Although lead has low solubility in soil and is not easy to move, due to the continuous development and destruction of nature by human beings and industry,
The development of lead pollution has caused increasingly serious global lead pollution. The toxic effect of lead on human body is potential and long-term [1].
Due to the continuous occurrence of lead poisoning, the research on lead pollution and lead poisoning has attracted more and more attention from scholars at home and abroad [1, 2]. have
Studies have shown that human blood lead level is directly related to soil lead content [2]. In order to finally solve the problem of lead pollution, on the one hand,
Pollution sources should be reduced; On the other hand, it is necessary to control and repair the polluted soil. This paper introduces the pollution of lead to soil and plants.
The remediation technology is summarized, which provides a basis for the research and practice of lead-contaminated soil remediation.
1 lead pollution in soil
The average abundance of lead in the crust is 12 15μ g/g, and the lead content in soil is generally 2 ~ 200μ g/g, with an average variation range of 13 ~
42 μ g/g. The basic statistical results of soil background value in China show that the highest lead content in China is 1 143μg/ g, and the lowest is1000μ g/g..
It is 0 168 μ g/g, with an average of 26 μ g/g [3]. According to different sources, lead in the environment can be divided into "primary" and "exogenous"
Two kinds. Lead remaining in soil parent material during soil formation is called primary lead, which mainly comes from rock minerals. The rocks are weathering.
In the process of soil removal, most of the lead remains in the soil. The lead content of pollution-free soil is only slightly higher than that of parent rock. Maternal removal
In addition to the natural primary lead in soil, the weathering of rocks can also cause pollution due to human activities, which leads to the increase of lead content in soil.
Lead that enters the soil through dust deposition and various pollution routes is called exogenous lead. Exogenous lead in soil mainly comes from atmospheric migration and deposition.
Put it down. The density of lead is very high, and lead-containing particles in the air can easily settle and accumulate in the soil.
Table1Global Lead Production from 1970s to 1990s
1975 1980 1985 1990
Pb output/103t/ year-1343212 344812 34312.
Table 1 lists the global lead production from 1970s to 1990s. According to statistics, the lead released into the soil in 1980s reached 796 ×.
103t/ year [4]. The development and utilization of lead by human beings has broken the balance of lead in biogeochemical cycle, causing serious pollution.
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guangdong trace elements science
200 1 Xue ke, Su Yuan, Wei Liang, Guangdong, Vol.8 No.9.
1995-2006 Tsinghua tongfang optical disc co., ltd all rights reserved.
1923 lead was added to gasoline as an antiknock agent, which accelerated the global lead pollution. So it can be said that today's world
It is difficult to find a "pure land" where the lead content in soil is not affected by human activities. Kabata-Pendias and Rendias[5] reported that they relied on.
The lead content in a piece of soil near the highway is as high as 7000μg/ g/g. Pan et al. [6] studied the effect of lead in automobile exhaust on vegetables on both sides of the highway.
Pollution situation. The test results show that vegetables growing within 200 m on both sides of the road are polluted by lead in automobile exhaust. Pipes/pipes
Jianguo [7] and others studied the pollution of vegetables around the metal smelter and within 200 m on both sides of the road, and found that the investigated vegetables were average.
The lead content of cauliflower exceeds the national food hygiene standard. Peng Shanshan et al. [8] determined the lead in some common teas in China and drew a conclusion.
The results show that the lead content in tea exceeds the standard, which should be paid attention to.
Most of the lead in the soil forms PbS, and a small part forms inorganic compounds such as PbCO3, PbSO4 and PbCrO4, or reacts with organic compounds.
Chelating. Most inorganic compounds of lead are difficult to dissolve, and the migration ability of lead in soil is also high, for the following reasons.
Weak: (1) Complexation of soil organic matter with lead. —SH and —NH2 genes of soil organic matter can form stable with lead ions.
Complicated. (2) Adsorption of lead by soil clay minerals. The cation exchange sites of clay minerals can exchange lead ions.
Adsorption. In addition, lead ions enter the coordination shell of hydrated oxides and directly combine with the solid surface through valence bonds or coordination bonds. because
Lead has weak migration ability and low solubility in soil, so lead pollution caused by human factors mostly stays on the soil surface and follows the soil.
