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Avec les remerciements pour Nathalie Cheviron, Virginie Grondin et Christelle Marrauld; Microcystin-leucine-arginine (MC-LR) is a cyclic heptapeptide hepatotoxin produced by cyanobacteria such as Microcystis aeruginosa. Being highly toxic, this compound is a threat to water quality, agriculture, and human and animal health. In particular, MC-LR has been frequently detected at high concentrations in surface waters. So far, the fate of MC-LR in soils is unknown. Here, we studied degradation and soil–plant transfer of 14C-radiolabelled MC-LR in an artificial system of agricultural soil and tomato seedlings. 14C-MC-LR was dissolved in water and applied by soil irrigation, one or two times with an interval of 28 days. Results show that the 14CO2 from the degradation of 14C-MC-LR amounted to 11 % of total 14C initial input; 74–80 % of 14C-MC-LR occurred in extractible fractions analysed by HPLC. Less than 14 % of 14C-MC-LR was adsorbed on soil particles. Overall, our findings evidence for the first time a high risk of toxin leaching from the soil toward groundwater.

The insecticide chlordecone is a contaminant found in most of the banana plantations in the French West Indies. This study aims to search for fungal populations able to grow on it. An Andosol heavily contaminated with chlordecone, perfused for 1 year in a soil-charcoal system, was used to conduct enrichment cultures. A total of 103 fungal strains able to grow on chlordecone-mineral salt medium were isolated, purified, and deposited in the MIAE collection (Microorganismes d'Intérêt Agro-Environnemental, UMR Agroécologie, Institut National de la Recherche Agronomique, Dijon, France). Internal transcribed spacer sequencing revealed that all isolated strains belonged to the Ascomycota phylum and gathered in 11 genera: Metacordyceps, Cordyceps, Pochonia, Acremonium, Fusarium, Paecilomyces, Ophiocordyceps, Purpureocillium, Bionectria, Penicillium, and Aspergillus. Among predominant species, only one isolate, Fusarium oxysporum MIAE01197, was able to grow in a liquid culture medium that contained chlordecone as sole carbon source. Chlordecone increased F. oxysporum MIAE01197 growth rate, attesting for its tolerance to this organochlorine. Moreover, F. oxysporum MIAE01197 exhibited a higher EC50 value than the reference strain F. oxysporum MIAE00047. This further suggests its adaptation to chlordecone tolerance up to 29.2 mg l(-1). Gas chromatography-mass spectrometry (GC-MS) analysis revealed that 40 % of chlordecone was dissipated in F. oxysporum MIAE01197 suspension culture. No chlordecone metabolite was detected by GC-MS. However, weak amount of (14)CO2 evolved from (14)C10-chlordecone and (14)C10-metabolites were observed. Sorption of (14)C10-chlordecone onto fungal biomass followed a linear relationship (r (2) = 0.99) suggesting that it may also account for chlordecone dissipation in F. oxysporum MIAE01197 culture.

Kinetic EDTA and citrate extractions were used to mimic metal mobilization in a soil contaminated by metallurgical fallout. Modeling of metal removal rates vs. time distinguished two metal pools: readily labile (QM1) and less labile (QM2). In citrate extractions, total extractability (QM1 + QM2) of Zn and Cd was proportionally higher than for Pb and Cu. Proportions of Pb and Cu extracted with EDTA were three times higher than when using citrate. We observed similar QM1/QM2 ratios for Zn and Cu regardless of the extractant, suggesting comparable binding energies to soil constituents. However, for Pb and Cd, more heterogeneous binding energies were hypothesized to explain different kinetic extraction behaviors. Proportions of citrate-labile metals were found consistent with their short-term, in-situ mobility assessed in the studied soil, i.e., metal amount released in the soil solution or extracted by cultivated plants. Kinetic EDTA extractions were hypothesized to be more predictive for long-term metal migration with depth.

