chemicalWATCH Factsheet
SYNTHETIC PYRETHROIDS
Pesticide products containing pyrethroids properties. They are not easily absorbed nasal stuffiness, headache, nausea, incoor- are often described by pest control opera- through the skin, but are absorbed through dination, tremors, convulsions, facial flush- tors and community mosquito management the gut and pulmonary membrane. Tests of ing and swelling, and burning and itching bureaus as "safe as chrysanthemum flow- some pyrethroids on laboratory animals re- sensations. The most severe poisonings ers." While pyrethroids are a synthetic ver- veal striking neurotoxicity when administered have been reported in infants, who are not sion of an extract from the chyrsanthemum, by injection or orally. Systemic toxicity by able to efficiently break down pyrethroids they were chemically designed to be more inhalation and dermal absorption is low. The (ETN, Pyrethroids, 1994). With orally in- toxic with longer breakdown times, and are acute toxicity, calculated by LD50's, ranges gested doses, nervous symptoms may oc- often formulated with synergists, increas- from low to high, depending on the specific cur, which include excitation and convulsions ing potency and compromising the human formulation. Low toxicity is attributed to two leading to paralysis, accompanied by mus- body's ability to detoxify the pesticide. factors: limited absorption of some pyre- cular fibrillation and diarrhea (ETN, Pyre- throids, and rapid biodegradation by mam- throids, 1994). Death in these cases is due to What are Synthetic Pyrethroids? malian liver enzymes (ester hydrolysis and respiratory failure. Symptoms of acute expo- Synthetic pyrethroids are synthesized de- oxidation). Insects, without this liver func- sure last about 2 days. rivatives of naturally occurring pyrethrins, tion, exhibit greater susceptibility to the which are taken from pyrethrum, the oleo- chemicals (Reigart et al., 1999). Endocrine Disruption and Breast Cancer resin extract of dried chrysanthemum flow- Many pyrethroids have also been linked to ers. The insecticidal properties of pyrethrins Pyrethroids interfere with the ionic conduc- disruption of the endocrine system, which are derived from ketoalcoholic esters of tance of nerve membranes by prolonging the can adversely affect reproduction and sexual chrysanthemic and pyrethroic acids. These sodium current. This stimulates nerves to development, interfere with the immune sys- acids are strongly lipophilic and rapidly pen- discharge repeatedly causing hyper-excit- tem and increase chances of breast cancer. etrate many insects and paralyze their ner- ability in poisoned animals. The World Health Pyrethroids contain human-made, or vous system (Reigart et al., 1999). Both pyre- Organization explains that synthetic pyre- xenoestrogens, which can increase the thrins and synthetic pyrethroids are sold as throids are neuropoisons acting on the axons amount of estrogen in the body (Garey et al., commercial pesticides used to control pest in the peripheral and central nervous sys- 1998). When tested, certain pyrethroids dem- insects in agriculture, homes, communities, tems by interacting with sodium channels in onstrate significant estrogenicity and in- restaurants, hospitals, schools, and as a topi- mammals and/or insects. The main systems crease the levels of estrogen in breast can- cal head lice treatment. Various formulations for metabolism include breakage of the ester cer cells (Go et al., 1999). Because increased of these pesticides are often combined with bond by esterase action and oxidation at cell division enhances the chances for the other chemicals, known as synergists, to in- various parts of the molecule. Induction of formation of a malignant tumor in the breast, crease potency and persistence in the envi- liver microsomal enzymes has also been ob- artificial hormones, like those found in pyre- ronment. served (WHO, 1999). throids, may increase breast cancer risk (PCBR, 1996). Some pyrethroids are classi- While chemically and toxicologically similar, Signs and symptoms of poisoning by pyre- fied by EPA as possible human carcinogens. pyrethrins are extremely sensitive to light, throids may take several forms. Because of heat and moisture. In direct sunlight, half- the similarities to crude pyrethrum, pyre- Pyrethroids and the Environment lives that can be measured in hours. How- throids may act as dermal and respiratory While the development of the synthetic pyre- ever, the pyrethroids, the synthetic ana- allergens. Exposure to pyrethroids has re- throids was heralded with claims of logues of naturally occurring pesticides, sulted in contact dermatitis and asthma-like selective toxicity to insects, both