Tile Drainage Management Influences On the Movement of Veterinary Antibiotics to Groundwater and Surface-Water Following Liquid Swine Manure Application On Macroporous Clay Loam.

The spread of veterinary antibiotics (VAs) in the environment presents a risk to soil, groundwater, and surface-water systems, and the biota that rely on these systems. This talk highlights results from a field experiment designed to evaluate the fate and transport characteristics of liquid-swine-manure (LSM) borne VAs and their degradation products, under controlled (CD) and free draining (FD) tile drain conditions. Preliminary analysis shows that of the four VAs (tylosin, chlortetracycline, tetracycline, and oxytetracycline) and their associated products (4-epichlortetracycline, isochlortetracycline (ISOCTT), 4-epitetracycline, 4-epianhydrotetracycline, anhydrotetracycline) detected in the LSM, 17 – 28 % of the ISOCTT total mass was in the LSM liquid phase, while 0 – 4 % of the mass of the other species was in the liquid phase. Correspondingly, ISOCTT was also the most prevalent VA species in shallow groundwater and surface-water following LSM application.

Drainage management was found to influence VA transport. Under FD conditions, VAs were detected in tile effluent within one hour of LSM application. Under CD conditions, tiles did not flow until the first post application rainfall, which resulted in the abatement of application induced movement of VAs to surface water. During periods when all tiles (CD and FD) were flowing, the concentration of VAs was significantly higher (p ≤ 0.05) in tile effluent from the CD plots. However, because tile flow rates were lower at the CD plots, no significant difference in total mass loading rates between CD and FD conditions was observed. In shallow groundwater there was no significant difference in VA concentration between the CD and FD conditions, and in both drainage management scenarios VAs were detected in groundwater within 2 d, and absent within 126 d of LSM application.