Feminizing Frogs

Atrazine, a widely used herbicide, has been extensively studied for its endocrine-disrupting effects, most notably in amphibians, where laboratory and field research led by biologist Tyrone Hayes showed that exposure to concentrations as low as 0.1 to 2.5 parts per billion (ppb) could alter hormone signaling in frogs, causing feminization, hermaphroditism, and reduced fertility in male Xenopus laevis.

These effects are linked to atrazine’s ability to increase aromatase activity, an enzyme that converts testosterone into estrogen, thereby disrupting normal sexual development.

In humans, atrazine does not bioaccumulate significantly, but exposure is widespread; its metabolites are commonly detected in urine samples, especially in agricultural regions.

Regulatory limits reflect this concern: in the United States, the EPA sets a maximum contaminant level of 3 ppb for atrazine in drinking water, and average public exposure is typically well below this threshold, though seasonal spikes can occur near farm runoff zones.

While epidemiological studies in humans suggest possible associations with reproductive and developmental outcomes, results remain mixed, and atrazine continues to be debated as a case study in how low-dose chemical exposure can interact with hormonal systems across species.