Dissolved organic matter influences the activation and release risks of arsenic and thallium in mine stream sediments

Dissolved organic matter (DOM) is widely distributed in sediments, however its potential effects on heavy metals at mine area remain insufficiently investigated. This study focused the influence of DOM on the activation and release of arsenic (As) and thallium (Tl) from mine-impacted sediments. Results showed that DOM governs the spatial heterogeneity, mobilization dynamics, and associated health risks of heavy metals in mine sediments. As and Tl concentrations in mine stream sediments significantly exceeded local background levels, and their spatial distributions exhibited a strong positive correlation with DOM. With increasing of DOM concentrations and more labile, microbially derived components collectively elevated, the concentrations of activated As and Tl increased by 144 % and 221 %, respectively. DOM accounts for over 99 % of the spatial variance of activated As and Tl through reductive dissolution of iron oxides, release proton or direct complexation while its molecular composition governs As and Tl mobility and associated health risks. The protein-like and fulvic acid-like DOM increased both short-term hazards and long-term carcinogenic risks above safety thresholds. Fulvic acid-like DOM mobilized As, while protein-like DOM co-released As and Tl. Fulvic acid-like DOM uniquely enhanced As(III) mobility while most effectively suppressing Tl(III) solubility. This study clarifies the DOM for the release of As and Tl in sediments at mine area, providing a scientific basis for heavy metals risk assessment and control in mine.