植物修复在治理矿区重金属污染土壤中的应用

矿业活动是环境中污染土壤的重金属的主要来源,采用植物修复技术具有物理、化学修复方法所无法比拟的费用低廉、不破坏场地结构、不造成地下水的二次污染等优点。文章从植物稳定、植物提取和植物一微生物以及动物的协同修复等三个方面简要介绍了对矿区污染土壤进行植物修复的研究进展。     

Biotechnological advances in bioremediation of heavy metals contaminated ecosystems: an overview with special reference to phytoremediation

The ability of heavy metals bioaccumulation to cause toxicity in biological systems—human, animals, microorganisms and plants—is an important issue for environmental health and safety. Recent biotechnological approaches for bioremediation include biomineralization (mineral synthesis by living organisms or biomaterials), biosorption (dead microbial and renewable agricultural biomass), phytostabilization (immobilization in plant roots), hyperaccumulation (exceptional metal concentration in plant shoots), dendroremediation (growing trees in polluted soils), biostimulation (stimulating living microbial population), rhizoremediation (plant and microbe), mycoremediation (stimulating living fungi/mycelial ultrafiltration), cyanoremediation (stimulating algal mass for remediation) and genoremediation (stimulating gene for remediation process). The adequate restoration of the environment requires cooperation, integration and assimilation of such biotechnological advances along with traditional and ethical wisdom to unravel the mystery of nature in the emerging field of bioremediation. This review highlights better understanding of the problems associated with the toxicity of heavy metals to the contaminated ecosystems and their viable, sustainable and eco-friendly bioremediation technologies, especially the mechanisms of phytoremediation of heavy metals along with some case studies in India and abroad. However, the challenges (biosafety assessment and genetic pollution) involved in adopting the new initiatives for cleaning-up the heavy metals-contaminated ecosystems from both ecological and greener point of view must not be ignored.     

Carcinogenic risk evaluation for human health risk assessment from soils contaminated with heavy metals

Human activities have progressively increased in recent years. Consequently, significant environment deterioration resulted. Soils have a particularly varied vulnerability to heavy metal pollution, especially in the vicinity of industrial areas. Heavy metal contamination of soil may induce risks and hazards to humans and the ecosystem, while toxic metals in soil can severely inhibit the biodegradation of organic contaminants. This paper is focused on human health risk assessment from extremely contaminated soil with heavy metals, mainly with carcinogenic elements. The study refers to an agricultural area in the vicinity of an old metallurgical processing industrial facility. The contaminants evaluated in the present paper are beryllium (Be), cadmium (Cd), chromium (Cr), nickel (Ni) and lead (Pb). Contamination level is pointed out through laboratory analysis results of soil samples taken from 0–0.2 m, 0.2–0.4 m soil layers and up to 2.1 m soil depth. Some heavy metal concentrations (Cd, Cr and Pb) exceed the intervention thresholds for sensitive areas, as they are stipulated in the national regulation in Romania. The identified average concentration levels of Cd, Cr^VI and Pb in the first layer of the investigated land are 23.83, 7.71 and 704.22 mg/kg_d.w, respectively. The results show that the potential risk of human health is relevant (higher than the acceptable one after World Health Organization) and a possible solution for the remediation should become a major concern for the investigated area.     

Comparative plant growth promoting traits and distribution of rhizobacteria associated with heavy metals in contaminated soils

The heavy metals at high concentration are generally toxic to the plants for their metabolism and growth; therefore, interactions among metals, rhizosphere microbes and plants have attracted attention because of the biotechnological potential of microorganisms for metal removal directly from contaminated soils or the possible transference of them to the plants. The aim of this study was to compare the relationships between the physiological in vitro characteristics of rhizobacteria isolated from plant metal accumulators and their distribution relating with the heavy metals content in contaminated soils. The results of this study showed that the heavy metals present in the rhizosphere of the plant species analyzed, decrease the microbial biomass and content of heavy metals caused a different distribution of rhizobacteria found. Gram negative rhizobacteria (90 %) and gram positive rhizobacteria (10 %) were isolated; all of them are metal-resistant rhizobacteria and 50 % of the isolated rhizobacteria possess both traits: higher indol acetic acid and siderophore producers. The inoculation with these rhizosphere microorganisms that possess metal-tolerating ability and plant growth promoting activities, can be recommended with a practical importance for both metal-contaminated environment and plant growth promotion.     

