Permethrin

Permethrin
Chemical structure of permethrin
IUPAC name 3-Phenoxybenzyl (1RS)-cis,trans-3-(2,2-dichlorovinyl) -2,2-dimethylcyclopropanecarboxylate
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number	52645-53-1 Y
ATC code	P03AC04,QP53AC04
SMILES
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula	C21H20Cl2O3
Molar mass	391.28 g/mol
Appearance	colourless crystals
Density	1.19 g/cm³, solid
Melting point	34 °C, 307 K, 93 °F
Boiling point	200 °C, 473 K, 392 °F
Solubility in water	Insoluble (5.5 x 10-3 ppm)
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
MSDS	External MSDS
Main hazards	Irritating to skin and eyes, damaging to lungs
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Related pyrethroids	Bifenthrin Deltamethrin
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox 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 highly toxic to cats and fish. It generally has a low mammalian toxicity and is poorly absorbed by skin.

Uses

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 notably used for US military uniforms and mosquito nets)
  • in pet collars.

Agriculture and forestry

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. It is also extensively used in Europe as a timber treatment against wood-boring beetle (woodworm). 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, aquatic life, and small mammals such as mice.

Personal insect control

Permethrin is toxic to cats. Many cats die after being given flea treatments intended for dogs, or by contact with dogs who have recently been treated with permethrin.

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. However, the British National Formulary states that permethrin has low efficiency in eradicating head lice.

Permethrin kills ticks on contact with treated clothing. A method of reducing deer tick populations in terms of rodent vectors involves utilizing biodegradable cardboard tubes stuffed 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. 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." Permethrin is also used on humans for lice or scabies; the common prescription is Permethrin with 5% concentration for scabies, and OTC (over the counter) treatment for head lice/crabs is usually permethrin with 1% concentration.

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. Malaria kills 1-3 million people per year. Military personnel training in malaria-endemic areas may be instructed to treat their uniforms with permethrin as well. An application should last several washes.

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.

• (1S)-trans-permethrin.svg

  (1S)-trans-acid moiety
• Cis-permethrin-A-2D-skeletal.png

  one cis enantiomer
• Cis-permethrin-B-2D-skeletal.png

  the other cis enantiomer

Toxicology and safety

Permethrin acts as neurotoxin, slowing down the nervous system through binding to sodium channels. This action is negatively correlated to temperature, thus generally 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.

Permethrin does not present any notable genotoxicity or immunotoxicity in humans and farm animals.

Permethrin is classified by the United States Environmental Protection Agency (EPA) a likely human carcinogen, based on reproducible studies in which mice fed permethrin developed liver and lung tumors. 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.

Studies by Bloomquist et al., 2002 suggested a link of permethrin exposure to Parkinson's disease, including very small (per kg.) exposures.

"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 involved in Parkinson's Disease [...] We have found effects consistent with a pre-parkinsonsian condition, but not yet full-blown parkinsonism." 

A more recent study by the same researcher concluded that

"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"

Due to high toxicity for aquatic life, permethrin and permethrin-contaminated water should be properly disposed of. Degradation is quick and should the chemical be trashed far from any aquatic life, the negative effects would be minimized. Ideally, in a non-industrial context, the contaminant can be set in the light to induce photodegradation. Contaminated water set in direct sunlight exposure will be cleared of the permethrin and any known pollutant subproducts after a few hours.

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.

The use of the substance has been restricted by the United States government, although such restriction is outdated now.

Human exposure

Excessive exposure to permethrin can cause nausea, headache, muscle weakness, 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 quantitation of permethrin in serum or plasma.

See also

• Methoprene
• Pyrethrin

External links

• "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 Fact Sheet - National Pesticide Information Center
• Permethrin-treated Clothing Hot Topic - National Pesticide Information Center
• Permethrin Pesticide Information Profile - Extension Toxicology Network
• Permethrin chemical data

cs:Permethrin fi:Permetriini