New research from USF is finding that a commonly-used fungicide may be toxic to aquatic life.
The chemical is chlorothalonil, the most commonly used synthetic fungicide in the United States. It’s used on peanuts, tomatoes, potatoes, and turf grass.
It’s in the same family as DDT, the chemical that was banned after conservationist Rachel Carson’s 1962 book “Silent Spring.”
USF biologist Taegan McMahon, a doctoral candidate in the USF Department of Integrative Biology, has published two papers with associate professor Jason Rohr about the dangers of chlorothalonil.
In the first, published last year in Environmental Health Perspectives, they looked at how the average amount of the chemical found in runoff near ponds directly affected amphibians.
“It basically killed all of the amphibians within 24 hours and, at slightly higher concentrations than that, it killed all of the amphibians in less than 24 hours,” she said.
Their latest study is in the July issue of the journal Ecology Letters. This time, they set up freshwater ecosystems similar to the normal Florida pond, and once again exposed them to that average chlorothalonil concentration—164 parts per billion.
“We found that chlorothalonil depleted most of the organisms that we put into the systems, that includes amphibians, snails, some of the aquatic floating plants, and it totally depleted the diversity within the system,” she said.
The reaction began with the reduction of the algae floating on top of the simulated pond.
“This let a lot of light into the tank,” she said. “It also reduced all of the algae-eaters in the tank, so your amphibians and your snails, which allowed for the little tiny bits of algae that are still left around the outside edges of the tank to really bloom. So we went from a very diverse tank to a tank that was just a big algae bloom.”
While it’s tough to say with 100 percent accuracy that we’d see the same results in the real world, McMahon says there should be some reasons for concern.
“They’ve found up to almost 300 parts per billion out in runoff near agricultural fields and we studied 164, so you can imagine those higher concentrations may have stronger effects,” she said.
McMahon points out that chlorothalonil has its advantages as a fungicide.
“Part of the argument for its use is that it’s got a very short half-life, so chlorothalonil breaks down very quickly, and so if you go in a week or two after application, you may not find much chlorothalonil in the water, and that is considered a good thing,” she said.
But even that good news comes with a warning.
“We have to consider the fact that chlorothalonil breaks down into other chemicals, and we don’t really know what those other chemicals do to the environment,” she said.
“So even though chlorothalonil itself is broken down, those other chemicals that it’s broken down into may also be detrimental,” she said.
And even though the work focuses on the effect chlorothalonil has on amphibians and their environment, McMahon thinks humans should be wary as well.
“We can’t prove it directly but we know it affects their immune systems and it may be an endocrine disruptor and those are things that you’d want to consider if you’re going to be ingesting food that has this chemical on it,” she said.