Biodegradation of ethylene dibromide (1,2-dibromoethane [EDB]) in microcosms simulating in situ and biostimulated conditions
Department of Civil and Environmental Engineering, University of Massachusetts, Amherst, MA 01003, USA. Journal of hazardous materials
(Impact Factor: 4.53).
03/2012; 209-210:92-8. DOI: 10.1016/j.jhazmat.2011.12.067
Although 1,2-dibromoethane (EDB) is a common groundwater contaminant, there is the lack of knowledge surrounding EDB biodegradation, especially under aerobic conditions. We have performed an extensive microcosm study to investigate the biodegradation of EDB under simulated in situ and biostimulated conditions. The materials for soil microcosms were collected from an EDB-contaminated aquifer at the Massachusetts Military Reservation in Cape Cod, MA. This EDB plume has persisted for nearly 40 years in both aerobic and anaerobic EDB zones of the aquifer. Microcosms were constructed under environmentally relevant conditions (field EDB and DO concentrations; incubated at 12°C). The results showed that natural attenuation occurred under anaerobic conditions but not under aerobic conditions, explaining why aerobic EDB contamination is so persistent. EDB degradation rates were greater under biostimulated conditions for both the aerobic and anaerobic microcosms. Particularly for aerobic biostimulation, methane-amended microcosms degraded EDB, on average, at a first order rate eight times faster than unamended microcosms. The best performing replicate achieved an EDB degradation rate of 7.0 yr(-1) (half-life (t(1/2))=0.10 yr). Residual methane concentrations and the emergence of methanotrophic bacteria, measured by culture independent bacterial analysis, provided strong indications that EDB degradation in aerobic methane-amended microcosms occurred via cometabolic degradation. These results indicate the potential for enhanced natural attenuation of EDB and that methane could be considered co-substrate for EDB bioremediation for the EDB-contaminated groundwater in aerobic zone.
Available from: Meng Wang
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ABSTRACT: The lead scavenger 1,2-dibromoethane (EDB), a former additive to leaded gasoline, is a common groundwater contaminant, yet not much knowledge is available for its targeted bioremediation, especially under in situ conditions. The study site was an aviation gas spill site, which, although all hydrocarbons and most of the EDB were remediated in the mid-1990s, still exhibits low levels of EDB remaining in the groundwater (about 11 μg EDB/l). To evaluate the effect of phenol on biostimulation of low concentration of EDB, microcosms were established from an EDB-contaminated aquifer. After 300 days at environmentally relevant conditions (12 ± 2 °C, static incubation), EDB was not significantly removed from unamended microcosms compared to the abiotic control. However, in treatments amended with phenol, up to 80 % of the initial EDB concentration had been degraded, while added phenol was removed completely. Microbial community composition in unamended and phenol-amended microcosms remained unchanged, and Polaromonas sp. dominated both types of microcosms, but total bacterial abundance and numbers of the gene for phenol hydroxylase were higher in phenol-amended microcosms. Dehalogenase, an indicator suggesting targeted aerobic biodegradation of EDB, was not detected in either treatment. This finding suggests phenol hydroxylase, rather than a dehalogenation reaction, may be responsible for 1,2-dibromoethane oxidation under in situ conditions. In addition, biostimulation of EDB is possible through the addition of low levels of phenol in aerobic groundwater sites.
Available from: Katholiki Skopelitou
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ABSTRACT: Haloalkane dehalogenases catalyze the hydrolytic cleavage of carbon–halogen bonds in a broad range of environmental pollutants such as aliphatic mono-, di-, and polyhalogenated alkanes. From the biotechnology point of view haloalkane dehalogenases attract attention because of many potential uses for the bioremendation of soil, water and air. In the present study, different Rhizobium strains (Sinorhizobium meliloti 1021, Rhizobium leguminosarum bv. trifolii, Mesorhizobium loti MAFF, Bradyrhizobium japonicum usda 110) were screened for their ability to produce stable and active 1,2-dibromoethane-degrading dehalogenase. The results showed that B. japonicum produces the most potent dehalogenase. This enzyme was cloned, expressed in Escherichia coli BL21(DE3), purified and was entrapped in tetraethylorthosilicate derived sol–gel. The tetraethylorthosilicate sol–gel entrapped haloalkane dehalogenases exhibited higher storage and operational stability at 4 °C and 25 °C, compared to the free enzyme. Kinetic analysis of the entrapped enzyme using 1,2-dibromoethane showed that substrate turnover was limited by partitioning effects or diffusion through the sol–gel matrix. The biocatalyst was used in a packed bed bioreactor for the biodegradation of 1,2-DBE. Under selected conditions the sol–gel entrapped dehalogenase was able to hydrolyze 91.8% of the loaded 1,2-DBE, within 16.7 h. The results of the present study suggest that the use of HLD biocatalysis may provide a ‘green chemistry’ tool for sustainable remediation of 1,2-DBE.
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ABSTRACT: 1,2-Dibromoethane (ethylene dibromide; EDB) is a probable human carcinogen that was previously used as both a soil fumigant and a scavenger in leaded gasoline. EDB has been observed to persist in soils and groundwater, particularly under oxic conditions. The objective of this study was to evaluate options to enhance the aerobic degradation of EDB in groundwater, with a particular focus on possible in situ remediation strategies. Propane gas and ethane gas were observed to significantly stimulate the biodegradation of EDB in microcosms constructed with aquifer solids and groundwater from the FS-12 EDB plume at Joint Base Cape Cod (Cape Cod, MA), but only after inorganic nutrients were added. Ethene gas was also effective, but rates were appreciably slower than for ethane and propane. EDB was reduced to <0.02μg/L, the Massachusetts state Maximum Contaminant Level (MCL), in microcosms that received ethane gas and inorganic nutrients. An enrichment culture (BE-3R) that grew on ethane or propane gas but not EDB was obtained from the site materials. The degradation of EDB by this culture was inhibited by acetylene gas, suggesting that degradation is catalyzed by a monooxygenase enzyme. The BE-3R culture was also observed to biodegrade 1,2-dichloroethane (DCA), a compound commonly used in conjunction with EDB as a lead scavenger in gasoline. The data suggest that addition of ethane or propane gas with inorganic nutrients may be a viable option to enhance degradation of EDB in groundwater aquifers to below current state or federal MCL values.
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