Chiral Environmental Contaminants

Abstract

This article highlights techniques by which the enantiomers of chiral environmental pollutants can be separated and quantified. A large number of organic chemicals are chiral and exist as pairs of mirror images called enantiomers . These chemicals include legacy persistent organic pollutants (POPs) (e.g. polychlorinated biphenyls (PCBs)) and pesticides (e.g. dichlorodiphenyltrichloroethane (DDT)), as well as current‐use pesticides (e.g. pyrethroids), flame retardants (e.g. hexabromocyclododecane), and pharmaceuticals (e.g. ibuprofen). Understanding the environmental behavior of chiral xenobiotic compounds is important because enantiomers of a chiral compound may have different biological and toxicological effects, which must be delineated for accurate risk assessment of hazards, if any, posed by such chemicals. In addition, chiral chemicals are markers of biochemical activity in the environment, as enantiomer compositions are unaffected by physical and chemical processes but can change from differential enantiomer interactions with other chiral molecules (e.g. enzymes). For these reasons, the chirality of environmental pollutant occurrence, fate, and effects has been studied since the 1990s, when analytical capacity to measure chiral chemicals became widely available. We discuss major techniques for separating pollutant enantiomers including gas chromatography (GC), high‐performance liquid chromatography (HPLC), and capillary electrophoresis (CE). Enantioselective analytical separations are often coupled to mass spectrometry (MS) and tandem mass spectrometry (MS/MS) for quantification under environmentally relevant conditions (i.e. low concentrations to parts per trillion and below, in highly complex matrices such as wastewater and biological tissues). Issues involving sample preparation, data handling, and quality assurance/quality control are also described. Finally, we also illustrate applications of enantiomer‐specific measurements to gain insights into pollutants affecting environmental processes that could otherwise not be obtained, such as assessing pollutant biodegradation and delineating pollutant sources.