重金属超富集植物及植物修复技术研究进展

Hyperaccumulators and phytoremediation of heavy metal contaminated soil:a review of studies in China and abroad

植物修复技术 ( Phytoremediation)是近年来发展起来的一种主要用于清除土壤重金属污染的绿色生态技术。重金属超富集植物 ( hyperaccumulator)及植物修复技术是当前学术界研究的热点领域 ,目前虽已有 Cd、Co、Cr、Cu、Mn、Ni、Pb、Zn等超富集植物发现的报道 ,但尚无一例报道来自于中国。中国具有广袤的国土面积、丰富的植物类型和多种 (处 )古老的矿山开采与冶炼场所 ,在中国开展超富集植物的寻找、研究与开发工作 ,将会有重要突破 ,并具有重要的理论与实践意义。

It has been estimated that more than 20 million hectares of farmland have been contaminated in China,accounting for 20% of the total in the country.Furthermore,a reduction of more than 10 million tons of food supplies results from this soil contamination.Techniques currently employed control soil contamination include cover with improted soil,application of lime and chemical washing.However,most of these are expensive,labour intensive and can result in further contamination problems or leaching/deposition of nutrient elements during in situ treatment.Phytoremediation,a technique using plants to remove contamination from soil and water,has become a topical research field in the last decade as it is safe and potentially cheap compared to traditional remediation techniques.Based on information from the Phytoremediation Bitiliography produced by the US EPA,in 1977 there were only 7 reports published relating to phytoremediation,whereas in 1997,the total literature of phytoremediation increased to 214. In 1583,A.Cesalpino,an Italian botanist discovered an unusual plant which grew on soils over ‘black stone’(ultramafic rocks).This was probably the first ever report of a metal hyperaccumulator plant.It was later named as Alyssum bertolonii in 1814 by Desvaux and the nickel content of its leaves was reported as 7900 μg/g in 1848 by C.Minguzzi and O.Vergnano.Similar plants,designated ‘indicator plants’,such as Elsholtzia haichowensis Sun,a copper accumulator,were discovered early in China and employed in prospecting for copper mineralization.R.R.Brooks,a geochemist from New Zealand first named these special accumulator plants ‘hyperaccumulators’ in 1977,and in 1982 R.Chaney from the USA first suggested the concept of phytoremediaton using these hyperaccumulators.A hyperaccumulator has been defined by Baker and Brooks(1989)as a plant that can accumulate cadmium>100 μg/g,cobalt,copper,nickel,lead>1000 μg/g,manganese and zinc>10000 μg/g in their shoot dry matter.Furthermore,an operational definition was proposed by Baker(1981)that in accumulator plants the metal contents in shoots are invariably greater than that in rooots,showing a special ability of the plants to absorb and transport metals and store them in their above ground parts.To date,more than 400 species of metal hyperaccumulator plants have been reported in the literature.Among them,315 are nickel hyperaccumulators,24 are copper hyperaccumulators but the numbers of other metal hyperaccumulators for other metals are low and they are restricted in their distribution in some specific localities in the world. The hyperaccumulators are mostly discovered in the heavy metal contaminated area such as mining and smeliting localities.The author of this paper suggests that there may exit some “potential hyperaccumulators” on the earth.More attention should be paid to some plants that growing in some relatively “low” heavy metal content areas.The plants may not have very high tolerance but may have some extent degree of accumulation,by culturing the plants and adding some kinds of reagents in their growing media,they may reveal character of hyperaccumulation. A systematic survey of plant and soil chemistry in the copper mining areas along the lower middle reaches of Yangtze River has revealed a few copper accumulators such as Elsholtzia haichowensis Sun, Commelina communis L.and Rumex acetosa L.;the maximum leaf copper contents are 600,160 and 100 μg/g(dry matter basis)respectively,for copper contents in the soil around their roots ranging from 5000 to 20000 μg/g.We initiated pioneering research on hyperaccumulators and phytoremediation in China early in 1998.Several surveys were conducted in south China,and through systematic field investigation and glasshouse studies,we have now identified a hyperaccumulator of arsenic Pteris vittata L.(Chinese brake fern).This is the first hyperaccumulator discovered in China.Unlike other reported hyperaccumulators,this plant can reach 2 m in height,with a fresh shoot biomass of up to 36t/km 2.T