A novel strategy using biodegradable EDDS for the chemically enhanced phytoextraction of soils contaminated with heavy metals

For the sake of cost and potential environmental risk, it is necessary to minimize the amount of chelates used in chemically-enhanced phytoextraction. In the present study, a biodegradable chelating agent, EDDS was added in a hot solution at 90℃ to the soil in which garland chrysanthemum （Chrysanthemum coronarium L.） and beans （Phaseolus vulgaris L., white bean） were growing. The application of hot chelate solutions was much more efficient than the application of normal chelate solutions （25℃） in improving the uptake of heavy metals by plants. When 1 mmol kg1 of EDDS as a hot solution was applied to soil, the concentrations ofCu, Zn and Cd and the total phytoextraction by the shoots of the two plant species exceeded or approximated those in the shoots of plants treated with 5 mmol kg^-1 of normal EDTA solution. The concentrations of metals in the shoots of beans were significantly correlated with the relative electrolyte leakage rate of root cells, indicating that the root damage resulting from the hot solution might play an important role in the process of chelate-enhanced metal uptake. The soil leaching study demonstrated that decreasing the dosage of chelate resulted in decreased concentrations of soluble metals in soils. On the 28th day following the application of chelate, the concentrations of soluble metals in the EDDS treated soil were not significantly different from the concentrations in the control soil to which chelates had not been applied.     

Effect of sheep manure and EDTA on the leaching of potassium from heavy metals contaminated calcareous soils

In this study, we examined the movement of potassium (K) in columns of contaminated calcareous soils by sheep manure and ethylene diamine tetraacetic acid (EDTA). Glass tubes, 4.9 cm in diameter and 40 cm in length, were packed with contaminated soils. The resulting 20-cm long column of soil had a bulk density of 1.3–1.4 g cm⁻³. Columns were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl₂, and sheep manure extract solutions. The amounts of K leached varied considerably between different soils (sandy loam and loamy sand) and leaching solutions. The amount leached with EDTA solution, varied from 7.2 to 66.7% of the extractable K when 20 pore volumes had passed through the column. The breakthrough curves of K in the EDTA and CaCl₂ were approximately similar, indicating they have similar ability to displace K from these contaminated calcareous soils. Thus, among leaching solutions application of EDTA and CaCl₂ on contaminated soils might enhance the mobility of K and large amounts of K will be leached.     

The distribution characteristics of heavy metals in Guiyang urban soils

Guiyang is located in southwestern China,which is a famous tourism city,and is awarded the title of"the Summer Capital of China".A study on heavy metals in Guiyang urban soils was conducted.The results showed that the concentrations of Cd,Cu,Ni,Pb and Zn in Guiyang urban soils are significantly higher than their background values and Cu,Zn and Pb in Guiyang soils are accumulated seriously.The distribution characteristics of heavy metals in 3 districts are described as follows:the level of heavy metals in soils follows the order of Nanming District> Yunyan District>Xiaohe District.The spatial distribution of metals in urban soils of Guiyang shows that the level of metals in the central and eastern parts of Guiyang is relatively high,and its characteristics are attributed to the influence of commercial activities,heavy traffic and industrial emission.Compared with some other cities in China,Guiyang is characterized by relatively high accumulation level of Cd,Cu,and Zn in its soils.     

