Crayfish shell biochar shows contrasting effects on arsenic pollution in soils

A new study reveals that biochar made from crayfish shells can either reduce or increase arsenic risks in soil, depending on soil type, offering both opportunities and cautions for sustainable remediation strategies.

“Biochar is often viewed as a universal solution for soil contamination, but our findings show that its effects can vary dramatically depending on environmental conditions,” said the study’s lead researcher. “Understanding these differences is essential for safe and effective application.”

Arsenic contamination is a global environmental challenge that threatens soil health, food safety, and human well-being. Millions of people are exposed to arsenic through contaminated soils and groundwater, making it urgent to develop cost-effective and environmentally friendly remediation methods. Biochar, a carbon-rich material produced from biomass, has gained attention for its ability to immobilize pollutants and improve soil quality.

In this study, researchers investigated a novel biochar derived from crayfish shells and its impact on arsenic behavior in both acidic and alkaline soils under aerobic conditions. The results showed a striking dual effect.

In alkaline soils, crayfish shell biochar reduced arsenic availability by up to 9.9 percent, effectively lowering environmental risk. This improvement is attributed to the biochar’s ability to provide additional adsorption sites and promote strong interactions with arsenic, including electrostatic attraction and surface complexation.

However, in acidic soils, the same biochar had the opposite effect. Arsenic availability increased by 19.6 to 26.8 percent after biochar application. The researchers found that this increase was driven by changes in soil chemistry and biology.

Specifically, the biochar raised soil pH and altered dissolved organic matter, making it more chemically active and mobile. These changes promoted arsenic release from soil particles. At the same time, the biochar reshaped the soil microbial community, increasing the abundance of microorganisms and genes that enhance arsenic mobility.

Key microbial groups associated with arsenic transformation became more active in acidic soils, along with genes responsible for arsenic reduction and transport. These biological processes further contributed to the release of arsenic into more bioavailable forms.

“Our results highlight that biochar does not act in isolation,” the researchers explained. “It interacts with soil chemistry, organic matter, and microbial communities in complex ways that ultimately determine whether arsenic is stabilized or mobilized.”

The study also found that dissolved organic matter played a central role. In acidic soils, biochar increased the humification level and reduced molecular weight of organic compounds, both of which are known to enhance arsenic mobility. In contrast, these effects were less pronounced in alkaline soils, where adsorption mechanisms dominated.

Overall, the findings demonstrate that crayfish shell biochar can be an effective and sustainable amendment for arsenic-contaminated alkaline soils, but it may pose risks if applied to acidic environments without careful evaluation.

The researchers emphasize that soil-specific strategies are critical when using biochar for environmental remediation. Tailoring biochar application to local soil conditions could maximize benefits while avoiding unintended consequences.

“This work provides new insight into how biochar influences contaminant behavior in soils,” the team noted. “It also underscores the importance of integrating chemical and biological perspectives when designing remediation technologies.”

As biochar continues to gain attention as a climate-friendly and circular solution, studies like this highlight the need for precision in its application to ensure both environmental safety and long-term sustainability.

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Journal Reference: Sun, T., Sun, Y., Pei, P. et al. Dual roles of crayfish shell biochar on the fate of arsenic in acid and alkaline aerobic soils: insights from dissolved organic matter and metabolism genes. Biochar 7, 47 (2025).   

https://doi.org/10.1007/s42773-025-00454-2   

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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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