Biochar and smart water could make rice safer in polluted soils
Researchers from the study published in Biochar have demonstrated that using iron and manganese modified biochar (FMBC) with specific irrigation strategies can significantly reduce cadmium and mercury levels in rice grown in co-contaminated paddy fields. This approach could enhance the safety of rice by stabilizing these metals and reducing their uptake, offering a viable solution for managing heavy metal contamination in agricultural soils.
Iron and manganese modified biochar, combined with specific irrigation strategies, can mitigate cadmium and mercury accumulation in rice, according to a recent study. This approach offers a viable solution for safer food production in soils contaminated with both metals.
Cadmium and mercury pose significant risks in agricultural soils, particularly in rice paddies. These metals can enter rice plants, accumulating in grains and posing health risks to consumers. The challenge is compounded by the differing behaviors of these metals in flooded fields. While flooding can reduce cadmium uptake, it may increase the formation of toxic methylmercury. Conversely, aerobic irrigation can lower mercury levels but may increase cadmium absorption.
Published in the journal Biochar, the study explored the use of iron and manganese oxide modified biochar (FMBC) to address this issue. Researchers tested FMBC with two irrigation methods—continuous flooding and continuous aerobic irrigation—in pot experiments using soils contaminated with both cadmium and mercury.
Corresponding author Yuebing Sun noted the difficulty rice farmers face in choosing water conditions that mitigate one metal without exacerbating the other. The study demonstrated that engineered biochar can stabilize both metals and influence microbial processes that control methylmercury formation.
Results indicated a "see-saw" effect of water management. Continuous flooding reduced cadmium bioavailability and encouraged iron and manganese plaques on rice roots, acting as a barrier to cadmium uptake. With FMBC, cadmium concentrations in rice grains decreased to 0.05 mg kg⁻¹, below China's safety limit of 0.2 mg kg⁻¹.
However, flooding alone promoted mercury-methylating microorganisms, increasing methylmercury formation. Aerobic irrigation reduced mercury and methylmercury levels but increased cadmium uptake. FMBC under aerobic conditions minimized mercury risks, with total mercury at 0.02 mg kg⁻¹ and methylmercury at 6.89 μg kg⁻¹, while also limiting cadmium uptake.
FMBC's effectiveness is attributed to its surface functional groups and metal oxides, which bind metals in less available forms. It also enhances root plaque formation, strengthens natural barriers against cadmium, and reduces mercury-methylating microorganisms.
Health risk assessments confirmed the benefits of combining FMBC with water management. Flooding with FMBC reduced cadmium-related dietary risks, while aerobic irrigation with FMBC achieved the lowest hazard quotients for mercury.
The study suggests that the optimal management strategy depends on the dominant contaminant. Continuous flooding with FMBC is most effective for cadmium control, whereas aerobic irrigation with FMBC is best for mercury management. This flexible strategy could improve rice safety in contaminated fields.
Future field studies are needed to validate these findings under real farming conditions. However, the study provides a promising foundation for safer rice production in contaminated regions.
Source: Biochar Feed