Oxidation of Anoxic Soils and Sediments: How Can We Evaluate the Risk of Heavy Metal Release?;pp. 77-101
Authors: (Cappuyns Valérie, Swennen Rudy, European University College Brussels (HUB), Centre for Corporate Sustainability, Brussels, Belgium, and others)
Abstract: The understanding of the behaviour and fate of contaminants in soils, sediments and dredged materials is essential to deal with their management. In the present study, heavy-metal contaminated anoxic soils and sediments originating from different locations in Belgium were exposed to oxidizing conditions during 8 to 20 weeks. The possibility of predicting and quantifying the evolution of porewater composition during sediment ripening, based on relevant physico-chemical properties and based on the results of leaching tests and/or rapid oxidation tests („resuspension experiment‟), was assessed. In general, for all the samples studied, pH was the most important factor explaining heavy metal release during oxidation. Clay-rich samples mostly displayed a higher acid-neutralizing capacity than sandy samples, which resulted in a less important pH-decrease during oxidation and a more limited release of heavy metals. The release of heavy metals was not related to their total content as higher metal concentrations were sometimes released into the porewater from sediments with a lower total metal load. Additionally, other factors, such as the precipitation of Fe-(hydr)oxides or the formation of secondary minerals influenced heavy metal concentrations measured in the porewater. In the resuspension test, the oxidation rate increased with a factor of 4 to 10 compared to the „normal‟ oxidation. Nevertheless, the patterns of metal release and the evolution of sediment properties (e.g. pH) were similar in both types of oxidation experiments, so that the resuspension test can be used to predict heavy metal release from contaminated sediments.