Glenn Waller's 100 acres of soybeans in Washington County, Georgia, are the highest yielding in the state. But the "Mr. Efficiency" award winner is worried about rust.

Soybean farmers in the Southeast survived a bout with the crop-destroying fungus in 2005 by using pesticides to halt its spread. But Waller remains worried about a rust resurgence.

"I'm afraid we're going to kind of put it on the back burner and it's going to jump back up and get us,” he said.

Waller, who has farmed for 51 years, increasingly has turned to fungicides to ward off pests and increase his crop yields. Farmers around the country are doing the same, causing an unprecedented surge in fungicide use. But as widespread contamination of waterways near these farms emerges, experts warn that there is inadequate environmental monitoring and information on the chemicals' safety.

"It's concerning," said Jason Belden, an environmental toxicologist at Oklahoma State University. "We have limited toxicological data for a lot of these compounds."

Fungicides are contaminating the majority of water bodies tested in states where there is heavy use, such as in Maine, Idaho and Wisconsin. Some are known to be highly toxic to aquatic creatures, but little is known about whether they are actually harming frogs or other animals in the environment. The potential threats to people are unknown, with new research on lab mice linking them to obesity.

Farmers have historically sprayed fungicides to stop disease. But over the past decade, in an effort to squeeze extra bushels from their crops, they have been spraying more kinds of fungicides on more acres. Wheat, corn, soybeans, citrus and cotton are among the crops that often are sprayed.

The fungicide explosion prompted Kathryn Kuivila, an environmental organic chemist with the U.S. Geological Survey, to see if fungicides were escaping farms and winding up in nearby streams. In a 2012 study of 33 fungicides used on potatoes, Kuivila's lab found that 75 percent of surface waters tested and 58 percent of ground water samples were contaminated with traces of at least one fungicide.

A fungicide called boscalid – used on a variety of crops from food to turf grass – was the most common, found in 72 percent of water samples. The team tested 24 bodies of ground water and shallow water in Maine, Idaho and Wisconsin; the scientists noted that the results may vary nationwide.

The fungicides were found below levels that would kill creatures at the bottom of the food web, such as zooplankton and amphipods, the authors said. But Belden said that doesn't mean there's no threat. Fungicides degrade rapidly so monthly testing in water might not "see all the pulses" of fungicides application, he said. More work is needed to get a better idea of how much aquatic creatures are exposed.

"Is it a red alert that these things should be banned? I don't think so," Belden said. "Is it an alert that we need to do a lot more research relatively quickly to figure out what's going on? I do think that."

There is little information from manufacturers on how much is applied to crops. But all signs suggest that fungicides are now in vogue.

With an estimated $8-billion global market in 2005, before the recent surge, industry experts now predict $21 billion worth of fungicides will be sold annually by 2017.

Spraying of soybean crops quadrupled between 2002 and 2006 in an effort to fight Asian Soybean Rust, according to the latest data available from the U.S. Department of Agriculture. Rust is a windblown disease that attacks soybean leaves, causing lesions and eventually killing the plant.

Fungicides were routinely applied on up to 30 percent of the nation's 220 million acres of corn, soybean and wheat, according to a 2009 estimate.

University of Kentucky plant pathologist Paul Vincelli estimates that 10 to 15 percent of all U.S. crops are treated with fungicide.

But experts acknowledge that without mandatory reporting, the amounts used are merely a best guess. "We don't have anything close to real data on the acreage being treated," Vincelli said.

In 2006, four fungicides were approved for combating Asian Soybean Rust, plus five more were allowed only for emergency uses. In 2009, it swelled to 14, according to data from the U.S. Environmental Protection Agency and the West Virginia Department of Agriculture.

"In the past 10 years there's been a huge change in the fungicides available," said Kuivila.

In 2008, farmers had a new incentive to use the chemicals. Studies from Iowa State University and the University of Missouri [PDF] found that so-called preventive use of fungicides increased soybean yields by as much as 20 percent. For corn, it increased yields by 5 percent, according to industry research. Disagreement between industry research and university studies over the efficacy of these kinds of treatments is ongoing, Vincelli said. A 2011 study that he was involved with found that farmers had a low likelihood of recovering the costs of applying fungicides when there was no disease.

Some scientists and agricultural experts are concerned about this rise in fungicide use. In a 2009 letter [PDF] to the EPA, 40 university scientists expressed their concern over the relabeling of pyraclostrobin, sold by BASF under the name Headline and used on a variety of crops including corn, cotton and wheat.