were developed to capture the effective in- reactions. Persons, especially children, with pyrethroids and pyrethrins are extremely secticidal activity of this botanical insecti- a history of allergies or asthma are particu- toxic to aquatic or- ganisms, including fish cide, with increased stability in light, yield- larly sensitive, and a strong cross-reactivity such as the bluegill and lake trout, with LC50 ing longer residence times (Gosselin et al., with ragweed pollen has been recognized. values less than 1.0 parts per billion. These 1984). Severe anaphylactic (allergic) reactions with levels are similar to those for mosquito, peripheral vascular collapse and respiratory blackfly and tsetse fly larvae, often the Pyrethroids and Health Effects difficulty are rare. Other symptoms of acute actual target of the pyre- throid application. Pyrethroids have irritant and/or sensitizing toxicity due to inhalation include sneezing, Lobster, shrimp, mayfly nymphs and zooplankton are the most
susceptible non-target aquatic organisms cluding the active ingredients of pesticides. about 12 hours. A study on laboratory (Mueller-Beilschmidt, 1990). The nonlethal Specifically, it has been shown to inhibit he- mice shows that bifenthrin causes gene effects of pyrethroids on fish include dam- patic microsomal oxidase enzymes in labora- mutation in white blood cells (ETN, age to the gills and behavioral changes. tory rodents and interfere in humans. Be- Bifenthrin, 1995). EPA classifies bifenthrin cause these enzymes act to detoxify many as a Class C (possible human) carcinogen
drugs and other chemicals, a heavy expo- (EPA, 1997). Of concern in the environ- Pyrethroids are moderately toxic to birds, sure to an insecticidal synergist may make a ment, bifenthrin is very highly toxic to fish, with most LD values greater than 1000 mg/ 50 person temporarily vulnerable to a variety crustaceans, other aquatic animals and kg. Birds can also be indirectly affected by of toxic insults that would normally be eas- bees, and is moderately toxic to birds. pyrethroids, because of the threat to their ily tolerated. Symptoms of PBO poisoning Scientists are particularly concerned about food supply. Waterfowl and small insectivo- include anorexia, vomiting, diarrhea, intesti- possible bioaccumulation in birds. rous birds are the most susceptible (Mueller- nal inflammation, pulmonary hemorrhage and TM TM Beilschmidt, 1990). Because pyrethroids are Cypermethrin (Ammo , Cymbush , perhaps mild central nervous system depres- TM toxic to all insects, both beneficial insects Demon ) sion. Repeated contact may cause slight skin Cypermethrin, one of a handful of light- and pests are affected by pyrethroid appli- irritation. Chronic toxicity studies have stable synthetic pyrethroids, is registered cations. In some cases, predator insects may shown increased liver weights, even at the to control cockroaches, fleas and other be susceptible to a lower dose than the pest, lowest doses, 30 mg/kg/day. While not con- indoor pests in homes, restaurants, disrupting the predator-prey relationship. sidered a carcinogen by EPA, animal studies hospitals, schools and food processing
have shown hepatocellular carcinomas, even plants, and also in agriculture to control Pyrethroids Residues / Persistence treatments as low as 1.2% (Takahashi et al., pests on cotton, fruits and vegetables. As mentioned before, pyrethroids are de- 1994). About 90% of the cypermthrin manufac- signed to breakdown more slowly than the tured worldwide is used to combat pests naturally occurring pyrethrins. While pyre- TM TM feeding on cotton crops (WHO, 1989). thrins, extremely sensitive to light, heat and Bifenthrin (Talstar , Brigade , TM Depending on the specific product moisture, break down in a few hours, the syn- Capture ) formulation, EPA classifies pesticides thetic pyrethroids are stable and persist in Bifenthrin is an off-white to pale tan waxy solid, characterized by its slightly sweet containing cypermethrin as toxicity class II the environment much longer. As a general or III (I = most toxic, IV = least toxic) and rule, pyrethroids break down most quickly smell. As a Restricted Use Pesticide, must display the word WARNING or in direct sunlight, usually just a few days bifenthrin may only be purchased or CAUTION on the labels. Compared to after application, with a few exceptions. applied by certified applicators or persons other pyrethroids, cypermethrin is rela- However, in areas with limited sunlight, such under the direct supervision of a certified applicator. EPA has registered bifenthrin tively stable, with a half-life of 8 - 16 days as grain silos and subway tunnels, pyre- in direct sunlight. In soil, studies have throids can persist for months. For more spe- for use on greenhouse ornamentals and shown the half-life to be as long as 8 cific breakdown times see the sections be- cotton. Studies show bifenthrin to be weeks, and in water as long as 100 days low on resmethrin, permethrin and sumithrin. relatively insoluble in water. Its half-life in soil can range anywhere from 7 days to 8 (ETN, Cypermethrin, 1996). After treat-
