Responding to pressure from environmental groups and the requirements of regulators, the U.S. Environmental Protection Agency (EPA) and a scientific advisory panel have held public hearings on the risks of atrazine, an agricultural pesticide. It's the most commonly used farm chemical in the U.S. and 90 other countries. Atrazine has been banned by the European Union since 2004, and some studies suggest it may be harmful to human health and the environment.
Every year, U.S. farmers apply more than 35 million kilograms of the pesticide atrazine on their fields of corn, sugarcane, sorghum and other crops.
But a growing body of scientific evidence - including the discovery of small amounts of atrazine in many US waterways - have raised new concerns about its safety.
Recently, the U.S. Environmental Protection Agency, or EPA, convened a scientific advisory panel and held public hearings to review the impact of atrazine on humans and the environment.
"There is probably agreement among everyone that, at a high enough exposure, at a high enough dose, atrazine can cause effects," said Steven Bradbury, the EPA's director of pesticide programs.
During four days of hearings, scientists and activists offered conflicting views on the safety of atrazine.
Kerry Kriger heads Save the Frogs, an environmental group.
He said at least 2,000 amphibian species are threatened with extinction.
"The vast majority of the world's amphibian biologists agree that atrazine is extremely harmful to amphibians. Abundant scientific literature from labs around the world has demonstrated atrazine's harmful effect on an array of wild life," he said.
Kriger said the adverse effects on frogs include infertility, miscarriages and weakened immune systems.
But Syngenta, the main producer of atrazine, says the chemical is safe, and the company sent several of its scientists to the hearings to make that case.
Keith Solomon was one of them. "There is no strong evidence supporting a causal relationship between exposure to atrazine and adverse effects in amphibians and if you want, include fish and reptiles, as well you could," he said.
Government scientists also presented evidence suggesting that atrazine may be more toxic to plants than to animals.
"In the case of effects on aquatic ecosystems, the peer review was looking at what is the potential effect of atrazine on aquatic plants and aquatic plants' community structure, sort of like the house for the whole ecological system," Bradbury said.
Atrazine's license is up for federal renewal next year.
The advisory panel has three months to present its recommendations to the US government.