Spatial Distribution of As, Cr, Pb, Cd, Cu, and Zn in the Water and Sediment of a River Impacted by Gold Mining

Abstract

Historical and active mining has adversely affected the geochemistry of the Jiehe River in the Jiaodong Peninsula, which has the largest gold ore reserves in China. Water and sediment samples were collected along the 37.8 km long river during the critical low flow season. Samples were analyzed for their geochemical properties, total concentrations of As, Cr, Pb, Cd, Cu, and Zn in the sediment, and dissolved/particulate concentrations of trace elements in filtered/unfiltered water samples. Our results demonstrate that substantial amount of these elements have been released into the Jiehe River during the processes of extracting, selecting, processing, and smelting at the many historical and active gold mining sites in the watershed. High concentrations of potentially toxic elements (1.9–1,004 μg L−1 As, 4.2–210 μg L−1 Cr, 7.9–9,529 μg L−1 Pb, 2.0–855 μg L−1 Cd, 47.4–8,494 μg L−1 Cu, and 105–11,336 μg L−1 Zn) have seriously affected water quality in the region. In addition, these contaminants have accumulated in the bed sediment (7.7–181 mg kg−1 As, 24.1–726 mg kg−1 Cr, 9.9–1,100 mg kg−1 Pb, 0.1–51.8 mg kg−1 Cd, 22.1–1,524 mg kg−1 Cu, and 53.5–5,484 mg kg−1 Zn). Spatial distribution of these contaminants in water and sediment is controlled by the discharge from point and non-point sources as well as the reactive transport processes. Spatial analysis conducted on the sediment and stream concentration of As, Pb, Cd, and Zn suggests that two mining-related sources, at 4.3 and 17.6 km downstream of the headwaters, contributed most of the As, Pb, Cd, and Zn load as particulates. In contrast, high levels of Cr and Cu in the sediment are not related to the current loading pattern and may be due to historical sources. As the first comprehensive study on the pollution caused by intensive gold mining in this area, this research has provided much needed information to establish effective management and remediation strategies.