months depending on the soil type and the ments in the home, cypermethrin persists Synergists amount of air in the soil (ETN, Bifenthrin, for about three months (Wright et al., Both pyrethroids and pyrethrins are often 1995). Bifenthrin is one of a few synthetic 1993). formulated with oils or petroleum distillates pyrethroids that are relatively stable in Cypermethrin is considered to be moder- and packaged in combination with syner- direct sunlight. EPA has classified prod- ately toxic (oral male rat LD50 = 187 to 326 gists, such as piperonyl butoxide (PBO) and ucts containing bienthrin as toxicity class mg/kg, dermal rat LD50 = 1600 mg/kg) and n-octyl bicycloheptene dicarboximide II (I = most toxic, IV = least toxic), and the like all pyrethroids, affects the central (Gosselin et al., 1984). Synergists are added word WARNING must appear on all nervous system (ETN, Cypermethrin, to increase the potency of the pesticide. A product labels. 1996). Symptoms of cypermethrin poison- range of products from repellants to foggers ing in humans include numbness, burning, to pediculicides (lice killers) to garden sprays Bifenthrin is moderately toxic to mammals loss of bladder control, vomiting, incoordi- contain synergists. Many formulations of when ingested (oral rat LD50 = 54 to 70 nation, seizures, coma and death. In permethrin, resmethrin and sumithrin, includ- mg/kg), and like all pyrethroids affects the lM lM central nervous system. Symptoms of California, cypermethrin is the fourth most ing Scourge and Anvil , used along the poisoning include incoordination, tremor, common cause of pesticide-related illness East Coast for mosquito control to combat salivation, vomiting, diarrhea, and irritabil- in pest control operators. EPA classifies the West Nile Virus, contain the synergist ity to sound and touch (ETN Bifenthrin, cypermethrin as a class C (possible PBO. 1995). Although bifenthrin does not cause human) carcinogen (EPA, 1997). Studies in
inflammation or irritation on human skin, it laboratory animals have shown exposure PBO inhibits important liver enzymes re- can cause a tingling sensation, lasting to cypermethrin to cause reproductive sponsible for breakdown of some toxins, in-
effects, including abnormal sperm and microsomal enzyme induction, irritability, is extremely toxic to bees and fish, and is disruption of sex hormones (Cox, 1996). peripheral vascular collapse, rhinorrhea, slightly toxic to birds. TM TM Cypermethrin should not be applied near serum alkaline phosphatase elevation, Permethrin (Pounce , Torpedo , TM water, because it is very toxic to fish and tremors, vomiting and death due to Dragnet ) other aquatic organisms. respiratory failure. Deltamethrin is a Prior to 1978, permethrin was registered for Deltamethrin (ButoflinTM, ButossTM, suspected endocrine disruptor. use on cotton crops only. During the early CrackdownTM) Deltamethrin is also toxic to fish, aquatic 1980's registration was expanded to Deltamethrin is pyrethroid insecticide that organisms, amphibians and bees. include use on livestock and poultry, eggs, TM kills insects on contact and through Fenvalerate (Esfenvalerate, Sumifly , vegetables and fruit. Today uses also TM digestion. It works by paralyzing the Sumiflower ) include lice treatments and urban/subur- insects' nervous system and therefore Fenvalerate is registered for use on a wide ban pest control. Permethrin resembles giving a quick knock-down effect. It is array of crops including cotton, soybeans, pyrethrins chemically, but is chlorinated to used commonly to control caterpillars on corn, vegetables, apples, peaches, pears increase its stability. There are four apples, pears and hops, and for the control and nuts, as well as a termiticide and insect isomeric forms, two cis and two trans of of aphids, mealy bugs, scale insects, and repellent. Fenvalerate was first formulated technical permethrin. Although the acute whiteflies on glasshouse cucumbers, for agricultural use in 1974, but was toxicity of the mixture (oral rat LD50 > 5000 tomatoes, peppers, potted plants, and approved as a termiticide in 1987, as an mg/kg, oral mouse LD50 = 500) is less than ornamentals (ETN, Deltamethrin, 1995). It alternative to the voluntarily cancelled that of natural pyrethrins, the cis-isomer is is also