Biochar reduces antibiotic transport by altering soil hydrology and enhancing antibiotic sorption

The performance of biochar (BC) in reducing the transport of antibiotics under field conditions has not been sufficiently explored. In repacked sloping boxes of a calcareous soil, the effects of different BC treatments on the discharge of three relatively weakly sorbing antibiotics (sulfadiazine, sulfamethazine, and florfenicol) via runoff and drainage were monitored for three natural rain events. Surface application of 1% BC (1%BC-SA) led to the most effective reduction in runoff discharge of the two sulfonamide antibiotics, which can be partly ascribed to the enhanced water infiltration. The construction of 5% BC amended permeable reactive wall (5%BC-PRW) at the lower end of soil box was more effective than the 1%BC-SA treatment in reducing the leaching of the most weakly sorbing antibiotic (florfenicol), which can be mainly ascribed to the much higher plant available and drainable water contents in the 5%BC-PRW soil than in the unamended soil. The results of this study highlight the importance of BC’s ability to regulate flow pattern by modifying soil hydraulic properties, which can make a significant contribution to the achieved reduction in the transport of antibiotics offsite or to groundwater. Environmental Implication Veterinary antibiotics may be transported from farmland to rivers via runoff and leached into groundwater. It is necessary to evaluate the performance of BC, a versatile soil amendment, in reducing the transport of antibiotics under field conditions, and to understand the underlying mechanisms. This field study revealed that both the changes in soil hydrology and the improvement of antibiotic sorption induced by BC treatments play an important role in controlling antibiotic discharge via runoff and drainage.