Stabilities of heavy metals in soils treated with red mud

This paper discussed the stabilities of heavy metals in soils treated with red mud. Soil has been polluted by heavy metals more and more seriously during recent several decades, and they are harmful to mankind and animals. The current tendency is to develop in-situ technique by using industrial processing waste as additives to stabilized heavy metals to minimize the disturbance of contaminated soils. Soil samples were collected from the Niujiaotang mining area, Guizhou Province, southwestern China. They were farmed soils polluted weakly by fly ash （QBT） and polluted badly by waste water （BXT） from smelter, respectively. One of the red mud samples （BRM） was collected from Bayer process and the other （CRM） from confederate process in the Alumina Plant of Guizhou. Free metal ion concentrations were analyzed with Donnan Membrane Technique and predicted with ECOSAT. The concentrations of free heavy metal ions in QBT increased after appending CRM, but decreased when adding BRM. The more the red mud was added, the higher the concentration would be, and the free concentrations of nickel and cadmium ions would vary more greatly than those of copper and zinc ions. When appending red muds into BXT, the free concentrations of copper and zinc ions varied little. While those of free nickel and cadmium decreased obviously at the ratio of 2.00%. The variation of the concentration was still biggish after appending BRM at the ratio of 0.50%, but smaller than that of 2.00%. The concentrations of free cadmium ions increased after adding CRM at the ratio of 0.50%. All experimental processes were modeled through ECOSAT. The predicted and measured results were consistent, except for zinc. Contributions of soil sorbents to the heavy metal adsorptions were also modeled through ECOSAT. The sorbents in soil included soil organic matter, iron hydroxides, clay and the Donnan gel of soil organic matter. Compared to the soils without red muds, no matter what kind of red mud and how much was added in soil, the contributions changed slightly.     

Accumulation of heavy metals in soil and uptake by plant species with phytoremediation potential

Contamination of heavy metals represents one of the most pressing threats to water and soil resources, as well as human health. Phytoremediation can be potentially used to remediate metal contaminated sites. In this study, concentrations of copper, zinc, iron, and magnesium accumulated by native plant species were determined in field conditions of Hame Kasi iron and copper mine in the central part of Iran in Hamadan province. The results showed that metal accumulation by plants differed among species and tissue bodies. Species grown in substrata with elevated metals contained significantly higher metals in plants. Metals accumulated by plants were mostly distributed in root tissues, suggesting that an exclusion strategy for metal tolerance exists widely amongst them. The mentioned species could accumulate relatively higher metal concentrations far above the toxic concentration in the plant shoots. With high translocation factor, metal concentration ratio of plant shoots to roots indicates internal detoxification metal tolerance mechanism; thus, they have potential for phytoextraction. The factors affecting metal accumulation by plant species including metal concentrations, pH, electrical conductivity, and nutrient status in substrata were measured. Mostly, concentrations of zinc and copper in both aboveground and underground tissues of the plants were significantly, positively related to their total in substrata, while iron, zinc, and copper were negatively correlated to soil phosphorus.     

Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: Environmental implications

Total concentrations of chemical elements in soils may not be enough to understand the mobility and bioavailability of the elements. It is important to characterise the degree of association of chemical elements in different physical and chemical phases of soil. Another geochemical characterisation methodology is to apply sequential selective chemical extraction techniques. A seven-step sequential extraction procedure was used to investigate the mobility and retention behaviour of Al, Fe, Mn, Cu, Zn, Pb, Cr, Co, Ni, Mo, Cd, Bi, Sn, W, Ag, As and U in specific physical–chemical and mineral phases in mine tailings and soils in the surroundings of the abandoned Ervedosa mine. The soil geochemical data show anomalies associated with mineralised veins or influenced by mining. Beyond the tailings, the highest recorded concentrations for most elements are in soils situated in mineralised areas or under the influence of tailings. The application of principal components analysis allowed recognition of (a) element associations according to their geochemical behaviour and (b) distinction between samples representing local geochemical background and samples representing contamination. Some metal cations (Mn, Cd, Cu, Zn, Co, Cr, Ni) showed important enrichment in the most mobilisable and bioavailable (i.e., water-soluble and exchangeable) fractions due likely to the acidic conditions in the area. In contrast, oxy-anions such as Mo and As showed lower mobility because of adsorption to Fe oxy-hydroxides. The residual fraction comprised largest proportions of Sn and Al and to a lesser extent Zn, Pb, Ni, Cr, Bi, W, and Ag, which are also present at low concentrations in the bioavailable fractions. The elements in secondary mineral phases (mainly Fe, Mn, Cu, Zn, Cd, Pb, W, Bi, Mo, Cr, Ni, Co, As and U) as well as in organic matter and sulphides are temporarily withheld, suggesting that they may be released to the environment by changes in physico-chemical conditions.     

