Soil water solutes reduce the critical micelle concentration of quaternary ammonium compounds

Abstract

Quaternary alkyl ammonium compounds (QAACs) are produced in large quantities for use as surfactants and disinfectants and also found in soils, sediments, and surface waters, where they are potentially involved in the selection of antibiotic resistance genes. Micelle formation influences fate and effects of QAACs. The critical micelle concentration (CMC) of six homologs of benzylalkylammonium chlorides (BAC) was determined in deionized water, 0.01 M CaCl2 solution, and aqueous soil extracts, using both spectrofluorometric and tensiometric methods. Additionally, eight organic model compounds were employed at concentrations of 15 mg C L−1 as background solutes in order to test the effect of dissolved organic carbon (DOC) on CMCs. Results found CMCs decreased with an increasing length of the alkyl chain from 188 mM for BAC-C8 to 0.1 mM for BAC-C18. Both methods yielded similar results for measurements in water and CaCl2 solution; however, the spectrofluorescence method did not work for soil extracts due to fluorescence quenching phenomena. In soil extracts, CMCs of BAC-C12 were reduced below 3.7 mM, while the CMC reduction in soil extracts was less pronounced for BAC-C16. Besides ionic strength, molecular structures of BACs and dissolved organic compounds also affected the CMC. The number of carboxyl groups and small molecular weights of the DOC model compounds reduced the CMCs of BAC-C12 and BAC-C16 at pH 6. This study highlights that CMCs can be surpassed in soil solution, pore waters of sediments, or other natural waters even at (small) concentrations of QAACs typically found in the environment.

An Investigation of Thermal Air Degradation and Pyrolysis of Per- and Polyfluoroalkyl Substances and Aqueous Film-Forming Foams in Soil

“…91−95 Landfill leachate is rich in dissolved organic matter that may reduce the critical micelle concentration of PFAS. 96 The concave-upward isotherms (Figure 1) may reflect the transition from region 1 to region 2.…”

“…This implies a decrease in adsorption as the concentration falls during the natural dilution of the liquid phase. Sorption of surfactants is typically characterized by a normal isotherm at a low concentration (region 1) and then a concave-upward curve due to the formation of hemimicelles (region 2) or micelles (region 3). − Landfill leachate is rich in dissolved organic matter that may reduce the critical micelle concentration of PFAS . The concave-upward isotherms (Figure ) may reflect the transition from region 1 to region 2.…”

Multi-site fungicides suppress banana Panama disease, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4

“…Panama disease of bananas is considered uncontrollable by fungicides [ 1 , 9 ]. This may either be due to resistance of the pathogen and/or a hindering effect of soil due to its interaction with fungicides [ 30 , 31 , 32 ]. To test the hypothesis that FocTR4 and FocR1 show innate fungicide resistance, a quantitatively assessment of microconidia growth on fungicide-supplemented potato dextrose agar (PDA) plates, using 21 compounds from 7 main fungicide classes, was performed.…”

“…Indeed, the fate of fungicides in soil depends on their biophysical properties. This determines their mobility in soil [ 30 , 31 , 32 ], which may underpin their differential efficacy in soil and in vitro cultures. However, this remains speculative and merits future research.…”

Quaternary ammonium compounds of emerging concern: Classification, occurrence, fate, toxicity and antimicrobial resistance

“…The current advancement in next-generation sequencing allows more in-depth study into the microbial community through metagenomics sequencing. While critical micelle concentration (CMC) plays an important role in deciding the fate of QACs in environmental matrices, Mulder et al (2020) ( Mulder et al, 2020 ) postulated that the number of carboxyl groups and small molecular weights of dissolved organic matter could reduce the CMC of BAC C12 and BAC C16 at pH 6.…”