A new study reveals that biochar can do more than simply trap pollutants. It may actively redirect antibiotic movement in structured soils, helping reduce the risk of contamination in nearby water systems.
Antibiotics used in agriculture can enter soil through manure, wastewater irrigation, and other pathways. Once there, they may travel quickly through large soil pores, known as macropores, which act like hidden highways during rainfall or irrigation. These fast pathways can carry antibiotic residues past the soil matrix before natural filtration has time to occur, increasing the risk that contaminants reach groundwater, rivers, and other aquatic ecosystems.
A new study published in Biochar provides direct experimental evidence that biochar can regulate this process by shifting antibiotic transport from rapid macropore flow into the slower soil matrix, where pollutants are more likely to be retained.
The research team studied two weakly hydrophobic antibiotics, sulfadiazine and florfenicol, using a newly designed dual-domain soil column apparatus. Unlike conventional columns, this system physically separates water and solutes moving through macropores from those moving through the surrounding soil matrix. This allowed the researchers to measure, for the first time, how biochar affects antibiotic movement in each domain under controlled hydraulic conditions.
"Our findings show that biochar is not only a passive sorbent sitting in the soil," said corresponding author Dr. Yang He. "When macropores and the soil matrix are hydraulically connected, biochar can actively reshape the transport pathway of antibiotics and help move them into zones where they are more likely to be immobilized."
The study compared control soils and biochar-amended soils under two conditions: impermeable macropores, where exchange between macropores and the matrix was blocked, and permeable macropores, where water and solutes could move between the two domains. The difference was striking. When macropores were isolated, biochar had little effect because antibiotics bypassed the amended soil matrix. But when macropores were permeable, biochar significantly reduced antibiotic losses.
In connected systems, the cumulative mass flux of sulfadiazine decreased from 0.72 to 0.61, while florfenicol decreased from 0.81 to 0.72. These reductions indicate that biochar became much more effective when it could interact with contaminants moving between fast and slow flow regions.
To explain the mechanism, the researchers used partial least squares structural equation modeling. The results showed that biochar changed the causal pathways controlling antibiotic movement. Dissolved organic matter and colloids acted as mobile carriers, while the biochar-amended matrix became a stronger immobilizing zone. At the same time, biochar counteracted the rapid advective flux represented by bromide tracer movement.
Based on these findings, the team proposed a new concept called the "biochar sorption pump." This framework describes biochar as an active flux regulator that draws contaminants away from fast macropore pathways and into the soil matrix, where longer residence time and stronger sorption can reduce pollutant export.
The study has important implications for precision soil remediation. Instead of applying biochar uniformly without considering soil structure, future strategies could be designed around soil hydraulic connectivity, macropore behavior, and contaminant transport pathways.
"Understanding where and how biochar works is essential for protecting vulnerable water bodies," Dr. He said. "By matching biochar applications with soil hydraulic properties, we may improve its performance in real agricultural landscapes."
This work reframes biochar from a simple pollutant sponge into a dynamic tool for managing contaminant flux in structured soils.
===
Journal Reference: Liu, X., He, Y., Li, J. et al. Biochar-regulated transport of weakly hydrophobic antibiotics between macropore and matrix domains in structured soil. Biochar 8, 86 (2026).
https://doi.org/10.1007/s42773-026-00596-x
===
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.
