Mobility of 2,2',5,5'-tetrachlorobiphenyl in model systems containing bottom sediments and water from the lower Fox River, Wisconsin

Sediment-water partitioning and diffusive transport of 2,2',5,5'- tetrachlorobiphenyl, PCB congener IUPAC 52 (TCB52) were examined in laboratory experiments with sediments from two sites in the lower Fox River, Wisconsin. Native water was pumped at controlled flow rates through cells containing sediments amended with a known activity of carbon-14-labeled TCB52. Concentrations of TCB52 in water and sediments were determined by liquid scintillation measurements of carbon-14 activity. Sediment-water partitioning was independent of flow rate for rates up to 8 m/d. Distribution coefficients (K(d)) and soil-sorption coefficients (K(oc)) were found to be at maximum levels 5-10 cm below the surface, despite an absence of significant variation in the fraction of organic carbon (f(oc)) through the same profile. Other factors, such as the effects of colloids and microbial activity in the sediments, are likely to be important in controlling the PCB distribution. Log K(d) and log K(oc) ranges were 4.1-4.9 and 5.3-6.1, respectively, and calculated effective diffusivities at the sediment-water interface ranged from 3 to 8 x 10-10 cm2/s. Gradual increases with time in TCB52 concentrations in the water phase, possibly due to effects of microbial activity, were observed. Diffusion experiments and models showed that the TCB52 migration rate within the sediment column is 8-9 mm/yr.