Vertical migration of antibiotics during rainfall throughout a year in long-term manure-fertilized soils differing in pH.

The vertical migration behavior of antibiotics in long-term manure-fertilized soils during rainfall remains unclear. Here, we examined antibiotics in soil profiles (0-60 cm) and leachates following each rainfall event throughout a year for three soils (acidic, neutral, and calcareous) with a 13-year history of manure application. The total concentrations of all the antibiotics in the soil profile (11.04-190.32 μg/kg) and the yearly cumulative load of these antibiotics in the leachate (4070-6900 ng/m2) were significantly higher in the acidic and neutral soils than in the calcareous soil. Rainfall caused the migration of antibiotics (especially tetracyclines, quinolones, and sulfonamides) from soil to leachate, while the migration dynamics of some antibiotics differed among the three soil profiles. Random forest analysis revealed that precipitation, soil organic carbon content, pH, sand content, and the partition coefficient (Kow) of antibiotics were the key factors influencing the migration of antibiotics. Environmental risk assessment suggested that antibiotics in leachates pose low toxicity risks to aquatic organisms. Nevertheless, the vertical migration of some antibiotics (e.g., sulfachaloropyridazine and sufamerazine) was positively correlated with the dissemination of high-risk antibiotic resistance genes in leachates. This study advances our understanding of the precipitation-caused vertical migration of antibiotics in soil exposed to manure application, considering future increases in severe rainfall events.