# Mechanistic Pathways Controlling Cadmium Bioavailability and Ecotoxicity in Agricultural Systems: A Global Meta-Analysis of Lime Amendment Strategies

## TL;DR

This study uses a global meta-analysis to show how lime-based materials reduce cadmium in crops, offering strategies for effective and cost-efficient soil remediation.

## Contribution

The study provides a mechanistic framework for cadmium remediation through comparative analysis of lime amendment strategies.

## Key findings

- Lime-based materials reduced grain cadmium by 45% through chemical fixation and ionic competition.
- Calcium hydroxide rapidly reduced bioavailable cadmium by 59%, while calcium carbonate provided 66% long-term grain protection.
- Calcium carbonate was found to be 5–10 times more cost-effective than other lime-based materials.

## Abstract

Cadmium contamination in agricultural soils threatens food safety through crop bioaccumulation, particularly in rice. Lime-based materials (calcium carbonate, calcium hydroxide, and calcium oxide) are commonly applied to mitigate cadmium uptake, yet comparative effectiveness and mechanistic understanding remain limited. This meta-analysis synthesized data from 55 studies encompassing 260 field experiments to evaluate how these three materials regulate cadmium transfer from soil to grain. Results indicate all materials reduced grain cadmium by approximately 45%, operating through dual mechanisms: chemical fixation transforms cadmium into stable soil forms, while ionic competition involves calcium blocking cadmium entry at root membranes. Calcium hydroxide demonstrated rapid soil immobilization capacity, reducing bioavailable cadmium by 59%. Calcium carbonate exhibited superior long-term grain protection (66% reduction) via sustained calcium release synchronized with critical grain-filling stages. Economic analysis revealed calcium carbonate provides 5–10 fold better cost-effectiveness than alternatives. These findings enable targeted material selection: calcium hydroxide for emergency soil remediation versus calcium carbonate for sustained crop protection. This mechanistic framework advances cadmium remediation from empirical application toward process-based strategies that integrate geochemical stabilization with plant physiological protection.

Cadmium (Cd) contamination in agricultural systems poses significant ecotoxicological risks through bioaccumulation in food chains. While lime-based amendments are widely applied for Cd immobilization, mechanistic understanding of bioavailability control pathways remains limited. This study employed a meta-analysis methodology based on 260 datasets from 55 publications to systematically investigate the mechanisms and differences in the effectiveness of calcium hydroxide, calcium carbonate, and calcium oxide in regulating Cd migration in acidic soil–plant systems. The study revealed that lime-based materials synergistically regulated Cd migration through two processes: chemical fixation and ionic competition. Results showed lime application reduced soil available Cd by 33.0%, decreased grain Cd by 44.8%, increased soil pH by 15.6%, and enhanced exchangeable Ca by 35.2%. Chemical fixation was evidenced by Cd transformation from labile to stable forms (residual Cd: +29.5%, acid-soluble Cd: −17.5%). Ionic competition was quantitatively confirmed through strong negative correlation between exchangeable Ca and grain Cd (R2 = 0.704). Among the materials, Ca(OH)2 exhibits the highest efficiency in rapid pedogenic passivation (58.7% reduction in available Cd), whereas CaCO3 demonstrates superior long-term grain Cd attenuation (65.7% inhibition) via sustained Ca2+ release and rhizosphere-regulated dissolution. This study advances mechanistic understanding of Cd bioavailability control and establishes quantitative frameworks for predicting ecotoxicological outcomes, providing scientific basis for optimizing remediation strategies to minimize Cd transfer through agricultural food chains.