Sequestration of Antibiotics By Black Carbon to Reduce Their Mobility and Bioavailability.

Global overuse of antibiotics in human medicine and animal agriculture has led to the proliferation of antibiotics and antibiotic-resistant genes in the environment. Antibiotic resistance is becoming a global health threat demanding innovative mitigation measures. In-situ sequestration of antibiotics by soil geosorbents holds great promises to reduce the transport and bioavailability of antibiotics, thus mitigating their adverse impacts on human and ecosystem health. Our recent work investigated the kinetic and quasi-equilibrium sorption behaviors of antibiotics on black carbon, specifically biochars, to help better understand the transport and fate of antibiotics in biochar-amended soils. Using lincomycin as a model antibiotic compound, we screened the 2-day and 30-day sorption potential of 34 biochars produced from a range of feedstock and pyrolysis temperature at pH 6 and 9. Statistical correlation between sorption capacities and biochar properties were then analysed to select the optimal type of biochars for antibiotic sequestration. Lincomycin sorption was controlled by two-step kinetics with the short-term fast sorption completed within the first 2 days and the long-term slow sorption continuing over 6 months. It is perceived that the rapid short-term sorption was controlled by surface reactions and the slow long-term sorption by pore diffusion. The rapid sorption data showed an interplay of solution pH and ionic strength in modulating lincomycin sorption at pH 6.0–7.2, implying the role of electrostatic interaction. Substantial lincomycin sorption could still occur at pH 9.8–10.3, indicating the important contribution from non-electrostatic interactions. Conversely, the sorption of tetracycline by biochars was much faster with equilibrium reached in an hour. Tetracycline sorption was attenuated by the presence of organic acids such as acetic, fumaric, and citric acids. The attenuated effect was greatest for citric acid with three carboxyl groups, and increased with organic acid concentration. Our results indicate that biochars may serve as a long-term sink for antibiotics, modulated by solution chemistry (e.g., pH and organic matter concentrations). Biochar soil amendment would likely alter bioavailability, distribution, fate and transport of antibiotics in soils.