International audience | Glyphosate (N-phosphonomethylglycine; GLP) and its main metabolite AMPA (aminomethylphosphonic acid), are frequently detected in relatively high concentrations in European agricultural topsoils. Glyphosate has a high sorption affinity, yet it can be detected occasionally in groundwater. We hypothesized that shrinkage cracks occurring after dry periods could facilitate GLP transport to greater depths where subsoil conditions slow further microbial degradation. To test this hypothesis, we simulated a heavy rainfall event (HRE) on a clay-rich arable soil. We applied 2.1 kg ha−1 of 100% 13C3, 15N-labeled GLP one day before the simulated rainfall event. Microbial degradation of translocated GLP over a 21-day period was assessed by quantifying 13C incorporation into phospholipid fatty acids. Microbial degradation potential and activity were determined by quantifying the abundance and expression of functional genes involved in the two known degradation pathways of GLP; to AMPA (goxA) or sarcosine (sarc). We confirmed that goxA transcripts were elevated in the range of 4.23 x 105 copy numbers g−1 soil only one day after application. The increase in AMPA associated with a rise in goxA transcripts and goxA-harboring microorganisms indicated that the degradation pathway to AMPA dominated. Based on 13C-enrichment 3 h after the HRE, fungi appeared to initiate glyphosate degradation. At later time points, Gram+-bacteria proved to be the main degraders due to their higher 13C-incorporation. Once GLP reached the subsoil, degradation continued but more slowly. By comparing GLP distribution and its microbial degradation in macropores and in the bulk soil, we demonstrated different time- and depth-dependent GLP degradation dynamics in macropores. This indicates the need for field studies in which soil properties relevant to GLP degradation are related to limiting environmental conditions, providing a realistic assessment of GLP fate in soils.

Glyphosate (N-phosphonomethylglycine; GLP) and its main metabolite AMPA (aminomethylphosphonic acid), are frequently detected in relatively high concentrations in European agricultural topsoils. Glyphosate has a high sorption affinity, yet it can be detected occasionally in groundwater. We hypothesized that shrinkage cracks occurring after dry periods could facilitate GLP transport to greater depths where subsoil conditions slow further microbial degradation. To test this hypothesis, we simulated a heavy rainfall event (HRE) on a clay-rich arable soil. We applied 2.1 kg ha⁻¹ of 100% ¹³C₃, ¹⁵N-labeled GLP one day before the simulated rainfall event. Microbial degradation of translocated GLP over a 21-day period was assessed by quantifying ¹³C incorporation into phospholipid fatty acids. Microbial degradation potential and activity were determined by quantifying the abundance and expression of functional genes involved in the two known degradation pathways of GLP; to AMPA (goxA) or sarcosine (sarc). We confirmed that goxA transcripts were elevated in the range of 4.23 x 10⁵ copy numbers g⁻¹ soil only one day after application. The increase in AMPA associated with a rise in goxA transcripts and goxA-harboring microorganisms indicated that the degradation pathway to AMPA dominated. Based on ¹³C-enrichment 3 h after the HRE, fungi appeared to initiate glyphosate degradation. At later time points, Gram⁺-bacteria proved to be the main degraders due to their higher ¹³C-incorporation. Once GLP reached the subsoil, degradation continued but more slowly. By comparing GLP distribution and its microbial degradation in macropores and in the bulk soil, we demonstrated different time- and depth-dependent GLP degradation dynamics in macropores. This indicates the need for field studies in which soil properties relevant to GLP degradation are related to limiting environmental conditions, providing a realistic assessment of GLP fate in soils.

International audience | Accumulation of copper (Cu) in soils due to the application of fungicides may be toxic for organisms and hence affect winegrowing sustainability. Soil parameters such as pH and dissolved organic matter (DOM) are known to affect the availability of Cu. In this study, we investigated the contribution of chromophoric and fluorescent DOM properties to the prediction of Cu availability in 18 organic vineyard soils in the Bordeaux winegrowing area (France). The DOM parameters, assessed through absorbance and fluorescence analyses, and proxies for Cu availability (total soluble Cu and free ionic Cu2+) were measured in 0.01 M KCl extracts. Total soluble Cu (CuKCl) varied 23-fold while free ionic Cu2+ varied by a factor of 4600 among the soils. DOC concentrations were similar among the soils, but the samples differed in the quality of DOM as assessed by optical spectroscopy. Multilinear regression models with and without DOM quality parameters were investigated to predict Cu availability. The best model for CuKCl successfully explained 83% of variance and included pH, CuT, and two DOM fluorescence quality indices, the FI fluorescence index, which distinguishes between microbial and higher plant origins, and the HIX humification index. For the prediction of Cu2+, pH alone explained 88% of variance and adding DOM parameters did not improve modelling. The two Cu availability proxies were related to pH. This study confirms the prominent role of pH in Cu availability and underlines the importance of DOM quality to better predict Cu solubility

Accumulation of copper (Cu) in soils due to the application of fungicides may be toxic for organisms and hence affect winegrowing sustainability. Soil parameters such as pH and dissolved organic matter (DOM) are known to affect the availability of Cu. In this study, we investigated the contribution of chromophoric and fluorescent DOM properties to the prediction of Cu availability in 18 organic vineyard soils in the Bordeaux winegrowing area (France). The DOM parameters, assessed through absorbance and fluorescence analyses, and proxies for Cu availability (total soluble Cu and free ionic Cu²⁺) were measured in 0.01 M KCl extracts. Total soluble Cu (CuKCₗ) varied 23-fold while free ionic Cu²⁺ varied by a factor of 4600 among the soils. DOC concentrations were similar among the soils, but the samples differed in the quality of DOM as assessed by optical spectroscopy. Multilinear regression models with and without DOM quality parameters were investigated to predict Cu availability. The best model for CuKCₗ successfully explained 83% of variance and included pH, CuT, and two DOM fluorescence quality indices, the FI fluorescence index, which distinguishes between microbial and higher plant origins, and the HIX humification index. For the prediction of Cu²⁺, pH alone explained 88% of variance and adding DOM parameters did not improve modelling. The two Cu availability proxies were related to pH. This study confirms the prominent role of pH in Cu availability and underlines the importance of DOM quality to better predict Cu solubility.

