Compound-specific carbon isotopic analysis of Aroclors, Clophens, Kaneclors, and Phenoclors

Advances in instrumentation have allowed the measurement of the isotopic composition of C-13/C-12 (delta(13)C) in the effluent of a gas chromatograph for each individual peak; this technique is called compound-specific isotope analysis (CSIA). CSIA has been used in a variety of biogeochemical studies to determine the sources of hydrocarbons. We have utilized the technique of CSIA to examine delta(13)C of the individual congeners in the polychlorinated biphenyl (PCB) mixtures Aroclor 1242 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 bulk delta(13)C Values (i.e., the entire mixture) were determined for comparison to the CSIA values. Bulk delta(13)C Values ranged from -22.34 parts per thousand (Phenoclor DP-3) to -26.95 parts per thousand (Clophen A30). The analogues Aroclor 1254, Clophen A50, Kanechlor 500, and 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 delta(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 increasing chlorine content. Values for congeners within a PCB mixture also showed a wide range of delta(13)C isotope values; for example, delta(13)C Values in the Kanechlor 600 mixture range from -18.65 parts per thousand (PCB 52) to -27.98 parts per thousand(PCB 180). Large differences in delta(13)C values for individual congeners between mixtures were found (e.g., PCB congener 52, Clophen A30-2835 parts per thousand vs Kanechlor 600-18.65 parts per thousand). The delta(13)C values for individual congeners in the PCB mixtures showed a similar pattern of C-13 depletion with increasing chlorine content, this trend is probably a result of kinetic isotope effects caused by the position of the chlorine atom on the biphenyl molecule. The wide range in delta(13)C ratios between PCB mixtures and individual congeners may prove to be a powerful tool in the determination of sources of PCBs in the environment, and this technique may have wide applications in environmental chemistry.