Enhancing soil sorption capacity of an agricultural soil by addition of three different organic wastes

• Pesticide sorption capacity of three unmodified organic wastes was studied.
• Sorption was greater for the most hydrophobic compounds.
• Sorption capacity increased as the organic matter concentration increased.
• Sorption capacity was positively correlated with the organic carbon content.

This study evaluated the ability of three unmodified organic residues (composted sewage sludge, RO1; chicken manure, RO2; and a residue from olive oil production called ‘orujillo’, RO3) and a soil to sorb six pesticides (atrazine, lindane, alachlor, chlorpyrifos, chlorfenvinphos and endosulfan sulfate) and thereby explored the potential environmental value of these organic residues for mitigating pesticide pollution in agricultural production and removing contaminants from wastewater. Pesticide determination was carried out using gas chromatography coupled with mass spectrometry. Adsorption data were analyzed by the Langmuir and Freundlich adsorption approaches. Experimental results showed that the Freundlich isotherm model best described the adsorption process and that Kf values increased with an increase in organic matter (OM) content of the amended soil. The order of adsorption of pesticides on soils was: chlorpyrifos ≥ endosulfan sulfate > chlorfenvinphos ≥ lindane > alachlor ≥ atrazine. The sorption was greater for the most hydrophobic compounds and lower for the most polar ones, as corroborated by a negative correlation between Kf values and solubility. Sorption increased with an increase in organic matter. Sorption capacity was positively correlated with the organic carbon (OC) content. The organic amendment showing the maximum sorption capacity was RO3 in all cases, except for chlorfenvinphos, in which it was RO2. The order of adsorption capacity of the amendments depended on the pesticide and the organic dosage. In the case of the 10% amendment the order was RO3 > RO2 > RO1 > soil, except for chlorfenvinphos, in which it was RO2 > RO3 > RO1 > soil, and atrazine, where RO2 and RO3 amendments had the same effect on the soil sorption capacity (RO2 ≥ RO3 > RO1 > soil).