Soil Weathering as an Engine for Manganese Contamination of Well Water

Abstract

Manganese (Mn) contamination of well water is recognized as an environmental health concern. In the southeastern Piedmont region of the United States, well water Mn concentrations can be >2 orders of magnitude above health limits, but the specific sources and causes of elevated Mn in groundwater are generally unknown. Here, using field, laboratory, spectroscopic, and geospatial analyses, we propose that natural pedogenetic and hydrogeochemical processes couple to export Mn from the near-surface to fractured-bedrock aquifers within the Piedmont. Dissolved Mn concentrations are greatest just below the water table and decrease with depth. Solid-phase concentration, chemical extraction, and X-ray absorption spectroscopy data show that secondary Mn oxides accumulate near the water table within the chemically weathering saprolite, whereas less-reactive, primary Mn-bearing minerals dominate Mn speciation within the physically weathered transition zone and bedrock. Mass-balance calculations indicate soil weathering has depleted over 40% of the original solid-phase Mn from the near-surface, and hydrologic gradients provide a driving force for downward delivery of Mn. Overall, we estimate that >1 million people in the southeastern Piedmont consume well water containing Mn at concentrations exceeding recommended standards, and collectively, these results suggest that integrated soil-bedrock-system analyses are needed to predict and manage Mn in drinking-water wells.

The Role of Manganese Carbonate Precipitation in Controlling Fluoride and Uranium Mobilization in Groundwater

“…Concentrations of these contaminants and co-ions are governed by groundwater-sediment interactions, involving the primary mineral phase of concern and secondary processes. For instance, dissolution of calcite has been identified to release coprecipitated F, As, Ba, U, and Sr at some locations. , Also, dissolution of evaporite minerals is known to affect pH and alkalinity of groundwater, which were found to induce mobilization of contaminants from primary host minerals (e.g., desorption of U from U-bearing minerals). , Furthermore, among the prevalent co-ions in groundwater high dissolved Mn is often taken as a proxy for the presence of Mn oxide-rich phases, which are known to favorably adsorb dissolved U­(VI) . Controlled lab experiments have shown that under oxic conditions high dissolved Mn may even promote U­(IV) mineral dissolution through the formation of a redox couple between the short-lived Mn­(III) and U­(VI), , where dissolved Mn­(II) converts to Mn­(III) after consuming dissolved oxygen.…”

Evaluation of the Mn(II) adsorption potential of SiO2 obtained by different wet chemical methods

“…Metals such as cobalt (Co), copper (Cu), manganese (Mn), and zinc (Zn) are beneficial to live beings because they participate in vital processes in their bodies, but in high quantities, they become toxic and contaminate the environment . The presence of manganese in high concentrations in aquatic environments, usually from industrial processes such as mining and ore processing, causes inorganic pollution due to the fact that the metal is not biodegradable, presents toxicity and can accumulate in humans and animals, causing adverse reactions . Therefore, the removal of such metals from polluted water has attracted considerable attention .…”

Factors Controlling the Risks of Co-occurrence of the Redox-Sensitive Elements of Arsenic, Chromium, Vanadium, and Uranium in Groundwater from the Eastern United States

“…Another possible explanation is that close to the water table, there may be more solid-phase manganese oxides to catalyze Cr oxidation, which has been widely recognized as an important pathway for Cr oxidation. Gillispie et al 65 showed that chemically reactive Mn oxides accumulate near the water table in the weathered saprolite in the North Carolina Piedmont. Cr oxidation catalyzed by Mn oxides could explain the higher Cr(VI) concentration in this zone, and especially the well with orders of magnitude higher Cr(VI) than any other monitoring well, including other wells in the same cluster and aquifer lithology.…”