Enhancement of microbial PCB dechlorination by chlorobenzoates, chlorophenols and chlorobenzenes

Abstract

We investigated the effects of chlorobenzoates (3-, 2,3-, 2,4-, 2,5-, 2,3,5- and 2,4,6-chlorobenzoate), chlorophenols (2,3-, 3,4-, 2,5-, 2,3,6- and penta-chlorophenol), and chlorobenzenes (1,2-, 1,2,3-, 1,2,4- and penta-chlorobenzene) on polychlorinated biphenyl (PCB) dechlorination and on the enrichment of PCB-dechlorinating microorganisms. When the natural microbial populations eluted from St. Lawrence River sediments were enriched with each of the 15 haloaromatic compounds (HACs) in PCB-free sediments, PCB-dechlorinating microorganisms were found in all but pentachlorophenol-amended sediments. Similarly, dechlorinating microorganisms were also found in PCB-spiked sediments amended with all HACs, except for those with pentachlorophenol. In HAC-amended PCB sediments there was a long lag in PCB dechlorination until the HACs were reduced to a plateau level. Despite this lag, once PCB dechlorination started it was faster in the HAC-amended sediments compared to the unamended controls. The overall extent of PCB dechlorination was significantly enhanced by all HACs except pentachlorophenol and pentachlorobenzene, but the extent as well as the pattern of the enhancement varied. Of the 13 effective HACs, six (2,3-, 2,4- and 2,4,6-chlorobenzoates; 3,4- and 2,3,6-chlorophenols; and 1,2,3-chlorobenzene) enhanced only meta-dechlorination, whereas five (3-chlorobenzoate; 2,3- and 2,5-chlorophenols; and 1,2- and 1,2,4-chlorobenzenes) increased both meta- and para-dechlorination, and two (2,5- and 2,3,5-chlorobenzoates) promoted overall, substitution non-specific dechlorination. When the maximum extent of dechlorination was plotted against the highest number of PCB-dechlorinating microorganisms for each HAC, there was a linear relationship (P<0.01), suggesting that dechlorination enhancement was related to the increase in their population size. However, there was also evidence to suggest that different dechlorinating microorganisms were selected.

Strategy for the Rapid Dechlorination of Polychlorinated Biphenyls (PCBs) by Dehalococcoides mccartyi Strains

“…Wu et al found that halopriming with 2,6-BB increased the cell density of OHRB, leading to increased dechlorination rates . Halogenated benzoates and other halogenated aromatic compounds (e.g., chlorobenzenes and chlorophenols) have also been used as haloprimers for PCB dechlorination. , The range of haloprimers was later expanded to include pentachloronitrobenzene, which could better stimulate increased dechlorination of weathered PCBs than tetrachlorobenzene . Chlorinated ethenes have been utilized to scale up non- Dehalococcoides OHRB as bioamendment for PCB dechlorination in mesocosms.…”

“…Although halopriming can be used to increase the biomass of OHRB and may induce genes required for dehalogenation, a significant lag period (from 4 months to 1 year) in PCB dechlorination activity remains. Several studies have demonstrated the initiation of PCB dechlorination following halopriming occurs only after the concentration of the haloprimer was reduced past a critical threshold. , Furthermore, most of the effective electron acceptors thus far applied as haloprimers are halogenated aromatic compounds, the release of which into the environment is generally hazardous.…”

“…Cross-inhibition generally occurs when one dehalogenating strain or distinct microbial populations are exposed simultaneously to different categories of potential halogenated substrates . In previous studies on biostimulation, PCB dechlorination could be initiated after the haloprimer decreased down to a critical concentration; , however, little is known about the potential cross-inhibition to PCB dechlorinating strains when exposed to both haloprimers and PCB simultaneously. Strains CG1, CG4, and CG5 are able to dechlorinate a sole electron acceptor (i.e., single PCE, TCE, or PCB), but it is not clear how they respond to multiple substrates, e.g., concurrently dechlorinating multiple chlorinated compounds or preferring one compound.…”

Effects of a rhamnolipid biosurfactant on the reductive dechlorination of polychlorinated biphenyls by St. Lawrence River (North America) microorganisms

“…Biosurfactant amendment can be achieved through the in situ enrichment of surfactant‐producing microorganisms or a direct application of prepared surfactants. Combined with the direct on‐site selective enrichment of dechlorinating populations or an application of selected dechlorinators enriched in mass culture [32], surfactant application can maximize reductive dechlorination of PCBs to the extent that the final products can be mineralized readily by aerobic degradation.…”

Enrichment of a dioxin‐dehalogenating Dehalococcoides species in two‐liquid phase cultures

“…One promising strategy to overcome these limitations may be the addition of more bioavailable alternative compounds. ‘Priming’ by organohalogens, such as brominated biphenyls or halogenated benzoates, has been used previously to stimulate certain patterns of polychlorinated biphenyls (PCB) dechlorination (VanDort et al ., 1997; Deweerd and Bedard, 1999; Wu et al ., 1999), as well as selectively enrich distinct groups of PCB dechlorinators (Wu et al ., 1999; Cho et al ., 2002).…”