Influence of chemical and mineralogical soil properties on the adsorption of Sulfamethoxazole and Diclofenac in Mediterranean soils

The adsorption of organic pollutants onto soils allows a control of their bioavailability for living organisms and their leaching. The adsorption is influenced by properties of contaminants (solubility, chemical composition) and soils (organic matter content, pH, mineralogy). This study aimed to investigate the adsorption of two contaminants of emerging concerns (CECs) with different properties, sulfamethoxazole (SMZ) and diclofenac (DFC), onto three soils (Altamura, Sibari and Noci) with different organic carbon content and mineralogical composition. The isotherms data showed that the adsorption of DFC on the three soils closely matched all models considered (linear, Freundlich and Langmuir), while the SMZ was adsorbed onto Noci according to the linear model, and onto Sibari and Altamura according to the Freundlich model. In all cases, the Kd value was the highest for Altamura soil and the lowest for Noci one, according mainly to their content of organic carbon and feldspar, quartz and, to a lesser extent, amorphous Al oxides as inorganic components. A negative correlation was found between Kd value of each soil and the corresponding pH and, since this parameter influenced the net charge of clay minerals, the latter exhibited a low contribution in adsorbing the anionic forms of the two CECs. Finally, between the two CECs studied, DFC was more adsorbed with respect to SMZ also because of the lower solubility of the former.