Enantioselective behavior of environmental chiral pollutants: A comprehensive review

Enantiomeric profiling of chiral environmental contaminants is an actual and imperative issue. Despite having similar physicochemical properties, enantiomers may differ in their interactions with enzymes, receptors and other chiral molecules leading to different biological response. Their differences in bio-degradation, transformation or accumulation should be carefully considered when assessing health risks since they can affect living organisms in a different way. This work reviews the behavior of several groups of environmentally relevant chiral contaminants including pharmaceutical compounds, personal care products, perfluoroalkyl substances, brominated flame retardants, pesticides and polychlorinated biphenyls and their main metabolites. The enantioselectivity and fate of these compounds in: i) wastewater treatment plants, ii) aquatic and terrestrial environments; and iii) living organisms is discussed. It cannot be predicted whether each specific enantiomer of a chiral compound will be preferably enriched or degraded. The extent of stereoselectivity is associated to several factors, including the specific chiral pollutant, the environmental matrix, the treatment technology used, as well as the season and local environmental factors (pH, soil texture, porosity, organic amended), which are in turn influenced by the activity of the microbial communities. Therefore the environmental fate of enantiomers always needs to be investigated.