Renowned biologist Tyrone Hayes, Ph.D., delivers lecture at Holy Names University (HNU) on the dangers of the herbicide atrazine

Tyrone Hayes, PhD, professor of integrative biology at UC Berkeley, visited HNU on April 22 to deliver an Earth Day lecture entitled “From Silent Spring to Silent Night: A Tale of Toads and Men,” regarding the dangerous effects of the herbicide atrazine on animals, humans, and the environment.

Even as a child, Hayes was fascinated with amphibians. “I want to tell you a story today that starts with a little boy who likes frogs,” he said. He explained that some of his earliest memories are of exploring the forest behind his grandmother’s house, chasing frogs, toads, snakes, and birds. He became interested, even at a young age, in how environmental factors can affect amphibian development.

Hayes went to college at Harvard University, where he majored in biology. As a graduate student, he traveled to Africa as part of a trip organized by National Geographic. While in Africa, Hayes was introduced to a frog species, Hyperolius argus, whose male and female members look drastically different—males are bright green and females are red-brown with spots. Hayes and his colleagues brought some of the frogs back to their lab and found that both sexes of the species start off bright green, and the females change color when they reach sexual maturity. Hayes hypothesized that estrogen was involved in the frogs’ color change and he and his colleagues did simple experiments to test this hypothesis. What they found was that, when they dipped the frogs in a testosterone solution, nothing happened, but when they dipped the frogs in an estrogen solution, they changed color.

This led to Hayes’s creation of the Hyperolius argus endocrine screen—a test that uses the frog’s color-changing reaction to estrogen and estrogen-mimicking chemicals—and to his research that showed that, of the dozens of compounds that he and his colleagues screened, every one that made the frogs change color was also known to promote breast cancer. The endocrine screen was also an effective test of estrogen blockers; compounds such as tamoxifen (which is used to treat breast cancer) would prevent the frogs from changing color, and so Hayes was able to use the screen to test chemicals that might be effective in the treatment of breast cancer.

After the development of the endocrine screen, Hayes was contacted by Novartis, a pharmaceutical and chemical company, and was asked to test the herbicide atrazine to determine whether it was an endocrine disruptor. Atrazine is a weed-killer and has been used primarily on corn crops. Atrazine has been in use in the U.S. since 1958 and American agriculture applies approximately 80 million pounds of the herbicide to crops every year. It was banned in the European Union (EU) in 2004 due to its persistent contamination of EU groundwater.

Novartis asked Hayes to look at atrazine’s effects on the African clawed frog. The frog is used within developmental biology studies for a number of reasons, one of which is that the frog reacts to the human pregnancy hormone HCG. “This illustrates the similarity between amphibian hormones and human hormones, or just hormones in general,” Hayes said. “The estrogens that will promote breast cancer in you are exactly the same that will make my frog [Hyperolius argus] change color. The human pregnancy hormone that’s responsible for all of you and that will be responsible for all of your kids is so similar to the African clawed frog’s hormones, it will make this frog lay eggs. So as I tell you what atrazine does to the hormones of this frog, you should be thinking, ‘Well, what might atrazine do to me if we’re so similar?’”

Hayes and his research team discovered that if tadpoles are exposed to atrazine during their development, their voice boxes or larynxes do not work. This implied that atrazine was affecting the testosterone levels in the frogs and perhaps affecting the development of their gonads. Through their research, Hayes and his team came to believe that atrazine activates an enzyme called aromatase, which can convert testosterone to estrogen—this meant that male frogs were simultaneously demasculinized (the aromatase used up existing testosterone) and feminized (the frogs began producing estrogen).

Hayes and his team published a paper about this research, “Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses,” in Proceedings of the National Academy of Sciences in 2002. “The company [Novartis] didn’t like the data, and they certainly didn’t like the title,” Hayes said.

In subsequent experiments, Hayes also discovered that 10 percent of male frogs exposed to atrazine become fully female; the 90 percent of male frogs that do not become female are not able to compete with healthy males nor are they able to successfully copulate with females in isolation. Affected males also frequently develop eggs within the tissue of their testes.

Hayes has shared much of his data regarding atrazine with the Environmental Protection Agency (EPA), but the EPA stated that they did not view the effects as being adverse enough to trigger reevaluation and regulation of atrazine.

Near the end of his presentation, Hayes spoke about a new study that he is conducting that has not yet been published as a paper. He and his team have analyzed tadpoles collected from various points in the Salinas River. What they have found is that the tadpoles taken from upriver, near Santa Margarita, show normal development, whereas tadpoles taken from areas of the river further north—closer to the heavy agriculture and attendant runoff in the Salinas Valley—show retarded development and growth, high mortality rates, and evidence of immunosuppression.

Hayes quoted a passage from John Steinbeck’s East of Eden, which was published in 1952—“Six years before the use of atrazine” as Hayes put it, to illustrate the extent of the damage done to the environment and wildlife in Salinas Valley:

“Salinas was surrounded and penetrated with swamps, with tule-filled ponds, and every pond spawned thousands of frogs. With the evening, the air was so full of their song that it was a kind of roaring silence. It was a veil, a background, and its sudden disappearance, as after a clap of thunder, was a shocking thing. It is possible that if in the night the frog song should have stopped, everyone in Salinas would have awakened, feeling there was a great noise. In their millions the frog songs seemed to have a beat and a cadence, and perhaps it is the ears’ function to do this just as it is the eyes’ business to make stars twinkle.”

Hayes then played a field recording taken from the environs of present-day Salinas. It was silent. “I haven’t heard a single native frog call in the six years that I’ve been working there,” Hayes said. “I think this [Steinbeck’s quote] is better than a piece of scientific literature. This is not a scientist in 1952, before we started using all the pesticides, who wrote down how many frogs there were. It’s better because a literary artist recognized the importance of amphibians in that habitat—so much so that he wrote about it for half a page in a book that had nothing to do with frogs. And now that’s gone.”

For those who are interested in learning more about atrazine and its effects, Hayes maintains a website with information about other scientific studies regarding the herbicide.

Article for Holy Names University’s website and email newsletter.