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materials in their standard state (at 25 °C, 100 kPa)
Infobox disclaimer and references
Permethrin is a common synthetic chemical, widely used as an insecticide, acaricide, and 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. It is not known to rapidly harm most mammals or birds, but is dangerously toxic to cats and fish. In general, it has a low mammalian toxicity and is poorly absorbed by skin.
In medicine, permethrin is a first-line treatment for scabies; a 5% (w/w) cream is marketed by Johnson & Johnson under the name Lyclear. In Nordic countries and North America, it is marketed under trade name Nix, often available over the counter.
Permethrin is used:
- as an insecticide
- in agriculture, to protect crops
- in agriculture, to kill livestock parasites
- for industrial/domestic insect control
- as an insect repellent or insect screen
- in timber treatment
- as a personal protective measure (cloth impregnant, used primarily for US military uniforms and mosquito nets)
- in pet flea preventative collars or treatment.
Pest control Edit
In agriculture, permethrin is mainly used on cotton, wheat, maize, and alfalfa crops. Its use is controversial because, as a broad-spectrum chemical, it kills indiscriminately; as well as the intended pests, it can harm beneficial insects including honey bees, and aquatic life.
Permethrin kills ticks on contact with treated clothing. A method of reducing deer tick populations by treating rodent vectors involves stuffing biodegradable cardboard tubes with permethrin-treated cotton. Mice collect the cotton for lining their nests. Permethrin on the cotton instantly kills any immature ticks that are feeding on the mice. It is important to put the tubes where mice will find them, such as in dense, dark brush, or at the base of a log; mice are unlikely to gather cotton from an open lawn.
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. This increases the effectiveness of the bed net by killing parasitic insects before they are able to find gaps or holes in the net. Military personnel training in malaria-endemic areas may be instructed to treat their uniforms with permethrin, as well. An application should last several washes.
Personal healthcare Edit
Permethrin is used on humans to eradicate parasites such as head lice or mites responsible for scabies and as a pest-repellent clothing treatment. Permethrin is more effective in reducing itch persistence than crotamiton or lindane.The common prescription is a 5% concentration of permethrin for scabies and a 1% concentration for the over-the-counter (OTC) treatment for head lice or crabs. Pharmaceutical grade permethrin 99% is differentiated from pesticide grade 94% by a higher purity, well specified impurities, and lower content of the toxic CIS component at 25% as opposed to 40% in the pesticide grade. Pharmaceutical grade permethrin is used extensively by agencies working in forest areas such as the US Army.
In order to better protect soldiers from the risk and annoyance of biting insects, the US and British armies are treating all new uniforms with permethrin.
Toxicology and safetyEdit
Permethrin acts as a neurotoxin, slowing down the nervous system through binding to sodium channels. This action is negatively correlated to temperature, thus, in general, showing more acute effects on cold-blooded animals (insects, fish, frogs...) over warm-blooded animals (mammals and birds):
- Permethrin is extremely toxic to fish and aquatic life in general, so extreme care must be taken when using products containing permethrin near water sources.
- Permethrin is also highly toxic to cats, and flea and tick-repellent formulas intended and labeled for (the more resistant) dogs may contain permethrin and cause feline permethrin toxicosis in cats.
- Very high doses will have tangible neurotoxic effects on mammals and birds, including human beings.
Due to high toxicity for aquatic life, permethrin and permethrin-contaminated water should be properly disposed. Permethrin is quite stable, having a half life of 51-71 days in an aqueous environment exposed to light. It is also highly persistent in soil.
According to the Connecticut Department of Public Health, permethrin "has low mammalian toxicity, is poorly absorbed through the skin and is rapidly inactivated by the body. Skin reactions have been uncommon."
Excessive exposure to permethrin can cause nausea, headache, muscle weakness, excessive salivation, shortness of breath, and seizures. Worker exposure to the chemical can be monitored by measurement of the urinary metabolites, while severe overdosage may be confirmed by measurement of permethrin in serum or blood plasma.
