5.7 Contamination of sediments
A combination of past industrial activities and continuing stormwater inflows has contaminated sediments in some areas of NSW.
Some waterways in the Sydney Region contain sediments with elevated concentrations of a number of contaminants. Surveys of Sydney Harbour have detected levels of dioxin exceeding human health and safety guidelines for the consumption of fish and prawns. The origin of the contaminants is former industries adjacent to Homebush Bay on the Parramatta River.
The full extent of sediment contamination in NSW is unknown.
Status of indicator
Status: Historical industrial sources of much sediment contamination have ceased. However, stormwater and sewage are ongoing sources.
Trend: The rate of sediment contamination is thought to be falling, but there is insufficient information to assess the trend.
Information quality: Sites of known contamination have moderate data, but statewide data is lacking, leading to an overall poor rating.
Response(s): Fishing restrictions have been implemented in response to high levels of dioxin in Sydney Harbour, and sources of contamination are being rehabilitated.
Sediment contaminants can enter aquatic ecosystems from point sources, such as sewage treatment plants, intensive agriculture, mining, manufacturing and other industries; diffuse sources, including stormwater runoff from rural and urban areas; and contaminant spills and incidents (see Land 4.6). Contaminants from these sources can include a wide range of metals, organic compounds (such as pesticides) and nutrients, many of which readily accumulate in aquatic sediments where they can remain or be recirculated, depending on conditions. These sediments can therefore act as a source of further contamination while also behaving as a 'sink' of existing and past pollution (see EPA 2000a).
Stormwater runoff from urban areas can be a significant source of a range of toxicants to urban waterways, such as heavy metals (including lead, copper, zinc and cadmium) and organic contaminants (including hydrocarbons and various biocides). Studies investigating the ecological significance of these pollutants in urban streams have produced mixed results, although longer-term studies have more consistently demonstrated the toxic effects of urban runoff on instream animals and plants. These effects are likely to be exacerbated by the increased frequency of flows from storm events in urbanised catchments, compared to rural or undeveloped catchments. The accumulation of these contaminants within the sediment of lakes, estuaries and other 'standing' waterbodies is also an issue of concern (Walsh et al. 2004).
Contaminated sediments can have significant impacts on aquatic ecosystems. The most serious impacts occur when contamination makes the sediments toxic to organisms. 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 to 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 2000a).
Contaminants from sediments can also accumulate in aquatic organisms that may be consumed by other organisms, including humans, with effects on ecosystem or human health. For more information on sediment contamination, see EPA 2000a.
There is no integrated framework for the collection of data on sediment contamination in waterways across NSW. SoE 2000 and SoE 2003 described studies in Sydney Harbour and Lake Macquarie (EPA 2000c; DEC 2003). However, there has been no significant large-scale sampling of contaminants in sediments for the purposes of assessing environmental condition. There is emerging concern overseas about many newer classes of compounds resulting from the increased production and use of brominated flame retardants (polybrominated diphenylethers), antibacterial products (triclosan) and additives to paint and pharmaceuticals (perfluorinated compounds similar to Teflon® and Scotchgardâ„¢) that are being found in sediments and may cause ecosystem or human health impacts. The recent findings of elevated concentrations of dioxin in the blood of Sydney Harbour fishers and their families illustrates how compounds thought previously to be confined to the sediments can enter the food chain.
Current status and trends
A recent survey of dioxins in sediments found levels ranging from 0.002 to 520 picograms of toxic equivalent units per gram (pg TEQ/g) dry weight across Australia (Gatehouse 2004). A picogram is 10–12 grams, and TEQ units indicate the total toxicity of similar but variously toxic compounds that are measured or modelled together. The highest levels were found in the lower Parramatta River (up to 520 pg TEQ/g) at Silverwater and the western section of Port Jackson in Sydney (up to130 pg TEQ/g). Similar levels of dioxin were found in a survey of seafood in the Parramatta River funded by NSW Maritime, except that samples collected east of Gladesville Bridge (outside the prohibited fishing zone) also showed high levels of dioxin (NSW Food Authority 2006). This project was designed to provide baseline data for assessing the effectiveness of the remediation work at Homebush Bay that began in 2006.
Several smaller studies have examined the impacts of contaminated sediment, based on previous sediment quality work. As reported in SoE 2003, a University of Sydney research group has described patterns of contamination in Sydney Harbour. The same group has since undertaken a large-scale study to evaluate standard sediment assessment procedures (ANZECC & ARMCANZ 2000) using sediments from Sydney Harbour and other places in NSW. Results from Sydney Harbour indicate that sediments are toxic at guideline levels, but not all tests were equally effective at detecting toxicity.
Every three years, Sydney Water Corporation monitors the impact of deep ocean sewage outfalls on the sediments and benthic organisms of the Sydney coast. This long-term program aims to assess the potential for impacts from the discharge of treated sewage and to determine whether the impact is spreading due to sediment remobilisation. An abbreviated study, covering a subset of chemical and biological tests, is conducted in the intervening two years. A major three-year study was completed in 2005. The results indicate that benthic macroinvertebrate communities remain diverse and abundant, and there is no obvious build-up of contaminants in sediments around the outfalls (SWC 2005).
The NSW Environmental Trust funded a study to develop procedures for measuring the risk posed by metal-contaminated sediment (DEC 2005d). Work included studying metal uptake by sediment-dwelling organisms and developing new testing procedures. This work formed the basis for a new guidance manual (Simpson et al. 2005).
Response to the issue
Based on the findings about dioxin in Sydney Harbour, NSW Department of Primary Industries imposed a ban on commercial prawn harvesting in the harbour in late 2005 and banned all commercial fishing in early 2006. Up to $5 million is being spent in 2006 to buy out commercial fishing businesses from Sydney Harbour. Recreational fishing has not been banned, but fishers are advised to limit their consumption of seafood from the harbour. Further testing on a range of fish species in different parts of the Harbour is underway to assess the extent of the contamination.
As part of the response to dioxin contamination in Sydney Harbour, the NSW Government committed $21 million in 1997 towards a remediation program for contaminated sediments in Homebush Bay.
There is a need for an integrated and systematic framework for monitoring and research into sediment contamination in waterways. The framework or program should target known areas of contamination and is needed to develop programs for the protection of human and ecosystem health.