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TA7 Bioaccumulation and Kinetics of POPs
() Partitioning of PCBs between water-phytoplankton and water-zooplankton; two field studies supporting equilibrium partitioning.
Sobek, A1, Gustafsson, Ö1, Hajdu, S2, Larsson, U2, 1 ITM, Stockholm University, Stockholm, Sweden2 Dep. Systems Ecology, Stockholm University, Stockholm, Sweden
ABSTRACT- In order to accurately predict the fate of hydrophobic organic contaminants (HOCs) and particularly their uptake into the base of the aquatic food web, the HOC water-plankton distribution needs to be understood under realistically varying ecological and biogeochemical conditions. From previous laboratory and field studies it remains unclear whether partitioning of HOCs to phytoplankton from water is kinetically limited or may be treated as an equilibrium process. It also remains unclear whether the concentrations of HOCs in zooplankton are determined by biomagnification or a passive diffusive uptake from the surrounding water. Here, we report on the partitioning of polychlorinated biphenyls (PCBs) to particulate organic carbon (POC) in two different field studies; i) POC of three different sizes relevant of zooplankton (20-200m, 200-500m, >500m) along a transect in surface water of the Arctic Ocean, and ii) POC dominated by planktonic primary production in the open Baltic Sea during a 25-month study. Preliminary data of PCB levels in zooplankton in the Arctic Ocean showed a significantly linear relationship between the extractable organic carbon normalized partition coefficient (log Keom) and log Kow, indicative of an uptake dominated by passive equilibrium with the surrounding water and not biomagnification. Data for the Baltic Sea study was collected monthly and at all 21 sampling occasions the log Koc (organic carbon normalized) − log Kow regression was significantly linear, despite a large variation in biogeochemical parameters such as POC concentration and composition, primary production and phytoplankton species composition. This data strongly suggest that partitioning of PCBs to POC in temperate surface waters is equilibrated and therefore not kinetically limited by factors such as rapid phytoplankton growth rate or large cell size. The partitioning of PCBs to the POC was described throughout seasonal cycles by log Koc = 0.88±0.07 log Kow + 0.90± 0.47 (95% confidence interval).
Key words: partitioning, PCB, phytoplankton, Koc
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