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International audience; Antimony (Sb) is a naturally occurring element; it is enriched in the environment by anthropogenic activities. Like other metalloid species, Sb partitions to mineral phases such as oxyhydroxides. In reducing environments, Fe(III) may serve as a terminal electron acceptor during dissimilatory iron reduction leading to its transformation. Relatively little is known concerning the effect of Sb(V) on the precipitation of biogenic minerals in relation to microbiologically mediated redox reactions. To further our understanding, Sb-bearing ferrihydrites (0.5 g) with variable Sb/(Fe + Sb) molar ratios of 0.04, 0.06 and 0.1, were incubated in the presence of Shewanella oneindensis MR-1 (1 × 108 cell mL−1) under N2 atmosphere. Additionally, we synthesized abiotic GR1(CO32−) in the presence of Sb(V) to examine the effect of Sb(V) on this mineral formation and stabilization. A combination of wet chemistry and solid analysis techniques (XRD, Mössbauer and Raman spectroscopies) was used to characterize the reactions.The Sb loading affected the rate and the extent of bio-reduction compared with pure ferrihydrite. Only a minor fraction of the total Sb, less than 0.5%, was released into the solution by the end of the incubation period, suggesting that the metalloid partitioned mainly in a newly formed phase. Furthermore, XPS analyses showed the presence of Sb(V) and Sb(III) species on the biogenic minerals. Magnetite was the main biogenic precipitate (91%) in the absence of Sb(V). Increasing of the molar ratios [Sb/(Fe + Sb)] to 0.1 resulted mainly in the precipitation of carbonated green (47%) rust and goethite (37%). Abiotic green rust synthesis carried out in the presence of Sb(V) indicated the latter’s stabilizing effect on the green rust structure, as for phosphate species. Thus, it is likely that Sb(V) preserve biogenic green rust, hindering its transformation to more thermodynamically stable phases.

International audience; Constructed wetlands (CWs) are useful for reducing pesticide transfer from drainage into surface water, though little was known about the influence of hydrodynamics on their mitigation. We thus assessed the influence of design parameters (aspect ratio, water depth, flow rate) on hydraulic performance simultaneously to pesticide mitigation. We performed our work on four pesticides with contrasted properties: boscalid (BSC), cyproconazole (CYP), isoproturon (IPU) and dimethachlor (DMT), under three controlled flow-rate conditions (including no-flow) by using two pilots with contrasted designs (pond and ditch) over 62 days. Hydraulic performance and pesticide mitigation were less effective in a pond than in the ditch whatever the flow. Moreover, pesticide mitigation was more significant at low than at high flow rates for both pilots. M high flow rate, water transport is mainly governed by convection, but at low flow rates both water transport and mitigation are governed by hydrodynamic dispersion, inducing a longer contact time between pesticides and substrate due to longer hydraulic retention. Finally, BSC and CYP are better mitigated than DMT and IPU, even if they are also more strongly released during low flow rates. In addition, the mitigation of pesticides and some of their metabolites produced inside the pilots was almost complete during stagnation.

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International audience; In Burkina Faso, significant amounts of endosulfan are applied to cotton fields; in addition, urban vegetable agriculture is often characterised by high fertiliser inputs, such as urban solid wastes containing heavy metals (e.g., Cu and Cd). Thus, the relevance of surrounding cotton and urban vegetable plots with vetiver (Vetiveria zizanioides) hedges to reduce environmental pollution by micropollutants was investigated using a leaching experiment, with outdoor lysimeters filled with two representative agricultural soils of Burkina Faso: Vertisol and Lixisol. After 6 months, little Cu was found in the leachates (< 0.010% of the applied amount) due to its high adsorption coefficient and its tendency to remain at the soil surface. Despite leachate and bromide recoveries being greater in soils planted with vetiver grass than in the bare soils, smaller amounts of endosulfan and Cd were found in the effluents from the planted soils (0.01% to 0.70% of the applied amount) than in those from the bare soils (0.01% to 1.48% of the applied amount), in agreement with their adsorption coefficients. These results may also be explained by a greater degradation of endosulfan in planted soils compared to bare soils and the absorption of Cd by vetiver. Thus, vetiver may decrease the risk of groundwater contamination, especially for Cd and endosulfan, which are more mobile than Cu. In addition, despite the smaller amounts of endosulfan and Cd measured in the Vertisol leachates (0.01% and 0.04% of the applied amount, respectively) compared to the Lixisol leachates, vetiver was more effective in decreasing the leaching of micropollutants if planted on Lixisol rather than on Vertisol. Further field monitoring is necessary to demonstrate the effectiveness of vetiver under the climatic conditions of Burkina Faso.

