Adsorptive Inhibition of Antibiotic Resistance Gene Proliferation and Transmission By a Wet-State Biochar-Ferrihydrite Composite

Decreasing bioaccessible antibiotics, heavy metals, and antibiotic resistance genes (ARGs) in soil by adsorption is an attractive, but unrealized, approach for reducing (co)selection pressure from antibiotics and heavy metals on bacteria and ARG horizontal transfer to pathogens for ARG risk reduction. Here, a wet-state biochar-ferrihydrite composite (BC-Fe(W)) synthesized by loading ferrihydrite onto rice straw-derived biochar was examined for i) adsorption of oxytetracycline and Cu 2+ to reduce (co)selection pressure and ii) adsorption of extracellular antibiotic resistance plasmid pBR322 to inhibit ARG horizontal transfer. BC-Fe(W) gained the adsorption priority of biochar (for Cu 2+ ) and wet-state ferrihydrite (for oxytetracycline and pBR322) and showed adsorptive enhancement (for Cu 2+ and oxytetracycline) from a more wrinkled and exposed surface from biochar silica-stabilized ferrihydrite, and the adsorption capacity for BC-Fe(W) was 17~135 times that of soil. Correspondingly, 10 g/kg BC-Fe(W) amendment increased the soil adsorption coefficient K d by 31%~1417% and reduced the selection pressure from dissolved oxytetracycline, co-selection pressure from dissolved Cu 2+ , and horizontal transfer frequency of pBR322 (assessed with Escherichia coli ). These results demonstrate the effects and mechanism of biochar modified with ferrihydrite on soil ARG pollution reduction, presenting a new practical strategy for ARG pollution control via simultaneous adsorptive inhibition of ARG proliferation and transmission