Ciprofloxacin and Trimethoprim Adsorption/Desorption in Agricultural Soils

The current research focuses on the adsorption/desorption characteristics of the antibiotics ciprofloxacin (CIP) and trimethoprim (TRI) taking place in 17 agricultural soils, which are studied by means of batch-type experiments. The results show that adsorption was higher for CIP, with Freundlich K_F values ranging between 1150 and 5086 Lⁿ µmol^1-n kg^-1, while they were between 29 and 110 Lⁿ µmol^1-n kg^-1 in the case of TRI. Other parameters, such as the Langmuir maximum adsorption capacity (q_m(ads)), as well as the K_d parameter in the linear model and also the adsorption percentages, follow the same trend as K_F. Desorption was lower for CIP (with K_F(des) values in the range 1089-6234 Lⁿ µmol^1-n kg^-1) than for TRI (with K_F(des) ranging between 26 and 138 Lⁿ µmol^1-n kg^-1). The higher irreversibility of CIP adsorption was also confirmed by its lower n_F(des)/n_F(ads) ratios, compared to TRI. Regarding soil characteristics, it was evidenced that nitrogen and carbon contents, as well as mineral fractions, had the highest influence on the adsorption/desorption process. These results can be considered relevant as regards the fate of both antibiotics when they reach the environment as pollutants and therefore could be considered in assessment procedures focused on environmental and public health aspects.