The historic use of chlordecone (C 10 Cl 10 O) as a pesticide to control banana weevil infestations has resulted in pollution of large land areas in the French West Indies. Although currently banned, chlordecone persists because it adsorbs strongly to soil and its complex bishomocubane structure is stable, particularly under aerobic conditions. Abiotic chemical transformation catalyzed by reduced vitamin B 12 has been shown to break down chlordecone by opening the cage structure to produce C9 polychloroindenes. More recently these C9 polychloroindenes were also observed as products of anaerobic microbiological transformation. To investigate the anaerobic biotransformation of chlordecone by microbes native to the French West Indies, microcosms were constructed anaerobically from chlordecone impacted Guadeloupe soil and sludge to mimic natural attenuation and eletron donor-stimulated reductive dechlorination. Original microcosms and transfers were incubated over a period of 8 years, during which they were repeatedly amended with chlordecone and electron donor (ethanol and acetone). Using LC-MS, chlordecone and degradation products were detected in all the biologically active microcosms. Observed products included monohydro-, dihydro-and trihydrochlordecone derivatives (C 10 Cl 10-n O 2 H n ; n = 1,2,3), as well as "open cage" C9 polychloroindene compounds (C 9 Cl 5-n H 3+n n = 0,1,2) and C10 carboxylated polychloroindene derivatives (C 10 Cl 4-n O 2 H 4+n , n = 0-3). Products with as many as 9 chlorine atoms removed were detected. These products were not observed in sterile (poisoned) microcosms. Chlordecone concentrations decreased in active microcosms as concentrations of products increased, indicating that anaerobic dechlorination processes have occurred. The data enabled a crude estimation of partitioning coefficients between soil and water, showing that carboxylated intermediates sorb poorly and as a consequence may be flushed away, while polychlorinated indenes sorb strongly to soil. Microbial community analysis in microcosms revealed enrichment of anaerobic fermenting and acetogenic microbes possibly involved in anaerobic chlordecone biotransformation. It thus should be possible to

ABSTRACTChlordecone (C10Cl10O) is a bishomocubane molecule, that has been used as pesticide, in many countries in Europe, America, and Africa, from the 1960’s to 1990’s. In the French West Indies, the historic use of chlordecone to control banana weevil infestations has resulted in pollution of large land areas. Although currently banned, chlordecone persists because it adsorbs strongly to soil and its complex structure is stable, particularly under aerobic conditions. A leaching model established that CLD pollution will last in French west indies soils several decades to half a millennium depending on soil type. However, abiotic chemical transformation catalyzed by reduced vitamin B12 has been shown to break down chlordecone by opening the cage structure to produce C9 polychloroindenes, and more recently these C9 polychloroindenes were also observed as products of anaerobic microbiological transformation by Citrobacter. To assess the potential for bioremediation, the anaerobic biotransformation of chlordecone by microbes native to soils from the French West Indies was investigated. Anaerobic microcosms were constructed from chlordecone impacted Guadeloupe soil and sludge to mimic natural attenuation and eletron donor-stimulated reductive dechlorination. Original microcosms and transfers were incubated over a period of 8 years, during which they were repeatedly amended with chlordecone and electron donor (ethanol and acetone). Using LC/MS, chlordecone and degradation products were detected in all the biologically active microcosms. Observed products in active incubations included monohydro-, dihydro- and trihydrochlordecone derivatives (C10Cl10−nO2Hn, n= 1,2,3), as well as “open cage” C9 polychloroindene compounds (C9Cl5−nH3+n, n=0,1,2) and C10 carboxylated polychloroindene derivatives (C10Cl4−nO2H4+n, n=0−3). Products with as many as 9 chlorine atoms removed were detected. These products were not observed in sterile incubations. Chlordecone concentrations decreased in active microcosms as concentrations of products increased, indicating that anaerobic dechlorination processes have occurred. An crude estimation of partitioning coefficients between soil and water showed that carboxylated intermediates sorb poorly, and as a consequence may be flushed away while polychlorinated indenes sorb strongly to soil. Microbial community analysis in microcosms showed enrichment of anaerobic fermenting and acetogenic microbes possibly involved in anaerobic chlordecone biotransformation. It thus should be possible to stimuilate anaerobic dechlorination through donor amendment to contaminated soils, particularly as some metabolites (in particular pentachloroindene) were already detected in field samples as a result of intrinsic processes. Extensive dechlorination in the microcosms, with evidence for up to 9 Cl atoms removed from the parent molecule is game-changing, giving hope to the possibility of using bioremediation to reduce the impact of CLD contamination.

Banana has been a main agricultural product in the French West Indies (Guadeloupe and Martinique) since the 1960s. This crop requires the intensive use of pesticides to prevent attacks by insect pests. Chlorinated pesticides, such as hexachlorocyclohexane (HCH), chlordecone and dieldrin, were used until the beginning of the 1990s, resulting in a generalized diffuse contamination of the soil and water in the areas of banana production, hence the need to develop solutions for cleanup of the polluted sites. The aims of this work were (i) to assess lindane degradation in soil slurry microcosms treated with lindane at 10 mg/L and (ii) to detect the catabolic genes involved in the HCH degradation pathway. The soil slurry microcosm system showed a 40% lindane degradation efficiency at the end of a 30-day experiment. Lower lindane removal was also detected in the abiotic controls, probably caused by pesticide adsorption to soil particles. Indeed, the lindane concentration decreased from 6000 to 1330 ng/mL and from 800 to 340 ng/mL for the biotic and abiotic soils, respectively. Nevertheless, some of the genes involved in the HCH degradation pathway were amplified by polymerase chain reaction (PCR) from crude deoxyribonucleic acid (DNA) extracted from the Guadeloupe agricultural soil, suggesting that HCH degradation is probably mediated by bacteria closely related to the family Sphingomonadaceae.

No abstract