A powerful herbicide is a friend to farmers, but may not be a friend to frogs.

More than half the corn crops in the United States are treated with a herbicide called Atrazine. Golf courses and Christmas tree farms also get the Atrazine treatment to keep weeds under control. The chemical is used in Canada as well, though it is no longer used in the European Union.

In 1997, biologist Tyrone Hayes received funding from the maker of the chemical -- a company that would later become Syngenta -- to study its effects on the environment. He found Atrazine caused sexual abnormalities in frogs. He says Syngenta tried to stop him from publishing his findings and that it launched a campaign to discredit his research.

But Tyrone Hayes continued, looking into Atrazine as a professor of Integrative Biology at University of California, Berkeley. Documents released in a class-action law suit in 2005 suggest the company tried to side-line Professor Hayes and his work.

Tyrone Hayes was in Berkeley, California.

"Syngenta stands by the safety of atrazine. Nearly 7,000 studies have been conducted to establish the safety of atrazine during the past 50 years and the science is clear. Atrazine does not cause adverse effects to humans or environmental health at real-world exposure levels."

"Registering an active ingredient in the United States or Canada is a long and stringent process. The U.S. Environmental Protection Agency (EPA) requires more than 120 scientific studies, as well as numerous regulatory submissions. To maintain a registration, this process is repeated at regular intervals. EPA asks for public comments and evaluates the overall weight of evidence in deciding registration eligibility. This strict, transparent, science-based process provides a high degree of safety for any product on the market. Health Canada's Pest Management Regulatory Agency (PMRA) has similar requirements and also conducts regular reviews and re-evaluations."

"EPA and PMRA are not alone in their assessments. Australia, the World Health Organization and science-based regulators in 60 other countries have repeatedly approved atrazine as safe, effective and suitable for use. While it is not used in the EU, atrazine has received favorable safety reviews from European Union regulators."

"Syngenta focuses on the science and safety of atrazine - and on communicating these facts simply and clearly. We've also shared our study data with EPA and PMRA and regularly follow Good Laboratory Practices, the highest standard in the world for establishing the quality of a study. Academic studies are not necessarily held to that same high standard."

"Syngenta wants to unambiguously share the facts about atrazine: It is a well-tested, safe and beneficial product that is critical to agriculture and the global economy."

In a phone message a representative from a PR company that works for Syngenta said the company has declined our request for an interview because "we pretty much know what the other side is going to say. Its the same story we have heard for a long, long time and we know there is not much truth there."

Health Canada also declined our request for an interview and sent us this statement:

About the registration of Atrazine:

"As a condition of continued registration of atrazine, and to confirm our original conclusion that the use of atrazine and associated end-use products does not pose an unacceptable risk to the environment, the PMRA required additional information as outlined in our Re-evaluation Decision document, RVD2007-05, Atrazine (Environmental Assessment), on the reproductive and developmental effects of atrazine on amphibians. Continued registration of atrazine is acceptable."

"Since 2007, the PMRA has registered eight new products containing atrazine and approved several changes, including re-instating uses that were previously withdrawn by registrants following the re-evaluation decision, changes to the product formulation, additional crops and label improvements requested by the PMRA."

Scientific Foundation:

"The PMRA participatd in a 2012 Scientific Advisory Panel (SAP), Problem formulation of ecological effects from atrazine. At this meeting, the results of 57 additional open literature studies were considered. The studies and EPA summaries are outlined in the attached document, Open Literature Review of Amphibian Data."

"The PMRA continues to monitor new information as it becomes available and is following the activities of the EPA and other regulatory authorities regarding atrazine and amphibians. "

"During the re-evaluation of the chronic effects of atrazine to amphibians, the Pest Management Regulatory Agency (PMRA) examined a number of laboratory and field studies, which are listed in the United States Environmental Protection Agency (EPA) document, "White Paper on Potential Developmental Effects of Atrazine on Amphibians - In Support of an Interim Reregistration Eligibility Decision on Atrazine", available through the EPA's website at http://www.epa.gov/scipoly/sap/meetings/2003/june/finaljune2002telconfreport.pdf. These studies were deemed inconclusive by the EPA and the Scientific Advisory Panel (SAP), in which the PMRA participated. Consequently, additional studies were requested and the 2006-2007 Hosmer/Kloas studies were submitted for review."

"The PMRA participated in reviewing the Hosmer/Kloas and other new studies during the 2007 SAP meeting. A summary review of these studies and the EPA's conclusions are outlined in the U.S. EPA public document, "White Paper on Potential Developmental Effects of Atrazine on Amphibians (2007) - In Support of an Interim Reregistration Eligibility Decision on Atrazine"; website link is shown below: http://www.epa.gov/scipoly/sap/meetings/2007/october/2007_amphibian_white_paper.pdf. Only the Hosmer/Kloas studies were considered acceptable by the EPA. "

"Results of two SAPs convened by the US-EPA specifically to discuss the issue of the effects of atrazine on amphibians were considered by the PMRA. Health Canada agrees with the general conclusions of the EPA and of the SAP, that atrazine does not adversely affect amphibian reproductive development."

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