An overview of the enantioselective determination of polychlorinated biphenyls in environmental samples

Megson, David ORCID: https://orcid.org/0000-0002-8881-3860, Niepsch, Daniel and O'Sullivan, Gwen (2024) An overview of the enantioselective determination of polychlorinated biphenyls in environmental samples. In: Comprehensive Analytical Chemistry COAC Volume Number 111. Elsevier.

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Abstract

Polychlorinated biphenyls (PCBs), are one of the most infamous environmental pollutants. There are a total of 209 different PCBs but not all are chiral. Only congeners with three or four chlorines in the 2,2′ or 6,6′ positions have two optical isomers (enantiomers). There are hundreds of published analytical methods to measure PCBs, but these tend to focus on determining either the WHO12 PCBs, or a subset of indicator PCBs (e.g. i3 or i7). Chiral separations can be much more complicated as they require not only the separation of the enantiomers from each other, but separation from other PCBs and potential interferants. Analysis of chiral PCBs is predominantly preformed using gas chromatography and cyclodextrin based columns, and separation can be enhanced using multidimensional chromatography. PCBs in commercial mixtures are racemic (EF of 0.5) and are unaltered by abiotic processes. However, enantioselectivity can occur in organisms, which results in enrichment of one enantiomer relative to the other. This has been observed in humans and a wide range of biota. Enantioselectivity is believed to be driven by CYP450 enzymes, but exact mechanisms are not fully understood. Higher mammals and organisms with the greatest PCB concentrations tend to have the largest degree of fractionation, but there are contradictions within the literature and EFs can cover wide ranges. In some cases, enrichment of the two different enantiomers has been reported. Enantiomer fractions are understudied, but can provide powerful lines of evidence to help understand the environmental fate and transport of PCBs.