"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."
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."