Acute and chronic effects of strobilurin fungicides on non-target organism, Bufo cognatus

Fungicide applications in the United States have increased tenfold in the last five years. Formulations and active ingredients (AIs) have been demonstrated to cause acute mortality to amphibian life stages. However, there has been little to no discrimination between the toxicity of fungicide formulations and their AIs. Therefore, we compared the acute toxicity of the active ingredients and formulations of the fungicides HeadlineRTM, StrategoRTM, and QuiltRTM using Bufo cognatus tadpoles exposed to four concentrations and a control. Also, little is known about sublethal effects in amphibians. We designed an experiment exposing larval amphibians ( Bufo cognatus) throughout metamorphosis to the fungicide formulations HeadlineRTM, StrategoRTM, QuiltRTM, and a control to determine effects on development and growth. Formulations were tested at 1.7, 50, and 400 &mgr;g/L for HeadlineRTM, StrategoRTM, and QuiltRTM, respectively.;All fungicides, including AIs and formulations, demonstrated toxicity to tadpoles, with HeadlineRTM and StrategoRTM causing 100% mortality at the highest concentrations. Exposure to QuiltRTM formulation and its AIs resulted in 50-60% tadpole mortality. Overall, toxicity was comparable between AIs and formulations for all fungicides and concentrations, with the exception of HeadlineRTM at 5 microg/L, where formulation exposure resulted in 79% mortality versus no mortality from exposure to the AI. Results suggest the AIs are responsible for most mortality for QuiltRTM and StrategoRTM. Results for HeadlineRTM however suggest that although the AI is toxic to tadpoles at environmentally relevant concentrations, adjuvant(s) in the HeadlineRTM formulation also contribute to mortality, making it the most toxic of the fungicides studied. Fungicide exposure did not result in any effect on mass or snout-vent length at metamorphosis. However, exposure to HeadlineRTM at 1.7 mug/L increased the development rate of tadpoles by approximately five days compared to the control, an effect not observed for StrategoRTM and QuiltRTM. StrategoRTM caused a lethal effect resulting in approximately 35% mortality. Results from the experiment suggest that sublethal effects of strobilurin fungicides on development and growth to Bufo cognatus may be few, but could be apparent at environmentally relevant concentrations.