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<br />INTRODUCTION <br /> <br />Chlorpyrifos (phosphorothioic acid 0, O-diethyl 0-(3,5,6-trichloro- <br />2-pyridinyl) ester), also known commonly as Dursban and Lorsban, was first <br />registered as a broad spectrum insecticide in 1965, and subsequently was used <br />widely to control a variety of pests such as fire ants, turf and ornamental <br />plant insects, cockroaches, mosquitos, termites, hornflies, lice, and fleas <br />(EPA 1986). In 1982, total agricultural use of chlorpyrifos was estimated at <br />2.2 to 3.2 million kg, and industrial uses ranged between 0.68 and 1.04 <br />million kg (EPA 1982). In 1984, about 0.15 million kg (0.33 million pounds) <br />of chlorpyrifos was applied to about 600,000 ha (1.48 million acres) of <br />wetlands in the United States for mosquito control (Odenkirchen 1987). <br />Treatment programs in which chlorpyrifos concentrations suitable for mosquito <br />control and other insect pests were used have been shown to be detrimental to <br />nontarget species, including aquatic organisms, waterfowl, and terrestrial <br />organisms from surrounding ecosystems (Linn 1968; Hurlbert et al. 1970, 1972; <br />Atkins 1972; Streu and Cruz 1972; Nelson and Evans 1973; Butcher et al. 1977; <br />Thirugnanam and Forgash 1977; Tagatz et al. 1982; Goodman et al. 1985a; McEwen <br />et al. 1986; Mayer 1987; Odenkirchen 1987; Smith 1987). Domestic use of <br />chlorpyrifos has resulted in the death of an I1-day-old infant (CDC 1980) and <br />the poisoning of office workers (Hodgson et al. 1986). Prophylactic use of <br />chlorpyrifos on farm animals has caused reproductive impairment of livestock <br />(Everett 1982). Chlorpyrifos-resistant strains of insects have been detected <br />recently; they include the German cockroach (Blattella germanica) in Florida <br />and Nebraska (Milio et al. 1987) and the sawtoothed grain beetle (Oryzaephilus <br />surinamensis) in Australia (Collins 1985). <br /> <br />This report was prepared in response to requests for information from <br />environmental specialists of the U.S. Fish and Wildlife Service. It is part <br />of a continuing series of brief reviews on chemical contaminants and natural <br />resources. <br /> <br />1 <br />