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Abstract
Enantiomeric fraction (EF) analysis of chiral pharmaceuticals has been proposed as a potential indicator of biological transformations of environmental pollutants. Ibuprofen, naproxen and ketoprofen, which are chiral nonsteroidal anti-inflammatory drugs (NSAIDs), were selected for assessment of their potential to be used as such indicators.
A highly sensitive and reliable method for the enantioselective analysis of these NSAIDs in wastewater and environmental water samples was developed. An indirect method for enantioseparation was achieved by the derivatization of the (R)- and (S)-enantiomers to amide diastereomers using (R)-1-phenylethylamine. Separation and detection of the individual diastereomers was undertaken by gas chromatography–tandem mass spectrometry (GC–MS/MS). The method is sufficiently sensitive for the detection of targeted drugs in a real tertiary treated wastewater sample, revealing measurable concentrations of both (R)- and (S)-enantiomers of the drugs. Isotope dilution using racemic D3-ibuprofen, racemic D3-ketoprofen and racemic D3-naproxen was shown to be an essential aspect of this method for accurate quantification and EF determination.
The microbial degradation of both enantiomers of the NSAIDs was observed over 10 days in a Closed Bottle Test (CBT) under controlled laboratory conditions. (S)-ibuprofen was shown to be degraded faster than (R)-ibuprofen while non-enantioselective degradation was observed for ketoprofen. A very minor change was observed in naproxen EF, with a slight increase in (R)-naproxen concentration indicating the formation of this enantiomer during the experimental process. It is proposed that this formation occurred as the result of chiral inversion of (S)-naproxen.
The enantiospecific fate of the NSAIDs was then monitored before and after treatment by a laboratory-scale membrane bioreactor (MBR) treating synthetic wastewater and a full-scale MBR treating real municipal wastewater. Evidence of enantioselective biodegradation for ibuprofen and naproxen were again observed. Clear evidence for the formation of (R)-naproxen in the laboratory-scale reactor is presented and measurable concentrations of (R)-naproxen were consistently observed in full-scale MBR effluent.
This work has expanded our knowledge of the fate of these compounds during wastewater treatment to an understanding of the specific behaviours of the individual enantiomers. The variability of EF observed in the final effluent therefore may provide a useful indicator of the overall biodegradation performance of the wastewater treatment plant. The observation of chiral inversion during wastewater treatment has not previously been reported and adds a new dimension to the important topic of transformation products during wastewater treatment processes.