Endpoints for responses of fish to chronic toxic exposures

Abstract

AbstractThe concept of chronic toxicity has caused confusion in fish toxicology because it has developed four connotations: long duration, inclusion of all life stages, low severity, and high sensitivity. To compare alternate chronic tests and expressions of test results, we extracted concentration‐response data from published life‐cycle, partial‐life‐cycle, and early life‐stage tests and derived concentration‐response relationships by nonlinear regression. The effects examined were reductions in parental survival, fecundity, hatching success, larval survival, weight of early juveniles, and weight of early juveniles per egg. On the average, the most sensitive effect was reduction in fecundity, not effects on early life stages. We also found that maximum acceptable toxicant concentrations (MATCs) corresponded to fairly high levels of effect; mean reductions at the MATC were parental survival, 20%; fecundity, 42%; hatching, 12%; larval survival, 19%; weight, 20%; and weight/egg, 35%. These results indicate that, on average, MATCs are concentrations that cause substantial effects and that MATCs estimated from early life‐stage tests are not good substitutes for life‐cycle tests. We suggest that the acute‐chronic dichotomy be abandoned in favor of tests and benchmarks based on concentration‐duration‐response dynamics.