Reductive Dehalogenation of Dichlorobenzenes and Monochlorobenzene to Benzene in Microcosms

Abstract

Anaerobic microcosms were constructed using sediments from a historically chlorobenzene-contaminated site and were provided with yeast extract as an electron donor. In these methanogenic microcosms, all three isomers of dichlorobenzene (DCB) were reductively dehalogenated to monochlorobenzene (MCB) when added together or individually, with 1,2-DCB dehalogenation being the most rapid and 1,4-DCB the slowest. When nearly all of the DCBs were consumed, benzene was detected and its accumulation was concomitant with MCB disappearance. Small amounts of toluene were also detected along with benzene. Subsequent MCB doses were also converted to benzene, and benzene reached levels in excess of 5000 micromol/L in some microcosms. An initial DCB dose stimulated, and in some cases was necessary for, MCB dehalogenation. Subsequent doses of DCB or MCB were dehalogenated more rapidly than previous ones, consistent with a growth-related process. Addition of a ca. 4% inoculum from microcosms that had consumed DCBs or MCB stimulated DCB and MCB dehalogenation in fresh microcosms, also indicative of growth and suggests thatthe chlorobenzene-dehalogenating microorganisms in these microcosms are candidates for bioaugmentation at anaerobic DCB or MCB contaminated sites. These studies add to evidence that benzene production from chlorobenzenes needs to be considered when modeling processes at contaminated sites.

Characterization of Microbes Capable of Using Vinyl Chloride and Ethene as Sole Carbon and Energy Sources by Anaerobic Oxidation

“…Microcosms constructed from a sample from a freshwater site we have previously studied (Fung et al, 2009;Nelson et al, 2011) did consume ethene, but not VC, when amended with sulfate as the electron acceptor. Figure 4.1 shows a typical microcosm amended with sulfate.…”

“…Sediment samples were obtained from a canal in Salem County, New Jersey entering the Delaware River from a site Zinder and colleagues have previously demonstrated reductive dehalogenation of chlorobenzenes (Fung et al, 2009;Nelson et al, 2011). Microcosms were inoculated using the sediment from a core sample 20-36 cm from water sediment interface obtained in May 2009 and stored at 4 o C in glass jars before use.…”

Characterization of a Highly Enriched Microbial Consortium Reductively Dechlorinating 2,3-Dichlorophenol and 2,4,6-Trichlorophenol and the Corresponding cprA Genes from River Sediment

“…As part of anaerobic dehalogenation processes, reductive dechlorination has triggered considerable interest for the potential detoxification of anthropogenic groundwater contaminants . Anaerobic reductive dechlorination has been studied in a number of sedimentary environments (Lake et al, 1992;Alder et al, 1993;Wu et al, 1998;Fagervold et al, 2005;Fung et al, 2009;Itoh et al, 2010). These investigations were made possible using laboratory microcosms.…”

How Early Diagenesis Reveals in Situ Biodegradation of Herbicides in Sediment

“…Presently the only chlorinated benzene congener that appears to resist being dehalorespired is monochlorobenzene. There is however no thermodynamic reason why microorganisms should not be able to grow with this compound as electron acceptor: the hunt is on (Fung et al 2009). Dichloroelimination is a special case of reductive dechlorination, where two chloral substituents are removed from adjacent carbon atoms, while the aliphatic C-C bond is converted into an unsaturated C=C bond (Fig.…”