Soil contamination with mercury (Hg) poses a significant environmental threat. While biochar is commonly used to stabilize Hg, it can unintentionally increase the formation of methylmercury (MeHg), a highly toxic form. This study explored a safer strategy using co-modified biochar with selenium (Se) and phosphorus (P) to address this challenge.

By modifying straw biochar with Se and P, researchers aimed to enhance its Hg adsorption capacity and reduce MeHg formation. The findings revealed promising results:

• Co-modification with Se and P significantly increased biochar’s surface area, pore volume, and Hg adsorption capacity. This translates to better trapping of Hg in the soil.
• Biochar application initially increased bioavailable Hg forms. However, Se-P-modified biochar (Se-P-BC) effectively reduced these forms,indicating its ability to transform Hg into less harmful states.
• Se-P-BC led to the most substantial reductions in soil MeHg, total Hg, and MeHg uptake by plants. This demonstrates its superior efficacy in mitigating Hg contamination and related risks.
• The synergistic effect of Se and P is attributed to increased soil Se availability, facilitated by phosphorus addition. This Se presence suppresses Hg methylation and bioavailability.
• Reduced dissolved organic carbon and elevated sulfate concentrations in Se-P-BC treated soil further contribute to reduced Hg methylation and uptake.

This study highlights the potential of Se-P-co-modified biochar as a promising strategy for managing Hg contamination in soil. By effectively reducing bioavailable Hg and MeHg, it offers a safer and more sustainable approach compared to conventional biochar application. Further research can optimize the approach for wider application and explore its long-term effectiveness in real-world scenarios.