Evidence for Anaerobic Dechlorination of Dechlorane Plus in Sewage Sludge

Abstract

The environmental occurrence of dechlorination moieties from the high production volume flame retardant, Dechlorane Plus (DP), has largely been documented; however, the sources have yet to be well understood. In addition, few laboratory-based studies exist which identify the cause for the occurrence of these chemicals in the environment or humans. Anaerobic dechlorination of the two DP isomers was investigated using a laboratory-simulated wastewater treatment plant (WWTP) environment where anaerobic digestion is used as part of the treatment regime. Known amounts of each isomer were added separately to sewage sludge which provided the electron-donating substrate and at prescribed time points in the incubation, a portion of the media was removed and analyzed for DP and any dechlorination metabolites. After 7 days, monohydrodechlorinated products were observed for both the syn- and anti-DP which were continued throughout the duration of our study (49 days) in an increasing manner giving a calculated formation rate of 0.48 ± 0.09 and 0.79 ± 0.12 pmols/day for syn- and anti-DP, respectively. Furthermore, we observed a second monohydrodechlorinated product only in the anti-DP isomer incubation medium. This strongly suggests that anti-DP is more susceptible to anaerobic degradation than the syn isomer. We also provide compelling evidence to the location of chlorine loss in the dechlorination DP analogues. Finally, the dechlorination DP moieties formed in our study matched the retention times and identification of those observed in surficial sediment located downstream of the WWTP.

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

“…The six compounds were added separately (10 μg) to 65 mL of laboratory-simulated sewage sludge and mixed thoroughly in a 100 mL brown incubator bottle. Seed sludge (15 mL) was added to each of the incubator bottles as a cosubstrate to begin the digestion 46 . The sewage consisted of yeast extract, meat extract, peptone, urea, (NH 4 ) 2 SO 4 , K 2 HPO 4 , CaCl 2 , MgSO 4 , and trace element solution 47 .…”

Insights into the Occurrence, Fate, and Impacts of Halogenated Flame Retardants in Municipal Wastewater Treatment Plants

“…106 More recently, Sverko and colleagues reported anaerobic biotransformation of DP by the microbiome of digested sludge in the laboratory, showing dechlorination of approximately 1.3% and 2.9% of syn-and anti-DP to Cl 11 -DP after 49 days, respectively, consistent with observations in full-scale anaerobic sludge digesters. 110 However, that study did not control for potential abiotic transformation, making it difficult to conclude that the observed dechlorination was due to biological activity. Detection of diester products, which can be used to identify biotransformation of ClOPFRs, has been reported in digested sludge in China 41 and confirmed by laboratory experimentation.…”

“…Interestingly, f syn was <0.22 or >0.50 in 43% and 4% of wastewater treatment solids samples in Asia, respectively, but 45% samples from North America had f syn > 0.50. The divergence of f syn in wastewater treatment solids from technical DP implies extensive and distinct biotransformation of DP isomers in the sludge. , The α- and γ-HBCD isomers are predominant in wastewater treatment solids, with no apparent differences between the regions (SI Figure S5). Concentrations of HBCD in Europe increased from 1998–2005 but have decreased steadily since then.…”

“…The richness of wastewater sludge microbiomes and diversity of niches in WWTPs provide a number of different possible pathways for HFRs biotransformation in wastewater treatment systems and anaerobic digesters. Indeed, biotransformation of HFRs in wastewater sludge has been investigated at lab-, pilot-, and full-scale in numerous studies. ,,,− Additionally, efforts have been made to enrich, isolate and characterize the functional HFR-transforming microorganisms in wastewater sludge. − Aerobic biotransformation of HFRs in WWTPs usually occurs via oxidative transformation during aerobic treatment processes (Table ). Kim and Oh evaluated the mass balance of PBDEs in a full-scale WWTP in South Korea and concluded that a 40% mass loss of PBDEs was most likely caused by oxidative biotransformation mediated by the activated sludge microbiome; this conclusion was based on the formation of hydroxylated and methoxylated PBDEs during aerobic biological wastewater treatment .…”

“…A nationwide investigation frequently detected undecachloropentacyclooctadecadiene (Cl 11 -DP) in digested sludge samples from different locations in China (26 of 62 samples), indicating widespread biotransformation of DP, although the biotransformation product Cl 11 -DP was minimal (∼1%) compared to DP . More recently, Sverko and colleagues reported anaerobic biotransformation of DP by the microbiome of digested sludge in the laboratory, showing dechlorination of approximately 1.3% and 2.9% of syn - and anti -DP to Cl 11 -DP after 49 days, respectively, consistent with observations in full-scale anaerobic sludge digesters . However, that study did not control for potential abiotic transformation, making it difficult to conclude that the observed dechlorination was due to biological activity.…”