Department of Plant and Soil Sciences, University of Delaware, Newark, Delaware 19716, USA.
Environ Sci Technol. 2012 Dec 18;46(24):13176-83. doi: 10.1021/es3025337. Epub 2012 Nov 29.
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(L), 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 on arsenic uptake.
砷污染的大米可能会对全球人类健康构成威胁。由于 H₃AsO₃⁰ 是稻田孔隙水中主要的砷形态，且 H₄SiO₄⁰ 和 H₃AsO₃⁰ 具有相同的吸收途径，因此人们提出添加硅来减少砷的吸收，从而降低谷物中的砷浓度。在这里，我们评估了两种在溶解性上存在差异的硅酸盐矿物（+Si(L)，硅藻土，0.29 mM Si；+Si(H)，硅凝胶，1.1 mM Si）对矿物组成不同的土壤中砷在水稻中的浓度的影响。+Si(L)的添加既没有改变孔隙水中的砷浓度，也没有改变相对（+As--Si）对照的谷物砷含量。+Si(H)的添加增加了孔隙水中的砷，但与（+As--Si）对照相比，它显著降低了谷物中的砷含量。只有+Si(H)的添加导致稻草和稻壳中的硅含量显著增加。总谷物和稻草中的砷与孔隙水中的硅呈负相关，并且这种关系在两种表现出不同矿物学特征的土壤之间存在差异。这些不同的结果是由于 H₄SiO₄⁰ 和 H₃AsO₃⁰ 之间对土壤固相吸附位点的竞争以及随后的植物吸收所致，这说明了硅矿物学对砷吸收的重要性。
