Synthetic Pyrethroids
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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 LD s, ranges 50 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- bodys 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 selec- logues of naturally occurring pesticides, sulted in contact dermatitis and asthma-like tive toxicity to insects, both pyrethroids and were developed to capture the effective in- reactions. Persons, especially children, with pyrethrins are extremely toxic to aquatic or- secticidal activity of this botanical insecti- a history of allergies or asthma are particu- ganisms, including fish such as the bluegill cide, with increased stability in light, yield- larly sensitive, and a strong cross-reactivity and lake trout, with LC values less than 1.0 50 ing longer residence times (Gosselin et al., with ragweed pollen has been recognized. parts per billion. These levels are similar to 1984). Severe anaphylactic (allergic) reactions with those for mosquito, blackfly and tsetse fly peripheral vascular collapse and respiratory larvae, often the actual target of the pyre- Pyrethroids and Health Effects difficulty are rare. Other symptoms of acute throid application. Lobster, shrimp, mayfly Pyrethroids have irritant and/or sensitizing toxicity due to inhalation include sneezing, nymphs and zooplankton are the most Beyond Pesticides 701 E Street, S.E., Suite 200 Washington DC 20003 202-543-5450 (v) 202-543-4791 (f) [email protected] www.beyondpesticides.org 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 Pyrethroids are moderately toxic to birds, drugs and other chemicals, a heavy expo- (EPA, 1997). Of concern in the environ- with most LD values greater than 1000 mg/ sure to an insecticidal synergist may make a ment, bifenthrin is very highly toxic to fish, 50 kg. Birds can also be indirectly affected by person temporarily vulnerable to a variety crustaceans, other aquatic animals and pyrethroids, because of the threat to their of toxic insults that would normally be eas- bees, and is moderately toxic to birds. food supply. Waterfowl and small insectivo- ily tolerated. Symptoms of PBO poisoning Scientists are particularly concerned about rous birds are the most susceptible (Mueller- include anorexia, vomiting, diarrhea, intesti- possible bioaccumulation in birds. Beilschmidt, 1990). Because pyrethroids are nal inflammation, pulmonary hemorrhage and Cypermethrin (AmmoTM, CymbushTM, toxic to all insects, both beneficial insects perhaps mild central nervous system depres- DemonTM) and pests are affected by pyrethroid appli- sion. Repeated contact may cause slight skin Cypermethrin, one of a handful of light- cations. In some cases, predator insects may irritation. Chronic toxicity studies have stable synthetic pyrethroids, is registered be susceptible to a lower dose than the pest, shown increased liver weights, even at the to control cockroaches, fleas and other disrupting the predator-prey relationship. lowest doses, 30 mg/kg/day. While not con- indoor pests in homes, restaurants, sidered a carcinogen by EPA, animal studies hospitals, schools and food processing Pyrethroids Residues / Persistence have shown hepatocellular carcinomas, even plants, and also in agriculture to control As mentioned before, pyrethroids are de- treatments as low as 1.2% (Takahashi et al., pests on cotton, fruits and vegetables. signed to breakdown more slowly than the 1994). About 90% of the cypermthrin manufac- naturally occurring pyrethrins. While pyre- tured worldwide is used to combat pests thrins, extremely sensitive to light, heat and Bifenthrin (TalstarTM, BrigadeTM, feeding on cotton crops (WHO, 1989). moisture, break down in a few hours, the syn- CaptureTM) Depending on the specific product thetic pyrethroids are stable and persist in Bifenthrin is an off-white to pale tan waxy formulation, EPA classifies pesticides the environment much longer. As a general solid, characterized by its slightly sweet containing cypermethrin as toxicity class II rule, pyrethroids break down most quickly smell. As a Restricted Use Pesticide, or III (I = most toxic, IV = least toxic) and in direct sunlight, usually just a few days bifenthrin may only be purchased or must display the word WARNING or after application, with a few exceptions. applied by certified applicators or persons CAUTION on the labels. Compared to However, in areas with limited sunlight, such under the direct supervision of a certified other pyrethroids, cypermethrin is rela- as grain silos and subway tunnels, pyre- applicator. EPA has registered bifenthrin tively stable, with a half-life of 8 16 days throids can persist for months.