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Excerpts from "Wreaking Havoc with Life: Minute atrazine levels lead to hermaphroditic frogs and cancer"
by Tyrone Hayes, PH.D.

I was a consultant for Novartis and Syngenta, the makers of atrazine. And I learned a lot.

For the past five years, I worked on the widely used herbicide atrazine. It has been used for 40 years, exposing us for many generations. We use more than 76 million pounds annually in the U.S. Atrazine is one of the top contaminants of ground and surface waters. In the U.S. and throughout the world (used in more than 80 countries), it is the largest selling chemical manufactured by the largest chemical company in the world. It is used on our No. 1 crop in the U.S.—corn. Although just reregistered in the U.S., the European Union (EU) banned it. In fact, it has never been used in Switzerland, which is where Syngenta is based.


What atrazine does is the following. Normally, if you are male, you should make testosterone. It is testosterone in humans that controls masculine development like a deep voice, beard growth, and sperm production. Atrazine turns on the enzyme aromatase. Aromatase is responsible for converting androgen (a male hormone, such as testosterone) to estrogen.

So amphibians exposed to atrazine suffer two consequences. First, they are demasculanized or chemically castrated because they are losing the androgen. As a result, male frogs' voice boxes do not develop. Secondly, they are feminized because they are now making the female hormone, estrogen or estrodial.

The consequences: An African frog exposed to 0.1 parts per billion (ppb) atrazine developed two testes, two ovaries, followed by another testis and two more ovaries. This is not a normal animal. The manufacturer argues that there is good reason and we are just studying something that naturally occurs. You should not have seven gonads and you should certainly not have a mixture of testes and ovaries in your body … even if you are a frog. They are pretty much like humans in that regard.

Let's take a laboratory animal; a normal, healthy North American frog. The same type of effect occurs. Under a microscope, a male frog has testes with testicle tubules. The female has ovaries, with eggs or oocytes that have accumulated in the ovaries. These are normal animals. A North American frog that has been exposed to 0.1 ppb atrazine exhibits two testes, so this frog is not a true hermaphrodite. But, the frog has developed eggs in its testes and the eggs are bursting through the surface of that testis. That is not normal. These two laboratory studies are very well controlled so that we can look very specifically at the impact of atrazine.


What I want to do is give you some perspective. I keep referring to 0.1 ppb or 0.1 micrograms per liter. Is this a big or little number? Imagine a grain of salt. Now divide the weight of that gram of salt by 1,000. That is how much atrazine we are adding to the aquaria to produce the kind of effects being described. One thousandth of a grain of salt. Almost nothing.

With this visual, is this what is called "ecologically relevant doses?" Atrazine formulations contain 2.9 to 29 parts per million for use on farms. So that is 290 million times what we are using in the laboratory.


I used to think that there was a connection between environmental health and public health. I no longer think that. They are one and the same. The people that we have to worry about even more than the "every day people (or non-farm workers)," are the farm workers who are exposed to high levels all the time.

This is relevant to humans. People often say, "It is just frogs, so who cares?" Well it doesn't matter whether you are a frog, a dog, a bat, a cat, or a human. The compounds and the genes and the hormones that we are talking about are the same.

I spend a lot of time in hotel rooms now where they deliver USA Today. On the front page the other day was an article about a brand new cancer drug. Forty thousand women per year die of cancer, and they have a new drug that is 92 percent effective at blocking the return of breast cancer. When a woman has breast cancer, aromatase converts testosterone to estradiol and estradiol binds to a receptor and causes breast cancer cells to divide. The typical treatment is tamoxifen, which blocks the estrogen receptor. This new breast cancer drug, called exemestane, reduces aromatase, so it reduces the available estrogen to begin with. Now this is crazy, because what atrazine does, and one million people are exposed per day, is just the opposite of our new breast cancer treatment. We know that in humans, it turns on aromatase, promotes estrogen production, and breast cancer. So chemical companies sell you both the cause and the antidote.


I have to make one more point. People always ask, why frogs? Well, what happens is the following: These tadpoles have the ability to metabolize the pesticide and urinate it out, but they live and drink and reabsorb their urine all the time. We can make this analogy with another aquatic organism, that can also metabolize the pesticides, but they live and drink and reabsorb their urine all of the time—a human fetus.

Recently, I heard someone read a passage that I think expresses this better than I could. This passage is about a woman who just has had amniocentesis: "Before it is baby pee, amniotic fluid is water. I drink water and it becomes blood plasma, which suffuses through the amniotic sac and surrounds the baby who also drinks it…. Whatever is inside my womb and whatever is in the world's water is here in my hands." This is from the book Having Faith, by Sandra Steingraber.

These excerpts are from a talk that Tyrone Hayes, Ph.D., a tenured professor of integrative biology, specializing in the developmental endocrinology of amphibians, at the University of California (U.C.), Berkeley, gave to the 22nd National Pesticide Forum, United for Change: New Approaches to Pesticide and Environmental Health, April 2-4, 2004 at UC Berkeley. The complete article was published in Pesticides and You, Vol. 24, No. 2, 2004.

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