Metal contaminants in urban stormwater runoff: composition, biological interactions and impacts
McDonald, Sarah Isobel Mary (2021) Metal contaminants in urban stormwater runoff: composition, biological interactions and impacts. PhD thesis, The University of Melbourne.
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Abstract
Anthropogenic activities associated with urbanisation have increased the presence of a diverse range of pollutants in waterways. Often these pollutants are delivered to receiving waterways via stormwater runoff. Among the variety of pollutants present in stormwater, metals continue to be identified as a priority due to their ubiquity, legacy, and ability to bioaccumulate and cause impacts in aquatic organisms. Monitoring of stormwater has revealed that discharges into receiving waterbodies tend to occur over short-term (2-48 h) ‘pulses’. As a consequence, organisms that access these environments tend to be subject to intermittent, short term exposures rather than a continuous exposure. The water quality guidelines (WQGs) currently set by Australian and New Zealand regulatory bodies to protect these ecosystems are typically derived from continuous toxicity tests. This is an issue as these guidelines may not be protective of episodic, short-term exposures typical of stormwater runoff. The key aim of this research was to investigate the forms of metal contaminants over a pulse storm event, and the resulting impact these short-term exposures have on representative aquatic organisms.
Field investigations aimed to provide detailed information on the changes to metal partitioning across a storm hydrograph, with a focus on the fraction of metals that are potentially bioavailable to aquatic organisms. Water samples in a representative system were collected and diffusive gradients in thin films (DGTs) were deployed to measure the DGT-labile metal concentrations. Results indicated that dissolved metal concentrations exhibited narrow pollutographs over the storm, with the concentration of six key metals exceeding WQGs. However, the portion of labile metal as measured by DGTs indicated that a substantial fraction of metals in the system are complexed during the storm and pose minimal risk to aquatic organisms. Following on from the field investigation, a series of laboratory studies examined the response of local aquatic organisms to metal contaminants following short-term aqueous and dietary exposures. These studies intended to assess the bioaccumulation kinetics and organ distribution of two common stormwater metal contaminants through the use of gamma-emitting radioisotope tracers. Whole-body metal concentrations determined by gamma spectrometry indicated the uptake of metals in an invertebrate over the pulsed exposure period. The fish species preferentially accumulated metals via diet.
Finally, a systematic review of the current literature focused on the experimental design and statistical analysis of aquatic live animal radiotracing studies. The review was able to provide clear guidance on the analysis and interpretation of data collected from a range of experimental designs common to radiotracing studies and highly relevant to the broader field of ecotoxicology.
Together, the data presented in this thesis provides an insight into the composition and dynamics of metals in urban stormwater runoff, and how these contaminants impact local biota. This research improves the understanding of metal contaminants in a dynamic urban environment and assists with the development of improved approaches for the assessment and management of short-term, intermittent discharge events.
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