Combined collection systems of sewage and rainfall runoff seriously affect the spatial distributions of natural estrogens and their conjugates in river water: insights from the Pearl River of China

So far, little has been known about how combined sewage and runoff collection system (CCSs) affect emerging contaminants in river water. To fill up the knowledge gap, this study was conducted to investigate the spatial distributions of three natural estrogens (NEs, i.e., estrone (E1), 17β-estradiol (E2) and estriol (E3)) and their conjugates (C-NEs) in the Pearl River in the wet and dry seasons. Results showed that the respective average concentrations of NEs and C-NEs at different locations alongside the Pearl River in the wet season were 7.3 and 1.8 times those in the dry season. Based on estrogen equivalence (EEQ), the average estimated EEQ level in the Pearl River waters in the wet season was nearly 10 times that in the dry season. These seemed to imply that the CCSs in the wet season not only cause untreated sewage into the receiving water body, but greatly decrease the removal efficiency of NEs and C-NEs in wastewater treatment plant. Furthermore, the estimated annual loads of E1, E2, and E3 to the Pearl River in the wet season accounted for about 88.6%, 100%, and 99.3 of the total annual loads. Consequently, this work for the first time demonstrated that the CCSs in cities with high precipitation are unfavorable for controlling of emerging contaminants.