Sorption and Desorption Characteristics of Tylosin in Three Louisiana Soils and Clay Minerals

Abstract

Tylosin, a macrolide class and widely used antibiotic in animal production, could contaminate environment through manure application to soil and further to river and ground water. Tylosin transport and movement in the environment are largely determined by its sorption and desorption in soils, which are poorly understood so far. Therefore, the purpose of this study was to determine (1) the optimal conditions for tylosin stability, (2) sorption and desorption characteristics of tylosin by poultry litter-impacted three Louisiana soils and (3) sorption and desorption of tylosin by selected clay minerals, the main components of soil which have strong potential application in environmental clean-up. To this end, tylosin stability was evaluated in terms of light exposure (light and dark), solvents (H2O and 0.01M CaCl2), pH (4.5 to 7.5), and temperature (4 oC and 25 oC) conditions. Sorption and desorption of tylosin were carried out at different pHs with three Louisiana soils namely Briley, Ruston and Savannah with or without organic matter being removed. For clay minerals, tylosin sorption and desorption were carried out with montmorillonite, kaolinite and illite. Tylosin in 0.01M CaCl2 was stable under light at pH 4.5, 6.0 and 7.5, and at 25 oC for about 12 days. Tylosin sorption was well described by the Freundlich equation, with sorption in the order of Briley > Savannah > Ruston. Tylosin sorption was affected by pH, with higher sorption at acid pH for Briley, and at pH 6 to 7 for Ruston and Savannah, but with low sorption as pH further increased. Removal of organic matter dramatically increased tylosin sorption and changed sorption pattern at lower pH < 6. Tylosin desorption was in the order of Ruston > Briley > Savannah, with higher desorption under acid conditions, and lower desorption between pH 6.0 to 7.5. Tylosin was strongly sorbed by monotmorillonite followed by illite and kaolinite, and desorption in the order of illite > kaolinite > montmorillonite. The results indicated that both pH and organic matter significantly affected tylosin sorption and desorption behaviors in soil and three clay minerals exhibited different degree of sorption strength as reflected by the difference in desorption.