Institute of Groundwater Ecology, Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg, Germany.
Environ Sci Process Impacts. 2020 Mar 1;22(3):792-801. doi: 10.1039/c9em00503j. Epub 2020 Feb 24.
Atrazine is a frequently detected groundwater contaminant. It can be microbially degraded by oxidative dealkylation or by hydrolytic dechlorination. Compound-specific isotope analysis is a powerful tool to assess its transformation. In previous work, carbon and nitrogen isotope effects were found to reflect these different transformation pathways. However, chlorine isotope fractionation could be a particularly sensitive indicator of natural transformation since chlorine isotope effects are fully represented in the molecular average while carbon and nitrogen isotope effects are diluted by non-reacting atoms. Therefore, this study explored chlorine isotope effects during atrazine hydrolysis with Arthrobacter aurescens TC1 and oxidative dealkylation with Rhodococcus sp. NI86/21. Dual element isotope slopes of chlorine vs. carbon isotope fractionation (Λ = 1.7 ± 0.9 vs. Λ = 0.6 ± 0.1) and chlorine vs. nitrogen isotope fractionation (Λ = -1.2 ± 0.7 vs. Λ = 0.4 ± 0.2) provided reliable indicators of different pathways. Observed chlorine isotope effects in oxidative dealkylation (ε = -4.3 ± 1.8‰) were surprisingly large, whereas in hydrolysis (ε = -1.4 ± 0.6‰) they were small, indicating that C-Cl bond cleavage was not the rate-determining step. This demonstrates the importance of constraining expected isotope effects of new elements before using the approach in the field. Overall, the triple element isotope information brought forward here enables a more reliable identification of atrazine sources and degradation pathways.
莠去津是一种经常在地下水中检测到的污染物。它可以通过氧化脱烷基化或水解脱氯作用进行微生物降解。化合物特异性同位素分析是评估其转化的有力工具。在以前的工作中，发现碳和氮同位素效应反映了这些不同的转化途径。然而，氯同位素分馏可能是自然转化的一个特别敏感的指标，因为氯同位素效应在分子平均值中完全表示，而碳和氮同位素效应则被非反应原子稀释。因此，本研究探讨了节杆菌 TC1 水解和红球菌 NI86/21 氧化脱烷基作用过程中的氯同位素效应。氯与碳同位素分馏的双元素同位素斜率（Λ=1.7±0.9 对 Λ=0.6±0.1）和氯与氮同位素分馏的双元素同位素斜率（Λ=-1.2±0.7 对 Λ=0.4±0.2）提供了不同途径的可靠指标。在氧化脱烷基化过程中观察到的氯同位素效应（ε=-4.3±1.8‰）非常大，而在水解过程中（ε=-1.4±0.6‰）则较小，表明 C-Cl 键的断裂不是速率决定步骤。这表明在现场应用该方法之前，约束新元素预期同位素效应的重要性。总的来说，这里提出的三元素同位素信息可更可靠地识别莠去津的来源和降解途径。
