Growth inhibition in early life-stage tests predicts full life-cycle toxicity effects of lead in the freshwater pulmonate snail, Lymnaea stagnalis

Abstract

The freshwater pulmonate snail, Lymnaea stagnalis, is the most sensitive freshwater organism tested to date for several metals (Co, Cu, Pb, Ni) based on 28d early life-stage (ELS) tests in which growth was the most sensitive endpoint. The United States Environmental Protection Agency (USEPA) has expressed concern that growth in 28d ELS tests with mollusks may overpredict toxicity because of the potential for recovery in a full life-cycle (LC) test. Consequently, the USEPA only accepts the survival endpoint for these tests in establishing water quality criteria (WQC). To address this concern, the current study aimed to test the sensitivity of L. stagnalis to Pb in a 56d full LC test evaluating survival, growth, reproductive and embryonic growth endpoints and compare the estimated effect levels to those established using the 28d ELS test design. The most sensitive endpoints in this study were 28d growth and 56d egg mass production, both with a NOEC of <1.0μgL−1 and a LOEC of 1.0μgL−1, showing that the ELS growth endpoint is predictive of the 56d reproduction endpoint. Snails exposed to 1.0 and 2.7μgL−1 Pb showed full and partial recovery from growth inhibition between 28 and 56d. While this recovery supports the USEPA's concern about the 28d growth endpoint; considering the reproductive lifespan of L. stagnalis and the recovery dose-response, we conclude that the 28d growth endpoint will be within a factor of 3 of full LC endpoints. This is consistent with the level of precision previously determined for fish ELS tests, which the USEPA accepts for WQC derivation, and suggests that tests using 28d ELS growth endpoint for L. stagnalis may be acceptable for inclusion in WQC derivation.