Precipitation scavenging of polychlorinated biphenyl congeners in the great lakes region

Ten precipitation events were sampled in the fall of 1986 in Madison, WI and analyzed for individual congener and total polychlorinated biphenyl (PCB) levels in both the dissolved and particulate phases. Total PCB concentrations were generally at the lower end of ranges recently reported for precipitation. Operationally defined dissolved and particulate phase congener distribution patterns for the two events of highest concentration were qualitatively similar to gas-phase and particle-bound patterns for northern Wisconsin air samples. Higher than predicted dissolved-phase concentrations may indicate non-equilibrium processes during scavenging and/or sample processing, the presence of colloids and micro-particulates, and/or more efficient gas-phase transfer to hydrometeors with organic coatings. Observed organic carbon-normalized distribution coefficients increased slightly with increasing octanol-water partition coefficient, giving the relationship log K_oc = 0.22 log K_ow + 4.64. The data indicate that a third organic-rich colloidal phase could be influencing partitioning, and could explain the higher than expected apparent gas scavenging efficiency for PCBs from the atmosphere. Precipitation-weighted mean fluxes of PCBs in the dissolved and particulate phases were 1.2 and 1.4 μg m^-2 year^-1, respectively, indicating that precipitation remains a significant source of PCBs to the upper Great Lakes.