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Biologist discusses impact of pesticide on African claw frog

<rleton’s students, faculty, and staff were welcomed into the Chapel to hear Tyrone Hayes’ talk, “From Silent Spring to Silent Night: A Tale of Toads and Men” on Atrazine, a pesticide used on cornfields, like those in Minnesota, and its negative effects on development in species from amphibians to humans.

Tyrone Hayes is a biologist and herpetologist who graduated from Harvard in 1989 and who received his Ph.D. from the University of California, Berkeley, in the Department of Integrative Biology. He began teaching at Berkley in 1994, and received tenure in 1998.

Hayes’ most recent research, which he presented at Convo, involved the use of African claw frogs to “assess the impact that Atrazine might have on the environment…we exposed tadpoles to the pesticide and then watched their development.”

Hayes found that “exposure to Atrazine turns on aromatase, which converts testosterone into estrogen. In males this decrease in testosterone levels caused male frogs to have less testosterone compared to females and a lower sperm [count]…fertility in Atrazine treated males is 15%; they become incapable of fertilizing eggs.”

As Hayes put it, the males have become “chemically castrated.” Furthermore, of the “80% of males [that became] chemically castrated, 10-20% of the males mated as if they were females…they become functionally female and lay eggs.”

Hayes conducted similar studies on the Northern Leopard Frog, to conclude that the results were not restricted to the African Claw Frog species. Hayes also did observations in the field, in areas affected by Atrazine use.

“Atrazine is being applied by 200 million times what we are using in the lab…it is in the runoff, temporary pool, permanent, and precipitation water…half a million pounds of Atrazine come down in our rain water every year.”
Hayes’ results from the lab were confirmed by his observations in the field. “Everywhere Atrazine was used we found hermaphrodites [in species that are not normally hermaphroditic..[Further] there are only hermaphrodites when… Atrazine [is] used.”

Next, Hayes examined the use of Atrazine in combination with many other pesticides used in the fields. He found a delayed metamorphosis when tadpoles were introduced into an environment with Atrazine and other chemicals. In other words, tadpoles are less likely to mature before their environment, e.g. drainage from the fields dries up.

“Frogs that take longer to metamorphosize are more likely to be smaller and thus more likely to be preyed upon and less likely to find food themselves.”

Hayes also found that none of the other chemicals were the direct cause of hermaphrodites and that in addition to this effect, use of Atrazine also caused a form of Meningitis to develop, an immune suppression.

Hayes concluded with the fact that the presence of pesticides caused stress hormones to increase in the specimen’s system, leading to immunosuppressant, decreased growth, retarded development, and inhibited metamorphosis.

But Hayes’ findings go far beyond tadpoles. Similar results have been found in rats, fish, reptiles, birds, and mammals, including humans. “[Workers] that apply Atrazine have low sperm count and cannot get their wives pregnant. No work has been published on this because [most of the workers are] Mexican-Americans. This is a racial-political issue [as well],” said Hayes.

It has also been linked to an increase in breast cancer. Since Atrazine “turns on” proteins that make estrogen, and estrogen is a receptor for cancer growth cells, Atrazine encourages cancerous cells to grow.

“We will be seeing the effects of Atrazine two generations from now,” said Hayes.

Hayes has received numerous awards including the Distinguished Teaching Award from Berkley, the Distinguished Mentor Award from Berkley, the Jennifer Altman Award for Integrity in Science from the Jennifer Altman Foundation, the Rachel Carson Memorial Award from the Pesticide Action Network, the National Geographic Emerging Explorer Award from the National Geographic Society, the President’s Citations Award from the American Institute of Biological Science. January 24, 2005 was proclaimed Dr. Tyrone Hayes Day by the Mayor of Minneapolis, Minnesota.

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