Exposure duration and composition are important variables to predict short-term toxicity of effluents to a tropical copepod, Acartia sinjiensis

Predicting the toxicity of effluent exposures which vary in duration composition and concentration poses a challenge for ecological risk assessments Effluent discharges may frequently result in the exposure of aquatic organisms to high concentrations of mixed contaminants for short durations In the receiving environment effluents will undergo dilution and physical or chemical processes that further reduce contaminant concentrations at varying rates To date most studies comparing toxicity risks of continuous and pulsed contaminant exposures have focused on individual contaminants In this study the toxicity to the tropical euryhaline copepod Acartia sinjiensis of two complex effluents was assessed comparing 6 and 18 h pulses and 78 h continuous exposures Observations of larval development success and population size were completed after a 78 h incubation period to observe for latent effects after pulse exposures The chemical compositions of the effluents were assessed over time and different contaminants i e metals ammonia or organics declined at differing rates These were characterized as either a minimal steady or rapid decline Nauplii development and population after 78 h were more impacted by effluent exposures following an 18 h pulse compared to a 6 h pulse Based on pulse exposure concentrations the 50 effect concentrations EC50 were similar for continuous and 18 h exposures but up to 3 fold greater lower toxicity for the shorter 6 h exposures Time weighted average concentrations did not accurately predict toxicity from pulse exposures of the effluents Concentration addition toxicity modelling using toxicity data from pulse exposures of single contaminants was useful for predicting the toxicity of chemical mixtures exposed for varying durations Recommendations for modified approaches to assessing risks of short term effluent discharges are discussed 2022 Elsevier Ltd