Fate of Antibiotics and Antibiotic Resistance Genes after Land Application of Swine Manure.

Livestock wastes generated from confined animal feeding operations (CAFOs) represent a major source of antimicrobials and antimicrobial resistance genes (ARGs) in the environment when these wastes are applied to land.  In this study, we investigated the influence of various land application strategies on the fate and transport of antimicrobials and ARGs after land application of swine manure slurry.  We also investigated the potential for antimicrobial and ARG removal from runoff in the presence of a narrow grass hedge.   Finally, we evaluated the influence of rainfall timing relative to manure application.  Manure was applied and rainfall simulation experiments were performed at 1 week, 2 week or 3 week intervals to evaluate if degradation processes at the soil surface would reduce antibiotic or ARG occurrence in runoff.  We determined that broadcast (surface) application resulted in higher antmicrobial and ARG concentrations in runoff, but runoff concentrations were reduced when runoff passed through the narrow grass hedge.  Finally, our initial results indicate that increased timing between manure application and rainfall may lead to reduced antimicrobial concentrations in runoff, however ARG concentrations were not influenced by the timing of rainfall.