Runoff Losses of Excreted Chlortetracycline, Sulfamethazine, and Tylosin from Surface-Applied and Soil-Incorporated Beef Cattle Feedlot Manure

Veterinary antimicrobials in land-applied manure can move to surface waters via rain or snowmelt runoff, thus increasing their dispersion in agro-environments. This study quantified losses of excreted chlortetracycline, sulfamethazine, and tylosin in simulated rain runoff from surface-applied and soil-incorporated beef cattle (Bos taurus L.) feedlot manure (60 Mg ha(-1), wet wt.). Antimicrobial concentrations in runoff generally reflected the corresponding concentrations in the manure. Soil incorporation of manure reduced the concentrations of chlortetracycline (from 75 to 12 mu g L-1 for a 1: 1 mixture of chlortetracycline and sulfamethazine and from 43 to 17 mu g L-1 for chlortetracycline alone) and sulfamethazine (from 3.9 to 2.6 mu g L-1) in runoff compared with surface application. However, there was no significant effect of manure application method on tylosin concentration (range, 0.02-0.06 mu g L-1) in runoff. Mass losses, as a percent of the amount applied, for chlortetracycline and sulfamethazine appeared to be independent of their respective soil sorption coefficients. Mass losses of chlortetracycline were significantly reduced with soil incorporation of manure (from 6.5 to 1.7% when applied with sulfamethazine and from 6.5 to 3.5% when applied alone). Mass losses of sulfamethazine (4.8%) and tylosin (0.24%) in runoff were not affected by manure incorporation. Although our results confirm that cattle-excreted veterinary antimicrobials can be removed via surface runoff after field application, the magnitudes of chlortetracycline and sulfamethazine losses were reduced by soil incorporation of manure immediately after application.