Approaches to the determination of polychlorinated biphenyl (PCB) concentrations in soils/sediments by dechlorination to biphenyl

A method for the dechlorination of PCB mixtures (Aroclor formulations) to b iphenyl was extended to soils. The contaminated sample was mixed with magne sium flakes, potassium hexachloropalladiate (K2PdCl6), propan-2-ol and wate r then permitted to react for up to six hours. Biphenyl, recovered by extra ction into hexane, was quantified by gas chromatography with flame ionizati on detection. The reaction was very efficient in propan-2-ol / water (simil ar to 95%), surfactant emulsion or sand mixture and virtually complete in s oil provided that excess magnesium (2 g) and the K2PdCl6 were added to the sample prior to the addition of water. Higher PCB loadings were readily det ermined in field contaminated soils either by direct determination within t he matrix or by standard additions. However, analyte concentrations were ap preciably over-estimated in Soxhlet or sonication extracts of a certified r eference material that contained sub-ppm levels of analyte. The over-estima tion is considered to result from the conversion in part of natural organic matter to biphenyl.