METALS IN SEDIMENTS FROM THE STOCKHOLM REGION: GEOGRAPHICAL POLLUTION PATTERNS AND TIME TRENDS
The city of Stockholm is intersected and surrounded by water. Freshwater flows eastward and mixes with slightly brackish water in central Stockholm to finally reach the Baltic Sea. In order to estimate the magnitude and geographical impact of Stockholm as a source of metals to the aquatic environments, sediments from 117 stations in the Stockholm region have been analysed for metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn). This paper reports on the geographical pollution pattern and on the time trends in metal pollution in Stockholm during the 20th century. Stockholm is a strong source of Cd, Cu, Hg, Pb and Zn whereas the Cr concentrations are moderately perturbed. In contrast, the concentrations of As, Co, and Ni are in general close to preindustrial levels. The concentrations of Cd, Cu, Hg, Pb and Zn are highest in central Stockholm and eastwards (i.e., in the water flow direction). Sediments upstream of Stockholm and in lakes that are not hydrologically connected to central Stockholm show a significantly lower impact. This may be indicative of metals emitted in Stockholm mainly being transported by the water route. Of Cd, Hg, Pb, and Zn, Cd shows the most pronounced decline in accumulation rates over the last two decades.