|A preliminary assessment of zinc, copper, arsenic, lead and cadmium in surfical sediment and biota within Botany Bay, NSW, Australia|
|Applied Ecology Research Group
University of Canberra
Prior to the utilisation of fish cages within the aquaculture industry it is essential to assess the potential for contaminant release, to both the cultured organisms and the environment. The main aim of the current research was to determine spatial distributions of zinc (Zn), copper (Cu), arsenic (As), lead (Pb) and cadmium (Cd) concentrations in surfical sediment and biologically available in the water column of Botany Bay, Australia. This will provide the preliminary data to support the choice of a study location for an aquaculture cage mesh study being funded by Broken Hill Petroleum (BHP). Additionally, this preliminary assessment will establish trace metal input zones in the bay and discuss the factors that may influence trace metal distributions.
The surfical sediments along the western shoreline of Botany Bay have significantly greater concentrations of Zn, Cu, As and Pb than the southern shoreline. Trace metal input from the Cooks River has been reported by past research, and is the probable source of the western shorelines elevated trace metal concentrations. Cadmium concentrations did not significantly vary between sampling location throughout the program. Only cadmium showed significant temporal variations. All concentrations of Zn, Cu, As and Pd were substantially lower than the Australian New Zealand Environmental Conservation Council (ANZECC, 1999) Low Sediment Quality Guidelines.
Oysters were deployed at each sampling location to measure the bioavailable trace metal concentrations within the water column. Biologically available fractions of Zn, Cu, As and Cd did not significantly increase during the three month deployment period. Lead concentrations increased at sites six and seven throughout the trial, these sites being in close proximity to the Cooks River. This increase in lead concentrations has been substantiated by past research that has identified that the area near the Cooks River input to Botany Bay has elevated concentrations of lead. The concentrations of Zn, Cu, As, Pb and Cd in oyster tissues prior to deployment were high, exceeding the National Food Authorities (1992) recommended concentrations for human consumption. This may have prevented the uptake of trace metals and invalidated their use as indicator of bioavailable trace metals.
The southern shoreline was identified as the most suitable area for the fish cage trial to be undertaken. The basis of this resides in the significantly lower trace metal concentrations within the surfical sediment of the southern shoreline, and lower biologically available lead concentrations. Lower concentrations of iron in sediment were measured in this area. Iron can influence surfical sediment trace metal concentrations by scavenging ambient trace metals and providing adsorbance phases in the sediment. The bay's morphology and tidal circulation patterns also support the selection, sand bars that extend along the southern shoreline restricts sediment deposition to other parts of the bay. Moreover, the recent dredging activities at the entrance of the bay have effectively provided a transport channel for suspended sediment that excludes the adjacent shallow southern shoreline.
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