Antibiotics are extensively used in human health care and livestock industry, resulting in rapid increases in their environmental concentrations. These anthropogenic antibiotics are considered emerging contaminants, and their increased concentrations in the environment have raised serious concerns on the proliferation of antibiotic resistant bacteria and associated impacts to human and ecosystem health. Therefore, innovative management strategies are needed to manage the risks of antibiotic resistance. Engineered black carbon (BC) materials (e.g., biochars and activated carbon) may be used as sorbents to sequester antibiotics from contaminated soils and waters in situ, thus decreasing the mobility and bioavailability of antibiotics in the environment. To this end, a better understanding of mechanisms controlling the sorption of antibiotics to BC (specifically biochars) is critically needed for developing scientifically-sound mitigation strategies. The first research topic aimed to investigate sorption of lincomycin (one class of antibiotics) to manure-based biochars and their potentials for the long-term lincomycin immobilization. Lincomycin sorption to biochars was greater at solution pH (6.0–7.5) below the pKa of lincomycin (7.6) than at pH (9.9–10.4) above its pKa. The enhanced lincomycin sorption at lower pH likely resulted from electrostatic attraction between the positively charged lincomycin and the negatively charged biochar surfaces. This was corroborated by the observation that lincomycin sorption decreased with increasing ionic strength at lower pH (6.7) but remained constant at higher pH (10). Long-term lincomycin sorption was characterized by two-stage kinetics with fast sorption reaching quasi-equilibrium in the first two days, followed by slow sorption over the long term. The fast sorption was primarily attributed to surface adsorption, whereas the long-term slow sorption was controlled by slow pore diffusion. Specially, lower-temperature (300°C) biochars had higher sorption capacity and faster sorption kinetics than higher-temperature (400–600°C) biochars. The continuous release of dissolved organic carbon (DOC) from the lower-temperature biochars may enhance the lincomycin sorption by decreasing biochar particle size and/or increasing the accessibility of sorption sites initially blocked by DOC. This study further quantified and characterized the DOC extracted by deionized water, 0.1 M HCl, and 0.1 M NaOH from 46 biochars produced from diverse feedstocks and pyrolysis conditions. A quick, easy and robust UV-vis spectrometric method was developed to measure the DOC concentrations in diverse biochar samples. Our findings highlight that biochars may have the potential to be used as soil amendment to immobilize antibiotics in situ over the long term. The second research topic was to understand the unintended consequence of BC nanoparticles on the transport of antibiotics in soils. BC nanoparticles are ubiquitous in nature, and may act as carriers to facilitate the transport of antibiotics. Hence, we investigated the facilitated transport of three veterinary antibiotics (lincomycin, oxytetracycline, and sulfamethoxazole) by BC nanoparticles in saturated sand columns at solution pH of 7, and ionic strength of 0.1, 1, or 10 mM. The total transport of antibiotics was enhanced in the presence of BC nanoparticles in low-salinity water, but decreased at high-salinity water, implying that the facilitated transport of antibiotics may occur under rainfall or irrigation that can decrease soil salinity.
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