Dissipation and leaching of oxytetracycline and tylosin in typical agricultural fields

Antibiotics used in livestock production may be present in manure and slurry as parent compounds and/or metabolites. And environments may therefore be exposed to these antibiotics due to the application of animal manure in agricultural lands. In order to understand the environmental fate of two typical antibiotic compounds tylosin (C₄₆H₇₇NO₁₇) and oxytetracycline (C₂₂H₂₄N₂O₉HCl) in agricultural fields, liquid pig slurry was fortified with the antibiotics and then applied on field plots. The leaching, dissipation and surface runoff under field conditions were investigated. The results show that both degradation and leaching behaviors of the antibiotics are related with antibiotic kind and soil property. Vertical migration of the antibiotics is greater in sandy soils than in clay-loam soils. Transfer capacity of tylosin in soils is greater than that of oxytetracycline. Dissipation rate of antibiotics in surface layers is greater in sandy soils than in clay-loam soils at the initial stage, but eventually becomes similar for both soil types. Degradation rate of oxytetracycline in surface soils of both soil types is greater than that of tylosin. It is observed that degradation rates of the antibiotics measured under field conditions are much smaller than those measured under laboratory conditions. This suggests that antibiotics become stable as they enter into the deeper soil layer. Runoff losses of antibiotics mainly occur at the initial stage of manure application. Concentrations of the antibiotics in runoff are greater in sandy soils than in clay-loam soils. Tylosin poses a greater risk of ground surface water contamination.