**1.6 Methods to understand glyphosate mobility**

Sorption coefficients provide accurate information needed for reliable risk assessments of groundwater contaminants by pesticides [25]. In a study related to sorption

and leaching of 14C-glyphosate in agricultural soils, non-extractable glyphosate residues become available eventually and take part in biodegradation and leaching. Empirical constants (KF) of Freundlich sorption isotherm were 16.6 for the clay loam, 33.6 for the silty clay loam, and 34.5 for the sandy clay loam indicating that it is the soil structure which dictates the glyphosate sorption behaviour [26]. Leaching of glyphosate was dependent on hydrodynamic and biodegradation properties of soils [26]. Application of char can be used as a strategy to increase the sorption of glyphosate [27].

Movement of pesticides and their bioavailability and biotransformation are controlled by adsorption/desorption mechanisms operating at the interface between organic and inorganic soil colloids. High-resolution magic angle spinning and nuclear magnetic resonance techniques can distinguish mobile and immobile phases of pesticides like glyphosate [28]. Another study on glyphosate transport parameters suggested that glyphosate sorption is a kinetic process that depends on pore-water velocities and residence time of soil solution [29].
