Abstract/Summary

The objective of this study was to determine the fate of commonly used veterinary antibiotics in their naturally excreted form when manure-based amendments are applied to soil. Beef cattle were administered sulfamethazine, tylosin, and chlortetracycline and dairy cows were treated with pirlimycin according to standard animal production practice. The resulting manure was composted for 42 days under static or turned conditions and applied at agronomic N rates to sandy, silt, and silty clay loam soils and compared with amendment with corresponding raw manures in sacrificial microcosms over a 120-day period. Antibiotic dissipation in the raw manure-amended soils followed bi-phasic first order kinetics. The first phase half-lives for sulfamethazine, tylosin, chlortetracycline, and pirlimycin ranged from 6.0 to 18 days, 2.7 to 3.7 days, 23 to 25 days, and 5.5 to 8.2 days, respectively. During the second phase, dissipation of sulfamethazine was negligible, while the half-lives for tylosin, chlortetracycline, and pirlimycin ranged from 41 to 44 days, 75 to 144 days, and 87 to 142 days, respectively. By contrast, antibiotic dissipation in the compost-amended soils followed single-phase first order kinetics with negligible dissipation of sulfamethazine and half-lives of tylosin and chlortetracycline ranging from 15 to 16 days and 49 to 104 days, respectively. Pirlimycin was below the detection limit in the compost-amended soils. After incubating 120-days, antibiotics in compost-amended soils (up to 3.1 ug/kg) were significantly lower than in the manure-amended soils (up to 19 ug/kg; p<0.0001), with no major effect of soil type on the dissipation. Risk assessment suggested that manure composting can reduce antibiotic resistance selection potential in manure-amended soils.