Stability of residual levels of polychlorinated biphenyls in cold-extracted herring oil

The measurement of residual concentrations of polychlorinated biphenyl (PCB) in a variety of foodstuffs and other biological materials has been characterized by a large (up to 50%) interlaboratory variation (bias). An interlaboratory coefficient of variation of 14% was reported for a study in which exact methodological details and quantitative standard solutions were supplied to participants who were asked to determine the levels of a suite of six chlorobiphenyls (CB) present at trace levels in eel fat. Following the completion of the earlier study, remaining vials of fortified (approximately 1 mg Aroclor 1,254/kg herring oil) and control oils were stored and analyzed sporadically to determine if any changes in measured PCB concentrations in the oils resulted from changes in PCB and the oil during storage of approximately eight years.