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