Biogeochemical Controls on the Potential for Long-Term Contaminant Leaching from Soils Developing on Historic Coal Mine Spoil

Abstract

Coal mine spoil is widespread in US coal mining regions, and the potential long-term leaching of toxic metal(loid)s is a significant and underappreciated issue. This study aimed to determine the flux of contaminants from historic mine coal spoil at a field site located in Appalachian Ohio (USA) and link pore water composition and solid-phase composition to the weathering reaction stages within the soils. The overall mineralogical and microbial community composition indicates that despite very different soil formation pathways, soils developing on historic coal mine spoil and an undisturbed soil are currently dominated by similar mineral weathering reactions. Both soils contained pyrite coated with clays and secondary oxide minerals. However, mine spoil soil contained abundant residual coal, with abundant Fe- and Mn- (oxy)hydroxides. These secondary phases likely control and mitigate trace metal (Cu, Ni, and Zn) transport from the soils. While Mn was highly mobile in Mn-enriched soils, Fe and Al mobility may be more controlled by dissolved organic carbon dynamics than mineral abundance. There is also likely an underappreciated risk of Mn transport from coal mine spoil, and that mine spoil soils could become a major source of metals if local biogeochemical conditions change.

Surface Coal Mine Soils: Evidence for Chronosequence Development

“…Surface mining within the watershed and at HR-25 became dominant in the late 1940s and ceased in the late 1970s [24], and this 30-year timeframe is believed to correspond to the oldest (deposited ~70-80 years ago) and newest spoil piles (deposited ~50 years ago) of the current investigation. This is also consistent with the size and density of the trees at the field site, in comparison to trees dated with growth rings within the same subwatershed [25]. During this period when surface mining dominated the extractive activities at the site, mining practices and equipment remained relatively consistent, and remediation has not occurred where mine soils are developing.…”

Complex Speciation and Distribution of Iron, Sulfur, and Trace Metals in Coal Mine Soils Reflect Grain- and Sub-Grain-Scale Heterogeneity during Pyrite Oxidative Dissolution

“…However, despite the success in improving the surface water quality, abandoned mine waste and spoils continue to leach non-point sources (e.g., mine spoils) and have the potential to continually release toxic elements over a time period of approximately decades, resulting in ongoing negative impacts on the local ecosystem. Previous studies have focused on abandoned spoils adjacent to the current study sites [26][27][28][29], and these previous projects provide further information about the history, climate, and remediation activities of the Huff Run Watershed and sub-watershed 25.…”

Mercury Accumulation in Commercial Varieties of Oryza sativa L. Cultivated in Soils of La Mojana Region, Colombia

“…The concentrations of the available K (124.8 mg kg −1 ) and available P (18.9 mg kg −1 ) were lower than those necessary for the physiological development of the plant [35]. A clay loam soil has a moderate content of clay, which can adsorb metallic cations because it contains minerals that enable their immobilization [36]. However, the acidic nature of this soil can promote the mobility of metal ions, leading to the increased absorption of mercury by the rice plants [37].…”