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PCB Partitioning in Sediment-Water Systems: The Effect of Sediment Concentration¹

ABSTRACT

The effect of sediment concentration variations on polychlorinated biphenyl (PCB) sorption to natural lake sediment (Saginaw Bay, Mich.) and montmorillonite clay has been investigated. In studies utilizing tritiated 2,4,5,2',4',5'-hexachlorobiphenyl (HCBP), partition coefficient values for adsorption isotherms (_a) were found to increase as sediment concentrations (m) were decreased from m = 1000 mg/L to m = 50 mg/L. HCBP adsorption to montmorillonite (m = 1000 mg/L, _a = 2900 L/kg; m = 50 mg/L, _a = 10 600 L/kg) appeared to be more sensitive to sediment concentration than did adsorption to the Saginaw Bay sediment (m = 1000 mg/L, _a = 9900 L/kg; m = 50 mg/L, _a = 17 100 L/kg). Evidence suggests that these variations are not the result of nonlinear isotherms. Although variations in solution chemical composition and kinetic effects were found to affect partitioning, neither factor appeared to adequately account for the magnitude of the observed sediment concentration effect. In experiments in which sediment concentrations were decreased (m = 1000 mg/L to 10 mg/L) while equilibrium aqueous HCBP concentrations were maintained at approximately constant levels, _a values for adsorption increased. The behavior was in conformity with the isotherm results. The observed behavior might be due to direct solid phase interactions between suspended particles. The occurrence of such interactions in natural waters could have potentially significant implications for efforts to predict sediment-water PCB distributions.

Key Words: adsorption • toxic organics • PCB sorption • natural lake sediment • montmorillonite clay • hexachlorobiphenyl

¹ Contribution of the Environmental Engineering and Science Department of Manhattan College, Bronx, NY 10471. This work was funded by the U.S. Environmental Protection Agency Large Lakes Research Station (Grosse Ile, Mich.) through grant #CR 805229.

Although the research described in this article has been funded in part by the USEPA through contract or grant # Cr 805229 to Manhattan College, it has not been subjected to the Agency's required peer and policy review, and therefore does not necessarily reflect the views of the Agency and no official endorsement should be inferred.

² Environmental Chemist and Associate Professor of Environmental Engineering respectively, Manhattan College. Current address of senior author: Envirosphere Co., 2 World Trade Center, New York, NY 10048.

Received for publication February 7, 1983.