LAUSR

Abstract Mining-contaminated waters may contain high levels of arsenic (As) and iron (Fe), among various metals and metalloids. The complex behavior of As makes its contamination difficult to remediate. This study aimed to determine the sources, possible association of As and Fe with colloids and their speciation and mobility in the Jiehe River, a stream impacted by gold mining. Particulate (>450 nm), colloidal (7–450 nm), and truely dissolved ( −1 with a median of 140 μg L −1 . Total Fe was 0.4–68.2 mg L −1 with a median of 15.0 mg L −1 . Arsenic was mainly adsorbed on ferrihydrite, goethite, and hematite in the upstream water samples. In contrast, it was mostly in truely dissolved forms in the water samples at downstream. Visual MinteQ 3.0 modelling results revealed that As adsorbed on, or co-precipitated with, stream sediment can be easily released under the environmental conditions of the downstream reach (11.4–37.5 km). These findings would benefit the environmental management of gold mining impacted Jiehe River, and indicate the need for further quantitative research on As migration facilitated by Fe (hydr)oxide colloids and the release of As from contaminated stream sediments.