Chemical forms and distribution of heavy metals in core sediments from the Gdansk Basin, Baltic Sea

Short sediment cores (30 cm length) were taken along a transect of the Gdansk Basin from the mouth of the Vistula River out into the Baltic Sea in June 1996. The chemistry and mineralogy of surficial and buried sediments were determined and Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn were analyzed in total and in fractions using a sequential extraction procedure. The bulk and clay mineralogy of the sediments were determined by XRD and SEM. The concentrations of some of the trace metals in sediments are above pre-anthropogenic background. In particular, the surficial samples are substantially enriched in Cu, Pb and Zn, suggesting an anthropogenic origin. The concentrations of Cu, Pb and Zn range from 21-71 ^g-g"1, 56-210 ^g-g"1 and 21-83 ^g-g-1, respectively. Unexpectedly, the concentrations of trace metals increase seawards within the Gdańsk Basin. The forms of binding are different for each metal. Cobalt, Cr and Fe are mainly associated with the residual mineral fraction of the sediment, although in samples with high Fe concentrations there is a significant correlation with organic compounds. In contrast, Mn, Ni, Pb and Zn are predominantly associ­ated with oxides and the organic fractions, with a significant percentage associated with the carbonate and exchangeable cation fractions, whilst Cu is mainly bound with the organic fraction.