Using an improved Si-rich husk ash to decrease inorganic arsenic in rice grain.

Area of Science:

• Agricultural Science
• Environmental Chemistry
• Soil Science

Background:

• Paddy rice readily accumulates arsenite (As) due to shared uptake pathways with silicic acid (Si).
• Increasing soil Si availability is a strategy to limit As entry into rice plants.

Purpose of the Study:

• To develop an effective method for releasing Si from rice husk for soil amendment.
• To evaluate the impact of Si-ash on As accumulation in rice and soil.

Main Methods:

• Rice husk underwent ethanol-aided open combustion to produce Si-ash, rich in amorphous silica.
• Si-ash was incorporated into soil, and its effect on Si dissolution, As concentration in porewater, and As sequestration was measured.
• Inorganic As (iAs) levels in white rice were quantified.

Main Results:

• Si-ash showed a threefold increase in amorphous silica content compared to raw rice husk.
• Si-ash application led to higher Si dissolution in the rice rhizosphere and reduced porewater As by 15.9–40.5%.
• As sequestration in soil and root plaque increased, and inorganic As in white rice decreased to 0.17 mg kg⁻¹, below the Chinese food safety standard.

Conclusions:

• Ethanol-aided combustion effectively produces Si-rich ash from rice husk.
• Si-ash application mitigates inorganic As accumulation in rice by enhancing soil Si and promoting As co-precipitation.
• Si-ash offers a promising approach for securing rice production and ensuring food safety through fortified Si nutrition.