Some studies in cell culture point to a possible biochemical explanation for the observed effects on amphibian sex organs. John P. Giesy, a professor of zoology at Michigan State University in East Lansing, and his colleagues found last year that, at large doses, atrazine ups production of the enzyme aromatase, which converts androgen hormones to estrogen hormones. Extrapolating these results from mammalian cells to amphibians, Hayes argues that atrazine could feminize male frogs by promoting the conversion of male hormones to female hormones. The lowered androgens would interfere with voice box development, while increased estrogens would promote ovaries within the testes.
More than 60 million pounds of the herbicide were applied last year in the United States alone. Manufacturer Syngenta estimates that farmers use the herbicide to control weeds on about two-thirds of all U.S. corn and sorghum acreage. On average, it improves corn yield by slightly more than four percent. The compound is generally considered safe, however, because it quickly decomposes in the environment and, being water soluble, is quickly excreted from the body.
Aquatic life, however, swim and breed in atrazine-contaminated field runoff. Though previous studies showed deformities and abnormalities in adult amphibians only at very high doses, no one had looked in detail at hormone levels in frogs or at effects on tadpoles, the larval stage of frogs.
Prodded by the EPA, Syngenta approached Hayes, an expert on amphibian hormones, to find out if atrazine disrupts sex hormones in amphibians. He has developed several very sensitive assays to detect chemicals that affect hormones, including a test for estrogen-like chemicals that might induce human breast cancer.
Though Hayes initially r
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Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
15-Apr-2002