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Purpose <p>Green waste compost (GWC) is widely applied as an organic mulch, growth substrate, and soil fertilizer or amendment. To assess how GWC versus peat immobilize Pb and Cd in contaminated soil subjected to freeze–thaw cycling, and to determine how soil bulk density and soil water content (SWC) regulate metal speciation and key physico-chemical properties.</p> Materials and methods <p>In a soil-culture experiment, peat served as the control amendment against GWC. We quantified total concentrations and fractions of Pb and Cd across gradients of bulk density (1.0–1.4&#xa0;g cm⁻³) and initial SWC (10–20%), under alternating freeze–thaw cycles. Concurrently we recorded dissolved organic carbon, porosity, pH and electrical conductivity to capture amendment-induced changes accompanying speciation shifts.</p> Results and discussion <p>Both GWC and peat decreased the acid-soluble Pb fraction while increasing oxidizable and residual pools, and passivation strengthened as bulk density decreased. At low bulk density, GWC immobilized Pb more effectively, and its response to SWC was stronger: higher water content further lowered soluble Pb. Peat maintained stable Pb and Cd passivation across 10–20% SWC. Relative to the non-cycled condition, freeze–thaw cycling further decreased the acid-soluble fractions of Pb and Cd. This decrease was larger in peat amended soils than in soils amended with GWC.</p> Conclusions <p>GWC and peat effectively immobilize Pb and Cd under freeze–thaw conditions. Their efficacy is co-governed by soil compaction and SWC: lower bulk density favors passivation, GWC is more moisture-responsive for Pb, and peat exhibits robust freeze–thaw enhancement. Freeze–thaw also increased DOC, enlarged porosity, and lowered pH and EC, indicating coupled structural–chemical controls relevant to remediation in cold regions.</p>

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Freeze–thaw cycling effects on Pb and Cd immobilization by green waste compost in contaminated soil

  • 期刊论文

  • 发表日期：

    2026年1月29日

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  • Jie Ma,
  • Chenchen Wang,
  • Linna Suo,
  • Yuanxin Liu,
  • Xiangyang Sun

摘要

Purpose

Green waste compost (GWC) is widely applied as an organic mulch, growth substrate, and soil fertilizer or amendment. To assess how GWC versus peat immobilize Pb and Cd in contaminated soil subjected to freeze–thaw cycling, and to determine how soil bulk density and soil water content (SWC) regulate metal speciation and key physico-chemical properties.

Materials and methods

In a soil-culture experiment, peat served as the control amendment against GWC. We quantified total concentrations and fractions of Pb and Cd across gradients of bulk density (1.0–1.4 g cm⁻³) and initial SWC (10–20%), under alternating freeze–thaw cycles. Concurrently we recorded dissolved organic carbon, porosity, pH and electrical conductivity to capture amendment-induced changes accompanying speciation shifts.

Results and discussion

Both GWC and peat decreased the acid-soluble Pb fraction while increasing oxidizable and residual pools, and passivation strengthened as bulk density decreased. At low bulk density, GWC immobilized Pb more effectively, and its response to SWC was stronger: higher water content further lowered soluble Pb. Peat maintained stable Pb and Cd passivation across 10–20% SWC. Relative to the non-cycled condition, freeze–thaw cycling further decreased the acid-soluble fractions of Pb and Cd. This decrease was larger in peat amended soils than in soils amended with GWC.

Conclusions

GWC and peat effectively immobilize Pb and Cd under freeze–thaw conditions. Their efficacy is co-governed by soil compaction and SWC: lower bulk density favors passivation, GWC is more moisture-responsive for Pb, and peat exhibits robust freeze–thaw enhancement. Freeze–thaw also increased DOC, enlarged porosity, and lowered pH and EC, indicating coupled structural–chemical controls relevant to remediation in cold regions.