Rajan Michael, Darrow Jeannine, Hua Michael, Barnett Brandy, Mendoza Miguel, Greenfield Ben K, Andrews Joy C
Department of Chemistry and Biochemistry, California State University East Bay, 25800 Carlos Bee Boulevard, Hayward, California 94542, USA.
Environ Sci Technol. 2008 Aug 1;42(15):5568-73. doi: 10.1021/es800284v.
Eichhornia crassipes (water hyacinth) is a non-native plant found in abundance in the Sacramento-San Joaquin River Delta (hereafter called Delta). This species has become a problem, clogging waterways and wetlands. Water hyacinth are also known to accumulate mercury. Recent attempts to curb its proliferation have included shredding with specialized boats. The purpose of this research is to better understand the ability of water hyacinth to phytoremediate mercury and to determine the effect of shredding and anoxic conditions on mercury speciation in plant tissue. In the field assessment, total mercury levels in sediment from the Dow Wetlands in the Delta were found to be 0.273 +/- 0.070 ppm Hg, and levels in hyacinth roots and shoots from this site were 1.17 +/- 0.08 ppm and 1.03 +/- 0.52 ppm, respectively, indicating bioaccumulation of mercury. Plant samples collected at this site were also grown in nutrient solution with 1 ppm HgCl2 under (1) aerobic conditions, (2) anaerobic conditions, and (3)with shredded plant material only. The greatest accumulation was found in the roots of whole plants. Plants grown in these conditions were also analyzed at Stanford Synchrotron Radiation Laboratory using Hg L3 X-ray Absorption Near Edge Spectroscopy (XANES), a method to examine speciation that is element-specific and noninvasive. Least-squares fitting of the XANES data to methylated and inorganic mercury(II) model compounds revealed that in plants grown live and aerobically, 5 +/- 3% of the mercury was in the form of methylmercury, in a form similar to methylmercury cysteine. This percentage increased to 16 +/- 4% in live plants grown anaerobically and to 22 +/- 6% in shredded anaerobic plants. We conclude that shredding of the hyacinth plants and, in fact, subjection of plants to anaerobic conditions (e.g., as in normal decay, or in crowded growth conditions) increases mercury methylation. Mechanical removal of the entire plant is significantly more expensive than shredding, but it may be necessary to avoid increased biomagnification of mercury in infested areas.
凤眼蓝（水葫芦）是一种非本地植物，在萨克拉门托 - 圣华金河三角洲（以下简称三角洲）大量生长。该物种已成为一个问题，堵塞了水道和湿地。水葫芦还已知会积累汞。最近控制其扩散的尝试包括使用专门的船只进行切碎。本研究的目的是更好地了解水葫芦对汞进行植物修复的能力，并确定切碎和缺氧条件对植物组织中汞形态的影响。在实地评估中，发现三角洲道湿地沉积物中的总汞含量为0.273±0.070 ppm汞，该地点水葫芦根和茎中的汞含量分别为1.17±0.08 ppm和1.03±0.52 ppm，表明汞的生物积累。在该地点采集的植物样本还在含有1 ppm HgCl₂的营养液中在（1）有氧条件、（2）厌氧条件和（3）仅与切碎的植物材料一起的情况下生长。在整株植物的根中发现积累量最大。在这些条件下生长的植物还在斯坦福同步辐射实验室使用汞L₃ X射线吸收近边光谱法（XANES）进行了分析，这是一种用于检查特定元素且非侵入性的形态的方法。将XANES数据与甲基化和无机汞（II）模型化合物进行最小二乘拟合表明，在有氧生长的活体植物中，5±3%的汞以甲基汞的形式存在，其形式类似于甲基汞半胱氨酸。在厌氧生长的活体植物中，这一百分比增加到16±4%，在切碎的厌氧植物中增加到22±6%。我们得出结论，切碎水葫芦植物，实际上使植物处于厌氧条件下（例如在正常腐烂或拥挤的生长条件下）会增加汞的甲基化。机械清除整株植物比切碎要昂贵得多，但为了避免受侵染地区汞的生物放大作用增加，可能有必要这样做。
