OCCURRENCE, SEDIMENTATION, AND SPATIAL VARIATIONS OF ORGANOCHLORINE CONTAMINANTS IN SETTLING PARTICULATE MATTER AND SEDIMENTS IN THE NORTHERN PART OF THE BALTIC-SEA

Sediment trap sampling of settling particulate matter (SPM) was carrie d out in remote coastal and offshore stations in the Bothnian Bay (BB) and the Bothnian Sea (BS) located in the northern Baltic Sea. This wa s done to investigate occurrence, composition profiles, sedimentation, and spatial differences of PCBs, HCHs, hexachlorobenzene, DDTs, chlor dane compounds, and dieldrin. The contamination load at the coastal st ations was compared to that of surface bottom sediments. At one coasta l station, sediment samples were collected in two different seasons (a utumn and spring) in order to compare seasonal variations. Ail compoun d groups were found in the SPM and sediment samples analyzed. The cont aminant concentrations in SPM at the coastal stations ranged, on dry w eight basis, from 0.41 to 8.6 ng/g for chlordanes and HCHs and at the offshore stations from 3.2 to 31 ng/g for hexachlorobenzene and PCBs. The levels in SPM at the offshore stations were 10 limes higher (on th e average) than the coastal stations, likely because of an increased c arbon content in the offshore SPM. The profiles of compounds in SPM re flect the corresponding sediment profile, and only small differences i n concentrations and profile of compounds between autumn and spring su rface sediments were observed. A comparison between the BS and the BE for offshore and coastal stations showed that the concentrations of co mpounds were similar although the sedimentation of contaminants, estim ated by down fluxes collected in the sediment traps per unit of time, was 3-5 times higher in the BS than the BE. The total annual sedimenta tion volume of PCBs was approximately 1.1 ton/yr in the BS and 0.4 ton /yr in the BE. An extrapolation to total sedimentation of PCBs during 7 year in the whole Baltic Sea resulted in an approximate value of 7 t on/yr.