Compound-specific chlorine isotope fractionation in biodegradation of atrazine

Christina Lihl, Benjamin Heckel, Anna Grzybkowska, Agnieszka Dybala-Defratyka, Violaine Ponsin, Clara Torrentó, Daniel Hunkeler, Martin Elsner

Research output: Contribution to journalArticlepeer-review

19 Scopus citations


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 (ΛArthroCl/C = 1.7 ± 0.9 vs. ΛRhodoCl/C = 0.6 ± 0.1) and chlorine vs. nitrogen isotope fractionation (ΛArthroCl/N =-1.2 ± 0.7 vs. ΛRhodoCl/N = 0.4 ± 0.2) provided reliable indicators of different pathways. Observed chlorine isotope effects in oxidative dealkylation (ϵCl =-4.3 ± 1.8‰) were surprisingly large, whereas in hydrolysis (ϵCl =-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.

Original languageEnglish
Pages (from-to)792-801
Number of pages10
JournalEnvironmental Science: Processes and Impacts
Issue number3
StatePublished - Mar 2020


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