Transformation et transport des pesticides inorganiques et de synthèse dans les sols de bassins versants agricoles

Despite homologation tests of pesticides and metals, alarming concentrations are measured in the environment. A better knowledge of the transformation processes undergone by these products in agrosystems is needed to predict and limit the pollution. This PhD. thesis allowed to understand the transformation and transport of pesticides and metals in agricultural soils during 200 days and with respect to different hydro-climatic conditions using sequential extraction and isotopic fractionation of pesticides (compound specific isotopic analyses, CSIA) and metals. This work revealed the relevant of soil organic matter on the speciation of pollutants, the relationship between hydro-climatic conditions, the dissipation and the transformation mechanisms of peticides, and how pollutant infiltration is controlled both by rainfall length and frequency. These resuls will improve the transport models of pesticides in agrosystems.Malgré les tests d’homologation des pesticides et métaux, des teneurs alarmantes de ces produits sont relevées dans l’environnement. Une meilleure connaissance des processus subis par ces produits dans les agrosystèmes est nécessaire afin de réduire les pollutions liées à leur utilisation. Cette thèse vise à améliorer la compréhension de la transformation et du transport des pesticides et métaux pas l’étude détaillée de ces polluants dans les sols agricoles durant 200 jours, en fonction des conditions hydro-climatiques et l’analyse isotopique des pesticides (par composés spécifiques, CSIA) et des métaux. Ces travaux révèlent l’importance de la matière organique sur la spéciation des polluants, les relations entre les conditions, la dissipation et les mécanismes de transformation des pesticides, mais aussi le contrôle de l’infiltration des polluants par la durée et la fréquence des pluies. Ces résultats permettent d’améliorer la prédiction du transport des polluants dans les agrosystèmes

Transformation and transport of inorganic and synthetic pesticides in soils of agricultural catchments

Malgré les tests d’homologation des pesticides et métaux, des teneurs alarmantes de ces produits sont relevées dans l’environnement. Une meilleure connaissance des processus subis par ces produits dans les agrosystèmes est nécessaire afin de réduire les pollutions liées à leur utilisation. Cette thèse vise à améliorer la compréhension de la transformation et du transport des pesticides et métaux pas l’étude détaillée de ces polluants dans les sols agricoles durant 200 jours, en fonction des conditions hydro-climatiques et l’analyse isotopique des pesticides (par composés spécifiques, CSIA) et des métaux. Ces travaux révèlent l’importance de la matière organique sur la spéciation des polluants, les relations entre les conditions, la dissipation et les mécanismes de transformation des pesticides, mais aussi le contrôle de l’infiltration des polluants par la durée et la fréquence des pluies. Ces résultats permettent d’améliorer la prédiction du transport des polluants dans les agrosystèmes.Despite homologation tests of pesticides and metals, alarming concentrations are measured in the environment. A better knowledge of the transformation processes undergone by these products in agrosystems is needed to predict and limit the pollution. This PhD. thesis allowed to understand the transformation and transport of pesticides and metals in agricultural soils during 200 days and with respect to different hydro-climatic conditions using sequential extraction and isotopic fractionation of pesticides (compound specific isotopic analyses, CSIA) and metals. This work revealed the relevant of soil organic matter on the speciation of pollutants, the relationship between hydro-climatic conditions, the dissipation and the transformation mechanisms of peticides, and how pollutant infiltration is controlled both by rainfall length and frequency. These resuls will improve the transport models of pesticides in agrosystems

Bioréduction de ferrihydrite substituée par du Cu et du Pb:impact sur la biodisponibilité de ces éléments?

International audienc

Ageing of copper, zinc and synthetic pesticides in particle-size and chemical fractions of agricultural soils

International audienc

Bioreduction of Pb-substituted ferrihydrite: impact on the nature of the biogenic minerals formed, the speciation and bioavailability of Pb

