Flow confluence affects the distribution and accumulation of Sb from the effluent of a sewage treatment plant in the plain river network of the Yangtze river estuary

Complicated hydrodynamic conditions can significantly impact sediment disturbance and pollutant movement in river networks. Yet, the influence of river‒lake confluence areas on the distribution and accumulation of heavy metals in river networks remains unknown. This paper focused on antimony (Sb) contamination, as Sb is an emerging contaminant in non-mining areas.

This study investigated the distribution and accumulation characteristics of Sb in water and sediment in the confluence area of Taipu River and Beijing-Hangzhou Canal in the Taihu Lake basin, China. We used ArcGIS 10.8 to map the distribution of Sb in three phases: dissolved, suspended particulate matter (SPM), and riverbed sediment. The Inverse Distance Weighting (IDW) interpolation method was applied to analyze the spatial distribution of Sb in the confluence area. Furthermore, Pearson correlation analysis was conducted to investigate the relationship between Sb concentration in the water and the amount of Sb in different fractions in the sediment. The risk of Sb in water and sediment was evaluated by the single factor pollution index method and geo-accumulation index assessment, respectively.

The results showed that the distribution of Sb in water was significantly affected by the local textile industries. Dissolved Sb concentration showed a high degree of variation (CV = 102.1%) in the study area, ranging from 0.49 to 7.28 µg L⁻¹, as Sb concentration was positively correlated with the more drainage outlets. The maximum concentrations of Sb in SPM and riverbed sediment were both found in the eastern part of the study area, with values of 0.62 µg L⁻¹ and 6.00 mg kg⁻¹, respectively. The presence of Sb in tailwater has a great influence on the accumulation of sediments in the surrounding waters, especially in the local area of hydraulic intersection, it becomes the “sink” of trace Sb in the tailwater of the sewage treatment plant.

When studying the potential impact of tailwater of sewage treatment plant on the receiving water body, it is of great importance to consider the role of Sb and reasonably improve the Sb discharge standard of sewage treatment plant. The helps to reduce the pollutant index in tailwater and to control the risk of Sb in the regional water source environment.