Antibiotics are used at subtherapeutic levels in swine production for growth promotion, disease treatment, and disease prevention. These antibiotics are not fully metabolized and at subtherapeutic concentrations are thought to be linked to antibiotic resistance. These antibiotics enter the environment through the land application of swine manure. In the Iowa, most agricultural fields are drained using subsurface drainage, lowering the water table and removing excess water from the rootzone. With this movement of water, antibiotics have the potential to enter the subsurface soil and be transported to surface water by drainage systems. The studies described in this dissertation include; monitoring of tylosin and sulfamethazine in a tile drained agricultural watershed using Polar Organic Integrative Sampler (POCIS), the sediment concentrations of tylosin, sulfamethazine, and atrazine, in a tile drained watershed, and investigating the persistence and transport of atrazine and veterinary antibiotics to a tile drain system following swine manure injection.

A reconnaissance study of the South Fork watershed (SFIR) of the Iowa River, was conducted from 2013 – 2015. All analytes were detected, and detection frequencies ranged from 69 – 100% showing the persistence in the watershed. Antibiotics at sub-inhibitory concentrations were detected at a higher frequency using POCIS when compared to grab samples. We observed statistically significant seasonal trends for SMZ and ATZ concentrations during growing and harvest seasons. Time weighted average (TWA) concentrations quantified from the POCIS were 1.87 ng L-1 (SMZ), 0.30 ng L-1 (TYL), and 754.2 ng L-1 (ATZ), in the watershed. SMZ and TYL concentrations were lower than the minimum inhibitory concentrations (MIC) for E. coli. All analytes were detected in tile drain effluent, confirming tile drainage as a pathway for antibiotic transport. SMZ, TYL, and ATZ were detected in instream SFIR sediments, detection frequencies ranged from 42 – 84%. Statistical analysis revealed annual and seasonal significance for sediment TYL concentrations. On an annual basis TYL concentrations were statistically significant in 2013 and 2014. Seasonal significant concentrations occurred during the growing and harvest seasons, which coincide with the heaviest precipitation periods in the watershed, contributing to the transport of TYL via runoff. On a field scale, TYL, SMZ, TET, and ATZ residue concentrations were detected in fields with history of swine manure application. TYL and TET soils residues were concentrated at the 0 – 30 cm soil depth, while ATZ was concentrated from 0 – 60 cm. The detection of TYL and SMZ in tile drainage water indicates their ability to leach from the surface soil where manure slurry was injected. ATZ residues in tile drainage had a detection frequency of 100%, in the absence of application.