Pyrethroid
A pyrethroid is an
In household concentrations pyrethroids are generally harmless to humans.
Mode of action
Pyrethroids are
Chemistry and classification
Pyrethroids are classified based on their mechanism of biological action, as they do not share a common chemical structure. Many are 2,2-dimethylcyclopropanecarboxylic acid derivatives, like
Pyrethroids which lack an α-cyano group are often classified as type I pyrethroids and those with it are called type II pyrethroids. Pyrethroids that have a common name starting with "cy" have a cyano group and are type II. Fenvalerate also contains an α-
Some pyrethroids, like
Examples
- Allethrin, the first pyrethroid synthesized
- Bifenthrin, active ingredient of Talstar, Capture, Ortho Home Defense Max, and Bifenthrine
- Cyfluthrin, an active ingredient in Baygon, Temprid, Fumakilla Vape Aerosol, Tempo SC, and many more, dichlorovinyl derivative of pyrethrin
- Cypermethrin, including the resolved isomer alpha-cypermethrin, dichlorovinyl derivative of pyrethrin. Commonly found in crawling insect killers and some mosquito sprays.
- Cyphenothrin, active ingredient of K2000 Insect spray sold in Israel. Mostly used in some aerosols as a Cypermethrin substitute in developing countries.
- Deltamethrin, dibromovinyl derivative of pyrethrin
- Dimefluthrin
- Esfenvalerate
- Etofenprox
- Fenpropathrin
- Fenvalerate
- Flucythrinate
- Flumethrin
- Imiprothrin
- lambda-Cyhalothrin
- Metofluthrin
- Permethrin, dichlorovinyl derivative of pyrethrin and most widely used pyrethroid.
- Phenothrin (Sumithrin), active ingredient of Anvil
- Prallethrin
- Resmethrin, active ingredient of Scourge
- Silafluofen
- tau-Fluvalinate
- Tefluthrin
- Tetramethrin
- Tralomethrin
- Transfluthrin, an active ingredient in Baygon and other products.
Environmental effects
Pyrethroids are toxic to insects such as
Biodegradation
Pyrethroids are usually broken apart by sunlight and the atmosphere in one or two days, however when associated with sediment they can persist for some time.[9]
Pyrethroids are unaffected by conventional secondary treatment systems at municipal wastewater treatment facilities. They appear in the effluent, usually at levels lethal to invertebrates.[10]
Safety
Humans
Pyrethroid absorption can happen via skin, inhalation or ingestion.[11] Pyrethroids often do not bind efficiently to mammalian sodium channels.[12] They also absorb poorly via skin and human liver is often able to metabolize them relatively efficiently. Pyrethroids are thus much less toxic to humans than to insects.[13]
It is not well established if chronic exposure to small amounts of pyrethroids is hazardous or not.[14] However, large doses can cause acute poisoning, which is rarely life threatening. Typical symptoms include facial paresthesia, itching, burning, dizziness, nausea, vomiting and more severe cases of muscle twitching. Severe poisoning is often caused by ingestion of pyrethroids and can result in a variety of symptoms like seizures, coma, bleeding or pulmonary edema.[11] There is an association of pyrethroids with poorer early social-emotional and language development.[4]
Other organisms
Pyrethroids are very toxic to
Resistance
The use of pyrethroids as insecticides has led to the development of widespread resistance to them among some insect populations, especially mosquitoes.[18] Although
Knockdown resistance (kdr) is one of the stronger kinds of resistance.[28] kdr mutations confer target-site resistance to DDT and pyrethroids and cross-resistance to DDT.[28] Most kdr mutations are within or proximate to the two arthropod sodium channel genes.[28]
History
Pyrethroids were introduced by a team of Rothamsted Research scientists in the 1960s and 1970s following the elucidation of the structures of pyrethrin I and II by Hermann Staudinger and Leopold Ružička in the 1920s.[29] The pyrethroids represented a major advancement in the chemistry that would synthesize the analog of the natural version found in pyrethrum. Its insecticidal activity has relatively low mammalian toxicity and an unusually fast biodegradation. Their development coincided with the identification of problems with DDT use. Their work consisted firstly of identifying the most active components of pyrethrum, extracted from East African chrysanthemum flowers and long known to have insecticidal properties. Pyrethrum rapidly knocks down flying insects but has negligible persistence — which is good for the environment but gives poor efficacy when applied in the field. Pyrethroids are essentially chemically stabilized forms of natural pyrethrum and belong to IRAC MoA group 3 (they interfere with sodium transport in insect nerve cells).[30]
The first-generation pyrethroids, developed in the 1960s, include bioallethrin, tetramethrin, resmethrin, and bioresmethrin. They are more active than the natural pyrethrum but are unstable in sunlight. With the 91/414/EEC review,[31] many 1st-generation compounds have not been included on Annex 1, probably because the market is not big enough to warrant the costs of re-registration (rather than any special concerns about safety).
By 1974, the Rothamsted team had discovered a second generation of more persistent compounds notably:
References
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- ^ Daily Californian. Retrieved 9 June 2012.
- ^ a b Pyrethroids fact sheet from the Illinois Department of Public Health.
- ^
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- ^ Craggs, Samantha (November 20, 2014). "DDT repeal would do nothing to combat bed bugs, experts say". CBC News. Retrieved 14 November 2016.
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- ^ Voiland, Adam. "You May not be Alone" Archived 2011-11-07 at the Wayback Machine U.S. News & World Report 16 July 2007, Vol. 143, Issue 2, p53–54.
- S2CID 27422270.
- JSTOR 3496140.
- NDSU Agriculture and Extension. 2021-08-26. Retrieved 2022-01-08.
- ^ Marsden, Christy (2021-10-15). "Diamondback Moth". Wisconsin Horticulture. Retrieved 2022-01-08.
- University of California Agriculture and Natural Resources(UCANR).
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- ^ "EUR-Lex - 31991L0414 - EN - EUR-Lex". europa.eu. 15 July 1991.