Evaluation of the ecotoxicological impact of the organochlorine chlordecone on soil microbial community structure, abundance, and function

International audienceThe insecticide chlordecone applied for decades in banana plantations currently contaminates 20,000 ha of arable land in the French West Indies. Although the impact of various pesticides on soil microorganisms has been studied, chlordecone toxicity to the soil microbial community has never been assessed. We investigated in two different soils (sandy loam and silty loam) exposed to different concentrations of CLD (D0, control; D1 and D10, 1 and 10 times the agronomical dose) over different periods of time (3, 7, and 32 days): (i) the fate of chlordecone by measuring C-14-chlordecone mass balance and (ii) the impact of chlordecone on microbial community structure, abundance, and function, using standardized methods (-A-RISA, taxon-specific quantitative PCR (qPCR), and C-14-compounds mineralizing activity). Mineralization of C-14-chlordecone was inferior below 1 % of initial C-14-activity. Less than 2 % of C-14-activity was retrieved from the water-soluble fraction, while most of it remained in the organic-solvent-extractable fraction (75 % of initial C-14-activity). Only 23 % of the remaining C-14-activity was measured in nonextractable fraction. The fate of chlordecone significantly differed between the two soils. The soluble and nonextractable fractions were significantly higher in sandy loam soil than in silty loam soil. All the measured microbiological parameters allowed discriminating statistically the two soils and showed a variation over time. The genetic structure of the bacterial community remained insensitive to chlordecone exposure in silty loam soil. In response to chlordecone exposure, the abundance of Gram-negative bacterial groups (beta-, gamma-Proteobacteria, Planctomycetes, and Bacteroidetes) was significantly modified only in sandy loam soil. The mineralization of C-14-sodium acetate and C-14-2,4-d was insensitive to chlordecone exposure in silty loam soil. However, mineralization of C-14-sodium acetate was significantly reduced in soil microcosms of sandy loam soil exposed to chlordecone as compared to the control (D0). These data show that chlordecone exposure induced changes in microbial community taxonomic composition and function in one of the two soils, suggesting microbial toxicity of this organochlorine

Evaluation de l'impact écotoxicologique du chlordécone sur la structure, l'abondance et l'activité de la communauté microbienne de sols agricoles

National audienceL’insecticide chlordécone appliqué pendant plusieurs décades dans les bananeraies contamine environ 20 000 hectares de sols arables dans les Antilles. Bien que l’impact de nombreux pesticides sur les microorganismes du sol ait été étudié, l’écotoxicité du chlordécone n’a jamais été évaluée. Afin d’y remédier, nous avons évalué son écotoxicité sur deux sols agricoles (l’un sableux et l’autre limoneux) exposés à différentes concentrations de chlordécone (D0, contrôle; D1 and D10, 1- et 10-fois la dose agronomique). Le devenir du chlordécone a été évalué en établissant le bilan de masse du 14C-chlordécone. L’impact écotoxicologique du chlordécone sur l’abondance (qPCR taxon spécifique), la structure (empreinte génétique A-RISA) et l’activité catabolique (radiorespirométrie) de la communauté bactérienne a été évalué. Dans les deux sols, les fractions minéralisée et soluble du 14C-chlordécone étaient les plus faibles représentant à elles deux moins de 5% de la quantité initiale de 14C-chlordécone. La plupart du chlordécone était dans la fraction extractible (75% de la quantité initiale de 14C), le restant formant des résidus liés. Toutes les mesures des paramètres microbiens ont permis de discriminer les deux sols. L’exposition au chlordécone n’a pas affecté la structure génétique de la communauté bactérienne, toutefois dans le sol sableux, elle a significativement modifié l’abondance de groupes bactériens (-, - proteobacteries, Planctomycetes and Bacteroidetes) et l’activité catabolique (minéralisation du 14C- acétate de sodium) de la communauté bactérienne. Ces résultats montrent que l’exposition au chlordécone modifie l’abondance de groupes bactériens et l’activité catabolique de la communauté bactérienne, révélant la toxicité microbienne de cet organochloré

Relaxation Dynamics in Photoexcited Chiral Molecules Studied by Time-Resolved Photoelectron Circular Dichroism: Toward Chiral Femtochemistry

Unravelling the main initial dynamics responsible for chiral recognition is a key stepin the understanding of many biological processes. However this challenging task requires a sensitive enantiospecic probe to investigate molecular dynamics on their natural femtosecond timescale. Here we show that, in the gas phase, the ultrafast relaxationdynamics of photoexcited chiral molecules can be tracked by recording Time-ResolvedPhotoElectron Circular Dichroism (TR-PECD) resulting from the photoionisation bya circularly polarized probe pulse. A large forward/backward asymmetry along theprobe propagation axis is observed in the photoelectron angular distribution. Its evolution with pump-probe delay reveals ultrafast dynamics that are inaccessible in theangle-integrated photoelectron spectrum nor via the usual electron emission anisotropyparameter (β). PECD, which originates from the electron scattering in the chiral molecular potential, appears as a new sensitive observable for ultrafast molecular dynamicsin chiral systems.Imagerie Moléculaire par effet tunnel et recollision en champ for