International audienceLevels of metals in terrestrial environments are an increasing concern, due to their threat to human health and ecosystem quality (Panagos et al., 2013). While metals risk assessment studies focused on their total concentration, research are currently oriented toward the evaluation of their speciation and bioavailability. Ferrihydrites (Fh), due to their large surface area and reactive surface properties, are important carrier phases in soils on which metals can be adsorbed or coprecipitated with (Tiberg, 2016). However, anaerobic transformation of such oxides in presence of dissimilatory iron reducing (DIR) bacteria like Shewanella oneidensis sp., may result in metals redistribution between the soil solution and the new (bio)formed Fe minerals (Frierdich et al., 2011). Further, the presence of metals in Fh may influence the nature of the (bio)formed minerals. To further our understanding, pure and Pb-substituted Fh (Pb/(Pb+FeIII) molar ratios of 2 and 5 %) were synthesized by coprecipitation (Schwertmann and Cornell, 2000). These Fh were incubated separately in anaerobic conditions with Shewanella oneidensis MR-1 cells in an appropriate liquid medium, for: i) 21 days (prolonged bioreduction), and ii) two 7-day periods separated by a 7-day aerobic oxidation (successive redox cycles). The nature of the (bio)formed minerals was assessed using XRD and Mössbauer spectroscopy. The bioreduction extent was measured thanks to the ferrozine method and UV-visible spectroscopy, and the partitioning of Pb between the liquid and solid phases was assessed using AAS. Finally, Pb bioavailable content in solution was determined using whole cell biosensors. Magnetite (M) was the main mineral obtained after the prolonged bioreduction (97 %), and increasing proportions of goethite (Gh) formed with Pb substitution (22 and 35 % for systems made with Pb/(Pb+FeIII) molar ratios of 2 and 5 % respectively). Gh and lepidocrocite were found to form in shorter bioreduction periods (1st anaerobic period of the successive redox cycles). The aerobic oxidation converts all the (bio)formed minerals to a poorly crystallized phase except in the highest Pb substituted system. Following the 2nd anaerobic period, M and Gh formed, while no change occurred in the highest Pb substituted system. Only minor amounts of the Pb introduced in the systems within the Fh used were found in the liquid phase and were not bioavailable. Most of the Pb introduced was associated to the (bio)formed minerals, whatever the nature of those minerals. Our results show the complex succession of (bio)formed minerals during bioreduction, the impact of a Pb substitution within ferrihydrite on the nature of the (bio)formed minerals and how these minerals act as efficient carrier phases of Pb

Pb-Bearing Ferrihydrite Bioreduction and Secondary-Mineral Precipitation during Fe Redox Cycling

International audienceThe significant accumulation of Pb from anthropogenic activities threatens environmental ecosystems. In the environment, iron oxides are one of the main carriers of Pb. Thus, the redox cycling of iron oxides, which is due to biotic and abiotic pathways, and which leads to their dissolution or transformation, controls the fate of Pb. However, a knowledge gap exists on the bioreduction in Pb-bearing ferrihydrites, secondary-mineral precipitation, and Pb partitioning during the bioreduction/oxidation/bioreduction cycle. In this study, Pb-bearing ferrihydrite (Fh_Pb) with various Pb/(Fe+Pb) molar ratios (i.e., 0, 2, and 5%) were incubated with the iron-reducing bacterium Shewanella oneidensis MR-1 for 7 days, oxidized for 7 days (atmospheric O2), and bioreduced a second time for 7 days. Pb doping led to a drop in the rate and the extent of the reduction. Lepidocrocite (23–56%) and goethite (44–77%) formed during the first reduction period. Magnetite (72–84%) formed during the second reduction. The extremely-low-dissolved and bioavailable Pb concentrations were measured during the redox cycles, which indicates that the Pb significantly sorbed onto the minerals that were formed. Overall, this study highlights the influence of Pb and redox cycling on the bioreduction of Pb-bearing iron oxides, as well as on the nature of the secondary minerals that are formed

Impact of rainfall patterns and frequency on the export of pesticides and heavy-metals from agricultural soils

The combined influence of soil characteristics, pollutant aging and rainfall patterns on the export of pollutants from topsoils is poorly understood. We used laboratory experiments and parsimonious modeling to evaluate the impact of rainfall characteristics on the ponding and the leaching of a pollutant mixture from topsoils. The mixture included the fungicide metalaxyl, the herbicide S-metolachlor, as well as copper (Cu) and zinc (Zn). Four rainfall patterns, which differed in their durations and intensities, were applied twice successively with a 7 days interval on each soil type. To evaluate the influence of soil type and aging, experiments included crop and vineyard soils and two stages of pollutant aging (0 and 10 days). The global export of pollutants was significantly controlled by the rainfall duration and frequency (P < 0.01). During the first rainfall event, the longest and most intense rainfall pattern yielded the largest export of metalaxyl (44.5 ± 21.5% of the initial mass spiked in the soils), S-metolachlor (8.1 ± 3.1%) and Cu (3.1 ± 0.3%). Soil compaction caused by the first rainfall reduced in the second rainfall the leaching of remaining metalaxyl, S-metolachlor, Cu and Zn by 2.4-, 2.9-, 30- and 50-fold, respectively. In contrast, soil characteristics and aging had less influence on pollutant mass export. The soil type significantly influenced the leaching of Zn, while short-term aging impacted Cu leaching. Our results suggest that rainfall characteristics predominantly control export patterns of metalaxyl and S-metolachlor, in particular when the aging period is short. We anticipate our study to be a starting point for more systematic evaluation of the dissolved pollutant ponding/leaching partitioning and the export of pollutant mixtures from different soil types in relation to rainfall patterns