In Agricultural Areas, Male Toads Feminized

(Beyond Pesticides, July 17, 2008)

In a new study published in Environmental Health Perspectives, researchers have found an increased occurrence of intersex toads in areas with greater agricultural land cover. This points to a link between certain pesticides and endocrine disruption, a change in the hormonal balance that can have sexual and reproductive effects. Such results implicate pesticides in the decline of amphibian populations, and suggests that these chemicals are also adversely affecting humans.

The study, which was conducted in south Florida, looked at cane toads, Bufo marinus, at five sites with differing land use patterns ranging from suburban to nearly completely agricultural (primarily sugarcane and vegetables). Researchers examined physical characteristics such as coloration, sexual organs, and forelimb length, as well as hormone concentrations, and found a higher rate of feminization for toads in agricultural areas. In these areas, glyphosate (the active ingredient in Round Up herbicide) and atrazine (an herbicide) use is common.

Tyrone Hayes, PhD, was one of the first to document the endocrine disrupting effects of atrazine on frogs in a laboratory setting. Countering any doubts of why this work is important, Dr. Hayes said, “People often say, ‘It is just frogs, so who cares?’ Well it does not matter whether you are a frog, a dog, a bat, a cat or a human. The compounds and the genes and the hormones that we are talking about are the same.”

This latest study, following on others, takes the issue out of the laboratory and attempts to address the effects of pesticides on amphibians in the environment. Because of the complexity of environmental factors and, as the authors say, the “milieu” of chemicals that may exist in the environment, it is much more difficult to prove definitive links between cause and effect outside the laboratory. In another study addressing frogs in the environment, researchers actually found increased intersex frogs in suburban areas. The two results do not necessarily contradict each other, and may indicate that a wide variety of chemicals are having endocrine disrupting effects on amphibians.

All of this work highlights the need for the Environmental Protection Agency (EPA) to develop a robust Endocrine Disruptor Screening Program that takes into account the effects, at all doses, pesticides can have on humans and wildlife, and eliminate the use of pesticides that are endocrine disruptors. The European Commission has taken steps to adopt a precautionary principle with endocrine disrupting chemicals.