International audience; Constructed wetlands are designed to mitigate nutrient and pesticide fluxes from agricultural catchments. Nevertheless, information on their efficiency in removing non-degradable contaminants such as metals is still scarce. This study aimed to explore the metallic signature and fate of metals within the Rampillon wetland (France) receiving water from a drained 355-ha catchment under intensive agriculture. Original monitoring coupling classic, time-integrated and bioaccumulation-based tools was achieved to characterise spatiotemporal dynamics of various metals (As, Cd, Cr, Co, Cu, Mn, Ni, Pb, Sb, Se and Zn). To assess metal inflows and mitigation, samples of dissolved and particulate metals were collected bimonthly at the inlet and outlet of the wetland over 3 months. Simultaneously, time-integrated (sediment traps and passive samplers) and bioaccumulation-based (caged gammarids and biofilms) tools were deployed to monitor temporal changes in metal speciation and bioavailability. To gain insight into the spatial distribution of metals between abiotic and biotic matrices, sediments and indigenous invertebrates with contrasted ecologies were sampled in different cells of the wetland. The results showed time-integrated tools were more suitable than bimonthly samples to quantify metal mitigations because of temporal fluctuations and low contamination levels. Significant mitigations were thus observed in trapped sediments for all metals (ranged 11–23%, except Mn) as well as in the DGT-labile fraction for Cd, Cr, Co, Mn and Ni (ranged 13–51%). Bioaccumulation levels in biofilms also revealed a decrease in metal bioavailability at the outlet. Furthermore, the spatial survey supported the central role of sediments in metal trapping and the beneficial effect of this wetland for local biodiversity in terms of exposure. To conclude, this study provides valuable information on the ecodynamics and bioavailability of metals required for sustainable management of such artificial ecosystems and furthermore, of agricultural areas.

Non-human biota in radiological risk assessment is typically evaluated using Reference Organisms (ROs) or Reference Animals and Plants (RAPs), for all exposure situations. However, it still remains open whether the use of an increased number of species would improve the ability to demonstrate protectiveness of the environment. In this paper, the representativeness of a broader list of fauna is tested in terms of the geometrical characteristics and habits for radiological risk assessments in the case of routine discharges from a nuclear installation: the Cadarache centre. A list of terrestrial animal species, compiled from ecological inventories carried out around it was evaluated. A first survey around the centre inventoried >400 terrestrial fauna species, which were then filtered to reduce the number to 28 species for which dose assessments were carried out. Despite the differences between geometries for those site-specific species and the ROs (including RAPs), the absorbed dose rates calculated for both were very close (within a factor of two). Regardless of the studied organism, the absorbed dose rates calculated for the discharge scenario were mainly related to internal exposure, particularly for tritium (3H) and carbon 14 (14C), showing that there would be an acceptable dose rates difference between species from the same organism group. Additionally, sensitivity analyses were conducted to determine if the use of generic, predefined ROs was enough to assure an adequate protection of endangered species. It was observed that for every radionuclide the difference between assessments for site-specific species and ROs are unlikely to exceed a factor of 3. Hence, the result of this evaluation indicates that the use of generic ROs for non-human biota radiological risk assessment covers sufficiently other species, including endangered ones.

Avec les remerciements à Christelle Marrauld; Nowadays, the influence of biomass plantations in polluted soils as a remediation strategy has mainly been considered in the view of phytoextraction, but little of soil biodiversity. Our objective was to assess the impact of Miscanthus × giganteus plantations on soil macroinvertebrates in trace metal contaminated soils. We hypothesized (1) that miscanthus plantations host more numerous and diverse communities than comparable annual crop soils and (2) that functional traits permit to decrypt the biological strategies underlying invertebrate community response. We selected fields on sandy and loamy-clay soils contaminated either by urban wastewater or atmospheric deposition, respectively. Our results showed that in comparison to annual cropping systems, miscanthus plantation enhanced higher densities and diversity of soil invertebrates but not of ground-dwelling invertebrates. Miscanthus cropping led to an increase in the proportion of resident, detritivores and rhizophages species, and a trend was revealed for larger invertebrates. Thus, the use of a trait-based approach provided fine opportunities to elucidate invertebrate responses to land use changes in contaminated areas.

