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

• Applicant: Professorin Dr. Ines Mulder
• Subject Area: Soil Sciences
• Term: from 2016 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 321417592

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.

• DFG Programme: Research Grants