Elucidating\nthe\nFate of the Organochlorine Pesticide\nChlordecone under Abiotic Reductive and Oxidative Processes: Kinetics,\nTransformation Products, and C vs Cl Isotope Fractionation

Pollution of French\nWest Indies (FWI) soils by the organochlorine\npesticide chlordecone poses environmental and societal concerns due\nto its long-term persistence. Assessing chlordecone degradation remains\nchallenging due to analytical constraints to identify transformation\nproducts. Here, multielement compound-specific isotope analysis (ME-CSIA)\nwas used to identify changes in stable isotope signatures of chlordecone\nproduced during abiotic transformation reactions under reducing and\noxidative conditions. Effective chlordecone transformation was shown\nin reactions with zerovalent iron (ZVI), vitamin B<sub>12</sub> and\nsodium sulfide (VSS), alkaline ascorbic acid (AA), and sodium persulfate\nactivated by microwave irradiation (MWPS). Significant enrichment\nof <sup>13</sup>C and <sup>37</sup>Cl was observed in all abiotic\nreactions, with ε<sub>C,bulk</sub> and ε<sub>Cl,bulk</sub> values ranging from −4.3 ± 0.4‰ to −2.3\n± 0.2‰ and from −2.6 ± 0.4‰ to −1.3\n± 0.3‰, respectively. Distinct mechanisms were evidenced\nin dual isotope plots, resulting in Λ values of 1.17 ±\n0.28 for ZVI, 1.26 ± 0.50 for VSS, 2.06 ± 0.30 for AA, and\n2.90 ± 0.50 for MWPS. Two major products were formed, 10-monohydrochlordecone\nand 8-monohydrochlordecone. Cl-CSIA data suggested that the first\nCl substitution at the C<sub>10</sub>-position likely produced secondary\nCl isotope effects (via nucleophilic substitution). Overall, results\nsuggest that ME-CSIA can help quantify <i>in situ</i> chlordecone\ndegradation, distinguishing between different ongoing degradation\nmechanisms and fingerprinting pollutant sources from chlordecone formulations\n(Curlone).