Sturchio Neil C, Böhlke John Karl, Beloso Abelardo D, Streger Sheryl H, Heraty Linnea J, Hatzinger Paul B
University of Illinois at Chicago, Chicago, Illinois 60607, USA.
Environ Sci Technol. 2007 Apr 15;41(8):2796-802. doi: 10.1021/es0621849.
Perchlorate is a widespread environmental contaminant having both anthropogenic and natural sources. Stable isotope ratios of O and Cl in a given sample of perchlorate may be used to distinguish its source(s). Isotopic ratios may also be useful for identifying the extent of biodegradation of perchlorate, which is critical for assessing natural attenuation of this contaminant in groundwater. For this approach to be useful, however, the kinetic isotopic fractionations of O and Cl during perchlorate biodegradation must first be determined as a function of environmental variables such as temperature and bacterial species. A laboratory study was performed in which the O and Cl isotope ratios of perchlorate were monitored as a function of degradation by two separate bacterial strains (Azospira suillum JPLRND and Dechlorospirillum sp. FBR2) at both 10 degrees C and 22 degrees C with acetate as the electron donor. Perchlorate was completely reduced by both strains within 280 h at 22 degrees C and 615 h at 10 degrees C. Measured values of isotopic fractionation factors were epsilon(18)O = -36.6 to -29.0% per hundred and epsilon(37)Cl = -14.5 to -11.5% per hundred, and these showed no apparent systematic variation with either temperature or bacterial strain. An experiment using (18)O-enriched water (delta(18)O = +198% per hundred) gave results indistinguishable from those observed in the isotopically normal water (delta(18)O = -8.1% per hundred) used in the other experiments, indicating negligible isotope exchange between perchlorate and water during biodegradation. The fractionation factor ratio epsilon(18)O/epsilon(37)Cl was nearly invariant in all experiments at 2.50 +/- 0.04. These data indicate that isotope ratio analysis will be useful for documenting perchlorate biodegradation in soils and groundwater. The establishment of a microbial fractionation factor ratio (epsilon(18)O/ epsilon(37)Cl) also has significant implications for forensic studies.
高氯酸盐是一种广泛存在的环境污染物，有来自人为和自然的来源。给定高氯酸盐样品中氧和氯的稳定同位素比率可用于区分其来源。同位素比率对于识别高氯酸盐的生物降解程度也可能有用，这对于评估这种污染物在地下水中的自然衰减至关重要。然而，要使这种方法有用，必须首先确定高氯酸盐生物降解过程中氧和氯的动力学同位素分馏作为环境变量（如温度和细菌种类）的函数。进行了一项实验室研究，其中监测了在10℃和22℃下以乙酸盐作为电子供体时，两种不同细菌菌株（猪氮螺菌JPLRND和脱氯螺菌属FBR2）降解过程中高氯酸盐的氧和氯同位素比率。在22℃下，两种菌株在280小时内将高氯酸盐完全还原，在10℃下在615小时内完全还原。测量的同位素分馏因子值为ε(18)O = -36.6至-29.0‰，ε(37)Cl = -14.5至-11.5‰，并且这些值在温度或细菌菌株方面没有明显的系统变化。使用富含(18)O的水（δ(18)O = +198‰）的实验结果与在其他实验中使用的同位素正常水（δ(18)O = -8.1‰）中观察到的结果没有区别，表明生物降解过程中高氯酸盐与水之间的同位素交换可忽略不计。在所有实验中分馏因子比率ε(18)O/ε(37)Cl几乎不变，为2.50±0.04。这些数据表明同位素比率分析将有助于记录土壤和地下水中高氯酸盐的生物降解。微生物分馏因子比率（ε(18)O/ε(37)Cl）的确定对法医研究也有重要意义。
