcarbamate) is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid previously sold under the brand name Sevin, which was a trademark of the Bayer Company. Template:Update span<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Union Carbide discovered carbaryl and introduced it commercially in 1958. Bayer purchased Aventis CropScience in 2002, a company that included Union Carbide pesticide operations. Carbaryl was the third-most-used insecticide in the United States for home gardens, commercial agriculture, and forestry and rangeland protection. As a veterinary drug, it is known as carbaril (INN).

ProductionEdit

Carbaryl is often inexpensively produced by direct reaction of methyl isocyanate with 1-naphthol.<ref name = unger>Template:Cite book</ref>

C₁₀H₇OH + CH₃NCO → C₁₀H₇OC(O)NHCH₃

Alternatively, 1-naphthol can be treated with excess phosgene to produce 1-naphthyl chloroformate, which is then converted to carbaryl by reaction with methylamine.<ref name = unger/> The former process was used in the chemical plant that caused the Bhopal. In comparison, the latter synthesis uses exactly the same reagents required for the synthesis of methyl isocyanate. This route avoids the potential hazards of methyl isocyanate, allbeit at a higher cost.

BiochemistryEdit

Carbamate insecticides are slowly irreversible inhibitors of the enzyme acetylcholinesterase. They resemble acetylcholine, but the carbamoylated enzyme undergoes the final hydrolysis step very slowly (minutes) compared with the acetylated enzyme generated by acetylcholine (microseconds). They interfere with the cholinergic nervous system and cause death because the effects of the neurotransmitter acetylcholine cannot be terminated by carbamoylated acetylcholinesterase.

ApplicationsEdit

The development of the carbamate insecticides has been called a major breakthrough in pesticides. The carbamates do not have the persistence of chlorinated pesticides. Although toxic to insects, carbaryl is detoxified and eliminated rapidly in vertebrates. It is neither concentrated in fat nor secreted in milk, so is favored for food crops, at least in the US.<ref name=Ullmann>Robert L. Metcalf "Insect Control" in Ullmann's Encyclopedia of Industrial Chemistry Wiley-VCH, Weinheim, 2002. {{#invoke:doi|main}}</ref> It is the active ingredient in Carylderm shampoo used to combat head lice until infestation is eliminated.<ref>Carbaryl against lice</ref>

EcologyEdit

Carbaryl kills both targeted (e.g., malaria-carrying mosquitos) and beneficial insects (e.g., honeybees), as well as crustaceans.<ref name= "Carbaryl Fact Sheet">Carbaryl General Fact Sheet - National Pesticide Information Center</ref> Because it is highly toxic to zooplankton, the algae they feed on experience blooms. Boone & Bridges 2003 find that larger algae eaters such as Bufo woodhousii benefit from this effect.<ref name="Kendall-et-al-2010">Template:Cite book 5.4.1 Taxon-Wide Impacts — Pesticides and Contaminants, and Their Roles in the Decline of Amphibian Populations. Moore, Robin D.; Claude Gascon. pp.Template:Nbs111-145.</ref>

Although it can increase survival rates for organisms that benefit from consequential algae blooms, the long term effects of these changes in competition levels and predation can be detrimental to many aquatic ecosystems, particularly those dominated by Anurans.<ref>Template:Cite journal</ref>

It is approved for more than 100 crops in the US. Carbaryl has been illegal in the EU since 21 November 2007<ref name="EU Commission Decision 2007/355/EC">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and Angola.<ref name="Carbaryl Insecticide Hazard Data">Carbaryl Insecticide Hazard Data Template:Webarchive</ref>

SafetyEdit

Carbaryl is a cholinesterase inhibitor and is toxic to humans. It is classified as a likely human carcinogen by the United States Environmental Protection Agency (EPA.)<ref>Interim Reregistration Eligibility Decision for Carbaryl Template:Webarchive, U.S. EPA, June 2003.</ref> The oral Template:LD50 is 250 to 850 mg/kg for rats and 100 to 650 mg/kg for mice.<ref name= "Carbaryl Fact Sheet"></ref>

Carbaryl can be produced using methyl isocyanate (MIC) as an intermediary.<ref name = unger/> A leak of MIC used in the production of carbaryl caused the Bhopal disaster, the most lethal industrial accident in history.<ref name="Eckerman2005">Template:Cite book</ref>

ReferencesEdit

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External linksEdit

Template:Insecticides Template:Acetylcholine metabolism and transport modulators Template:Authority control