Tracing the In Situ Microbial Degradation of PBDEs and PCBs in Sediments from an E-Waste Site by the Coupling of Compound-Specific Stable Carbon Isotope Analysis and Conventional Evaluation Approaches

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) are two classes of environmental pollutants that have frequently been detected in various environmental samples. However, little is known about the fate of these compounds, and in particular, about the microbial degradation potential in situ. In the present study, three composite sediment cores were collected from a closed pond contaminated by e-waste dismantling activities to investigate the in situ microbial degradation of PBDEs and PCBs using compound-specific isotope analysis and conventional evaluation approaches. The potential microorganisms relevant to the degradation of PBDEs and PCBs were also assessed to aid in the understanding of in situ biodegradation. The positive matrix factorization (PMF) results suggested that reductive debromination of PBDEs took place in the sediments. The debromination signal (ratio of the concentration of factor 5 (PMF result) to the total PBDE content) was positively correlated with the relative abundance of Dehalococcoidetes at different core depths. The clear ¹³C enrichment of five PBDE congeners (BDE 28, 47, 49, 99, and 153) with increasing core depth indicated that a measurable change in isotope composition might have occurred during PBDE biodegradation. The in situ biodegradation of PBDEs was further validated by the widespread detection of mono-BDE congeners (BDE 2, BDE 3) and diphenyl ether in the sediments. The enantiomeric fractions of PCB 91, 132, 135, 176 were significantly greater than 0.5 (p<0.5), providing evidence of the microbial degradation of these congeners in sediments. The remarkable ¹³C enrichment or depletion of some PCB congeners with increasing core depths were detected. The comparisons among δ¹³C values of detected congeners, chlorine per diphenyl, and Log dehalococcoides/TPCB in three sediment cores indicated that these congeners could been generated from the dechlorination of higher chlorinated PCBs and degradation extent in site 3 was greater than that in site 1 and 2. This study provides new evidence to enhance our understanding of the in situ microbiodegradation of PBDEs and PCBs.