Inorganic pollution of the sediments of 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. With the exception of chromium, the concentration of every metal investigated lies above the national trigger value for sediment quality at some point along the course of the river. The sediments of the headwaters exhibit high values of copper and zinc, although 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 at some locations far beyond the threshold for ecological damage. Several industrial sites are also 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 diluted by mixing with relatively uncontaminated deposits.