Characterisation of chlorinated hydrocarbons from chlorine and carbon isotopic compositions: scope of application to environmental problems

A set of chlorinated hydrocarbons (TCE, PCE, DCM, 1,1,1-TCA, chloroform) provided by four manufacturers has been isotopically characterised for both C and Cl, using a new sensitive method. A very large range of δ13C (from −51.66 to −24.07‰/PDB) associated with a very large range of δ37Cl (from −2.7 to +3.4‰/SMOC) was obtained. This range of δ37Cl is much larger than that of inorganic Cl (±1‰ SMOC) and most individual solvents show a very distinct δ37Cl compared to inorganic Cl isotopic signatures. Moreover, δ37Cl/δ13C pairs are distinct from one solvent/manufacturer to another. In a δ13C versus δ37Cl diagram, δ37Cl / δ13C pairs show different trends for the products of a single manufacturer compared to another. This suggests that Cl isotopic compositions are probably highly fractionated during organic synthesis. The δ37Cl values can be interpreted in terms of the probable manufacturing processes. Unlike the data published previously, with one exception, all the new results for samples reported here have positive δ37Cl values which might differentiate natural Cl from that derived from degradation. This method has significant potential as a tool for investigating environmental pollution problems; in particular, it offers the possibility for validating models of transport and fate of pollutants.