La conférence de Bali sur les changements climatiques a fait un pas vers le principe de rémunération de la réduction de la déforestation dans le cadre de la préparation du régime post-Kyoto. La déforestation contribuant à hauteur de 12-22% des émissions annuelles de CO2, la réduire est essentiel. Cependant, l'architecture et les modalités de mise en oeuvre du mécanisme nommé REDD (Réduction des émissions issues de la déforestation et de la dégradation) n'ont pas été définies et font l'objet de débats serrés, notamment sur la période de référence par rapport à laquelle mesurer la réduction de la déforestation au cours de la prochaine période d'engagement. Les pays qui considèrent que l'essentiel des épisodes de déboisement est derrière eux, plaident pour l'adoption d'une référence portant sur une période passée; à l'inverse, les pays à faible déboisement jusqu'à présent mais qui anticipent une déforestation accrue dans l'avenir, veulent pouvoir adopter une référence fondée sur un scénario tendanciel de déforestation future. L'autre divergence porte sur la nature des «récompenses»: crédits carbones échangeables sur le marché du même nom, ou argent issu d'un fonds spécial de lutte contre la déforestation ? On peut craindre que l'inclusion de REDD dans le marché du carbone n'entraîne une surabondance des permis d'émission et une baisse de leurs prix, compromettant l'efficacité, déjà toute relative, du système mis en place à Kyoto. On peut identifier trois problèmes récurrents avec l'architecture la plus évoquée pour REDD: la légitimité de l'extrapolation à partir de tendances historiques; la capacité d'estimation des scénarios de référence de type prédictif; enfin, la possibilité réelle d'imputer à différentes politiques publiques la baisse du taux de déforestation et d'en mesurer l'effet net. Le risque est réel pour qu'un tel mécanisme soit fortement générateur de réductions fictives d'émissions. II semble plus avisé de constituer un Fonds international contre la déforestation pour financer les politiques et les réformes structurelles nécessaires pour arrêter, à terme, la déforestation, ainsi que des programmes de paiements pour services environnementaux où les rémunérations iraient aux paysans plutôt qu'aux gouvernements. (Résumé d'auteur)

The ability of the free ion activity model (FIAM), the terrestrial biotic ligand model (TBLM), the diffusive gradients in thin films (DGT) technique and a plant-based biotest, the RHIZOtest, to predict root copper (Cu) concentration in field-grown durum wheat (Triticum turgidum durum L.) was assessed on 44 soils varying in pH (3.9e7.8) and total Cu (32e184 mg kg_1). None of the methods adequately predicted root Cu concentration, which was mainly correlated with total soil Cu. Results from DGT measurements and even more so FIAM prediction were negatively correlated with soil pH and over-estimated root Cu concentration in acidic soils. TBLM implementation improved numerically FIAM prediction but still failed to predict adequately root Cu concentration as the TBLM formalism did not considered the rhizosphere alkalisation as observed in situ. In contrast, RHIZOtest measurements accounted for rhizosphere alkalisation and were mainly correlated with total soil Cu. (Résumé d'auteur)

Environmental contamination by heavy metals is a common fact in Central Asia. In the present study two sampling procedures were achieved: (i) Sampling of fodder, camel raw milk and shubat (fermented camel milk) in 8 farms closed to pollution sources from the South of Kazakhstan for copper, iron, manganese, zinc, arsenic and lead analysis, (ii) sampling of camel milk in 4 regions of Kazakhstan (63 samples) analyzed for lead, chrome and zinc contamination. In first sampling, camel milk contained 0.07 ± 0.04, 1.48 ± 0.53, 0.08 ± 0.03, 5.16 ± 2.17, <0.1 and 0.025 ± 0.02 ppm respectively for Cu, Fe, Mn, Zn, As and Pb. In shubat (fermented milk) the mean content was 0.163 ± 0.164, 1.57 ± 0.46, 0.088 ± 0.02, 7.217 ± 2.55 and 0.007 ppm respectively. Arsenic was detected in some samples of milk and shubat only. The trace elements concentration increase in shubat compared to milk but lead concentration decreased. No clear correlation was observed with fodder composition. In second sampling, the lead content was on average 250 ± 56 ppb in the camel milk with no significant differences between regions. The maximum value was observed at Atyrau (532 ppb). Zinc content in milk (5.42 ± 0.2 ppm) did not change significantly between regions. In reverse, chrome (59.5 ± 45.4 ppb) was higher in Shymkent region compared to others. These values were discussed according to the proximity of pollution sources. Specially, higher concentrations were experienced in fodder from pastures close to some industrial sites or high traffic road. (Résumé d'auteur)

