Adsorption/desorption of sulfamethoxypyridazine and enrofloxacin in agricultural soils.

Adsorption and desorption processes were studied for the antibiotics sulfamethoxypyridazine (SMP) and enrofloxacin (ENR) in 20 agricultural soils devoted to wheat-potato and vine cultivation. Batch experiments were used to conduct kinetic studies, as well as to evaluate adsorption and desorption for different concentrations of antibiotics. The results indicated that adsorption curves were linear for SMP, while presented a certain curvature in the case of ENR. The adsorption of both antibiotics was fitted to a linear equation and to the Freundlich model. In the case of the linear equation, the values of the distribution coefficient Kd were lower for SMP (0.9-26.0 L kg-1) than for ENR (121-2345 L kg-1). In the Freundlich model, the values of the adsorption constant KF ranged between 1.7 and 34.0 Ln μmol1-n kg-1 for SMP, and between 829 and 3019 Ln μmol1-n kg-1 for ENR. A multiple regression analysis showed that, in the case of SMP, 78% of the variance of the adsorption parameter Kd was explained by soil organic carbon (SOC) and exchangeable magnesium (Mge) contents, while for ENR no significant relation was found. In addition, for SMP, 66% of the variance of KF was explained by SOC, and for ENR 45% of the variability of KF was explained by nitrogen content. Desorption rates were higher for SMP (reaching up to 24%) than for ENR (which reached up to 7%). Desorption percentages showed a potential relation with the adsorption parameter Kd for both SMP and ENR. These results could be useful to elucidate the evolution and dynamics of these emerging pollutants in soils and other environmental compartments, which could be of aid in controlling public health risks associated to them.