A meta-analysis of remediation of Cd-contaminated soil: comparison of remediation agents, pot versus field studies, and biochar versus biochar mixed with other materials

Abstract

Cadmium (Cd) contamination in farmland soils poses a significant threat to agricultural sustainability and environmental safety. Although research on soil and crop Cd pollution has expanded, systematic comparative analyses of how different remediation materials affect core soil properties, Cd bioavailability, and crop attributes remain limited. To address this gap, we performed a meta-analysis of data from 116 published studies spanning the past 15 years. This study evaluates the efficacy of various remediation materials, including mixed amendments, synthetic agents, natural minerals, organic materials, and biochar, in remediating Cd-contaminated farmland. Biochar most comprehensively improved soil properties such as pH, soil organic matter (SOM), and available phosphorus, with pronounced enhancement of available P (effect size > 1) and cation exchange capacity (CEC) (effect size > 0.4), while effectively reducing soil bioavailable Cd (effect size = −0.37) and exchangeable Cd (effect size = −0.24). The consistency of biochar performance between pot and field experiments supports the translatability of laboratory findings to practical applications. Biochar efficacy was modulated by its properties: alkaline biochar was more effective at improving soil fertility, and biochar produced at temperatures above 600 °C exhibited stronger Cd immobilization capacity. Furthermore, biochar combined with other materials (biochar + x) outperformed biochar alone. This study addresses a critical gap in the evaluation of single remediation agents, clarifies the scientific basis for material selection, and establishes an integrated research framework from agent screening to field application.

Graphical abstract

Keywords

Cadmium / Biochar / Meta-analysis / Soil remediation / Farmland heavy metals

Highlight

	● Five soil Cd remediation agents were compared via quantitative meta-analysis.
	● Biochar promotes crop growth while reducing Cd accumulation.
	● Biochar showed consistent Cd remediation effects in pot and field experiments.
	● Biochar combined with other materials outperforms biochar alone.

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