COMPOUND-SPECIFIC CARBON ISOTOPIC ANALYSIS OF AROCLORS, CLOPHENS, KANECLORS, AND PHENOCLORS

Advances in instrumentation have allowed the measurement of the isotop ic composition of C-13/C-12 (delta(13)C) in the effluent of a gas chro matograph for each individual peak; this technique is called compound- specific isotope analysis (CSIA). CSIA has been used in a variety of b iogeochemical studies to determine the sources of hydrocarbons. We hav e utilized the technique of CSIA to examine delta(13)C of the individu al congeners in the polychlorinated biphenyl (PCB) mixtures Aroclor 12 42 and 1254; Clophen A30, A50, and T241; Kanechlor 200, 300, 400, 500, and 600; and Phenoclor DP-3, DP-4, DP-5, and DP-6. In addition, the b ulk delta(13)C Values (i.e., the entire mixture) were determined for c omparison to the CSIA values. Bulk delta(13)C Values ranged from -22.3 4 parts per thousand (Phenoclor DP-3) to -26.95 parts per thousand (Cl ophen A30). The analogues Aroclor 1254, Clophen A50, Kanechlor 500, an d Phenoclor DP-5 had different bulk delta(13)C values. The bulk values fall within the CSIA values and are similar to the average of the del ta(13)C values of the individual congeners. In both the bulk delta(13) C analysis and the CSIA, the PCBs show increased C-13 depletion with i ncreasing chlorine content. Values for congeners within a PCB mixture also showed a wide range of delta(13)C isotope values; for example, de lta(13)C Values in the Kanechlor 600 mixture range from -18.65 parts p er thousand (PCB 52) to -27.98 parts per thousand(PCB 180). Large diff erences in delta(13)C values for individual congeners between mixtures were found (e.g., PCB congener 52, Clophen A30-2835 parts per thousan d vs Kanechlor 600-18.65 parts per thousand). The delta(13)C values fo r individual congeners in the PCB mixtures showed a similar pattern of C-13 depletion with increasing chlorine content, this trend is probab ly a result of kinetic isotope effects caused by the position of the c hlorine atom on the biphenyl molecule. The wide range in delta(13)C ra tios between PCB mixtures and individual congeners may prove to be a p owerful tool in the determination of sources of PCBs in the environmen t, and this technique may have wide applications in environmental chem istry.