Abstract
The release of nanophase metal particles from sulfide mineral decomposition in mining-impacted environments is a growing concern because of the potential for the transport of nanoscale particles that could increase the distribution of the metals and their environmental impact. An analysis of total (unfiltered) and dissolved (450-nm filtered) metal concentrations in the mining-impacted Coeur d’Alene River indicates the leaching of dissolved metal forms from sediments and transport to and within the river. The distribution of metals between total and dissolved forms is driven by seasonal temperatures, hydraulic gradients, and ligand availability. Cd and Zn were the least influenced by changes in gradient and biological productivity between the upper and lower basins. Cd and Zn primarily travel as dissolved forms, with the lowest ratio of dissolved-to-total concentrations in spring and the highest in summer. Fe and Pb primarily travel as suspended particles, but their dissolved forms were greater during all seasons in the lower basin. A principal components analysis of upper basin data indicates that temperature and conductivity were correlated with dissolved Cd and Zn, and total Fe and Pb were correlated with streamflow. In the lower basin, dissolved Cd and Zn, conductivity, and temperature were correlated, and suspended sediment, total metals, and dissolved Pb, but not streamflow, were correlated. The correlation of metals and sediment in the lower basin is not from erosion but the availability of organic matter and Fe that form a range of dissolved to suspended metal particles. The summer decrease in surface water levels releases sediment porewater containing nanoscale-to-microscale metal particles that are transported to open water, where they may impact human and wildlife health. Such releases are unmitigated with current remediation strategies of sediment stabilization.
Highlights
The weathering of sulfide minerals may release potentially toxic metals into the environment that can continue to impact the health of human and wildlife populations for a period of decades to centuries [1,2,3,4,5]
The spring runoff increased river temperatures, followed by further increases during summer (Table 1 and Figure 3). Associated with this temperature change, conductivity increased in summer for water exiting the upper and lower basins compared to the dilute streamflow during the spring runoff
The higher gradient and lower biological productivity of the upper basin allows for greater erosion and the transport of geogenic metal forms such as free ions, multi-metal nanoparticles, or sediment-bound metals, but seasonal differences alter the ratio of dissolved to suspended metal particles
Summary
The weathering of sulfide minerals may release potentially toxic metals into the environment that can continue to impact the health of human and wildlife populations for a period of decades to centuries [1,2,3,4,5]. The introduction of sulfide minerals to the surface environment because of mining may allow for the weathering, release, and hydrologic transport of metals such as Cd, Fe, Pb, and Zn as inorganic and organic nano- to micro-scale particles [6,7]. The formation of transportable inorganic or organic metal nanoparticles poses substantial risks to water resources because of the potential for nanoparticles to have greater mobility, stability, and (or) bioavailability compared to free ions and (or) microparticles [8,9,10]. The goal of this study was to discriminate the seasonal release and transport of dissolved (
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