Contamination Status of Sydney Harbour: Contributions by Gavin Birch
Many great harbours of the world have experienced decades of influx of pollutants from a range of sources. Considerable efforts have been undertaken by public authorities to “cleanup” legacies of contamination and mitigate adverse impacts. Sydney Harbour is one such great harbour.
Commencing in the mid-1990s Gavin Birch and his team based in the School of Geosciences at University of Sydney have investigated contamination levels of sediments found within the bed of the Harbour as well as parts of catchments feeding its waterways (including Middle Harbour and Parramatta River). Much of this work has been reported in national and international journals. Here I wish I to focus on one report which should serve as a baseline for future work required to ensure the long-term health of these estuarine waters.
In 2004 I had the privilege of writing the Foreword to a handbook prepared by Gavin and his colleague, Stuart Taylor, entitled: The Contamination Status of Sydney Harbour Sediments: A Handbook for the Public and Professionals (Environmental, Engineering and Hydrogeology Specialist Group, Geological Society of Australia, Public Education and Information Monograph No.1). In introducing this publication I commented how the Harbour has switched from serving as a “cesspool” and waste remover to a place worthy of respect, a natural asset to treasure and protect from human abuses. Yet I pondered as to why so little systemic research had been undertaken at the scale of this natural system, and in particular that a study of its contamination status was long overdue. To fill this gap Gavin and colleagues set about sampling and analysing sediments. The issue was whether the level of concentrations of some very toxic contaminants were amongst the highest in the world, and that there was a continued inflow from stormwater adding to existing high levels.
The Handbook is divided into four sections: the context, the science, the implications and the recommendations. Here I will concentrate more on the science and its implications although the recommendations are far-reaching and quite pertinent to present-day and future management decisions. It aims to provide the first publicly accessible, comprehensive study of heavy metals and anthropogenic organic compounds in sediments of Sydney Harbour and catchment. Information on spatial distribution of contaminants provides an indication of sources “essential for management of the estuary and catchment and for developing appropriate remedial actions”. This is not just a monograph for scientists. There is a clear motivation to guide decision-makers with a clear purpose the Sydney Harbour’s contamination problem is serious and requires actions to make it healthy.
Approximately 1700 estuarine and 1000 catchment (fluvial) sediment samples were collected and analysed for this project. Maps are provided throughout the Handbook on locations for heavy metals (cadmium, cobalt, copper, iron, manganese, nickel, lead, zinc), total organic carbon, organochlorides (OC), polycyclic hydrocarbons (PAHs), and nutrients. They also undertook a limited analysis of polychlorinated biphenyls (PCBs), part of the dioxin family. Resource constraints limited the number of analyses in creeks and canals of the catchment. Methods used are detailed and results summarised in tables and graphs.
In summary, concentrations are highest in the upper reaches of bays especially those along southern shores (Homebush Bay, Hen and Chicken Bay, Iron Cove, Rozelle Bay and Blackwattle Bay). These areas are: (1) close to sources of contamination; (2) mantled in muddy sediments that have a chemical affinity for pollutants; and (3) relatively poorly flushed by tides and currents. However, even downstream from the Harbour Bridge there were parts of embayments on both northern (e.g. Neutral Bay) and southern sides (e.g. Rushcutters Bay) of the estuary, as well as Middle Harbour, where high concentrations of certain contaminants have been detected. In addition, their findings of heavy metals and OCs in fluvial sediments of the Harbour’s catchment are significant. They see this as indicating the importance of stormwater runoff as a continuing source of pollutants to the estuary from a variety of sources, especially in the southern central region of the Harbour. Many of the most contaminated parts of the Harbour are situated next to infill areas in the upper sections of embayments highlighting the release of heavy metals through seepage and the need for more research to quantify this possible source of contamination.
Birch and Taylor ask the question: how contaminated is Sydney Harbour compared to other estuaries? They are quite cautious in making comparisons because of different ways data have been collected and compiled. However, using information from a range of locations for mean concentrations of OCs and PAHs they graphically show Sydney Harbour to have among the highest known concentrations anywhere worldwide. It is considerably more polluted with respect to heavy metals than ports serving Melbourne, Adelaide, Brisbane and Darwin (but not Hobart). But for OCs it is higher than any other Australian estuary. This knowledge enables the authors to examine possible biological effects of these contaminated sediments as indicated using ANZECC sediment quality guidelines.
In looking further into management implications, Birch and Taylor note how managers were focused on water quality assessed through faecal indicators. They stated in 2004 that although water quality is important, “the quality of the underlying bottom sediment is of equal, and perhaps greater importance”. In making this point they return to the interpretation of their data which shows that most toxic substances being discharged are from stormwater not sewer overflows. Despite the great gains in waterway health following the passage of the NSW Clean Waters Act 1972, they demonstrate the continued need for further work to improve our understanding and management of total loads being delivered into the Harbour and the continued circulation of sediment contained below tidal levels. In this Handbook the point is made that data produced by their study should be superimposed onto hydrological and chemical models to allow the movement of sediments, suspended solids, nutrients and contaminants to be better predicted. However, they are concerned that this may be difficult in “the general absence of a coherent management structure in the past and lack of responsibility for control of Harbour water and sediment quality”.
Gavin Birch working with others continued his geochemical research well beyond the production of this Handbook in 2004. In particular, the paper in Marine Pollution Bulletin (2007, 54, 295-308) gave us a much-improved understanding of the source, distribution and potential mobilisation of chemical members of the dioxin family in sediments of Sydney Harbour. We owe Gavin a great deal for his dedication and leadership in pursuing this research for so many years. It constitutes an outstanding baseline for understanding future changes to the waterway health of this great Harbour.
Bruce Thom
Words by Prof Bruce Thom. Please respect the author’s thoughts and reference appropriately: (c) ACS, 2025. For correspondence about this blog post please email admin@australiancoastalsociety.org.au
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