地下水中稳定铬同位素的生物地球化学作用

铬是地下水中常见的一种变价重金属污染物，在自然界中广泛分布且应用广泛。将Cr(Ⅵ)还原为Cr(Ⅲ)是地下水铬污染防治中的主要策略。在Cr(Ⅵ)的非生物还原过程中存在铬同位素分馏现象，通过地下水中铬同位素组成的变化情况可以定量地指示Cr(Ⅵ)的还原程度和速率。这被认为是一个重要发现，在地下水铬污染防治中有着广阔的应用前景。文中对铬与铬的来源、地下水中铬同位素的测定方法、铬同位素的生物地球化学作用、铬同位素在地下水污染防治中的应用等进行了系统综述。研究认为：微生物广泛参与地下水中铬的氧化与还原作用，并有可能产生显著的铬同位素分馏。地下水中被还原的Cr(Ⅵ)在微生物作用下有可能被活化，用非生物还原条件下的铬同位素分馏规律指示地下水中Cr(Ⅵ)还原程度可能会产生较大的误差。开展地下水中铬同位素的生物地球化学作用研究，特别是生物氧化Cr(Ⅲ)过程中的铬同位素分馏规律研究，对于更全面地认识铬同位素的指示作用具有重要意义。

Biogeochemical processes of chromium stable isotope in groundwater

Chromium,a multivalent metal,is a common contaminant in groundwater,which are extensively distributed in nature and widely used in various industrial processes.Converting Cr(Ⅵ) to Cr(Ⅲ) is a key process in remediation schemes of chromium contaminated groundwater.It has demonstrated that there is isotope fractionation of Cr(Ⅵ) during abiotic reduction.So the measurement of Cr stable isotope abundances can be used to indicate the reduction rate and extent of Cr(Ⅵ),and hence,has broad application prospects in chromium contaminated groundwater.In this paper,the source of chromium,the measurement methods of chromium isotope in groundwater,the biogeochemical processes of chromium stable isotope in groundwater and the application of Cr stable isotope technique in groundwater were reviewed.It is shown that microbes play an important role in the redox processes of Cr,which may have a significant isotope fractionation.Under the role of microbes,the reduction product of Cr(Ⅵ) may be oxidated.Thus,there may be great errors by isotope fractionation law of chromium indicating the reduction extent of Cr(Ⅵ) under abiotic reduction in groundwater.Therefore,it is important to understand the biogeochemical processes of Cr isotope,especially the mechanism of Cr isotope fractionation in the process of Cr(Ⅲ) oxidation.