Mechanistic insights and environmental ramifications of Cr(III) oxidation to Cr(VI) in soil and groundwater systems: bridging geochemical mechanisms and emerging remediation strategies

Abstract

The oxidation of trivalent chromium [Cr(III)] to hexavalent chromium [Cr(VI)] is a significant environmental process that threatens soil and groundwater quality and poses serious ecological and human health risks. This review provides a critical synthesis of current knowledge about the abiotic, biotic, and thermally induced mechanisms that drive Cr(III) oxidation, including reactions with Mn(IV) oxides, hydrogen peroxide, photochemically generated oxidants, and wildfire-related thermal transformations. Environmental factors such as pH, redox potential, mineralogy, and organic matter content are revealed to play a key role in regulating Cr redox dynamics. Cr(VI) is highly soluble, mobile, and bioavailable , exerting toxic effects on microbial communities, plant growth, and human health even at trace levels. Key attenuation pathways, including chemical and microbial reduction, biosorption, and co-precipitation with Fe-bearing minerals, are critically discussed, with particular attention to re-oxidation, which undermines long-term remediation. This review further evaluates emerging remediation strategies , such as redox manipulation, biochar-assisted immobilization, and coupled plant–microbe systems, emphasizing the need for site-specific, adaptive approaches that account for spatial and temporal environmental variability. Future research should focus on Cr(VI) generation under post-fire scenarios, isotopic tracing, and field-scale testing of sustainable immobilization materials to improve predictive models and ensure long-term mitigation of Cr(VI) contamination in soil-groundwater systems.

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