Organic fertilizer compounds help biochar lock cadmium in contaminated soil
Separating dissolved organic matter by molecular size could improve the design of soil amendments that limit cadmium uptake by crops
Shenyang Agricultural University Collaborative Journals
image:
Enhancement of organic fertilizer-derived dissolved organic matter fractions on cadmium immobilization by biochar composites in contaminated soil
view moreCredit: Lan Wei, Danni Liu, Weisheng Chen, Lianxi Huang, Shaojun Jiang, Xiaodong Zheng, Zhongzhen Liu, & Yanhong Wang
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.
===
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
===
About Agricultural Ecology and Environment:
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.
Follow us on Facebook, X, and Bluesky.
Journal
Agricultural Ecology and Environment
Method of Research
Experimental study
Article Title
Enhancement of organic fertilizer-derived dissolved organic matter fractions on cadmium immobilization by biochar composites in contaminated soil
Turning rice straw into biochar may reduce heavy metal risks in rice
A greenhouse study suggests that converting rice straw into biochar could offer a safer and more sustainable alternative to directly incorporating straw into paddy soils
image:
Incorporating rice straw in the form of biochar: a sustainable measure to protect humans from heavy metal exposure
view moreCredit: Jiannan Liao, Wenjing Ning, Yu Gong, Wenli Tang, & Huan Zhong
Rice straw is often returned directly to agricultural fields to recycle nutrients, improve soil quality, and avoid open burning. However, new research shows that this common practice may have complex and potentially undesirable effects on the accumulation of heavy metals in rice grains.
In a study published in Environmental and Biogeochemical Processes, researchers evaluated how six rice straw management strategies affected the accumulation of arsenic, cadmium, copper, nickel, lead, and zinc in rice. Their findings indicate that converting rice straw into biochar before applying it to soil may provide greater environmental and food safety benefits than directly incorporating untreated straw.
“Rice straw is a valuable agricultural resource, but its effects on contaminants cannot be judged by examining only one metal,” said corresponding author Huan Zhong of Nanjing University. “Our results highlight the importance of evaluating multiple contaminants together and suggest that straw-derived biochar could help balance crop production, pollution control, and climate goals.”
The researchers conducted a greenhouse pot experiment using cadmium-contaminated paddy soil collected from Jiangsu Province, China. They compared untreated soil with five straw management approaches, including direct straw incorporation, accelerated straw decomposition, soil pH adjustment, modified water management, and the application of rice straw-derived biochar.
Direct incorporation of rice straw produced sharply different effects among the six metals. Arsenic concentrations in rice grains increased by 73.1%, while copper and lead concentrations decreased by 13.8% and 89.3%, respectively. Cadmium, nickel, and zinc concentrations did not change significantly under the experimental conditions.
Attempts to reduce the unintended increase in metal accumulation by accelerating straw decomposition, raising soil pH, or changing water availability were not consistently successful. In some cases, these measures created additional problems. Water-saving management, for example, caused grain cadmium concentrations to rise approximately 30-fold and exceed China’s national food safety limit.
These findings demonstrate why recommendations based on a single contaminant can be misleading. Organic matter released during straw decomposition may bind strongly to some metals, such as copper and lead, while changing soil chemistry and microbial activity in ways that increase the mobility or transformation of other elements, including arsenic.
By comparison, rice straw-derived biochar applied at a relatively low rate of approximately 0.3% did not significantly increase any of the six metals in rice grains. The biochar treatment also reduced copper and lead accumulation, improved several soil properties, and produced the highest grain and whole-plant biomass among the tested treatments.
Biochar is produced by heating biomass under oxygen-limited conditions. This process creates a stable, carbon-rich material that can be added to soil. Converting straw into biochar may also help avoid air pollution from open burning and reduce the greenhouse gas emissions associated with the decomposition of untreated straw in flooded paddies.
The authors caution that the experiment was conducted in pots using one type of contaminated soil. Field studies across different soils, climates, and rice varieties will be needed before large-scale recommendations can be made. Economic factors, including straw collection, biochar production, transportation, and application costs, must also be considered.
The study nevertheless identifies low-dose straw-derived biochar as a promising strategy for managing agricultural residues while supporting rice production, reducing heavy metal exposure, and improving environmental sustainability.
===
Journal reference: Liao J, Ning W, Gong Y, Tang W, Zhong H. 2026. Incorporating rice straw in the form of biochar: a sustainable measure to protect humans from heavy metal exposure. Environmental and Biogeochemical Processes 2: e012 doi: 10.48130/ebp-0026-0007
https://www.maxapress.com/article/doi/10.48130/ebp-0026-0007
===
About the Journal:
Environmental and Biogeochemical Processes (e-ISSN 3070-1708) is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.
Follow us on Facebook, X, and Bluesky.
Journal
Environmental and Biogeochemical Processes
Method of Research
Experimental study
Article Title
Incorporating rice straw in the form of biochar: a sustainable measure to protect humans from heavy metal exposure
A tiny gene edit makes rice safer without reducing harvests
Researchers identified a precise gene edit that lowers cadmium in rice grains while maintaining yield and essential mineral nutrients
image:
Base editing of OsNramp5 identified the I441T mutation, which significantly reduced cadmium (Cd) accumulation in brown rice while maintaining normal manganese (Mn) levels, highlighting its potential for developing safer rice varieties without affecting essential nutrient uptake
view moreCredit: Professor Jian Feng Ma from Okayama University, Japan
Cadmium (Cd) contamination poses a serious threat to global food safety. As a toxic and carcinogenic heavy metal, cadmium can accumulate in agricultural soils through industrialization and urbanization before entering the human food chain. Rice is especially vulnerable because it absorbs more cadmium than other major cereal crops, making it one of the largest dietary sources of cadmium exposure for nearly half of the world's population. Although researchers have long sought to develop rice varieties with lower cadmium levels, existing approaches often reduce the uptake of essential nutrients or compromise crop growth and grain yield, limiting their practical use.
