Sorption and transport of veterinary antibiotics in agroforestry buffer, grass buffer, and cropland soils
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Understanding sorption and transport of veterinary antibiotics (VAs) is important for assessing the risk of VAs reaching water resources. Vegetative buffer strips (VBS) may be a useful tool for mitigating veterinary antibiotic transport from agricultural lands. Sorption experiment results showed that oxytetracycline (OTC) was strongly adsorbed and not readily extractable, while sulfadimethoxine (SDT) and sulfamethazine (SMZ) were highly mobile in soil. For all the antibiotics studied, VBS soils had higher sorption capacity than cropland soils. Linear regression analyses indicate that clay content and pH were the most important soil properties controlling OTC and SDT adsorption, respectively. For SMZ, organic carbon content, pH, initial SMZ concentration, and clay content were the most important factors controlling sorption. Dissolved organic matter had a slight negative effect on SMZ sorption. Transport experiments of SMZ were conducted in glass columns repacked with agroforestry and cropland soils. Computer modeling using HYDRUS-1D software indicated that a three-site model containing two reversible sites and one irreversible site coupled with the Freundlich sorption component best describes SMZ transport through the columns. Data from equilibrium sorption experiments and column transport experiments suggest that the AGF soil has a larger capacity to retain SMZ than the cropland soil. Overall, this research facilitates our understanding of VA sorption and transport in the environment and supports the use of vegetative buffers to mitigate VA loss from agroecosystems.