Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, New Jersey 07102, USA.
Department of Civil Engineering, MSC01 1070, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Environ Sci Process Impacts. 2021 Feb 4;23(1):73-85. doi: 10.1039/d0em00306a.
We investigated the mechanisms of uranium (U) uptake by Tamarix (salt cedars) growing along the Rio Paguate, which flows throughout the Jackpile mine near Pueblo de Laguna, New Mexico. Tamarix were selected for this study due to the detection of U in the roots and shoots of field collected plants (0.6-58.9 mg kg-1), presenting an average bioconcentration factor greater than 1. Synchrotron-based micro X-ray fluorescence analyses of plant roots collected from the field indicate that the accumulation of U occurs in the cortex of the root. The mechanisms for U accumulation in the roots of Tamarix were further investigated in controlled-laboratory experiments where living roots of field plants were macerated for 24 h or 2 weeks in a solution containing 100 μM U. The U concentration in the solution decreased 36-59% after 24 h, and 49-65% in two weeks. Microscopic and spectroscopic analyses detected U precipitation in the root cell walls near the xylems of the roots, confirming the initial results from the field samples. High-resolution TEM was used to study the U fate inside the root cells, and needle-like U-P nanocrystals, with diameter <7 nm, were found entrapped inside vacuoles in cells. EXAFS shell-by-shell fitting suggest that U is associated with carbon functional groups. The preferable binding of U to the root cell walls may explain the U retention in the roots of Tamarix, followed by U-P crystal precipitation, and pinocytotic active transport and cellular entrapment. This process resulted in a limited translocation of U to the shoots in Tamarix plants. This study contributes to better understanding of the physicochemical mechanisms affecting the U uptake and accumulation by plants growing near contaminated sites.
我们研究了生长在流经新墨西哥州拉古纳普韦布洛附近杰克派勒（Jackpile）矿的帕瓜特河（Rio Paguate）的柽柳（Tamarix，盐柳）吸收铀（U）的机制。选择柽柳进行这项研究是因为在野外采集的植物的根和茎中检测到 U（0.6-58.9 mg kg-1），平均生物浓缩系数大于 1。对从野外采集的植物根部进行的基于同步加速器的微 X 射线荧光分析表明，U 的积累发生在根的皮层中。在受控实验室实验中进一步研究了柽柳根部 U 积累的机制，其中野外植物的活根在含有 100 μM U 的溶液中被捣碎 24 小时或 2 周。在 24 小时后，溶液中的 U 浓度降低了 36-59%，在两周后降低了 49-65%。显微镜和光谱分析检测到根细胞壁靠近根木质部的 U 沉淀，证实了来自野外样本的初始结果。高分辨率 TEM 用于研究根细胞内 U 的命运，发现直径<7nm 的针状 U-P 纳米晶体被困在细胞液泡内。EXAFS 逐壳拟合表明 U 与碳官能团有关。U 与根细胞壁的优先结合可能解释了 U 在柽柳根部的保留，随后是 U-P 晶体沉淀，以及胞饮主动运输和细胞捕获。这个过程导致 U 在柽柳植物中的向茎部的有限转运。这项研究有助于更好地理解影响在污染场地附近生长的植物吸收和积累 U 的物理化学机制。
