Intersex Frogs More Common in Suburban Areas

(Beyond Pesticides, April 10, 2008)

Common frogs that live in suburban areas are more likely than their rural counterparts to develop reproductive abnormalities, according to David Skelly, PhD, professor of ecology at the Yale School of Forestry and Environmental Studies. This phenomenon becomes a serious concern as the frog’s mating season begins, leaving researchers to wonder: will frogs be clear on their role in the annual ritual?

Research by Dr. Skelly, soon to be published, focuses on the common green frog, Rana clamitans, within the Connecticut River Valley. A total of 233 frogs were collected from various ponds and landscapes with the river valley and among them 13 percent have abnormalities occurring in their reproductive organs. In urban areas, 18 percent of the collected frogs are intersex, and in suburban areas 21 percent. Frogs collected from agricultural areas have the lowest rate of reproductive problems with just 7 percent classified as intersex. According to Dr. Skelly, the more suburban the land cover, the more likely the abnormalities.

“This is the first evidence that I think anyone has provided that agriculture is doing anything but pushing those rates higher,” remarked Dr. Skelly of the intersex phenomena.

In an attempt to explain the higher prevalence of intersex frogs in urban and suburban areas, the study notes that many suburban areas use septic systems that may be leaching chemicals or pharmaceuticals into streams or ponds. These areas also have higher rates of using herbicides and insecticides for lawn care and garden treatments.

Intersex frogs, also called hermaphroditic frogs, refer to frogs, mostly males observed to be producing eggs in their testes. There are many studies documenting this phenomenon, which is also blamed for the decline in many frog populations. Work by Tyrone Hayes, PhD, University of California, Berkeley, has linked the agricultural herbicide atrazine to reproductive disorders in frogs. A U.S. Geological Survey (USGS), also suggests a strong link between the abnormalities and agriculture. However, this study is the first to document the relationship with a non-agricultural setting.

Atrazine, which is classified as an endocrine disruptor, interrupts the workings of natural hormones. However, many household products, such as antibacterials and antimicrobials like triclosan and its cousin triclocarban, which are found in detergents, bar soaps, and other personal care products, have been shown to produce the same effects when released into streams and ponds. A recent study found that these antibacterials enhance endocrine disruption and have also been found to have the highest user rates among the wealthy. These antibacterials and other estrogenic chemicals are detected at high concentrations in the effluent discharged in the areas where the abnormalities are found. Lawn care chemicals like 2,4-D, permethrin, and glyphosate (Round-up) also cause damaging endocrine effects, even though the U.S. EPA does not currently evaluate or consider the endocrine disrupting properties of pesticides during registration or re-registration. These chemicals run off from treated lawn surfaces to contaminate nearby streams.

“Looking upstream and downstream from wastewater-treatment plants, we see there’s obviously been an impact by some of the chemicals discharged,” said Vicki S. Blazer, PhD, fish biologist at USGS.

Recent news reports have brought attention to antibacterials and pharmaceuticals in drinking water. While these chemicals pose serious health concerns to human populations, the harm posed to wildlife species being documented at alarming rates.

Source: New York Times