Study links popular herbicide to amphibian death


Herbicides are known to have ill affects on many parts of the environment, but a new study from USF researchers has found that one of the most popular and controversial herbicides may be contributing to the population crashes and localized extinctions of the amphibian population.

Jason Rohr, an associate professor of integrated biology, worked with Ph.D. candidate Neal Halstead to study the effects of different environmental stressors on frogs, setting out to better understand the recent worldwide decline in frog populations.

Rohr and his team exposed frog tadpoles to the herbicide atrazine, which is known to be used as an endocrine disrupter for wildlife.

Though the European Union banned the use of the chemical in 2004 due to unpreventable water contamination, it has been estimated that 80 million pounds of the chemical are sprayed on crops to kill weeds in the U.S. every year.

Environmental and conservation groups have been lobbying Congress in recent years because of its known affects on organisms and contamination of groundwater in some regions of the U.S.

Halstead said it’s better to know how atrazine may affect the problem rather than dealing with its repercussions.

“Ultimately, we want to be able to prevent an increased risk of disease as it is more cost effective than dealing with a diseases outbreak after it occurs,” he said.

The researchers then exposed the frogs to chytrid fungus, which has been linked to the decline in the amphibian population across the globe.

The team wanted to find out if early exposure to a stressor such as atrazine would affect the creature later in life.

“For half of our tanks, we exposed atrazine early in the frog’s development,” Halstead said. “The other half we waited until they were a little more developed and exposed the tadpoles to atrazine.”

The researchers said they wanted to test if the stage of life in which the tadpole or frog was exposed to the different stressors affected how the frog reacts to it. This is why some of the tadpoles were exposed to atrazine at an earlier stage of life than other ones.

The team was looking to see if there are direct effects of the pesticide on frog populations, and also looked to see how long the effects may last and what they are.

Team members said they chose to study this topic because they have been working with atrazine for a while and wondered if the effects of the herbicide might contribute to the frogs’ population decline.

“We knew atrazine can be an amino suppressant that may not kill frogs directly but may make them less strong with other stressors,” Halstead said.

The two researchers found that atrazine, no matter when the frogs were exposed to it, was deadly to the animal.

“We found that the frogs are just as likely to die in the long term and there was an increase in mortality risk (when exposed to the herbicide),” Rohr said.

Exposure to atrazine itself lowered the immune system of the frogs, so they were more vulnerable to the fungi introduced later in the study.

“Other studies had already suspected the fungi of being linked to the decline in amphibian species worldwide,” Halstead said.

Since this type of fungus is a typical one that frogs encounter, Halstead said the study can be helpful with the conservation and preservation of their habitats.

The scientists also see these findings as being able to be generalized to more animals and hope that it will lead to people being more cautious when using chemicals like atrazine in the environment.

“In areas with the fungus and where people care about amphibian decline, they need to limit the use of atrazine and other chemicals,” Halstead said.