Assessing the Impact of Sewage Sludge-Chinese Medicinal Herbal Residues-Biochar Amendment on Antibiotic Resistance Genes in Soil-Plant Systems

Sewage sludge (SL), Chinese Medicinal Herbal Residues (CMHRs), and Biochar (BC) raw materials are often considered as waste. However, their potential use in mitigating the environmental impact of antibiotics and antibiotic resistance genes (ARGs) is significant. This study investigates the impact of different proportions of SL-BC and SL-CMHRs-BC on the distribution of nine common ARGs in soil-plant systems. Varying proportions of SL-BC and SL-CMHRs-BC (0%, 5%, 10%, and 20%) have been applied in ARGs-contaminated soils for the lettuce growth planting experiments. Lettuce is irrigated with antibiotics-contaminated water with low or high levels of antibiotics to assess the potential for antibiotics and their corresponding ARGs to enter the food web. The results showed that the SL-CMHRs-BC amendments significantly reduced the abundance of ARGs and the concentration of antibiotics in both soils and lettuce tissues. 20% SL-CMHRs-BC amendment was found to be the most effective proportion for reducing antibiotic concentrations and their corresponding ARGs in soil and lettuce. Six ARGs (tetA, tetC, tetO, sulI, sulII, and sulIII) were found in higher concentrations in soil and lettuce tissues than the remaining three ARGs (tetB, tetE, tetM). A strong correlation was observed between the abundance of ARGs and the concentrations of their respective antibiotics in all soils and lettuce tissues. These findings underscore the potential of SL-CMHRs-BC in mitigating the risks associated with the spread of antibiotics and ARGs, a healthier food system can be promoted through the co-application by reducing the risk of antibiotic resistance transmission through the food web.