Fischer Anko, Theuerkorn Katja, Stelzer Nicole, Gehre Matthias, Thullner Martin, Richnow Hans H
Department of Isotope Biogeochemistry, UFZ-Centre for Environmental Research Leipzig-Halle, Permoserstr. 15, D-04318 Leipzig, Germany.
Environ Sci Technol. 2007 May 15;41(10):3689-96. doi: 10.1021/es061514m.
In recent years the analysis of stable isotope fractionation has increasingly been used for characterizing and quantifying biodegradation of contaminants in aquifers. The correlation of carbon and hydrogen isotope signatures of benzene in a BTEX-contaminated aquifer located in the area of a former hydrogenation plant gave indications that biodegradation mainly occurred under anoxic conditions. This finding was consistent with the investigation of hydrogeochemical conditions within the aquifer. Furthermore, the biodegradation of benzene was calculated by changes in carbon isotope signatures using the Rayleigh-equation-streamline approach. Since contaminant concentrations can be also affected by nonisotope-fractionating abiotic processes such as dilution, volatilization, or irreversible sorption to the aquifer matrix, the Rayleigh-equation-streamline approach was adjusted for scenarios assuming that biodegradation and abiotic processes occur either consecutively or simultaneously along a groundwater flow path between contaminant source and sampling well. The results of the scenarios differed significantly, indicating that an abiotic process (typically dilution) causes a decrease in benzene concentration within the investigated aquifer transect. This comparison of results derived from the different scenarios can help to identify whether biodegradation is the predominant process for decrease in contaminant concentration. However, for a proper quantification of biodegradation, the temporal sequence between biodegradation and dilution needs to be known. The uncertainty associated with the quantification of pollutant biodegradation by the Rayleigh-equation-streamline approach increases when nonisotope-fractionating abiotic processes cause a significant decrease in contaminant concentrations.
近年来，稳定同位素分馏分析越来越多地用于表征和量化含水层中污染物的生物降解。对位于原氢化厂区域的受BTEX污染含水层中苯的碳和氢同位素特征进行的相关性分析表明，生物降解主要发生在缺氧条件下。这一发现与对含水层内水文地球化学条件的调查结果一致。此外，利用瑞利方程流线法，通过碳同位素特征的变化计算了苯的生物降解。由于污染物浓度也可能受到非同位素分馏的非生物过程（如稀释、挥发或对含水层基质的不可逆吸附）的影响，因此针对生物降解和非生物过程沿污染物源与采样井之间的地下水流路径连续或同时发生的情况，对瑞利方程流线法进行了调整。不同情况的结果差异显著，表明非生物过程（通常是稀释）导致了所研究含水层断面内苯浓度的降低。对不同情况得出的结果进行比较，有助于确定生物降解是否是污染物浓度降低的主要过程。然而，为了正确量化生物降解，需要了解生物降解和稀释之间的时间顺序。当非同位素分馏的非生物过程导致污染物浓度显著降低时，利用瑞利方程流线法对污染物生物降解进行量化的不确定性就会增加。
