Plot-scale observation on antibiotics migration in surface runoff and leachate from chicken-raising orchard of Entisol during rainstorms.

Field investigation on manure-sourced veterinary antibiotics migrating via runoff processes under natural rainfalls is quite limited due to hydrological complexity. The impact of manure application on antibiotics migration in soil is also scarcely discussed at the plotscale. This study examined the dynamic changes of concentration and mass flux of eight antibiotics migrating from chicken-raising orchards during rainstorms. Results showed instantaneous presence of antibiotics in the flow samples collected upon generation of surface runoff and leachate. Their concentrations responded strongly towards the flow rate, with concentration peaks mostly overlapping with flow peaks. Chicken-raising treatment resulted in significantly higher runoff generation than orchard without chickens. The total mass flux of antibiotics reached up to 5.46 and 9.41 μg/(m2·h) for surface runoff and leachate respectively, with sulfonamides (SAs) showing the highest migration (0.02-4.52 μg/(m2·h)) and tetracyclines (TCs) and quinolones (QLs) the lowest (10-4-10-1 μg/(m2·h)). Leaching performed as an important pathway for contaminant migration in the studied soil, with mass fluxes 1.5-11 times higher than those of surface runoff, and manure-derived colloids accelerated antibiotics leaching. pH, colloid concentration and instantaneous rainfall intensity were the primary influencing factors, all displaying positive correlations with antibiotics migration (p < 0.05). This study implied that raising chickens in orchard poses a risk of antibiotic contamination to surrounding ecosystem. It also highlighted the importance of exploring soil hydrological process in assessing their migration, particularly the previously underestimated contribution of subsurface flow via leaching.