Effects of ammonium molybdate on phytoremediation by alfalfa plants and (im)mobilization of toxic metals in soils

Ammonium molybdate has been used to remove the toxic metals in waste water by forming precipitates, such as Pb. However, the ammonium molybdate has not been used to remediate the toxic metals contaminated soils. The objectives of this study were to report: (1) the reaction mechanisms of ammonium molybdate with toxic metals; (2) the effects of ammonium molybdate on (im)mobilization of the toxic metals in soils; (3) and the effects of ammonium molybdate on uptake toxic metals from soils by alfalfa (Medicago sativa L.) plants. In this paper, it was found that: the effects of ammonium molybdate on toxic metals are amphoteric-immobilization/mobilization. Cr and Zn can be precipitated with ammonium molybdate, but Cd, Ni, Cu can be formed more soluble fractions with ammonium molybdate. The ammonium molybdate can be named as half-chemical stabilization agent, half-extracting agent, or amphoteric agent. The contents and BCF values of toxic metals in alfalfa plants were increased after the soils were treated with ammonium molybdate. TF values of alfalfa plants (both controls and treatments) were lower than 1. The addition of ammonium molybdate can increase the acid soluble fractions of Cd, Ni, Cu, and residual fractions of Cr, Zn. In other words, the toxicities of Cd, Ni, and Cu to plants in soils have been increasing. Instead, the toxicities of Cr, Zn have been decreasing. The ammonium molybdate has promoted plants to produce more biomass, but the growths of shoot and root in seedling stages have been decreased by the increasing Cd, Ni, and Cu toxicities which caused by ammonium molybdate.     

Characterization of heavy metal contaminated soils in Northern Cyprus

The Lefke region of Northern Cyprus was a site of intense copper mining and smelting activities until the 1970s, which produced large tailings. This study was initiated to characterize the heavy metal contamination of soils of the area and to assess the influence of this site on the surface seawater quality along the coastline. Soil and seawater samples were collected and analysed. Copper and arsenic concentrations exceeded the limits for 'extremely polluted' soils for some samples, which can be classified as 'polluted' by zinc, cadmium and lead. The results showed that seawater was seriously polluted by chromium, nickel and copper in the vicinity of the smelting facility. Copper and iron concentrations increased tenfold after rainfall (wet period), indicating the contribution of tailings to marine pollution. There is an urgent need for remediation treatment for the site.     

The effect of organic materials on the mobility and toxicity of metals in contaminated soils

Organic materials such as compost are often proposed as suitable materials for the remediation of contaminated brownfield sites intended for soft end-use. In addition to vitalising the soil, they are also believed to immobilise metals thereby breaking contaminant-receptor pathways and reducing the ecotoxicity of the contaminants. However, some research has demonstrated contradictory effects between composts on metal immobilisation. In the present study, four different composts and a liming product containing organic matter (LimeX70) were tested to examine both their metal retention and toxicity reduction capabilities on three different metal contaminated soils. Leaching tests, a plant growth test with Greek cress (Lepidium sativum), an earthworm (Eisenia fetida) survival and condition test and a bacterial toxicity test using Vibrio fischeri were carried out. The leaching test results showed that spent mushroom compost caused an increase in metal concentration in the leachates, while LimeX70 caused a decrease. The variation in behaviour between different amendments for each soil was high, so a generic conclusion could not be drawn. Toxicity tests showed significant reduction of metal bioavailability and toxicity for Greek cress, earthworms and bacteria. The results also suggest that more research should be undertaken to understand the mechanisms involved in metal complexation using different types of organic matter, in order to optimise the use of organic materials like compost for soil remediation.     