Permethrin does not present any notable genotoxicity or immunotoxicity in humans and farm animals, but is classified by the United States Environmental Protection Agency (EPA) as a likely human carcinogen, based on reproducible studies in which mice fed permethrin developed liver and lung tumors. Carcinogenic action in nasal mucosal cells due to inhalation exposure is suspected, due to observed genotoxicity in human tissue samples, and in rat livers the evidence of increased pre-neoplastic lesions raises concern over oral exposure.
- 2002 study – "Our studies have documented low-dose effects of permethrin, doses below one-one thousandth of a lethal dose for a mouse, with effects on those brain pathways [that are] involved in Parkinson's Disease [...] We have found effects consistent with a pre-parkinsonsian condition, but not yet full-blown parkinsonism." 
However a more recent 2007 study by the same researcher concluded that there was "little hazard to humans"
- 2007 study – "long-term, low-dose exposure to permethrin alone did not cause signs of neurotoxicity to striatal dopaminergic neural terminals, or enhance the effects of MPTP. We conclude that, under typical use conditions, permethrin poses little Parkinsonian hazard to humans, including when impregnated into clothing for control of biting flies"
A 2006 study in South Africa, found residues of permethrin 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.
Domestic animals Edit
Pesticide grade permethrin is toxic to cats. Many cats die after being given flea treatments intended for dogs, or by contact with dogs having recently been treated with permethrin. Only the less toxic human, pharmaceutical grade permethrin with well defined impurities and a reduced CIS:TRANS ratio is considered safe for pet use.
- ↑ Permethrin Hazards For Cats. ASPCA National Animal Poison Control Center.
- ↑ Franny Syufy. Cat Flea Control Products Warning. About.com.
- ↑ Permethrin. Pmep.cce.cornell.edu. URL accessed on 5 January 2011.
- ↑ R. H. Ian (1989). Aquatic organisms and pyrethroids. Pesticide Science 27 (4): 429–457.
- ↑ Interventions for treating scabies at the Cochrane review
- ↑ Permethrin Factory-Treated Flame Resistant ACU’s: U.S. Army Public Health Command
- ↑ See entry for Complete Wood Preservative
- ↑ Insect-repelling ACUs now available to all Soldiers, United States Army
- ↑ report "Cats 'killed by flea treatment'". BBC News. URL accessed on 5 January 2011.
- ↑ Environmental Protection Agency Restricted Use Products (RUP) Report: Six Month Summary List. URL accessed on 1 December 2009.
- ↑ Environmental Protection Agency Permethrin Facts (RED Fact Sheet). URL accessed on 2 September 2011.
- ↑ "Environmental Fate of Permethrin".
- ↑ Kirby C. Stafford III. Tick Bite Prevention. Connecticut Department of Public Health.
- ↑ R. Baselt, Disposition of Toxic Drugs and Chemicals in Man, 8th edition, Biomedical Publications, Foster City, CA, 2008, pp. 1215–1216.
- ↑ Permethrin Facts, US EPA, June 2006.
- ↑ 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.
- ↑ 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.
- ↑  Neurotoxicology. 2002 Oct;23(4–5):537-44.
- ↑  BBC News, March 2006.
- ↑  Virginia Tech, March 2003.
- ↑ (2007). Neurotoxicity in murine striatal dopaminergic pathways following long-term application of low doses of permethrin and MPTP.. Toxicol Lett 171 (3): 154–161.
- ↑ (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.
- ↑ (2008). Permethrin toxicosis in cats. Australian Veterinary Journal 86 (1–2): 32–35.
- ↑ PERMETHRIN SPOT-ON TOXICOSES IN CATS, Jill A. Richardson, DVM ASPCA Animal Poison Control Center, Urbana, IL, USA
- Permethrin Technical Fact Sheet – National Pesticide Information Center
- Permethrin General Fact Sheet – National Pesticide Information Center
- Permethrin-treated Clothing Hot Topic – National Pesticide Information Center
- "Health Effects of Permethrin-Impregnated Army Battle-Dress Uniforms", National Research Council (1994, US)
- "Permethrin summary report", Committee for Veterinary Products, European Agency for the Evaluation of Medical Products (1998, EU)
- Pesticide link to Parkinson Disease
- Permethrin Pesticide Information Profile – Extension Toxicology Network
- Permethrin chemical data
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