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<p>Arsenic (As) remediation in flooded paddy soils through iron (Fe) redox cycling can be influenced by carbon-based amendments, yet the CO<sub>2</sub> emission in this process remain unclear. This study evaluated the effects of Fe oxides with contrasting crystallinity, goethite (Gt) and ferrihydrite (Fh), with or without biochar (BC) amendment, on As immobilization, geochemical fractionation and microbial-carbon dynamics from As-contaminated paddy soil under reduced conditions. The results showed that Fh and Gt, with BC addition, significantly (p &lt; 0.05) reduced As bioavailability by 87.5% (0.39&#xa0;mg&#xa0;kg<sup>−1</sup>) and 76.6% (0.73&#xa0;mg&#xa0;kg<sup>−1</sup>), respectively, compared to control. Partial Least Squares Path Modeling revealed a strong negative direct effect of Fe-oxides on As (β = -3.86), confirming their role as the principal gatekeepers for As sequestration. Iron oxides application increased the CO₂ flux; however, a dramatic decrease was observed with BC application to Fe oxide-treated soils. This elucidates that the increased C emission from As-contaminated soil induced by Fh or Gt can be compromised by BC application, although the extent of reduction depends on the type of Fe oxide. Microbial community analysis revealed increased relative abundance of <i>Pseudarthrobacter</i> and <i>Anaerolinea</i> in Fh-amended soils, highlighting their potential role in carbon cycling processes. Fe oxides recruited Fe(III)-reducing bacterial guilds (<i>Firmicutes</i><i>, </i><i>Proteobacteria</i>) to drive CO₂ emissions, whereas BC addition suppressed reshaped functional potentials of these taxa, explaining the trade-off between reduced CO₂ and As immobilization. This study provides an insight towards the mitigation of As contamination and GHG emission through co-application of Fe oxides and BC as a sustainable approach.</p> Graphical Abstract <p></p>

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Iron Oxide Types Determine the Regulatory Effects of Biochar on Carbon Emissions from Arsenic-Contaminated Soils

  • 期刊论文

  • 发表日期：

    2026年7月14日

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  • Qi Li,
  • Wenjing Li,
  • Yanyan Lu,
  • Sada Tanzil,
  • Wan Yang,
  • Muhammad Mahroz Hussain,
  • Shengsen Wang

摘要

Arsenic (As) remediation in flooded paddy soils through iron (Fe) redox cycling can be influenced by carbon-based amendments, yet the CO2 emission in this process remain unclear. This study evaluated the effects of Fe oxides with contrasting crystallinity, goethite (Gt) and ferrihydrite (Fh), with or without biochar (BC) amendment, on As immobilization, geochemical fractionation and microbial-carbon dynamics from As-contaminated paddy soil under reduced conditions. The results showed that Fh and Gt, with BC addition, significantly (p < 0.05) reduced As bioavailability by 87.5% (0.39 mg kg−1) and 76.6% (0.73 mg kg−1), respectively, compared to control. Partial Least Squares Path Modeling revealed a strong negative direct effect of Fe-oxides on As (β = -3.86), confirming their role as the principal gatekeepers for As sequestration. Iron oxides application increased the CO₂ flux; however, a dramatic decrease was observed with BC application to Fe oxide-treated soils. This elucidates that the increased C emission from As-contaminated soil induced by Fh or Gt can be compromised by BC application, although the extent of reduction depends on the type of Fe oxide. Microbial community analysis revealed increased relative abundance of Pseudarthrobacter and Anaerolinea in Fh-amended soils, highlighting their potential role in carbon cycling processes. Fe oxides recruited Fe(III)-reducing bacterial guilds (Firmicutes, Proteobacteria) to drive CO₂ emissions, whereas BC addition suppressed reshaped functional potentials of these taxa, explaining the trade-off between reduced CO₂ and As immobilization. This study provides an insight towards the mitigation of As contamination and GHG emission through co-application of Fe oxides and BC as a sustainable approach.

Graphical Abstract