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Pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums (''Chrysanthemum cinerariaefolium'' and ''C. coccineum''). Pyrethroids now constitute the majority of commercial household insecticides.〔Robert L. Metcalf “Insect Control” in Ullmann’s Encyclopedia of Industrial Chemistry” Wiley-VCH, Weinheim, 2002. 〕 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.〔(Pyrethroids fact sheet ) from the Illinois Department of Public Health.〕 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==
Pyrethroids are axonic excitoxins, the toxic effects of which are mediated through preventing the closure of the voltage-gated sodium channels in the axonal membranes. The sodium channel is a membrane protein with a hydrophilic interior. This interior is a tiny hole which is shaped precisely to strip away the partially charged water molecules from a sodium ion and create a favorable way for sodium ions to pass through the membrane, enter the axon, and propagate an action potential. When the toxin keeps the channels in their open state, the nerves cannot repolarize, leaving the axonal membrane permanently depolarized, thereby paralyzing the organism.〔D. M. Soderlund, et al., "Mechanisms of pyrethroid neurotoxicity: implications for cumulative risk assessment", Toxicology 2002 171, 3-59. 〕
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