Distribution characteristics and risk assessment of five categories of emerging contaminants in sediments of the Foshan section of the Pearl River

Emerging contaminants (ECs) are ubiquitous in sediments, and systematic assessment of their risks is essential for protecting aquatic ecosystems and ensuring drinking water safety. In this study, sediment samples were collected from 10 monitoring sites along the Foshan section of the Pearl River (including the Xijiang and Beijiang Rivers) during the pre- and post-flood seasons of 2024. The concentrations of 52 ECs from five categories were systematically measured. The ecological risk was evaluated using the Ecological Risk Quotient (P) method, and a comprehensive risk ranking was performed based on a Toxicological Priority Index (ToxPi) model optimized by random forest. The results indicated that 44 of the 52 target ECs were detected, with cumulative concentrations ranging from not detected (ND) to 60.5 ng·g⁻¹, and a mean concentration of 0.83 ng·g⁻¹. Per- and polyfluoroalkyl substances (PFASs) had the highest detection rate (72.5%), while phthalate esters (PAEs) exhibited the highest mean concentration (1.70 ng·g⁻¹). Bisphenol A (BPA) (8.57 ng·g⁻¹) was the substance with the highest concentration. Spatial analysis revealed that the mean EC concentration in the Beijiang River (1.28 ng·g⁻¹) exceeded that in the Xijiang River (0.64 ng·g⁻¹). Temporally, concentrations during the pre-flood season were generally higher than those observed in the post-flood season. High risk (P ≥ 1) was identified at 2.1 % of the monitoring sites, with ultraviolet absorbents (UVAs) and PAEs accounting for the largest shares of high-risk sites (5.5 % and 2.8 %, respectively). Phthalate di(2-ethylhexyl) ester (DEHP) and 2-(2-Hydroxy-5-tert-octylphenyl)benzotriazole (UV-329) were identified as key high-risk substances. The ToxPi model ranked the top 10 ECs in terms of overall risk, all of which were PFASs. The comprehensive risk scores for each category were as follows: PFASs (0.63) > hormones (HORMs, 0.47) > PAEs (0.33) > phenols (PCs, 0.30) > UVAs (0.24). This study presents a preliminary assessment of the occurrence and risk profiles of ECs in the Foshan section of the Pearl River, providing a scientific basis for targeted management of these contaminants in the region.