International audience; Two experimental plots amended with a co-compost of sewage sludge and green wastes (SGW) or with a municipal solid waste compost (MSW) were compared with a control plot without organic amendment (CONT) in terms of trace metals mobility. These plots were equipped with wick lysimeters, time-domain reflectometry probes and tensiometers for 6 yr (2004–2010). Different soil structures due to tillage and compost incorporation were identified in the tilled layers and reproduced in HYDRUS-2D for simulating water, Cu, and Cd transport. Two sorption estimation approaches were used, either assuming equilibrium between CaCl2 and ethylenediaminetetraacetic acid (EDTA) extractable metals (Kd-1) or using equations based on pedotransfer functions assuming nonlinear sorption for Cu (Kf) and linear sorption for Cd (Kd-2). Lysimeter data on Cu leaching were successfully reproduced with the Kd-1 approach for the SGW and CONT plots (model efficiency coefficient ESGW = 0.97, ECONT = 0.95), while the MSW plot showed better fitting with the Kf approach (EMSW = 0.77), which could be explained by the less stable organic matter of the MSW compost because it takes into account organic matter components (dissolved organic C and soil organic matter). The Cd leaching was reproduced with the Kd-2 approach for the two amended plots (ESGW = 0.12, EMSW = 0.80), while CONT simulation overestimated leaching. The percentage of measured Cu and Cd leached in reference to input mass was 0.6 and 2.7%, respectively, in the SGW plot compared with 5% for both metals in the MSW plot. Trace metal mobility appeared to be limited in the tilled layer by sorption to organic matter.

International audience; The global AsIII-oxidizing activity of microorganisms in eight surface soils from polluted sites was quantified with and without addition of organic substrates. The organic substances provided differed by their nature: either yeast extract, commonly used in microbiological culture media, or a synthetic mixture of defined organic matters (SMOM) presenting some common features with natural soil organic matter. Correlations were sought between soil characteristics and both the AsIII-oxidizing rate constants and their evolution in accordance with inputs of organic substrates. In the absence of added substrate, the global AsIII oxidation rate constant correlated positively with the concentration of intrinsic organic matter in the soil, suggesting that AsIII-oxidizing activity was limited by organic substrate availability in nutrient-poor soils. This limitation was, however, removed by 0.08 g/L of added organic carbon. In most conditions, the AsIII oxidation rate constant decreased as organic carbon input increased from 0.08 to 0.4 g/L. Incubations of polluted soils in aerobic conditions, amended or not with SMOM, resulted in short-term As mobilization in the presence of SMOM and active microorganisms. In contrast, microbial AsIII oxidation seemed to stabilize As when no organic substrate was added. Results suggest that microbial speciation of arsenic driven by nature and concentration of organic matter exerts a major influence on the fate of this toxic element in surface soils.

This work assesses relationships between characteristic aggregate microstructures related to biological activity in soils under different long-term land use and the distribution and extractability of metal pollutants. We selected two neighbouring soils contaminated with comparable metal loads by past atmospheric deposition. Currently, these soils contain similar stocks, but different distributions of zinc (Zn) and lead (Pb) concentrations with depth. One century of continuous land use as permanent pasture (PP) and conventional arable (CA) land, has led to the development of two soils with different macro- and micro-morphological characteristics. We studied distributions of organic matter, characteristic micro-structures and earthworm-worked soil by optical microscopy in thin sections from A, B and C horizons. Concentrations and amounts of total and EDTA-extractable Zn and Pb were determined on bulk samples from soil horizons and on size-fractions obtained by physical fractionation in water. Large amounts of Zn and Pb were found in 2–20-µm fractions, ascribed to stable organo-mineral micro-aggregates influenced by root and microbial activity, present in both soils. Unimodal distribution patterns of Zn, Pb and organic C in size-fractions were found in horizons of the CA soil. In contrast, bimodal patterns were observed in the PP soil, because large amounts of Zn and Pb were also demonstrated in stable larger micro-aggregates (50–100-µm fractions). Such differing distribution patterns characterized all those horizons markedly influenced by earthworm activity. Larger earthworm activity coincided with larger metal EDTA-extractability, particularly of Pb. Hence, land use-related biological activity leads to specific soil microstructures affecting metal distribution and extractability, both in surface and subsurface horizons.

