Rice is a staple food for more than half of the world's population, but in some mining-impacted regions, paddy soils can contain elevated levels of arsenic and antimony. These toxic metalloids can move from soil into rice plants, raising concerns for food safety and human health. A new study published in Biochar reports a promising strategy: a magnetic silicon-enriched biochar gel that can immobilize both arsenic and antimony in contaminated paddy soil and reduce their accumulation in rice grains.
The research team developed a functional biochar material known as FeRBG, made by combining rice husk biochar, iron oxides, and graphene into a three-dimensional porous gel network. Rice husk was selected because it is abundant agricultural waste and naturally rich in silicon, a beneficial element that can help plants tolerate stress and may reduce metalloid uptake. By adding iron and graphene, the researchers created a material with more active binding sites, improved stability, and stronger capacity to trap arsenic and antimony in soil.
"Our goal was to design a soil amendment that does more than simply adsorb pollutants in the laboratory," said the study authors. "We wanted to test whether an engineered biochar could work in the soil-rice system, reduce food-chain transfer, support plant growth, and reshape the soil environment in a beneficial way."
The study was conducted using paddy soil collected from the Qinglong Antimony Mine area in Guizhou Province, China, where soils are co-contaminated with very high levels of antimony and arsenic. In greenhouse pot experiments, the researchers compared untreated soil with soil amended with pristine rice husk biochar, iron-loaded biochar, and the new iron-loaded biochar gel.
The results showed that FeRBG was the most effective treatment for simultaneously reducing the bioavailability of both arsenic and antimony. Compared with untreated soil, FeRBG reduced phosphate-extractable antimony and arsenic by 23.1% and 22.3%, respectively. It also shifted these contaminants into more stable soil fractions, including residual and iron oxide-bound forms, making them less available for plant uptake.
Most importantly, FeRBG was the only amendment that significantly lowered both arsenic and antimony in rice grains. Grain arsenic decreased by 34.0%, while grain antimony decreased by 16.1% compared with the control. Under the FeRBG treatment, rice grain arsenic dropped to 0.14 mg kg⁻¹, below China's national food safety limit for brown rice.
The material also supported healthier plant growth. FeRBG improved root system architecture, increasing total root length, surface area, mean diameter, and root tip number. Rice productivity also improved, with higher fresh weights in roots, stems, and panicles, and a 13.1% increase in thousand-grain mass.
The team found that FeRBG worked through multiple reinforcing mechanisms. Iron oxides on the biochar surface formed stable Fe-O-As and Fe-O-Sb complexes, while the porous gel structure provided more adsorption sites. Silicon from rice husk biochar may have helped reduce arsenic transport in rice, and improved root growth likely supported stronger plant resilience. The amendment also reshaped soil bacterial communities, enriching microbial groups linked to nutrient cycling and stress adaptation.
"This work shows that functionalized biochar can act as an integrated remediation tool, not only locking toxic elements in soil but also improving the biological and physiological conditions for rice growth," the authors said.
The findings suggest that magnetic silicon-rich biochar gel could offer a sustainable approach for remediating arsenic and antimony co-contaminated paddy fields, especially in mining-affected agricultural regions. Further field-scale studies will be needed to evaluate long-term performance, economic feasibility, and environmental safety under real farming conditions.
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Journal Reference: Gao, Y., Chen, H., Wang, F. et al. Magnetic silicon-enriched biochar for effectively mitigating As and Sb in soil-rice continuum: from integrated geochemical, microbial, and phytophysiological insights. Biochar 8, 74 (2026).
https://doi.org/10.1007/s42773-026-00579-y
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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.
