New sulfur-iron biochar shows powerful ability to lock up arsenic and cadmium in contaminated soils

(Press-News.org) Researchers have developed a novel engineered biochar that can simultaneously immobilize arsenic and cadmium in contaminated water and agricultural soils, offering a promising new strategy for addressing two of the world’s most dangerous toxic elements.

The study, recently published in Agricultural Ecology and Environment, introduces a sulfur-ferrihydrite-modified biochar designed to tackle the complex challenge of co-contamination by arsenic and cadmium. These pollutants frequently occur together in agricultural regions impacted by mining, industrial emissions, and long-term fertilizer use, posing serious risks to food safety and human health.

“Arsenic and cadmium behave very differently in soils, which makes it extremely difficult to control both at the same time,” said corresponding author Dan Liu. “Our goal was to design a multifunctional material that could stabilize both contaminants through complementary mechanisms.”

Arsenic typically exists in negatively charged forms, while cadmium occurs as a positively charged metal ion. Because of these contrasting chemical behaviors, conventional soil amendments often perform well for one contaminant but poorly for the other. The new composite material integrates sulfur chemistry and iron mineral phases within a porous biochar framework, creating reactive sites capable of capturing both types of pollutants simultaneously.

Laboratory adsorption experiments showed that the modified biochar achieved a maximum cadmium uptake capacity of 76.69 milligrams per gram and an arsenic uptake capacity of 8.28 milligrams per gram, significantly outperforming unmodified biochar and iron-only modified materials. The material remained highly effective across a broad pH range, an important factor for real-world soil conditions.

The researchers found that cadmium was immobilized primarily through ion exchange, surface complexation, and the formation of stable cadmium sulfide and iron sulfide precipitates. In contrast, arsenic underwent oxidation from a more toxic and mobile form to a less mobile species, followed by strong binding to iron hydroxyl groups on the material’s surface. These coupled redox and coordination processes created synergistic reactive interfaces capable of stabilizing both contaminants at once.

To evaluate real-world performance, the team conducted soil incubation experiments using contaminated paddy soil. Application of the sulfur-iron biochar reduced bioavailable cadmium concentrations by up to 41 percent and bioavailable arsenic by up to 64 percent. In addition, both elements were transformed from easily exchangeable forms into more stable residual fractions, lowering their mobility and potential uptake by crops.

“Our findings demonstrate that integrating iron and sulfur functionalities into biochar creates a cooperative system that cannot be achieved with single modifications alone,” Liu explained. “This approach provides a new pathway for designing next-generation soil amendments for multi-metal contamination.”

Beyond its strong adsorption capacity, the material also exhibits hierarchical porosity and enhanced surface reactivity, features that contribute to long-term stability in soil systems. The researchers note that future work will focus on evaluating long-term environmental stability under varying redox conditions and assessing sulfur cycling processes in field environments.

Co-contamination by arsenic and cadmium affects millions of hectares of farmland worldwide, particularly in regions with intensive rice cultivation. By offering an effective, multifunctional remediation strategy, sulfur-ferrihydrite-modified biochar may help reduce contaminant transfer into crops and support safer agricultural production.

“This material shows strong potential as a practical soil amendment for remediating contaminated agricultural land,” Liu said. “With further field validation, it could contribute to protecting food security and environmental health in vulnerable regions.”

 

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Journal Reference: Xu W, Huang D, Huang H, Zheng B, Teng X, et al. 2026. Sulfur-ferrihydrite-modified biochar for simultaneous immobilization of arsenic and cadmium in co-contaminated water/soil: performance and mechanisms. Agricultural Ecology and Environment 2: e005 doi: 10.48130/aee-0026-0002   

https://www.maxapress.com/article/doi/10.48130/aee-0026-0002   

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About Agricultural Ecology and Environment: 

Agricultural Ecology and Environment (e-ISSN 3070-0639) 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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