Pyrethrin
The pyrethrins are a class of organic compounds normally derived from Chrysanthemum cinerariifolium that have potent insecticidal activity by targeting the nervous systems of insects.
Pyrethrin naturally occurs in chrysanthemum flowers and is often considered an organic insecticide when it is not combined with piperonyl butoxide or other synthetic adjuvants.
Pyrethrins are gradually replacing organophosphates and organochlorides as the pesticides of choice as the latter compounds have been shown to have significant and persistent toxic effects to humans.
[2] The pyrethrins occur in the seed cases of the perennial plant pyrethrum (Chrysanthemum cinerariaefolium), which has long been grown commercially to supply the insecticide.
Pyrethrins were identified as the potent chemical in the Chrysanthemum plants responsible for the insecticidal properties in the crushed flowers around 1800 in Asia.
The key step in the biosynthesis of the naturally occurring pyrethrins involves two molecules of dimethylallyl pyrophosphate, which join to form a cyclopropane ring by the action of the enzyme chrysanthemyl diphosphate synthase.
Growing these plants does not require much water because semiarid conditions and a cool winter deliver optimal pyrethrin production.
[15] Pyrethrum extracted of the Persian chrysanthemum (painted daisy) was already imported to central Europe from Georgia in the middle of the 19th century.
[24] However, few cases leading to serious health effects or mortality in humans have occurred, which is why pyrethroids are labeled "low-toxicity" chemicals and are ubiquitous in home-care products.
[25] Specific pest species that have been successfully controlled by pyrethrum include: potato, beet, grape, and six-spotted leafhopper, cabbage looper, celery leaf tier, Say's stink bug, twelve-spotted cucumber beetle, lygus bugs on peaches, grape and flower thrips, and cranberry fruitworm.
Pyrethrins have shorter environmental persistence than synthetic pyrethroids because their chemical structure is more susceptible to the presence of UV light and changes in pH.
[citation needed] The use of pyrethrin in products such as natural insecticides and pet shampoo, for its ability to kill fleas, increases the likelihood of toxicity in mammals that are exposed.
One fatal case of an 11-year-old girl with a known asthmatic condition and who used shampoo containing only a small amount (0.2% pyrethrin) to wash her dog was documented.
[31] In mammals, toxic exposure to pyrethrum can lead to tongue and lip numbness, drooling, lethargy, muscle tremors, respiratory failure, vomiting, diarrhea, seizures, paralysis, and death.
[29] Exposure to pyrethrum in high levels in humans may cause symptoms such as asthmatic breathing, sneezing, nasal stuffiness, headache, nausea, loss of coordination, tremors, convulsions, facial flushing, and swelling.
[29] Infants are unable to resourcefully break down pyrethrum due to the ease of skin penetration, causing similar symptoms as adults, but with an increased risk of death.
[29] To combat the accumulation of pyrethroids in bodies of water, the Environmental Protection Agency (EPA) has introduced two labeling initiatives.
The Environmental Hazard and General Labeling for Pyrethroid and Synergized Pyrethrins Non-Agricultural Outdoor Products was revised in 2013 to reduce runoff into bodies of water after use in residential, commercial, institutional, and industrial areas.
