Mayo docs hear from researcher on suspected atrazine, cancer links

Tyrone Hayes
California researcher Tyrone Hayes, who claims links between deformities found in frogs in Minnesota and the herbicide atrazine, spoke with doctors at the Mayo Clinic Wednesday about potential links between cancer and atrazine.
MPR Photo/Sea Stachura

The Mayo Grand Rounds is usually where new medical research gets discussed each week. But pediatric radiologist Dr. Alan Hoffman says he thought his colleagues needed to hear from amphibian endocrinologist Tyrone Hayes.

For years Hayes has been producing research that he claims links atrazine, made by the Swiss-firm Syngenta, to frog deformities. In recent years deformed frogs have turned up in Minnesota. Syngenta originally sponsored Hayes'research, but now it disputes his findings.

The Mayo Clinic's Hoffman says Hayes' research is courageous.

Deformed frog
This frog has deformed legs, and research conducted by a professor in California links such deformities to the use of atrazine, a common corn herbicide.
Photo courtesy of the MPCA

"He's fighting this company, this big agriculture business, about an important thing -- and he's playing fair. He's doing good science. And we know in this world when business runs up against things, they produce not such good science," said Hoffman.

But the Environmental Protection Agency and Syngenta have questioned Hayes' research, which has been published in journals such as Science.

Atrazine has been used to kill weeds on crops like corn since 1958. In Minnesota farmers apply just under two million pounds of it each year, and it can run off into streams and groundwater. Its effects on humans and animals have been disputed for years.

In Hayes' initial research, he took lab tadpoles and put atrazine in the water they lived in. Hayes says water is a tadpole's amniotic fluid. Tadpoles absorb whatever is in that fluid.

[Tyrone Hayes is] doing good science. And we know in this world when business runs up against things, they produce not such good science.

"One of the things we discovered is that atrazine chemically castrates the frog, meaning that it causes a reduction in the male hormone, testosterone, which results in things like decreased sperm count, a decrease in the voice box, controls the male's ability to attract mates," Hayes said in an interview with Minnesota Public Radio news.

But in his talk at Mayo, Hayes moved beyond frogs. He says the enzyme that atrazine activates in frogs is the same one found in humans. It converts testosterone into estrogen.

"This same enzyme, or machinery if you will, controls estrogen production in humans. And atrazine is associated in laboratory rodents with development of mammary cancer, or breast cancer, and there are epidemiological studies that associate atrazine exposure to breast cancer in humans," Hayes said in the interview.

About 40 studies on atrazine's effects on humans and animals exist. Hayes will publish a study this spring that uses human cell lines. He says the study shows atrazine interrupts the endocrine system and mutates human hormones. Those mutations, he says, are the same ones found in breast cancer.

Regional scientists are interested in what Hayes has to say. The Upper Mississippi River Conservation Committee, made up of DNR scientists from Minnesota and other states and U.S. Fish and Wildlife officials, will host Hayes at its annual conference in March. Those scientists are concerned that the growth of the ethanol industry will mean more corn and more atrazine in the environment.

The Environmental Protection Aagency says the use of atrazine is safe. The EPA's Anne Lindsay in the Office of Pesticides says the agency has looked at the studies linking atrazine and frog deformities, including Hayes,' and found them lacking.

"All of the studies we looked at, and there were 17 laboratory and field studies total, were flawed," she said.

Lindsay does acknowledge that studies have shown atrazine has caused abnormalities in the endocrine systems of lab rats.

The EPA expects to update its view of the chemical's safety sometime in 2007. Lindsay says the agency will take into account findings from a study by the National Cancer Institute. That study is looking at whether atrazine has caused any diseases in humans.

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