Multi-element compound-specific isotope analysis of chlordecone during abiotic transformation reactions

Chlordecone (CLD; C₁₀Cl₁₀O) is an organochlorine pesticide extensively used between 1960s and 1990s in the French West Indies (FWI). Its massive use led to soil and river pollution which prompted its ban in 1993. CLD has a bis-homocubane structure and various chlorine atoms making it highly recalcitrant in the environment. To date, several environmental compartments of the FWI continue facing the legacy of CLD pollution. This study aims at improving the monitoring of the degradation (or recalcitrance) extent of CLD in the soils of the FWI following in situ chemical reduction (ISCR). Multi-element compound-specific isotope analysis (ME-CSIA) was used to identify changes of stable isotopes of CLD (i.e., ¹³C/¹²C and ³⁷Cl/³⁵Cl) produced during distinct abiotic reductive transformation reactions. Reductive transformation of CLD was tested in abiotic microcosms in the presence of either zero-valent iron, ascorbic acid, vitamin B_12, or persulfate activated by microwave irradiation. CLD transformation was evidenced by the detection of several hydrochlordecones (after losses of one or two chlorine atoms) under all conditions. Enrichment of the ¹³C isotopes of CLD relative to ¹²C revealed distinct signatures during transformation reactions of CLD to maximum Δδ¹³C of +7.2 ‰. A novel stable Cl isotope analysis was performed by liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS). Ongoing Cl isotope analysis may establish a multi-element assessment in which abiotic CLD degradation pathways may be distinguished based on stable C-Cl signatures. Altogether, our results may provide an improved strategy to elucidate CLD degradation in contaminated soils of the FWI.