Remobilization of polychlorinated biphenyl from Baltic Sea sediment: comparing the roles of bioturbation and physical resuspension.

The release of a [¹⁴C]-labeled tri-chloro-biphenyl compound ([¹⁴C]PCB 32) from sediment to water was quantified weekly in a 30 d microcosm experiment with re-circulating water. Two modes of bioturbation-driven PCB release: 1) bioturbation by the amphipod Monoporeia affinis (a particle bio-diffuser) and 2) bioturbation by the polychaete Marenzelleria sp. (a bio-irrigator) were compared to the PCB release caused by physical sediment resuspension generated by a motor-driven paddle, used twice a week. Bioturbation by the amphipod M. affinis caused a significantly higher remobilization of both particle-associated (PCBpart) and dissolved PCB (PCBdiss) than the other treatments. Bioturbation by Marenzelleria sp. and physical resuspension caused a similar release of PCBdiss despite a significantly higher amount of total suspended solids in the water column after physical resuspension. In all treatments, the release of PCBdiss was more than one order of magnitude higher than of PCBpart, indicating a significant potential exposure route to pelagic organisms, such as fish, of the most bioavailable PCB form. Calculated mass transfer coefficients (0.3-1.3 cm/d) correspond to previously reported values for tri-chlorinated PCBs. Results from this experiment indicate that biological reworking of sediments can be just as, or even more, important than physical resuspension for the remobilization of sediment-bound contaminants.