Sorption and leaching of diuron on natural and peat-amended calcareous soil from Spain

The sorption and leaching processes of diuron from a 0.02 M CaCl2 aqueous solution at 25°C, by a calcareous soil from the Southeastern of Spain after organic carbon (OC) amendment with a commercial peat (from 0.18% to 4.61%) have been studied by using batch and soil column experiments. The experimental sorption isotherms may be classified as L type of the Giles classification which suggests, in general, a moderate affinity of the diuron molecules by the active sites of the adsorbents. Nevertheless, according to the slope of the initial portion of these isotherms, the affinity increases as the organic matter content increases. In order to calculate the adsorption capacity (Kf) of the samples for the herbicide diuron, the experimental data point were fitted to the Freundlich equation. The Kf values ranged between 2.17 mg kg−1 for the original soil (containing 0.18% OC) and 34.28 mg kg−1 for the peat-amended sample containing 4.61% OC. The breakthrough curves and distribution of diuron along the soil profile, obtained from the step-function type and pulse type experiments by using the soil column studies, indicate that the amount of diuron retained range from 359.3 mg kg−1 for the column filled with the original soil to 439 mg kg−1 for that filled with the peat-amended soil containing 4.61% OC. The amount of diuron desorbed (373.0 mg kg−1) from the soil containing the higher percentage of organic carbon (4.61%) was greater than that desorbed (300.8 mg kg−1) from the original soil, which might be due to the joining of diuron to the soluble fraction of the organic matter moving through the column.