Sorption characteristics of oxytetracycline, amoxicillin, and sulfathiazole in two different soil types

We performed this study to investigate the influences of soil pH and soil organic matter content on the sorption behaviors of veterinary pharmaceuticals (VPs; oxytetracycline, amoxicillin, and sulfathiazole) in two different soil types (silt loam and sandy loam). We evaluated both the Langmuir and Freundlich sorption isotherms and found that the Freundlich sorption isotherm fit the data better than did the Langmuir sorption isotherm because the coefficient of Freundlich sorption isotherm (> 0.8) was considerably greater than those of the Langmuir sorption isotherm (< 0.4). The sorption capacities of the VPs increased with decreasing soil pH and increasing soil organic matter content. The sorption capacities of the VPs in silt loam soil were greater than those in sandy loam soil. Furthermore, our results indicated that amoxicillin and sulfathiazole were highly mobile in soils and could therefore be rapidly transported to field drains and ultimately entered surface waters. However, oxytetracycline was highly sorbed in clay minerals under acidic and high soil organic matter conditions. Together, our results indicated that the sorption of VPs by soil was influenced by environmental factors such as soil pH, soil organic matter content, and soil texture.