Abstract: This study focuses on the Duliu River, which has been contaminated due to antimony mining. Water and suspended particulate samples were collected from the upstream reaches and analyzed using tangential ultrafiltration, S isotope technology, and ion chromatography to obtain the physical and chemical properties. The aim is to investigate the effects of mining activities on the concentration of antimony (Sb) in rivers and the mechanisms behind the transformation and purification of Sb in different hydrological conditions. Results show that from the initial pollution point to the Sandu county section, the concentration of dissolved Sb decreased from 148.77 μg/L to 49.98 μg/L. Affected by antimony mining, the δ³⁴S value in mainstream Duliu River increased, ranging from -0.58‰ to 1.21‰ and exhibiting a significant positive correlation with Sb concentration (r=0.71,p<0.05). The contribution ratio of producing and closed mines to the Sb concentration in the downstream section was 1.3:1. The concentration of dissolved Sb, including truly dissolved and colloidal Sb, was approximately 170 times that of particulate Sb, with truly dissolved Sb accounting for over 80%, mainly in the form of SbO^-₃. Despite lower concentration of suspended particulates in the reservoir compared to river sections, the Sb concentration in reservoir was higher. Sb was less likely to transform into colloid and particulate and was not easily removed through adsorption and agglomeration. Moreover, health risk assessment indicated that the HI and CR values were in the ranges of 3.59-10.77 and 2.52×10^-3-7.55×10^-3, respectively, implying possible carcinogenic risks to humans. In conclusion, truly dissolved Sb was the primary form posing a health hazard. This study provides a scientific basis for Sb pollution control and ecological protection in the contaminated Duliu River.

Key words: water environment, mining, Sb pollution, S isotope, health risk assessment