Enhancing oxytetracycline degradation and reducing its transfer to lettuce using biochar combined with carbohydrate carbon sources

Abstract Biochar has been widely recognized for its ability to adsorb soil antibiotics (like oxytetracycline, OTC) and inhibit their translocation to plants, but there remain limitations in further reducing OTC toxicity. In this study, lettuce was used as the test crop, with treatments including biochar alone (BC), biochar combined with carbohydrate carbon sources (CCS), and a control treatment without biochar (CK). Specifically, the treatments that combined biochar and CCS included biochar-glucose (BCG), biochar-sucrose (BCSU), and biochar-starch (BCST). The objectives were to improve the soil degradation efficiency of OTC, lower its toxicity, reduce its transfer to lettuce roots and leaves, and promote lettuce growth. In addition, the study explored the mechanisms of soil improvement and OTC degradation when biochar was combined with CCS. The results showed that BC increased the soil OTC degradation efficiency by 22–67% and reduced the translocation of OTC to lettuce leaves by approximately 0.51–1.23 mg kg −1 , while slightly increasing microbial activity. By activating redox enzyme activity without reducing soil mineralization, the BCG, BCSU, and BCST treatments significantly enhanced OTC degradation efficiency to 87%, 86%, and 92%, respectively. However, because low-molecular-weight sugars metabolize quickly, the BCG and BCSU treatments did not maintain a prolonged enhancement of soil enzyme activity and OTC degradation efficiency. In contrast, the BCST treatment exhibited superior performance, characterized by a gradual increase in soil enzyme activity, a 55% increase in microbial biomass carbon (MBC) throughout the experimental period, and a reduction in the OTC half-life to approximately 8 days. Furthermore, there were no significant differences in lettuce biomass among the treatments, but the BCST significantly improved nitrogen uptake and Soil and Plant Analyzer Development (SPAD) values in lettuce. These findings provide an effective strategy for promoting the degradation of non-prescription drugs and offer valuable insight for further eliminating antibiotics from soil. Highlights Biochar accelerated soil OTC degradation by 22–67% and reduced OTC transfer to lettuce leaves. Carbohydrate carbon sources promoted soil OTC degradation by activating oxidoreductase activity. Compared to biochar with glucose and sucrose, biochar combined with starch was more effective in degrading OTC. Graphical Abstract