Estimating terrestrial amphibian pesticide body burden through dermal exposure

Abstract

Dermal exposure presents a potentially significant but understudied route for pesticide uptake in terrestrial amphibians. Our study measured dermal uptake of pesticides of varying hydrophobicity (logKow) in frogs. Amphibians were indirectly exposed to one of five pesticide active ingredients through contact with contaminated soil: imidacloprid (logKow = 0.57), atrazine (logKow = 2.5), triadimefon (logKow = 3.0), fipronil (logKow = 4.11) or pendimethalin (logKow = 5.18). All amphibians had measurable body burdens at the end of the exposure in concentrations ranging from 0.019 to 14.562 μg/g across the pesticides tested. Atrazine produced the greatest body burdens and bioconcentration factors, but fipronil was more permeable to amphibian skin when application rate was considered. Soil partition coefficient and water solubility were much better predictors of pesticide body burden, bioconcentration factor, and skin permeability than logKow. Dermal uptake data can be used to improve risk estimates of pesticide exposure among amphibians as non-target organisms.

Pesticide Uptake Across the Amphibian Dermis Through Soil and Overspray Exposures

“…This experiment is unique in comparing pesticide accumulation through the dermis in amphibians after direct overspray and indirect soil exposure treatments that simulate pre-emergent pesticide applications. The amphibian BCFs we report here for the indirect treatment are consistent with those we reported for barking and green treefrogs in Van Meter et al (2014) for atrazine, triadimefon, fipronil, and pendimethalin. Indirect exposure to imidacloprid resulted in a higher BCF in the current study for barking treefrogs, and the direct exposure treatment produced much higher BCFs than our previously reported data for both species (Van Meter et al 2014) as expected.…”

“…Hydrophobic pesticides (i.e., high logK OW ) were found to permeate excised frog skin in a flow-through cell more readily than hydrophilic pesticides (Quaranta et al 2009). Although the current study was not designed to investigate logK OW exclusively as a factor in pesticide accumulation, the data corroborates the report of Van Meter et al (2014) showing that logK OW is not the best predictor of pesticide accumulation in living terrestrial amphibians. In both direct overspray and indirect soil exposure treatments, atrazine and imidacloprid led to higher body burdens and BCFs compared with pendimethalin, a much more hydrophobic pesticide.…”

“…Extraction methods for both whole-body amphibians and soils are detailed in Van Meter et al (2014). Briefly, 5 mL of methanol (MeOH) was added to each sample followed by sonication, vortexing, and centrifugation.…”

“…The potential for pesticide uptake through dermal exposure in terrestrial-phase amphibians is supported by a small, but growing, number of studies (Henson-Ramsey et al 2008;Storrs Mendez et al 2009;Bernal et al 2009;Dinehart et al 2009;Belden et al 2010;Edge et al 2011;Brühl et al 2013;Van Meter et al 2014) and was recently reviewed by Brühl et al (2011). The majority of these studies report mortality among post-metamorphic amphibians directly exposed to pesticide formulations through a simulated overspray exposure scenario (Bernal et al 2009;Dinehart et al 2009;Belden et al 2010;Edge et al 2011;Brühl et al 2013).…”

“…Mortality rates among these studies range from 0 to 100 %. Three controlled laboratory experiments document dermal uptake of pesticides in amphibians through indirect soil exposure scenarios using pesticide active ingredients (Henson-Ramsey et al 2008;Storrs Mendez et al 2009;Van Meter et al 2014). Differences across these studies in measured endpoints, study designs, as well as active ingredients and formulations used, limit our deductive ability about pesticide risk in terrestrial habitats.…”