Isotopic fractionation of carbon and chlorine by microbial degradation of dichloromethane

Microbial culture experiments were performed at 22 degrees C to investigate isotopic fractionation of carbon (C) and chlorine (Cl) during aerobic degr adation of dichloromethane (DCM) by MC8b, a gram-negative methylotrophic or ganism closely related to the genera Methylobacterium or Ochrobactrum. Valu es of the isotopic fractionation factor, alpha, were estimated from the exp erimental results. These values are 0.9576 +/- 0.0015 for C and 0.9962 +/- 0.0003 for Cl, corresponding to kinetic isotope effects (KIE) of 1.0424 for C and 1.0038 for Cl. The C isotope effect accompanying aerobic degradation of DCM by MC8b is roughly twice that resulting from microbial oxidation of CH4. Further studies of this type, for a variety of chlorinated aliphatic hydrocarbons (CAHs) under a range of biogeochemical conditions, may find im portant applications in the characterization and remediation of sites conta minated with CAHs. (C) 1999 Elsevier Science Ltd. All rights reserved.