A pyrethroid is an pyrethrins produced by the flowers of pyrethrums (Chrysanthemum cinerariaefolium and C. coccineum). Pyrethroids now constitute the majority of commercial household insecticides. In the concentrations used in such products, they may also have insect repellent properties and are generally harmless to human beings in low doses but can harm sensitive individuals. They are usually broken apart by sunlight and the atmosphere in one or two days, and do not significantly affect groundwater quality.
- Mode of action 1
- Pesticide formulation 2
- History 3
Classes of pyrethroids 4
- Types 4.1
- Environmental effects 5
Safety and effectiveness 6
- Resistance 6.1
- References 7
- External links 8
Mode of action
- Pyrethrins and pyrethroids on the EXTOXNET
- Multiple Chemical Sensitivity Awareness, J. Edward Hill, MD, President & Executive Committee Member, AMA
- Environmental Health Perspectives Journal Estrogenic Potential of Certain Pyrethroid Compounds...
- Robert L. Metcalf “Insect Control” in Ullmann’s Encyclopedia of Industrial Chemistry” Wiley-VCH, Weinheim, 2002. doi:10.1002/14356007.a14_263
- Pyrethroids fact sheet from the Illinois Department of Public Health.
- "Permethrin, Resmethrin, Sumithrin: Synthetic Pyrethroids For Mosquito Control".
- D. M. Soderlund, et al., "Mechanisms of pyrethroid neurotoxicity: implications for cumulative risk assessment", Toxicology 2002 171, 3-59. doi:10.1016/s0300-483x(01)00569-8
- Bulletin of Entomological Research / Volume 88 / Issue 06 / December 1998, pp 601-610, I. Denholm, G.J. Devine
- "EUR-Lex - 31991L0414 - EN - EUR-Lex". europa.eu.
- "prallethrin". alanwood.net.
- Household Pesticide Is Finding Its Way Into California Rivers, Study Suggests - New York Times
- Zaveri, Mihir (February 4, 2010). "Study Links Pesticides to River Contamination". The Daily Californian (The Daily Californian). Retrieved 9 June 2012.
- Weston, Donald P.; Michael J. Lydy (February 2, 2010). "Urban and Agricultural Sources of Pyrethroid Insecticides to the Sacramento-San Joaquin Delta of California". Environmental Science and Technology 44 (5): 1833–40.
- Richardson JR, et al. "Developmental pesticide exposure reproduces features of attention deficit hyperactivity disorder.". nih.gov.
- Jim E. Riviere & Mark G. Papich Eds.: Veterinary Pharmacology and Therapeutics. Iowa State University Press, 2009. ISBN 9780813820613, (p. 1194)
- DDT Ban Takes Effect, EPA.
Earlier studies suggested that most vertebrates have sufficient enzymes for rapid breakdown of pyrethroids. A recent study, however, suggests that developing mice exposed to deltamethrin (a pyrethroid pesticide) show neurological and behavioral changes resembling Attention-Deficit/Hyperactivity Disorder (ADHD) in humans. In terms of LD50 for rats, Tefluthrin is the most toxic at 29 mg/kg. Pyrethroids are also highly toxic to cats because they do not have glucuronidase, which participates in hepatic detoxifying metabolism pathways. Anaphylaxis has been reported after pyrethrum exposure, but allergic reaction to pyrethroids has not been documented. Increased sensitivity occurs following repeated exposure to cyanide, which is found in pyrethroids like beta-cyfluthrin (Multiple Chemical Sensitivity Awareness, J. Edward Hill, MD, President & Executive Committee Member, AMA).
Safety and effectiveness
Pyrethroids have been found to be unaffected by secondary treatment systems at municipal wastewater treatment facilities in California. They appear in the effluent, usually at levels lethal to invertebrates.
.food webs that constitute the base of many aquatic and terrestrial invertebrates, and gadflies, mayflies pyrethroids are lethal to  Aside from the fact that they are also toxic to beneficial insects such as
- Allethrin, the first pyrethroid synthesized (active ingredient of Raid)
- Bifenthrin, active ingredient of Talstar, Capture, Ortho Home Defense Max, and Bifenthrine
- Cyfluthrin, an active ingredient in Baygon, dichlorovinyl derivative of pyrethrin
- Cypermethrin, including the resolved isomer alpha-cypermethrin, dichlorovinyl derivative of pyrethrin
- Cyphenothrin, active ingredient of K2000 Insect spray sold in Israel and the Palestinian territories
- Deltamethrin, dibromovinyl derivative of pyrethrin
- Permethrin, dichlorovinyl derivative of pyrethrin
- Prallethrin, active ingredient in Baygon and All Out (India)
- Resmethrin, active ingredient of Scourge
- Sumithrin, active ingredient of Anvil
- Transfluthrin, an active ingredient in Baygon
The earliest pyrethoids are related to pyrethrin I and II by changing the alcohol group of the organic synthesis. Members of this extensive class include the dichlorovinyl and dibromovinyl derivatives. Still others are tefluthrin, fenpropathrin, and bioethanomethrin.
Classes of pyrethroids
By 1974, the Rothamsted team had discovered a 2nd generation of more persistent compounds notably: permethrin, cypermethrin and deltamethrin. They are substantially more resistant to degradation by light and air, thus making them suitable for use in agriculture, but they have significantly higher mammalian toxicities. Over the subsequent decades these derivatives were followed with other proprietary compounds such as fenvalerate, lambda-cyhalothrin and beta-cyfluthrin. Most patents have now expired, making these compounds cheap and therefore popular (although permethrin and fenvalerate have not been re-registered under the 91/414/EEC process). One of the less desirable characteristics, especially of 2nd generation pyrethroids is that they can be an irritant to the skin and eyes, so special formulations such as capsule suspensions (CS) have been developed.
The 1st 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. Activity of pyrethrum and 1st generation pyrethroids is often enhanced by addition of the synergist piperonyl butoxide (which itself has some insecticidal activity). With the 91/414/EEC review, many 1st generation compounds have not been included on Annex 1, probably because the market is simply not big enough to warrant the costs of re-registration (rather than any special concerns about safety).
Pyrethroids were introduced in the late 1900s by a team of Rothamsted Research scientists following the elucidation of the structures of pyrethrin I and II by Hermann Staudinger and Leopold Ružička in the 1920s. 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).