The potential use of metal ratios in the gills of rainbow trout as biomarkers for acute waterborne copper exposure

This thesis examined the effects of short-term, acute copper poisoning on the metal concentrations in the gills of rainbow trout (Oncorhynchus mykiss) with the aim of developing possible biomarkers under such exposure regimes. The experiments were designed principally to mimic the spillage of high copper contaminants such as industrial or mining wastes into an environment which would flush the contaminant quickly through the water system, resulting in a brief, but acute exposure to copper for the inhabitants of the environment. A variety of water quality conditions were investigated including in fresh and brackish waters, in conjunction with elevated zinc levels in fresh waters and in brackish waters high in dissolved organic carbons. The use of the gill copper concentrations in a ratio to other metals in the gills was investigated for their potential role as biomarkers for acute copper exposure and in fish kills. The depuration rates of metals from the gills were also examined in the carcasses of animals killed through exposure to elevated levels of dissolved copper in fresh and brackish waters. Data from fish kills in Macquarie Harbour, a large, brackish inlet on the western coast of Tasmania, Australia, historically known for its copper contamination, were included in the thesis. It was demonstrated that in short-term, acute exposure to copper, hepatic copper levels will not reflect the exposure whereas copper/metal ratios in the gills of rainbow trout may do so. Circulating copper levels in the animal's blood plasma were unaffected. When exposed to mixtures of copper and zinc, the ratios may still be effective indicators, particularly the copper/sodium ratio. Copper residues in the gills were elevated while sodium levels in the gills and calcium levels in the plasma also decreased significantly indicating an interruption to the animal's ability to iono-regulate. However in brackish waters copper ratios appear less viable as biomarkers. Altered physiological requirements between the animals in a hypotonic, isotonic and hypertonic ionic environment affected copper accumulation at the gills and the concentrations of other metal in the gills. Metal concentrations in the gills equilibrated to environmental levels in 6 to 45 hours post-mortem. It was observed the postmortem depuration of sodium from gill tissue in both fresh and brackish water may provide a means of quantifying the time since death of animals in fish kills. Copper loads in the gills of animals from fish kills in Macquarie Harbour were as high as those of animals killed by copper exposure in laboratory trials in waters of the same salinity, yet the copper/zinc ratios did not indicate that copper exposure was the cause of mortality. Data was also presented indicating high levels of naturally occurring dissolved organic carbon in brackish waters can have an ameliorative effect on the toxicity of copper to rainbow trout. The concentrations of copper that accumulated in the gills of the exposed rainbow trout decreased as the levels of dissolved organic carbons increased. The concentrations of copper correlated better with the total measured copper in the water column than with the ASV-labile measurements of copper. This indicated ASV-labile copper does not provide a good indicator of the bioavailable fraction of the total measured copper.