Improving the risk assessment of short-term stormwater and effluent discharges to aquatic environments

Anthropogenic activities introduce diverse chemicals with differing concentration-profiles to the aquatic environment, unintentionally (e.g., stormwater overflow) or intentionally (e.g., licensed industrial discharges). In the dynamic aquatic environment chemical concentrations can fluctuate, resulting in short-term exposures of organisms. Current ecotoxicity methods may be unsuitable to assess the risk of short-term contaminant exposures. This is because there is evidence to suggest that aquatic organisms can tolerate higher concentrations of some contaminants when exposed for a shorter duration compared to continuous exposure over the test duration. Because of these limitations, continuous exposure toxicity data may result in overly conservative toxicity estimates for short-term exposure durations, potentially resulting in unnecessary risk management outcomes. There are knowledge gaps that may be inhibiting the accurate prediction of variable effluent toxicity. For example, the lack of short-term (i.e., pulse) toxicity data available for tropical organisms, including the effects of organism life stage, time-of-exposure, mode of action and contaminant mixtures. This thesis investigated the chemistry and ecotoxicity of short-term contaminant discharges to the aquatic environment. Two pulse exposure toxicity testing methods were developed using four tropical organisms. These methodologies were applied to assess the toxicity-modifying factors of exposure duration, organism life stage and time-of-exposure. Several common contaminants were investigated, including metals, ammonia, and pesticides. Contaminant mixtures were also assessed. Results showed that Acartia sinjiensis (a copepod) could tolerate greater concentrations of individual contaminants in short pulse exposures, compared to a continuous exposure. Chronic toxicity was frequently observed in the absence of acute effects. Regarding contaminant mixtures, time-dependant tolerance trends were less pronounced and generally not proportional to concentration-time. Younger organisms were generally more sensitive compared to older organisms. A microalgal multispecies flow cytometry-based bioassay was used to assess the pulse toxicity of copper, atrazine and metolachlor. Microalgae tolerated short pulses of high contaminant concentrations and chronotoxicity was observed for copper. Fluorescence shifts were linked to physiological diel changes. While generalisations for predictions of risk based on TAC (time-weighted average concentration) were effective for common metal contaminants and herbicides, the TAC-approach was not effective for ammonia, propoxur or contaminant mixtures. Pragmatic approaches to assess the risk of pulse discharges are discussed considering the experimental data produced in this thesis. Continuous toxicity thresholds were always protective of pulse exposures. The findings presented in this thesis contributes to understanding the risk of pulse contaminant exposures and assists with developing improved approaches to assess the risk of and regulate short-term contaminant discharges.

Author dc:creator

• Stone, Sarah

Statement dc:rights

• info:eu-repo/semantics/openAccess
• The author owns the copyright in this thesis including all reproduction and reuse rights for the work. The work may not be altered without the permission of the copyright owner. Attribution is essential when quoting or paraphrasing from this thesis.
• © 2023 Sarah Stone
• au.edu.uts.lib/cph

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10453/172298

OAI identifier oai:identifier

oai:opus.lib.uts.edu.au:10453/172298