Degradation of sulfamethazine, tetracycline, and tylosin in prairie strip soils and row crop soils
The livestock industry in the United States is heavily reliant on veterinary antibiotics for disease prevention and disease treatment. These compounds go on to be excreted into manure, which is applied to farmland as fertilizer. Once introduced to the soil environment, there is risk that these compounds can accumulate and create selective pressure for antibiotic resistant bacteria strains, or travel to nearby water resources, where they may come into contact with humans. The goal of this study was to determine whether the incorporation of prairie buffer strips on farmland may enhance degradation rates of these antibiotic compounds and thus lower the risk they pose to humans.
A lab-based incubation study was conducted to test degradation rates of sulfamethazine, tetracycline, and tylosin mixed with swine manure slurry in a soil environment at a starting concentration of 10 μg kg-1 to reflect common veterinary antibiotic concentrations in soil and overland runoff following manure application. Two soil treatments, prairie strip soil and row crop soil, were evaluated from three different sampling locations in central Iowa. Antibiotic concentrations were quantified at six time points throughout a 72-day incubation period using LC-MS and fit to the first-order rate equation to calculate decay-rate and half-lives. Tetracycline degraded significantly faster in row crop soil than prairie strip soil, while sulfamethazine and tylosin demonstrated no significant difference. Each antibiotic returned to near-background levels over the course of the incubation period. This study suggests that prairie strips may not serve as a mechanism to enhance antibiotic degradation in farm fields, but that antibiotics are unlikely to persist throughout the growing season in either crop soil or strip soil.