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Public Radio's Environmental News Magazine (follow us on Google News)

Herbicide Toxicity

Air Date: Week of

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A new study finds that very low doses of a common herbicide mixture can cause miscarriages in mice. Host Steve Curwood talks with University of Wisconsin toxicologist Warren Porter about his study.


CURWOOD: A new study published in the journal Environmental Health Perspectives has found that in laboratory animals, extremely low doses of a common herbicide mixture tend to promote miscarriages. The chemicals are found in many commercial farming and consumer lawn care products.

Joining me now is Warren Porter. He’s a zoologist and an environmental toxicologist at the University of Wisconsin in Madison, and was a principal researcher on this study. Professor Porter, welcome to Living on Earth.

PORTER: Thank you very much. Hello.

CURWOOD: Professor, why did you choose to exam this particular batch of chemicals?

PORTER: I chose to use that particular batch of chemicals because it was an extremely common herbicide being used by a very well-known lawn care company. And it was available on shelves for personal use. Our particular weed and feed mixture contains dicamba, and it contains 2,4-D, and it contains mecoprop.

CURWOOD: Walk us through the method you used in this study, if you could, please.

PORTER: Basically, we simply took it off the shelf, diluted it to the appropriate concentrations that match some of the EPA recommended levels, and went above and below that, and gave it to our mice in their drinking water so that we could get known concentrations, and let them get pregnant and have their babies. And then, we tested the babies and the moms.

CURWOOD: So, what were your results?

PORTER: We found that there were pregnancy losses up to 20%, basically losses of fetuses by miscarriage. And as we went down in dose, the lower we went, the greater the effect. We got down to 20% loss of the fetuses that were originally implanted. Twenty percent of those were lost. We don’t actually know yet how low we can go and still get effects.

CURWOOD: Now Professor, this seems really counterintuitive that the lower the dose of the herbicide, the stronger the effect, that is, more spontaneous abortions you saw in the mice that you studied. How could that be?

PORTER: We think that what’s happening here is that these lower doses are closer to the natural body hormone levels. And it’s interfering with the establishment of pregnancy or the maintenance of pregnancy.

CURWOOD: So, how does the amount that you found to have an effect compare with what we’d commonly find in our drinking water?

PORTER: Well, these levels are below what you could find in water here in this country.

CURWOOD: I think it’s fair to say that there’s rarely a straight line from an animal study to potential implications for human health. But, what about the results of this study do you find troubling in that regard?

PORTER: Well, there’s an awful lot of loss of human fetuses. Over 50% of fetuses currently conceived are lost. What really bothers me is the tremendous increase we’re seeing in childhood developmental problems, especially learning disabilities, behavior disabilities, and birth defects. All of these may be associated with environmental contaminants of various kinds, and some of them might be associated with herbicides.

CURWOOD: In this mix of chemicals that you’ve tested, one of them, 2,4-D, is a fairly common herbicide, perhaps the most common herbicide these days. The United States Environmental Protection Agency is now performing a safety review of 2,4-D and drinking water. The EPA is supposed to make a final decision on 2,4-D in the year 2004. Tell us, Professor, what’s your message to regulators if, indeed, a smaller dose seems to have a more potent effect than a larger one?

PORTER: We need to be looking in the world of the physiological realm rather than the pharmacological realm. We have been finding that at ultra low doses you really get into a completely different world instead of a toxicological, poison kind of world. You’re down into the low dose physiological ranges where we’re talking parts per trillion to parts per billion, which is where the body tends to operate.

But, you know, the question almost is-- how shall I say this? I think it needs to be rephrased. Because, you see, the focus is on 2,4-D. And, in our study, the focus was on the product that the consumer buys. Now, the reason that I make this distinction is because, when you look at 2,4-D, that chemical has been purified. And, only recently, very recently, have I found out that 2,4-D and dicamba, two of the three ingredients in this weed and feed mix are still being contaminated with dioxin. This is a very potent endocrine disrupter. And it, in fact, may have a partial role in some of the results that we have found.

CURWOOD: Warren Porter is a toxicologist and zoologist at the University of Wisconsin in Madison. Thanks for joining me today.

PORTER: Thank you. It was a pleasure.

CURWOOD: If you’d like to read an EPA Consumer Fact Sheet on the herbicide, 2,4-D, including the brand names of products that contain the chemical, you can go to our website at loe.org.

[MUSIC: Vernon Reid, "Uptown Drifter," Mistaken Identity (Sony, 1996)]



Dr. Warren Porter’s website

An EPA consumer fact sheet on 2,4-D

See the study, published in the journal, Environmental Health Perspectives


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