International audience | 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.

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.

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

International audience | Intercropping or assistant endophytes promote phytoremediation capacities of hyperaccumulators and enhance their tolerance to heavy metal (HM) stress. Findings from a previous study showed that intercropping the hyperaccumulator Sonchus asper (L.) Hill grown in HM-contaminated soils with maize improved the remediating properties and indicated an excluder-to-hyperaccumulator switched mode of action towards lead. In the current study, RNA-Seq analysis was conducted on Sonchus roots grown under intercropping or monoculture systems to explore the molecular events underlying this shift in lead sequestering strategy. The findings showed that intercropping only slightly affects S. asper transcriptome but significantly affects expression of root-associated microbial genomes. Further, intercropping triggers significant reshaping of endophytic communities associated with a ‘root-to-shoot’ transition of lead sequestration and improved phytoremediation capacities of S. asper . These findings indicate that accumulator activities of a weed are partially attributed to the root-associated microbiota, and a complex network of plant–microbe-plant interactions shapes the phytoremediation potential of S. asper . Analysis showed that intercropping may significantly change the structure of root-associated communities resulting in novel remediation properties, thus providing a basis for improving phytoremediation practices to restore contaminated soils.

Intercropping or assistant endophytes promote phytoremediation capacities of hyperaccumulators and enhance their tolerance to heavy metal (HM) stress. Findings from a previous study showed that intercropping the hyperaccumulator Sonchus asper (L.) Hill grown in HM-contaminated soils with maize improved the remediating properties and indicated an excluder-to-hyperaccumulator switched mode of action towards lead. In the current study, RNA-Seq analysis was conducted on Sonchus roots grown under intercropping or monoculture systems to explore the molecular events underlying this shift in lead sequestering strategy. The findings showed that intercropping only slightly affects S. asper transcriptome but significantly affects expression of root-associated microbial genomes. Further, intercropping triggers significant reshaping of endophytic communities associated with a ‘root-to-shoot’ transition of lead sequestration and improved phytoremediation capacities of S. asper. These findings indicate that accumulator activities of a weed are partially attributed to the root-associated microbiota, and a complex network of plant–microbe-plant interactions shapes the phytoremediation potential of S. asper. Analysis showed that intercropping may significantly change the structure of root-associated communities resulting in novel remediation properties, thus providing a basis for improving phytoremediation practices to restore contaminated soils.

International audience | Soil trace metal concentrations (e.g., cadmium, copper, lead, zinc) in vegetable gardens have often been observed as exceeding the geochemical background levels. These metals are a threat both to soil and plant functioning and to human health through consumption of contaminated vegetables. We used a mass balance-based model to predict the four metal (Cd, Cu, Pb, Zn) concentrations in soils after a century’s cultivation for 104 urban vegetable gardens, located in three French metropolises, Nancy, Nantes, and Marseille, based on a survey of gardening practices. If current gardening practices are maintained, an increase in soil Cd (35% on average), Cu (183%), and Zn (27%) contents should occur after a century. Soil Pb concentration should not vary consistently. Organic amendments are the major source of Cd, Pb, and Zn, followed by chemical fertilizer while fungicide application is the major source of Cu. Cessation of chemical fertilizer use would only slightly reduce the accumulation of the four metals. The solubility of the four metals would decrease significantly after a century, when pH increases by one unit. A liming practice of acidic soils should therefore be a feasible way to prevent any increase in the metal mobility and bioavailability.

Soil trace metal concentrations (e.g., cadmium, copper, lead, zinc) in vegetable gardens have often been observed as exceeding the geochemical background levels. These metals are a threat both to soil and plant functioning and to human health through consumption of contaminated vegetables. We used a mass balance-based model to predict the four metal (Cd, Cu, Pb, Zn) concentrations in soils after a century’s cultivation for 104 urban vegetable gardens, located in three French metropolises, Nancy, Nantes, and Marseille, based on a survey of gardening practices. If current gardening practices are maintained, an increase in soil Cd (35% on average), Cu (183%), and Zn (27%) contents should occur after a century. Soil Pb concentration should not vary consistently. Organic amendments are the major source of Cd, Pb, and Zn, followed by chemical fertilizer while fungicide application is the major source of Cu. Cessation of chemical fertilizer use would only slightly reduce the accumulation of the four metals. The solubility of the four metals would decrease significantly after a century, when pH increases by one unit. A liming practice of acidic soils should therefore be a feasible way to prevent any increase in the metal mobility and bioavailability.

