Trends in polychlorinated biphenyl concentrations in Hudson River water five years after elimination of point sources

Industrial discharge of polychlorinated biphenyls (PCBs) to the Hudson River from 1950 to the mid-1970 's has resulted in serious degradation of the water. Contaminated river-bottom sediments continue to contribute PCBs to the river water. Concentrations in the sediment range from several hundred micrograms per gram near the outfall to less than 10 micrograms per gram in the lower estuary. PCBs are supplied by bottom sediments to the overlying water by two mechanisms--desorption and resuspension. Because desorption is a relatively constant process, concentrations of PCBs decrease as water discharge increases. At high flow, however, scouring by turbulence causes resuspension of PCB-laden sediment. Transport rates indicate that most PCBs enter the water from the most contaminated sediments, which are within 20 kilometers of the outfall. Mean daily transport from the upper river (except during high discharges) has decreased from 10 kilograms in 1976 to 5 kilograms in the late 1970 's and to 1 kilogram in 1981. This decrease probably results from the burial of highly contaminated sediments by cleaner sediments originating upstream. (USGS)