Ni, Cu, Zn, Cd and Pb in sediments in the city-centre of Stockholm, Sweden Origins, deposition rates and bio-availability

A study on the sediments in the city centre of Stockholm was undertaken in August and September 2010. This study had three aims: *To estimate yearly fluxes of the metals Ni, Cu, Zn, Cd, Ba, Sb and Pb to the sediments in the city centre of Stockholm. *To estimate the flows of the metals Ni, Cu, Zn, Cd, and Pb to the sediments in the city centre of Stockholm from the important sources in the city: atmospheric deposition, storm water runoff from buildings and other infrastructure including roads, and WTPs.*To assess the bioavailability to the benthic organisms of the metals Cr, Ni, Cu, Zn, As, Cd and Pb dissolved in the sediment pore water. The bioavailability was defined according to the SEM/AVS (Simultaneous extraction of metals/Acid volatile sulphur) ratio. The conclusions from the study were: The concentrations of Cu in the water samples from both Lake Mälaren and Saltsjön are below the PNECs derived by the chronic Cu BLM (EURAS version 109), MEC/PNEC = 0.04 to 0.3. The sediments in both Lake Mälaren and Saltsjön the city centre of Stockholm is far from toxic with regards to pore water concentrations of the metals Cr, Ni, Cu, Zn, As, Cd and Pb according to the SEM/AVS method.Differences in surface sediment concentrations for the metals Ni, Cu, Zn, Cd and Pb between the sediments in freshwater Lake Mälaren and brackish water Saltsjön can be explained by a combination of differences in local sources and differences in metal speciation. The surface sediment concentrations of Cu and Zn have decreased since 1996 in both Lake Mälaren and Saltsjön in the city centre of Stockholm. The surface sediment concentrations of Cd and Pb have decreased since 1996 in Lake Mälaren in the city centre of Stockholm. Direct runoff of roads can make up a major portion of the Cu and Zn that is buried in Lake Mälaren sediments in the city centre of Stockholm. The effluents from the WTPs can make up significant parts of the Ni, Cu, Zn and Cd that is buried in the sediments in Saltsjön in the city centre of Stockholm. However, the locations of the measured sediment fluxes in relation to the discharge points of the WTPs indicate that this is not the case. Runoff of copper-roofs can only be an insignificant source of Cu to the sediments in Lake Mälaren and Saltsjön in the city centre of Stockholm.