Avec les remerciements pour Jodie Thénard; Generic biomarkers are needed to assess environmental risks in metal polluted soils. We assessed the strength of the relationship between earthworm energy reserves and metal availability under conditions of cocktail of metals at low doses and large range of soil parameters. Aporrectodea caliginosa was exposed in laboratory to a panel of soils differing in Cd, Pb and Zn total and available (CaCl2 and EDTA-extractable) concentrations, and in soil texture, pH, CEC and organic-C. Glycogen, protein and lipid contents were recorded in exposed worms. Glycogen contents were not linked to the explaining variables considered. Variable selection identified CaCl2 extractable metals concentrations and soil texture as the main factors affecting protein and lipid contents. The results showed opposite effects of Pb and Zn, high inter-individual variability of biomarkers and weak relationships with easily extractable metals. Our results support the lack of genericity of energy reserves in earthworms exposed to field-contaminated soils.

The ability of three models (PEARL, MACRO and PRZM) to describe the water transfer and leaching of the herbicides S-metolachlor and mesotrione as observed in an irrigated maize monoculture system in Toulouse area (France) was compared. The models were parameterized with field, laboratory and literature data, and pedotransfer functions using equivalent parameterization to better compare the results and the performance of the models. The models were evaluated and compared from soil water pressure, water content and temperature data monitored at 0.2, 0.5 and 1 m depth, together with water percolates and herbicide concentrations measured in a tension plate lysimeter at 1 m depth. Some hydraulic (n, θ(s)) parameters and mesotrione DT50 needed calibration. After calibration, the comparison of the results obtained by the three models indicated that PRZM was not able to simulate properly the water dynamic in the soil profile. On the contrary, PEARL and MACRO simulated generally quite well the observed water pressure head and volumetric water content at the three different depths during wetting periods (e.g. irrigated cropping period) while a poorest performance was obtained for drying periods (fallow period with bare soil and beginning of crop period). Similar water flow dynamics were simulated by PEARL and MACRO in the soil profile although in general, and due to a higher evapotranspiration in MACRO, PEARL simulated a wetter soil than MACRO. For the whole simulated period, the performance of all models to simulate water leaching at 1m depth was poor, with an overestimation of the total water volume measured in the lysimeter (ranging from 2.2 to 6.6 times). By contrast, soil temperature was properly reproduced by the three models. The models were able to simulate the leaching of herbicides at 1m depth in similar appearance time and order of magnitude as field observations. Cumulative observed and simulated mesotrione losses by leaching were consistently higher than the observed and simulated losses of the less mobile herbicide, S-metolachlor. In general, PRZM predicted the highest concentrations for both herbicides in the leachates while PEARL simulated the observed herbicide concentrations better than MACRO and PRZM.

The use of pesticides in agriculture has highly increased during the last 40 years to increase crop yields. However, today most pesticides are polluting water, soil, atmosphere and food. Pesticides are also impact soil enzymes, which are essential catalysts ruling the quality of soil life. In particular, the activity of soil enzymes control nutrient cycles, and, in turn, fertilization. Here, we review the effects of pesticides on the activity of soil enzymes in terrestrial ecosystems. Enzymes include dehydrogenase, fluorescein diacetate hydrolase, acid phosphatase, alkaline phosphatase, phosphatase, beta-glucosidase, cellulase, urease and aryl-sulfatase. Those enzymes are involved in the cycles of carbon, nitrogen, sulfur and phosphorus. The main points of our analysis are (1) the common inhibition of dehydrogenase in 61 % of studies, stimulation of cellulase in 56 % of studies and no response of aryl-sulfatase in 67 % of studies. (2) Fungicides have mainly negative effects on enzymatic activities. (3) Insecticides can be classified into two groups, the first group represented by endosulfan having an overall positive impact while the second group having a negative effect. (4) Herbicides can be classified into two groups, one group with few positive effect and another group with negative effect.