registered for use on livestock and cyclodiene termiticides. During the late considerably more toxic (oral mouse LD50 for public health uses. Depending on the 1980's, fenvalerate received national press = 100), and in rats, the metabolites of the product formulation, deltamethrin pesti- coverage due to over 200 dog and cat cis-isomer are more persistent biologically. cides may range in toxicity from EPA poisonings, including 26 deaths, following (The cis and trans isomers differ in the toxicity class I to class III (I = most toxic, the use of BlockadeTM, a product contain- spatial arrangement of the atoms.) Product IV = least toxic), bearing the words ing fenvalerate in combination with DEET, formulations of permethrin can vary DANGER-POISON, WARNING or CAU- a common insect repellant. EPA classifies greatly in isomeric content. Compared to TION on the label (PANNA, 2000). fenvalerate products as toxicity class II (I = other pyrethroids, permethrin is very Deltamethrin products may be general or most toxic, IV = least toxic), and include stable, even when exposed to ultraviolet Restricted Use Pesticides. Most the word WARNING on all product labels. light. Permethrin is strongly absorbed to deltamethrin products persist from one to Some formulations are Restricted Use soil and other organic particles, with half- two weeks in the environment, with shorter Pesticides, and may only be purchased or lives in soil of up to 43 days. When used times in direct sunlight (ETN, Deltamethrin, applied by certified applicators or persons as a termiticide, permethrin can persist up 1995). under the direct supervision of a certified to 5 years. Deltamethrin produces different signs of applicator. The half-life of fenvalerate Permethrin receives an EPA toxicity class ranges from 15 days to 3 months in soil, 21 poisoning than other pyrethroids. When rating of II or III (I = most toxic, IV = least days in water and 2-4 weeks on vegetation. exposed to deltamethrin, mammals exhibit toxic), and carries either the word WARN- Fenvalerate is considered to be moderately typical type II motor symptoms, which ING or CAUTION on its label, depending toxic (oral rat LD50 = 486 mg/kg). Symp- include a writhing syndrome in rodents, as on the formulation. While it is not ex- toms of poisoning through direct contact well as copious salivation. The acute oral tremely toxic to humans, there are numer- include dizziness, burning and itching LD in male rats has been reported as low ous reports of transient skin, eye and 50 (which is worsened by sweating and as 128 mg/kg to greater than 5,000 mg/kg respiratory irritation. Like all pyrethroids, washing), blurred vision, tightness in the depending on the carrier and conditions of permethrin is a central nervous system chest, and convulsions. When ingested by the study (ETN, Deltamethrin, 1995). Some poison. Workers and researchers report laboratory animals, symptoms of poison- studies have shown deltamethrin to cause tingling in face and hands, and some ing include muscle incoordination, tremors, skin irritation. Especially characteristic of report allergic reactions. Based on studies convulsions, nerve damage, and weight deltamethrin poisoning is rolling convul- demonstrating carcinogenicity, EPA ranks loss. Fenvalerate is a strong eye irritant sions. The sequence of the signs of permethrin as a class C, or possible human and a suspected endocrine disruptor carcinogen (U.S. EPA, 1997). Other studies poisoning is clearly defined, progressing (PANNA, 2000). Sweden has banned the have shown effects on the immune system, from chewing, salivation, and pawing to chemical for use in forestry following enlarged livers and at high doses, de- rolling convulsions, tonic seizures, and health related complaints from workers. creased female fertility and endocrine death (ETN, Deltamethrin, 1995). In disruption. Permethrin is extremely toxic to humans, symptoms of poisoning include Studies have found that immediate aquatic life, bees and other wildlife. It ataxia, convulsions leading to muscle application of vitamin E to exposed areas should not be applied in crops or weeds fibrillation and paralysis, dermatitis, edema, can lessen the painful effects. Fenvalerate diarrhea, dyspnea, headache, hepatic
