Metal-sulphide formation in the contaminated anoxic sludge of the Venice Canals

The transformations of different anthropogenic heavy metal compounds exposed to anoxic conditions in the contaminated sludge of the Venice canals have been investigated in detail by SEM/EDS. Macroscopic metal wastes and heavy-weight micro-particles, including authigenic Fe-sulphides and fragments of metal alloys, were isolated from the sludge and analyzed. The analyses emphasize the importance of Fe-sulphides as end-products of Fe diagenesis and their role as heavy metal scavengers in anoxic environments. The possible formation of other discrete metal-sulphides in some particular microenvironments was further demonstrated by the transformations observed on specimens of Cu, Zn and Sn alloys.