Geochemistry of Priority Pollutants in Anoxic Sludges: Cadmium, Arsenic, Methyl Mercury, and Chlorinated Organics

Abstract

It has been stressed in the preceding chapter on the ``Assessment of metal mobility in dredged material and mine waste by pore water chemistry and solid speciation'' that redox change of the sludges is one of the most important factors controlling pollutant mobility. Thus, particular attention will be given to the question whether anoxic conditions alone are suitable for long-term retention of pollutants. However, such an evaluation even on the limited number of priority pollutants will be beyond the scope of this book. Thus, it has been decided to present case studies on some of the most important pollutants covering a broad range of characteristics, pathways and fates within natural environments: the trace metal cadmium, the trace metalloids arsenic and mercury with the latter in its methylated form, and the group of xenobiotic organic chemicals such as PCBs have been selected to be treated within this review. This is due to (1) their highest pollution potentials in terms of accumulation, toxicity and ecological risk index (Håkanson 1980) among all pollutants discovered to date; (2) their quite different, but well-investigated properties and behaviour as to sediment-water systems; and last not least (3) their citation in every priority pollutant list known to the author. Thus, as to the four different groups of pollutants and the wide variety of other pollutants for which they stand, this brief review will be well suited for an evaluation of the secondary pollution impact of typical anoxic dredged sludges and mine tailings introduced into aquatic systems.