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 L(n) µmol(1−n) kg(−1), while they were between 29 and 110 L(n) 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 L(n) µmol(1−n) kg(−1)) than for TRI (with K(F(des)) ranging between 26 and 138 L(n) 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.