With the increase of soil depth, its content decreases sharply and tends to natural level below 20 cm.
Lead entering the soil may be absorbed by plants, or dissolved in surface water, and enter animals and humans through the food chain and drinking water.
The body, which in turn affects human health. In recent years, it has been found that lead has an irreversible long-term impact on human health [9].
Page[2] and other studies show that there is a certain relationship between human blood lead and soil lead content:
0 1 12 (Pb - B,μg/ 100mg) = ln (Pb - S,μg/ g) - 4 185
This relationship only shows the special situation of a certain area, and has no extensive application value, but it is enough to show that the lead content in soil is related to the lead content in soil.
Human health is directly related.
2 lead contaminated soil remediation technology
Due to the strong toxicity of lead to human body, the remediation of lead-contaminated soil has been widely concerned in recent years. Lead pollution
Soil remediation technology can be divided into two categories: physical and chemical remediation technology and biological remediation technology. Physical and chemical remediation techniques can be divided into two parts.
It includes isolation embedding technology, curing stabilization technology, pyrometallurgical separation technology, chemical stabilization technology and electric repair technology.
Bioremediation technology can be divided into natural attenuation and phytoremediation technology.
2 1 1 isolation and inclusion technology.
This method uses physical methods to isolate lead-contaminated soil from its surrounding environment, thus reducing lead pollution to the surrounding environment or increasing lead.
Soil environmental capacity. The concrete measures are: building isolation around contaminated soil with materials such as steel, cement, bentonite or mortar.
Wall, and prevent the groundwater in the polluted area from flowing to the surrounding area. Cement is the cheapest and most widely used. In order to reduce
The infiltration of surface water can also cover a layer of synthetic film on the polluted soil, or mix a layer of cement and stones under the polluted soil.
Layer.
2 12 solidification and stabilization technology.
Solidification and stabilization technology includes two aspects: reducing the solubility and extractability of lead in soil by chemical methods, and adopting
Physical method embeds polluted soil into solid matrix. Wheeler reports [10] adding a mixture of cement, slag and lime to sewage.
The polluted soil is stirred evenly and solidified to form a big stone, and the polluted soil is embedded in it. Some people also use electricity to generate heat.
The principle of heating soil is that when the soil is cooled, the soil solidifies into a glassy block structure, which is called vitrification. The method comprises the following steps
Step 3: (1) Insert electrodes at both ends of the soil to form a loop through the soil, and the soil temperature will rise and melt. (2) in
In the process of natural cooling, the soil solidifies to form glassy clods. (3) Cover the clods with a layer of clean soil. This technology has been realized.
International application of lead contaminated soil remediation.
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guangdong trace elements science
200 1 Xue ke, Su Yuan, Wei Liang, Guangdong, Vol.8 No.9.
1995-2006 Tsinghua tongfang optical disc co., ltd all rights reserved.
2 13 pyrometallurgical separation
At a certain temperature, metal will melt or sublimate into gas. Pyrometallurgical separation technology utilizes this principle,
Heavy metals such as lead "evaporate" from the polluted soil to achieve the purpose of purifying the soil. The "evaporated" metal can be returned.
Metal-rich residues can also be used for further refining [1 1]. Lead contaminated soil should enter before high temperature melting.
Pretreatment is carried out to promote the melting of lead. This technology is mainly suitable for heavily polluted soil, with high remediation efficiency (5% ~ 10%).
20 %) 。
2 14 chemical stabilization technology (chemical stabilization)
Chemical stabilization technology is to use chemical reaction to oxidize or reduce heavy metals in polluted soil, thus reducing the weight in soil.
Activity of metal [1 1]. For lead contaminated soil, reducing agents (sulfur dioxide, sulfite or ferrous sulfate) can be used to reduce lead ions.
So as to reduce the extractable amount of lead in the soil. This technology can also be used as pretreatment for other repair technologies (such as curing stabilization technology).
Steps. However, it must be noted that the application of reducing agent may cause secondary pollution. Preliminary research shows that the application of lime can adjust the soil.
