Effect of Humic Acid on Adsorption of Polychlorinated Biphenyls onto Organoclay

Mitigation of risks stemming from contaminated sediments in freshwater and estuarine environments remains an important challenge to the field of environmental science and engineering. Capping sediments with reactive materials is one approach that has recently been the subject of research and development. This research evaluated the use of organoclay as a sorbent in a reactive cap for in situ remediation of contaminated sediments, and provides an original contribution by presenting the sorption characteristics of individual polychlorinated biphenyls (PCB) congeners in the presence of high concentrations of humic acids typical of sediment porewater environments. Sorption of coplanar and noncoplanar PCBs on three commercially available organoclays was studied in this work. Studies were conducted to evaluate the kinetics of adsorption of PCBs on organoclay and to determine the effect of humic acid on the kinetics of adsorption. Isotherm studies were conducted to determine the adsorption affinity of PCBs for organoclays in the presence and absence of humic acid. Studies showed a 45 to 96% reduction in the sorption affinity for organoclays after preloading with high concentrations of humic acid, depending both on the congener and the composition of organoclay. Desorption of PCBs upon addition of humic acid after PCBs were equilibrated with organoclay was statistically significant, although the magnitude of the effect was much smaller than that observed from preloading of humic acid.