With a few months to go until the end of the Environmental Protection Agency’s public comment period on its risk assessment of the herbicide atrazine (the deadline was recently extended from August 5 to October 4), a battle is raging between environmentalists and farmers. Environmentalists, on the side of EPA, are pointing to evidence that atrazine affects human and animal health, particularly frog reproduction.

Farmers are siding with the agrochemical industry, questioning the science behind the assessment and asserting the herbicide is completely safe.

Seemingly contradictory scientific evidence and claims of significant economic impact are causing confusion. This has resulted in an unclear picture of a vital issue—one that could impact future generations, as well as plants and animals on land and in the water.

This leaves consumers in a difficult position. Who’s right? Are we safe? And is there something we should be doing?

Feminizing frogs

The second most widely used weedkiller in the U.S. after glyphosate (the main ingredient in Monsanto’s popular RoundUp herbicide), atrazine kills weeds that affect crops like maize and sugarcane by disrupting photosynthesis so they can’t make energy from sunlight. But it also affects hormones, making it a potential threat to humans and wildlife.

Atrazine tends to linger in the top six inches of soil, which helps to prevent the growth of new weeds. But this also makes it prone to being washed into groundwater; with around 70 million pounds of the chemical being released into the environment every year, the impact could be significant. Much of it becomes part of the water cycle: In the U.S., over half a million pounds of atrazine are precipitated in rainfall every year.

Amphibians appear to be hardest hit. A number of studies conducted in the early 2000s revealed that when exposed to very low levels of atrazine (0.0001 milligrams per liter (mg/L), far below the EPA’s safe limit of 0.003 mg/L), frogs grow to have several testes and ovaries. Some males even grew eggs in their testes, and some became females; they mated with other males and had the capacity to lay eggs, even though they were genetic males.

One study, published in the journal Proceedings of the National Academy of Sciences showed exposure to low levels of atrazine caused African clawed frogs (Xenopus laevis) to develop as hermaphrodites and led to a ten-fold decrease in testosterone. Another study published in the journal Nature revealed 10-92 percent of male wild leopard frogs (Rana pipiens) had gonadal abnormalities following exposure to the herbicide.

The biologist behind these studies is Tyrone Hayes, a biology professor at UC Berkeley. After publishing his findings, Hayes campaigned to ban atrazine, taking part in a documentary and a TED talk on the topic. The effects, he believes, are much more serious than altering frogs’ development.

He explains that atrazine switches on an enzyme called aromatase, which converts testosterone into estrogen, causing the chemical castration in male frogs. This action also impacts the development of breast cancer in humans, he says, which is controlled by estrogen.

As the evidence for the negative impacts of atrazine on the environment, wildlife and human health have built up over the years, there has been bubbling concern in the U.S., leading to a growing movement of environmentalists calling for a ban on the herbicide.

Building a body of evidence

To be used in the U.S., a pesticide (including herbicides, fungicides and other substances used for pest control) has to have the support of 120 scientific studies saying it’s safe. According to the manufacturer Syngenta, despite these damning results there are 7,000 studies showing the safety of atrazine. Syngenta’s website quotes several studies that say the herbicide doesn’t harm human or animal health, but the most recent is from 2008.

Four major scientific reviews of the effects of atrazine on amphibians and fish were carried out before 2008—and all were funded by Syngenta.

In 2010, researchers from the University of South Florida carried out a more comprehensive meta-analysis published in the journal Environmental Health Perspectives. Their study showed consistent health impacts of atrazine on amphibians and fish, namely that the pesticide disrupts reproduction, metamorphosis and immune function.

Why the discrepancy? It’s down to the method, according to the researchers. Previous reviews, they say, “did not clearly define their inclusion criteria, did not make it clear which studies affected their conclusions (or how they came to their conclusions), and regularly dismissed significant effects of atrazine.”

The new EPA report is a risk assessment “based on the results from hundreds of toxicity studies on the effects of atrazine on plants and animals, over 20 years of surface water monitoring data, and higher tier aquatic exposure models.”

But critics from the agriculture industry are already calling the science behind the assessment into question.

Dale Moore, executive director of public policy for the American Farm Bureau Federation, an industry lobbying group, commented on the assessment: “There appears to be no scientific basis to withhold re-registration of the product.” And Gary Marshall, executive director of the Missouri Corn Growers Association said: “EPA’s flawed atrazine report is stomping science into the dirt and setting farmers up for significant economic hardship.”

One issue, again, could be the methodology used. A relatively new approach to risk assessment called systematic review, where a standardized method is used to analyze a large amount of data, could have helped the EPA defend its position, explained chemical risk assessment expert Paul Whaley, an independent scientific consultant and researcher at Lancaster University:

It’s a very polarized environment; the EPA will be criticized whatever they do. Part of the fallback is always to use the best possible methods for evaluating the evidence. One reason systematic review is good is that it allows you to demonstrate a greater degree of objectivity. I would certainly encourage the EPA to introduce systematic review methods into these sorts of assessments as a means to helping with credibility, addressing concerns about the methods they used and reducing some subjectivity.

