Biochar and selenium: a two-pronged strategy to safeguard rice from cadmium contamination

A comprehensive review by scientists at the University of Science and Technology of China, Nanjing Agricultural University, and other collaborating institutions details a promising approach to combat cadmium contamination in rice. Cadmium, a toxic heavy metal, poses a significant threat to global food safety as it accumulates in paddy soils and is readily absorbed by rice plants. This contamination reduces crop yields and presents serious health risks to the more than 50% of the global population that relies on rice as a primary food source. The study examines how applying biochar and selenium to the soil can effectively limit cadmium uptake, leading to safer rice and improved harvests.

The Global Cadmium Problem

Cadmium enters agricultural ecosystems through both natural processes and human activities, including industrial pollution and the use of certain fertilizers. Once in the soil, it is highly mobile and easily absorbed by rice roots, eventually concentrating in the edible grains. Chronic dietary exposure to cadmium is linked to severe health conditions, including kidney and liver malfunction, osteoporosis, and an increased risk of certain cancers. The historical "Itai-Itai" disease in Japan serves as a stark reminder of the devastating public health consequences of consuming cadmium-contaminated rice. The review, led by first author Ofori Prince Danso, consolidates existing research to present effective management strategies.

How Biochar Locks Away Toxins

One of the key strategies examined is the use of biochar, a charcoal-like material produced by heating biomass in a low-oxygen environment. When added to soil, biochar acts like a sponge for cadmium. Its porous structure and large surface area allow it to immobilize the toxic metal through adsorption and precipitation. This process locks cadmium in the soil, converting it into a form that is less soluble and therefore less available for rice plants to absorb through their roots. The review notes that in addition to detoxifying the soil, biochar offers co-benefits by improving soil structure, increasing pH, and enhancing nutrient retention.

Selenium's Protective Role

The second component of the strategy is selenium, a micronutrient essential for human health. While not required for plant growth, selenium application has been shown to counteract cadmium toxicity in rice plants. According to the research, selenium works through multiple mechanisms. It can compete with cadmium for uptake by the plant's roots, form inert cadmium-selenium complexes in the soil, and bolster the plant's internal antioxidant defense system. This helps the plant withstand the oxidative stress caused by cadmium exposure, protecting its cells and metabolic functions, such as photosynthesis.

A Powerful Combination for Safer Rice

The review emphasizes that the combined application of biochar and selenium creates a synergistic effect, offering greater protection than either amendment alone. Biochar improves the soil conditions, which in turn enhances the retention and availability of selenium in the root zone. This allows selenium to more effectively compete with cadmium and fortify the plant's defenses. Studies show this dual approach significantly reduces the amount of cadmium that is transported from the roots to the shoots and ultimately to the rice grains, bringing contamination levels down to safe limits for human consumption.

Boosting Yields and Improving Health

Beyond making rice safer to eat, the application of biochar and selenium also contributes to better plant health and higher crop yields. In cadmium-contaminated environments, rice plants often experience stunted growth and reduced grain production. By mitigating cadmium's toxic effects and improving overall soil fertility, these amendments help rice plants grow more robustly. The research demonstrates that this integrated strategy can lead to substantial increases in plant height, biomass, and the final grain yield, presenting a valuable method for farmers to maintain productivity in affected areas.

A Path Forward for Sustainable Agriculture

The authors conclude that managing cadmium with biochar and selenium is a convincing method for safer and more sustainable rice production. Corresponding authors Xuebin Yin and Renbin Zhu suggest that future work should focus on optimizing application methods and dosages for different soil types and environmental conditions. They also call for continued research into the long-term effectiveness of these amendments and their potential to address other agricultural challenges, such as drought. The review advocates for establishing stronger international communication and stringent contamination standards to ensure the safety of the global rice supply chain.

Corresponding Author:

Xuebin Yin or Renbin Zhu

Original Source:

https://doi.org/10.1007/s44246-023-00073-1

Contributions:

Prince Ofori Danso conceived the presented idea and wrote the manuscript. Adolf Acheampong Assisted in writing the manuscript and contributed to the final version of the manuscript. Zezhou Zhang, Song Jianping, Jun Dai and Tang Zhi: contributed to the final version of the manuscript. Xuebin Yin, Renbin Zhu and Zhangmin Wang acquisition of the financial support for the project leading to this publication and supervised the study. All authors read and approved the final manuscript.