The well-informed recycling of organic waste to agricultural land becomes increasingly desirable in dynamic, developing regions worldwide. Pursuing locally optimal benefit-risk ratios, agro-environmental research in support of OW recycling does not focus on avoiding contamination perse, but on the control of dynamics, in soil and other environmental compartments, in order not to exceed risk thresholds. We present a series of empirical research efforts that inform decision making in regions under OW pressure on OW-contained trace contaminant fate under local conditions. Their results illustrate that the present understanding of trace elements fate allows for the ex-ante assessment of fate under specific use scenarios and local conditions, with a limited set of simplifications. A well-established set of analytical tools provides the information required by such assessments. Understanding of OW-borne organic contaminants is less advanced, but the present capacity to project fate under local conditions does allow for the approximate appreciation of risk levels, the major benefit of which is to focus subsequent research on substances of concern. Ongoing long-term field trials may critically advance our understanding of OW-borne contaminant fate in soil. Developing a reasonable capacity to assess biological contaminant fate is one of its priorities.

The French West Indies face nowadays a diffuse and long term environmental pollution related to historical use of organochlorine insecticide in banana fields, Chlordecone (CLD). Due to its stability, it now pollutes soil, waters, agricultural products and leads to a global exposure of people and ecosystems. We wonder how to manage such a complex pollution system involving all environmental compartments, linked each other. For that, we have been conducting research studies for more than 15 years in the field of agronomy and environment to explore the fate of the molecule in the environment, the impact on food safety, and also the remediation options. Three main points are addressed: i) how to characterize the pollution and to make easier the diagnosis? ii) how to assess the impacts on environmental compartments and agricultural products? iii) How to manage the pollution? The tools we developed make a diagnosis of such pollution easier at different scales (field, farm, watershed, and territory). We built monitoring support systems for the water quality of rivers with models helping to understand variability of water contamination. We built also decision support systems to farmers to manage their soil pollution and choose the crops that will ensure food security. Now CLD content of local crop products on the market complies with the Maximum Residue Limit. Management is more complex for animal products, and further investigations are needed. We investigated alternative solution to enhance CLD soil sequestration, using physical properties of French West Indies volcanic soil and organic matter amendment. Increased organic matter content in soil reduced drastically the CLD transfer from soil to water, but this effect was not perennial and amendment had to be regularly applied. Our results show that an integrative approach is needed to build efficient policies to manage such pollution than to prevent new ones.

This text focuses on the identification, efficiencies, classification and management of landscape features having a potential buffer function regarding diffuse phosphorus, because of their specific structure (vegetation-soil) and of their location at the interface between sources (farm infrastructures, emitting fields…) and surface water bodies. These buffers are very diverse and correspond to natural landscape features (wetlands, riparian areas…) as well as manmade structures (constructed buffer strips or intermediate cases such as field margins, hedgerows). Their role and efficiency depends on the local factors controlling the retention processes (internal organisation and properties of the buffer), on the position within the watershed, and on the landscape context which reciprocally determines the overall buffer capacity of a watershed. On that basis, we recognize the diversity of the buffers in structure and functioning and thus in the way they attenuate the signal, their limitations (sustainability, side effects) and their hierarchic organisation at the watershed scale.

Organic waste (OW) reuse in agriculture is a common practice fostered by benefits in terms of waste recycling and crop production. However, OW amendments potentially affect the fate of pesticide spread on fields to protect the crops from pests and weeds. The influence of OW on the sorption, degradation, and leaching of pesticides is generally studied for each mechanism separately under artificial laboratory conditions. Our study aims at evaluating the balance of these mechanisms under more realistic conditions to clarify the influence of three common OW amendments on the fate, in soil, of the widely used herbicide S-Metolachlor. We performed leaching experiments in large undisturbed soil cores amended with raw sewage sludge, composted sludge, and digested pig slurry (digestate), respectively. We monitored S-Metolachlor and its two main metabolites MET-OA and MET-ESA in the leachates during a succession of 10 rainfall events over 126 days. We also quantified the remaining S-Metolachlor and metabolites in the soil at the end of the experiments. S-Metolachlor leaching didn't exceed 0.1% of the applied dose with or without OW amendment. Despite a soil organic carbon increase of 3 to 32%, OW amendments did not significantly affect the amount of S-Metolachlor that leached through the soil (0.01 to 0.1%) nor its transformation rate (6.0 to 8.6%). However, it affected the degradation pathways with an increase of MET-OA relative to MET-ESA formed after OW amendment (28 to 54%) compared to the controls (8%). Concentration of S-Metolachlor and metabolites in the leachates of all treatments greatly exceeded the regulatory limit for groundwater intended for human consumption in Europe. These high concentrations were probably the consequence of preferential macropore flow. Colloids had comparable levels in the leachates after S-Metolachlor application. Dissolved organic carbon was also comparable in the controls, digestate, and sludge treatments but was 65% higher in the compost-amended cores. These results, along with a great variability among replicates inherent to experiments performed under realistic conditions, partly explain the limited impact of OW on the transport of S-Metolachlor

