Horizontal and Vertical Distribution of PCBs in Southern Lake Michigan Sediments and the Effect of Waukegan Harbor as a Point Source

The spatial distribution of PCBs in southern Lake Michigan sediments was obtained from the analysis of 66 box cores and 8 grab samples. PCB concentrations in surficial sediments were closely related to sedimentation zone and to the oxidizable organic matter content of the sediments. Average surficial sediment concentrations ranged from 81 ng/g in depositional zones to 7.2 ng/g in non-depositional zones. The vertical distribution of PCBs was determined at several sites and was used to estimate the areal burden and flux of PCBs in each of the southern sedimentation zones. The total sediment PCB burden in the southern portion of the lake was estimated to be 5,900 kg. Southern Lake Michigan has received PCBs since approximately 1930 at an average flux of 7.1 μg/m ² yr.

The effect of Waukegan Harbor as a point source of PCBs to Lake Michigan was evaluated by comparing the PCB distribution and Aroclor composition of harbor sediments to those of sediments of decreasing distances from the harbor. Significant differences in total PCB concentration between non-depositional zones near the harbor and those in other areas of the basin indicate that Waukegan Harbor has influenced the PCB burden of Lake Michigan.