The occurrence of harmful cyanobacterial blooms in surface waters is often accompanied by the production of a variety of cyanotoxins. These toxins are designed to target in humans and animals specific organs on which they act: hepatotoxins (liver), neurotoxins (nervous system), cytotoxic alkaloids, and dermatotoxins (skin), but they often have important side effects too. When introduced into the soil ecosystem by spray irrigation of crops they may affect the same molecular pathways in plants having identical or similar target organs, tissues, cells or biomolecules. There are also several indications that terrestrial plants, including food crop plants, can bioaccumulate cyanotoxins and present, therefore, potential health hazards for human and animals. The number of publications concerned with phytotoxic effects of cyanotoxins on agricultural plants has increased recently. In this review, we first examine different cyanotoxins and their modes of actions in humans and mammals and occurrence of target biomolecules in vegetable organisms. Then we present environmental concentrations of cyanotoxins in freshwaters and their fate in aquatic and soil ecosystems. Finally, we highlight bioaccumulation of cyanotoxins in plants used for feed and food and its consequences on animals and human health. Overall, our review shows that the information on the effects of cyanotoxins on non-target organisms in the terrestrial environment is particularly scarce, and that there are still serious gaps in the knowledge about the fate in the soil ecosystems and phytotoxicity of these toxins.

Avec les rermerciements pour Christelle Marrauld; Mediterranean climate characteristics and carbonate are key factors governing soil heavy-metal accumulation, and low organic matter (OM) content could limit the ability of microbial populations to cope with resulting stress. We studied the effects of metal contamination on a combination of biological parameters in soils having these characteristics. With this aim, soils were spiked with a mixture of cadmium, copper, lead, and zinc, at the two limit values proposed by current European legislation, and incubated for ≤12 months. Then we measured biochemical (phosphatase, urease, β-galactosidase, arylsulfatase, and dehydrogenase activities) and microbial (fungal and bacterial DNA concentration by quantitative polymerase chain reaction) parameters. All of the enzyme activities were strongly affected by metal contamination and showed the following inhibition sequence: phosphatase (30–64 %) < arylsulfatase (38–97 %) ≤ urease (1–100 %) ≤ β-galactosidase (30–100 %) < dehydrogenase (69–100 %). The high variability among soils was attributed to the different proportion of fine mineral fraction, OM, crystalline iron oxides, and divalent cations in soil solution. The decrease of fungal DNA concentration in metal-spiked soils was negligible, whereas the decrease of bacterial DNA was ~1–54 % at the lowest level and 2–69 % at the highest level of contamination. The lowest bacterial DNA decrease occurred in soils with the highest OM, clay, and carbonate contents. Finally, regarding the strong inhibition of the biological parameters measured and the alteration of the fungal/bacterial DNA ratio, we provide strong evidence that disturbance on the system, even within the limiting values of contamination proposed by the current European Directive, could alter key soil processes. These limiting values should be established according to soil characteristics and/or revised when contamination is produced by a mixture of heavy metals.

The use of sludge as soil amendment is widely encouraged by its high contents in organic matter and plant nutrients. Nevertheless, agrochemicals potentially present in sludge could be harmful to terrestrial ecosystems. The present work aimed to apply standard statistical methods for suitable assessment of the ecotoxicological impacts of sludge amendments on soil, involving the following factors: the type of treated sludge, their application dose, and their contents in agrochemicals. Terrestrial Model Ecosystems were used to assess the effects of sludge amendments on endpoints from different trophic levels of the soil ecosystem, including an in vitro estrogenic bioassay on soil leachates. Here, we show the significant negative effects of the highest dose of sludge in most of the soil bioassays. Thermally dried sludge increased significantly the microbial activity leading to lower contamination of leachates with endocrine disrupting molecules. Agrochemicals contents of sludge have only significant impacts on increasing the delay of germination of plant seeds. Soil bioassays are thus complementary to sludge chemical analysis when the impacts of its application on soil should be assessed: significant negative impacts were related to the intrinsic composition of sludge rather than its agrochemicals contents. We conclude that standard statistical methods are relevant tools for the analysis of complex data generated from this type of experiment.

