Thiol-modified biochar stabilizes toxic mercury in soils under extreme climate conditions

As climate change intensifies heatwaves around the world, soils are increasingly exposed to repeated drying and rewetting cycles that can mobilize toxic contaminants. A new study shows that a specially engineered biochar material can keep mercury locked safely in soil even under these stressful environmental conditions.

Mercury is a highly toxic and persistent pollutant that can enter the food chain and pose serious risks to human health and ecosystems. When soils undergo frequent dry and wet cycles, such as those triggered by heatwaves, their mineral structure changes, potentially releasing mercury into water or making it more bioavailable.

In a new study published in Biochar, researchers investigated how thiol-modified biochar, a sulfur-functionalized carbon material, influences the behavior of mercury in contaminated soils exposed to repeated drying and wetting cycles.

“We wanted to understand whether this material could maintain its effectiveness under realistic climate stress conditions,” said the study’s corresponding author. “Our results show that thiol-modified biochar not only remains stable, but actively reshapes the soil environment to reduce mercury risks.”

The team simulated 30 cycles of drying and wetting to mimic heatwave conditions. They found that soils treated with thiol-modified biochar showed dramatically reduced mercury mobility and bioavailability compared to untreated soils. In particular, the amount of mercury that could be leached under acidic conditions dropped by more than 80 percent in some treatments.

The key lies in how the material interacts with soil minerals. The biochar promotes natural weathering processes, including the dissolution of calcium carbonate and the transformation of iron and aluminum minerals into forms that bind mercury more strongly. At the same time, it increases soil pH and enhances the release of organic matter, both of which help trap mercury in stable forms.

As shown in the study’s experimental results, mercury gradually shifts from highly mobile and bioavailable forms into more stable forms associated with metal oxides and organic matter. This transformation significantly reduces environmental risk and limits the formation of methylmercury, a particularly toxic form that can accumulate in food chains.

The study also found that the biochar altered the soil microbial community, increasing diversity and promoting beneficial microbial groups. These microbial changes may further support long-term mercury stabilization by creating a more resilient soil ecosystem.

Importantly, the material maintained its performance even under simulated acid rain conditions, suggesting strong potential for real-world applications. In column experiments representing long-term rainfall exposure, mercury release from treated soils remained minimal.

“Our findings highlight a new mechanism,” the authors explained. “By driving mineral transformations and redistributing mercury species, thiol-modified biochar creates a stable geochemical environment that prevents mercury from becoming mobile again.”

This research provides important evidence that engineered biochar materials can offer durable solutions for soil remediation in a changing climate. As extreme weather events become more frequent, technologies that remain effective under dynamic environmental conditions will be critical.

The findings offer a promising pathway for managing mercury-contaminated soils, particularly in regions facing increasing heatwave intensity and hydrological variability.

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Journal Reference: Wang, Z., Zhang, L., Hu, H. et al. Redistribution of soil mercury species mediated by thiolated biochar under dry–wet cycles. Biochar 8, 90 (2026).   

https://doi.org/10.1007/s42773-026-00608-w   

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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. 

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