Occurrence and Fate of Psychiatric Pharmaceuticals in Wastewater Treatment Plants in Hong Kong: Enantiomeric Profiling and Preliminary Risk Assessment

Psychiatric pharmaceuticals are receiving widespread attention as emerging contaminants. Wastewater treatment plants (WWTPs) represent primary point sources for pharmaceuticals in the aquatic environment. In this study, the occurrence and fate of 10 psychiatric pharmaceuticals, half of which are chiral compounds, were investigated in six WWTPs in Hong Kong over a period of one year. Average levels of the analytes among these WWTPs in influent, effluent, and sludge ranged from <0.1 ng/L (clomipramine) to 84.6 ng/L (sertraline), from 0.3 ng/L (risperidone) to 45.6 ng/L (citalopram), and from <0.1 ng/g dry weight (dw) (risperidone) to 174 ng/g dw (sertraline), respectively. Overall, 26.1% of the analytes were sorbed to suspended solids in influent, indicating the necessity of identifying psychiatric pharmaceuticals in both dissolved and solid phases instead of filtered wastewater only. Mass balance results revealed back-transformation of the studied psychiatric pharmaceuticals compensated for their loss via degradation. Average removal efficiencies in the investigated WWTPs ranged from 20.4% (diazepam) to 50.8% (sertraline). The enantiopure pharmaceutical (+)-cis-1S,4S-sertraline, among four sertraline enantiomers, was the only enantiomeric form detected in all samples. Fluoxetine, citalopram, and mirtazapine did not show significant enantioselectivity during treatment in most cases. Three of the five chiral pharmaceuticals probably posed high ecological risks to aquatic organisms, calling for more comprehensive enantiospecific ecotoxicity studies of these pharmaceuticals.