The In Situ Chemical Reduction (ISCR) process was tested in a nitisol in a French Caribbean banana plantation using five different soil amendments. The addition of 2.8% or 4.0% of Zero Valent Iron (ZVI; dw/dw, 2 different trial plots) in the 0–40-cm soil layer lowered the initial chlordecone (CLD) concentration by up to 74% or 69% in 37 days or 94 days, with 75% of the decrease achieved after only 21 or 24 days of treatment depending on the trial plot. The addition of commercially available Daramend® was also tested by applying the 6% dose (dw/dw) recommended by the manufacturer and using either the regular alfalfa-based product or a bagasse-based product specifically formulated for the study. Both significantly lowered CLD concentrations, but to a lesser extent than with the ZVI-only amendment. A bagasse-ZVI mixture prepared on site produced results slightly better than the two Daramend®. The percentage decreases in CLD concentrations were correlated with the negative redox potentials achieved. In all the trial plots, dechlorinated transformation products appeared in the soil and soil water as the CLD concentrations decreased, with H atoms replacing up to 4 and 7 of the 10 Cl atoms, respectively. None of these degradation products appeared to accumulate in the soil or soil water during the treatment. Instead, the reverse occurred, with an overall downward trend in their concentrations over time. The effects of ISCR treatment on agronomic and human health–related parameters were measured in three different crops. The radishes produced with some treatments were visually of lower quality or smaller in size than those grown in the control plots. Lower yields were observed for the cucumbers and sweet potatoes grown after applying the bagasse-based amendments. Mortality among cucumber seedlings was observed after treatment with ZVI only. Simple operational solutions should suffice to remedy these negative agronomic effects. As regards human health–related effects, the CLD concentrations in radishes grown with three of the amendments were significantly lower than in the two control plots and well below the maximum residue level (MRL), which was substantially exceeded in the radishes grown on untreated soil. For cucumbers, the treatments with regular Daramend® and with a local bagasse-ZVI mixture produced fruits with CLD below the MRL and also below the concentrations in one of the two control plots. As for the sweet potatoes, adding a bagasse-ZVI mixture had a significant positive effect by decreasing contamination below the levels in the two control plots and below the MRL.

In Guadeloupe, the use between 1972 and 1993 of chlordecone, an organochlorine insecticide, has permanently contaminated the island's soil, thus contaminating the food chain at its very beginning. There is today a strong societal requirement for an improved mapping of the contaminated zones. Given the extent of the areas to be covered, carrying out soil tests on each plot of the territory would be a long and expensive process. In this article, we explore a method of demarcating polluted areas. The approach adopted consists in carrying out, using surface water analyses, a hydrological delimitation that makes it possible to distinguish contaminated watersheds from uncontaminated ones. The selection of sampling points was based on the spatial analysis of the actual and potential contamination data existing at the beginning of the study. The approach was validated by soil analyses, after having compared the contamination data of the watersheds with the soil contamination data of the plots within them. The study thus made it possible to highlight new contaminated areas and also those at risk of contamination and to identify the plots to be targeted as a priority during future analysis campaigns by State services.

Ce travail fait un état des lieux de la qualité temporelle et de la densité spatiale des séries pluviométriques du Cameroun, Gabon, Congo, RCA et RDC, en particulier sur la période récente (1973-2014) grâce à la base de données internationale GSOD. Face aux énormes lacunes observées, ces résultats vont permettre d'orienter les choix métrologiques et analytiques in situ du programme FORGREENE (Tropical forests greeness and cloudiness in Central Africa: present conditions and future evolution). Une comparaison avec des estimations satellitaires (de type RFE) indique aussi leur potentiel intéressant, à condition qu'elles s'appuient sur des validations in situ. (Résumé d'auteur)

Due to diffuse atmospheric fallouts of process particles enriched by metals and metalloids, polluted soils concern large areas at the global scale. Useful tools to assess ecotoxicity induced by these polluted soils are therefore needed. Earthworms are currently used as biotest, however the influence of specie and earthworm behaviour, soil characteristics are poorly highlighted. Our aim was therefore to assess the toxicity of various polluted soils with process particles enriches by metals and metalloids (Pb, Cd, Cu, Zn, As and Sb) collected from a lead recycling facility on two earthworm species belonging to different ecological types and thus likely to have contrasted behavioural responses (Eiseina hortensis and Lumbricus terrestris). The combination of behavioural factors measurements (cast production and biomass) and physicochemical parameters such as metal absorption, bioaccumulation by earthworms and their localization in invertebrate tissues provided a valuable indication of pollutant bioavailability and ecotoxicity. Soil characteristics influenced ecotoxicity and metal uptake by earthworms, as well as their soil bioturbation.

Predicting the transfer of contaminants in soils is often hampered by lacking validation of mathematical models. Here, we applied Hydrus-2D software to three agricultural soils for simulating the 1900–2005 changes of zinc and lead concentration profiles derived from industrial atmospheric deposition, to validate the tested models with plausible assumptions on past metal inputs to reach the 2005 situation. The models were set with data from previous studies on the geochemical background, estimated temporal metal deposition, and the 2005 metal distributions. Different hypotheses of chemical reactions of metals with the soil solution were examined: 100% equilibrium or partial equilibrium, parameterized following kinetic chemical extractions. Finally, a two-site model with kinetic constant values adjusted at 1% of EDTA extraction parameters satisfactory predicted changes in metal concentration profiles for two arable soils. For a grassland soil however, this model showed limited applicability by ignoring the role of earthworm activity in metal incorporation.

The introduction of glyphosate-tolerant (GT) crops is expected to mitigate the environmental contamination by herbicides because glyphosate is less persistent and toxic than the herbicides used on non-GT crops. Here, we compared the environmental balances of herbicide applications for both crop types in three French field trials. The dynamic of herbicides and their metabolites in soil, groundwater and air was simulated with PRZM model and compared to field measurements. The associated impacts were aggregated with toxicity potentials calculated with the fate and exposure model USES for several environmental endpoints. The impacts of GT systems were lower than those of non-GT systems, but the accumulation in soils of one glyphosate metabolite (aminomethylphosphonic acid) questions the sustainability of GT systems. The magnitude of the impacts depends on the rates and frequency of glyphosate application being highest for GT maize monoculture and lowest for combination of GT oilseed rape and non-GT sugarbeet crops. The impacts of herbicide applications on glyphosate-tolerant crops could be higher than expected due to the accumulation of a metabolite of glyphosate in soils.