Distribution of individual chlorobiphenyls (PCB) in solution and suspension in the Baltic Sea

Single and multidimensional GC-ECD techniques were applied to determine individual chlorobiphenyls (CBs) in solution and in suspended particles in the Baltic Sea (some data were also obtained for the adjacent German Bight in the North Sea). Large volumes (up to 1100 dm3) were analysed in transects in November 1988 and 1989 and in spring 1991. Salinity and temperature were measured continuously along the sampling tracks in all three cruises; nutrients and pH only in the latter two cruises. Concentrations of individual CBs in solution were in the sub- and low pg dm−3 range (detection limit being 0.05 pg dm−3), and of their sum between 2 and 237 pg dm−3. These concentrations are considerably lower than previously reported data. This is mainly the result of the elimination of contamination and interference problems in the sampling, clean-up and GC-ECD procedures. It may also partly reflect the reduction in the production and use of PCBs in the last decade. The highest concentrations in solution originated from local sources in the Belt Sea and the Gulf of Finland. Regional differences were found for the compositions of the CB mixtures in solution. The lowest concentrations of CBs in solution were found in areas and periods of plankton production (spring 1991), with ΣCB concentrations between 2 and 14 pg dm−3. The compositions of the CB mixtures showed regional differences in each cruise. These could be interpreted in terms of mixing between different water bodies. The classification of transects on the basis of these CB patterns agreed well with the distinction of water bodies on the basis of T-S diagrams and hydrochemical data. Concentrations of individual CBs in suspension were generally 0.1–0.5 pg dm−3, those of their sum (ΣCB) between 4 and 6 pg dm−3 during the autumn cruises. Extremely high values were found in the Belt Sea-Kattegat area in spring 1991 (up to 589 pg dm−3 for individual CBs and up to 2859 pg dm−3 for ΣCB). This probably reflects the uptake of CBs into particulates during a plankton bloom. Primary production may effectively remove CBs from the water column into the sediments. The amounts of chlorobiphenyls presently stored in the sediments of the Baltic Sea exceed the amounts in the water column by several orders of magnitude. The compositions of the CB mixtures differed considerably between solution and suspension. The relations between log K′d (apparent particle/water partition coefficient) and log Kow (octanol-water distribution coefficient) suggest the existence of (quasi-)equilibrium conditions in autumn. Deviations from this behaviour arise from biological activity in spring. The contribution of toxic congeners to the CB mixtures was dominated by the mono- and di-ortho-Cl substituted derivatives of the most toxic non-ortho-Cl CBs. The toxicity of the CB mixtures in solution was between 0.01 and 12fg dm−3 TEQs (TCDD toxic equivalents). CBs-77, -118, -105 and -156 had the largest contributions to TEQs.