Analysis, fate and toxicity of chiral non-steroidal anti-inflammatory drugs in wastewaters and the environment: a review

Non-steroidal anti-inflammatory drugs (NSAIDs) are found in the aquatic environment globally. Such drugs including naproxen, ibuprofen and ketoprofen are chiral molecules. Enantiomers of those drugs have identical physicochemical properties but can behave and interact differently in chiral environments due to differences in their three-dimensional shape. This results in enantiospecific differences in environmental fate and toxicity, which is often overlooked. Therefore, we review the analytical methods, occurrence and fate, and toxicity of chiral non-steroidal anti-inflammatory drugs at the enantiomeric level. The advancement of enantioselective chromatography methods, particularly the use of polysaccharide-based stationary phases, has enabled trace determination of enantiomers in complex environmental matrices. Macrocosm and microcosm studies of engineered and natural environments revealed that such drugs can undergo both enantioselective degradation and chiral inversion. Enantioselectivity has been reported during wastewater treatment, in surface waters and in agricultural soils. The use of microcosms spiked with individual enantiomers over racemates is essential to evaluate these degradation and inversion fate processes. The chiral inversion process whereby one enantiomer converts into its antipode can be significant if the more toxic enantiomers are formed. Existing enantiospecific effect studies report less than an order of magnitude difference in enantiomer toxicity. However, toxicity data for enantiomers are limited and further research is needed to better appreciate the environmental risk at the enantiomeric level.