University of Rostock, Soil Science, Justus-von-Liebig-Weg 6, D-18059 Rostock, Germany.
University of Rostock, Institute of Physics, Albert-Einstein-Str. 23-24, D-18051 Rostock, Germany; University of Cairo, Faculty of Science, Department of Chemistry, 12613 Giza, Egypt.
Sci Total Environ. 2017 May 15;586:527-535. doi: 10.1016/j.scitotenv.2017.02.007. Epub 2017 Feb 21.
The herbicide glyphosate (GLP) is supposed to be rapidly degraded or adsorbed strongly by soil solids but findings in soil years after application and concentrations in waters above legal limits question a harmless disappearance. Therefore, we conducted batch sorption experiments with 23 thoroughly characterized arable surface soils, correlated isotherm coefficients with numerous inorganic and organic soil parameters, and investigated GLP-SOM-complexes by quantum-chemical modeling. The Freundlich sorption model yielded the best fits, and coefficients K and n were correlated positively with the contents of clay/silt. The contents of organic C (C) and of the mass-spectrometrically determined SOM-compound classes carbohydrates, phenols/lignin monomers, lignin dimers, lipids, alkylaromatics, non-amide N and amides and sterols all were strongly positively correlated with the Freundlich coefficients. Quantum-chemical modeling showed that both GLP phosphonic and carboxylic functional groups interact similarly with the polar SOM functional groups via H-bond formation but the GLP phosphonic moiety is most important in the GLP-SOM-interaction. Moreover, the interaction mechanism between GLP and every modeled SOM-compound class was explored indicating the importance of the polarity, electron density, and site of attack of the SOM fragments in the GLP-SOM-interaction. Partial binding energies were combined to a total binding energy (E) of GLP to the SOM, considering the mass spectrometrically quantified compound classes for each individual soil sample. The resulting strongly positive correlation between the E and the C provided compelling new experimental-theoretical evidence for the importance of SOM on the GLP binding and its behavior in the environment. In conclusion, the multitude of binding mechanisms to clay minerals and organic colloids make the occurrence of free GLP rather unlikely but a leaching of GLP complexes via preferential flow path through soil and transfer to waterways rather likely.
除草剂草甘膦（GLP）据推测会被土壤固体迅速降解或强烈吸附，但在施药多年后的土壤中发现以及水中浓度超过法定限量都表明其不会无害消失。因此，我们进行了 23 次彻底特征化耕地表层土壤的批量吸附实验，将等温线系数与众多无机和有机土壤参数相关联，并通过量子化学建模研究了 GLP-SOM 复合物。Freundlich 吸附模型拟合效果最佳，系数 K 和 n 与粘土/粉土含量呈正相关。有机 C（C）的含量以及通过质谱测定的 SOM 化合物类别的含量，包括碳水化合物、酚类/木质素单体、木质素二聚体、脂质、烷基芳烃、非酰胺 N 和酰胺以及甾醇，均与 Freundlich 系数呈强正相关。量子化学建模表明，GLP 的膦酸和羧酸官能团均通过氢键形成与极性 SOM 官能团相似地相互作用，但 GLP 膦酸部分在 GLP-SOM 相互作用中最为重要。此外，还探索了 GLP 与每一种建模 SOM 化合物类别的相互作用机制，表明 SOM 片段的极性、电子密度和攻击位点在 GLP-SOM 相互作用中的重要性。将部分结合能组合成 GLP 与 SOM 的总结合能（E），考虑到每个单独土壤样品的质谱定量化合物类别的情况。E 与 C 之间的强烈正相关为 SOM 对 GLP 结合及其在环境中行为的重要性提供了新的有力的实验-理论证据。总之，与粘土矿物和有机胶体的多种结合机制使得游离 GLP 的出现不太可能，但 GLP 复合物通过优先流途径通过土壤淋滤并转移到水道中则更为可能。
