AbstractWhile organic corrosion inhibitors are ubiquitous in aquatic environments, knowledge on their occurrence, sources and transport in urban surface water is still scarce. In this study, the spatial and seasonal variations of organic corrosion inhibitors and their potential sources were investigated in the Pearl River Delta (PRD), one of the most highly urbanized watersheds in China. A total of 8 compounds belonging to benzothiazole (BTH) and benzotriazole (BTR) groups respectively, were identified in the Pearl River. In addition, there were clear spatial and temporal differentiations in the concentration profiles. The dry season provided higher concentrations of BTH (213–1082 ng L−1) and BTR (112–1279 ng L−1) compared to the wet season (30–574 ng L−1 for BTH and 23–482 ng L−1for BTR), indicating a dominant process of dilution. Remarkably higher concentrations and similar composition features of targets were observed in the effluent samples from two sewage treatment plants (STPs). Our study indicated that rainfall runoff from urban traffic roads during wet season may also be an important contributor to the Pearl River water environment. The annual total mass loading of corrosion inhibitors from the main channel of the Pearl River is 53.2 tons and exhibited strong seasonal variation. Effluents discharge from STPs and urban rainfall runoff from traffic roads are main sources of corrosion inhibitors to the Pearl River.