Assessing the ecological significance of contaminants in sediments
The CSIR, in partnership with the Engineer Research and Development Centre of the United States Army Corps of Engineers, is evaluating the use of various approaches to assess the ecological risk posed by the dredging and disposal of contaminated sediment, using the Victoria and Alfred Basins in the Port of Cape Town as a case study.
The research findings will be used to advise the Department of Environmental Affairs, which is responsible for regulating the disposal of dredged material in South African marine waters, as well as Transnet National Ports Authority, which manages South African ports, on tools that can be used in the short- and long-term to determine if sediment identified for dredging in South African ports is of a suitable quality for disposal offshore, and to identify ecological risks associated with various management options.
Dredging is an excavation activity that involves gathering underwater sediment to keep waterways navigable or to enlarge existing shipping channels or terminals where ships load and unload. Typically the sediment is disposed of at a different location.
Various forms of physical, chemical and biological evidence were used to assess the quality of sediment in the basins and the ecological risk posed by sediments and its simulated dredging and disposal.
Bottom sediment collected at 12 locations across the Victoria and Alfred Basins was analysed for a wide range of potential chemical contaminants, including metals, oils, pesticides and polychlorinated biphenyls. The toxicity of the sediment and particles were tested under controlled conditions in the laboratory, using amphipods and mysids (two types of small shrimp-like crustaceans that are sensitive to water pollution).
The structure and composition of the organisms that live in or on the bottom of sediments were also evaluated. The relationship between sediment contaminant concentrations, toxicity and the structure and composition of the organisms that live in or on the bottom of the sediment will be used to determine if the various tools provide complementary information.
Dr Brent Newman