Fate of lincomycin in snowmelt runoff from manure-amended pasture.

Livestock manure containing antimicrobials becomes a possible source of these compounds to surface and ground waters when applied to agricultural land as a plant nutrient source. The potential for the transport of the veterinary antimicrobial, lincomycin, to surface waters via snowmelt runoff was assessed following field-scale fall injection of liquid swine manure into perennial grassland in Saskatchewan, Canada. This was achieved by monitoring snow melt runoff which accumulated in nineteen closed basin depressions, four ephemeral wetlands and two dugouts (small constructed reservoirs), approximately 6 months after manure injection. Following solid-phase extraction of the snowmelt runoff samples, LC-MS-MS was used to quantify lincomycin in the extracts. Lincomycin was detected in all snowmelt samples and concentrations in the closed basin depressions, ephemeral wetlands and dugouts ranged from 0.008 to 0.84 microgL(-1). Significantly higher concentrations in the closed basin depressions most likely occurred because the liquid manure was injected directly into the depressions and because snow, which had accumulated in the ephemeral wetlands, and water, which remained in the dugouts from the previous year, would have diluted snowmelt runoff entering these water bodies. The time for 50% dissipation (DT50) of lincomycin concentrations in the two dugouts and in two of the ephemeral wetlands which retained snowmelt runoff for greater than 4 weeks ranged from 18 to 49d. This study demonstrates that the management practice of fall incorporation of liquid manure from confined animal feeding operations into pasture land may result in antimicrobial transport to surface waters via snowmelt runoff.