Antibiotic residues in agricultural soils are an emerging environmental concern, with potential impacts on soil health, crop safety, and the spread of antimicrobial resistance. A new study published in Biochar reports a promising solution: an iron-modified biochar that helps soil use its own oxygen and iron chemistry to break down sulfamethoxazole, a commonly detected antibiotic pollutant.
The research team developed a Fe-loaded biochar, named BC-Fe, from waste sawdust through a pyrolysis, impregnation, and second pyrolysis process. Unlike conventional advanced oxidation technologies that often rely on added chemical oxidants, this approach uses naturally abundant oxygen in soil and activates it through iron redox cycling to generate hydroxyl radicals, highly reactive molecules that can degrade organic contaminants.
"Our goal was to design a soil-friendly material that could work with natural biogeochemical processes rather than overwhelm them," said corresponding author Lei Zhang. "By combining biochar's electron transfer capacity with active iron species, we created a catalyst that can continuously support pollutant oxidation in soil."
The key material, HBC-Fe400, showed the strongest performance. It contained optimized iron loading and a high proportion of Fe(II), allowing it to act both as an electron highway and a redox modulator. In simple terms, the biochar stores and transfers electrons, while the iron repeatedly cycles between Fe(II) and Fe(III). This paired "charging and discharging" process sustains the activation of oxygen and promotes long-lasting hydroxyl radical production.
In laboratory soil incubation tests, HBC-Fe400 triggered a 4.2-fold increase in hydroxyl radical production, reaching 881.6 μM. The material also maintained a 3.58-fold enhancement under field conditions, suggesting that the strategy may remain effective beyond controlled laboratory systems.
The researchers found that the system worked through two coordinated pathways. One was a direct pathway, in which the iron-modified biochar catalyzed oxygen activation. The other was an indirect pathway, in which the biochar stimulated soil iron cycling and microbial Fe(III) reduction, further increasing Fe(II) availability. Together, these pathways created a self-reinforcing Fenton-like process in soil.
Importantly, the material also achieved strong pollutant removal. Under favorable soil moisture conditions, sulfamethoxazole degradation reached 81.2%. Chemical analysis showed that the antibiotic was broken down through three main pathways: opening of the isoxazole ring, hydroxylation, and cleavage of the S-N bond. Toxicity prediction and plant tests indicated that degradation products became less harmful, and remediated soil supported better cherry radish seed germination, fresh weight, and stem growth compared with contaminated soil.
"This study shows that biochar can do more than immobilize contaminants," Zhang said. "With proper design, it can actively regulate electron transfer, stimulate soil iron cycling, and drive cleaner degradation of antibiotics in farmland."
The findings point to a waste-to-remediation strategy that transforms sawdust into a functional material for soil cleanup. By relying on oxygen and naturally occurring iron chemistry, the approach could reduce the need for aggressive chemical oxidants and help protect soil ecological functions.
The authors note that future studies should further evaluate long-term field performance, different soil types, and the fate of degradation products under realistic agricultural conditions. Still, the work provides a new blueprint for designing advanced iron-based biochar catalysts for sustainable pollution control and safer agricultural production.
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Journal Reference: Du, H., Zhang, L., Liu, W. et al. In-situ and long-enduring oxidation of SMX by Fe-modified biochar activated O2 in soil: bridging Fe-redox cycling and electron transfer modulation. Biochar 8, 76 (2026).
https://doi.org/10.1007/s42773-026-00585-0
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
