Reductive Dechlorination Of Polychlorinated Biphenyls Research Articles

Reductive dechlorination of polychlorinated biphenyls is coupled to nitrogen fixation by a legume-rhizobium symbiosis

Chlorinated persistent organic pollutants, including polychlorinated biphenyls (PCBs), represent a particularly serious environmental problem and human health risk worldwide. Leguminous plants and their symbiotic bacteria (rhizobia) are important components of the biogeochemical cycling of nitrogen in both agricultural and natural ecosystems. However, there have been relatively few detailed studies of the remediation of PCB-contaminated soils by legume-rhizobia symbionts. Here we report for the first time evidence of the reductive dechlorination of 2,4,4′-trichlorobiphenyl (PCB 28) by an alfalfa-rhizobium nitrogen fixing symbiont. Alfalfa (Medicago sativa L.) inoculated with wild-type Sinorhizobium meliloti had significantly larger biomass and PCB 28 accumulation than alfalfa inoculated with the nitrogenase negative mutant rhizobium SmY. Dechlorination products of PCB 28, 2,4′-dichlorobiphenyl (PCB 8), and the emission of chloride ion (Cl−) were also found to decrease significantly in the ineffective nodules infected by the mutant strain SmY. We therefore hypothesize that N2-fixation by the legume-rhizobium symbiont is coupled with the reductive dechlorination of PCBs within the nodules. The combination of these two processes is of great importance to the biogeochemical cycling and bioremediation of organochlorine pollutants in terrestrial ecosystems.

Analysis of a microbial community associated with polychlorinated biphenyl degradation in anaerobic batch reactors.

The degradation of polychlorinated biphenyls (PCBs) was investigated under fermentative-methanogenic conditions for up to 60 days in the presence of anaerobic biomass from a full-scale UASB reactor. The low methane yields in the PCBs-spiked batch reactors suggested that the biomass had an inhibitory effect on the methanogenic community. Reactors containing PCBs and co-substrates (ethanol/sodium formate) exhibited substantial PCB reductions from 0.7 to 0.2 mg mL(-1). For the Bacteria domain, the PCBs-spiked reactors were grouped with the PCB-free reactors with a similarity of 55 %, which suggested the selection of a specific population in the presence of PCBs. Three genera of bacteria were found exclusively in the PCB-spiked reactors and were identified using pyrosequencing analysis, Sedimentibacter, Tissierela and Fusibacter. Interestingly, the Sedimentibacter, which was previously correlated with the reductive dechlorination of PCBs, had the highest relative abundance in the RCS-PCB (7.4 %) and RCS-PCB-PF (12.4 %) reactors. Thus, the anaerobic sludge from the UASB reactor contains bacteria from the Firmicutes phylum that are capable of degrading PCBs.

Effects of activated carbon on reductive dechlorination of PCBs by organohalide respiring bacteria indigenous to sediments

Polychlorinated biphenyls (PCBs) have accumulated in aquatic sediments due to their inherent chemical stability and their presence poses a risk due to their potential toxicity in humans and animals. Granular activated carbon (GAC) has been applied to PCB contaminated sediment sites to reduce the aqueous concentration by sequestration thus reducing the PCB exposure and toxicity to both benthic and aquatic organisms. However, it is not known how the reduction of PCB bioavailability by adsorption to GAC affects bacterial transformation of PCBs by indigenous organohalide respiring bacteria. In this study, the impact of GAC on anaerobic dechlorination by putative organohalide respiring bacteria indigenous to sediment from Baltimore Harbor was examined. It was shown that the average Cl/biphenyl after dehalogenation of Aroclor 1260 was similar between treatments with and without GAC amendment. However, GAC caused a substantial shift in the congener distribution whereby a smaller fraction of highly chlorinated congeners was more extensively dechlorinated to mono- through tri-chlorinated congeners compared to the formation of tri- through penta-chlorinated congeners in unamended sediment. The results combined with comparative sequence analysis of 16S rRNA gene sequences suggest that GAC caused a community shift to putative organohalide respiring phylotypes that coincided with more extensive dechlorination of ortho and unflanked chlorines. This shift in activity by GAC shown here for the first time has the potential to promote greater degradation in situ by promoting accumulation of less chlorinated congeners that are generally more susceptible to complete mineralization by aerobic PCB degrading bacteria.

