Analytical method of Cr stable isotope and its application to water pollution survey

High Cr (VI) concentration is a potential serious risk to environment and ecologic system. Thus, it is essential to effectively monitor Cr contamination in water systems and scientifically evaluate its evolution trend. A new method of in-situ tracer technique by Cr isotopic analysis for quantitatively estimating Cr-contamination and its regional evolution in natural waters as well as a case application are reported in this paper. Based on documented literatures, an experimental procedure for chemical separation and purification of Cr in water samples and its analytical method for Cr isotopic measurement by thermal ionization mass spectrometry (TIMS) are established. Eleven samples collected around a chemical factory in Hubei Province were analyzed by this technique. These samples show delta Cr-53 values ranging from -1.7aEuro degrees to 7.3aEuro degrees and an elevating trend with an increasing in distance from the sampling site to pollution source. A functional correlation following Rayleigh fractionation law was established between sample's delta Cr-53 value and its extent of Cr contamination. This study suggests that Cr isotopic analysis is an effective method to reveal the spatial distribution and its evolution trend of Cr contamination in the regional water system. It is thus helpful to assessing the self-purifying ability of local water system according to Cr isotopic fractionation.