Source apportionment of polychlorinated biphenyls using compound specific isotope analysis

Reported here are results of the compound specific carbon isotopic analysis (CSIA) of individual PCB congeners. This investigation was designed to determine the suitability of CSIA on this class of compounds in natural materials. Samples of duck tissue, duck liver, duck egg and grass carp were collected from the Housatonic River, Massachusetts, and compared with samples of fresh Aroclorfi 1242, 1254,1260, and 1262. Twenty congeners were selected for isotopic analysis based on their ability to be separated chromatographically and their expected abundance in tissue samples. Animal tissue samples showed variable PCB patterns and abundances although all animals were expected to have been exposed to Aroclorfi 1260. These characteristics are thought to be related to the structure of the food web or metabolic and physiological features of the individual animals. Grass carp samples had excellent correlation in the isotopic compositions of the congeners. Although the correspondence of δ13C in congeners from fresh Aroclor 1260 to congeners from tissue samples may not be expected to be identical, the patterns of similarity were very supportive of the maintenance of the isotopic signal into the food chain. The patterns observed in these and other samples suggest a fractionation process where residual congener pools can become progressively enriched while the congeners produced from degradation are more depleted. The isotopic patterns provide insight to degradation processes and into relative metabolic stability of the various congeners in different animals. The results of this study suggest that CSIA analysis of PCBs at natural abundance can provide significant insight into tracing these compounds through the natural environment. The data also suggest that tracking PCB mixtures may be possible using CSIA techniques after standard chromatographic matching or other fingerprinting techniques become blurred.