Stable Isotopic Characterisation of Extent of Anaerobic Bacterial Dehalogenation of Chlorinated Solvents: A Feasibility Study

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Objectives

The main objective of this feasibility study was to determine if bacterial reductive dehalogenation of chlorinated solvents produces a characteristic chlorine stable isotope composition, indicative of the extent of degradation. To confirm this, it was necessary to:

  • establish if the isotopic composition, if produced, is independent of the rate of degradation
  • confirm that chlorine isotopic composition of solvents is unaffected by contact with aqueous chloride.

Approach

Laboratory degradation experiments

The progress of dehalogenation was monitored and a pilot experiment performed to compare the effects of successive samplings from the same vessel and running replicate experiments for different periods of time. Two sets of controls will be run, without bacteria and with autoclaved bacteria.

Isotopic validity check

This tested for isotopic exchange between phases, which, as expected, was negligible.

Sample analysis

All samples from the laboratory experiments and the field were analysed in the same way. Organic phases were analysed by gas chromatography, which was used as a preparative step for isotopic analysis. Chloride in water was measured by ion-chromatography.

Isotopic analysis

Solvent samples used in the degradation experiments and separated, extracted organic phases were prepared for isotopic analysis using a newly developed method.

Interpretation

The effect for d 37CI was calibrated for the various laboratory experiments. The results were also related to other variables: reaction rate, microbial species and growth conditions.

Summary of principal achievements of the work

i) Scientific achievements (and beneficiaries)

First measurement of chlorine isotope fractionation factor for anaerobic dechlorination (Contaminated land problem holders, Other researchers)

Demonstrated that the isotopic effect is similar for different organisms and that it is sufficiently regular to conform to a Rayleigh Distillation fractionation model (Other researchers)

ii) Practical (and beneficiaries)

Demonstrated feasibility of a robust approach to quantify extent (and thus rate) of microbial degradation of CAH (Those owning, seeking to develop or responsible for regulating, contaminated land: e.g. Industrial companies, National Government [e.g.MoD], Local authorities.

Start date/duration

June 1998 Eight months

Lead Organisation

University of Reading

Deliverables

The hypothesis has been proven in this study, the next stage will be to develop the methods in collaboration with problem holders and other academic researchers.

Further Details

Further information is available from the following contacts:

Lead Researcher: Prof M L Coleman

Tel: 0118 931 6627, Fax: 0118 931 0279, e-mail: m.l.coleman@reading.ac.uk

URGENT Programme Manager: Graham Leeks

Tel: 01491 692203, Fax: 01491 692313, e-mail: gjll@ceh.ac.uk