PARAMETERS AFFECTING THE ADSORPTION OF PCBS TO SUSPENDED SEDIMENTS FROM THE DETROIT RIVER

In previous work, the adsorption and partitioning of a hydrophobic org anic chemical, hexachlorobenzene, to sediments from the Detroit River were investigated by means of long-term (lip to 6 months) batch mixing experiments. Effects on the adsorption and partitioning due to colloi ds from the water and from the sediments, the flocculation of these co lloids and of the sedimentary particles, particle size, and the amount of organic matter were determined. In the present experiments, these investigations have been extended to three PCB congeners: a monochloro biphenyl, a dichlorobiphenyl, and a hexachlorobiphenyl. Long-term expe riments were done in order to be certain that a steady state was alway s attained. From this steady state, a unique equilibrium partition coe fficient was determined for each congener which was independent of sed iment concentration. The parameters on which these partition coefficie nts and the adsorption rates depended were also determined. For hexach lorobenzene and the three PCB congeners, the time to steady state incr eased as the value of the equilibrium partition coefficient increased. For each of these same four chemicals over a wide range of dissolved chemical concentrations, the amount of chemical sorbed to the sediment s was linearly dependent on the amount of chemical dissolved, and ther efore the sorption isotherm for each chemical is linear over this rang e of chemical concentrations. The slow adsorption rates that were demo nstrated can significantly affect the sediment-water fluxes of contami nants and the sediment toxicity as compared with the assumption of equ ilibrium partitioning.