Biodegradation of low concentrations of 1,2-dibromoethane in groundwater is enhanced by phenol

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.

Dual Carbon–Bromine Stable Isotope Analysis Allows Distinguishing Transformation Pathways of Ethylene Dibromide

“…However, many of these compounds are considered to be toxic, carcinogenic or even mutagenic . One of these brominated contaminants is ethylene dibromide (EDB, 1,2-dibromoethane), extensively used in the past as a lead scavenger in gasoline as well as an agriculture fumigant. − EDB is susceptible to abiotic reactions and can be biodegraded under oxic and anoxic conditions. − In general, all EDB transformations in the environment can follow several different mechanistic pathways: nucleophilic substitution (e.g., hydrolysis), dehydrobromination, dibromo­elimination, or radical oxidation (via proton abstraction). Under certain conditions, EDB degradation may occur through multiple reaction types.…”

Aerobic and Anaerobic Biodegradation of 1,2-Dibromoethane by a Microbial Consortium under Simulated Groundwater Conditions

“…However, the corresponding OD 600 increased significantly within the range of 40–160 mg/L. This phenomenon may be because the yeast extract cannot induce the degrading enzymes, such as oxygenase enzymes, to promote EDB biodegradation [17], but can act as a carbon source for microbial growth.…”

“…Enhanced cometabolic degradation by adding co-substrates or nutrients to stimulate pollutant degradation activity has attracted broad attention due to the practicality of the field applications. It was found that cometabolism with phenol [16,17], ethane [16], and methane [2] under aerobic conditions, and lactate [2,18] under anaerobic conditions, could increase the biodegradation rate of EDB. However, it was observed that dissolved oxygen (DO) concentrations in groundwater often change dynamically between aerobic and anaerobic conditions during the engineering applications of enhanced reductive debromination of EDB in the field.…”

Cometabolism of Fluoroanilines in the Presence of 4-Fluoroaniline byRalstoniasp. FD-1

“…Microorganisms are ubiquitously filled in the nature and have tremendous metabolic ability to utilize most toxic compounds as sources of energy and nutrient for growth. Some of them possess specifically characteristic degrading enzymes for biodegradation of pollutants into nontoxic substances [13]. However, owing to the distinct properties of fluorine such as a large van der Waals radius (1.45Å, which is between that of hydrogen and oxygen), a high electronegativity (4.0 is the strongest of all atoms), and a strong carbon-fluorine (C-F) bond energy (C-F, 485 kJ/mol; C-H, 414 kJ/mol; C-OH, 359 kJ/mol; C-C, 345 kJ/mol; C-Cl, 339 kJ/mol) [14], only a small number of bacteria capable of degrading fluorinated compounds have been isolated [15,16].…”

“…Though many refractory organisms could not be utilized by isolated bacteria as the sole source of carbon, nitrogen, and energy, these pollutants could be transformed by some isolating bacteria as non-growth supporting substrate, generally in the presence of a growth supporting substrate, a process termed cometabolism [18]. Cometabolism was proved to be useful for degrading a variety of minimally degradable compounds, especially isomers and homologs of an identified parent compound [13,19]. Definitely, cometabolism broadens the application of microbial degradation on fluorine contamination remediation.…”