Silicate Mineral Impacts on the Uptake and Storage of Arsenic and Plant Nutrients in Rice (Oryza sativa L.)

Arsenic-contaminated rice grain may threaten human health globally. Since H3AsO30 is the predominant As species found in paddy pore-waters, and H4SiO40 and H3AsO30 share an uptake pathway, silica amendments have been proposed to decrease As uptake and consequent As concentrations in grains. Here, we evaluated the impact of two silicate mineral additions differing in solubility (+Si-I, diatomaceous earth, 0.29 mM Si; +Si-H, Si-gel, 1.1 mM Si) to soils differing in mineralogy on arsenic concentration in rice. The +Si-L addition either did not change or decreased As concentration in pore-water but did not change or increased grain-As levels relative to the (+As-Si) control. The +Si-H addition increased As in pore-water, but it significantly decreased grain-As relative to the (+As-Si) control. Only the +Si-H addition resulted in significant increases in straw- and husk-Si. Total grain- and straw-As was negatively correlated with pore-water Si, and the relationship differed between two soils exhibiting different mineralogy. These differing results are a consequence of competition between H4SiO40 and H3AsO30 for adsorption sites on soil solids and subsequent plant-uptake, and illustrate the importance of Si mineralogy cn arsenic uptake.