Addressing this challenge, a research team led by Dr. Sheng Huang and Professor Jian Feng Ma from the Institute of Plant Science and Resources, Okayama University, Japan, together with Professor Jiayang Li’s group from the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, China, used precise base-editing technology to identify a beneficial point mutation in the rice metal transporter gene OsNramp5. Through saturation mutagenesis targeting OsNramp5, the researchers screened hundreds of genome-edited rice lines to identify variants that accumulated less cadmium while maintaining normal manganese uptake and plant performance. They discovered that replacing a single amino acid, isoleucine with threonine at position 441 (OsNramp5I441T), produced the most promising result. Their findings were published in Volume 123 of the journal Proceedings of the National Academy of Sciences (PNAS) on June 18, 2026.
The researchers generated more than 1,600 genome-edited rice lines using adenine and cytosine base editors and screened them for reduced cadmium accumulation. After identifying the most promising mutant, they carried out detailed physiological analyses, gene expression studies, protein localization experiments, yeast transport assays, and field trials on cadmium-contaminated soil.
The results showed that the OsNramp5I441T mutation reduced cadmium accumulation in both shoots and grains without altering gene expression, protein abundance, cellular localization, or grain yield. In field experiments, cadmium concentration in brown rice decreased by 48%, from 0.14 mg/kg in the wild-type plants to 0.07 mg/kg in the edited plants, while concentrations of essential micronutrients, including iron, manganese, and zinc, remained unchanged.
Further investigation revealed why this single amino acid change was so effective. Although OsNramp5 was already known to transport manganese and cadmium, the researchers discovered that it also transports zinc. The I441T mutation increased the transporter's preference for zinc, allowing more zinc to accumulate in root cells. This elevated zinc then competed with cadmium during root-to-shoot transport, reducing the movement of cadmium into the shoots and eventually the grains. Rather than blocking cadmium uptake completely, the mutation selectively limited its translocation, solving a long-standing challenge of lowering grain cadmium without disrupting the plant's supply of essential minerals.
The study offers a practical solution for improving food safety through precision breeding. Existing strategies to reduce cadmium in rice, including soil amendments, water management, or complete knockout of OsNramp5, can be costly, time-consuming, or negatively affect plant growth because OsNramp5 also transports manganese, an essential nutrient. By modifying only a single amino acid instead of disabling the entire gene, the researchers preserved normal plant growth, grain yield, and the accumulation of essential micronutrients while substantially lowering cadmium levels.
“We have been working on cadmium accumulation in rice for more than 20 years and have identified several key genes involved in this process. Because OsNramp5 also transports essential metals, we aimed to alter its metal selectivity rather than eliminate its function, leading us to this successful point mutation,” explains Prof. Ma.
Overall, the discovery provides a valuable genetic resource for breeding rice varieties with safer grain and demonstrates how precise genome editing can overcome limitations that conventional breeding or gene knockout approaches cannot. The researchers believe the newly identified OsNramp5I441T allele could accelerate the development of low-cadmium rice cultivars suitable for cultivation on mildly contaminated soils while maintaining productivity and nutritional quality. “This mutation provides an effective strategy for reducing cadmium accumulation in rice grain without compromising yield or essential mineral nutrition, offering a promising approach for producing safer rice for consumers,” Prof. Ma concludes.
Reference
DOI: https://doi.org/10.1073/pnas.2610609123
About Okayama University, Japan
As one of the leading universities in Japan, Okayama University aims to create and establish a new paradigm for the sustainable development of the world. Okayama University offers a wide range of academic fields, which become the basis of the integrated graduate schools. This not only allows us to conduct the most advanced and up-to-date research, but also provides an enriching educational experience.
Website: https://www.okayama-u.ac.jp/index_e.html
About Assistant Professor Sheng Huang from Okayama University, Japan
Dr. Sheng Huang is an Assistant Professor (Specially Appointed) and plant molecular biologist at the Institute of Plant Science and Resources, Okayama University, Japan. He earned his Ph.D. in Plant Nutrition from Okayama University, where he began his doctoral research in 2017. His research focuses on sustainable and safe crop production by uncovering how plants respond to mineral stresses. His expertise includes plant mineral nutrition, mineral transporters, molecular biology, biochemistry, genetics, and agricultural sciences, with particular emphasis on grains, xylem, and vascular bundles. He has authored 28 research articles, six reviews, and two book chapters with 2,147 citations and an h-index of 20.
Journal
Proceedings of the National Academy of Sciences
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Genome-edited rice variety with low-cadmium accumulation in the grain
Article Publication Date
18-Jun-2026
COI Statement
Based on the results reported in this article, a China patent application (202410081586.2) has been applied by Institute of Genetics and Developmental Biology with associated authors J.L., H.Y., W.C., X.M., W.W., and Y.J.
