Chlorine Isotope Fractionation of the Major Chloromethane Degradation Processes in the Environment

Abstract

Chloromethane (CH 3 Cl) 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 (ε Cl ) associated with the major abiotic and biotic CH 3 Cl sinks in the environment, namely, CH 3 Cl 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 CH 3 Cl with • OH and • Cl radicals, whereas a large chlorine isotope fractionation (ε Cl ) of −10.9 ± 0.7‰ (n = 3) and −9.4 ± 0.9 (n = 3) was found for CH 3 Cl degradation by M. extorquens CM4 and L. methylohalidivorans MB2, respectively. The large difference in chlorine isotope fractionation observed between tropospheric and bacterial degradation of CH 3 Cl provides an effective isotopic tool to characterize and distinguish between major abiotic and biotic processes contributing to the CH 3 Cl 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.

13C‐chloromethane incubations provide evidence for novel bacterial chloromethane degraders in a living tree fern

“…However, microorganisms living in close association with these plant hosts might substantially mitigate fluxes of CH 3 Cl into the atmosphere. In this context, recent isotopic mass balances of atmospheric CH 3 Cl, including isotopic analysis of carbon (Bahlmann et al, 2019), hydrogen (Keppler et al, 2018) and chlorine (Keppler et al, 2019), point to large unidentified terrestrial sinks and sources of CH 3 Cl. The present study reveals the complexity of CH 3 Cl budgetassociated processes.…”

Novel bacterial chloromethane degraders of a living tree fern evidenced by 13C-chloromethane incubations

“…However, microorganisms living in close association with these plants might substantially mitigate the emission of CH3Cl into the atmosphere. In this context, recent isotopic mass balances of atmospheric CH3Cl including isotopic analysis of carbon [115], hydrogen [116] and chlorine [117] Acknowledgments: EK gratefully acknowledges support through the DFG. FB acknowledges the Bio-Informatic MicroScope platform at Evry (France) for annotation and comparative analysis of MAGs.…”

“…For future studies, incubations under lower, environmentally observed concentrations (~600 pptv), coupled with targeted proteomics and/or transcriptomics approaches, may help to identify as yet unidentified CH3Cl degradation pathways. Finally, the application of triple element isotope analysis [117] might provide clues on the global relevance of vegetation and their associated microbes in mitigating emissions of CH3Cl to the atmosphere.…”

“…For future studies, incubations under lower, environmentally observed concentrations (~600 pptv), coupled with targeted proteomics and/or transcriptomics approaches, may help to identify as yet unidentified CH3Cl degradation pathways. Finally, the application of triple element isotope analysis[117] might provide clues on the global relevance of vegetation and their associated microbes in mitigating emissions of CH3Cl to the atmosphere.Availability of data and materialRead data of the tree fern metagenomes have been submitted to the National Center for Biotechnology Information (NCBI) under the BioProject number PRJNA659413. The metagenome assembled Fern CH3Cl SIP LEAF bin s3 , Fern CH3Cl SIP LEAF bin co1 , Fern CH3Cl SIP LEAF bin co3 , Fern CH3Cl SIP LEAFWASH bin co7 , Fern CH3Cl SIP SOIL bin s1 , Fern CH3Cl SIP SOIL bin s7 , B P with BioSample Accession numbers SAMN17394138, SAMN17394139, SAMN17394140, SAMN17394141, SAMN17394142, SAMN17394143, respectively.…”

Probing the Atmospheric Cl Isotopic Ratio on Mars: Implications for Planetary Evolution and Atmospheric Chemistry

“…The role of atmosphere‐surface interactions in determining the variation and present values of δ 37 Cl on Mars is an outstanding scientific question, which can only be solved by atmospheric measurements supporting existing modeling efforts. While on Earth these dynamics are well studied (e.g., Keppler et al., 2020; Laube et al., 2010), there is no definite explanation of the peculiarly “light” Cl isotopic composition found at Mars’ surface. The widespread observation of perchlorates by the Phoenix lander (Hecht et al., 2009) and by the sample analysis at Mars (Mahaffy et al., 2012) onboard Curiosity rover (Glavin et al., 2013) suggested mechanisms similar to those in place for the Atacama perchlorates.…”