Fig. 1. A schematic of the proposed multireaction model (MRM) with equilibrium and kinetic adsorption sites and one first-order degradation (irreversible) reaction. The term C is concentration in soil solution, S_e represents the amount sorbed on the equilibrium sites, S_k is that sorbed kinetic sites, and S_i the amount retained irreversibly, where K_e, k₁, k₂, and k₃ are the respective rates of reactions.