Recent studies have indicated that some chiral chemicals may undergo enantiomeric inversion in wastewater environments. This unusual transformation reaction is significant since many chiral chemicals tend to have one enantiomer that is significantly more toxic than the other. Transformation from the predominantly non-toxic enantiomer to a more toxic enantiomer, may indicate that the overall toxicity of a chiral chemical present in wastewater may increase, even as its overall concentration decreases.  Enantioselective analysis of chiral emerging contaminants is of interest since enantiomeric pairs can have quite different toxicity to each other and thus, the enantiomeric ratio can be an important consideration for environmental risk assessment. However, current ‘safe’ environmental threshold levels of emerging contaminants being used by some international authorities, do not differentiate between the enantiomer pairs, and may consequently lead to an inaccurate estimation of the ecotoxicity of the compound.  In this work, we have used a series of bioassays to show differential ecotoxicity among the enantiomers of some common pharmaceuticals drugs. The drugs that we have focused on are 2-arylpropionic acids including ibuprofen, naproxen and ketoprofen. Furthermore, we have used isotope-labelled versions of 2-arylpropionic acids to provide mechanistic insights as to what changes are occurring during biodegradation and engineered biological treatment processes.  The results from this work challenge the way environmental scientists think about the increasingly high profile issue of chemical ‘transformation products’ from wastewater treatment process. Furthermore, they reveal limitations in current analytical methodology, which may fail to fully account for changes in ecotoxicological risks for some trace chemicals.

Biologically mediated chiral inversion of emerging contaminants: Role of wastewater treatment

2019 Fall National Meeting

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