The 42 plots of the Versailles long-term bare fallow experiment offer exceptional opportunities to study the impacts of fertilizers and amendments on soil physical properties. In this experiment, continuous annual applications since 1928 of 16 different treatments – including nitrates, phosphates, manure, ammonium, calcium, and potassium salts – have led to strongly diverging physical and chemical properties in the soil's surface layer. In this work, the proportion of water dispersible clay (WDC), which is considered a good indicator of soil structural stability and sensitivity to crusting and erosion, was determined in all plots of the experiment. The results showed the influence of the valence of cations and pH on soil structure and clay dispersability. Application of sodium or potassium salts deteriorated the degree of soil aggregation, with increased bulk density and WDC values, whereas amendment with manure or calcium salts ameliorated soil aggregation, with decreasing bulk density and WDC. The strong acidification of the soils receiving ammonium-based fertilizers was another factor related to the increase of water dispersible clay, and therefore the deterioration of soil structure. This study emphasizes the role of potassium and ammonium, associated with fertilizer additions, on the deterioration of soil structure and on the increase of the risk of erosion.

This work is concerned with the effect of five earthworm species on short-term soil dynamics through carbon (C) mineralisation and large soil aggregate characteristics (production, stability, organic matter content and composition) in laboratory experiments. We hypothesised that the influence of earthworms on soil behaviour depends on individual species and land use history. Substrates were a sequence of three similar luvisols that had been subjected to different land use histories and represented increasing C contents from 10 mg kg −1 (cropped soil), to 20 mg kg −1 (5-year-old pasture soil) and 33 mg kg −1 (permanent pasture soil). We found that relative C mineralisation was slower in pasture than in cropped soils, which can be explained by differences in the physical protection of soil organic matter (SOM). Land use history influenced (i) the amount of large macro-aggregate production through earthworm behaviour (casting activity), and (ii) the size distribution of water stable soil fractions within the large macro-aggregate produced. No effect of earthworm species on SOM composition was observed with near infrared spectrometry indicating that the chemistry of large macro-aggregates was mainly driven by land use type. Earthworm species had more pronounced effects on physical (large aggregate production and stability) than on biological (C mineralisation promotion) or biochemical (SOM composition) features. This paper shows that, although earthworm effects on soil processes are now obvious, a number of factors may interact in such complex systems so that we should hesitate to make generalisations.

International audience; Enzymes are known to be sensitive indicators of soil quality. Nevertheless, the natural variability of their activities needs to be considered for a relevant interpretation of activity levels, especially in contaminated soils. We first monitored the variability of enzymatic activities (acid and alkaline phosphatases, β-glucosidase, N-acetyl-β-glucosaminidase, urease and dehydrogenase) in two agricultural sites in north-western France during a seasonal April–October cycle. For both sites, two types of long-term different agricultural managements, grassland and intensive cropping were considered. Our results revealed great variability of enzymatic activities in space and over time, yet more pronounced for grassland than for cropped soils. Then, we assessed the impact of copper on enzymes activity on Terrestrial Model Ecosystems (TMEs) filled with undisturbed soil, and incubated for 70 days in open-field conditions. Copper was added at two concentration levels corresponding to a regulated annual agronomic input (2 mg kg−1) or to a high soil contamination (200 mg kg−1). In comparison to effects of natural spatiotemporal variability of soil conditions, copper addition did not show significant impacts on enzymatic activities. Finally, our results confirmed that for assessing effective impacts of contaminants in soils under real field conditions, natural spatiotemporal soil variability must be considered.

