Tyrone Hayes: How Do Common Chemicals Affect Frogs, Rats — And Maybe Us? Biologist Tyrone Hayes talks about the concerning effects of the herbicide atrazine, which is part of a group of chemicals that are found in everyday food and household products.

Tyrone Hayes: How Do Common Chemicals Affect Frogs, Rats — And Maybe Us?

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But first, the worst nuclear accident in history is one thing. But what about the toxins we all encounter every single day?

TYRONE HAYES: I mean, we're exposed to chemicals all the time.

RAZ: They're all around us?

HAYES: Yeah.

RAZ: By the way, this is Dr. Tyrone Hayes.

HAYES: Oh, Tyrone's fine.

RAZ: OK, great.

HAYES: (Laughter) As, you know, I say, nobody has to call me doctor unless you're a cop pulling me over for no reason.



RAZ: Tyrone is a biologist at the University of California at Berkeley.

HAYES: And my research focuses on endocrine-disrupting chemicals in the environment.

RAZ: Endocrine-disrupting chemicals describes a whole group of chemicals that mimic the body's natural hormones like estrogen or testosterone. And it turns out, those chemicals are in all kinds of stuff we use every day - in food, food packaging, cleaning products, baby products, toys, even in water.

HAYES: I mean, one of the most troubling things is most of the chemicals we use we know very, very little about.

RAZ: But we knew even less about them 20 years ago. That was when Tyrone began studying one particular chemical called atrazine.

And real quick, what is atrazine used for?

HAYES: It's an herbicide. For example, it's mostly used on corn in this country. So you would spray atrazine all over the soil so that nothing grows up. And when you plant the corn, then there's nothing that - there's no weeds to compete with the corn. It's also used in forestry. It's also used on golf courses. And in some states, it can be used on your lawn.

RAZ: So how are humans exposed to atrazine?

HAYES: Atrazine exposure for humans is mostly through the drinking water.

RAZ: Tyrone did some of the earliest studies on atrazine and whether it was the kind of chemical that could throw natural hormones out of whack. And the way he did this was by studying frogs.

HAYES: Amphibians are of particular interest because they have to deal with the aquatic environment. They have to deal with the terrestrial environment. They through these amazing transitions where they're completely vulnerable to the environment. They can't regulate their temperature. You know, when they're developing as embryos, they have no placenta, no eggshells to protect them from the environment.

RAZ: So Tyrone took a bunch of frogs and exposed them to atrazine. And eventually, he came up with some pretty surprising results, which he described on the TED stage.


HAYES: We were a bit surprised when we found out that when we exposed frogs to very low levels of atrazine - 0.1 parts per billion - that it produced animals that look like this. These are the dissected gonads of an animal that has two testis, two ovaries, another large testis, more ovaries, which is not normal...


HAYES: ...Even for amphibians. And some cases in other species like the North American leopard frog, we show that males exposed to atrazine grew eggs in their testis. And you can see these large yoked up eggs bursting through the surface of this male's testis. We show that some of these animals when they're exposed to atrazine, some of the males grow up and completely become females. So these are actually two brothers consummating a relationship. And not only do these genetic males mate with other males, they actually have the capacity to lay eggs even though they're genetic males.

What we proposed and what we've now generated support for is that what atrazine is doing is wreaking havoc, causing a hormone imbalance. Normal testis should make testosterone, the male hormone. But what atrazine does is it turns on an enzyme - the machinery if you will - aromatase, that converts testosterone into estrogen. And as a result, these exposed males lose their testosterone - they're chemically castrated - and they're subsequently feminized because now they're making the female hormone.

RAZ: That's unbelievable. And were you just, like, bathing these frogs in atrazine, I mean, just exposing them to crazy levels of it?

HAYES: Oh, no, it's not crazy levels. We were exposing the levels that you can find in rainwater. So it's a ubiquitous...

RAZ: (Laughter) Wow.

HAYES: ...Contaminant. It's the most common contaminant of drinking water and most common contaminant of groundwater.

RAZ: So I'm assuming after this study that you did came out, it was banned in the U.S.?

HAYES: (Laughter) No, it wasn't banned in the U.S.

RAZ: This is not banned in the U.S? (Laughter).

HAYES: No. The U.S. EPA was - only now has the EPA come out with a report saying that atrazine is a threat to wildlife. And they have another report coming out where they review its effects on humans. And in California under Prop 65, atrazine has just been labeled a reproductive toxin. So the European Union denied regulatory approval for atrazine all the way back in 2002.

