矿区常见乔木叶片重金属特征及其修复应用

Foliar concentration of heavy metals in the leaves of trees in mining area as a mechanism for phytoremediation

对广西河池大厂矿区内的植被和立地条件进行调查分析,旨在寻找一些可用于植物生态修复重金属污染的乔木,并估算其去除重金属的能力。在调查区内设立了3个村屯采样点,对常见树木,如沙梨(pyrus pyrifolia(burm·f.)nakai)、板栗(Castaneamollissima Blume)、拐枣(Hovenia acerba)、柚子树(Citrus maxima)、银杏(Ginkgo biloba)、樟树(Cinnamomum camphora)、柿子树(Diospyros kaki)和枇杷(Eriobotrya japonica)等8种植物叶片及周围表层土壤进行采样,检测叶片和土壤中重金属总量(Mn、Zn、Cu、As、Cd、Sn、Sb、Pb)。对植物叶片采用ICP-MS及ICP-AES进行测定,土壤的重金属用ICP-AES进行检测。结果发现表土重金属含量均超过广西土壤背景值的5-1200倍,其中Cd污染最严重,为背景值的1200多倍。3个采样点位之间及同一采样点内不同植物叶片对重金属的吸收无显著性差异(Mn除外),8种植物叶片固定重金属的范围如Cu为3.331 9 mg·kg-1-10.885 1 mg kg-1,As为1.7811 mg·kg-1-46.217 8 mg·kg-1,Cd为0.046 55 mg·kg-1-4.989 7 mg·kg-1;其中拐枣树叶对Mn有较高吸收,分别达811.11 mg·kg-1,352.31 mg·kg-1,220.11 mg·kg-1。以生物量估测模式计算的屯一8种植物单株叶片总量对重金属的总吸收量,单株拐枣叶总量可吸收21.25 g Mn、3.003 g Zn、0.20 g Cu、0.28 gAs、0.066 g Cd,、0.014g Sn、0.17 g Sb和1.23 g Pb,而单株樟树叶可吸收1.55 g Mn、0.79 g Zn、0.17 g Cu、0.12 g As、0.011 g Cd、0.017 g Sn、0.14g Sb和0.40 g Pb。但所调查果树中的梨树和板栗树单株叶总量吸收重金属也较高,梨可吸收2.90 g Mn、3.32 g Zn、0.57 g Cu、0.11 g As、0.043 g Cd、0.014 g Sn、0.13 g Sb和0.79 g Pb;而板栗则吸收99.82 g Mn、5.20 g Zn、0.28 g Cu、0.24 g As、0.048g Cd、0.017 g Sn、0.26 g Sb和0.94 g Pb。但这些果树存在食品安全风险,故建议选择拐枣和樟树作为该矿区的植物修复的优选树种。

Mining has a range of deleterious effects on the environment, including increasing the concentration of heavy metals in soils. Natural revegetation may contribute to phytoremediation by removing heavy metals. Therefore it’s important to determine which trees are most effective at phytoremediation. The vegetation and the topsoil of the mining area in Dachang Mine of Hechi city, Guangxi Province, China, were investigated, to determine which trees are more suitable for phytoremediation for the heavy metal pollution. The total content of heavy metals （Mn, Zn, Cu, As, Cd, Sn, Sb and Pb） in the leaves of eight tree species and in the topsoil were measured in the three sites in the mining area. The trees were：Pyrus pyrifolia （burm.f.） nakai, Castanea mollissima, Hovenia acerba, Citrus maxima, Ginkgo biloba, Cinnamomum camphora, Diospyros kaki, Eriobotrya japonica. The concentrations of heavy metals in leaves were detected by ICP-MS and ICP-AES, and in soil by ICP-AES. The concentrations of heavy metals were over 5-1200 times background values for soils in the Guangxi Province; with Cd more than 1200 times background values. There were no significant differences in foliar heavy metal contents among the three sampling sites except for Mn;and there were no significant differences among tree species in foliar heavy metal concentrations, either. Concentrations per leaf were converted to values per tree using an equation for tree leaf biomass. H. acerba and C. camphora accumulated more different heavy metals than the others overall. For example a single H. acerba tree can absorb 21.25 g Mn, 3.003g Zn, 0.20 g Cu, 0.28 g As, 0.066 g Cd, 0.014 g Sn, 0.17 g Sb and 1.23 g Pb, while a C. camphora tree can absorb 1.55 g Mn, 0.79g Zn, 0.17 g Cu, 0.12 g As, 0.011 g Cd, 0.017 g Sn, 0.14 g Sb and 0.40 g Pb. The values for the two fruit trees, P. pyrifolia and C. mollissim were also high, for P. pyrifolia can uptake 2.90 g Mn, 3.32 g Zn 0.57 g Cu, 0.11 g As, 0.043 g Cd, 0.014 g Sn, 0.13 g Sb, 0.79 g Pb;for C. mollissima can uptake 99.82 g Mn, 5.20 g Zn, 0.28 g Cu, 0.24 g As, 0.048 g Cd, 0.017 g Sn, 0.26 g Sb, 0.94 g Pb;but would be inappropriate to use due to the risk of people consuming the potentially toxic fruit. Therefore H. acerba and C. camphora may be good trees to plant when restoring mining areas.