Cadmium contamination in paddy soils poses a serious challenge for rice production and food safety. Flooding can rapidly remove oxygen from soil, creating chemical conditions that may release cadmium and make it more available to plant roots. A new study reports that loading biochar with oxygen nanobubbles could help overcome this problem by actively regulating the environment around rice roots.
Researchers developed an oxygen-nanobubble-loaded biochar, called ONBC, and evaluated its ability to stabilize cadmium in contaminated paddy soil. In a greenhouse pot experiment, the team compared ONBC with untreated biochar, iron-loaded biochar, and soil without any amendment.
Unlike conventional biochar, which mainly acts as a passive surface for trapping contaminants, ONBC gradually released oxygen and maintained a more oxidizing environment throughout flooded rice cultivation.
"Our results show that oxygen loading can transform biochar from a passive adsorbent into an active platform that regulates soil chemistry and microbial activity around plant roots," said corresponding author Zhimin Sha of Shanghai Jiao Tong University. "This combined redox and biological regulation offers a promising new direction for reducing cadmium risks in flooded agricultural soils."
During the experiment, ONBC maintained dissolved oxygen concentrations of approximately 3 to 4 milligrams per liter during important stages of cultivation. It also kept rhizosphere redox potential positive, while untreated soil and the other biochar treatments moved closer to oxygen-depleted conditions.
These changes had a major effect on how cadmium was distributed in the soil. Compared with the untreated control, ONBC reduced the most mobile exchangeable cadmium pool by about 67 to 70 percent. It also shifted cadmium into less available forms associated with iron and manganese minerals, organic matter, and residual mineral phases.
Rice roots grown with ONBC contained 2.7 times less cadmium than roots in untreated soil, while cadmium concentrations in shoots were reduced by 1.9 times. ONBC performed better than both conventional biochar and iron-loaded biochar.
The researchers also examined the microorganisms living near rice roots using metagenomic sequencing. ONBC increased bacterial diversity and enriched microorganisms associated with iron and manganese oxidation. These microbial processes can promote the formation of reactive mineral surfaces that capture cadmium and help keep it away from plants.
In addition, ONBC altered microbial genes involved in cadmium resistance. It reduced genes associated with cadmium entering microbial cells while increasing genes linked to cadmium export, detoxification, stress response, and binding. Genes involved in carbon, nitrogen, and phosphorus turnover were also enhanced.
The benefits extended beyond contaminant stabilization. ONBC increased whole-plant fresh biomass by 44.7 percent, root activity by 64.5 percent, and superoxide dismutase activity by 85.4 percent compared with the untreated control. These improvements suggest that ONBC reduced cadmium stress while creating a healthier rhizosphere environment.
The study was conducted in pots under controlled greenhouse conditions, and grain cadmium could not be reliably measured because the plants had not reached full grain maturity. The researchers note that field trials across different soils, climates, and rice varieties will be needed before broad agricultural application.
Nevertheless, the findings suggest that oxygen-nanobubble-loaded biochar could provide a new strategy for managing cadmium-contaminated paddy soils by combining oxygen delivery, mineral stabilization, microbial regulation, and improved plant growth.
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Journal reference: Chu Q, Li D, Xu S, Pan D, Cao H, et al. 2026. An oxygen-nanobubble-loaded biochar for cadmium stabilization in contaminated paddy soil. Biochar X 2: e018 doi: 10.48130/bchax-0026-0015
https://www.maxapress.com/article/doi/10.48130/bchax-0026-0015
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About the Journal:
Biochar X (e-ISSN: 3070-1686) is an open access, online-only journal aims to transcend traditional disciplinary boundaries by providing a multidisciplinary platform for the exchange of cutting-edge research in both fundamental and applied aspects of biochar. The journal is dedicated to supporting the global biochar research community by offering an innovative, efficient, and professional outlet for sharing new findings and perspectives. Its core focus lies in the discovery of novel insights and the development of emerging applications in the rapidly growing field of biochar science.
