Retinoids and oestrogenic endocrine disrupting chemicals in saline sewage treatment plants: Removal efficiencies and ecological risks to marine organisms

Discharge of partially treated effluent from sewage treatment plants (STPs) is a significant source of chemical contaminants, such as retinoids and oestrogenic endocrine disrupting chemicals (EDCs), which are continuously input into the marine environments of densely populated and urbanized coastal cities. In this study, we successfully developed three analytical methods to detect and qualify retinoic acids (at-RA, 13c-RA & 9c-RA), their metabolites (at-4-oxo-RA, 13c-4-oxo-RA & 9c-4-oxo-RA), and oestrogenic EDCs using high pressure liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Using these methods, we found that the total concentrations of retinoids in the influents and effluents of three saline STPs in Hong Kong were 7.1-29 ng/L and 3.7-9.1 ng/L, respectively, and those of EDCs were 3107-5829 ng/L and 1225-2638 ng/L, respectively. Retinoids were dominated by at-4-oxo-RA or 13c-4-oxo-RA in wastewater, whereas at-RA and 13c-RA were the most abundant in sludge. Alkylphenols and bisphenol A were the dominant EDCs in wastewater, whilst alkylphenols, triclosan, and triclocarban were dominant in sludge. Overall, the sewage treatment processes in the STPs of Hong Kong were not highly efficient in the removal of retinoids and EDCs from wastewater influents, with removal efficiencies in the aqueous phase of 41-82% and 31-79%, respectively. The removals were attributed mainly to sorption and degradation. Due to such limited removal, the effluents from STPs and the adjacent seawaters (i.e., receiving water bodies) still exhibited relatively high concentrations of retinoids (2.0-4.3 ng/L in seawaters) and EDCs (71-260 ng/L in seawaters), which posed medium ecological risks to the coastal marine ecosystem of Hong Kong (i.e., hazard quotients: 0.1-1).