Mobility of trace metals in retention pond sediments

This paper presents the results of a study on trace metal mobility in the sediments of several road and urban infiltration/decantation ponds in France; the trace metal concentrations are indeed high. The potential mobility of trace metals (cadmium, nickel, chromium, copper, lead and zinc) was evaluated by application of the sequential extraction BCR protocol. Results have been compared with those from the IHSS protocol, which allows for the extraction of various forms of organic matter. Cadmium is the most easily exchangeable element in the case of variations in physical-chemical conditions (50% to 60% of Cd is exchangeable and 70% to 80% of Cd remains within the fulvic acid fraction) and is thus easily releasable within an acidic medium. Zinc is also potentially mobile and stays mainly concentrated in fulvic acids, except in the case of the Ronchin sediment (more than 50% in humin). In contrast, nickel and chromium are primarily present in the residual fraction and do not exhibit high mobility. Copper and lead are concentrated in both the humic acid fraction (IHS5 protocol) and the organic phase (BCR scheme); consequently, their mobility is limited.