TA7 Bioaccumulation and Kinetics of POPs
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8:00 AM - 12:00 PM, Tuesday

() The Importance of the Microbial Loop in Bioaccumulation of PBTs.

Swackhamer, D1, Hudson, M1, Cotner, J1, Muir, D2, 1 University of Minnesota, Minneapolis, MN, USA2 National Water Research Institute, Environment Canada, Burlington, Ontario, Canada

ABSTRACT- Current food web models of bioaccumulation of persistent, bioaccumulative toxic chemicals (PBTs) do not include the microbial loop, despite its importance in carbon transfer in many aquatic systems. This is largely due to the lack of studies of bioaccumulation of PBTs in bacteria and the difficulty of isolating this part of the food web for PBT analysis. As much as half of the carbon that moves through food webs may move through the microbial loop, with DOC being consumed by bacteria which are then consumed by dinoflagellates. These are consumed by ciliates which are then consumed by other zooplankton within the pelagic food web. The importance of the microbial loop to carbon dynamics increases with increasing oligotrophy. We have shown in the laboratory that natural populations of Lake Superior bacteria readily take up PBTs and that the contaminants reach equilibrium in about 24 hrs. We have also collected field samples from Lake Superior, and the log organic-carbon normalized bioaccumulation factors for PCBs of 7.2 are consistent with the lab studies and are greater than the bioaccumulation factors to phytoplankton. The microbial loop may increase the transfer of contaminants to higher trophic levels in oligotrophic vs eutrophic systems, and should be incorporated in bioaccumulation models.

Key words: PBTs, bioaccumulation, microbial loop, Lake Superior

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