Suburban Estrogen Could Be Changing Frogs’ Sex Ratios

Increased levels of estrogen in suburban ponds could be affecting the sex ratio of frogs, according to new research.

“The more suburban [the frogs] got the more sexually proportionate to females,” said Max Lambert, a post-doctoral researcher in forestry and environmental studies at Yale University and the lead author of a new study published in the Proceedings of the National Academy of the Sciences.

The study looked at the ratio of male to female frogs in different kinds of environments around New Haven, Ct., varying from manicured lawns, shrubs and gardens to heavily forested areas.

Researchers found that suburban areas sometimes had twice the number of female frogs compared to males, and this is likely due to increased amounts of estrogen in those areas. The male frogs in these areas seemed to exhibit “feminized gonads” in many cases, according to Lambert.

Suburban ponds contain traces of estrogen, which researchers believe may come from natural sources such as the plants that are often favored in backyards or from septic system leaks. Image Credit: Max Lambert/Yale University

There are likely two different sources of this estrogen, Lambert said. The first could be leaking from septic systems around settlements — humans naturally excrete estrogen or it could be from the digested byproducts of certain medications.

Another possible source is more natural — the phytoestrogens produced by clovers and certain legumes commonly found in suburban areas.

“There’s no smoking gun for what’s causing endocrine disruption in backyards,” he said, though he noted that some frogs are capable of changing sex. He added that further studies are needed to determine whether the feminized male frogs are actually capable of producing fit tadpoles.

This recent finding has implications for other amphibian species that may be affected — and, according to Lambert, studies could show in the future that the well water many people in this part of New England rely on also contains estrogen.

“It could be also affecting the ground water and drinking water in wells,” he said.