SoE 2003 > Water > 5.7 Contamination of sediments

5.7 Contamination of sediments

Sediments have been contaminated in some areas of NSW, mainly as a result of past industrial activities

Some bays and estuaries in the Sydney region contain sediments with high concentrations of a wide range of contaminants. Other areas with a high urban density and/or a history of industrial activity are also affected, including the Hunter River, Lake Macquarie and Tuggerah Lakes.

The distribution of contaminants often shows a strong relationship with stormwater canals, suggesting land-based sources for most of the contamination. Because it is not known whether contaminated sediments occur outside of the study areas reported here, the full extent of sediment contamination in NSW is unknown.

NSW Indicator

Importance of the issue

Sediment contaminants can enter aquatic ecosystems from point sources, such as sewage treatment plants, intensive animal agriculture, mining, manufacturing and other industries; diffuse sources, including stormwater runoff from rural and urban areas; and contaminant spills and incidents. Contaminants from these sources commonly include a wide range of metals, organic compounds, such as pesticides, and nutrients. Many of these readily bind to and accumulate in aquatic sediments, where they can remain for long periods. These sediments can then act as a source of contamination themselves, becoming both a source and a 'sink' for contaminants (see EPA 2000c).

Contaminated sediments can have significant impacts on aquatic ecosystems. The most serious impacts occur when contamination makes the sediments toxic to biota. The ecological impacts of sediment contamination include:

• interference with the growth or reproduction of some organisms
• changes to the abundance of individual species, as well as the composition and diversity of biological communities
• changes to the overall productivity and functioning of aquatic ecosystems
• the development of algal blooms caused by the release of nutrients stored in sediments to overlying waters (see EPA 2000c).

Contaminants in sediments sometimes accumulate in the tissues of aquatic organisms. This has implications for human health as many species that are eaten by humans may live in contaminated areas. For more information on sediment contamination, see EPA 2000c.

There is no integrated framework for the collection of sediment contamination data across NSW. However, various bodies have conducted studies on sediment contamination.

Sediments in estuaries, lagoons and coastal lakes

Over the past 10 years, the Environmental Geology Group at the University of Sydney has systematically studied contaminated sediments in NSW estuaries, lagoons and coastal lakes. Samples from the Sydney, Newcastle and Wollongong areas have been analysed for nine metals, organochlorine and polycyclic aromatic hydrocarbon compounds, and nutrients.

One of the metals being assessed is lead, a common contaminant of aquatic ecosystems and originating mainly in urban runoff (see EPA 2000c). Map 5.4 shows the concentrations of lead in sediments in the region. Even though it only shows lead concentrations, Map 5.4 provides a good indication of the overall status of sediment condition and the likely presence of a range of other contaminants.

Map 5.4: Lead in coastal waterways in the Sydney–Newcastle–Wollongong area

Source: University of Sydney, Environmental Geology Group data, as at 2002

Sediments containing high concentrations of lead as well as a wide range of other contaminants are found in extensive parts of Port Jackson, especially Homebush Bay, Hen and Chicken Bay, Iron Cove and Blackwattle/Rozelle Bay. Contaminant distributions show strong declining gradients away from stormwater canals at the heads of these bays. Bedload and stormwater in these canals also contain high contaminant concentrations, suggesting the majority of pollutants entering Port Jackson have land-based sources.

The study also found evidence of contamination in other areas. Table 5.7 summarises some of the results from the study.

Table 5.7: Sediment contamination in selected NSW water bodies

Source: University of Sydney Environmental Geology Group data, as at 2002

The University of Sydney Environmental Geology Group has more information on the study.

Lake Macquarie

At the request of the Premier's Lake Macquarie Taskforce, the EPA has investigated the concentration of metals in the lake sediment and any environmental and biological impacts from it.

The concentrations of metals in Lake Macquarie sediments fell significantly between 1985 and 1998. This reduction was most likely a result of lower pollution loads entering the lake and the input of less contaminated sediments from the catchment. Despite the decreases, the levels of cadmium, copper, lead, mercury, selenium, silver and zinc were found to be significantly above natural levels in the lake sediments.

