Source of heavy metals in sediments of the Port Jackson estuary, Australia

The Port Jackson estuary has a highly urbanised and industrialised catchment and is central to Sydney, which with a population of approximately 4 million, comprises almost a quarter of Australiaʹs population. The estuary has a long history of contamination which has resulted in extensive areas of polluted sediments mainly associated with the most industrialised/commercialised parts of the catchment. The highest concentrations of sedimentary heavy metals occur at the headwaters of embayments and tributaries in the estuary, especially in the central city region where gradients decline rapidly away from canals. High total suspended solids, elevated concentrations of heavy metals in sediment and in particulates in canals draining large catchments are evidence that drainage from these areas is a major source of contaminants to this estuary. Another possible important point source of heavy metals is leachates from reclamation areas, whereas licenced polluters do not impact on a regional scale. Of the diffuse sources, atmospheric contributions may be substantial, but storm water drains with small catchments and sewer overflows have no observable impression on the regional distribution of heavy metals in surficial sediments. Biological effects criteria suggest that heavy metal concentrations in sediments are sufficiently high to adversely affect biota over large areas of Port Jackson. Large volumes of contaminated sediment and a continuing supply of heavy metals to the estuary will make remediation difficult.