Department of Geology, University of Illinois, Urbana, Illinois 61801, USA.
Environ Sci Technol. 2010 Feb 1;44(3):1043-8. doi: 10.1021/es902280s.
Chromium stable isotope ratios show promise as indicators of Cr(VI) reduction in groundwater, but no published study has yet demonstrated that expected relationships between (53)Cr/(52)Cr and Cr(VI) concentration, position, and time occur in an actual groundwater plume. We present an extensive data set from a point-source plume in Berkeley, CA; data extend over 5 years and 14 locations covering the entire plume. We interpret the data using a Rayleigh distillation model with an effective fractionation factor that incorporates an intrinsic fractionation factor determined from incubations of site sediments and accounts for reservoir effects in the restricted subsurface zones where Cr(VI) reduction is thought to occur. The groundwater (53)Cr/(52)Cr and Cr(VI) concentration data are consistent with a scenario where the system has reached a steady state: Cr(VI) reduction continues, the extent of reduction at any point is constant over time, reduction proceeds to completion at the downgradient edge of the plume, and the plume is no longer advancing. The overall consistency of the results with a reasonable model for the site supports the use of Cr isotope-based estimates of reduction, but we discuss current uncertainties and limitations of the approach as well.
铬稳定同位素比值有望成为地下水六价铬还原的指示剂，但目前尚无研究表明，（53）Cr/（52）Cr 与六价铬浓度、位置和时间之间的预期关系在实际地下水流中存在。我们提供了来自加利福尼亚州伯克利市点源羽流的大量数据；数据涵盖了 5 年和 14 个地点，涵盖了整个羽流。我们使用带有有效分馏因子的瑞利蒸馏模型来解释数据，该分馏因子结合了从现场沉积物中进行的孵育确定的内在分馏因子，并考虑了在被认为发生六价铬还原的受限地下区域中的储层效应。地下水（53）Cr/（52）Cr 和六价铬浓度数据与系统达到稳定状态的情况一致：六价铬还原仍在继续，任何一点的还原程度随时间保持不变，在羽流的下游边缘完全还原，并且羽流不再向前推进。结果与现场合理模型的整体一致性支持使用基于铬同位素的还原估计，但我们也讨论了该方法目前存在的不确定性和局限性。