The study found elevated levels of selenium, cadmium, lead and zinc in the tissues of adult fish from the lake. Of these, only selenium exceeded health guidelines for human consumption and the exceedences were small and at just one location. The rates of skeletal abnormalities in larval fish were higher in some contaminated areas of the lake compared with rates in populations from relatively unpolluted locations.

While these results show that trace metals are having an impact in some areas of Lake Macquarie, the study concludes that most of the ecosystem and biological effects are localised. There appears to have been little impact on the commercial and recreational fish stocks of the lake with most not affected by trace metal contaminants. The study also concurred with the NSW Health finding that there is little risk to human health from eating fish from the lake.

Sydney deep ocean outfalls

Sydney Water is required to monitor the impact of discharges from its deep ocean sewage outfalls on sediment and organisms living on the sea floor nearby. The outfalls discharge treated effluent from the North Head, Bondi and Malabar sewage treatment plants. The program's main aim is to assess whether there is a chronic environmental impact from the discharge and if so whether any impact is spreading. Sites are sampled and analysed for a range of metal and organic toxicants, particle size and benthos at 12 locations off the NSW coast between Terrigal and the Shoalhaven (AWT 2000).

Results indicate that the benthic communities around the outfalls remain abundant and diverse. Preliminary data also indicates that the concentrations of metals and organic contaminants in sediments are variable but generally very low. The highest concentrations of a number of constituents were found in sediment at North Head. These included polycyclic aromatic hydrocarbons, arsenic and some metals. No organochlorine pesticides were detected.

AWT 2000, AWT 2001a, AWT 2001b and SWC 2001 have more information on the monitoring program.

Response to the issue

Because many of the aquatic sediment contaminants originate from land-based activities, addressing point- and diffuse-source pollution is a vital part of their management. Water 5.3 and Water 5.6 discuss management of these pollutants.

Contaminated sites are generally dealt with case-by-case. Sometimes formal management mechanisms are established. The Lake Macquarie Project Management Committee, for example, was established in 2000 to implement the high-priority recommendations of the Premier's Taskforce Report over three years (see EPA 2000b). This involves:

• stabilisation of Salts Bay, construction of wetlands to improve stormwater quality and numerous foreshore rehabilitation projects
• monitoring programs providing data to identify problems and allow the completed works to be evaluated
• community education and public involvement in preparing management plans.

For information on managing contaminated land, see Land 4.6.

Effectiveness of responses

There is little information on the extent of sediment contamination in NSW or long-term trends. The Lake Macquarie results indicate that reductions in pollutant loads can improve sediment quality, so it may be the case that sediment contamination has been reduced in other areas where pollution reduction programs have been implemented, such as Sydney Harbour.

Future monitoring of Lake Macquarie will determine the effectiveness of the projects implemented and help to further improve its sediment and water quality. If successful, these may provide a guide for the management of other areas with sediment contamination.

Future directions

Reducing point- and diffuse-source pollution will be vital in preventing sediment contamination. Information on what can be done to help reduce point- and diffuse-source pollution is presented in Water 5.3. The Department of Infrastructure, Planning and Natural Resources, EPA, Sydney Catchment Authority, Sydney Water and Hunter Water have more information and advice on how to reduce the pollution of waterways.

A systematic documenting and identification of contaminated sediment sites would assist in the long-term management of potential health and ecological impacts.

Where contamination is found, the removal of affected sediment is likely to be impractical and may actually spread contamination or destroy important habitat. A reduction in pollutant loads is the most appropriate way to improve sediment quality. Once incoming pollutants are reduced, ecosystem health is likely to improve as contaminated sediments are gradually buried by subsequent depositions of less polluted sediments. However, to determine the effectiveness of measures to prevent contamination, further monitoring would be required.

Linked issues

2.1 Population and settlement patterns

4.1 Land-use changes

4.2 Soil erosion

4.6 Chemical contamination: land

5.1 Freshwater riverine ecosystem health

5.3 Surface water quality

5.6 Marine and estuarine water quality

6.6 Aquatic ecosystems

6.7 Aquatic species diversity

6.9 Aquatic harvesting