Comparative acute toxicity of pesticides to tadpoles of a tropical anuran (Epipedobates anthonyi), a North American native anuran (Lithobates sphenocephalus) and a standard fish species

Abstract

Global amphibian declines have the highest incidence in tropical regions, but most of the ecotoxicological data on amphibians is collected on temperate northern hemisphere anuran species. We tested the hypothesis that tropical anuran larvae (Epipedobates anthonyi) would be more sensitive to pesticides than a North American native species (Lithobates sphenocephalus). For 12 pesticides, 96-hr range-finding acute toxicity tests were conducted to determine if mortality occurred at environmentally relevant levels. Based on those studies, two substances were selected for additional time-to-event analyses in both species as well as median lethal concentration (LC50) calculations. Time-to-event results indicated that the two species appear to be roughly equivalent in their sensitivity to the two tested pesticides. Significant differences between species were not consistent across concentrations for either the insecticide terbufos or the herbicide pendimethalin. The utility of LC50 data was mixed with one LC50 providing an arbitrarily large standard error around the LC50 precluding informative comparisons across species. However, standard LC50 methods allowed data collection that continues to contribute to our understanding of the protectiveness of fish as surrogates for anuran larvae. While our data set is limited, it appears that testing temperate species would be protective for tropical species in ecological risk assessments. Our data also support the continued use of fish as surrogates for amphibian larvae as none of the species were more sensitive to the tested pesticides than rainbow trout (Oncorhynchus mykiss), the standard sensitive fish species used for acute toxicity testing.