Distinct Carbon Isotope Fractionation Signatures during Biotic and Abiotic Reductive Transformation of Chlordecone

Chlordecone is a synthetic organochlorine pesticide, extensively used in banana plantations of the French West Indies from 1972 to 1993. Due to its environmental persistence and bioaccumulation, it has dramatic public health and socio-economic impact. Here we describe a method for carbon-directed compound specific isotope analysis (CSIA) for chlordecone and apply it to monitor biotic and abiotic reductive transformation reactions, selected on the basis of their distinct product profiles (polychloroindenes versus lower chlorinated hydrochlordecones). Significant carbon isotopic enrichments were observed for all microbially mediated transformations (ε_bulk = -6.8‰ with a Citrobacter strain and ε_bulk = -4.6‰ with a bacterial consortium) and for two abiotic transformations (ε_bulk = -4.1‰ with zerovalent iron and ε_bulk = -2.6‰ with sodium sulfide and vitamin B₁₂). The reaction with titanium(III) citrate and vitamin B₁₂, which shows the product profile most similar to that observed in biotic transformation, led to low carbon isotope enrichment (ε_bulk =-0.8‰). The CSIA protocol was also applied on representative chlordecone formulations previously used in the French West Indies, giving similar chlordecone δ¹³C values from -31.1 ± 0.2‰ to -34.2 ± 0.2‰ for all studied samples. This allows the in situ application of CSIA for the assessment of chlordecone persistence.