Unit 9

Unit 9
Extraction of Metals Through the Plants
In this unit , we will know
金属污染的来源 金属污染物影响农作物的收成 什么是生物排污法 生物提取的机理是什么
1. 肥料 2. 促进发展者 3. 受精媒介物
Metal pollution of the environment comes from many sources, including mining and smelting activities, municipal wastes, fertilizer impurities and from sewage sludge. There is increasing concern about the wider environmental and health impacts of such contaminants, 立法 which has led to pressure for the identification and clean up of metal-polluted sites. Sadly, this type 法规 of 立法机构的审议 pollution is likely to get worsen in the UK and the事项 rest of Europe for several reasons. Sewage sludge disposal on land will increase after 1998 as a consequence of the EU ban on dumping it at sea and tighter EU legislation on water treatment. More recycling of urban and industrial waste is also likely because of the increasing costs of landfill. The problem is exacerbated because heavy metals are strongly retained by soil and do not wash away—once in the soil they can remain there for thousands of years.
初期, 初期, 幼年 期
目前一种利用某种植物清除金属污染的 技术正在研究中，这些植物被视为超级 金属累积植物，比其他的普通植物可以 多吸收成百上千倍的金属，种植这些植 物来回收金属——称为植物提取技术— —可提供有效而且低成本的排污方法， 金属排出之后，还可以提高肥力。从世 界范围来看这项技术还在研究初期，并 没有投入使用
更便宜以及破坏性小的消除土壤中 有毒金属的方法，非常亟需。因此， 有毒金属的方法，非常亟需。因此， 生物排污法——用活体生物组织减 生物排污法 用活体生物组织减 少与工业和其他废弃物有关的环境 危害物——是人们日益关注的焦点。 是人们日益关注的焦点。 危害物 是人们日益关注的焦点 生物的排污技术有着更可观的市场 潜力， 潜力，而且和传统技术相比有着耗 资少、 资少、破坏少的更多好处
1. 集中[C][U] 2. 专心,专注[U] 3. 浓缩;浓度[U][S1]
Metal pollution in soil can have dramatic effects. At high concentrations, some metals can directly affect the yields of crops and can adversely affect food quality. Even quite low concentrations of metals can interfere with the diversity and activity 干预，干涉 of microbial communities in the soil and this in turn 妨碍, 打扰; 抵触; 冲突 has serious effects on soil biomass and fertility— the very basis of nutrient cycling and sustainable agriculture. Amar Chaudri and co-workers at IACR-Rothamsted, for example, showed that numbers of the nitrogen-fixing bacteria Rhizobium are much lower in metal-contaminated soils. This 可持续的 means that less nitrogen is fixed by clover, for example, and therefore fewer clover plants manage to grow in the area.
Well，over 400 hyperaccumulators have so far been 附近 reported throughout the world, covering many different families of flowering plants, including herbaceous species as well as shrubs and trees. These plants grow naturally on metal-contaminated sites such as in the vicinity of mining operations, or in serpentine (nutrient-poor soil derived from ultra-mafic rock : high in Mg, Cr and Ni but low in Ca) and other soils that are rich in heavy metals. Robert Boyd at auburn university and Scott Martens at the University of California have suggested a number of reasons why the plants have evolved at these sites. For example, they could be filing a niche-few other plants grow in these areas of high metal contamination, so they can avoid competition from faster growing, larger plants. Alternatively, the high metal concentrations in the plants many offer protection from herbivores and pathogens because it discourages insects from feeding, or serve as drought resistance strategy. 另外
公顷
有很多清理包括重金属污染在内的污染场所 的技术， 的技术，这些技术主要是对受污染的土壤进 行消除、处理以及更换。 行消除、处理以及更换。这些处理措施包括 酸性物质的过滤、电解质的渗透、 酸性物质的过滤、电解质的渗透、热处理以 及玻璃化技术， 及玻璃化技术，而这些基本上都会破坏土壤 的生物及结构组成。 的生物及结构组成。并且这些措施也将非常 昂贵。例如，清理１ 深的１ 昂贵。例如，清理１m深的１公顷土壤将会 耗资高达２百万美元。 耗资高达２百万美元。
垃圾填埋
环境中的金属污染来自多方面，包括矿物的开采， 环境中的金属污染来自多方面，包括矿物的开采，金 属的熔炼，城市的垃圾肥料的杂质以及污水。 属的熔炼，城市的垃圾肥料的杂质以及污水。这类 污染对环境和健康的影响引起了更广泛的关注， 污染对环境和健康的影响引起了更广泛的关注，而 且已经给金属污染的鉴定与处理带来了压力。 且已经给金属污染的鉴定与处理带来了压力。糟糕 的是，由于种种原因这类污染在ＵＫ ＵＫ和欧洲其他国 的是，由于种种原因这类污染在ＵＫ和欧洲其他国 家有可能越来越严重。 家有可能越来越严重。因为欧盟对向海中倾倒污染 的禁令以及保护水资源的立法， 的禁令以及保护水资源的立法，1998年以后陆地上 年以后陆地上 的污染物处理将会增加。 的ቤተ መጻሕፍቲ ባይዱ染物处理将会增加。城市垃圾和工业垃圾的回 收也会因为陆地填埋的费用增多变得增多。 收也会因为陆地填埋的费用增多变得增多。重金属 在土壤中残留并且不会被冲走， 在土壤中残留并且不会被冲走，而且一旦在土壤中 将会残留上千年，这无疑将加重金属污染。 将会残留上千年，这无疑将加重金属污染。
土壤中的金属污染物有着我们想象不到的作 用，高浓度的金属含量直接影响耕地而且影 响农作物的质量，即使金属的浓度相当低， 响农作物的质量，即使金属的浓度相当低， 也能影响土壤中微生物群的种类和活性， 也能影响土壤中微生物群的种类和活性，并 反过来对土壤的微生物量和肥力——这正是 反过来对土壤的微生物量和肥力 这正是 营养循环和可持续农业的真正基础——产生 营养循环和可持续农业的真正基础——产生 恶劣影响。 恶劣影响。在IACR-Rothamsted 的Amar Chaudri 和他的合作者研究表明在金属污染 的土壤里，固氮菌的含量很低，这将意味着， 的土壤里，固氮菌的含量很低，这将意味着， 固氮植物（苜蓿）的固氮量降低， 固氮植物（苜蓿）的固氮量降低，而导致固 氮植物在这一地区的生长受到阻碍。 氮植物在这一地区的生长受到阻碍。
One radical approach currently being explored is the use of certain plants to clean up sites contaminated with metals. these plants, known as “hyperaccumulators”, can collect hyperaccumulators” hundreds or thousands of times more metal in 植物 their above-ground parts than normal plants. above提取 Growing these plants to collect the metal-a metal技术 technique called phytoextraction-could phytoextractionprovide an effective and affordable way of removing pollutants that also preserves soil fertility after the metal has been removed. Worldwide, this technology is still in its infancy and as yet is not being used commercially.