Effective remediation and phytotoxicity assessment of oxytetracycline and Cd co-contaminated soil using biochar

Heavy metal-antibiotic complex contamination in soil has raised much attention. Biochar is a common soil conditioner and pollutant barrier agent. However, there has rare research about biochar control effectiveness on heavy metals and antibiotics in plant-soil system. This work evaluated the impact of applying unmodified biochar (M) and H3PO4-modified biochar (PM) on Cd, OTC, and antibiotic resistance genes (ARGs) distribution in pakchoi (Brassica chinensis L.) and soil by pot experiment. Biochar can improve quality, antioxidative defense responses of plant and enzymes activity, physiochemical properties, microbial community of soil. The content of OTC, Cd, and ARGs in pakchoi were significantly reduced after applying biochar. There was a 73.08–78.48% decrease rate in relative abundance of ARGs, 58.96%–59.66% decrease rate in OTC content, and 71.65%–79.64% decrease rate in available Cd content when biochar had been added to soil with OTC and Cd contaminations. The addition of 1.5% biochar converted exchangeable Cd to residual fraction. Furthermore, applying PM biochar led to a greater reduction in Cd mobility and OTC in soil and their accumulation in pakchoi compared to M biochar. The biochar also mitigated the OTC and Cd phytotoxicity and improved plant quality and soil enzymes activity. Biochar could reduce Proteobacteria, Actinobacteria, Planctomycetes, Gemmatimonadetes, and Firmicutes abundancies. Soil organic matter accounted for the greatest proportion of variation in ARGs. Overall, the use of biochar, particularly PM biochar, was a promising approach for remediating soil contaminated with multiple pollutants.