Permethrin

Permethrin is a common synthetic chemical, widely used as an insecticide and acaricide and as an insect repellent. It belongs to the family of synthetic chemicals called pyrethroids and functions as a neurotoxin, affecting neuron membranes by prolonging sodium channel activation.

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Uses

In agriculture, permethrin is mainly used on cotton, wheat, maize, and alfalfa crops, and is also used to kill parasites on chickens and other poultry. Its use is controversial since, as a broad-spectrum chemical, it kills indiscriminately; as well as the intended pests, it can harm beneficial insects including honey bees, aquatic life,^[1] and small mammals such as mice. Permethrin is toxic to cats and many cats die each year after being given flea treatments intended for dogs, or by contact with dogs who have recently been treated with permethrin.

However, permethrin can be used in a targeted manner as well. This is the basis for a method of reducing populations of the deer tick Ixodes scapularis (I. dammini). Biodegradable cardboard tubes stuffed with permethrin-treated cotton, are sold under the brand name Damminix,^[2] Mice collect the cotton for lining their nests, and the pesticide on the cotton kills any immature ticks that are feeding on the mice.^[3]

Permethrin is also used in healthcare, to eradicate parasites such as head lice and mites responsible for scabies, and in industrial and domestic settings to control pests such as ants and termites.

Permethrin kills ticks on contact with treated clothing. According to the Connecticut Department of Public Health, it "has low mammalian toxicity, is poorly absorbed through the skin and is rapidly inactivated by the body. Skin reactions have been uncommon."^[4]

Permethrin is used in tropical areas to prevent mosquito-borne disease such as dengue fever and malaria. Mosquito nets used to cover beds may be treated with a solution of permethrin. Military personnel training in malaria-endemic areas may be instructed to treat their uniforms with permethrin as well. An application should last several washes.

Recently, in South Africa, residues of permethrin were found in breast milk, together with DDT, in an area that experienced DDT treatment for malaria control, as well as the use of pyrethroids in small-scale agriculture.^[5]

Products containing permethrin

Products containing 0.5% permethrin:

• Repel Permanone
• Permethrin Tick Repellent

• Bonide Ant Dust (0.25%)

• Nix 1% shampoo for head lice.

• Elimite 5% skin cream or generic equilvalent for scabies, lice, head lice, bird mites, tropical rat mites, bed bugs, and other mites.

• Lyclear 5% skin cream or generic equilvalent for scabies and crab lice.

• Most flea and tick repellant for dogs (Adams, Bio-Spot, K9-Advantix, Cutter)

• Dragnet, a pesticide for home use, also contains permethrin.

• Raid Ant and Roach killer, another home insecticide contains 2% permethrin.

• Cutter Bug Free Backyard contains 2.5% permethrin

• Flit

Products containing 12.6% permethrin:

• Raid fumigator

Stereochemistry

Permethrin has four stereoisomers (two enantiomeric pairs), arising from the two stereocentres in the cyclopropane ring. The trans enantiomeric pair is known as transpermethrin.

Toxicity

Permethrin is extremely toxic to fish. Extreme care must be taken when using products containing permethrin near water sources. Permethrin is also highly toxic to cats.^[6] Flea and tick repellent formulas intended (and labeled) for dogs may contain permethrin and cause feline permethrin toxicosis in cats: specific flea and tick control formulas intended for feline use, such as those containing fipronil, should therefore be used for cats instead.

Currently, permethrin is not considered a carcinogen by any recognized authoritative body, but a few studies have lead the US EPA to classify the substance as a Category C carcinogen: Possible human carcinogen (the data show limited evidence of carcinogenicity in the absence of human data)^[7]. Carcinogenic action in nasal mucosal cells for inhalation exposure is suspected due to observed genotoxicity in human tissue samples, and in rat livers the evidence of increased preneoplastic lesions lends concern over oral exposure.^[8][9] However, these results are seen as preliminary and marginal, at best.

References

1. ^ R. H. Ian (1989). "Aquatic organisms and pyrethroids". Pesticide Science 27 (4): 429-457. doi:10.1002/ps.2780270408.
2. ^ Damminix Tick Tubes (Official site).
3. ^ Lyme disease and related tick-borne infections. University of Maryland Medical Center (18 Jan 07).
4. ^ Kirby C. Stafford III (Feb 1999). Tick Bite Prevention. Connecticut Department of Public Health.
5. ^ H. Bouwman, B. Sereda and H. M. Meinhardt (2006). "Simultaneous presence of DDT and pyrethroid residues in human breast milk from a malaria endemic area in South Africa". Environmental Pollution 144 (3): 902-917. doi:10.1016/j.envpol.2006.02.002.
6. ^ http://news.bbc.co.uk/1/low/uk/7088397.stm
7. ^ [1]US EPA List of Chemicals Evaluated for Carcinogenic Potential
8. ^ M. Tisch, P. Schmezer, M. Faulde, A. Groh and H. Maier (2002). "Genotoxicity studies on permethrin, DEET and diazinon in primary human nasal mucosal cells". European Archives of Oto-Rhino-Laryngology 259 (3): 150-153. doi:10.1007/s004050100406.
9. ^ K. Hakoi, R. Cabral, T. Hoshiya, R. Hasegawa, T. Shirai and N. Ito (1992). "Analysis of carcinogenic activity of some pesticides in a medium-term liver bioassay in the rat". Teratogenesis, Carcinogenesis, and Mutagenesis 12 (6): 269-276. doi:10.1002/tcm.1770120605.

See also

• Methoprene