Eutrophication increases the association of PCB to dissolved organic matter in marine microcosms

Partitioning of 14C-2,2′,4,4′-TCB (tetrachlorobiphenyl) between sediment, and water and suspended particles was studied in eutrophic and oligotrophic benthic microcosms, respectively. Microcosms consisted of glass aquaria with homogenized clay sediment, circulated with natural seawater (60 m, 34‰). Organic enrichment in the eutrophic treatment was obtained by adding a phytoplankton culture of the marine diatom Phaeodactylum tricornutum into the water column; the oligotrophic aquaria received only filtered seawater. 14C-TCB was added to the water using a generator column technique. Phytoplankton and TCB were continuously added during an exposure phase of 8 days, followed by a semi-static phase in which TCB and phytoplankton were left to equilibrate and sediment during one month. Presence of phytoplankton induced a higher concentration of TCB in the water column. Higher concentration of TCB in the water was not caused by higher amounts of TCB bound to algal cells but due to an association of TCB with an increased production of dissolved organic matter and bacteria in the eutrophic treatment. TCB concentration in the sediments was not significantly different between treatments. The observed partitioning of TCB between water and sediment was in accordance with a predicted distribution, based on the equilibrium partitioning model.