Current applications of the weed killer atrazine are thought to have few deleterious effects on animals, but its water solubility results in high concentrations of the compound building up in water bodies supplied by agricultural run-off. In April 16 Proceedings of the Academy of Sciences USA, Tyrone Hayes and colleagues at the Department of Integrative Biology, University of California, Berkeley, show that these concentrations can cause tadpole hermaphroditism and demasculinization in adult Xenopus laevis frogs (Proc Natl Acad Sci USA 2002, 99:5476-5480).

Hayes et al. exposed X. laevis larvae to atrazine concentrations of 0.1-200 ppb and examined gonad histology and laryngeal size at metamorphosis and adult testosterone levels. Atrazine levels of ≥ 0.1 ppb induced hermaphroditism and at concentrations of 1.0 ppb ≥ 80% of male larynx were smaller than average (male frogs use the vocal organ to attract females). In addition plasma testosterone levels...

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