Acute Toxicity of Two Commonly Used Fungicides to Midwestern Amphibians

Abstract Fungicide usage has increased globally in response to the rise in fungal pathogens, especially in the agricultural sector. Consequently, fungicides are not only increasingly found in water quality surveys, but they are also often the most detected pesticide type. However, research examining the toxicity of fungicides is still limited for many aquatic species. In this study, we examined the acute toxicity of two widely used fungicides, chlorothalonil and pyraclostrobin, on six larval amphibian species across multiple families using 96-h LC50 tests. We found that pyraclostrobin was approximately 3.5x more toxic than chlorothalonil; estimated LC50 values ranged from 5–18 µg/L for pyraclostrobin and 15–50 µg/L for chlorothalonil. Comparing across amphibian groups, we found that salamanders were 3x more sensitive to pyraclostrobin than anuran species and equally as sensitive to chlorothalonil. Notably, our estimated LC50 values are close in magnitude to the expected environmental concentration for these fungicides suggesting environmental exposures could lead to direct mortality in these species. Given the widespread and increasing usage of fungicides, additional work should be conducted to assess the general risk posed by these chemicals to amphibian and their associated aquatic habitats.