Fate of the new phytosantary, hydroxypyridone alkaloids, in the vadose zone of the carbonate Beauce aquifer (France)
Résumé
Introduction The pollution of water resources by phytosanitary products is a recurrent problem, due to the intensive use of these substances in modern agriculture. The research of new pesticides with similar structure of natural bioactive molecules is necessary to offer solutions devoid of toxicity for humans and the environment. Natural alkaloids with a 4-hydroxy-2-pyridone (4H2P) core offer a wide variety of structures, giving them diverse biological activities: insecticide (Wachira et al., 2014), fungicide (Jessen and Gademann, 2010), bactericide (Xiao et al., 2023), cytotoxic activity (Ding et al., 2014), and seem to be excellent candidates for new types of phytosanitary products. However, the fate of these new substances in soils are unknown. The understanding of the mechanisms controlling their reactivity (physical, chemical or with microorganisms), and their mobility in the vadose zone (interaction with carbonate rocks and oxyhydroxides) is essential for assessing the risks of their transfer to groundwater. Several molecules with a 4H2P core have thus been synthesized during the DEMETER project (funded by French Centre-Val-de-Loire Region). This study will present the mobility of some of them through agricultural and limestone soils, and their reactivity with mineral phases constituting these soils of the vadose zone. Material and Methods In order to study the behavior of the 4H2P alkaloids, agricultural, and limestone soils were sampled on the O-ZNS observatory site located at Villamblain (Beauce, Eure-et-Loir, France). These soils were characterized by Rock-Eval analysis to determine the total organic carbon, and by XRD to characterize the reactive phase. The mobility of these alkaloids was studied on a 30 cm column of directly sampled agricultural soil, and on a 30 cm column of reconstructed limestone soil, after determination of hydrodynamic parameters of soil columns with a tracer (2,6-DFBA). Adsorption isotherms were performed on the main reactive phases detected, and on the soils. Concentrations of the alkaloids were measured on UV-Vis spectrophotometer. Results The 2,6-DFBA present similar elution curve in the 2 soils with same restitution rates (95.0% for agricultural soil, and 94.3% for limestone soil), and similar residence time (3000 min). Depending on the structure and substituents on the 4H2P ring, the behavior of two studied alkaloids is not identical on the reconstructed limestone column: the one with the ethylene 32nd International Meeting on Organic Geochemistry (IMOG) Porto, Portugal glycol side chain is more retained on the column with a recovery rates of 72%, whereas the second with a methyl carboxylate side chain has a residence time similar to that of the tracer, without being fully recovered. In agricultural soils, the 4H2P alkaloids are more retained than in the limestone soil, probably due to their interaction with mineral reactive phases and organic matter in the soil. XRD experiments showed that Villamblain soils are mainly composed of smectite, kaolinite, goethite and calcite. Adsorption isotherms for the molecules with a 4H2P core performed on the different soils, and mineral phases of these soil showed that this molecule is mainly adsorbed on smectite, and to a lesser extent on kaolinite. As confirmed by XRD, the presence of reactive sites in the interlayer space of smectite promotes adsorption. However, the modelling of the results obtained indicates that the mean free energy values are low (< 8KJ/mol) and, and are of physisorption type. The molecule would be retained in the soil, and remobilized without too much energy, particularly in soils that are low in organic matter. The elution data obtained experimentally were simulated using STANMOD software, and the transfer, sorption and interaction parameters thus calculated were used to model the reactive transport of these molecules. Conclusion The reactivity, and mobility of two 4H2P alkaloids in agricultural soil and Beauce aquifer limestone have been studied in the laboratory through dynamic (columns), and static (isotherm adsorption batches) experiments. These molecules are principally retained in the soil surface due to their interaction with smectite and organic matter, then the fate of each alkaloid is different: the one with the methyl carboxylate side chain cross the limestone at the rate of water in the vadose zone and the second has more interactions with the minerals and its elution across this soil is delayed, underlining the influence of the side chain on molecule retention. References Ding et al., 2014. Collective Synthesis of 4-Hydroxy-2-pyridone Alkaloids and Their Antiproliferation Activities. Chemistry - An Asian Journal 9, 2548‑2554. DOI: 10.1002/asia.201402466. Jessen and Gademann, 2010. 4-Hydroxy-2-pyridone alkaloids: Structures and synthetic approaches. Natural Product Reports 27, 1168-1185. DOI: 10.1039/B911516C Wachira et al., 2014. Toxicity of six plant extracts and two pyridone alkaloids from Ricinus communis against the malaria vector Anopheles gambiae. Parasites & Vectors 7, 312. DOI: 10.1186/1756-3305-7-312 Xiao et al., 2023. Exploiting Natural Maltol for Synthesis of Novel Hydroxypyridone Derivatives as Promising Anti-Virulence Agents in Bactericides Discovery. Journal of Agricultural and Food Chemistry 71, 6603-6616. DOI: 10.1021/acs.jafc.3c00465
| Origine | Fichiers produits par l'(les) auteur(s) |
|---|---|
| Licence |