The aim of this study was to identify primary flow paths involved in the chlordecone (CLD) river contamination and quantify the CLD fluxes to assess CLD pollution levels and duration according to a typical catchment of the banana cropping area in the French Indies (Guadeloupe): the Pérou Catchment (12 km2) characterized by heavy rainfall (5686 mm year?1). Three sub-catchments (SC1, SC2 and SC3) were studied during the hydrological year 2009–2010: a pedological survey combined with a spatialized hydrochemical approach was conducted. The average soil concentration is higher in the Pérou Catchment (3400 ?g kg?1) than in the entire banana cropping area in Guadeloupe (2100 ?g kg?1). The results showed that CLD stocks in soils vary largely among soil types and farming systems: the weakest stocks are located upstream in SC1 (5 kg ha?1), where a majority of the area is non-cultivated; medium stocks are located in Nitisols downstream in SC3 (9 kg ha?1); and the greatest stocks are observed in SC2 on Andosols (12 kg ha?1) characterized by large farms. The annual water balance and the hydro-chemical analysis revealed that the three sub-catchments exhibited different behaviors. Pérou River contamination was high during low flows, which highlighted that contamination primarily originated from groundwater contributions. The results showed that only a small part of the catchment (SC2), contributing little to the water flow, comprises a major CLD contribution, which is in agreement with the highly contaminated andosol soils observed there. Another significant result considers that at least 50 years would be required to export the totality of the actual CLD soil stocks retained in the topsoil layer. The actual time for soil remediation will however be much longer considering (i) the necessary time for the chlordecone to percolate and be stored in the shallow aquifers and (ii) its travel time to reach the river. (Résumé d'auteur)

Due to the persistent pollution of soils by an organochlorine, chlordecone (CLD also known as Kepone ©) in the French West Indies, some crops may be contaminated beyond the European regulatory threshold, the maximum residue limit (MRL). Farmers need to be able to foresee the risk of not complying with the regulatory threshold in each field and for each crop, if not, farmers whose fields are contaminated would have to stop cultivating certain crops in the fields concerned. To help farmers make the right choices, we studied the relationship between contamination of the soil and contamination of crops. We showed that contamination of a crop by CLD depended on the crop concerned, the soil CLD content and the type of soil. We grouped crop products in three categories: (i) non-uptakers and low-uptakers, (ii) medium-uptakers, and (iii) high-uptakers, according to their level of contamination and the resulting risk of exceeding MRL. Using a simulation model, we computed the soil threshold required to ensure the risk of not complying with MRL was sufficiently low for each crop product and soil type. Threshold values ranged from 0.02 ?gkg?1 for dasheen grown in nitisol to 1.7 ?gkg?1 for yam grown in andosol in the high-uptake category, and from 1 ?gkg?1 for lettuce grown in nitisol to 45 ?gkg?1 for the leaves of spring onions grown in andosol in the medium-uptake category. Contamination of non-uptakers and low-uptakers did not depend on soil contamination. With these results, we built an easy-to-use decision support tool based on two soil thresholds (0.1 and 1 ?gkg?1) to enable growers to adapt their cropping system and hence to be able to continue farming. (Résumé d'auteur)tttttt

Insecticidal Cry, or Bt, proteins are produced by the soil-endemic bacterium, Bacillus thuringiensis and some genetically modified crops. Their environmental fate depends on interactions with soil. Little is known about the toxicity of adsorbed proteins and the change in toxicity over time. We incubated Cry1Ac and Cry2A in contrasting soils subjected to different treatments to inhibit microbial activity. The toxin was chemically extracted and immunoassayed. Manduca sexta was the target insect for biotests. Extractable toxin decreased during incubation for up to four weeks. Toxicity of Cry1Ac was maintained in the adsorbed state, but lost after 2 weeks incubation at 25 °C. The decline in extractable protein and toxicity were much slower at 4 °C with no significant effect of soil sterilization. The major driving force for decline may be time-dependent fixation of adsorbed protein, leading to a decrease in the extraction yield in vitro, paralleled by decreasing solubilisation in the larval gut. (Résumé d'auteur)

