Simultaneous decrease of arsenic and cadmium in rice (Oryza sativa L.) plants cultivated under submerged field conditions by the application of iron-bearing materials

The Codex Alimentarius Commission has recently adopted maximum levels for inorganic arsenic (As; in 2014) and total cadmium (Cd; in 2006) in polished rice grains to maintain food safety and to decrease the risk to human health. As rice is a staple crop in Japan and monsoon Asian countries, reducing concentrations of As and Cd in rice is an urgent matter. In flooded conditions, Cd concentration in soil solution decreases whereas As concentration increases. Therefore, we aimed to evaluate the efficiency of iron-bearing materials to decrease As concentration in soil solution and rice (Oryza sativa L.) grain under submerged cultivation, while also considering Cd concentration. In experiments conducted in paddy fields in six regions, As concentrations in the soil solution during the cultivation period decreased in the following order: control (REF) > steel converter furnace slag (SCS) > non-crystalline iron hydroxide (FH) > zero-valent iron (ZVI). The concentrations of As in brown rice were in the same order, with ZVI achieving particularly strong reduction. Cadmium concentrations were low, probably owing to submerged cultivation conditions. Application of iron-bearing materials slightly and insignificantly reduced the yields of brown rice and straw. Application of these materials did not have a significant negative impact on the quality of rice. Our data indicate that the application of iron-bearing materials effectively reduces As concentrations in soil solution and rice grains without negative effects on yield and quality, with a particularly powerful effect of ZVI which is possibly explained by arsenic sulfide formation.国际食品法典委员会（Codex Alimentarius Commission）近期分别于2014年和2006年制定了精米籽粒中无机砷（inorganic arsenic, As）与总镉（total cadmium, Cd）的最大限量标准，旨在保障食品安全、降低人体健康风险。鉴于水稻是日本及季风亚洲国家的主粮作物，降低稻米中砷与镉的浓度已成为亟待解决的问题。在淹水条件下，土壤溶液中的镉浓度会降低，而砷浓度则会升高。为此，本研究旨在评估含铁材料在淹水栽培模式下，对土壤溶液及水稻（Oryza sativa L.）籽粒中砷浓度的消减效果，同时同步考察镉浓度的变化。针对6个地区稻田开展的田间试验结果显示，栽培期内土壤溶液中的砷浓度按以下顺序递减：对照组（REF）>转炉钢渣（steel converter furnace slag, SCS）>非晶态氢氧化铁（non-crystalline iron hydroxide, FH）>零价铁（zero-valent iron, ZVI）。糙米中的砷浓度也遵循这一排序，其中零价铁的降砷效果尤为显著。试验中镉浓度整体偏低，这可能与淹水栽培的环境条件有关。施用含铁材料仅会对糙米及稻秆的产量造成小幅且无统计学显著性的降低，且未对稻米品质产生显著负面影响。本研究数据表明，施用含铁材料可有效降低土壤溶液及稻米籽粒中的砷浓度，且不会对产量与品质造成负面影响；其中零价铁的效果尤为突出，其作用机制可能与硫化砷（arsenic sulfide）的形成有关。