Adsorption-desorption and leaching behavior of diuron on selected Kenyan agricultural soils

In this work, the adsorption-desorption dynamics of diuron in three typical Kenyan agricultural soils, Nzoia (NZ), Thika (TH) and Machakos (MK) was investigated. The equilibrium adsorption data, tested against three classical nonlinear adsorption isotherms, was best described by the Freundlich model. The Freundlich adsorption constant, (K(F)), increased in the order MK > TH > NZ soil. Additionally, the negative Gibb's free energy values indicate the adsorption processes were thermodynamically spontaneous and physical. Multiple linear regression analysis indicated that the adsorption-desorption behavior was controlled by the clay and phosphorus contents of the soil. Phosphorus negatively affected the adsorption of diuron and promoted desorption. The groundwater ubiquity score (GUS) indicated that diuron movement rating in MK soil was ‘moderate’ while the movement in TH and NZ soils was ‘high’.