Binding of polychlorinated biphenyls to aquatic humic substances: The roleof substrate and sorbate properties on partitioning

Two ortho- (2,2',5 and 2,2',5,6') and a non-ortho- (3,3',4,4') substituted polychlorinated biphenyl (PCB) congeners were used to study the effects of sorbate structure in binding processes to two lacustrine fulvic acids. Bind ing constants were determined by solubility enhancement of the solutes by t he fulvic acids. The binding of the orthotrichlorobiphenyl was significantl y less than the non-ortho-substituted tetrachlorobiphenyl to both fulvic ac ids. Surprisingly, the measured ortho-trichlorobiphenyl binding constant to both fulvic acids was approximately the same as the ortho-substituted tetr achlorobiphenyl. The effect of the chlorines in the ortho position inhibits free rotation around the 1,1' carbon bond, thereby making the molecule les s able to interact effectively with the fulvic acid substrate relative to i ts non-ortho-substituted congeners. Finally, binding of all three PCBs to t he Great Dismal Swamp fulvic acid was significantly higher than for the Pon y Lake sample. This observation is attributable to the former substrate's h igher degree of aromaticity and polarizability, which can potentially inter act more favorably with the PCBs through an increase in van der Waals type interactions.