Metal pollution during pulse stormwater events: bioaccumulation kinetics of cadmium and zinc in a freshwater decapod crustacean
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Date
2019-09-03
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Australian Nuclear Science and Technology Organisation
Abstract
Stormwater runoff has been identified as a major source of metal pollutants in urban waterways, where organisms that access these environments tend to be exposed to multiple pulses, rather than a constant exposure, of contaminants. Current water quality guidelines (WQGs) are generally derived using data from continuous exposure toxicity tests, where the assumption is that chronic exposures provide a meaningful way of assessing metal bioaccumulation kinetics and effects in an organism. In this study the radioisotopes 109Cd and 65Zn were used to explore the uptake, depuration and organ distribution of a non-essential and essential metal in a decapod crustacean over the course of three short-term (< 10 hours) pulse exposures followed by a 7-day depuration. The freshwater shrimp (Paratya australiensis) was exposed to radiolabelled cadmium only, zinc only and a mixture of cadmium and zinc at environmentally relevant stormwater concentrations. Whole-body metal concentrations were determined by daily live-animal gamma-spectrometry. Anatomical distribution of the radioisotopes was visualised using autoradiography at multiple time points throughout the depuration period. Metal uptake and efflux rates were similar in the individual and mixed-metal exposures, where both metals accumulated to a greater extent when presented individually. Interestingly, the rate of cadmium uptake in the whole-body of the organism over the course of the three ‘pulses’ decreased with each successive pulse. The rate of zinc uptake remained linear over the course of the three pulsed exposures. The efflux rate for cadmium regardless of exposure treatment (single or multi-metal) was close to zero. Zinc concentrations decreased in the whole-body of the organism over the course of the depuration period, with the efflux rate being greater for zinc exposed individually. Autoradiography indicated the presence of both metals in the gills and hepatopancreas of the animals regardless of depuration time. This study reveals how cadmium bioaccumulation kinetics may differ between repeated ‘pulse’ exposures where, unlike zinc, the rate of uptake decreases with each successive pulse. This demonstrates how repeated exposures, rather than a constant exposure, can influence the bioaccumulation kinetics of metals, highlighting the important consideration for incorporating pulsed toxicity tests in frameworks when deriving WQG values.
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Keywords
Metals, Zinc, Cadmium, Pollution, Biological accumulation, Fresh water, Crustaceans, Decapods
Citation
McDonald, S., Creswell, T. & Hassell, K. (2019). Metal pollution during pulse stormwater events: bioaccumulation kinetics of cadmium and zinc in a freshwater decapod crustacean. Paper presented at the ANSTO Young Researchers' Conference, Lucas Heights, NSW, Australia, 3 September 2019. Retrieved from: https://events01.synchrotron.org.au/event/98/book-of-abstracts.pdf