Antibiotics have been widely used for agriculture, aquaculture, and livestock, as well as for human disease treatment, in recent decades. However, antibiotics cannot be completely absorbed, and most of them are excreted through urine and feces. A substantial part of the antibiotics enter soils through fertilization and irrigation. Antibiotics persist in the soil environment and threaten human and ecological security. Identifying the composition, distribution, and factors affecting antibiotics in soils with different land use types can help in understanding the spatial distribution and migration processes of antibiotics. In this study, a typical peri-urban catchment located in the Yangtze River delta was selected as the study area, and 82 sampling sites were selected based on land use and topographical features. Soil samples were collected at depths of 0-40 cm at each sampling site. The types and quantity of antibiotics in each soil sample were identified and analyzed by using HPLC-MS/MS in the laboratory. The composition and concentration of antibiotics in different soil layers and the land use types were compared, and the factors affecting the spatial distribution of soil antibiotics were analyzed. Results from this study showed that the total concentration of antibiotic compounds (total) ranged from 0.05 μg·kg-1 to 395.55 μg·kg-1 in the study area, and a significant spatial distribution of antibiotics was found between different land use types. The total in cropland ranged from 0.35 μg·kg-1 to 395.55 μg·kg-1, and tetracyclines (TCs) were the dominant antibiotics (81.45%). The total in forestland ranged from 0.07 μg·kg-1 to 3.65 μg·kg-1, with values significantly lower than those in cropland (P<0.05). The total in orchard soil were significantly lower than in cropland (P<0.05), and no significant differences in antibiotics were found between orchards and forestland (P>0.05). The analysis of the composition and quantity of antibiotics in the soils showed that tetracyclines (TCs) and quinolones (QNs) were the dominant antibiotic types in orchards (TCs:67.63%, QNs:29.55%) and forestland (TCs:13.25%, QNs:70.04%). The indices, including distance to town, distance to road, elevation, and C/N value in soils, were selected to explore the influence of human activity on soil antibiotic concentration. Results of the correlation analysis showed that the concentration of soil antibiotics decreased with increasing values of the four indices. This indicated that the concentrations of soil antibiotics in peri-urban areas were dominantly affected by land use and its spatial distribution, and the concentrations increased with the intensity of human activities. Results of this study can provide scientific guidance for soil management and soil security.
Keywords: affecting factors; antibiotics; land use; soils; spatial distribution.