Fate of Quaternary Ammonium Compounds in Soil - Experiments with model soil constituents

季铵化合物（QAC）是一类用作表面活性剂和消毒剂的两性阳离子有机化合物。生产和消费数据表明，排放到环境中的数量暂时比例如药品的情况高出几个数量级。在农业领域，它们的应用尤其广泛，从畜牧业中的消毒剂和洗涤剂到农药配方中的佐剂。QACs作为消毒剂，对多种生物具有杀灭和毒性作用。土壤中抗生素抗性基因的共选择造成了QACs的存在，对环境和人类健康造成了不可预见的风险。由于肥料、污水污泥或废水被用于农民的农田进行养分循环，QAC对农业生态系统的投入可能很高。此外，由于QACs的分子性质，这些化合物可能会被土壤粘土矿物和土壤有机质（SOM）吸附和保留。与这些观察结果相反，目前没有关于土壤中QAC浓度的数据，对土壤中QAC的命运和影响的理解是初步的。我们提出，在农业土壤中，QACs将主要保留在可膨胀的2:1粘土矿物的层间区域。因此，它们的生物降解被延缓，它们的急性毒性降低，土壤中QAC的总体浓度会随着时间的推移而增加。正如抗生素所证明的那样，被隔离的QACs可能会释放回土壤溶液中。通过这种方式，土壤中QAC的隔离导致土壤微生物群落长期暴露于亚抑制性QAC浓度水平。这项为期一年的计划的主要目标是证明QACs在农业土壤中可逆封存的概念。主要目标是：1)开发和建立从土壤中提取QAC的合适方法并分析其含量；2)表征QAC在土壤中的命运，重点研究其结合和固存。利用模型土壤组分进行试验来研究复杂系统土壤。这些实验应包括吸附和解吸实验，以及x射线衍射（XRD）研究，这些研究有望提供有关土壤中QAC命运过程的新数据和见解，作为改进风险评估的基础。实验结果将使用复杂的吸附模型进行分析，考虑静电相互作用和QACs与土壤组分之间相互作用的动力学过程。

Quaternary ammonium compounds (QAC) are a group of amphoteric cationic organic compounds used as surfactants and disinfectants. Production and consumption data indicate that volumes that are released into the environment are tentatively orders of magnitudes higher than is the case for example for pharmaceuticals. In the agricultural sector, their applications are especially broad and range from disinfectants and detergent in animal husbandry to their use as adjuvants in pesticide formulations. As disinfectants, QACs exert biocidal and toxic effects to several groups of organisms. In soils the presence of QACs has been inflicted in the co-selection for antibiotic resistance genes with unforeseeable risks for environmental and human health. Inputs of QAC into agroecosystems are potentially high where manures, sewage sludge or wastewater are applied to the farmer's fields for nutrient recycling. Furthermore, due to the molecular nature of QACs, it appears likely, that these compounds will be adsorbed and retained by soil clay minerals and soil organic matter (SOM). In opposition to these observations, there are currently no data available on QAC concentrations in soils and the understanding of the fate and effects of QACs in soils is rudimentary. We propose that in agricultural soils QACs will dominantly be retained in the interlayer regions of expandable 2:1 clay minerals. Thereby, their biodegradation is retarded, their acute toxicity reduced and the overall QAC concentration in soil can increase over time. As demonstrated for antibiotics, a release of sequestered QACs back into soil solution could occur. In this way the sequestration of QACs in soil leads to a long-term exposure of soil microbial communities to sub-inhibitory QAC concentrations levels. The main goal of the proposed one-year program is to proof the concept of a reversible sequestration of QACs in agricultural soils. Main objectives are i) to develop and establish suitable methods to extract QACs from soils and analyze their QAC contents and ii) to characterize the fate of QACs in soils with a focus on binding and sequestration. Experiments with model soil constituents will be conducted to approach the complex system soil. These experiments shall encompass sorption and desorption experiments, as well as x-ray diffraction (XRD) studies that are expected to deliver novel data and insights into processes on QAC fate in soils as a basis for an improved risk assessment. Experimental results will be analyzed using sophisticated sorption models considering electrostatic interactions and kinetic processes of interactions between QACs and soil constituents.