Uptake Processes of Polychlorinated Biphenyls at the Base of the Pelagic Food Web

Sammanfattning: Hydrophobic organic contaminants (HOCs) are persistent, toxic to biota and are known to bioaccumulate in food webs. In this thesis, polychlorinated biphenyls (PCBs) were used as model compounds to study the fate and transport of HOCs in the aquatic environment. PCBs are transported globally and are found in environmental matrices far from their main sources. The Arctic Ocean is no exception, and bioaccumulation of PCBs in Arctic ecosystems has been the focus of much concern. There is however still limited knowledge of the actual seawater concentrations of PCBs in the central Arctic Ocean. The transfer from water into the organic carbon of phyto- and zooplankton constitutes a major pathway of HOCs into aquatic food webs. However, from previous studies it remains unclear whether PCB concentrations in plankton are mainly governed by kinetic processes or by passive partitioning with surrounding water.The main objectives of the thesis were to i) evaluate the sampling step in the total analytical process of determining seawater concentrations of PCBs, ii) test the hypothesis of a northward latitudinal fractionation of PCBs and an effective transport to the Arctic, iii) determine PCB seawater concentrations in the central Arctic Ocean and iv) study the uptake of PCBs in phyto- and zooplankton by investigating the relative importance of passive partitioning versus kinetic processes such as growth dilution and biomagnification. Field samples were collected in the open Baltic Sea, the Arctic Ocean, the Gullmar Fjord on the Swedish west coast and along a transect from the Norwegian Sea to the Arctic Ocean (62°N – 89°N).From results presented in this thesis, it can be concluded that variations in PCB seawater concentrations exceeding 40-50 % may be interpreted as natural variations not stemming from the sample handling. Following protocols of ultra clean sampling and clean up procedures, seawater concentrations in the central Arctic Ocean could be determined. Concentrations of PCB 52 varied between 70-260 fg L-1 and PCB 180 between 12-15 fg L-1, north of 85°N. Concentrations generally decreased along a northward transect (62°N – 89°N), while the relative contribution of less chlorinated PCB congeners to the total PCB amount increased with latitude, in support of latitudinal fractionation of PCBs during atmospheric transport. Several studies in this thesis presented support for that the uptake of PCBs in phyto- and zooplankton may be described by equilibrium or near-equilibrium partition models, based on large field data sets from different seasons with varying biogeochemical parameters. Thereby, previous hypotheses of kinetic limitations (such as growth dilution) in phytoplankton or biomagnification in zooplankton were not supported. These results may have implications for food-web models, which may reduce the complexity in parameterizations of HOC concentrations in both phyto- and zooplankton.