Contrasting optical properties of dissolved organic matter in rivers around an antimony mine, Hunan Province, China: implications for antimony mobility

Previous studies have verified that dissolved organic matter (DOM) is an important factor affecting the migration and transformation of antimony (Sb) in aquifers. However, the influence of DOM on Sb mobilisation in surface water remains unclear. A total of 35 samples were collected from river water to compare the spectroscopic characteristics and chemical properties of DOM between high- and low-Sb river water and determine the role of DOM in Sb mobility in river water. The DOM concentrations in the high-Sb river water ranged from 0.62 to 1.31 mg/L, with a mean value of 0.97 mg/L. In contrast, the DOM concentration in low-Sb river water varied from 0.65 to 3.90 mg/L, with a mean value of 1.30 mg/L. DOM mainly originates from protein-like substances, followed by terrestrial humic-like and fulvic-like components. Complexing agents with Sb(Fe-Sb) and competitive adsorption with Sb are considered the predominant formation mechanisms for DOM-controlled Sb in river water. The different contributions of humic-like, fulvic acid-like, and protein-like substances in high- and low-Sb river water are due to the mixing behaviours of various DOM sources downstream of the mining area. The findings of this study will further enhance our understanding of the mechanisms responsible for elevated Sb concentrations driven by DOM in river water.