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.