Atrazine is the most commonly used herbicide in the U.S. But a new study shows that it can turn male frogs into hermaphrodites. Host Steve Curwood speaks with UC Berkeley biologist Tyrone Hayes about his research into the weed-killer's effects on these amphibians.
CURWOOD: It’s been known for some time now that frogs are in trouble. They’ve been turning up with limb deformities and their populations are crashing worldwide. Studies point to culprits ranging from parasites to ultraviolet light to various forms of pollution. Now new research shows that atrazine, the most commonly used herbicide used in the U.S., might be playing a role. In a recent study, researchers found that up to 20 percent of male frogs raised in water containing low levels of atrazine developed abnormal reproductive organs. The researchers also found that adult male frogs had lower testosterone levels after exposure to the herbicide.
Tyrone Hayes, a professor of biology at the University of California at Berkley led the research and joins me now. Professor Hayes, what types of deformities did you find in these frogs?
HAYES: Well, weve shown that very low levels, very low doses of atrazine, will induce gonadal abnormalities. These include, in some cases, multiple testes— so you might have an animal with six distinct testes, but also, more dramatically, includes true hermaphrodites-- animals with both ovaries and testes. This might include an ovary one side, a testes on another, or two testes followed by two ovaries, or a mix of three testes and three ovaries all mixed up together.
CURWOOD: How do the amounts of atrazine that you used in your study compare with the amounts of atrazine that you find in Americas waterways?
HAYES: I think thats whats most shocking is we find effects starting at point one part per billion. And whats shocking is that point one part per billion is incredibly low. Atrazine can be found in rainwater in Iowa-- its been reported at 40 parts per billion. Its allowed in drinking water at three parts per billion. It can come off of cornfields as high as parts per million in the spring. So its an incredibly low dose, relative to how much atrazine is present in the environment.
CURWOOD: Well, wait a second. If atrazine is so prevalent, Professor, how can you conduct an experiment? How do you find unexposed frogs to compare with?
HAYES: [Laughs.] You know, thats one of the problems. The animals that were working with in the laboratory, we use ultra-pure filtered water. So we know that the water, which weve also had tested in the lab, is atrazine-free. When we go into the field it does generate problems because theres virtually no atrazine-free environment, although we can find localities that have atrazine levels below the level where we see effects.
CURWOOD: Professor Hayes, tell us, what exactly did you find in terms of a frogs ability to produce offspring, given your concerns about atrazine?
HAYES: We have shown that in reproductively mature males, that atrazine eliminates testosterone. Were now examining whether or not the animals will recover once theyre not exposed to atrazine. Were also examining effects of, or the ability of, atrazine-treated males to fertilize and reproduce, but those data arent published yet.
CURWOOD: What kind of message does your research tell folks who are concerned about human health? If atrazine causes frogs to have lower testosterone levels, what kind of effects might it have on human testosterone production?
HAYES: You know, I want to say first, Im not a human biologist or a mammalian biologist. I do know the mechanism is there. I mean, we make testosterone and estrogen the same way frogs do. My opinion is that in a whole organism, in a whole human, that theres not enough atrazine would not likely accumulate to cause this problem because its not that soluble. If you drink atrazine, your kidneys filter it and you urinate it out.
What I dont know, and what I would be concerned about, is how a fetus, which is effectively an aquatic organism, would respond to a high atrazine load. Perhaps people should focus on farm workers who are exposed to high levels of atrazine. And in particular, pregnant women who might be exposed to high levels of atrazine through occupation or just through the area that they live in.
CUWOOD: The U.S. Environmental Protection Agency has been working on a reassessment of the dangers of atrazine for some time now, and I guess theyre looking at as much science as they can find on the herbicide. Perhaps theyll change regulations. What involvement have you had with this reassessment?
HAYES: I know that my published data have been available and weve also made available any other data that weve had. Weve been very open, and I have been contacted by the EPA. So, you know, what impact itll have, I dont know, but I know that its being taken into account as they make the assessment.
CURWOOD: As you stand back and look at your work, whats the significance of this paper that youve just studied in the broad scheme of things?
HAYES: I think that the fact that these effects occur at such low doses, I think what its telling us is that we need to take a step back and look at how we evaluate safety. The animals, they dont have cancer, they arent dying. If you look at them from the outside they look normal. Its not until you get to the histological, to the microscopic analysis of the gonads that you realize that theyre not normal. And I think that of course, being able to produce crops and food in order to feed a growing human population is important, but also I think we have to take a close look at how that might have an impact on the environment.
CURWOOD: Tyrone Hayes is a biologist at U.C. Berkley. Thanks for joining us.
HAYES: Thank you very much for having me.
[MUSIC: Freezepop, "Freezepop Forever," FOREVER (Archenemy – 2000)]
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