Contaminated sediments in the River Torrens, South Australia

The River Torrens plays a vital role in the economic, social and environmental life of South Australia. The river rises on the Adelaide Hills and flows west across the Adelaide Plains, bisecting the city of Adelaide and reaching the sea at the Gulf of St Vincent. The bed sediments of the Torrens were sampled from its headwaters to the coast and analysed for cadmium, chromium, copper, lead, phosphorus and zinc.

The sediments of the headwaters exhibit high values of copper, zinc and, to a lesser extent, lead. However, these probably reflect natural background conditions rather than pollution. By contrast, in the residential areas that dominate the Adelaide Plains, almost every site is contaminated by lead and zinc, some to well beyond the point of biological damage. Several residential sites, notably those downstream of the city of Adelaide, are also polluted by cadmium.

Within the industrial zone around the city, every site is contaminated by lead and zinc, with concentrations reaching values that are amongst the highest recorded in Australian aquatic environments. Several industrial sites are also badly polluted by cadmium and copper.

There are no national guidelines against which to assess the phosphorus content of the sediments. However, there is strong evidence that human activities have had a significant impact on phosphorus levels in the river. Major cyanobacterial blooms along the lower Torrens have been linked to the release of nutrients from the sediments and phosphorus concentrations in the water have reached dramatic levels.

Much of this contamination appears to be a consequence of past pollution practices. In particular, the severe pollution along the reach immediately to the west of the city may be largely attributed to the former concentration of metallurgical and chemical industries in that area. These problems are likely to persist indefinitely as modifications to the flow behaviour of the river mean that bed sediments are neither being moved downstream and flushed out of the system nor being diluted by mixing with relatively uncontaminated deposits.

The results of this study have received extensive media attention and have galvanised political activity, resulting in the formation of City and State bodies charged with addressing the problems of the pollution of the Torrens. There have also been criticisms of this work, notably from the Adelaide and Mount Lofty Ranges Natural Resources Management Board. Not a single one of these withstands considered examination and the results of the investigation arc fully vindicated.