(Beyond Pesticides, April 14, 2011)
Researchers at the University of South Florida have discovered that the most widely used fungicide in the U.S., chlorothalonil, is lethal to frogs even at low doses. Chemical pollution, according to the researchers, is considered the second greatest threat to aquatic and amphibious species in the U.S. Because many vital systems of amphibians are similar to those in humans, researchers believe that amphibians may be an underused model for studying the impacts of chemicals in the environment on human health and set out to quantify amphibian responses to chlorothalonil. The study, lead by Teagan McMahon, PhD, was published in Environmental Health Perspectives and opens the door for researchers to quantify the effects of the chemical on other species as well as other toxic pesticides on amphibian populations and human health.
Researchers looked at Rana sphenocephala (Southern leopard frog) and Osteopilus septentrionalis (Cuban treefrog) in outdoor aquatic mesocosms (experimental water enclosures) with and without the expected environmental concentration as well as twice the amount of chlorothalonil. They also conducted two dose-response experiments on O. septentrionalis, Hyla squirella (squirrel treefrog), H. cinerea (green treefrogs), and R. sphenocephala, evaluating the effects of the fungicide on the stress hormone corticosterone. At the expected environmental concentration levels in the mesocosm experiment, researchers find that chlorothalonil kills 87% of the population. At twice the expected environmental concentration levels, 100% of the species are killed. In the dose-response experiments, at concentrations to which humans are frequently exposed, it increases mortality in frogs and increases levels of corticosterone and changes in immune cells.
Chlorothalonil is a broad-spectrum fungicide originally registered in 1966. The chemical is widely used on field crops such as peanuts, vegetables and fruit (including citrus) and on turf in chemical lawn care products. It is registered for use against plant diseases such as powdery mildew, early and late blight and various rots and molds. The U.S. Environmental Protection Agency (EPA) considers chlorothalonil to be a likely carcinogen. It is a neurotoxin that has been linked to reproductive effects, kidney and liver damage and is a sensitizer/irritant.
Previous studies have found higher concentrations of chlorathalonil in bee hives, which leads researchers to question whether it could be partly responsible for the bee population decline. Large concentrations of the fungicide have also been previously discovered in high altitudes, where polluted air from farm land often gets pushed, which helps to shed light on shrinking amphibian populations at high altitudes.