Background levels and baseline values of available heavy metals in Mediterranean greenhouse soils (Spain)

This study determines extractable levels of Cd, Cu, Pb, Zn, Ni and Co in western Almería (Spain) greenhouse surface soil horizons using EDTA solution, which is identified as the fraction available for organisms and plants. It also establishes background levels, geochemical baseline concentration and reference values (RV), and investigates the possible relationships between soil properties and elemental concentrations. The results show that the soil concentration of these extractable heavy metals was high as those reported by other authors for Spanish agricultural soils. The available RV concentrations obtained (mg kg⁻¹) were: Cd 0.17, Cu 1.6, Pb 13.8, Zn 5.0 Ni 1.7 and Co 2.9. Using the upper baseline criterion, 95% of greenhouse soils present a relatively higher content of extractable heavy metals given their Cd and Cu concentration. Significant correlations between total and EDTA-extractable metal levels were found for Zn, Pb, Cu, Cd and Ni. Soil properties also related to heavy metals content, suggesting that Cd, Cu, Pb and Zn are of similar origin and relate to anthropic activities, and implies the same interactions and/or relationships among these metals.     

Temporal variability of selected heavy metals in automobile soils

Studies on seasonal changes of heavy metal concentration in soils provide vital information for best management options at all times. The study investigated temporal variation in concentration of heavy metals in three towns having automobile service centres in Imo State. The study site is characterized by two major seasons in a year. Heavy metals were found in both arable and automobile soils, but more concentrations were recorded on the latter. Mean values of Cd, Cr, Ni, Hg and Pb were 6.2 mg/kg, 4.7 mg/kg 6.5 mg/kg, 0.02 mg/kg and 71.9 mg/kg respectively in the dry season while 2.9 mg/kg Cd, 2.2 mg/kg Cr, 1.9 mg/kg Ni, 0.01 mg/kg Hg and 51.9 mg/kg Pb were recorded during the rainy season of the experimental period. Higher values of heavy metal concentration were found in automobile soils as follows: 18.1 mg/kg Cd, 12.0mg/kgCr, 16.3 mg/kg Ni, 4.8 mg/kg Hg and312.8 mg/kg Pb in rainy season, and 15.1 mg/kg Cd, 8.1 mg/kg Cr, 11.9 mg/kg Ni 2.7 mg/kg Hg and 267.9 mg/kg Pb. However, Cd showed highest variability in arable soils during the dry season (CV=79%) while Hg varied widely in automobile soils in the rainy season (CV=54%).     

Comparative assessment of baseline concentration of the heavy metals in the soils of Tehran (Iran) with the comprisable reference data

Industrial soil systems have become complex due to human activities, as they disturb the natural development of soil and add hazardous elements. Hence, there is a growing public concern over the accumulation of heavy metals in soil due to the rapid industrial development during the last decade in Iran. The objectives of the present study are to carry out comparative assessment of the heavy metals in soils of the Chitgar Industrial Area Tehran (Iran) with average world guidelines and to evaluate enrichment and normalized scatter coefficient. In this work the concentrations of seven heavy metals (Cr, Co, Cd, Cu, Pb, Ni and Zn) from the surface soils of the industrial area were quantified, based on 210 samples collected from 70 sampling stations in three consecutive seasons May 2007, November 2007 and May 2008 using 0.5 × l Km square mesh. Common comparison methods were employed to assess the quality of soils and guideline values were used to represent a desired level of elements. Comparison variables and enrichment factor showed that Pb has high-level value while normalized scatter coefficient demonstrates that Cd increases in soils more rapidly as compared to other elements. This study revealed that normalized scatter coefficient can be effectively used to evaluate soil pollution and is independent of the past.     

