Choosing the right biochar can lock toxic cadmium in soil, study finds

Cadmium contamination in agricultural soils is a growing global concern, threatening food safety, crop productivity, and human health. New research shows that not all biochars work the same way and that choosing the right type of biochar can make the difference between trapping toxic metals in soil or unintentionally making them more mobile.

In a study published online on January 15, 2026, researchers report that biochar produced at high temperatures can work together with soil microbes to effectively immobilize cadmium, one of the most hazardous heavy metals found in farmland worldwide. The findings offer new guidance for using biochar as a precise and reliable tool for soil remediation.

Biochar is a carbon rich material made by heating organic waste in low oxygen conditions. It has been widely promoted as a sustainable solution for improving soil quality and reducing pollution. However, past studies have produced mixed results, leaving farmers and land managers uncertain about how to use it effectively.

“Our results show that biochar is not a one size fits all solution,” said corresponding author Quan Chen of Kunming University of Science and Technology. “Its performance depends strongly on how it is made and how it interacts with soil microorganisms.”

The research team produced biochar from kitchen waste at three different temperatures: 300, 500, and 700 degrees Celsius. They then tested these biochars in pot experiments using cadmium contaminated agricultural soil and Chinese cabbage as a test crop. Some treatments also included the addition of a common, non pathogenic bacterium, Escherichia coli, to better understand microbial effects.

The results revealed a striking contrast. Low temperature biochar improved soil fertility and microbial activity but had little ability to lock cadmium in place. When combined with microbes, it even increased cadmium bioavailability and plant uptake, raising potential food safety risks.

In contrast, biochar produced at 700 degrees Celsius significantly reduced the most mobile and bioavailable forms of cadmium in soil. When paired with microbes, it showed a strong synergistic effect, further stabilizing cadmium and limiting its movement from roots to edible plant tissues.

“High temperature biochar creates a porous, alkaline microenvironment that favors beneficial microorganisms while restricting cadmium mobility,” Chen explained. “This synergy between biochar and microbes is the key to long term stabilization.”

The study found that high temperature biochar enriched specific microbial groups such as Bacillus, Rhodococcus, and Mucor, which are known to interact with metals through adsorption, biofilm formation, and mineral precipitation. These microbes formed a more tightly connected community that helped keep cadmium bound in less harmful forms.

Importantly, the research highlights that inappropriate biochar selection could backfire. Applying low temperature biochar in cadmium contaminated soils may increase metal uptake by crops, even if plant growth appears healthy.

“This work provides a clear warning,” said Chen. “If biochar is applied without considering its properties and microbial interactions, it may fail to reduce pollution or even worsen the problem.”

By demonstrating how biochar production temperature governs both chemical and biological processes in soil, the study offers a new theoretical basis for the selective and precise use of biochar in heavy metal remediation.

The findings support the development of tailored biochar strategies that maximize environmental benefits while minimizing risks. As countries seek sustainable solutions to soil contamination and food safety challenges, understanding these biochar microbe interactions could help turn organic waste into a powerful tool for cleaner and safer agriculture.

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Journal reference: Xiong Y, Lin R, Wang Y, Liu K, Guo J, et al. 2026. Selective application of biochars to realize biochar–microbe synergistic immobilization of soil cadmium. Environmental and Biogeochemical Processes 2: e001 doi: 10.48130/ebp-0025-0019   

https://www.maxapress.com/article/doi/10.48130/ebp-0025-0019  

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About the Journal:

Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment. 

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