Biodegradation of veterinary antibiotics in lagoon waters

The occurrence and fate of veterinary antibiotics in lagoon water and animal manure are an emerging area of interest due to the potential impact of these compounds on the aquatic environment. The objective of this study was to evaluate the degradation of oxytetracycline (OTC), sulfamethoxazole (SMX), tylosin (TYL), and monensin (MON) in dairy lagoon waters under aerobic and anaerobic conditions. Biodegradation of OTC, SMX, TYL and MON occurred at both 20 °C and 4 °C under aerobic and anaerobic conditions. More than 88% of all antibiotics were degraded at 20 °C under aerobic treatment. Concentrations decreased at 4 °C, but none of these compounds completely biodegraded in either treatment within 242 days at 4 °C. Calculated first-order degradation half-lives of OTC, SMX, TYL and MON at 20 °C were 12, 6.5, 16, and 9.2 days, respectively, under aerobic treatment and 17, 59, 19, and 71 days, respectively, under anaerobic treatment. At 4 °C, half-lives were 80, 204, 46, and 128 days, respectively, under aerobic treatment and 110, >242, 103, and 193 days, respectively, under anaerobic treatment. Therefore, these results show that degradation of antibiotics, in general, is faster under aerobic conditions, compared to anaerobic conditions. It was found that lower temperature (4 °C) reduced the biodegradation rate of antibiotics.