Distribution and transport of polychlorinated biphenyls in Little Lake Butte des Morts, Fox River, Wisconsin, April 1987-October 1988

Abstract

Polychlorinated biphenyls (PCB's) in the bottom sediment and water column of Little Lake Butte des Morts were studied by the Wisconsin Department of Natural Resources and the U.S. Geological Survey. The lake is a 8-kilometer-long impoundment of the Fox River between Lake Winnebago and Appleton, Wisconsin. Discharge of PCB's into the lake by paper mills and waste-treatment plants has resulted in their accumulation in the bottom sediment. The accumulation of PCB's in the sediment was estimated to be 1,100 kilograms in October 1987. The concentrations of PCB's in bottom-sediment core samples were as much as 190 micrograms per gram dry sediment. The congener distribution of the PCB's present in the lake most closely resembles that for the Aroclor 1242 PCB's mixture. Thirty-two water samples were collected at the outlet of the lake to determine concentrations of PCB's. Concentrations of PCB's in the water column varied seasonally and ranged from 3.5 to 137 nanograms per liter. Concentrations of PCB's decrease in the winter and increases in the summer months. Concentrations of PCB's in the water column for particulates generally were 2.5 times that of dissolved PCB's. The suspended-solids concentrations ranged from 3 to 44 milligrams per liter. Correlation analysis was used to identify the physical characteristics and water-quality characteristics having the highest degree of association with PCB's concentration in the water column. The highest correlation coefficients (r) for dissolved PCB's concentration were with water temperature (7=0.88) and particulate organic carbon concentration (7=0.72). The highest correlation coefficients for particulate PCB's concentration were with suspended- particulates concentration (r=0.77) and water temperature (n=0.70). Correlation coefficients for total PCB's (the sum of dissolved and particulate PCB's) concentration were similar to those for particulate PCB's concentration. The mass of PCB's transported from the lake in streamflow during 1987-88 was calculated to be 110 kilograms annually. The PCB's transport rate decreased 50 percent from 1987 to 1988, for the period April through September. Transport of PCB's was greatest during April and May of each year. The average flux rate of PCB's into the water column from the bottom sediment in the lake was estimated to be 1.2 milligrams per square meter per day. The PCB's load seems to increase at river discharges greater than 212 cubic meters per second. This increase in PCB's load might be caused by resuspension of PCB's-contaminated bottom-sediment deposits. There was little variation in PCB's load at flows less than 170 cubic meters per second. The bottom sediments are a continuing source of PCB's to Little Lake Butte des Morts and the lower Fox River.