International audience | Chlordecone (CLD), was widely applied in banana fields in the French West Indies from 1972 to 1993. The WISORCH model was constructed to assess soil contamination by CLD and estimated that it lasts from 100 to 600 years, depending on leaching intensity and assuming no degradation. However, recent studies demonstrated that CLD is degraded in the environment, hence questioning the reliability of previous estimations. This paper shows how to improve the model and provides insights into the long-term dissipation of CLD. In-situ observations were made in nearly 2545 plots between 2001 and 2020, and 17 plots were sampled at two dates. Results of soil analyses showed an unexpected 4-fold decrease in CLD concentrations in the soil, in contrast to simulations made using the first version of WISORCH at the time. Neither erosion, nor CLD leaching explained these discrepancies. In a top-down modeling approach, these new observations of CLD concentrations led us to implement a new dissipation process in the WISORCH model that corresponds to a DT50 dissipation half-life of 5 years. The new version of the improved model allowed us to update the prediction of the persistence of soil pollution, with soil decontamination estimated for the 2070s. This development calls for re-evaluation of soil pollution status. Further validation of the new version of WISORCH is needed so it can contribute to crop management on contaminated soil.

Chlordecone (CLD), was widely applied in banana fields in the French West Indies from 1972 to 1993. The WISORCH model was constructed to assess soil contamination by CLD and estimated that it lasts from 100 to 600 years, depending on leaching intensity and assuming no degradation. However, recent studies demonstrated that CLD is degraded in the environment, hence questioning the reliability of previous estimations. This paper shows how to improve the model and provides insights into the long-term dissipation of CLD. In-situ observations were made in nearly 2545 plots between 2001 and 2020, and 17 plots were sampled at two dates. Results of soil analyses showed an unexpected 4-fold decrease in CLD concentrations in the soil, in contrast to simulations made using the first version of WISORCH at the time. Neither erosion, nor CLD leaching explained these discrepancies. In a top-down modeling approach, these new observations of CLD concentrations led us to implement a new dissipation process in the WISORCH model that corresponds to a DT50 dissipation half-life of 5 years. The new version of the improved model allowed us to update the prediction of the persistence of soil pollution, with soil decontamination estimated for the 2070s. This development calls for re-evaluation of soil pollution status. Further validation of the new version of WISORCH is needed so it can contribute to crop management on contaminated soil.

International audience | Chlordecone (CLD), was widely applied in banana fields in the French West Indies from 1972 to 1993. The WISORCH model was constructed to assess soil contamination by CLD and estimated that it lasts from 100 to 600 years, depending on leaching intensity and assuming no degradation. However, recent studies demonstrated that CLD is degraded in the environment, hence questioning the reliability of previous estimations. This paper shows how to improve the model and provides insights into the long-term dissipation of CLD. In-situ observations were made in nearly 2545 plots between 2001 and 2020, and 17 plots were sampled at two dates. Results of soil analyses showed an unexpected 4-fold decrease in CLD concentrations in the soil, in contrast to simulations made using the first version of WISORCH at the time. Neither erosion, nor CLD leaching explained these discrepancies. In a top-down modeling approach, these new observations of CLD concentrations led us to implement a new dissipation process in the WISORCH model that corresponds to a DT50 dissipation half-life of 5 years. The new version of the improved model allowed us to update the prediction of the persistence of soil pollution, with soil decontamination estimated for the 2070s. This development calls for re-evaluation of soil pollution status. Further validation of the new version of WISORCH is needed so it can contribute to crop management on contaminated soil.

Chlordecone (CLD), was widely applied in banana fields in the French West Indies from 1972 to 1993. The WISORCH model was constructed to assess soil contamination by CLD and estimated that it lasts from 100 to 600 years, depending on leaching intensity and assuming no degradation. However, recent studies demonstrated that CLD is degraded in the environment, hence questioning the reliability of previous estimations. This paper shows how to improve the model and provides insights into the long-term dissipation of CLD. In-situ observations were made in nearly 2545 plots between 2001 and 2020, and 17 plots were sampled at two dates. Results of soil analyses showed an unexpected 4-fold decrease in CLD concentrations in the soil, in contrast to simulations made using the first version of WISORCH at the time. Neither erosion, nor CLD leaching explained these discrepancies. In a top-down modeling approach, these new observations of CLD concentrations led us to implement a new dissipation process in the WISORCH model that corresponds to a DT50 dissipation half-life of 5 years. The new version of the improved model allowed us to update the prediction of the persistence of soil pollution, with soil decontamination estimated for the 2070s. This development calls for re-evaluation of soil pollution status. Further validation of the new version of WISORCH is needed so it can contribute to crop management on contaminated soil.