Compound-Specific Carbon Isotopic Analysis of Aroclors, Clophens, Kaneclors, and Phenoclors

Advances in instrumentation have allowed the measure ment of the isotopic composition of 13 C/ 12 C (δ 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 δ 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 δ 13 C values (i.e., the entire mixture) were determined for comparison to the CSIA values. Bulk δ 13 C values ranged from −22.34‰ (Phenoclor DP-3) to −26.95‰ (Clophen A30). The analogues Aroclor 1254, Clophen A50, Kanechlor 500, and Phenoclor DP-5 had different bulk δ 13 C values. The bulk values fall within the CSIA values and are similar to the average of the δ 13 C values of the individual congeners. In both the bulk δ 13 C analysis and the CSIA, the PCBs show increased 13 C depletion with increasing chlorine content. Values for congeners within a PCB mixture also showed a wide range of δ 13 C isotope values; for example, δ 13 C values in the Kanechlor 600 mixture range from −18.65‰ (PCB 52) to −27.98‰ (PCB 180). Large differences in δ 13 C values for individual congeners between mixtures were found (e.g., PCB congener 52, Clophen A30−28.35‰ vs Kanechlor 600−18.65‰). The δ 13 C values for individual congeners in the PCB mixtures showed a similar pattern of 13 C 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 δ 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.