Kinetic and Mechanistic Modelling of Pyrimethanil Fungicide Adsorption onto Soils of Varying Physico-chemical Properties.

Pesticide transport in the environment is impacted by the kinetics of its adsorption onto soil. The adsorption kinetics of pyrimethanil was investigated in ten soil samples of varying physicochemical properties. The highest adsorption was in the soil having the maximum silt and CaCO₃ contents, pH and electrical conductance but the lowest amorphous Fe oxides and CaCl₂ extractable Mn. Pseudo-second order kinetics and intra-particle diffusion model best accounted the adsorption kinetics of pyrimethanil. The equilibrium adsorption estimated by pseudo-second order kinetics (q₀₂) was significantly and positively correlated with CaCl₂ extractable Cu content (r = 0.709) while rate coefficient (k₀₂) had a negative correlation with crystalline iron oxides content (r = -0.675). The intra-particle diffusion coefficient (k_i.d.) had inverse relationship with CaCl₂ extractable Mn content in soils (r = -0.689). FTIR spectra showed a significant interaction of pyrimethanil with micronutrient cations. Adsorption kinetic parameters of pyrimethanil could be successfully predicted by soil properties. The findings may help to evolve fungicide management decisions.