Vertical flux and particulate/water dynamics of polychlorinated biphenyls (PCBs) in the open Baltic Sea

Concentrations of PCBs in water (dissolved), suspended particles (SPM), sediment trap material, and sediments in the Baltic Sea are discussed in relation to the dynamics of organic carbon and lipids as the sorbing matrices. Both carbon- and lipid-normalized concentrations of PCBs in SPM increase during the sedimentation giving rise to an increase in observed log K-oc with more that one order of magnitude for most of the studied PCBs. It appears that hydrophobic organic compounds (HOCs) are retained within the settling particles while the organic carbon and the lipids are degraded, rather than there being a continuous uptake of PCBs during settling. However, the explanation for the high concentration maintained in the sediments over long time periods, must be an increasing capability of the organic matrix to sorb HOCs during the ageing process. The results are of importance for current models of the fate of HOCs in the environment and imply that the use of a single equation to estimate equilibrium concentrations of HOCs in SPM may significantly underestimate concentrations in settling particles.