Estimating mercury exposure in amphibians using non-lethal tissue sampling.

Amphibian populations worldwide are declining in response to environmental threats, including contaminants, yet our ability to study sensitive populations in their exposure and response to environmental contaminants is limited by the reliability and accuracy of non-lethal sampling methods. Mercury (Hg)—a widespread contaminant—can be transformed in freshwater systems to methylmercury (MeHg), a more bioavailable and toxic form, threatening amphibians using these habitats. We refined methodology for non-lethal sampling and Hg determination across 13 amphibian species, where we demonstrate the efficacy of toe and tail clip tissues to estimate whole-body Hg burdens by examining whether (1) the primary form of Hg (i.e., MeHg or total mercury [THg]) is consistent across tissues and taxonomic groups; (2) clipped tissues correlate with whole-body MeHg and THg concentrations, and (3) all-species or species-specific calculations are appropriate to estimate whole-body concentrations from clips. Across all taxa, MeHg was the primary form of Hg across tissues (averaging 72–78%); toe/tail clip tissues were positively correlated with whole-body Hg, regardless of Hg speciation (i.e., THg or MeHg); measuring MeHg in toe/tail clips was the best analysis to estimate whole-body THg and MeHg (e.g., MeHg relationships were 1.4x and 1.06x less variable than THg relationships for toe and tail clip to whole-body estimates, respectively); and there were no significant species × toe/tail clip to whole body interactions, indicating the all-species model estimates are appropriate to use across taxa. These non-lethal sampling techniques allow for estimation of population-level effects of Hg, especially for rare or imperiled species.