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

Abstract

Paddy rice is efficient at arsenite accumulation by sharing the uptake and transport pathway for silicic acid. To limit As entry into rice by increasing soil Si availability, rice husk with concentrated Si deposition was subject to an ethanol-aided open combustion in this work to promote Si release from organic matrix. Compared to original husk, the content of amorphous silica was almost tripled in the resultant ash (Si-ash) with an apparent elimination of hydrocarbon groups. Following its incorporation into soil, 3.4-fold higher Si dissolution was maintained in rice rhizosphere compared to control, which was accompanied by 15.9–40.5% decrease in porewater As from tillering to harvest. Correspondingly, As sequestration in soil solid phase and root plaque increased by 8.0% and 26.9% with Si-ash, which could result from promoted FeAs co-precipitation by the liming effect of Si-ash and was linked to a notable decline in As transport through node I. Consequently, inorganic As (iAs) in white rice decreased from 0.36 mg kg−1 in control to 0.17 mg kg−1 with Si-ash, which is 15% lower than Chinese food safety standard. Results from this study highlight the advantage of Si-ash in securing rice production by mitigating iAs accumulation in white rice with fortified Si nutrition.