RAZ: So, yeah, as a result of Tyrone's research, the EU banned atrazine. In the U.S., a lot of scientists are still split on whether atrazine is safe, whether it's as dangerous as Tyrone claims. And full disclosure - some of his studies have been hard to replicate. But if he's right, what can it mean for humans? Tyrone Hayes returns in just a minute. Today on the show - Toxic. I'm Guy Raz and you're listening to the TED Radio Hour from NPR.

RAZ: It's the TED Radio Hour from NPR. I'm Guy Raz. And on the show today - Toxic. And we were just hearing from UC Berkeley biologist Tyrone Hayes about his research on the herbicide atrazine. And he found that male frogs when exposed to atrazine - they grew ovaries and started to produce eggs...

HAYES: Which was very strange and abnormal.

RAZ: Now the obvious question is, what does this mean for humans, right? Well, frogs are different than humans in many ways. First of all, they're especially vulnerable before they're born because they hatch from eggs - and soft ones without any real shell. And humans, like most mammals in utero, are nourished and protected by the placenta, which helps remove waste and toxins from the fetus.


HAYES: But it turns out that this ancient structure that separates us from other animals - the placenta - cannot evolve or adapt fast enough because of the rate that we're generating new chemicals that it's never seen before.

RAZ: Here's Tyrone again on the TED stage.


HAYES: The evidence of that is that studies in rats - again, with atrazine - show that the hormone imbalance that atrazine generates causes abortion. Because maintaining a pregnancy is dependent on hormones. Of those that don't abort, atrazine causes impaired memory or breast development in the exposed daughters in utero, so that their breasts don't develop properly. And as a result when those rats grow up, their pups experience retarded growth and development because they can't make enough milk to nourish their pups. Given the life of many of these chemicals - years, dozens of years - that means that we right now are affecting the health of our grandchildren's grandchildren by things that we're putting into the environment today.

And this is not just philosophical. It's already known that chemicals like diethylstilbestrol and estrogen, PCBs, DDT cross the placenta and effectively determine the likelihood of developing breast cancer and obesity and diabetes already when the baby's in the womb. In addition to that, after the baby's born, our other unique invention as mammals is that we nourish our offspring after they're born. We already know that chemicals like DDT and DES and atrazine can also pass over into milk, again affecting our babies even after they're born.

RAZ: So how do these chemicals get into milk in the first place? Well, they're everywhere - flame retardants in furniture, dioxin in meat products, BPA in food packaging. And, yeah, those chemicals do affect animals. But it's still hard to say what effect they can have on us.

HAYES: You can't do a controlled experiment in humans. You can only say, well, you're exposed to this and you have, you know, this symptom or this condition that's associated with that chemical.

RAZ: In Kentucky, for example, women who used well water that contained atrazine were more likely to develop breast cancer. Now, that doesn't mean atrazine causes the cancer, but it does mean it can be linked.

HAYES: So what we see in rats, for example, is that atrazine increases estrogen. It decreases testosterone and increases estrogen. And so if you get breast cancer - which is estrogen-dependent - estrogen drives the cancer so to speak - atrazine itself may not be causing the cancer. But by causing this hormone imbalance, it creates a physiological environment that's conducive to breast cancer, that promotes breast cancer.

RAZ: So, again, this is controversial. And it's hard to nail down the exact toxicity of chemicals like atrazine. But a growing number of scientists, including Tyrone Hayes, say that obesity, diabetes, breast cancer, prostate cancer and even some birth defects can be linked to exposure to these kinds of chemicals.

HAYES: And atrazine is associated with at least three birth defects in humans. Gastroschisis, where the intestine's on the outside of the body. Choanal atresia, where there's a hole in the baby's face. And malformed male genitals. So when you're exposed to a chemical that decreases testosterone and increases estrogen, in every animal that has been studied you get a baby that looks like it has too little testosterone and too much estrogen.

RAZ: I feel like I need to move into a bubble and just, you know, just, like, that's it. Like, how do we deal with this? What can we do about it? How do we protect ourselves?

HAYES: I think being informed. I think making informed decisions about things that you purchase. I think being politically involved. And we can make choices. And as the phrase I've heard is vote with our dollars and, you know, decide that I'm going to buy this product but not this product. In terms of who we elect, in terms of what the environmental policy of our local government representatives are. And I think we need to refocus our efforts.

RAZ: Tyrone Hayes is a biologist at UC Berkeley. You can see his entire talk which he did with filmmaker Penelope Jagessar Chaffer at ted.com.

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