Occurrence, accumulation, attenuation and priority of typical antibiotics in sediments based on long-term field and modeling studies.

Long-term field and modeling studies were performed to measure and predict occurrence, accumulation, attenuation and priority of typical antibiotics in sediments of the Dagu River in China. The results indicated that the concentrations of antibiotics ranged from lower than the limit of detection to 12.4mg/kg, depending on the accumulation time of these antibiotics in sediments. Compared with the residential and industrial areas, the agricultural region of the watershed was a major source of antibiotic contamination in sediments. Accumulation and attenuation kinetics models were established and successfully applied in the field study. For instance, by 2100, the accumulation model predicted that the concentrations of roxithromycin and oxytetracycline would rise to 13 and 7.3mg/kg, respectively. The first and second order attenuation kinetics models revealed the fate of these antibiotics along the downstream and upstream sediments, respectively. The half-life distances of antibiotic attenuation ranged from 3.5 to 12.4km. Based on the contamination level and trend, a priority factor and an accumulation growth factor were defined to identify the priority pollutants from the antibiotics. Gentamicin and roxithromycin were recognized as the top priority pollutants among the tested antibiotics. In the future, a wider applicability of the methods and models needs to be explored and suggested.