Detection of methoxylated and hydroxylated polychlorinated biphenyls in sewage sludge in China with evidence for their microbial transformation

Abstract

The concentrations of methoxylated polychlorinated biphenyls (MeO-PCBs) and hydroxylated polychlorinated biphenyls (OH-PCBs) were measured in the sewage sludge samples collected from twelve wastewater treatment plants in China. Two MeO-PCB congeners, including 3'-MeO-CB-65 and 4'-MeO-CB-101, were detected in three sludge with mean concentrations of 0.58 and 0.52 ng/g dry weight, respectively. OH-PCBs were detected in eight sludge samples, with an average total concentration of 4.2 ng/g dry weight. Furthermore, laboratory exposure was conducted to determine the possible source of OH-PCBs and MeO-PCBs in the sewage sludge, and their metabolism by the microbes. Both 4'-OH-CB-101 and 4'-MeO-CB-101 were detected as metabolites of CB-101 at a limited conversion rate after 5 days. Importantly, microbial interconversion between OH-PCBs and MeO-PCBs was observed in sewage sludge. Demethylation of MeO-PCBs was favored over methylation of OH-PCBs. The abundant and diverse microbes in sludge play a key role in the transformation processes of the PCB analogues. To our knowledge, this is the first report on MeO-PCBs in environmental matrices and on OH-PCBs in sewage sludge. The findings are important to understand the environmental fate of PCBs.

Figure 1. Sampling locations and spatial distributions of the concentrations of PCBs, OH-PCBs, and MeO-PCBs in the sewage sludge samples from twelve wastewater treatment plants in Greater China.

The map was produced on ArcGIS 10.3.1 (http://www.esri.com/).

Figure 2

Amounts of exposure compounds and their metabolites in the sludge exposed to (A) CB-101, (B) CB-65, (C) 4′-OH-CB-101, (D) 3′-OH-CB-65, (E) 4′-MeO-CB-101, and (F) 3′-MeO-CB-65 during the 5-day study period.

Figure 3. Metabolic results of CB-65 and CB-101, with the homologous OH-PCBs and MeO-PCBs by the microbes in the sludge.