Recent studies suggest that more might be learned in the wild than in the lab about how chemicals can scramble hormone signals in animals. Researchers typically look at development and physiological changes in lab animals to set safety standards for human exposure to these chemicals. But a growing number of researchers say these methods ignore the subtle consequences these chemicals have on animal behavior. Host Steve Curwood talks with Prof. Ethan Clotfelter, who teaches biology at Amherst College, about the implications of the studies, one of which he co-authored.
CURWOOD: From the Jennifer and Ted Stanley studios in Somerville, Massachusetts, this is Living on Earth. I’m Steve Curwood.
For years, research has linked pollution from industrial and agricultural chemicals to physical abnormalities in animals. The chemicals are thought to scramble the ability to send and process hormones and other neuro-chemical signals that control growth and physiology. For example, alligators living in a Florida lake contaminated with pesticides have been found to have grossly malformed sex organs.
Now, there’s evidence linking these so-called endocrine disrupting chemicals to increased abnormalities in animal behavior. These phenomena are harder to observe than physical deformities, but they could be warning signs of population crashes for many species. Ethan Clotfelter of Amherst College co-authored an article in the journal Animal Behavior that details what scientists have so far been able to piece together about how chemical pollutants can change the way animals act.
Professor Clotfelter, just what are you seeing?
CLOTFELTER: Oh, there’s a whole list of kinds of behavioral changes that we’re seeing. Everything from really gross anatomical impairments – animals that can’t really stand up straight or can’t move in a coordinated way to much more complex social interactions. Courtship behaviors is a common one, but even things like being able to adequately construct a nest, in the case of birds, or really complicated cognitive functions. So in primates and rats, being able to solve a maze or solve some sort of a cognitive task really seems to be impaired by these chemicals. So really it’s a whole range of kinds of behaviors. Pretty much everything you can think of that animals do in some way has been affected.
CURWOOD: How might long-term exposure to these substances affect entire populations of animals, do you think?
CLOTFELTER: Well, the case of DDT in the 1970s is sort of the classic one that we all keep in the back of our minds as we’re thinking about these things. Where birds such as osprey, bald eagles and such began to experience massive population declines because of exposure to DDT. We certainly are mindful that long-term – even subtle changes in behavior – might have similar large-scale effects again, ultimately resulting in population declines or perhaps even extinctions in small areas.
CURWOOD: Now, as you studied these groups of animals who’ve been exposed to chemicals that disrupt hormone functions, what do you think the implications are for us as humans – human health from all of this?
CLOTFELTER: Well, I think it’s a pretty significant question, and I think it’s one that deserves a lot more attention. There are several very intriguing and very scary studies that have linked exposure to possible chemicals to changes in the way that children play. There was a really frightening study of schoolchildren in parts of Mexico where one population was heavily exposed to pesticides and the other wasn’t. And they found pretty marked differences in everything from just how coordinated these children were, to their ability to draw specific items, to how well they could pay attention. So certainly a lot of behavioral problems in children could conceivably be linked to exposure to these chemicals.
CURWOOD: Typically when you look at chemicals being dangerous, being toxic, the more of something is usually considered the more toxic. But in this area of research it seems that you and your colleagues are looking at situations where a low dose of some chemical might in fact be worse than a higher dose. How true is that? And how do you explain that?
CLOTFELTER: Well, I think how true it is is really a very hard question to answer, because there’s certainly some people who have done a significant amount of work showing that this phenomena of these non-linear types of responses are quite common. And some estimates may be as high as 40 percent of the chemicals tested actually have shown higher effects at small doses than at intermediate doses. So there certainly are some suggestions that it’s a fairly widespread phenomenon.
But a lot of people have resisted that idea. Certainly because the field of toxicology is largely based on this assumption that, you know, that the dose makes the poison. And so as you add more, then you have more of an effect. If a substantial number of chemicals in a substantial number of animals, including humans, have this sort of non-linear effect, then I think we have a much, much greater problem because all of our regulatory decisions from agencies like the EPA are based on this assumption that lower is better.
And so there have been a few studies by my colleagues that have shown that, at what are considered environmentally-acceptable doses of chemicals, that you see real behavioral and physiological effects in animals. So certainly that opens up a whole slew of questions about whether or not we’ve been missing all this, and that at these low doses there’s actually worse things that could happen.
CURWOOD: Ethan Clotfelter teaches biology at Amherst College. Thank you so much for taking this time with us today.
CLOTFELTER: Okay great, thanks for having me.
[MUSIC: Jon Anderson “Concerto Uno” EARTH MOTHER EARTH (Ellipsis Arts –1997)]
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