1 Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC, H4B 1R6, Canada; Quebec Centre for Advanced Materials, Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, H4B 1R6, Canada. Electronic address: adedapo.adeola@concordia.ca.
2 Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC, H4B 1R6, Canada; Quebec Centre for Advanced Materials, Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, H4B 1R6, Canada.
3 Department of Chemistry and Biochemistry and the Centre for NanoScience Research, Concordia University, Montreal, QC, H4B 1R6, Canada; Quebec Centre for Advanced Materials, Department of Chemistry and Biochemistry, Concordia University, Montreal, QC, H4B 1R6, Canada. Electronic address: rafik.naccache@concordia.ca.

The bioavailability and fate of pesticides in soil are largely influenced by soil's sorption characteristics. Therefore, the adsorption of pesticides, like glyphosate (GBH), onto soil natural organic matter (NOM) was investigated in this study. With the aid of sequential treatment methods of agricultural soil, NOM was modified to yield demineralized matter (DM), nonhydrolyzable carbon (NHC), and black carbon (BC). A comprehensive characterization of NOMs was carried out using BET, ICP-OES, pHpzc, SEM-EDS, XRD, and FTIR, which revealed alterations in the physical and chemical characteristics of NOMs as a result of the extraction and modification procedures. Experimental data demonstrated that the Sips isotherm model provided the best fit for NOM-glyphosate interactions, as indicated by the lowest chi-square values and correlation coefficient. The model suggests a complex interaction between the pesticide and NOMs, driven potentially by p-p interactions, as well as electrostatic interactions between charged NOMs due to their moieties and glyphosate ions in aqueous media. The predicted maximum adsorption capacity improved from 6.8 mg/g (bulk soil) to 8.7 mg/g (BC fraction), with experimental adsorption capacity following the order Bulk < DM < BC < NHC. Sorption was fairly enhanced under acidic conditions and sorption hysteresis was observed. Additionally, the NOM's chemical composition, particularly its percent organic carbon and mineralogy, which influenced the NOM's hydrophobic properties, played a key role in influencing adsorption behavior and potentially irreversible sorption, as reflected in H-indices. This study highlights the impact of different NOM fractions on glyphosate mobility, retention in soil and potential environmental risks.