Partitioning of polychlorinated biphenyls onto porewater–surface sediment systems collected along Umgeni River, KwaZulu-Natal, South Africa

Abstract

This study focuses on the sorption efficiency of porewater–sediment of eight selected polychlorinated biphenyls (PCBs) most monitored in the environment as recommended by the Environmental Protection Agency. Five river sediment samples were collected along the Umgeni River of KwaZulu-Natal province of South Africa that contained different soil contents. The Walkley–Black method was employed for the determination of soil organic matter in the sediments, while sediment mineralogy and morphology, as well as elemental composition, were evaluated using powder X-ray diffraction and scanning electron microscopy equipped with energy-disperse X-ray, respectively. The sorption studies between porewater and sediment systems were carried out using batch adsorption experiments. The results showed that sediment samples containing high clay and silt content (13.90%, 30.43% and 18.58%, 19.93%) (site AWW and IDI) have the highest sorption percentage between 65.86–89.81% and 61.39–70.43%, respectively, for all the PCBs, while sites IDO and BL with high sand content (86.29% and 85.20%) sorbed the least amount of PCBs (32.32–53.06% and 43.23–59.77%, respectively). Among the sediment physicochemical parameters, soil organic matter was observed to correlate positively and play an important role in the sorption of PCBs. Also, a decrease in the ratio of Si:(Al + Fe) was noticed to have a positive impact on the sorption of PCBs. This is the first study done on this river to critically evaluate the porewater–sediment distribution and transportation of PCBs. Sorption efficiency of sediments of known physicochemical properties similar to this study area can be predicted by the sorption results of the present study.