Metals in sediments and suspended matter of the river Elbe

Abstract

The metal content in surface sediments (0–2 cm, 13 samples), in a sediment core (50 cm, 1 cm slices), and in suspended particulate matter (SPM, > 0.4 μm, 28 samples) taken from an 88-km long section of the non-tidal Elbe river was investigated. Very high (Hg), moderately high (Cd, Cr, Cu, Zn) and slightly enhanced levels (Co, Pb, Ni) were found. By normalisation of the metal contents in the surface sediments using the organic carbon and Al as reference elements, the variability in the data set could be reduced nearly to the analytical level of errors. Except for Cr, the percentage of the total contents, extracted by dilute acid (0.5 N HCl) always exceeded 50% (Cd, Co, Fe) or even 80% (Cu, Mn, Ni, Pb, Zn). This may reflect both the anthropogenic origin of those metals and a high potential for their remobilisation. The SPM was enriched by a factor of 1.5-4 times in metals with respect to those in surface sediments. This was most pronounced for Cd and followed the order Cd > Zn = Pb > Cu = Mn > Fe = Ni. The profiles of some metals (Zn, Cr, Cu, Pb, Cd, Ni) obtained from the investigated core showed a distinct increase of the metal contents at depths below 22–23 cm. This is discussed in relation to possible changes in the metal load caused by the uranium industry in the former GDR. Provided such an explanation holds true, the sedimentation rate would be between 3 and 4 cm/year. The profiles of Cd and Mn are discussed with regard to redox mediated mobilisation and accumulation processes, respectively.