Degradation of tetracycline, sulfamethazine, and tylosin in soil from prairie strips and row crops in Iowa

Abstract

The livestock industry in the United States relies on antibiotics for disease prevention and treatment. As a result, antibiotic-laden manure is frequently applied to farmland to recycle nutrients. In the soil environment, antibiotics may accumulate and create selective pressure for antibiotic resistance in bacteria or travel to nearby water resources. This in vitro incubation study evaluated whether prairie buffer strips on farmland enhance degradation of three antibiotics—tetracycline, sulfamethazine, and tylosin—compared with degradation in soil from row crops adjacent to the strips. Soil from prairie strips of varying establishment ages and adjacent row crops were evaluated from three central Iowa sampling locations. Antibiotics mixed with swine manure slurry were added to soils at a starting concentration (10 μg kg–1) that reflects common veterinary antibiotic concentrations in soil and runoff after manure application. Antibiotic concentrations were quantified at six time points throughout a 72-d incubation period and fit to a first-order model to calculate decay rate constants and half-lives. The mean half-life for tetracycline was 0.54 d longer in prairie strip soil than row crop soil, whereas sulfamethazine and tylosin demonstrated no significant difference in persistence in strip or crop soil. Time since the establishment of the prairie strip did not affect antibiotic persistence. Concentrations of each antibiotic decreased to near-background levels throughout the incubation period. This study suggests that prairie strips do not consistently enhance antibiotic degradation in farm fields, but that antibiotics are unlikely to persist throughout the growing season in soil under strip or crop management.