Despite constraining legislation and increasing efficiency of pesticides (with a decrease in the applied amounts), their use still cause a contamination of environment (air, soil and water). To conciliate agricultural and environmental interests, a better understanding of the fate of pesticides is needed, in particular because it will determine the exposure and consequently the impact of pesticides on the target and non-target organisms. This goal requires new efforts of research at different scales (from molecular to field scale). Following application, most of the pesticides reach the soil either after direct application or after foliage wash-off. As a major interface between other environmental compartments, the soil plays a preponderant buffering role in the fate of pesticides. Apart volatilization, the main processes that control the fate of pesticides in soils are retention on soil particles and degradation (biotic and abiotic). These coupled bio-physico-chemical processes can lead to a transitory or permanent accumulation of pesticides in soils or, on the contrary, to their elimination from the environment. They determine the pesticide concentration in the soil solution, and have a large influence on pesticide transfer toward ground or surface waters and on their ecotoxicological impacts on soil organisms as well. The main difficulties in studying and predicting the retention and degradation of pesticides in soils are the diversity of chemical structures and reactivities of pesticides, the high diversity of soils and their heterogeneous composition and structure. In addition, the pedoclimatic conditions, in particular soil temperature and water content, have a strong influence on retention and degradation because of their effect on soil biological, chemical and physical properties. Therefore, the objective of this chapter is to provide an overview of the factors involved in the retention and degradation of pesticides in soils and to discuss and clarify the needs of new integrated approach. In particular, this work will examine (i) the pertinent scales (among elementary constituents, aggregates and mesoscopic scales) for both retention and degradation studies, (ii) the integrative properties that should be considered, such as hydrophobicity of the organo-clay granulometric fraction or soil structure, and (iii) the primordial role of water.

The contribution of particle-size fractions to carbon (C) and nitrogen (N) mineralization of sludge compost was investigated. Particle-size fractionation was performed using "dry" (sieving of total dry compost) and "wet" (dispersion of compost in water, followed by sieving) fractionation methods, then C and N mineralization of the separated fractions were measured during incubation in soil. The "dry" fractionation did not allow the actual particle-size distribution of compost to be estimated accurately. Out of all the "wet" fractions, the [0-50 microm] fraction was the most significant fraction in compost mass and contributed the most to the N mineralization of sludge compost in soil. Its low degradability, positive N mineralization and similarities with sludge OM suggest that the most humified sludge organic matter was located in this fraction, which would probably contribute to C storage and N availability after compost application in soil. Other fractions (200 microm) were more readily biodegradable and induced N immobilization.

Following application, pesticides can be intercepted and absorbed by weeds and/or crops. Plants containing pesticides residues may then reach the soil during the crop cycle or after harvest. However, the fate in soil of pesticides residues in plants is unknown. Two commonly used foliar herbicides, glyphosate and sulcotrione, 14 C-labeled, were applied on leaves of oilseed rape and/or maize, translocation was studied, and then soil incubations of aerial parts of plants containing herbicides residues were performed. Soil treated directly with herbicides was used as control. The effects of adjuvants on herbicide plant-absorption and subsequent soil-degradation were also investigated comparing herbicides application as active ingredients and as commercial formulations. The fate in soil of herbicides residues in plants was different from that of control, and different for glyphosate and sulcotrione. Mineralization in soil of glyphosate in crops decreased compared to control, and amounts of 14 C-extractable residues, mainly composed by the metabolite aminomethylphosphonic acid (AMPA), and non-extractable residues (NER) increased. In contrast, mineralization in soil of sulcotrione in maize increased compared to control, with a decrease in the 14 C-extractable residues and an increase in NER. The fate of both herbicides was influenced by the type of plant organ in which herbicide was incorporated, because of differences in herbicides bioavailability and organs biodegradability, but not by adjuvants. Absorption of both herbicides in plant delays their subsequent soil-degradation, and particularly, glyphosate persistence in soil could increase from two to six times. The modifications of herbicide degradation in soil due to interception by plants should be considered for environmental risks assessment.