Angering agriculture

The EPA is being criticized already. One common ag industry counterargument to the environmentalists and scientists concerned about the chemical’s impact on wildlife is that atrazine is actually good for the environment.

Pam Johnson, president of the National Corn Growers Association, points to the environmental benefits of atrazine:

Corn farmers rely on atrazine for no-till conservation agriculture on more than 44 million corn acres—a practice that is preventing soil erosion, protecting waterways and sequestering significant amounts of carbon dioxide across America. Specifically, the use of atrazine is an alternative to mechanical cultivation to control weeds, which reduces greenhouse gas emissions from plowing.

Industry groups like this can be persuasive: the NCGA represents 40,000 corn growers and the interests of more than 300,000 farmers impacted by corn growing. When such powers are involved in decisions about chemical use, there is a risk that the science will be overshadowed by political and economic considerations.

Indeed, many of the responses to the consultation so far cite cost as an important reason for the reregistration of atrazine. Don Coursey, an economist at the University of Chicago, estimated in 2010 that a ban on atrazine could “erase” between 21,000 and 48,000 jobs. “If all of that job loss were concentrated in the agricultural sector, its unemployment would grow by as much as 2.6 percent. Replacement costs for corn farmers could reach as high as $58 per acre,” he said.

The National Resources Defense Council, an environmental nonprofit, disagrees: In a 2009 report exposing the EPA’s lack of action on atrazine contaminated water, the organization wrote that according to data, atrazine provides only minimal economic benefits:

The U.S. Department of Agriculture estimates a ban on atrazine would result in crop losses of only 1.19 percent and decrease corn acreage in production by just 2.35 percent. Italy and Germany (both of which banned atrazine nearly 20 years ago) have not seen any drop in corn productivity or total acreage of land in production for corn since their ban on atrazine was put in place.=

Taking a more long-term view, a ban on atrazine could actually be economically beneficial by closing the price gap between conventionally and organically grown foods, according to Kerry Kriger, founder, executive director and ecologist at Save the Frogs!, an amphibian conservation group. This, she says, would benefit “the organic farmers who provide a valuable service to Americans by delivering us food that is safe to eat.”

Making science inform policy

Regardless of the potential financial impacts of a ban, continued use of atrazine would have far more costly environmental and health impacts that would be impossible to estimate in the long term.

“We’ve reached a point with atrazine where more scientific analysis is just unnecessary—atrazine needs to be banned now,” commented Nathan Donley of the Center for Biological Diversity, a nonprofit working to save threatened and endangered species. “When the government's own scientists say there's enough atrazine in streams and rivers right now to kill frogs and other imperiled wildlife, we should be worried. How many animals have to die before we do what Europe did 12 years ago and ban atrazine?”

Atrazine was banned in the European Union in 2004 after unacceptable levels of the herbicide were found in groundwater, and manufacturer Syngenta was unable to prove that the levels were safe or that the leakage could be prevented. Around the same time, the EPA conducted an assessment of its safety and concluded that atrazine is unlikely to cause cancer in humans. Several assessments since then have reached the same conclusion, resulting in the herbicide being reregistered repeatedly.

The EPA started the current risk assessment in 2013 after detecting levels that breach its own limit of 0.003 mg/L or 3000 ng/L, in some cases by almost 200 times. Three years on there are 520 pages of evidence showing that atrazine and the compounds it degrades into in the environment have significant impacts on humans, birds, animals, fish, amphibians and invertebrates.

And there’s more evidence to come. A year ago, the EPA reached a settlement with the Center for Biological Diversity that requires them to analyze the impacts of atrazine and another widely used pesticide, glyphosate, on 1500 endangered plants and animals in the U.S.

The EPA’s risk assessment is likely to lead to significant restrictions or a ban on the use of atrazine. Because of the strong opposition and the sheer volume of it being used in the U.S. today, the authorities will need to work closely with farmers and other users to phase it out, as Paul Whaley explained:

Atrazine is a blockbuster compound. If you have an established blockbuster compound, then you realize you have a fairly serious problem with it, removing that from the market becomes rather tricky because it can be very disruptive. One has to be aware of the consequences of banning a compound like atrazine and suddenly removing it from the market, but at the same time if it poses unacceptable environmental risks we have to think about how we’re going to get rid of it. I don’t think it’s acceptable to continue with the status quo in this case.

Although it is likely to be a disruptive move, the NRDC believes there are plenty of other options for farmers: “Integrated pest management techniques could help farmers eliminate the use of atrazine and control weeds while reducing their use of other dangerous chemicals.”

Ultimately, taking atrazine off the market might have a detrimental economic impact on farmers. But the opposite is also possible: a ban could force them to explore new techniques without the use of harmful chemicals, making organic farming more widespread and less costly for the producer and consumer. We could look back on this consultation as the turning point that put organic food in more American homes.

Kriger of Save the Frogs! said it best when she commented to the EPA: “In the interest of public and environmental health and to create a healthy planet, I urge you to take advantage of your privileged role in government and do what is best for the environment and the people of the United States of America: Place an immediate federal ban on the use and production of atrazine."

The atrazine risk assessment is open for public comment until October 4.