The wide use of silver ions (Ag⁺) and silver nanoparticles (AgNPs) and their inevitable release into the environment have caused great concern over their environmental and health risks. The understanding of their uptake and accumulation by plants, especially food crops, is important to evaluate their risks. We reported herein the distinct accumulation and translocation characteristics of Ag⁺ and AgNPs in a rice plant (Oryza sativa L.) at exposure doses of 2, 5, 10, and 20 mg L⁻¹, as well as the critical impact of iron plaque on their assimilation by the plant. As revealed by silver K-edge X-ray absorption near-edge structure (XANES), Ag⁺ in/on the roots was exclusively transformed into AgCl with Cl⁻ in hydroponic medium. As a result, AgCl maintained Ag⁺ on the root surface, lowering its bioavailability and translocation (with translocation factors, TFs, from 0.44 × 10⁻³ to 1.79 × 10⁻³). On the contrary, AgNPs were assimilated and translocated more effectively (with TFs from 2.44 × 10⁻³ to 1.23 × 10⁻²) in comparison to Ag⁺, although a fraction was transformed into ionic silver species. XANES demonstrated that the iron plaque present on the rice roots could oxidize AgNPs into ionic Ag species, such as AgCl and Ag⁺–thiol complexes, and increase the uptake and translocation of silver in the rice plant. Compared to iron plaque, dissolved iron was less effective in oxidizing AgNPs. Our findings highlighted the importance of Ag species interconversion and iron plaque in the uptake and translocation of Ag, providing useful data for an improved risk assessment of AgNPs and Ag⁺ under environmental scenarios.

中文翻译：

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水稻（Oryza sativa L.）中银纳米颗粒和银离子的转化和吸收：铁斑和溶解铁的影响

银离子（Ag ⁺）和银纳米颗粒（AgNPs）的广泛使用以及它们不可避免地释放到环境中引起了人们对其环境和健康风险的极大关注。了解植物（特别是粮食作物）对它们的吸收和积累对评估其风险很重要。我们在本文中报道了在暴露剂量为2、5、10和20 mg L ^-1的水稻植物（水稻）中Ag ⁺和AgNPs的独特积累和转运特性，以及铁斑的关键影响被植物吸收。正如银K边缘X射线吸收近边缘结构（XANES）所揭示的那样，根中/根上的Ag ⁺仅与Cl转化为AgCl。⁻在水培培养基中。结果，AgCl保持了根表面上的Ag ⁺，降低了其生物利用度和易位性（易位因子TFs从0.44×10 ^-3降至1.79×10 ^-3）。相反，与Ag ⁺相比，AgNP被同化和转移的效率更高（TF从2.44×10 ^-3到1.23×10 ^-2），尽管一部分被转化为离子银。XANES表明，水稻根部存在的铁斑可以将AgNPs氧化成离子Ag物质，例如AgCl和Ag ⁺-硫醇配合物，并增加稻米中银的吸收和转运。与铁斑块相比，溶解的铁在氧化AgNPs方面效果较差。我们的研究结果突显了Ag物种相互转化和铁斑块对Ag吸收和转运的重要性，为在环境情景下改进AgNPs和Ag ^+的风险评估提供了有用的数据。