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PRI's Environmental News Magazine

Deformed Frog Detectives

Air Date: Week of October 15, 1999

Deformed frogs have been appearing around the country, particularly in the Midwest, and scientists have speculated on a variety of causes: from chemicals in the environment, to ultraviolet radiation, to parasitic flatworms. Now, new research points to a mix of chemicals in the water as the culprit. Janet Raloff (RAL-off), senior editor of Science News and Living On Earth’s science correspondent, speaks with Steve Curwood about the latest findings.

Transcript

CURWOOD: For years, strangely-deformed frogs have been appearing in wetlands around the nation, particularly Minnesota and Vermont. Scientists have blamed the deformities on everything from chemicals in the environment, to ultra-violet radiation, to parasitic flatworms. But, they haven't been able to duplicate the exact same deformities in the lab -- until now. Recently, a group of government and private researchers was able to replicate the frog deformities and provide a major clue for what may be causing them. Janet Raloff, senior editor at Science News and Living on Earth's science correspondent, explains that, at least in some cases, a mixture of synthetic chemicals appears to be the culprit.

RALOFF: They find that a lot of chemicals that are in water supplies throughout the upper Midwest seem to work together to disrupt the production of thyroid hormone in developing amphibians. And this leads to a whole host of deformities in these frogs. These chemicals are ones that are pesticides, some of them are industrial pollutants, and some of them are just the chemicals that naturally occur in even pristine water supplies.

CURWOOD: Thyroid, that's intriguing. Isn't that related to neurological functioning, as well as pure thyroid functioning?

RALOFF: It's related to almost everything in development. That's everything from the development of the spine and all kinds of tissues to nerves and neurological development in people. It's related to things like learning and the ability to think, reason. In fact, it's actually related to IQ.

CURWOOD: Now, how did they figure this out? What was the new twist in research that gave them these answers?

RALOFF: Well, earlier work by this group, and this group is a pretty broad-ranging group -- and they'd noticed that if you incubated embryonic frogs in water from these areas, they developed with all kinds of deformities. So it looked like there was something in the water. The question was what? They then took this water into the lab in a test system, and started isolating various components of that water to see if they could still create the same kinds of deformities they saw in the field. And they could. And they kept sort of fractionating out what aspects of it seemed to do it. And it turns out that almost every lake they looked at was actually a chemical soup. It wasn't like it was contaminated with this pesticide or that pesticide. It would more likely have five, ten, even twenty different pesticides and other industrial pollutants in it. And then trying to find out whether it was one chemical in the soup or actually the mix, the whole recipe, that was leaning to the particular kinds of deformities they were seeing in the field. And they now think that's what it is.

CURWOOD: So, no wonder we can't really figure out what the effects of some of these chemicals are. It's very complicated. They have all these complicated interactions, and if you just test for one chemical at a time you might not ever find a reaction, is that right?

RALOFF: That's right, Steve. They know that some of these chemicals alone can cause some of the kinds of problems that are there, but they appear to be additive in many cases. And the other thing is, particularly it's interesting if the thyroid hormone is affected. This plays such a critical role in every phase of development in these amphibians, and in fact in all mammals, that if it's there being sort of screwed up from a very early age, you can get all kinds of major changes, including in the skin. The skin is really dependent on thyroid hormones. And so, in this case, they are finding that these frogs have thinner skin than usual and less pigment. That could render them more vulnerable to any kinds of other stressors, such as exposure to ultraviolet light, or even to other chemicals that may make their skin more permeable so that more chemicals can get in easily.

CURWOOD: Why are researchers so worried about frogs?

RALOFF: Frogs are a sentinel species. I mean, these people, actually, that I've talked to are very concerned about frogs because they're frogs. But when you push them, they're also very concerned about what they represent for the environment. They are a particularly vulnerable species, so they're going to be the first ones to feel the effects of pollutants in the water. And their concern is that if these frogs are going, there may be a host of other species that are also poised to feel the toxic effects, including humans.

CURWOOD: So, what does all this research mean for us humans?

RALOFF: Well, nobody quite knows. But there is some suspicion that if it's deforming the development of these amphibians, it may also play a role in the development of humans if they were exposed early on. So there is a study actually now underway in Minnesota that will be looking at whether rates of birth defects are higher in the areas where deformities are also high.

CURWOOD: Janet Raloff is senior editor at Science News and Living on Earth's science correspondent. Thank you, Janet.

RALOFF: Thank you, Steve.

 

 

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