Analysis of Polychlorinated Biphenyl Mixtures and Establishment of a Parameter Useful for PCB‐Degradation Studies

A prerequisite for the study of polychlorinated biphenyls (PCBs) is a reliable analytical determination of the substances involved. For this purpose a gas chromatographic (GC) separation method with detection by mass spectrometry (MS) was optimized. In addition, a new parameter—the “weighted average chlorination level”—was established. This forms the basis for a systematic investigation of the reductive dechlorination of PCBs by metals.

Polychlorinated Biphenyl Reductive Dechlorination by Vitamin B12s: Thermodynamics and Regiospecificity

Microbial reductive dechlorination reactions play an important role in determining the environmental fate of polychlorinated biphenyls (PCBs), especially for PCB congeners with more than four chlorines. Powerful chemical catalysts such as vitamin B12s provide an effective tool for the study of reductive dechlorination reactions. The reductive dechlorination of PCBs by titanium(III) citrate-reduced vitamin B12s was studied in batch reactors. Long-term experiments demonstrated reductive dechlorination of aqueous and sediment-sorbed 2,3,4,5,6-pentachlorobiphenyl (2,3,4,5,6-PeCB) to tetra-, tri-, di-, and monochlorobiphenyl products. Approximately 10% chlorine removal was observed in 36 days in aqueous experiments at 20 °C; the sediment experiment showed 40% chlorine removal in 42 days at 30 °C. Nearly all possible intermediates were produced and reductively dechlorinated, with no apparent accumulation of individual congeners. Short-term experiments were conducted to determine the pathway for vitamin B12s-catalyzed reductive dechlorination of aqueous 2,3,4,5,6-PeCB and its dechlorinated products; relative product distributions were measured for all possible tetra- and trichlorobiphenyl reductive dechlorination reactions. Theoretical product distributions based on free energies of formation agreed with observed product distributions for short- and long-term experiments. Reductive dechlorination was favored at positions with adjacent chlorines; on average, chlorines were removed equally from ortho, meta, and para positions.

ChemInform Abstract: Reductive Dechlorination of Polychlorinated Biphenyls by Anaerobic Microorganism from Sediments.

ChemInformVolume 20, Issue 12 Other Subjects ChemInform Abstract: Reductive Dechlorination of Polychlorinated Biphenyls by Anaerobic Microorganism from Sediments. J. F. III QUENSEN, J. F. III QUENSEN Dep. Crop Soil Sci., Michigan State Univ., East Lansing, MI 48824, USASearch for more papers by this authorJ. M. TIEDJE, J. M. TIEDJE Dep. Crop Soil Sci., Michigan State Univ., East Lansing, MI 48824, USASearch for more papers by this authorS. A. BOYD, S. A. BOYD Dep. Crop Soil Sci., Michigan State Univ., East Lansing, MI 48824, USASearch for more papers by this author J. F. III QUENSEN, J. F. III QUENSEN Dep. Crop Soil Sci., Michigan State Univ., East Lansing, MI 48824, USASearch for more papers by this authorJ. M. TIEDJE, J. M. TIEDJE Dep. Crop Soil Sci., Michigan State Univ., East Lansing, MI 48824, USASearch for more papers by this authorS. A. BOYD, S. A. BOYD Dep. Crop Soil Sci., Michigan State Univ., East Lansing, MI 48824, USASearch for more papers by this author First published: March 21, 1989 https://doi.org/10.1002/chin.198912330AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume20, Issue12March 21, 1989 RelatedInformation