Article on fungicide toxicity unnecessarily casts doubt on findings.

Posted by Tamara Tal at Apr 29, 2011 09:00 AM |

St. Petersburg Times article calls attention to the toxic effects of a widely used fungicide called chlorothalonil on frogs. The article accurately describes the main finding of the University of South Florida study: "It [chlorothalonil] killed nearly 90 percent of the frogs, no matter what species … When they doubled the dose, it killed all of them. Even weaker concentrations harmed the frogs' immune and liver systems and may have altered their stress hormone levels."

To estimate levels of chlorothalonil in water bodies following chemical application to fields or turf, the researchers used a publicly available tool created by the U.S. Environmental Protection Agency.

Reporter Craig Pittman went on to quote Ann Bryan, a representative from Syngenta – the company that produces the fungicide: "This study used a model that significantly overstated the potential exposure of amphibians to the fungicide chlorothalonil … The amount of chlorothalonil was 100 times higher than ever would be found in the real world."

In other words, the environmentally estimated level of chlorothalonil used in the study was too high. But, the researchers also assessed much lower levels of the fungicide in the study – in some cases 1,000 to 10,000 times less than the environmentally estimated level.

The researchers found that both low and high levels of the fungicide – but not intermediate levels – killed frog tadpoles. To put it another way, mortality occurred at levels far below in some cases 1,000 times less than – the environmentally predicted one that the industry representative took issue with. Tadpoles exposed to lower levels of chlorothalonil also had fewer liver immune cells and higher levels of the stress hormone corticosterone, calling the health and fitness of surviving frogs into question.

When evidence provides real scientific support for an opposing view, debate around the interpretation of scientific findings is always desirable. However, there is no evidence to support the claim that environmental levels of chlorothalonil are actually 100 times less than the estimated level used in the study. Even if it's true, mortality was observed in frogs exposed to up to 1,000 times less than the environmentally estimated level, depending on the species.

Instead of calling into question the legitimacy of the findings, readers would have benefited from a critical discussion of what’s currently known about real-world levels of chlorothalonil.


Comment, 4/29/11, Craig Pittman, St. Petersburg Times: The author of this post assumes I had an unlimited amount of space for the story so I could get into a lengthy discussion of the dosage levels. I did not, so I chose to present the information in the clearest way I could and let the readers draw their own conclusions. To me, the fact that the USF researchers used the EPA's formula for the dosage -- and that the manufacturer had no real counter to that -- spoke volumes about the accuracy of the study's findings as opposed to what the company said.

 

Corrected, 4/29/11

 

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