Distribution and Characterization of PCBs in Lake Michigan Water

Polychlorinated biphenyls (PCBs) were measured in the water column of Lake Michigan at 28 stations. Distributions between dissolved and particulate phases were used to evaluate the partitioning behavior of PCBs. The average PCB concentration in Lake Michigan was 1.8 ng/L, corresponding to a total PCB burden of 8,900 kg. The average PCB concentration was significantly lower in open lake (1.2 ng/L) than in nearshore zone samples (3.2 ng/L). Concentrations in Green Bay were elevated compared to the rest of the lake. Variations in concentration with depth were small. The average log of the water-particle partition coefficient (Kp) was 5.9. Little dependence of Kp on particulate organic carbon was observed. A relationship was found between log Kp and log SPM (suspended particulate matter) concentration, perhaps reflecting association of a non-filterable fraction of the SPM with the aqueous phase. Selected PCB congener Kp and Koc (Kp × organic carbon weight-fraction) values were measured and related to congener Kow (octanol-water partition coefficient), yielding the predictive relationship log Koc = 4.2 + 0.34 log Kow. Congener log Kp values are predicted to range from 4.8 to 6.1, indicating that congener fates in the water column differ and are partly controlled by their physical chemical properties.