Toxic Effects of Pollutants on the Mineralization of Acetate in Methanogenic River Sediment

Abstract

The functioning of anaerobic bacteria in river sediments is vital for the stability of freshwater ecosystems. The sensitivity of these organisms for pollutants is therefore important for the establishment of valid sediment quality criteria. Acetate is a key intermediate in the carbon cycle and was chosen as a model substrate for the activity of anaerobic bacteria. The effects of pollutant on the anaerobic mineralization of acetate was studied in sediment microcosms. A small amount (0.7 mug/l) of 14 radioactive C labelled acetate was added to bottles with fresh anaerobic river sediment. The acetate was converted methane and 14 radioactive carbondioxide with a half-life of 0.2 - 0.5 hours. Adding a toxicant decreased the mineralization rate of acetate. The IC10 is defined as the concentration which decreases the mineralization rate of acetate with 10%. Addition of mercury or zinc did not inhibit the acetate mineralization. Benzene, pentachlorophenol, 1,2-dichloroethane and chloroform inhibited the acetate mineralization and showed IC10 concentrations of 480, 19, 0.7 and 0.04 mg/kg sediment respectively. Benzene, 1,2-dichloroethane and chloroform are usually considered to be narcotic toxicants and they have a low octanol water partitioning coefficient. The high toxicity of 1,2-dichloroethane and chloroform shows that these compounds do not exhibit minimum toxicity on bacteria under these conditions but perform a specific mode of action. This indicates that sediment quality criteria solely based on tests with aerobic organisms will not always be sufficient to protect the anaerobic processes in the sediment.<br>