PH7 can reduce the solubility of lead in soil and the absorption of lead by plants [13]. Research shows that the application of hydroxyapatite [14], water
Manganese oxide [15] and phospholimestone [16, 17] can also promote the precipitation of lead and reduce the soluble and extractable lead in soil. Vidac and
Pohland[ 18] has applied this technology to groundwater remediation.
2 15 electric technology
Electrodes are inserted at both ends of the polluted soil, and after the power supply is turned on, the charged particles in the soil move to the electrodes with opposite electrical properties, and final gathering occurs.
Aggregation or precipitation on the electrode can achieve the purpose of removing heavy metals from polluted soil. In Europe, this technology is not only applied to lead pollution.
Soil [19] is also suitable for remediation of contaminated soil such as copper, zinc, chromium, nickel and cadmium.
2 16 natural attenuation
Microbial remediation mainly depends on the biochemical reaction of microorganisms to remove or stabilize harmful substances in the environment. According to different principles, it can
It can be divided into three types: biological reduction precipitation, biological methylation and biological adsorption. Biological reduction precipitation is desulfurization by sulfate reducing bacteria (SRB).
Acid radical is reduced to HS-, and then reacts with lead to form insoluble Pb2S. Biological methylation is the methylation of heavy metals in soil by microorganisms.
Methylated metals are more volatile and can be used as pretreatment for pyrometallurgical separation. Biosorption is the use of excellent bacteria.
Cells and algae adsorb harmful substances in groundwater or other polluted water bodies. Leusch et al. [20] reported an algae (S.F. Lutans).
The maximum adsorption capacity of lead can reach 369 mg/g. Rahmani et al. [2 1] studied the effect of duckweed on lead in polluted water.
The ability to remove. The results show that duckweed can effectively remove lead from water and reach sublethal level.
2 17 plant extraction technology
Plant extraction and remediation technology mainly uses super-accumulated plants to transfer a large number of excessive elements or compounds from soil to plants.
In vivo, especially the aboveground parts, so as to repair the contaminated soil [22]. Super-accumulative plants are equivalent to a solar-driven pump to extract soil.
Excess elements are continuously pumped into the factory [23]. Phytoremediation technology can be divided into two types. Salt et al. [24] uses hyperaccumulation plants for absorption.
The method of soil heavy metals is called continuous plant extraction. And the application of chelating agent in promoting plant growth.
The method of absorbing heavy metals in soil is called induced plant extraction.
2 17 1 1 continuous plant extraction
The key to the remediation of lead-contaminated soil by plant continuous extraction technology is the ability of plants to accumulate lead. It is generally believed that only lead
Only when the accumulation amount reaches 1000μg/ g (dry weight) can it be called lead hyperaccumulator [25]. The reported lead hyperaccumulator plants are Brassica plants.
Nicaragua [26], Brasilia. Beijingers [27], Brasilia. Juncus [27] and Plumbum Preparata [28]. Luotongmu
The lead accumulation in leaves is the largest, reaching 8200μg/ g (dry weight) [28]. At present, the absorption, transportation, accumulation and tolerance of lead in plants.
The mechanism of lead stress is rarely studied. Liu et al. [29] found that Indian mustard (Brassica juncea) can accumulate a lot of lead in its roots.
But only a small part was transported to the ground. On the one hand, it may be due to the high concentration of phosphate or carbonate in root cells.
When the intracellular pH is close to neutral, lead mainly precipitates in the root cell wall or cells in the form of phosphate or carbonate. on the other hand
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200 1 Xue ke, Su Yuan, Wei Liang, Guangdong, Vol.8 No.9.
1995-2006 Tsinghua tongfang optical disc co., ltd all rights reserved.
The migration of lead from root to stele was also blocked by Kjeldahl zone of endodermis. Wozny et al. [30] think that lead will generate steam after entering the intermediate column.
Liu Teng was passively transported to the above-ground part. During transportation, lead may be combined with cation exchange sites in the intermediate column, thus being fixed in.
Inside the stem column. Studies show that lead can chelate with a variety of small molecular organic compounds [3 1 ~ 33]. It is speculated that lead may also be related to various small molecules.
