Geochemistry of Iron, Sulfur and Related Heavy Metals in Metal-Polluted Taihu Lake Sediments*1

To understand the geochemical characteristics of iron and sulfur and the extent of iron-sulfide minerals influencing heavy metal behaviour in metal-polluted sediments of Taihu Lake, two sites, in Meiliang Bay (ML) and Wuli Lake (WL), were selected to study the fractionation of iron, sulfur and related heavy metals. There were relatively high concentrations of Fe2+ and low concentrations of total S2− in porewaters, indicating that conditions in these sediments favored iron reduction. The concentrations of acid volatile sulfides in sediments were 1.9–9.6 μmol g−1 at ML and 1.0–11.7 μmol g−1 at WL, both in the range of values detected in unpolluted lakes. Pyrite-S was 10.2–49.4 μmol g−1 at ML and 10.3– 33.0 μmol g−1 at WL, accounting for more than 69% of the reduced inorganic sulfur at both sites. The low degree of sulphidization (< 14%) and pyritization (< 10%) indicate that sulfate may be the limiting factor for pyrite formation. The extractability of Mn, Cu, Pb, Zn, Ni, and Cr in sediments all suggest that sulfides are not the major binding phase for these metals during early diagenesis. Sulfur may play a modest role in the geochemistry of iron and traced metals in the sediments.