Veterinary antibiotics (VAs), such as sulfamethazine (SMZ) are released into the environment by application of manure to agricultural fields. Understanding the fate and transport of VAs is important for assessing and mitigating possible environmental hazards. To study the effects of dissolved organic matter (DOM), soil series, soil solution chemistry, and vegetative management on the behavior of sulfamethazine in soil, sorption and column transport experiments were conducted.

Sorption experiments of SMZ were performed on three soils from Missouri planted to agroforestry buffers, grass buffers and row-crops with and without the presence of manure-derived DOM. The results show that sulfamethazine does not bind with DOM directly.  However, presence of DOM (150 mg C L^-1) resulted in lower adsorption coefficient values at intermediate initial SMZ concentrations. Sulfamethazine adsorption isotherms were best fit with the Freundlich adsorption model. Agroforestry buffer soils have significantly higher SMZ sorption capacity than grass buffer soils and cropped soils. Increasing pH resulted in decreased sorption on Armstrong grass buffer soil; however, pH change showed little effect on SMZ sorption to Huntington grass buffer soil. Multiple linear regression analyses indicate that organic carbon content, pH, initial SMZ concentration and clay content were the most important soil properties controlling SMZ adsorption.

Transport of ¹⁴C-labelled SMZ was studied in repacked soil columns containing Huntington crop soil and Huntington agroforestry buffer soil at a constant flow rate of 0.28 cm h^-1 under saturation with and without the presence of manure-derived DOM. Leachate was collected every half hour and analyzed for SMZ concentration. Breakthrough curves were constructed for both the bromide tracer and ¹⁴C-labelled SMZ. Breakthrough curves were fitted using the HYDRUS-1D model and transport parameters were estimated. Preliminary results show that breakthrough curves can be best fit with a three-site Freundlich adsorption model, and DOM has a slight effect on enhancing SMZ transport through the columns.