where foraging may occur (ETN, contact. In laboratory animals, chronic alcohol. It is a combination of two cis and Permethrin, 1996). toxicity studies have shown hypertrophy of two trans isomers. Sumithrin is slightly Resmethrin (ScourgeTM, Raid Flying the liver, prolifera- tive hyperplasia and toxic and is rated EPA toxicity class IV (I = Insect KillerTM) benign and cancerous liver tumors. EPA most toxic, IV = least toxic) bearing the Resmethrin is used for control of flying and reviewers noted slight, but significant, word CAUTION on its label. The oral rat crawling insects in homes, green- houses, increases in the number of offspring born LD50 is greater than 5,000 mg/kg, and the processing plants, commercial kitchens, dead and decreased viability, which they LC50 for inhalation is greater than 1210 airplanes and for public mosquito control. thought might be secondary to trans mg/m3. Sumithrin degrades rapidly, with a Resmethrin is considered slightly toxic to placental toxicity. Tests for neurotoxicity half-life of 1-2 days under dry, sunny humans and is rated EPA toxicity class III (I have been negative, but it is a suspected conditions. Under flooded conditions, the = most toxic, IV = least toxic), bearing the endocrine disruptor (PANNA, 2000). half-life increases to 2-4 weeks for the word CAUTION on its label. Resmethrin is extremely toxic to fish, other trans isomer and 1-2 months for the cis The oral rat LD50 is about 2500 mg/kg. aquatic life and bees. The domestic isomer. In grain silos, with no sunlight and Although resmethrin has a very short half- manufacturer of resmethrin, Penick little air circulation, most of the product life (under an hour in direct sunlight), it Company, will not identify the inert still remains after one year (WHO, 1990). persists much longer in soil with a half-life ingredients in its product, but recommends Symptoms of acute sumithrin poisoning of 30 days (ETN, Resmethrin, 1996). that it is not sprayed on paint, plastic or include hyperexcitability, prostration, slow Resmethrin breaks down into a smelly varnished surfaces, and that treatment of respiration, salivation, tremor, ataxia and byproduct, phenylacetic acid, which binds living areas or areas with large amounts of paralysis. Chronic feeding studies resulted strongly to textiles and dissipates slowly, textiles be avoided. in increased liver weights in both males TM smelling of urine. Sumithrin (Anvil , d-Phenothrin) and females. In rat studies, sumithrin was Resmethrin is absorbed rapidly and Sumithrin has been registered for use since completely excreted in 3-7 days (WHO, distributed to all tissues including the brain. 1975. It is used to control adult mosquitoes 1990). Studies have shown that sumithrin Skin absorption is low, although it should be and as an insecticide in transport vehicles, is an endocrine disruptor, demonstrating noted that some individuals manifest allergic commercial, industrial and institutional significant estrogenicity and increases the responses including dermatitis, asthma, non-food areas, in homes, gardens, level of estrogen in breast cancer cell, runny nose and watery eyes after initial greenhouses and on pets. Chemically, it is suggesting that sumithrin may increase the an ester of chrysanthemic acid and risk of breast cancer (Go et al., 1999).
Synthetic Pyrethroids chemica/WATCH Factsheet References
Information Profiles. Hallenbeck, W.H. and K.M. Cunningham- Cassagrande, R.A. 1989. "Considerations
Kolmodin-Hedman, B., et al. 1982. Scourge Insecticide Product Label U.S. EPA. 2000. For Your Information, "Occupational exposure to some with SBP-1382/Piperonyl Synthetic Pyrethroids for Mosquito synthetic pyrethroids (permethrin Butoxide 18% + 54% MF. U.S. Control. Washington, DC. May. and fenvalerate)." Arch. Toxicol. EPA Reg. No. 432-667. AgrEvo, 50:27-33. Montvale, NJ. U.S. EPA. 1997. Office of Pesticide Mueller-Beilschmidt, Doria. 1990. Programs list of chemicals evaluated Toxicology and Environmental Fate Takahashi, O., et al., 1994. "Chronic for carcinogenic potential. Memo from of Sythetic Pyrethrois." Journal of toxicity studies of piperonyl W.L. Burnman, HED, to HED branch Pesticide Reform. 10 (3):32-37. butoxide in F344 rats: induction chiefs. Washington, DC. February 19. of hepatocellular carcinoma." National Research Council. 1987. Fund. Appl. Toxicol. 22: 293- World Health Organization (WHO). 1990. Regulating Pesticides in Food: The 303. d-Phenothrin. Environmental Health Delaney Paradox. National Academy Criteria. Geneva. Press, Washington, DC. Thomson, W.T. 1984. Agricultural Chemicals: Insecticides. Wright, C., et al. 1981. "Insecticides in the Olkowski, W. 1989. "Natural and Thompson Publications, Fresno, ambient air of rooms following their synthetic pyrethrum insecticides: CA. application of control of pests." Bull. Finding your way through the Environ. Contam. Toxicol. 26:548-553. maze." Common Sense Pest U.S. EPA. 1979. Environmental Fate Quarterly. 5(1):8-12. Review of Permethrin (activated sludge metabolism study). Reigart, J., M.D. et al., Recognition and November 29. Office of Pesticide Management of Pesticide Programs. Washington, DC. Poisonings, EPA, 1999.