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. The Sevin trademark has since been acquired by GardenTech, which has eliminated carbaryl from most Sevin formulations.[needs update][3][4]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).
Alternatively, 1-naphthol can be treated with excess phosgene to produce 1-naphthylchloroformate, which is then converted to carbaryl by reaction with methylamine.[5] The former process was carried out in Bhopal. In comparison, the latter synthesis uses exactly the same reagents, but in a different sequence. This procedure avoids the potential hazards of methyl isocyanate.
Carbamate insecticides are slowly reversible 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.
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.[6] It is the active ingredient in Carylderm shampoo used to combat head lice until infestation is eliminated.[7]
Carbaryl kills both targeted (e.g., malaria-carrying mosquitos) and beneficial insects (e.g., honeybees), as well as crustaceans.[8] 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.[9]
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.[10]
It is approved for more than 100 crops in the US. Carbaryl is illegal in the EU[11] and Angola.[12]
Carbaryl can be produced using methyl isocyanate (MIC) as an intermediary.[5] A leak of MIC used in the production of carbaryl caused the Bhopal disaster, the most lethal industrial accident in history.[14]
^Kendall, Ronald; Lacher, Thomas E.; Cobb, George P.; Cox, Stephen B., eds. (2010). Wildlife Toxicology: Emerging Contaminant and Biodiversity Issues. Boca Raton: CRC. ISBN978-1-4398-1794-0. OCLC646404494. 5.4.1 Taxon-Wide Impacts — Pesticides and Contaminants, and Their Roles in the Decline of Amphibian Populations. Moore, Robin D.; Claude Gascon. pp.111-145.
