Fate and Effects of Quaternary Ammonium Compounds in Soil -The role of microaggregation

季烷基铵化合物（QAAC）是一种阳离子有机化合物，在农业等众多应用中用作表面活性剂和消毒剂。虽然土壤的浓度数据很少，但其他环境隔间的研究结果表明，它们普遍存在，并以特定物质积累。预测土壤环境浓度为3.5 mg kg-1，已证实土壤中存在抗qaac基因。抗生素耐药性的共同选择将给人类和环境带来风险。在前一年的项目中，在第一个“Nachwuchsakademie Agarökosystemforschung”中，我们假设农业土壤中的QAACs将主要保留在粘土矿物的中间层中，保护它们免受微生物降解并缓冲它们的急性毒性。通过对黏土矿物对不同模型细菌的最小抑菌浓度（MIC）影响的实验，我们证实了蒙脱石的加入使MIC向上移动，即缓冲了QAAC的急性毒性。吸附等温线证实蒙脱石降低了游离qaac浓度。透射电镜观察到QAAC加入后层间空间的膨胀。我们观察到，QAAC对絮凝和团聚体稳定性有控制作用。在土壤系统中，吸附在土壤颗粒上的物质的流动性很大程度上取决于吸附剂的大小。在具有内表面的团聚体的情况下，团聚体的大小和微观结构（土壤微团聚体=SMA）影响污染物进入、释放或隔离的方式。因此，研究表面活性剂对土壤颗粒微聚集的影响，了解稳定团聚体、团聚体不稳定和形成对QAAC生物利用度的控制，以及反之亦然，是后续项目阶段的任务。本课题的研究假设为：(1)QAAC促进SMA的形成并增加微团聚体的稳定性；(2)更高的SMA形成程度增加了QAAC的吸附-解吸滞后性；(3)微聚集减缓了QAAC的矿化；(4)微聚集有助于可测量的QAAC对土壤微生物毒性的缓冲。实验将借助人工制造的SMA模型以及从土壤中提取的SMA进行。流体动力半径和齐势的测量以及SMA几何形状和孔隙率的测定将有助于表征SMA的结构和性能。QAAC降解动力学研究应证明sma的影响。最后，将人工和“天然”微聚集体用于微生物mic值测试系统，并研究qaac毒性缓冲作用。

Quaternary alkylammonium compounds (QAAC) are cationic organic compounds used as surfactant and disinfectants in numerous applications, amongst others, in agriculture. Although only few concentration data are available for soils, findings for other environmental compartments point to their ubiquitous occurrence and accumulation with particular substance. A predicted environmental concentration for soils is 3.5 mg kg-1 and the occurrence of QAAC-resistant genes in soils has been demonstrated. Co-selection for antibiotic resistance would entail risks for humans and environment.In the preceding one-year project, granted within the first “Nachwuchsakademie Agarökosystemforschung”, we postulated that QAACs in agricultural soils will predominantly be retained in the interlayers of clay minerals, protecting them from microbial degradation and buffering their acute toxicity.With an experiment on the effect of clay minerals on the minimal inhibitory concentration (MIC) of QAAC for different model bacteria, we confirmed that addition of smectite shifts the MIC upwards, i.e. the acute QAAC toxicity is buffered. Sorption isotherms confirmed that smectites reduced free QAAC-concentrations. Transmission electron microscopy made the expansion of interlayer spaces upon QAAC addition visible. We observed, that QAAC exerts control over flocculation and aggregate stability. In the soil system the mobility of substances adsorbed to soil particles strongly depends on the size of the adsorbent. In case of aggregates with an internal surface, the size and microstructure of aggregates (soil microaggregate=SMA) affects the way a contaminant is accessed, released or sequestered. It is therefore the mission of the subsequent project phase, to understand the control stable aggregates, aggregate destabilization and formation exert on the bioavailability of QAAC and vice versa, to study the effect of the surfactant on microaggregation of soil particles.The research hypotheses of the proposed project are: (1) QAACs promote SMA formation and increase microaggregate stability, (2) a higher degree of SMA-formation increases QAAC sorption-desorption hysteresis, (3) microaggregation slows down QAAC mineralization and (4) microaggregation contributes to a measureable buffering of QAAC toxicity on soil microbes.Experiments will be performed with the help of artificially produced model SMA as well as with SMAs extracted from soil. Measurements of hydrodynamic radii and zetapotential and the determination of SMA geometry and porosity will serve to characterize SMA structure and properties. Kinetic QAAC degradation studies shall demonstrate the influence of SMAs. As a final step, artificial and “native” microaggregates will be employed in the microbial MIC-value test system and investigated for QAAC-toxicity buffering effect.