Factors influencing the toxicity of Headline® fungicides to terrestrial stage toads

Abstract

Amphibians are susceptible to exposure from contaminants via multiple pathways. Pyraclostrobin fungicides have been shown to be toxic to terrestrial amphibians at environmentally relevant concentrations; however, these studies did not account for factors that may influence exposure and effects, such as fungicide formulation, age of the individual, exposure route, and physiological state of the individual. We examined Headline® and Headline AMP® fungicide toxicity to adult Anaxyrus cognatus and Anaxyrus woodhousii by direct overspray, as well as acute toxicity of Headline AMP to juvenile A. cognatus through direct overspray, previously exposed soils, and diet. We also assessed effects of hydration state on fungicide toxicity in juvenile A. cognatus and sublethal effects of fungicide exposure on prey-orientation ability of juvenile A. cognatus. Neither formulation of Headline caused mortality of adult A. cognatus and A. woodhousii at up to 5 times the maximum label rate in North American corn (1052 and 879 mL formulation/ha for Headline AMP and Headline fungicides, respectively, corresponding to 1.52 and 2.2 μg pyraclostrobin/cm , respectively). Exposures of juvenile A. cognatus to Headline AMP via direct overspray and previously exposed soils (2 types) resulted in median lethal rate (LR50) values of 2.4, 3.34, and 3.61 μg pyraclostrobin/cm , respectively. Dietary Headline AMP exposure was not toxic, prey-orientations were not influenced by exposure, and effects were similar between dehydrated and hydrated treatments (LR50 = 2.4 and 2.3 μg pyraclostrobin/cm , respectively). These results, combined with exposure concentrations reported in previous studies, suggest that risk of acute mortality for amphibians in terrestrial environments is low and is dictated by body size and site-specific factors influencing exposure. Environ Toxicol Chem 2017;36:2679-2688. © 2017 SETAC.

Dermal Fungicide Exposure at Realistic Field Rates Induces Lethal and Sublethal Effects on Juvenile European Common Frogs (Rana temporaria)

“…Likewise, Mitchkash et al (2014) recorded effects on the best run time of spotted salamander ( Ambystoma maculatum ) after carbaryl exposure. In contrast, Webber et al (2010) and Cusaac et al (2017) did not find any effects on feeding behavior after exposure of juvenile Great Plains toads ( Anaxyrus cognatus ) to carbaryl and pyraclostrobin.…”

“…For logistical reasons, formulations could not be tested at the same time, but they were tested within 2 wk of each other. In a pretest, 3 individuals were exposed to soil contaminated with 100% of the maximum recommended field rate of Folpan WDG (FR max = 3.6 kg/ha), which led to 100% mortality after 24 h. To additionally consider pesticide exposure mitigation by interception of crops (Cusaac et al 2017), half of the maximum recommended field rate (50% FR max = 1.6 kg Folpan WDG/ha) of Folpan WDG was applied to the soil, which corresponds to 0.64 kg a.i./ha with an application volume of 200 L/ha. To allow comparison of effects induced by Folpan WDG and Folpan suspension concentrate, equal amounts of the active ingredient were applied for Folpan suspension concentrate, resulting in a field rate of 1.28 L Folpan suspension concentrate/ha with an application volume of 200 L/ha.…”

Effect of hydration status on pesticide uptake in anurans following exposure to contaminated soils

“…While in Cusaac et al (2017), the authors observed that dehydration did not influence mortality when amphibians were exposed to Headline AMP. In the current study, wholebody concentrations for each pesticide were shown to decrease with increasing dehydration time (Fig.…”

Advancing exposure assessment approaches to improve wildlife risk assessment

“…There is a need for more mixture and multimedia experiments in wildlife ecotoxicology (Glinski et al, 2019). Semifield experiments using enclosures have been used to quantify multimedia exposure under controlled but realistic conditions (Cusaac et al, 2015(Cusaac et al, , 2017Vyas et al, 2007). Use of complex effluents or contaminated soils in laboratory and field testing provides an opportunity to assess both bioavailability and uptake of weathered mixtures (Panico et al, 2022).…”