The use of sapropels as amendments in radiocaesium and radiostrontium contaminated soils

Two issues are addressed in this paper: the solid/liquid distribution behaviour of radiocaesium (¹³⁷Cs and ¹³⁴Cs) and radiostrontium (⁹⁰Sr) in sapropels, and the potential effectiveness of sapropels as amendments to remediate soils contaminated with these radionuclides. It is shown that the solid/liquid partitioning of radiocaesium and radiostrontium in sapropels is governed by the same processes as in soils. Experimental K_D values measured in a representative solution vary between 300 and 5000 dm³ kg⁻¹ for radiocaesium and between 15 and 50 dm kg⁻¹ for radiostrontium. These K_D values can be interpreted quantitatively on the basis of the main factors which govern the solid/liquid partitioning of these radionuclides.This quantitative approach also allows predictions to be made on the potential effectiveness of sapropel amendments in contaminated soils. These predictions agree very well with experimental results from simple laboratory experiments aimed at investigating the amendment effect. Addition of 1–4 wt.% doses of 2 sapropel samples with different radiocaesium retention characteristics had no significant effect on the radiocaesium distribution coefficient in sandy soils. It is therefore expected that the addition of such sapropels will not result in a decrease of the radiocaesium soil-to-plant transfer, at least not from the point of view of the increase of the radiocaesium retention in the amended soil. Addition of 1–4 wt.% doses of a high CEC sapropel to low CEC sandy soils increased the radiostrontium distribution coefficient up to 3.5 times. It can thus be expected that addition of such high CEC sapropel will increase the radiostrontium retention in the amended soil, and thus decrease the radiostrontium soil-to-plant transfer.     

Chemical associations of heavy metals and metalloids in contaminated soils near former ore treatment plants: a differentiated approach with emphasis on pHstat-leaching

Application of pH_stat-experiments on soil samples of two heavily contaminated sites in northern Belgium (Flanders) was used to make long-term risk predictions of environmentally relevant heavy metals (Pb, Cu, Ni, Zn, Cr) and arsenic. Implementation of the results of other techniques (sequential extractions and mineralogical research) and geochemical modeling with MINTEQA2 was used to obtain a refined understanding of the geochemical association and the processes that control pH-dependent leaching characteristics of the contaminants. The soil on the first site (a former arsenic refinery in Reppel) was extremely polluted with As, Cu (percentage level), Co and Ni (>0.5%) and leaching of contaminants, which is already alarming, will further increase in the near future by soil acidification. The second site was contaminated with so-called burnt pyrite (sulfuric acid industry) containing high concentrations of Pb, Cu, As and Zn (>0.1%) and a serious threat of metal leaching will manifest if no measures are taken. The kinetics of buffering reactions were evaluated by mathematically fitting of the titration curves. Thereby, two independent proton buffer reactions (rapid and slow) were differentiated and quantified. In the paper, some aspects of the pH_stat-procedure were also reconsidered and evaluated. It was shown that one of the critical parameters, namely the duration of the leaching, needs to be extended to 96 h. A 24-h test was observed to be inadequate in assessing heavy metal release properly.     

土壤重金属环境质量矿物学评价方法

利用环境矿物学理论和方法阐明了土壤矿物控制重金属活动状态,具体分析了重金属在矿物表面、层间域和孔道内可能的赋存位置。实验研究结果表明,矿物吸附重金属的作用受到介质pH值、介质离子强度等因素的影响。采用系统聚类分析方法,能定量地分析稳定的硫化物结合态微量有毒有害重金属元素的数量。利用粉晶X射线衍射分析方法,能定量地测定土壤矿物组成和含量。新提出土壤环境质量矿物学方法评价流程。该方法是在利用生态地球化学方法所完成的元素总量调查成果的基础上,开展单元性与剖面性土壤矿物组成与含量测定,查明表层土壤和深层土壤的矿物组成和分布,评价土壤中重金属的赋存状态及其对食物链的影响。旨在为农业地质环境评价提供新方法,切实提高农业地质环境调查质量与服务水平。