Ao Ming, Meng Ruichun, Zhou Rouyun, Luo Bolang, Bonaventure Loua-Augustin, Wu Pan, Qiu Rongliang, Wang Shizhong
Key Laboratory of Karst Georesources and Environment, Ministry of Education, College of Resource and Environmental Engineering, Guizhou University, Guiyang, 550025, China; School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou, 510006, China.
Key Laboratory of Karst Georesources and Environment, Ministry of Education, College of Resource and Environmental Engineering, Guizhou University, Guiyang, 550025, China.
Water Res. 2025 Nov 1;286:124263. doi: 10.1016/j.watres.2025.124263. Epub 2025 Jul 23.
Geogenic Cr(III) oxidative release in serpentine soils is a continuous source of Cr contamination in surface and groundwater. Although manganese (Mn) oxides have been shown to be a key factor driving Cr(III) oxidative release, their oxidative mechanism and release fluxes in serpentine soils remain unclear. In this study, the dual mechanism of δ-MnO regulating Cr release and migration from surface soil was revealed through column leaching experiments. The results showed that δ-MnO significantly promoted soil Cr release, and most of the Cr(VI) generated by oxidation went into the aqueous phase. δ-MnO addition slowed down the loss of mobile fractions Cr (F1, F3, and F4), 78-94 % of Cr in the effluent originated from organic fraction Cr (F4), while F6 and F7 were less affected, demonstrating chemical speciation selectivity. Validation experiments confirmed that δ-MnO primarily drives Cr release by oxidizing and desorbing OM-Cr(III), with minimal contribution from inorganic Cr-bearing minerals. Cr(III) accounted for >70 % of the Cr in the effluent, mostly migrating in the form of OM-Cr(III) colloids, while Cr(VI) accounted for only 30 %. This indicates that in OM-rich surface soils, the oxidation and decomposition of OM by natural oxidants (such as biogenic Mn oxides) and the release of bound Cr(III) are the core processes of Cr loss. Cr(III) is the main speciation entering the aqueous system. Therefore, in Cr-contaminated soils rich in OM, Mn input (such as the application of Mn-containing fertilizers or the use of Mn-containing irrigation water) should be avoided to inhibit the promotion of the Mn(II)-Mn(IV) cycle driven by Mn(II) oxidizing microorganisms on the release of OM-Cr(III) oxidation, thereby reducing the risk of Cr pollution in the water environment at the source.
蛇纹岩土中地质成因的Cr(III)氧化释放是地表水和地下水中Cr污染的持续来源。尽管锰（Mn）氧化物已被证明是驱动Cr(III)氧化释放的关键因素，但其在蛇纹岩土中的氧化机制和释放通量仍不清楚。本研究通过柱淋溶实验揭示了δ-MnO调节表层土壤中Cr释放和迁移的双重机制。结果表明，δ-MnO显著促进了土壤Cr的释放，氧化产生的大部分Cr(VI)进入水相。添加δ-MnO减缓了可移动组分Cr（F1、F3和F4）的损失，流出物中78-94%的Cr来自有机组分Cr（F4），而F6和F7受影响较小，表明具有化学形态选择性。验证实验证实，δ-MnO主要通过氧化和解吸OM-Cr(III)来驱动Cr释放，含无机Cr矿物的贡献最小。流出物中Cr(III)占Cr的>70%，大多以OM-Cr(III)胶体形式迁移，而Cr(VI)仅占30%。这表明在富含有机质的表层土壤中，天然氧化剂（如生物成因的Mn氧化物）对有机质的氧化分解以及结合态Cr(III)的释放是Cr流失的核心过程。Cr(III)是进入水体系的主要形态。因此，在富含有机质的Cr污染土壤中，应避免Mn输入（如施用含Mn肥料或使用含Mn灌溉水），以抑制Mn(II)氧化微生物驱动的Mn(II)-Mn(IV)循环对OM-Cr(III)氧化释放的促进作用，从而从源头上降低水环境中Cr污染的风险。
