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

季烷基铵化合物（QAAC）是阳离子有机化合物，在农业等许多应用中用作表面活性剂和消毒剂。虽然土壤中的浓度数据很少，但其他环境分区的调查结果表明，这些物质普遍存在，并与特定物质积累在一起。土壤中的预测环境浓度为3.5毫克千克-1，土壤中存在QAAC抗性基因。抗生素耐药性的共同选择会给人类和环境带来风险。在前一个为期一年的项目中，在第一个“Nachwuchsakademie Agarökosystemforschung”中获得批准，我们假设农业土壤中的QAAC主要保留在粘土矿物的夹层中，通过粘土矿物对微生物最小抑菌浓度（minimum inhibitory concentration，MIC）的影响实验，通过比较QAAC对不同模型细菌的MIC，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，蒙脱石减少游离QAAC浓度。透射电子显微镜使得层间空间的膨胀在QAAC添加时可见。我们观察到，QAAC发挥控制絮凝和聚集体的稳定性。在土壤系统中，吸附到土壤颗粒上的物质的流动性强烈地依赖于吸附剂的大小。在具有内表面的聚集体的情况下，聚集体的大小和微观结构（土壤微聚集体=SMA）影响污染物的接触、释放或隔离方式。因此，本项目后续阶段的使命是了解稳定团聚体的控制、团聚体的失稳和形成对QAAC生物有效性的影响，以及QAAC生物有效性对稳定团聚体的影响，研究表面活性剂对土壤颗粒微团聚体的影响。（1）QAAC促进SMA形成并增加微聚集体稳定性，（2）较高程度的SMA形成增加QAAC吸附-解吸滞后，（3）微团聚体减缓了QAAC的矿化作用;（4）微团聚体对QAAC对土壤微生物的毒性有一定的缓冲作用。流体动力学半径和zetapotential和SMA的几何形状和孔隙率的测定的测量将用于表征SMA的结构和性能。QAAC动态降解研究应证明SMA的影响。作为最后一步，将在微生物MIC值试验系统中使用人工和“天然”微聚集体，并研究QAAC毒性缓冲效应。

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.