ISTerre, Université Grenoble Alpes, CNRS, CS 40700, 38058 Grenoble , France.
State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry , Chinese Academy of Sciences , Guiyang 550081 , People's Republic of China.
Environ Sci Technol. 2018 Apr 3;52(7):3935-3948. doi: 10.1021/acs.est.7b05452. Epub 2018 Mar 14.
Plant leaves serve both as a sink for gaseous elemental mercury (Hg) from the atmosphere and a source of toxic mercury to terrestrial ecosystems. Litterfall is the primary deposition pathway of atmospheric Hg to vegetated soils, yet the chemical form of this major Hg input remains elusive. We report the first observation of in vivo formation of mercury sulfur nanoparticles in intact leaves of 22 native plants from six different species across two sampling areas from China. The plants grew naturally in soils from a mercury sulfide mining and retorting region at ambient-air gaseous-Hg concentrations ranging from 131 ± 19 to 636 ± 186 ng m and had foliar Hg concentration between 1.9 and 31.1 ng Hg mg dry weight (ppm). High energy resolution X-ray absorption near-edge structure (HR-XANES) spectroscopy shows that up to 57% of the acquired Hg is nanoparticulate, and the remainder speciated as a bis-thiolate complex (Hg(SR)). The fractional amount of nanoparticulate Hg is not correlated with Hg concentration. Variation likely depends on leaf age, plant physiology, and natural variability. Nanoparticulate Hg atoms are bonded to four sulfide or thiolate sulfur atoms arranged in a metacinnabar-type (β-HgS) coordination environment. The nanometer dimension of the mercury-sulfur clusters outmatches the known binding capacity of plant metalloproteins. These findings give rise to challenging questions on their exact nature, how they form, and their biogeochemical reactivity and fate in litterfall, whether this mercury pool is recycled or stored in soils. This study provides new evidence that metacinnabar-type nanoparticles are widespread in oxygenated environments.
植物叶片既是大气中气态元素汞 (Hg) 的汇，也是向陆地生态系统释放有毒汞的源。凋落物是大气 Hg 沉降到植被土壤的主要途径，但这种主要 Hg 输入的化学形态仍难以捉摸。我们首次观察到 22 种来自中国两个采样区的 6 个不同物种的完整叶片内活体形成的汞硫纳米颗粒。这些植物在自然条件下生长在硫化汞矿区及其热解区的土壤中，环境大气气态-Hg 浓度范围为 131 ± 19 至 636 ± 186 ng m，叶片 Hg 浓度在 1.9 至 31.1 ng Hg mg 干重（ppm）之间。高能量分辨 X 射线吸收近边结构（HR-XANES）光谱表明，高达 57%的获取 Hg 为纳米颗粒，其余的 Hg 以双硫代配合物（Hg(SR)) 形式存在。纳米颗粒 Hg 的分数与 Hg 浓度无关。这种变化可能取决于叶片年龄、植物生理学和自然变异。纳米颗粒 Hg 原子与四个硫化物或硫醇硫原子键合，形成辰砂型（β-HgS）配位环境。汞-硫簇的纳米尺寸超出了植物金属蛋白的已知结合能力。这些发现引发了有关其确切性质、形成方式以及在凋落物中生物地球化学活性和命运的挑战性问题，包括这个汞库是被循环利用还是储存在土壤中。这项研究提供了新的证据，证明辰砂型纳米颗粒在含氧环境中广泛存在。
