Microbial transformation of chlordecone (CLD) and two hydro-CLD issue from In Situ Chemical Reduction (ISCR) of CLD

Chlordecone (CLD) is a very persistent synthetic organochlorine pesticide found in the French West Indies, particularly in soils because of its intensive application in the 1970s and 1980s to control black banana weevil. It remains a proven public health problem. Recently published work has demonstrated the potential of zero valent iron to declorinate CLD by in situ chemical reduction (ISCR) in soils under water-saturated conditions, forming mono to penta-dechlorinated CLD transformation products. These transformation products are more mobile than CLD and less toxic, however, nothing is known about their further degradation, although more and more evidence of CLD biodegradation by bacteria are being found. The present study began with the enrichment from waste-water sludge of a CLD transforming community which was then inoculated in fresh media in presence of either CLD, or two of the main ISCR transformation products, a mono-hydroCLD (CLD-1Cl) and a tri-hydroCLD (CLD-3Cl). Carried out in triplicate batchs, and incubated at 38°C under anoxic conditions and in the dark, the cultures were sampled regularly during three months and analyzed for CLD, CLD-1CL, CLD-3Cl and other transformation products by GC-MS. At the end of the experiment, bacteria and archaea diversity was analyzed by sequencing a fragment of the rRNA 16S gene and further characterization of the transformation products was carried out. All inoculated batches showed a decrease of the added CLD or hydroCLD. In the CLD condition, this was concomitant with the formation of a 9-carbon compound (C9Cl5H3) of pentachloroindene as previously described, whereas both CLD-1Cl and CLD-3Cl underwent a sulfidation reaction, also as previously described for CLD and CLD-1Cl but not for CLD-3Cl. Also at the end of the experiment, diversity, which was low as expected in an enrichment, was mostly similar in the CLD and CLD-1Cl conditions to the inoculum with a dominant archaea genus, Methanobacterium, and four OTU affiliated to bacteria, identified at the family (Spirochaetaceae) or genus level (Desulfovibrio, Aminobacterium and Soehngenia). Whereas, in the CLD-3CL condition, although the same OTU were found, additionally Clostridium sensu stricto 7, Candidatus Cloacimonas and Proteiniphilum were also present at >2% sequences. Overall, these results contribute to increasing our knowledge on CLD and its transformation products, helping to progress towards effective remediation solutions.