Effects of pulsed copper exposures on early life-stage Pimephales promelas.

Effects of pulsed copper exposures were investigated using Pimephales promelas aged less than 24 h in short-term chronic testing (7 or 14 d) with moderately hard synthetic water. Concentrations tested were between the species mean chronic value (22 μg/L at a hardness of 100 mg/L as CaCO3) and the 7-d continuous exposure EC50 for survival (40 μg/L) to examine exposures that were not acutely toxic and representative of actual wastewater discharge permit exceedences. Factors tested included pulse duration, recovery time between pulses, and pulse frequency. Survival was the main endpoint affected in all treatments (analysis of variance, p 120 h) recovery times. Results suggest that the criteria averaging periods used in the United States, and the averaging periods typically used in wastewater discharge permit limits for copper, may not protect against effects of certain pulsed exposures.