尼泊尔酸模与珠芽蓼对铀矿修复区重金属的累积及化学形态特征

Characteristics of heavy metals accumulation and their chemical forms found for Polygonum viviparum and Rumex nepalensis in the remediation area of abandoned uranium mine

为了解蓼科植物对铀矿区铀及伴生金属的富集、耐受机制,选择若尔盖铀矿修复区的两种蓼科优势植物珠芽蓼(Polygonum viviparum)和尼泊尔酸模(Rumex nepalensis),研究它们对铀及伴生金属的累积特征及其在植物组织中的化学赋存形态.通过实地采样,分析珠芽蓼和尼泊尔酸模的重金属含量,并采用化学试剂连续提取重金属元素.结果显示,该区域受铀、镉、砷、锌、铜重金属污染;区域污染差异为Ⅰ(露天采矿点)>Ⅱ(人工修复区)>Ⅲ(附属河流);单因子指数和综合指数表明露天采矿点和人工修复区污染严重.采样区域植物体内的锌、镉、铜、铅含量都超过植物重金属含量正常范围.尼泊尔酸模对铀的转移系数和生物富集系数分别可达为16.03和1.11,而珠芽蓼的富集系数和转移系数分别为14.85和3.83,珠芽蓼和尼泊尔酸模适用于铀污染土壤的生态修复.尼泊尔酸模中铀元素以去离子水提取态为主,该植物铀的高富集量可能与有机酸有关,其他重金属以醋酸盐和盐酸提取态为主;珠芽蓼中大部分的重金属以迁移性较低的盐酸提取态、醋酸提取态和氯化钠提取态存在.因此,珠芽蓼和尼泊尔酸模对该铀矿修复区铀多金属胁迫具有良好的耐受与吸附性能;重金属以不活跃的化学赋存形态存在可能是两种蓼科植物应对重金属胁迫的重要耐受机制.

We studied the accumulation process of uranium and several other heavy metals, as well as their actual chemical forms in plant tissues, in Polygonum viviparum and Rumex nepalensis, which are dominant Polygonaceae plant species growing in the remediation area of the Zogie uranium mine. The results of this study will contribute to a better understanding of heavy metal absorption and tolerance by plants around polluted areas, which is important for improving remediation efficiency.The composition of heavy metals in P. viviparum and R. nepalensis were analyzed through field sampling. Their subsequent extraction from the sample using a special chemical separation method allowed to determine their chemical nature regarding their qualitative state of binding in the plant. The results showed that the soil in the remediation area was polluted by U, Cd,As, Zn, and Cu. The areas of contamination in declining order is as follows: I(open-pit mining site)>II(artificial restoration area)>III(affiliated river). Single factor index and Nemerow comprehensive pollution index showed that serious heavy metal pollution existed in open-pit mining sites and artificial restoration areas. Furthermore, Zn, Cd, Cu, and Pb in the plant samples exceeded the normal values. The bio-enrichment coefficient(BCF) and transfer factor(TF) of R. nepalensis were determined to be 16.03 and 1.11, respectively, and in P. viviparum, the values were 14.85 and 3.83, respectively. This indicates that both plants are suitable for use in ecological remediation of uranium-contaminated soil. Because uranium in R. nepalensis was mainly extracted with deionized water, organic acids might be the complexing ligand for uranium in the plants. For the other heavy metals, acetate and hydrochloric acid were mainly needed for their extraction from R. nepalensis, which means that they should have stronger ligands. In contrast, most of the heavy metals in P. viviparum could be extracted with hydrochloric acid, acetic acid, and sodium chloride. Both P. viviparum and R. nepalensis could be used for heavy metal remediation around a uranium mine. The plants show good tolerance and absorption properties for uranium and other heavy metals, such as Cd,in the investigated remediation area. The heavy metals found in these plants mentioned above are relatively strongly bound to their ligands, which indicates that both Polygonaceae plant species can cope with uranium and other heavy metal stressors.