Cadmium contamination in agricultural soil threatens crop safety because the toxic metal can be absorbed by plant roots and enter the food chain. A new study shows that combining biochar with selected components from organic fertilizer could help convert cadmium into less mobile forms, with larger organic molecules generally providing stronger protection.
Researchers prepared a series of biochar composites using dissolved organic matter, or DOM, extracted from a commercial organic fertilizer. They separated the DOM into three molecular weight groups and tested how each group influenced cadmium adsorption, soil chemistry, and cadmium uptake by Chinese cabbage.
The results reveal that the molecular size of organic fertilizer-derived DOM is an important factor controlling how effectively biochar immobilizes cadmium.
"Organic fertilizers contain a highly complex mixture of dissolved compounds, but these compounds do not interact with heavy metals in the same way," said corresponding author Yanhong Wang. "Our findings show that selecting suitable molecular fractions can help us design biochar amendments that hold cadmium more securely in soil and reduce its movement into crops."
The researchers produced biochar from pomelo branches and combined it with DOM fractions weighing less than 3 kilodaltons, between 3 and 10 kilodaltons, or more than 10 kilodaltons. Laboratory adsorption tests showed that loading DOM onto biochar increased its ability to capture cadmium ions. In general, adsorption performance improved as DOM molecular weight increased.
The strongest composite reached a maximum cadmium adsorption capacity of 84.25 milligrams per gram, compared with 54.53 milligrams per gram for the original biochar.
Chemical analyses indicated that different DOM fractions immobilized cadmium through different mechanisms. High-molecular-weight DOM relied mainly on interactions between cadmium and aromatic π-electrons, while lower-molecular-weight DOM provided oxygen-containing functional groups that could form complexes with cadmium.
The team then added the composites to cadmium-contaminated agricultural soil. During a 90-day incubation experiment, the amendments increased soil pH by 0.43 to 0.84 units and reduced available cadmium by approximately 71% to 74% by the end of the experiment.
They also changed the chemical form of the metal. Water-soluble and easily mobile cadmium declined, while the residual fraction, which is considered more stable and less accessible to organisms, increased by as much as 123.77%.
In pot experiments, all biochar-DOM composites reduced cadmium accumulation in the shoots of Chinese cabbage. The most effective treatments lowered shoot cadmium concentrations by up to 74.46%. Composites containing larger DOM molecules also reduced the plant enrichment and root-to-shoot transfer of cadmium more effectively.
The researchers noted that the highest-molecular-weight treatments produced the greatest cadmium reductions but also decreased cabbage biomass under some experimental conditions. This finding highlights the need to optimize application rates so that food safety improvements do not come at the expense of crop productivity.
The study provides a molecular basis for turning organic fertilizer components and agricultural residues into more precisely designed remediation materials. Future research will be needed to test the composites under long-term field conditions, across different soil types, and with a wider range of crops.
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Journal Reference: Wei L, Liu D, Chen W, Huang L, Jiang S, et al. 2026. Enhancement of organic fertilizer-derived dissolved organic matter fractions on cadmium immobilization by biochar composites in contaminated soil. Agricultural Ecology and Environment 2: e013 doi: 10.48130/aee-0026-0008
https://www.maxapress.com/article/doi/10.48130/aee-0026-0008
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Agricultural Ecology and Environment (e-ISSN 3070-0639) is a multidisciplinary platform for communicating advances in fundamental and applied research on the agroecological environment, focusing on the interactions between agroecosystems and the environment. It is dedicated to advancing the understanding of the complex interactions between agricultural practices and ecological systems. The journal aims to provide a comprehensive and cutting-edge forum for researchers, practitioners, policymakers, and stakeholders from diverse fields such as agronomy, ecology, environmental science, soil science, and sustainable development.