When field pollution is heterogeneous due to localized pesticide application, as is the case of chlordecone (CLD), the mean level of pollution is difficult to assess. Our objective was to design a decision support tool to optimize soil sampling. We analyzed the CLD heterogeneity of soil content at 0-30- and 30-60-cm depth. This was done within and between nine plots (0.4 to 1.8 ha) on andosol and ferralsol. We determined that 20 pooled subsamples per plot were a satisfactory compromise with respect to both cost and accuracy. Globally, CLD content was greater for andosols and the upper soil horizon (0-30 cm). Soil organic carbon cannot account for CLD intra-field variability. Cropping systems and tillage practices influence the CLD content and distribution; that is CLD pollution was higher under intensive banana cropping systems and, while upper soil horizon was more polluted than the lower one with shallow tillage (<40 cm), deeper tillage led to a homogenization and a dilution of the pollution in the soil profile. The decision tool we proposed compiles and organizes these results to better assess CLD soil pollution in terms of sampling depth, distance, and unit at field scale. It accounts for sampling objectives, farming practices (cropping system, tillage), type of soil, and topographical characteristics (slope) to design a relevant sampling plan. This decision support tool is also adaptable to other types of heterogeneous agricultural pollution at field level. (Résumé d'auteur)

We examined copper (Cu) absorption, distribution and toxicity and the role of a silicon (Si) supplementation in the bamboo Phyllostachys fastuosa. Bamboos were maintained in hydroponics for 4 months and submitted to two different Cu (1.5 and 100 mm Cu2þ) and Si (0 and 1.1 mM) concentrations. Cu and Si partitioning and Cu speciation were investigated by chemical analysis, microscopic and spectroscopic techniques. Copper was present as Cu(I) and Cu(II) depending on plant parts. Bamboo mainly coped with high Cu exposure by: (i) high Cu sequestration in the root (ii) Cu(II) binding to amino and carboxyl ligands in roots, and (iii) Cu(I) complexation with both organic and inorganic sulfur ligands in stems and leaves. Silicon supplementation decreased the visible damage induced by high Cu exposure and modified Cu speciation in the leaves where a higher proportion of Cu was present as inorganic Cu(I)S compounds, which may be less toxic. (Résumé d'auteur)

This study aimed at determining the fate of trace elements (TE) following soil organic waste (OW) application. We used a unique combination of X-ray absorption spectroscopy analyses, to determine TE speciation, with incubation experiments for in situ monitoring of TE availability patterns over a time course with the technique of the diffusive gradients in thin films (DGT). We showed that copper (Cu) and zinc (Zn) availability were both increased in OW-amended soil, but their release was controlled by distinct mechanisms. Zn speciation in OW was found to be dominated by an inorganic species, i.e. Zn sorbed on Fe oxides. Zn desorption from Fe oxides could explain the increase in Zn availability in OW-amended soil. Cu speciation in OW was dominated by organic species. Cu release through the mineralization of organic carbon from OW was responsible for the increase in Cu availability. (Résumé d'auteur)

Spreading livestock manure as fertilizer on farmlands is a widespread practice. It represents the major source of heavy metal(loid)s (HM) input in agricultural soils. Since zinc (Zn) is present at high concentrations in manure, it poses special environmental concerns related to phytotoxicity, groundwater contamination, and introduction in the food chain. Therefore, investigations on the fate and behavior of manure-borne Zn, when it enters the soil environment, are necessary to predict the environmental effects. Nevertheless, long-term field studies assessing Zn speciation in the organic waste matrix, as well as within the soil after manure application, are lacking. This study was designed to fill this gap. Using SEM-EDS and XAS analysis, we reported the following new results: (i) ZnS made up 100% of the Zn speciation in the pig slurry (the highest proportion of ZnS ever observed in organic waste); and (ii) ZnS aggregates were about 1-?m diameter (the smallest particle size ever reported in pig slurry). Moreover, the pig slurry containing ZnS was spread on the soil over an 11-year period, totaling 22 applications, and the resulting Zn speciation within the amended soil was analyzed. Surprisingly, ZnS, i.e. the only species responsible for a nearly 2-fold increase in the Zn concentration within the amended soil, was not detected in this soil. Based on SEM-EDS and XAS observations, we put forward the hypothesis that Zn in the pig slurry consisted of nano-sized ZnS crystallites that further aggregated. The low stability of ZnS nanoparticles within oxic and complex environments such as the studied soil was the key explanation for the radical change in pig slurry-borne Zn speciation after long-term amendments. (Résumé d'auteur)