Key Takeaways & Executive Findings
- •• • CBC and MBC treatments reduced DTPA-extractable Cd by 45.73% and 48.92%, respectively, demonstrating high efficacy in immobilizing cadmium in contaminated soils. • • The C5 treatment increased leaf area by 100%, and M7 increased plant height by 26.8%, indicating significant promotion of Brassica napus growth under Cd stress. • • M3 treatment reduced MDA by 72.5% and H2O2 by 61.2%, showing substantial alleviation of oxidative stress in plants. • • Phosphorus-enriched biochar exhibited sustained phosphorus release, improving soil phosphorus availability while minimizing environmental losses, as evidenced by changes in soil solution phosphorus.
Abstract
Cadmium (Cd) contamination in farmland soils poses a threat to food security, necessitating effective remediation strategies. This study prepared three types of phosphorus-enriched biochar (PBC) from rice straw and different phosphorus sources (fused calcium magnesium phosphate, citric acid-activated fused calcium magnesium phosphate, and monocalcium phosphate) to evaluate their potential in stabilizing Cd(II), releasing phosphorus, and enhancing plant resistance to heavy metal stress. Under Cd stress, PBC amendments significantly improved soil physicochemical properties and reduced Cd bioavailability through direct immobilization (adsorption, precipitation) and indirect mechanisms. Specifically, CBC and MBC treatments reduced DTPA-extractable Cd by 45.73% and 48.92%, respectively. The porous structure of biochar facilitated sustained phosphorus release, influencing soil solution phosphorus dynamics. In pot experiments with Brassica napus L., PBC application significantly improved agronomic traits and reduced oxidative stress markers. The C5 treatment increased leaf area by 100%, M7 increased plant height by 26.8%, and M3 reduced malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents by 72.5% and 61.2%, respectively. These findings demonstrate that PBC effectively alleviates Cd toxicity, promotes plant growth, and enhances stress resistance, offering a feasible strategy for remediating Cd-contaminated soils while providing a sustainable phosphorus source.
1. Introduction
Cadmium (Cd) contamination in agricultural soils is a pressing global issue, arising from industrial activities, mining, and improper waste disposal. Cd is highly toxic and readily accumulates in crops, posing severe risks to human health through the food chain. Conventional remediation techniques, such as soil washing or excavation, are often costly and disruptive. In situ immobilization using amendments like biochar and phosphate compounds has emerged as a cost-effective and environmentally friendly alternative. However, single amendments often have limitations: biochar alone may have limited sorption capacity for Cd, while soluble phosphate fertilizers can lead to eutrophication and rapid leaching. The combination of biochar with phosphorus sources, termed phosphorus-enriched biochar (PBC), aims to synergistically enhance Cd immobilization and provide a slow-release phosphorus fertilizer, addressing both soil remediation and nutrient management.
This study addresses the bottleneck of using low-grade phosphate rocks and their derivatives, which are often underutilized due to contamination issues. By employing three different phosphorus sources—fused calcium magnesium phosphate, citric acid-activated fused calcium magnesium phosphate, and monocalcium phosphate—the researchers prepared PBCs with distinct properties. The experimental protocol systematically evaluates the effects of these PBCs on soil Cd stabilization, phosphorus release kinetics, and plant physiological responses under Cd stress. The findings provide critical insights into the design of efficient PBCs for sustainable agriculture and soil remediation, offering a dual benefit of heavy metal immobilization and nutrient supply.
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LIN Yuhan, ZENG Yang, MA Ming, CHEN Hong (2026). Phosphorus-Enriched Biochar Promotes Brassica napus L. Growth under Cadmium Stress by Immobilizing Cadmium and Sustained Phosphorus Release. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2025011002
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Frequently Asked Questions
What are the specific mechanisms by which phosphorus-enriched biochar (PBC) immobilizes cadmium in soil?
PBC immobilizes Cd through direct mechanisms such as adsorption onto the biochar surface and precipitation with phosphate ions, forming insoluble Cd-phosphate complexes. Additionally, PBC alters soil physicochemical properties (e.g., pH, organic matter content), which indirectly reduces Cd bioavailability. The study observed reductions in DTPA-extractable Cd by up to 48.92% in MBC treatments, confirming effective immobilization.
How does the phosphorus release profile of PBC compare to conventional soluble phosphate fertilizers, and what are the implications for plant nutrition?
PBC exhibits a sustained-release pattern due to the porous structure of biochar, which restricts rapid phosphorus dissolution. This slow release aligns with plant uptake demands, reducing phosphorus loss and eutrophication risk. In the study, PBC treatments improved plant growth (e.g., 100% increase in leaf area) and reduced oxidative stress, indicating efficient phosphorus supply and enhanced stress tolerance.
What is the cost-effectiveness of using low-grade phosphate sources in PBC production compared to traditional phosphorus fertilizers?
Utilizing low-grade phosphate rocks and industrial by-products (e.g., fused calcium magnesium phosphate) reduces raw material costs and addresses waste management issues. The study demonstrates that these alternative phosphorus sources can be effectively activated (e.g., citric acid activation) to produce PBCs with comparable or superior performance, offering a cost-effective and sustainable approach for soil remediation and fertilization.
Are there any potential long-term risks associated with the application of PBC, such as secondary release of cadmium or phosphorus leaching?
The study suggests that PBC's porous structure and high surface area limit phosphorus release, reducing leaching potential. Additionally, the biochar matrix can stabilize cadmium, preventing secondary release. However, long-term field studies are needed to assess the persistence of these effects and the fate of immobilized Cd under varying environmental conditions.
How does the choice of phosphorus source affect the physicochemical properties and performance of the resulting biochar?
Different phosphorus sources influence the surface chemistry, porosity, and phosphorus release kinetics of the biochar. For instance, citric acid activation of fused calcium magnesium phosphate may enhance phosphorus solubility and biochar surface functionality. The study found that all three PBCs effectively reduced Cd bioavailability and promoted plant growth, but specific treatments (e.g., M3) showed superior reduction in oxidative stress markers, indicating source-dependent variations in performance.
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