Terrestrial exposure and effects of Headline AMP® Fungicide on amphibians

Abstract

Recent studies have demonstrated that a pyraclostrobin-containing fungicide (Headline(®) Fungicide--Headline(®) Fungicide and Headline AMP(®) Fungicide are registered trademarks of BASF) is toxic to amphibians at environmentally relevant concentrations. However, these studies were performed in a laboratory setting of a worst-case direct exposure in clean media. Interception of spray by the crop canopy and ground cover used by animals for security cover will influence exposure. Thus, risk to amphibians is unclear in an environmentally realistic field environment. We tested exposure and toxicity of Headline AMP(®) Fungicide to amphibians in multiple agricultural habitat scenarios (e.g., within treated crop vs. grassy areas adjacent to crop) and at two rates during routine aerial application. Specifically, we placed Woodhouse's toads (Bufo woodhousii) and Blanchard's cricket frogs (Acris blanchardi) in enclosures located within treated and untreated corn (VT stage, approximate height = 3 m), and in the potential drift area (adjacent to treated corn) during aerial application of Headline AMP Fungicide at either 731 or 1052 ml/ha (70 and 100 % the maximum application rate in corn, respectively). Mean concentrations of pyraclostrobin measured at ground level were ≤19 % of nominal application rate in all areas. Overall, mean mortality of recovered individuals of both species was ≤15 %, and mortality within Headline AMP Fungicide-treated corn (where risk was anticipated to be highest) was <10 %. It is important to understand that application timing, interception by the crop canopy (which varies both within and between crop systems), and timing of amphibian presence in the crop field influences risk of exposure and effects; however, our results demonstrate that amphibians inhabiting VT stage corn during routine aerial application of Headline AMP Fungicide are at low risk for acute mortality, matching existing laboratory results from acute toxicity studies of Headline Fungicide.

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

“…Juveniles are more likely to be present in crop fields later in the season when canopy cover is higher, which would reduce direct exposure from spray, and thus exposure to chemicals via alternate exposure routes or exposure to sublethal concentrations of chemicals may be more likely. Our results, in combination with data from Cusaac et al suggesting high rates of canopy interception in a routine corn exposure scenario, suggest that risk of Headline AMP fungicide exposure and acute effects (e.g., mortality) to terrestrial amphibians in a healthy corn system is minimal. Indeed, mortality of juvenile A. cognatus from Headline AMP fungicide may only be expected in the event of a direct overspray exposure, and there was no indication of sublethal toxicity as measured by prey orientation.…”

“…Nonetheless, direct exposure may result in some mortality, and because canopy cover is not ubiquitous throughout crop fields, animals could experience direct exposure to the fungicide during crop treatment. However, canopy interception reduces rates of the fungicide at ground level , and other factors likely govern exposure risk, including the activity period and habitat use by the animal . Toads may or may not be active during the daytime as a function of temperature, moisture, and other factors, all of which influence their presence in a given area .…”

Soil organic matter content effects on dermal pesticide bioconcentration in American toads (Bufo americanus)

“…Smalling et al [22] found 14 pesticide active ingredients and 3 pesticide metabolites in sediment samples from wetlands actively draining agricultural fields in Iowa. Interception by vegetation during the growing season may reduce pesticide exposure and related mortality among amphibians [52], indicating there is likely variation in pesticide accumulation and effects across seasons. Glyphosate is known to cause mortality in amphibians [49,50] and its mobility in soils can be affected by the presence of phosphate fertilizers [51].…”

A review of ecological risk assessment methods for amphibians: Comparative assessment of testing methodologies and available data

“…The authors did indicate, however, that deleterious effects were evident only under worst‐case exposure scenarios. In a follow‐up study in which adult amphibians were placed in pesticide‐treated and untreated fields, they found that toxicity was greatly reduced, which the authors attributed to a reduction in exposure resulting, most likely, from canopy interference (Cusaac et al ). Alternatively, Brühl et al () reported relatively high toxicity to the European common frog ( Rana temporaria ), resulting from direct overspray of 7 pesticides at environmentally relevant exposure levels.…”