Acute toxicity of three strobilurin fungicide formulations and their active ingredients to tadpoles

Abstract

Fungicide applications in the United States have increased tenfold in the last 5 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 Headline®, Stratego®, and Quilt® using Bufo cognatus tadpoles exposed to four concentrations and a control. All fungicides, including AIs and formulations, demonstrated toxicity to tadpoles, with Headline® and Stratego® causing 100 % mortality at the highest concentrations. Exposure to Quilt® 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 Headline® at 5 μg/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 Quilt® and Stratego®. Results for Headline® however suggest that although the AI is toxic to tadpoles at environmentally relevant concentrations, adjuvant(s) in the Headline® formulation also contribute to mortality, making it the most toxic of the fungicides studied.

Development of Helisoma trivolvis pond snails as biological samplers for biomonitoring of current‐use pesticides

“…Control mortality was less than 5% during toxicity tests, and no adverse effects were observed within treated units until 72 h into the exposure. This is in stark contrast to previous research using H. azteca amphipods and Bufo cognatus tadpoles, in which >80% of observed toxicity occurred within 8 h of exposure [3,29,31]. The LC50 (95% CI) based on time-weighted average pyraclostrobin concentrations was 441 mg/L (359-555 mg/L; Figure 1).…”

“…Although this remains unconfirmed for snails, indirect effects on pyraclostrobin toxicity could occur from metconazole and/or the additional formulation adjuvants. Regardless, previous investigations have demonstrated that the additional adjuvants of the commercial formulations did not significantly contribute to toxicity compared with individual strobilurin ingredients [3,31].…”

“…Values for LC50s have also been reported for water fleas (Daphnia magna) ranging from 14 mg/L to 120 mg/L [33], and for amphipods (H. azteca) at 21 mg/L [3]. Aquatic vertebrates have also shown sensitivity to pyraclostrobin: bluegills (Lepomis macrochirus) have reported LC50s of 11 mg/L [32], whereas LC50s for Great Plains toad (B. cognatus) tadpoles range from 3.7 mg/L to 10 mg/L [29,31]. Maximum environmentally relevant concentrations of pyraclostrobin are expected to be <150 mg/L based on direct overspray of Headline EC fungicide into a shallow wetland (i.e., 16-cm water depth), assuming full water incorporation [29].…”

“…For example, strobilurin fungicides have been the only effective means of controlling outbreaks of soybean rust (Phakopsora pachyrhizi) despite cultural practices of varying planting date, row width, and crop rotation [27,28]. Despite documented increases in fungicide application and reports of environmentally relevant toxicity to nontarget organisms [3,[29][30][31][32][33], detailed studies pertaining to environmental exposure concentrations are lacking.…”

Terrestrial pesticide exposure of amphibians: An underestimated cause of global decline?

“…The most toxic compound in our study, the top-selling fungicide Headline, is currently applied on 90 different crops from wheat in Canada to soy-beans in Argentina and its use may increase further due to proclamations of increase in crop yield and attractive discounts21. At present, several thousand pesticide products are registered globally and more than 2.3 million tons are applied on a major proportion of the land surface each year22.…”