The combination of organic acids and plant chelating peptides reduces the chance of combining with cation exchange sites, thus increasing the number of them entering leaves. author
In the investigation of soil in a lead-zinc mine area in western Zhejiang, a plant with high concentration of lead and zinc was found.
The results showed that the maximum accumulation of zinc and lead in the aboveground parts of plants reached 5000μg/ g and 1 182μg/ g, respectively. For the mass reproduction of this plant
The physiological and biochemical mechanisms of zinc and lead accumulation are being further studied.
2 17 12 induced plant extraction
For lead which is extremely difficult to move in soil, the application of chelating agent can promote the absorption of lead by plants. Using chelating agent to induce plants
Superconcentration is called chelation-induced repair technology. Romheld and Marschner[34] believe that after chelates are combined with metals, metals
Chelates can enter roots from cracks in the endodermis, and then quickly transfer to stems and leaves. Use 14C-EDTA-Pb as the tag.
Blaylock et al. [35] found that the aboveground parts of plants growing in the medium containing this marker can quickly accumulate lead, which indicates that.
The combination of lead and chelate is beneficial to the absorption of lead by plants Salt et al. [36] thought that the combination of metal and chelate prevented the precipitation of metal.
And the extractability of the metal is improved. Chelation-induced remediation technology can select both general plants and hyperaccumulator plants.
Things. Corn and peas were planted in polluted soil with lead concentration of 2500μg/ g, and the lead content in the aboveground parts of plants decreased after EDTA was added.
The concentration increased from 500 μ g/g to 10000 μ g/g; In addition, EDTA can greatly improve the transport capacity of lead from root to shoot.
After adding110g EDTA to each kilogram of soil for 24 hours, the lead concentration in maize xylem was 100 times higher than that in the control, from root to ground.
The transport conversion ability of plants is 120 times that of the control [37]. Effects of different chelating agents on lead absorption by plants and lead removal by chelating agents in soil
The soil desorption effect is consistent: EDTA >;; HEDTA & gtDTPA & gt; EGTA & gt; Ada. Adsorption of Hyperaccumulator Plants by Chelation Induction Technology
The strengthening effect of metal recycling is also obvious. Indian mustard is a plant that can enrich a variety of metals. Blaylock et al [35] studied lemons.
Effects of acid, malic acid, acetic acid, EDTA, EGTA and CDTA on cadmium and lead uptake by Indian mustard,
It is found that the combination of soil acidification and chelation can significantly improve the absorption efficiency of lead. Vassil et al [38] reported that lead and EDTA are the same.
The content of aboveground parts of Indian mustard is as high as 55 mmol/ kg (dry weight), which is 75 times of the lead concentration in the culture medium. On behalf of India
The direct determination of mustard stem extract showed that most of the lead in the stem was transported in the form of EDTA. Due to the presence of chelating agent
Generally, the price is expensive. Blaylock et al. [35] pointed out that chelating agents (EDTA and acetic acid) will increase the remediation cost per ton of lead-contaminated soil.
7 15 USD. In addition, chelating agents not only increase the bioavailability of heavy metals in soil, but also increase the mobility of heavy metal ions.
Therefore, it is necessary to systematically evaluate the environmental risk of chelate-induced remediation technology.
Because there are few species of lead super-accumulated plants found, and the plants grow slowly and have small biomass, chelation-induced remediation technology is adopted.
It is more noticeable than continuous extraction technology. But no matter which phytoremediation technology has advantages that other physical and chemical methods do not have:
(1) Low cost. It is estimated that if the lead accumulation in the stem of a plant reaches 1% and the annual output is 40 t/ hm2, then it will pass.
The planting cost of reducing the lead content in soil from 1 14% to 0 14% in 10 years is 245,000 dollars, and the physical and chemical remediation technology is as follows
Need1600,000 USD. (2) Plants use solar energy, which does not destroy the ecological balance, but also beautifies the environment and is easily accepted by the public.
Accept. (3) Utilization of lead-rich plant residues in plant smelting can generate economic benefits. On the contrary, although phytoremediation technology takes time
After a long time, the growth of plants is affected by the environment, but these shortcomings are not important problems. Predictably, phytoremediation
Remediation will be a widely used, environmentally friendly and economical method to remediate lead-contaminated soil.