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

High Dose/Low Dose

Air Date: Week of

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Living On Earth’s Steve Curwood speaks with toxicology professor Edward Calabrese about a paradigm shift that may be brewing in the toxicological field. The concept of hormesis may explain how our bodies react to very small amounts of toxins.


CURWOOD: For decades, toxicologists assumed that if high exposure to a chemical is bad for you, then exposure to a small amount will be bad for you too, but maybe not as bad. But today, some scientists think the situation is more complicated than that. They believe small doses might actually have the opposite effect of large doses of the same toxin. Dr. Edward Calabrese is a professor of Environmental Health Sciences at the University of Massachusetts at Amherst. He has just published a commentary in the journal Nature, about the need for a toxicological paradigm shift. He joins me now.

Dr. Calabrese, you’ve examined many studies that support the idea of hormesis. Just what is hormesis?

CALABRESE: Hormesis is a dose response phenomenon in which, essentially, if it’s talking about pollutants here, we could anticipate having a beneficial effect at a low dose, followed by the traditional adverse effect at a higher dose.

CURWOOD: So, hormesis implies that while a lot of some things is bad for you, a little might be good. The flip question--what evidence is there that small amounts might be toxic, and quite large amounts might be good for you?

CALABRESE: Usually, you don’t see that. I’ve seen situations where high doses could be bad, and very low doses could also be harmful. For example, with the prostate, where you could have a high dose cause a shrinkage of the prostate, whereas a low dose might cause an increase. And you’d be finding that any change from normal could be harmful.

CURWOOD: What very toxic chemicals could actually be perceived as good for us in small doses?

CALABRESE: I’d have to say that, probably, just about every one that could come to your lips. From the toxic heavy metals, including arsenic and cadmium, lead, mercury, these things that--

CURWOOD: Dioxin?

CALABRESE: Dioxin would be considered one of the most toxic chemicals known to mankind. The classic study that the U.S. EPA uses to derive the risk assessment numbers for us actually demonstrated that low levels of dioxin in the diet of the experimental rats actually significantly reduced tumors from, essentially, all the monitored sites in male and female rat bodies, only increasing the tumor incidence at the higher doses.

CURWOOD: If hormesis suggests that small, perhaps very small, doses of toxic chemicals might well be good for you, why doesn’t industry wildly promote this idea?

CALABRESE: Industry doesn’t know quite what to do with this because in the last 15 years or so, even though there’s been some sort of rancorous interactions between the U.S. EPA and industry, I think in many ways they’ve come to their accommodations, if you know what I mean. They understand the rules of the game. They know how to conduct their studies. They know how to fit into the EPA risk assessment scheme.

And what hormesis does, is it really changes the rules for both the government and industry. And I think, in many ways, it makes people on both sides of the equation uncomfortable because it creates uncertainty.

CURWOOD: What steps will have to be taken before regulators can get their arms around this concept?

CALABRESE: Well, you know, I think that the most important thing is for them to actually give it sufficient priority to look at the data. I think once people actually do look at the publications, actually do embrace the quest for truth in the low dose zone, I think that changes will naturally follow. But what hormesis is really arguing is that the field of toxicology should redefine itself to look at the entire dose response spectrum, including the low doses that we commonly encounter in our own personal lives. And once we do begin to look at the lower doses, we find that, gee, the predictive models that the EPA and the FDA have been using are really, for the most part -- I don’t want to call them antiquated -- but they’re inadequate to address the reality of where we live, which is in, for the most part, a low dose world.

CURWOOD: Dr. Edward Calabrese is a professor of Toxicology at UMass Amherst. Thanks for taking the time to speak with us today.

CALABRESE: Thank you very much.



CURWOOD: Just a few months ago I was in the back of a Land Rover driving across the African Savannah under a crystal clear sky. As the sun was setting, we came across a solitary leopard trying to pull an antelope up into a tree. As we watched, we realized the leopard had a cub with her. Now, our trackers have told us that these animals on the game preserves regard folks in Land Rovers as part of some relatively huge, benign animal, and usually they’ll let you get close.

But this mom, with her baby and antelope dinner, was in no mood for strangers. She walked right up to our truck and glared at us. A chill ran down my spine, as I realized that we were just one swat away from her. And that would happen long before our tracker could grab the rifle on the dashboard in the Land Rover. I’ll never forget the look in the leopard’s eyes. She said, “This is my meat, my kid, I’m the boss.”

Now, Living on Earth wants to give you chance at your own African Safari. Thanks to Heritage Africa, we’re giving away a 15-day trip for two on the ultimate African safari, with visits to several of Africa’s most spectacular game preserves such as Kruger, where I saw this leopard, and the Serengeti. For more details about how to win this 15-day African safari, just go to our website, loe.org. That’s www.loe.org, for the trip of a lifetime.




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