Development of an embryo toxicity test to assess the comparative toxicity of metal exposure on different life stages of freshwater gastropods

Early life stages are commonly thought to be highly sensitive to environmental contaminants and may offer insight into the future health of a population. Despite the importance of studying early life stages, very few standard protocols for benthic invertebrates commonly used in ecotoxicological assessments measure developmental endpoints. The goal of the present study was to develop and optimize a robust standard protocol for studying embryonic endpoints in freshwater gastropods. The developed method was then used to characterize the sensitivity of numerous embryonic endpoints (viability, hatching, deformities, and biomass production), in conjunction with juvenile and adult mortality, for the snail Planorbella pilsbryi exposed to a suite of metals (Cu, Cd, & Ni). Biomass production was typically the most sensitive endpoint but was relatively variable while embryo hatching was slightly less sensitive but highly consistent for all three metals. However, no single embryonic endpoint was consistently the most sensitive which demonstrates the importance of assessing a broad range of endpoints, life stages, and organisms in ecotoxicological risk assessment. Interestingly, the embryonic life stage of P. pilsbryi was considerably less sensitive to Cu exposure compared with juvenile and adult mortality. However, for Cd exposure, embryonic endpoints were the most sensitive and for Ni exposure were similarly sensitive to juvenile and adult mortality. This study has valuable applications in conducting developmental toxicity research with organisms lacking standardized testing protocol as well as future applications in multi-generational and in silico toxicity research.