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Redox reactions and the influence of natural Mn oxides on Cr oxidation in a contaminated site in northern Italy: evidence from Cr stable-isotopes and EPR spectroscopy

机译:氧化还原反应和天然Mn氧化物对意大利北部污染场地中Cr氧化的影响:Cr稳定同位素和EPR光谱的证据

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Hexavalent chromium-contaminated groundwaters and sediments in northern Italy have been studied using the Cr stable-isotope systematics and electron spin resonance spectroscopy (ESR), in order to explore redox changes and soil-groundwater interactions. The isotopic data indicate a possible Cr(VI) source released into the environment from an industrial plant. EPR spectra on the sediments which constitute the aquifers show a broad asymmetric absorption due to coupled Fe(III) and coupled Cr(III) ions and a well resolved hyperfine structure due to manganese ions, resulting from Mn(IV) and Mn(II). The isotopic and EPR data support the hypothesis of Cr(III) being oxidized by Mn oxides which are widespread in the aquifer, possibly related to the oscillation of the phreatic level. The obtained results highlight the usefulness of chromium stable isotopes as environmental tracers and support the observations that naturally occurring Mn oxides in soils may catalize Cr oxidation from the stable Cr(III) form to the toxic Cr(VI) soluble form, yielding valuable information in planning remediation interventions.Key words: Hexavalent chromium / Groundwaters / Chromium stable-isotopes / Chromium oxidation
机译:为了研究氧化还原的变化和土壤-地下水之间的相互作用,意大利北部使用六价铬稳定同位素系统和电子自旋共振光谱法(ESR)研究了六价铬污染的地下水和沉积物。同位素数据表明从工厂释放到环境中的可能的Cr(VI)来源。构成含水层的沉积物上的EPR光谱显示由于Fe(III)和Cr(III)耦合而引起的宽的不对称吸收,以及由于Mn(IV)和Mn(II)导致的锰离子而导致的超精细结构的良好解析。同位素和EPR数据支持Cr(III)被Mn氧化物氧化的假说,Mn氧化物广泛分布在含水层中,可能与潜水位的振荡有关。所得结果突出了铬稳定同位素作为环境示踪剂的有用性,并支持以下观察结果:土壤中天然存在的锰氧化物可能将铬的氧化从稳定的Cr(III)形式转化为有毒的Cr(VI)可溶性形式,从而产生了有价值的信息。关键词:六价铬/地下水/铬稳定同位素/铬氧化

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