Sediment contaminants off the coast of Sydney, Australia: A model for their distribution

A baseline study of sediments along the continental shelf adjacent to Sydney was conducted in 1990–1991. The aims of this study were to identify the distribution patterns of a range of inorganic and organic contaminants and to place these distributions in the context of both local sources and sediment/contaminant relationships. The baseline study identified three spatially discrete, shore parallel zones of contaminants. Highest contaminant concentrations occurred in a zone 2–4 km offshore, with lower concentrations occurring in zones less than 2 km and more than 4 km from the coast. Stepwise multiple regression models were used to identify and quantify heavy-metal/geochemical associations. Heavy-metal distributions in sediments were principally related to Fe content, organic carbon content and water depth. Weaker associations were also found with Mn, carbonate content and fine-sized particles (<63 μm). Multiple regression models, limited to these six variables, accounted for up to 66% of the variability in the distribution of a number of metals, including Ph, Cr, Zn, Ni, Cu, As, Hg, Cd and Se. Using Cu and Cr as examples, model residuals are shown to highlight discharges from significant point sources such as sewage outfalls and urbanized estuaries. The cohesiveness of residual distribution for a range of metals, and the association of these residuals only with point sources, suggests they represent anthropogenic inputs for those metals. The total mass of Cu and Cr residuals have been calculated in an effort to identify the contribution of identified point sources to the total offshore contaminant budget compared to other identified coastal sources.