Carbon isotope fractionation during aerobic mineralization of 1, 2-dichloroethane (1,2-DCA) by Xanthobacter autotrophicus GJ10 was investigated. A strong enrichment of (13)C in residual 1,2-DCA was observed, with a mean fractionation factor alpha +/- standard deviation of 0.968 +/- 0.0013 to 0.973 +/- 0.0015. In addition, a large carbon isotope fractionation between biomass and inorganic carbon occurred. A mechanistic model that links the fractionation factor alpha to the rate constants of the first catabolic enzyme was developed. Based on the model, it was concluded that the strong enrichment of (13)C in 1,2-DCA arises because the first irreversible step of the initial enzymatic transformation of 1,2-DCA consists of an S(N)2 nucleophilic substitution. S(N)2 reactions are accompanied by a large kinetic isotope effect. The substantial carbon isotope fractionation between biomass and inorganic carbon could be explained by the kinetic isotope effect associated with the initial 1,2-DCA transformation and by the metabolic pathway of 1,2-DCA degradation. Carbon isotope fractionation during 1,2-DCA mineralization leads to 1,2-DCA, inorganic carbon, and biomass with characteristic carbon isotope compositions, which may be used to trace the process in contaminated environments.

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Evidence of substantial carbon isotope fractionation among substrate, inorganic carbon, and biomass during aerobic mineralization of 1, 2-dichloroethane by Xanthobacter autotrophicus.

Biological transformations of 1,2-dichloroethane in subsurface soils and groundwater

Quantification of biotransformation of chlorinated hydrocarbons in a biostimulation study: added value via stable carbon isotope analysis.

Degradation of 1,2-dichloroethane by microbial communities from river sediment at various redox conditions

Aerobic bioremediation of 1,2 dichloroethane and vinyl chloride at field scale

Bioremediation strategies for an industrial site located in the Rotterdam Harbor Area, the Netherlands and contaminated with 1,2-dichloroethane (1,2-DCA), are under investigation. The contamination is present in a confined anaerobic aquifer. The objective of the research is to assess the potential of intrinsic (bio )degradation and enhanced biodegradation as effective risk reducing measures. Close to the contaminant source, 1,2-DCA is present at concentrations up to 500 mg per liter. From the possible intrinsic dechlorination products of 1,2-DCA (i.e. 2-chloroethanol, vinylchloride, chloroethane and ethene), vinylchloride (VC) is occuring at relatively high concentrations (up to 2 mg/liter). The type, rate and parameter dependency of the dechlorination processes occurring in this aquifer are currently being investigated by analyzing groundwater concentration profiles of the dechlorination products and by performing laboratory studies with material from the contaminated site. First results indicate that natural attenuation alone, is not sufficient to prevent the plume from further spreading. Therefore a field study at pilot-scale is underway to evaluate remediation strategies which are designed from screening studies at the laboratory scale.

Intrinsic dechlorination of 1,2-dichloroethane at an industrial site

The feasibility of intrinsic and enhanced bioremediation approaches for 16 contaminated sites in the Netherlands are discussed. At at least five out of 10 chlorinated solvent sites, natural attenuation can be used as one of the tools to prevent further dispersion of the plume. At two sites stimulation of the intrinsic dechlorination processes in a bioactived zone is required, and pilot field tests are currently under way. For three sulphatereducing/methanogenic aquifers contaminated with aromatic compounds, microcosm studies demonstrated that natural anaerobic degradation of the risk-determining benzene does not to occur spontaneously. Benzene biodegradation could be initiated by feeding small amounts of oxygen (in all samples) or nitrate (only in one sample), and these techniques are currently tested in field-pilot studies. Redox-microbiological characterisation of two locations contaminated with hexachlorocyclohexanes indicated significant intrinsic biodegradation of HCH's in methanogenic/sulphate-reducing parts of the contaminant plumes, and of the HCH-degradation products chlorophenol and benzene under sulphate/iron reducing conditons. Biostimulated zone's remain required to complete the degradation of HCH and the degradation product monochlorobenzene. Risk-based guideline's for assessing the feasibility of natural attenuation approaches for various contaminant situations are currently under development, making use of already existing protocols (USA) and taking European and National specific conditions, knowledge and regulatory constraints into account.

T.N.P. Bosma

Papers

Intrinsic dechlorination of 1,2-dichloroethane at an industrial site

Intrinsic and enhanced bioremediation in aquifers contaminated with chlorinated and aromatic hydrocarbons in The Netherlands