Biochar and ash derived from silicon-rich rice husk decrease inorganic arsenic species in rice grain

Area of Science:

• Environmental Science
• Agricultural Science
• Soil Chemistry

Background:

• Arsenic (As) in rice poses a global health risk.
• Limited understanding of rice residue impacts on arsenic phytoavailability.
• Need for sustainable methods to reduce arsenic in rice grain.

Purpose of the Study:

• To investigate the effects of rice husk biochar (RHB) and rice husk ash (RHA) on arsenic speciation and dynamics in paddy soils.
• To assess the impact of RHB and RHA on arsenic accumulation in rice grain.
• To understand the transformation of arsenic fractions in soil and their relationship with plant uptake.

Main Methods:

• Application of RHB and RHA (0.64% w/w) to paddy soil.
• Analysis of arsenic speciation in rice grain, soil porewater, and solid-phase fractions using sequential extraction.
• Quantification of inorganic arsenic in rice grain and soil.

Main Results:

• RHB and RHA treatments significantly reduced inorganic arsenic in rice grain to levels below the Codex maximum.
• The residual arsenic fraction (F6) dominated soil arsenic pools.
• Amendments promoted residual phase formation, decreasing arsenic availability and uptake by rice plants.

Conclusions:

• Rice husk biochar and ash are effective in mitigating inorganic arsenic accumulation in paddy rice.
• These amendments enhance the formation of stable arsenic fractions in soil, reducing bioavailability.
• RHB and RHA offer a sustainable strategy to improve rice safety and reduce human exposure to arsenic.