• Jolley, Dianne
• Stone, Sarah
• Mcknight, Kitty
• Binet, Monique

Abstract

Effluent discharges from industrial sources or urban stormwater can potentially result in high concentrations of contaminant mixtures entering aquatic environments for short-term durations (episodic, intermittent). Both the discharge duration and chemical composition of mixtures can vary greatly, resulting in chemical exposures to organisms varying spatially and temporally. Predicting risk of adverse environmental effects to aquatic organisms of such varying exposures poses a challenge for industry and regulatory bodies. To date, most literature has compared ecotoxicological effects of continuous and pulse exposures to individual contaminants, where organisms can generally tolerate greater concentrations of contaminants when exposed for shorter durations. There are few studies investigating pulse toxicity of contaminant mixtures. Investigating pulse exposures of chemical mixtures should improve the environmental relevance of pulse toxicity data and its use in management decisions. In this study we assessed the toxicity of two complex effluents, and two of the chemical components of each mixture individually (copper and ammonia), to the tropical euryhaline copepod Acartia sinjiensis. Differences in pulse toxicity were assessed comparing continuous exposure (78-h), with6-h and 18-h pulse exposures initiated at 24-h and 48-h. Regardless of exposure type, observations of larval development success were completed after 78-h incubation, accounting for latent effects. Detailed chemical analysis identified changes in concentrations of key chemical toxicants during the exposures, which were linked to differing toxic responses of pulse scenarios. For both mixtures and individual contaminant exposures, the copepod was shown to tolerate greater concentrations when exposed as a 6-h pulse compared to an 18-h pulse. For individual contaminants, the EC50 values differed from continuous exposure by 6 – 9-fold and up to 2-fold for 6-h and 18-h pulse exposures, respectively. For complex mixtures, EC50 values differed from continuous exposure by up to 2.5-fold for 6-h exposures but were similar for 18-h exposures. For a mixture with volatile organic compounds, organism survival was significantly reduced in pulsed exposures compared to continuous exposures. This research aims to fill knowledge gaps in pulse exposure toxicity testing by investigating the pulse toxicity of mixtures to improve recommendations for modified approaches to the regulation of pulse exposures.

Topics

• compound
• organic compound
• chemical composition
• copper
• toxicity