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<p>Soils in southern China are at risk due to heavy metal contamination and acid precipitation. Bioavailability of copper (Cu) and cadmium (Cd) in sudden pollution soil is higher than that in cumulative pollution soil, so the potential risk of this kind of soil is greater. Limestone plays a crucial role in the decontamination of these heavy metals. In the present study, the role of soil-iron oxides in binding heavy metals and immobilization was characterized by traditional and modified speciation extraction methods.&#xa0;The test soils include red soil (R) and paddy soil (P) to represent sudden and cumulative polluted soil, respectively. The process entails applying limestone to soil samples, followed by incubation experiments under controlled conditions. The study also examines physicochemical properties, heavy metal mobility, and interactions of soil and soil colloids.&#xa0;The results showed that after LS application, exchangeable and carbonate fractions of Cu and Cd (EC-Cu and EC-Cd) extracted by different speciation methods (classic Tessier method (T), modified extraction method T1 and T2) were reduced to 38.57 and 0.94&#xa0;mg·kg<sup>−1</sup>, respectively in R, demonstrating a better resistant effect compared to P. T1 and T2 highlighted the role of readily reducible iron-manganese fraction (FE) and amorphous/crystalline iron oxide fraction (FEA/FEC) for immobilization and binding of heavy metals in test soil. The extracted results (by 0.05&#xa0;mol·L<sup>−1</sup>HCl) of residual from various fractions in T/T1/T2 revealed that after extraction of iron and manganese oxide fraction in T/T1 (T/T1-FE), organic fraction in T1 (T1-OM) and amorphous iron oxide fraction in T2 (T2-FEA) of Cu, as well as T/T1-FE, T1-OM, T2-FEA, and crystalline iron oxide fraction in T2 (T2-FEC) of Cd, there still contains some availability in soil. Cu was more influenced by the amorphous iron oxide fraction, with the available Cu of amorphous iron oxide fraction in T2 (T2-FEA-HCl-Cu) increasing from 2.08% to 4.36% in R after LS application. In contrast, Cd was affected by easily reducible, amorphous, and crystalline iron oxide fractions.&#xa0;The immobilization pathways of LS for decontamination of Cu and Cd were inconsistent. After LS application, T2-FEC-Cu and T1-FEC-Cd in soil showed significant correlation with amorphous/crystalline iron oxide in soil colloids. Soil colloidal iron oxides are the main reason and pathway for reduction of Cu and Cd bioavailability in soils.</p>

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Effect and Mechanism of Limestone on the Bioavailability of Cu and Cd in Red and Paddy Soils Using Different Sequential Extraction Methods

  • 期刊论文

  • 发表日期：

    2025年10月27日

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  • Yuan Ding,
  • Zijin Tang,
  • Shiying Ao,
  • Chao Han,
  • Haiyuan Wang,
  • Asma Shaheen,
  • Rajesh Kumar Manavalan,
  • Hong Shi,
  • Min Liu

摘要

Soils in southern China are at risk due to heavy metal contamination and acid precipitation. Bioavailability of copper (Cu) and cadmium (Cd) in sudden pollution soil is higher than that in cumulative pollution soil, so the potential risk of this kind of soil is greater. Limestone plays a crucial role in the decontamination of these heavy metals. In the present study, the role of soil-iron oxides in binding heavy metals and immobilization was characterized by traditional and modified speciation extraction methods. The test soils include red soil (R) and paddy soil (P) to represent sudden and cumulative polluted soil, respectively. The process entails applying limestone to soil samples, followed by incubation experiments under controlled conditions. The study also examines physicochemical properties, heavy metal mobility, and interactions of soil and soil colloids. The results showed that after LS application, exchangeable and carbonate fractions of Cu and Cd (EC-Cu and EC-Cd) extracted by different speciation methods (classic Tessier method (T), modified extraction method T1 and T2) were reduced to 38.57 and 0.94 mg·kg−1, respectively in R, demonstrating a better resistant effect compared to P. T1 and T2 highlighted the role of readily reducible iron-manganese fraction (FE) and amorphous/crystalline iron oxide fraction (FEA/FEC) for immobilization and binding of heavy metals in test soil. The extracted results (by 0.05 mol·L−1HCl) of residual from various fractions in T/T1/T2 revealed that after extraction of iron and manganese oxide fraction in T/T1 (T/T1-FE), organic fraction in T1 (T1-OM) and amorphous iron oxide fraction in T2 (T2-FEA) of Cu, as well as T/T1-FE, T1-OM, T2-FEA, and crystalline iron oxide fraction in T2 (T2-FEC) of Cd, there still contains some availability in soil. Cu was more influenced by the amorphous iron oxide fraction, with the available Cu of amorphous iron oxide fraction in T2 (T2-FEA-HCl-Cu) increasing from 2.08% to 4.36% in R after LS application. In contrast, Cd was affected by easily reducible, amorphous, and crystalline iron oxide fractions. The immobilization pathways of LS for decontamination of Cu and Cd were inconsistent. After LS application, T2-FEC-Cu and T1-FEC-Cd in soil showed significant correlation with amorphous/crystalline iron oxide in soil colloids. Soil colloidal iron oxides are the main reason and pathway for reduction of Cu and Cd bioavailability in soils.