湖南柿竹园矿区土壤重金属含量及植物吸收特征

矿区重金属污染十分严重,寻找和发现适合当地气候与土壤条件的重金属耐性植物是矿区植被恢复和污染土壤修复的前提。对我国湖南柿竹园有色金属矿区调查发现,该地区选矿厂的重金属污染问题普遍比尾砂库严重。选矿厂土壤砷、镉、铅、锌严重超标,尾砂库周围也受到不同程度的重金属污染。土壤重金属胁迫效应影响着植物物种分布,选矿厂物种分布较少,相比之下尾砂库的植物多样性较为丰富。柿竹园矿区植物对重金属的吸收表现为富集型(如蜈蚣草Pteris Vittata L .和苎麻Boehmerianivea (L .) Gaud.)、根部囤积型(如攀倒甑Patrinia villosa和木贼Equisetum hyemale)和规避型(如蔓出卷柏Selaginelladavidii Franch和芒草Miscanthus sinensis Andlerss)等3种类型。     

Effects of Municipal Sewage Sludge Doses on the Chlorophyll Contents and Heavy Metal Concentration of Sugar Beet (Beta vulgaris var. saccharifera)

The present study was conducted to assess the suitability of sewage sludge amendment (SSA) in soil for Beta vulgaris var. saccharifera (sugar beet) by evaluating the heavy metal accumulation and physiological responses of plants grown at a 10%, 25%, and 50% sewage sludge amendment rate. The sewage sludge amendment was modified by the physicochemical properties of soil, thus increasing the availability of heavy metals in the soil and consequently increasing accumulation in plant parts. Cd, Pb, Ni, and Cu concentrations in roots were significantly higher in plants grown at 25% as compared to 50% SSA; however, Cr and Zn concentration was higher at 50% than 25% SSA. The concentrations of heavy metal showed a trend of Zn > Ni > Cu > Cr > Pb > Cd in roots and Zn > Cu > Ni > Cr > Pb > Cd in leaves. The only instance in which the chlorophyll content did not increase after the sewage sludge treatments was 50%. There were approximately 1.12-fold differences between the control and 50% sewage sludge application for chlorophyll content. The sewage sludge amendment led to a significant increase in Pb, Cr, Cd, Cu, Zn, and Ni concentrations of the soil. The heavy metal accumulation in the soil after the treatments did not exceed the limits for the land application of sewage sludge recommended by the US Environmental Protection Agency (US EPA). The increased concentration of heavy metals in the soil due to the sewage sludge amendment led to increases in heavy metal uptake and the leaf and root concentrations of Ni, Zn, Cd, Cu, Cr, Pb, and Zn in plants as compared to those grown on unamended soil. More accumulation occurred in roots and leaves than in shoots for most of the heavy metals. The concentrations of Cd, Cr, and Pb were more than the permissible limits of national standards in the edible portion of sugar beet grown on different sewage sludge amendment ratios. The study concludes that the sewage sludge amendment in the soil for growing sugar beet may not be a good option due to risk of contamination of Cr, Pb, and Cd.     

Phytochelatins as biomarkers for heavy metal stress in maize (Zea mays L.) and wheat (Triticum aestivum L.): combined effects of copper and cadmium

Heavy metal contaminated soils often show increased levels of more than one metal, e.g. copper (Cu), cadmium (Cd), zinc (Zn), lead (Pb) or nickel (Ni). In case such soils are used for crop production, prediction of yield reduction or quality decline due to heavy metals in the soil is inadequate when based only on chemical soil analysis. The use of biomarkers such as phytochelatins (PC), non-protein thiols specifically induced in plants upon exposure to heavy metals, may be an additional tool or diagnostic criterion in heavy metal research and in practice. In the present work, Cu and Cd uptake and induction of PC synthesis are studied with hydroponically grown maize and wheat plants exposed to mixtures of the two metals. We observed a close positive relationship between the concentrations of Cd and PC in the plant shoot material. A decreased shoot concentration of Cd after addition of Cu, due to metal competition at common root absorption sites, coincided with lower shoot PC levels. Also differences in metal uptake and xylary metal transport among the two plant species were reflected in corresponding differences in PC concentration. The observed direct relationship between shoot PC concentration and the degree of metal-induced growth inhibition makes the use of PC promising for the purpose tested for.     

Factors affecting the distribution of cadmium,copper and lead and their effect upon yield and zinc content in bush beans (Phaseolus vulgaris L.)

Summary Concentrations of Cd, Pb and Cu in the roots, stems and leaves of bulgarian bush beans (Phaseolus vulgaris L.) were determined for plants grown in various soils of increasing levels of contamination of these metals. Most of each heavy metal absorbed by plants was retained in roots. Concentrations of Cd, Pb and Cu in roots increased in response to soil concentrations, whereas, in stems, only Cd and Pb concentrations increased and Cu concentration was relatively constant. It is thought that Cu transport to the stele was metabolically controlled, whereas Cd and Pb reached the stem by leakage across non suberised areas of the endodermis. Uptake of heavy metals was associated with a decrease in zinc content in plants and a decrease in yield. By regression analysis decrease in both zinc content and plant yield could be best related to Cd content in stems. Possible reasons for these effects are discussed.     

The influence of heavy metals upon the growth of sitka-spruce in South Wales forests

Summary Experiments on sitka-spruce seedlings grown in acidic peaty gley soils under green-house conditions, where the soils where doped with increasing amounts of Cd, Cu and Pb up to maximum levels of metal added of 16 ppm, 32 ppm and 400 ppm respectively, showed that the levels of Cd and Pb in shoots and roots increased with increasing levels in the soil, whereas levels of copper appeared to be independent. The addition of these three metals to the soils did not influence the uptake of other heavy metals, or of the nutrients potassium or calcium. Increases in the shoot cadmium levels significantly reduced the yields of the plant shoots. However, the plant yields were only affected by the highest level of lead that was added to the soil (400 ppm Pb) and unaffected by all the copper treatments (0–32 ppm Cu in the soil). The lengths of the sitka-spruce roots were reduced when cadmium and lead levels in the soil exceeded certain threshold concentrations (2.5 ppm total Cd, where 0.3 ppm was extractable with 0.5 M acetic acid; and 48 ppm total Pb, where 1.7 ppm was extractable). However, root lengths were not reduced by copper. This was probably related to the fact that copper appears to be relatively unavailable in the type of soil used, as only 1.1. ppm Cu was extractable from a total of 32 ppm Cu added. Root branching was apparently reduced by increases in the soil levels of cadmium, copper and lead. The roots of some control plants had symbiotic mycorrhizal associations (4 out of 19 plants), whereas the roots of all the plants grown in the soils with added heavy metals did not develop these.     

Phytoavailability of Heavy Metals and Metalloids in Soils Irrigated with Wastewater,Akaki, Ethiopia: A Greenhouse Study

Irrigation with untreated wastewater from several industrial, commercial, and domestic discharges for decades caused accumulation of various heavy metals and metalloids in soils along the Akaki River in Ethiopia. Assessment of environmental threats and the potential phytoremediation of the soils require understanding of the toxic elements’ uptake and distribution in plant parts. Hence, a greenhouse study was performed to examine the phytoavailability and distribution of Cr, Ni, Co, Cu, Zn, Cd, Pb, Hg, Se, V, and As in forage grasses: Oat (Avena sativa), Rhodes grass (Chloris gayana), Setaria (Setaria sphacelata), and the legumes Alfalfa (Medicago sativa) and Desmodium (Desmodium unicinatum). The average contents of Cr, