Sorption and Degradation of Tetracycline and Tylosin in Dairy Lagoon Sediment Suspensions.

Tetracycline and tylosin has been widely used in animal production for preventing and treating diseases.  This study investigates the environmental factors controlling the behaviors of these antibiotics in dairy lagoon sediments. A laboratory microcosm incubation study was conducted on dairy lagoon sediments suspension under different pH (5.5, 7.0, 8.5) and redox potentials (E_h at -100 mV, 0 mV, +250 mV, + 350 mV).  Tetracycline was strongly sorbed by sediment and influenced little by changes in pH and redox potential conditions. Adsorption was the major mechanism of the tetracycline removal from the solution phase.  On the other hand, tylosin sorption and degradation was greatly affected by suspension pH and redox potential.  Under acidic (pH 5.5) and reduced (E_h -100 mV) condition, tylosin persisted in the solution phase of dairy lagoon sediment suspension much longer with resident time 77 days. Under oxidized (E_h +350 mV) condition, microbial degradation removed 68-75% of tylosin from the solution phase at pH 5.5 and 32-75% at pH 7.0 during the 20 day incubation.  In addition, at pH 8.5, abiotic transformation of tylosin A into unknown degradates rather than sediment adsorption and microbial degradation was the major mechanism controlling tylosin disappearance from the solution phase regardless of the status of redox potentials. These results have significant implications in understanding and managing tetracycline and tylosin in dairy lagoon sediment suspensions.