Chloromethane (CH3Cl) is an important source of chlorine in the stratosphere, but detailed knowledge of the magnitude of its sources and sinks is missing. Here, we measured the stable chlorine isotope fractionation (εCl) associated with the major abiotic and biotic CH3Cl sinks in the environment, namely, CH3Cl degradation by hydroxyl (·OH) and chlorine (·Cl) radicals in the troposphere and by reference bacteria Methylorubrum extorquens CM4 and Leisingera methylohalidivorans MB2 from terrestrial and marine environments, respectively. No chlorine isotope fractionation was detected for reaction of CH3Cl with ·OH and ·Cl radicals, whereas a large chlorine isotope fractionation (εCl) of -10.9 ± 0.7‰ (n = 3) and -9.4 ± 0.9 (n = 3) was found for CH3Cl degradation by M. extorquens CM4 and L. methylohalidivorans MB2, respectively. The large difference in chlorine isotope fractionation observed between tropospheric and bacterial degradation of CH3Cl provides an effective isotopic tool to characterize and distinguish between major abiotic and biotic processes contributing to the CH3Cl sink in the environment. Our findings demonstrate the potential of emerging triple-element isotopic approaches including chlorine to carbon and hydrogen analysis for the assessment of global cycling of organochlorines.

中文翻译：

---

环境中主要氯甲烷降解过程的氯同位素分馏。

氯甲烷（CH3Cl）是平流层中氯的重要来源，但缺少有关其来源和汇的大小的详细知识。在这里，我们测量了与环境中主要的非生物和生物CH3Cl汇相关的稳定氯同位素分馏（εCl），即对流层中的羟基（·OH）和氯（·Cl）自由基以及参考细菌甲基溴对CH3Cl的降解分别从陆地和海洋环境中夺走了CM4和甲基异丁香假单胞菌MB2。未检测到CH3Cl与·OH和·Cl自由基反应的氯同位素分馏，而发现大的氯同位素分馏（εCl）分别为-10.9±0.7‰（n = 3）和-9.4±0.9（n = 3） M. extorquens CM4和L.methylohalidivorans MB2对CH3Cl的降解作用。CH3Cl的对流层和细菌降解之间观察到的氯同位素分馏差异很大，这提供了一种有效的同位素工具，用于表征和区分造成环境中CH3Cl沉降的主要非生物过程和生物过程。我们的发现证明了新兴的三元素同位素方法的潜力，包括氯到碳和氢的分析，可用于评估有机氯的全球循环。