Long term biochar aging reshapes antibiotic transport in farmland soils, new study finds
image: Does biochar field aging reduce the kinetic retention for weakly hydrophobic antibiotics in purple soil?
Credit: Xinyu Liu, Yang He, Jinghan Li, Jiahui Li, Jianqiang Zhang & Xiangyu Tang
A new study published in Biochar reveals that biochar, a carbon rich soil amendment widely used to improve soil health and reduce pollution, continues to influence the movement of veterinary antibiotics in farmland soils even after five years in the field. The work shows that biochar’s ability to retain pollutants changes in surprising ways over time, shifting from adsorption driven effects in the first year to soil structure driven mechanisms after long term aging.
The research team, led by scientists at Southwest Jiaotong University and the Chinese Academy of Sciences, examined how fresh biochar, one year aged biochar, and five year aged biochar affect the behavior of two widely used veterinary antibiotics, sulfadiazine and florfenicol, in purple soil of the Sichuan Basin. By combining batch adsorption tests, soil column experiments and advanced Hydrus 1D modeling, the study reveals how the physical and chemical evolution of biochar regulates pollutant movement.
“We often assume biochar works the same way throughout its lifetime, but the soil environment continuously reshapes its structure and surface chemistry,” said lead author Xinyu Liu. “Our results show that aged biochar develops new functions that are different from fresh biochar, and these changes alter how antibiotics move through the soil.”
Fresh biochar initially improved antibiotic removal primarily through strong surface adsorption. One year old biochar showed the highest adsorption capacity, driven by a nearly doubled surface area and increased oxygen containing functional groups that enhanced interactions with antibiotics. In soil column experiments, one year aged biochar increased the retention of sulfadiazine to 16.57 percent and florfenicol to 24.78 percent, the highest among all treatments.
However, after five years, biochar’s surface area and adsorption ability decreased as soil minerals gradually filled pore spaces and the material became more oxidized. Even so, aged biochar did not lose its environmental benefits. Instead, it contributed to more stable pollutant regulation by modifying soil pore networks and hydrodynamic behavior. Modeling results showed that long term aged biochar increased soil dispersivity and altered water movement patterns, which helped maintain antibiotic retention even as adsorption declined.
“Five year aged biochar forms strong associations with soil particles, creating a more stable composite material,” said corresponding author Yang He. “This composite changes how water and solutes flow through soil, which helps slow antibiotic leaching even when adsorption weakens.”
The study highlights that antibiotic transport in biochar amended soils transitions from being controlled by surface adsorption to being influenced by soil structural changes as aging progresses. This finding has important implications for long term risk assessment and agricultural management, especially in regions where veterinary antibiotics are widely used.
“Understanding how biochar changes over time helps us design better soil remediation strategies,” Liu added. “Biochar does not simply degrade. It evolves, and its environmental functions evolve with it.”
The authors note that more research is needed to examine long term biochar aging in different soil types and climates, as well as its interactions with a broader spectrum of environmental contaminants.
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Journal Reference: Liu, X., He, Y., Li, J. et al. Does biochar field aging reduce the kinetic retention for weakly hydrophobic antibiotics in purple soil?. Biochar 7, 69 (2025).
https://doi.org/10.1007/s42773-025-00460-4
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About Biochar
Biochar 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.