Popular weed killer demasculinizes frogs, disrupts their sexual development

eceived funds from Syngenta for the studies, all the current published studies were conducted independent of Syngenta.

For his laboratory tests, he used the African clawed frog, Xenopus laevis, a popular research subject that, like many frogs, is very sensitive to hormones that mimic the effect of their own sex hormones. If raised in a pond with estrogen, for example, all Xenopus tadpoles turn into females. In the presence of androgens, frogs grow larger voice boxes, or larynges.

In laboratory experiments at various concentrations of atrazine, using two separate populations of frogs raised in three separate tanks - experiments replicated 51 times - they found atrazine to affect the sexual development of frogs at concentrations of 0.1 ppb and higher. That is 30 times lower than the allowable limit of 3 ppb in drinking water and 120 times lower than the proposed chronic exposure limit for aquatic life, 12 ppb.

At these concentrations, as many as 16 percent of the animals had more than the normal numbers of gonads - including one animal with six testes - or had both male and female organs (testes and ovaries). No control animal had such abnormalities.

Also, while normal males at metamorphosis have larger vocal organs than females, the organs of more than 80 percent of males exposed to 1 ppb or more of atrazine were smaller than average.

Sexually mature males showed a 10-fold decrease in testosterone levels, bringing them below levels found in normal females. This suggests that atrazine acts by disrupting the synthesis of sex hormones, which could also explain the smaller larynges and abnormal gonads.

"... the current data raise new concerns for amphibians with regard to atrazine," the researchers wrote in their paper. "If such effects occur in the wild, exposed animals would suffer impaired reproductive function."

In fact, Hayes and his colleagues subsequently conducted a reconnaissance of atrazine-contaminated po

Contact: Robert Sanders
University of California - Berkeley

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