Enhanced dechlorination of 2,2′,4,4′,5,5′-hexachlorobiphenyl in water-sediment mixture by adding anthraquinone-2,6-disulfonic acid

Abstract

Dechlorination of polychlorinated biphenyls (PCBs) in aquatic sediments and anaerobic bioreactors has been widely observed, and mechanisms have also been studied. However, the role of humic acid in the biotic dechlorination of PCBs has not been studied. The present study investigated the role of humic acid as the redox mediator in the anaerobic biotransformation of PCBs in water and sediment mixture. Degradation of 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) in water and sediment mixture was studied by adding different concentrations of anthraquinone-2,6-disulfonic acid (AQDS), which was a model substance for quinone moieties in humic acid. Chemical reduction of PCB 153 by sterile AH2QDS was performed to investigate the mechanisms involved. Decrease of PCB 153 was enhanced significantly by adding AQDS. The loss percentage of PCB 153 after 15 days of incubation was increased from 9.03 ± 2.73 % to 38.3 ± 3.27 % (P = 95 %) by adding 1 mM AQDS, while it was increased to 46.8 ± 4.41 % (P = 95 %) by adding 5 mM sodium acetate and 1 mM AQDS. Less chlorinated congeners PCB 101 and PCB 52 were identified as the products through the dechlorination of PCB 153 mainly in para positions. The results suggested that the quinone moieties in humic acid may play an important role in the dechlorination of PCBs in nature. This finding will help us to understand the natural attenuation of PCBs better and also provide a method to enhance the removal of higher chlorinated PCBs in waste treatment process.