PCB and DDT in laminated sediments from offshore and archipelago areas of the NW Baltic Sea

Temporal trend studies of PCBs and DDTs in two annually laminated sediment cores from the offshore NW Baltic proper and the Stockholm archipelago demo nstrate that studies of laminated sediments are useful tools for detecting time trends of HOCs. The concentration trends of PCBs and DDTs, on a dry we ight basis, from the two cores show quite large similarities to trends repo rted in pelagic biota from the NW Baltic proper, although the reduction in concentrations from the 1970s and onwards is approximately half of the redu ctions seen in biota. The sediment accumulation trend for these substances was not coupled to the concentration trend in biota but is closely linked t o climate-related erosion/resuspension dynamics. The gross accumulation rat e in the archipelago area proved to be 8 times higher compared to that of t he offshore NW Baltic proper (885 and 108 g m(-2) water area yr(-1), respec tively). Since PCB and DDT concentrations were similar in offshore and coas tal areas, and the burial rates of PCB and DDT were closely linked to gross accumulation rates, the sediment burial of contaminants in relation to wat er area was severalfold higher in the archipelago compared to the offshore area. The high burial of sPCB and sDDT in the archipelago indicated an impo rt of contaminants from the open sea to the archipelago. Although eutrophic ation-induced scavenging of contaminants may have occurred in the Baltic Se a, natural processes have obscured evidence of this.