Abstract

 Surface sediments were sampled from 14 sub-areas along a gradient through the city of Stockholm, Sweden. Concentrations of five metals (Cd, Cu, Hg, Pb and Zn) were analysed using nitric acid leaching followed by ICP-MS analysis. The degree of contamination in each sub-area was then assessed in three different ways. First, the metal concentrations in each sub-area were compared to the sub-area with the lowest concentrations found up-stream or down-stream of the city. Second, the concentration was compared to "comparative values" suggested by the Swedish EPA, and classified according to their deviation from these values. Third, the metal concentrations ([Me]) in the 14 sub-areas were compared to "consensus based" threshold effect concentrations (TEC) and probable effect concentrations (PEC) found in the literature. According to this assessment the sediments of different sub-areas were predicted to be probably non-toxic ([Me]<TEC), possibly toxic (TEC<[Me]<PEC), or probably toxic ([Me]>PEC).
  The results indicate that there is cause for concern for all five metals. Comparing only with the lowest local values, Hg shows the highest elevation, followed by Cd and Pb. If the values are compared to the national comparative values and classified according to the guidelines provided by the Swedish EPA, Cu is the most elevated metal. This classification also indicates extensive Zn contamination in the area. This may indicate that the whole Stockholm area has elevated Cu and Zn levels compared to the general situation in Swedish lakes, suggesting that these metals may be considered as "urban metals".
  Comparing measured concentrations with effect-based sediment quality guidelines found in the literature there is clear indication that in the central parts of the city, all metals except Cd are found in concentrations that probably cause harmful effects on biota. The most widespread toxicity is found for Cu and Pb, followed by Zn.