International audience | Sustainable solutions aiming at limiting Reynoutria japonica invasion consist of frequent removal of its aerial biomass. The aims of this study were to measure the accumulation of metallic trace elements (MTE) in R. japonica, and to assess the ecotoxicological risk related to the valorization of the produced biomass. R. japonica fragmented rhizomes were regenerated in pots for 41 days on a control soil (CTL) or a moderately MTE-contaminated soil (POL, 3.6 mg Cd kg −1 DM). Growth traits were recorded, as well as MTE bioconcentration (BCF) and translocation factors (TF) from soil to plant organs. Whatever the MTE and plant organs, BCF remained below one (mean Cd-BCF for stem and leaf: 0.07 and 0.29 for CTL and POL, respectively), conversely to TF (until 2.2 for Cd and Ni in POL soil). When grown on the POL soil, R. japonica stem and leaf Cd content was close to the EU maximum regulatory limit for organic amendments or animal feed. Model simulations suggested that liver and kidney Cd concentrations would exceed the regulatory limit in food when adult cattle or sheep constantly ingest R. japonica grown on the POL soil over 200 to 800 days. The results of the present study will be useful to help managers in selecting efficient and safe solutions for the control of R. japonica invasion.

Sustainable solutions aiming at limiting Reynoutria japonica invasion consist of frequent removal of its aerial biomass. The aims of this study were to measure the accumulation of metallic trace elements (MTE) in R. japonica, and to assess the eco-toxicological risk related to the valorization of the produced biomass. R. japonica fragmented rhizomes were regenerated in pots for 41 days on a control soil (CTL) or a moderately MTE-contaminated soil (POL, 3.6 mg Cd kg⁻¹ DM). Growth traits were recorded, as well as MTE bioconcentration (BCF) and translocation factors (TF) from soil to plant organs. Whatever the MTE and plant organs, BCF remained below one (mean Cd-BCF for stem and leaf: 0.07 and 0.29 for CTL and POL, respectively), conversely to TF (until 2.2 for Cd and Ni in POL soil). When grown on the POL soil, R. japonica stem and leaf Cd content was close to the EU maximum regulatory limit for organic amendments or animal feed. Model simulations suggested that liver and kidney Cd concentrations would exceed the regulatory limit in food when adult cattle or sheep constantly ingest R. japonica grown on the POL soil over 200 to 800 days. The results of the present study will be useful to help managers in selecting efficient and safe solutions for the control of R. japonica invasion.

International audience | Once previous industrial activity has ceased, brownfields are found in urban and suburban environments and managed in different ways ranging from being left untouched to total reconversion. These situations apply to large surface areas often impacted by residual diffuse pollution. Though significant and preventing any sensitive use, residual contamination does not necessarily require treatment. Moreover, conventional treatments show their technical and economic limits in these situations and gentle remediation options such as phytomanagement might appear more relevant to the management of those sites. Thus, these sites face up two major issues: managing moderate contamination levels and providing an alternative use of economic interest. This work proposes to assess a management strategy associating the phytoremediation of organic pollution along with the production of biomass for energy generation production. A 16-week controlled growth experiment was conducted on a soil substrate moderately impacted by multiple pollution (trace elements, mainly Zn and Pb, and hydrocarbons), by associating rhizodegradation with Medicago sativa or biomass production with Robinia pseudoacacia or Alnus incana in monocultures. The effect of a microbial inoculum amendment on the performances of these treatments was also evaluated. Results showed total hydrocarbons (TH), and to a lesser extent polycyclic aromatic hydrocarbons (PAH), concentrations decreased over time, whatever the plant cover. Good biomass production yields were achieved for both tree species in comparison with the control sample, even though R. pseudoacacia seemed to perform better. Furthermore, the quality of the biomass produced was in conformity with the thresholds set by the legislation concerning its use as a renewable energy source.

Once previous industrial activity has ceased, brownfields are found in urban and suburban environments and managed in different ways ranging from being left untouched to total reconversion. These situations apply to large surface areas often impacted by residual diffuse pollution. Though significant and preventing any sensitive use, residual contamination does not necessarily require treatment. Moreover, conventional treatments show their technical and economic limits in these situations and gentle remediation options such as phytomanagement might appear more relevant to the management of those sites. Thus, these sites face up two major issues: managing moderate contamination levels and providing an alternative use of economic interest. This work proposes to assess a management strategy associating the phytoremediation of organic pollution along with the production of biomass for energy generation production. A 16-week controlled growth experiment was conducted on a soil substrate moderately impacted by multiple pollution (trace elements, mainly Zn and Pb, and hydrocarbons), by associating rhizodegradation with Medicago sativa or biomass production with Robinia pseudoacacia or Alnus incana in monocultures. The effect of a microbial inoculum amendment on the performances of these treatments was also evaluated. Results showed total hydrocarbons (TH), and to a lesser extent polycyclic aromatic hydrocarbons (PAH), concentrations decreased over time, whatever the plant cover. Good biomass production yields were achieved for both tree species in comparison with the control sample, even though R. pseudoacacia seemed to perform better. Furthermore, the quality of the biomass produced was in conformity with the thresholds set by the legislation concerning its use as a renewable energy source.