According to the letter, Headline was relabeled to say its “benefits may include improved host plant tolerance to yield-robbing environmental stresses, such as drought, heat, cold temperatures, and ozone damage” as well as bacterial and viral infections. “These benefits often translate to healthier plants producing greater yields at harvest, especially under stressful conditions.”

The idea of an all-purpose fungicide did not sit well with many scientists, who wrote that it “invites increased, widespread use of this product...The environmental and biological impact of these uses in the absence of a disease threat may be considerable."

The EPA allowed the new label for Headline, and several other strobilurin fungicides have since been relabeled, leading to their popularity.

"The ones that have been increasing rapidly, especially within the Corn Belt, are the strobilurins," Belden said. The biggest strobilurin fungicides include Headline, Stratego, made by Bayer Crop Science, and Quilt, made by Syngenta.

CropLife America, which represents pesticide manufacturers, said in a statement to EHN that the EPA’s review of fungicides is "rigorous" and that "new application technologies by farmers will serve to further minimize any potential environmental impacts of crop protection products."

Those technologies include applying fungicides directly to the seed, using low-drift applications and preserving marginal lands near water bodies to prevent runoff.

"Crop protection products such as fungicides help farmers grow quality crops free of disease and achieve better yields, which keeps prices low for consumers," said Mike Leggett, senior director of environmental policy at CropLife America.

But even at low concentrations, research suggests that some fungicides can trigger subtle biological changes that might have health effects.

Recent studies in mice have linked some fungicides to obesity. Humans are exposed to traces of fungicides in fruits and vegetables.

Triflumizole (TFZ) is one fungicide that promoted obesity in mice exposed in the womb, according to a 2012 study by the University of California, Irvine. It occurred at levels that were approximately 400-fold below the U.S. Food and Drug Administration's reported "no observed adverse effect level."

"That would mean we're seeing effects at four times lower than the allowable human exposure," said senior author Bruce Blumberg, a professor of cellular and developmental biology. "We're seeing effects well below the level that humans are allowed to be exposed."

 Also, when pregnant mice were exposed to tributyltin, which is no longer licensed for use as a fungicide, their children and grandchildren who weren't exposed had increased body fat, according to a new study from the University of California, Irvine.

A similar compound, Triphenyltin (TPT), seems to be a better activator, Blumberg said. Triphenyltin is still licensed as a fungicide. Blumberg's lab hasn't tested specifically TPT in animals, but it "works terrifically well" at turning on this pathway in cell cultures. This work suggests early life exposure can cause damage to a person's genome that can be passed down through generations.

Blumberg's lab also is testing several chemicals for the National Toxicology Program, including many fungicides. "The majority of those [fungicides] are obesogenic," Blumberg said. "Fungicides and obesity is going to be a big story in the future."

In addition, some human and animal studies have linked the fungicides maneb and benomyl to Parkinson's disease.

While human health data is beginning to emerge, little is known about how fungicides might harm aquatic species. Studies have shown mixed results.

Azoxystrobin, a fungicide used on vineyards, has been shown in field studies to damage the DNA of fish, according to a 2008 study in France.

Headline killed tadpoles in the lab at doses used on crops, according to Belden's 2010 study. Even a dilute overspray could harm amphibians, Belden said. Quilt, on the other hand, doesn't seem to be very toxic.

"They're varied, but a couple of the really high use ones – especially Headline – seem like they have strong aquatic toxicity," Belden said.

However, a 2012 lab study conducted at Oklahoma State University by Belden's collaborator Scott McMurry did not find damage to the growth and development of tadpoles at the levels that Kuivila's research team found in waterways.

Other laboratory experiments found that sediment and crop cover can protect some creatures from fungicide exposure.

"There's a lot of environmental factors that are likely reducing exposure," Belden said. "At this point, we've identified a hazard to amphibians, but we still need to tease apart whether or not that hazard equates to a true environmental risk."

Kuivila would like to see increased monitoring of fungicides, but she acknowledges this won't be easy because they are hard to detect in sediment. Testing also is expensive. But the idea is gaining traction, she said.

"I'm starting to hear more and more people adding fungicides to their analytical methods," she said. "I'm happy to see that."

Waller, the Georgia soybean farmer, says he tries to limit the risk of fungicides escaping his 100 acres.

He says he's stingy with water so that he has very little runoff. He applies fungicides only during dry spells so that the fungicides will soak into the ground instead of washing off the field. He uses them at least twice each year – a tool to make his land as efficient as possible.

"I sing to 'em and pray to 'em and walk the field and pull the weeds and try to do everything I can for high yield," Waller said.

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.