Adsorption of paraquat on soil organic matter: Effect of exchangeable cations and dissolved organic carbon

► At pH > 5.5, the amount of PQ retained by the soil decreases due to the presence of DOM. ► The pH and ionic strength effect on PQ adsorption is of electrostatic nature. ► An electrostatic model is used to interpret the effect of the surface charge on PQ adsorption. ► The binding sites available for PQ are reduced by the presence of exchangeable cations.