Single and simultaneous adsorption of three sulfonamides in agricultural soils: Effects of pH and organic matter content

Veterinary antibiotics reaching the environment have become a matter of global concern, since they can cause serious negative impacts on human and ecological health. Therefore, a deep understanding of their behavior and fate once they reach the soil environment is of utmost importance to design and implement appropriate measures that could reduce their potential risks. With this aim, batch-type experiments were carried out to study competitive adsorption and desorption for three sulfonamide antibiotics (sulfadiazine -SDZ-, sulfamethazine -SMT-, and sulfachloropyridazine -SCP-) in six crop soils presenting different characteristics. The results obtained showed that sulfonamides have a low retention in soils, with average adsorption percentages of 40% for SDZ, 44% for SMT and 54% for SCP, and with desorption percentages up to 36% for SDZ and SCP and up to 29% for SMT. The retention of sulfonamides was strongly influenced by the soil organic carbon content (SOC), with higher adsorption and less desorption associated to higher SOC contents. In addition, the hydrophobicity of sulfonamides also had an influence, as higher hydrophobicity resulted in higher affinity for soils, showing the affinity sequences: SDZ ~ SMT <SCP in acid soils, and SDZ ~ SCP <SMT in neutral soils. The results obtained in the ternary systems were very similar to those found in simple systems, indicating the absence of substantial competition for adsorption sites among the three sulfonamides. Despite the low competition among them, these antibiotics have high mobility in soils and, therefore, they imply a significant risk of contamination of water bodies, as well as of entering the food chain, generating serious hazards for human and environmental health. Therefore, fertilization of soils with sulfonamide polluted manures should be controlled, implementing new measurements for the pretreatment of manures before their application, thus contributing to a reduction of potential risks.

Competitive adsorption/desorption of tetracycline, oxytetracycline and chlortetracycline on two acid soils: Stirred flow chamber experiments

The objective of this work was to study the competitive adsorption/desorption of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) on two acid soils. We used the stirred flow chamber technique to obtain experimental data on rapid kinetic processes affecting the retention/release of the antibiotics. Both adsorption and desorption were higher on soil 1 (which showed the highest carbon, clay and Al and Fe oxides content) than on soil 2. Moreover, hysteresis affected the adsorption/desorption processes. Experimental data were fitted to a pseudo-first order equation, resulting qamax (adsorption maximum) values that were higher for soil 1 than for soil 2, and indicating that CTC competed with TC more intensely than OTC in soil 1. Regarding soil 2, the values corresponding to the adsorption kinetics constants (ka) and desorption kinetics constants for fast sites (kd1), followed a trend inverse to qamax and qdmax respectively. In conclusion, competition affected adsorption/desorption kinetics for the three antibiotics assayed, and thus retention/release and subsequent transport processes in soil and water environments.