Hermaphrodite Frogs Linked to Pesticide Use

Frogs with both male and female reproductive organs were rare in the 19th and early 20th centuries but more common during the 1950s, when the largest volumes of the chemicals were used.

The findings, reported Tuesday in the journal Environmental Health Perspectives, add to the growing evidence that an array of pesticides and industrial chemicals can alter the sex hormones of animals.

The ability of certain chemicals to mimic or block estrogen and testosterone, which are key in sexual organ development and reproduction, is considered one of the most disturbing discoveries in environmental science of the last decade.

Scientists suspect that the phenomenon has been occurring for decades but it wasn't documented in wildlife until the early 1990s when it was first observed in Florida alligators and then among many other species.

Toxicologists and veterinarians at the University of Illinois at Urbana-Champaign, led by Amy Reeder, examined the reproductive organs of 814 cricket frogs collected in Illinois between 1852 and 2001 and stored at natural history museums.

Studying endocrine disruption of animals dating back more than a century has not commonly been done.

"It's a wonderful approach, and appropriate, because museums have this great collection of data that goes back through time," said Louis Guillette, a reproductive zoologist at the University of Florida and an expert on hormone disruption. "This is a very, very important study that suggests to us that some of the things we're seeing, even today, in frog populations may have a historical basis dating back to when we were using large amounts of these compounds." Guillette, who was not involved in the study, has linked hermaphroditic alligators to DDT.

Cricket frogs, once abundant, declined dramatically around Chicago and in other regions in the 1960s. Scientists found that the times and places with high rates of hermaphrodites, also called intersexes, overlapped with when and where the frog numbers dropped in Illinois.

The scientists theorize that DDT, industrial compounds called PCBs (polychlorinated biphenyls) and other contaminants had an antiestrogenic effect, reducing the proportion of females and causing them to develop abnormal sex organs, triggering a population crash, particularly in the Chicago region.