International audience; Microbial degradation is a promising soil remediation strategy for polycyclic aromatic hydrocarbons (PAHs) frequently polluting some post-industrial environments. Thirteen PAH-degrading bacterial strains were isolated from bare or ryegrass-vegetated aged-contaminated soil, based on their potential for phenanthrene biodegradation. 16S rRNA gene phylogeny showed that all isolates were affiliated with three closely related taxonomic subgroups within the Pseudomonas genus. Two of these subgroups were exclusively retrieved from planted soil. Genes encoding PAH-ring hydroxylating dioxygenases were detected in all strains and matched known sequences in other Pseudomonas strains from polluted environments. Genes for protocatechuate-3,4-dioxygenases (pcaH) and catechol-2,3-dioxygenases were also detected in all strains, whereas the catechol-1,2-dioxygenase gene was absent. The presence of pcaH genes, the utilization of protocatechuate, the strong inhibitory effect of salicylate and the detection of phthalate during phenanthrene biodegradation suggest that these isolates preferentially catabolize PAHs via the protocatechuate pathway. Metabolic profiling was further performed for three representative isolates on a large range of 61 organic substrates. Although closely related phylogenetically, they were able to use different sets of labile carbon compounds (e.g. sugars, amino acids), PAHs and their metabolites, and released different degradation products from phenanthrene. These contrasted metabolic capabilities might reflect differential adaptation to their respective environment.

cited By 0; International audience; Chloride is often considered as the main chlorine form in soils. However, recent studies show that chlorine is mostly present in soils as naturally produced organically bound molecules. The relative contribution of biotic, including microbial, and abiotic processes to formation of organically bound chlorine remains poorly understood. We performed a37Cl spiking batch experiment with a forest soil incubated under abiotic and biotic conditions over two time periods to simultaneously monitor the formation of organically bound chlorine from natural and tracer chlorine. To compare biotic and abiotic conditions without biased effect of sterilization technique for abiotic control, the soil was irradiated and reinoculated or not with soil microflora. Fifteen days after microbial inoculation, the natural non-extractable organic chlorine content in the inoculated soil was significantly higher than in the sterile soil, showing that microbial activity contributed to formation of organically bound chlorine. However, no significant difference was noted between the two incubation periods. The same trend was noted for tracer chlorine, yet without a significant difference. The present study shows that chlorination is mediated by microbial activity, but there is also some indication of abiotic formation of organically bound chlorine, with a non-extractable organic tracer chlorine formation of about 6% just after spiking in abiotic conditions. © 2016 Elsevier Ltd

International audience; Constructed wetlands are an effective and practicaloption for removing pesticide pollution from runoff or subsur-face drainage water. The objective of this study was to assessthe efficiencies of a ditch with a bundle of straw placed in itscentre and a vegetated pond installed in grass cover bands atdownstream of a drained plot. The dissipation rates of threeherbicides and three fungicides were monitored on four sub-strates commonly found in constructed wetlands (two soils,sediment and straw). The influence of water content was de-termined in a sequence of three steps (flooded-unsaturated-flooded) over 120 days. The pesticide dissipation rates ob-served during the 120 days of incubation ranged from 1.4 to100 %. Isoproturon and 2,4-MCPA (MCPA) showed thehighest dissipation rates, which ranged from 61.0 to 100 %of the applied quantities during the 120 days of incubation. Incontrast, boscalid and tebuconazole showed the lowest dissi-pation rates, which ranged from 1.4 to 43.9 % of the appliedquantities during the 120 days of incubation. The estimatedDT50values ranged from 20.5 days to more than 1 year andwere influenced by the substrate water content. The soil andstraw substrates had the lowest DT50values during the unsat-urated conditions, whereas the sediments had the lowest DT50values during the flooded conditions. These results couldbe explained by an adaptation of microbial communities totheir environmental conditions. Thus, the most favourableconditions of dissipation for soils and straw are observablewhen the drainage ceases (spring and summer). However,favourable conditions occur all year for the sediments, exceptwhen the constructed wetlands are dry. The results suggestthat the dissipation of pesticides in constructed wetlands con-tributes to the long-term effectiveness of these buffer zones forreducing water pollution.