Pharmaceuticals are receiving widespread attention as emerging contaminants because of their global occurrence in various environmental compartments and potential risks posed on nontarget organisms. Among various therapeutic classes of pharmaceuticals, antibiotics and psychiatric pharmaceuticals have received special attention due to the induction of bacteria resistance and rapid endocrinal disruption effects on nontarget organisms at environmentally relevant concentrations, respectively. Previous studies evidenced that the ecotoxicity of chiral pharmaceutical enantiomers could be stereoselective. However, there is relatively scarce information in this research area. Therefore, the main objectives of the present study were to investigate the occurrence of 29 antibiotics and 11 (chiral) psychiatric pharmaceuticals in wastewater, surface water and sediment in Hong Kong waters and the Pearl River Estuary (PRE), as well as to preliminarily assess their ecological risks and reveal the enantiomeric profiles of the chiral psychiatric pharmaceuticals.

Wastewater treatment plants (WWTPs) represent primary point sources for pharmaceuticals released into 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 one-year period in 2018−2019. Average levels of the analytes among these WWTPs in influent, effluent and sludge ranged from < 0.100 ng/L (clomipramine) to 84.6 ng/L (sertraline), 0.400 ng/L (risperidone) to 45.6 ng/L (citalopram) and < 0.100 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 determining psychiatric pharmaceuticals in both dissolved and solid phases instead of filtered wastewater only. Mass balance results revealed that 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), which is unsatisfactory. Biological treatment plants showed better performance in removal of psychiatric pharmaceuticals than chemically enhanced primary treatment (CEPT) plants did. The enantiopure pharmaceutical (+)-cis-1S,4S-sertraline, among four sertraline enantiomers, was the only enantiomeric form detected in all samples. Fluoxetine, citalopram and mirtazapine showed enantioselectivity after their excretion from humans and leading to WWTPs, compared with their marketed forms; nevertheless, they did not show significant enantioselectivity during treatment in most cases.

The occurrence of 29 antibiotics and 11 psychiatric pharmaceuticals in wastewater effluent, river water and seawater samples collected in 2020 in Hong Kong was further investigated, and their ecological risks were evaluated. The sampling points of river water and seawater were either carriers or receivers of wastewater outfalls, near landfills or near aquaculture zones. Levels of Ʃpharmaceuticals ranged from 3.62 ng/L to 1040 ng/L (median: 17.0 ng/L) in seawater, 0.682 ng/L to 1510 ng/L (median: 65.4 ng/L) in river water and 526 ng/L to 7090 ng/L (median: 2590 ng/L) in wastewater effluent. Kai Tak River, Yuen Long River, River Indus and Kwun Tong Typhoon Shelter were identified as hotspots of pharmaceutical contamination. Erythromycin-H₂O, clarithromycin, sulfamethoxazole, sulfadiazine, lincomycin, trimethoprim and diazepam were frequently detected in all samples, with detection frequencies > 80.0%. Notably, despite its low levels detected in wastewater effluent (max: 5.79 ng/L [STSTW, wet]), diazepam was commonly found in surface water samples at trace levels as high as 3.96 ng/L (KN1, dry). Regarding the geographic orientation of seawater sampling sites, seawater from the eastern side of Hong Kong was less polluted with less variance and lower levels of pharmaceuticals detected, due to relatively minor influence from wastewater outfalls. In most cases, the enantioselectivities of the chiral psychiatric pharmaceuticals in surface waters of Hong Kong were similar to those found in WWTPs. However, consistently lower EF values of the chiral psychiatric pharmaceuticals were found at Yuen Long Creek, turning citalopram and fluoxetine into R-preference form, requiring further studies to clarify the reasons. Still, (+)-cis-1S,4S-sertraline was the only form found in surface waters in Hong Kong. Our risk assessment, performed in the worst-case scenario, revealed that clarithromycin and azithromycin posed high risks to the aquatic organisms, whereas ceftazidime and ciprofloxacin showed high potential of inducing antimicrobial resistance (AMR) in the surface waters in Hong Kong. Several psychiatric pharmaceuticals, including fluoxetine, sertraline, citalopram and diazepam, can pose high risks to the nontarget aquatic organisms in Hong Kong surface waters.

We expanded our investigated regions to the Pearl River Delta (PRD), to which Hong Kong is adjacent, one of the most highly urbanized and industrialized regions in China. The Pearl River receives substantial domestic and industrial wastewater effluent and agriculture and aquaculture runoff, which run into the South China Sea (SCS) through eight estuary outlets. In the present study, surface and bottom water from these eight outlets was sampled simultaneously on three separate days during a typical subtropical wet season, featuring neap, moderate and spring tides, respectively. Surface sediment from the eight outlets was also analyzed. Spatial distribution in the receiving marine waters of the Lingding Sea was also investigated. In water samples of the riverine outlets, 15 out of the 40 target pharmaceuticals were detected, with total concentrations of all target pharmaceuticals (∑pharmaceuticals) ranging from 10.9 ng/L to 39.5 ng/L. Apparently higher concentrations of sulfamethazine (6.04–16.6 ng/L) were identified at Humen (HM), suggesting extra non-point sources. Diazepam was the only psychiatric pharmaceutical detected ranging from 1.23 to 1.61 ng/L. Higher concentrations of ∑pharmaceuticals were found in the sediment of the outlets, ranging from 6.79 to 141 ng/g dw, with 24 analytes detected. Several classes of antibiotics accounted for high proportions, including fluoroquinolones, tetracyclines and macrolides, many of which were not detected in water samples, indicating their preferential partitioning in sediment, accumulation potential and thereby preservation in sediment. In the Lingding Sea, the highest concentration of ∑pharmaceuticals was found at the point closest to the HM outlet at 24.7 ng/L. For other sampling sites, concentrations of ∑pharmaceuticals in the surface layer were quite comparable to each other, ranging from 8.35 to 13.5 ng/L. The statistical analysis implicated freshwater runoff as main source of pharmaceutical input in the Lingding Sea. Our results were among the best-case scenarios, compared with those of other studies worldwide, and thereby, no high risks were identified for either individual or mixtures of pharmaceuticals in the PRE.

Knowledge on the environmental enantioselectivities of chiral psychiatric pharmaceuticals remains scarce but is increasingly vital in environmental sciences. In the present study, I have revealed the enantioselectivities of psychiatric pharmaceuticals regarding their environmental occurrence and risk assessment, and highlighted the urgent need of ecotoxicity data at enantioselective level. For future studies, sampling and analysis of stormwater in Hong Kong should be conducted, which would be a good supplement to the pharmaceutical pollution situation in Hong Kong’s urban water system. Further studies should be performed to clarify the factors that influence the enantioselectivity of the target psychiatric pharmaceuticals in Hong Kong surface waters.