New biochar breakthrough offers hope for cleaner, safer farmland soils
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Synthesis, mechanism, and application of element-doped biochar for heavy metal contamination in agricultural soils
Credit: Jianhua Qu, Hongxuan Chu, Mengning Wang, Rui Yu, Siqi Wang, Tianqi Liu, Yue Tao, Siyue Han & Ying Zhang
Agricultural soils across the world are increasingly polluted by heavy metals such as cadmium, lead, chromium, and arsenic. These toxic elements, often introduced through industrial wastewater, fertilizers, and manure, can accumulate in crops and threaten human health through the food chain. Long-term exposure is linked to kidney damage, osteoporosis, and even cancer. Protecting soil health and food safety has therefore become an urgent global challenge.
In a new study published in Agricultural Ecology and Environment, researchers reviewed a promising strategy to tackle this crisis: using element-doped biochar to immobilize and neutralize toxic metals in farmland soils.
Biochar, a charcoal-like material made from crop residues such as rice husks or fruit peels, has long been recognized as a low-cost and eco-friendly soil additive. However, “plain” biochar does not always perform well in capturing heavy metals. To overcome this limitation, scientists are enhancing biochar by “doping” it with elements such as nitrogen, oxygen, sulfur, and phosphorus. These doped versions have special chemical groups on their surface that provide extra binding sites for heavy metals, improving their ability to lock contaminants in the soil and reduce their mobility.
“Element-doped biochar changes the game,” said corresponding author Ying Zhang. “By modifying the structure of biochar, we can greatly improve its ability to stabilize heavy metals, making farmland safer and crops healthier.”
The review highlights how different dopants work:
Nitrogen-doped biochar introduces active nitrogen groups that form strong bonds with metals like cadmium.
Oxygen-doped biochar increases carboxyl and hydroxyl groups that attract lead and chromium.
Sulfur-doped biochar binds mercury and cadmium through stable sulfur–metal interactions.
Phosphorus-doped biochar not only immobilizes toxic metals but also helps supply essential nutrients to plants.
Beyond laboratory studies, field applications have shown encouraging results. For example, phosphorus-doped biochar reduced lead and cadmium leaching in soils, while multi-element doping approaches demonstrated enhanced crop growth by lowering metal toxicity stress.
The authors emphasize that element-doped biochar is not just a temporary fix but could become a practical, scalable tool for sustainable agriculture. By turning agricultural waste into high-value soil amendments, this approach also supports recycling, reduces pollution, and promotes a circular economy.
Looking ahead, the researchers call for more real-world trials to evaluate the long-term stability of doped biochar under different farming conditions. They also suggest exploring multi-element doping strategies to further enhance performance.
“This technology has the potential to transform contaminated farmland into safe, productive soils,” Zhang said. “It represents a step forward in ensuring both food security and environmental sustainability.”
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Journal Reference: Qu J, Chu H, Wang M, Yu R, Wang S, et al. 2025. Synthesis, mechanism, and application of element-doped biochar for heavy metal contamination in agricultural soils. Agricultural Ecology and Environment 1: e002 https://www.maxapress.com/article/doi/10.48130/aee-0025-0004
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About Agricultural Ecology and Environment:
Agricultural Ecology and Environment is a multidisciplinary platform for communicating advances in fundamental and applied research on the agroecological environment, focusing on the interactions between agroecosystems and the environment. It is dedicated to advancing the understanding of the complex interactions between agricultural practices and ecological systems. The journal aims to provide a comprehensive and cutting-edge forum for researchers, practitioners, policymakers, and stakeholders from diverse fields such as agronomy, ecology, environmental science, soil science, and sustainable development.
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Method of Research
Literature review
Subject of Research
Not applicable
Article Title
Synthesis, mechanism, and application of element-doped biochar for heavy metal contamination in agricultural soils
Article Publication Date
17-Sep-2025
Seasonal freeze–thaw cycles may cause “green” biochar to leak toxic metals, new study warns
Manure-based biochar once thought stable could release heavy metals back into soil and water under harsh weathering
Biochar Editorial Office, Shenyang Agricultural University
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Reassessing the role of pyrolysis temperature: freeze–thaw aging challenges heavy metals stability in biochar
Credit: Xingdong Wang, Guidan Zhu, Yuanrong Yi, Jin Zhou & Victor Wei-Chung Chang
Turning livestock manure into biochar has been hailed as a climate-friendly way to recycle waste, lock away carbon, and make farming more sustainable. But new research suggests that this “green” solution may not be as stable as once believed—especially in regions with harsh winters.
A study published in Biochar by scientists from Monash University and Xinjiang University found that repeated freeze–thaw cycles—the kind of seasonal temperature swings common in northern climates—can damage biochar and trigger the release of toxic heavy metals it was supposed to lock up.
“Biochar is often seen as a win–win technology: it helps manage livestock waste and reduces environmental risks,” said lead researcher Xingdong Wang. “But our results show that when biochar is exposed to freeze–thaw aging, it can actually become more fragile and release pollutants back into the environment.”
The team tested chicken manure biochars made at different production temperatures (350 °C, 550 °C, and 750 °C). Surprisingly, the biochars made at the highest temperature—once considered the most durable—were the most vulnerable to cracking and oxidation during freeze–thaw stress. This breakdown released greater amounts of heavy metals such as zinc, copper, and lead, which can harm crops, soil organisms, and potentially contaminate groundwater.
In some cases, the bioavailable levels of zinc and copper in aged biochar were hundreds of times higher than in fresh samples—well above safe limits set for plants. “This shows that the way biochar is made has long-term consequences,” explained co-author Victor Wei-Chung Chang of Monash University. “We can’t just assume that higher-temperature biochars are automatically safer or more stable.”
The findings highlight an important lesson for climate-smart agriculture: it’s not enough to evaluate biochar when it is freshly produced. Farmers, policymakers, and researchers must also consider how environmental conditions—like freezing and thawing—will affect biochar years after it has been applied to soil.
The authors stress that biochar remains a promising tool for sustainable farming and waste recycling, but more research is needed to design materials that can resist weathering and keep heavy metals locked away safely. Potential solutions include protective surface treatments or additives that reduce metal mobility.
“This is a reminder that there’s no quick fix in environmental science,” said Chang. “If we want biochar to truly deliver climate and agricultural benefits, we have to think about its whole lifecycle in real-world conditions.”
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Journal reference: Wang, X., Zhu, G., Yi, Y. et al. Reassessing the role of pyrolysis temperature: freeze–thaw aging challenges heavy metals stability in biochar. Biochar 7, 86 (2025). https://doi.org/10.1007/s42773-025-00479-7
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Media Contact:
Wushuang Li
liwushuang@vip.126.com
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.
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Journal
Biochar
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Reassessing the role of pyrolysis temperature: freeze–thaw aging challenges heavy metals stability in biocha
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