Phasing out cadmium and lead--emissions and sediment loads in an urban area

This paper examines how fluxes in the aquatic environment reflect the reduced use of cadmium (Cd) and lead (Pb) in Stockholm, Sweden, between 1975 and 1995. The sediment deposition of Cd and Pb in the waters around Stockholm was investigated using laminated sediment cores, which facilitated reconstructions of historical annual metal deposition to the sediments. The resulting reconstructions were compared to independent estimations of the emissions to the aquatic environment during the phase-out period. The loads of Cd and Pb from sewage treatment plants, storm water and in atmospheric deposition were studied using literature data. The data set indicates a reduced load of Cd and Pb on the aquatic surroundings of Stockholm. The reduction is, however, not as pronounced in the sediment deposition as in the calculated emissions. This indicates that emissions may be delayed on their way to the sediments or that there are other sources, e.g. resuspension of older sediments. It is therefore argued that sediment investigations are an essential component in environmental monitoring, in order to get a complete picture of the metal fluxes to and in the environment in urban areas.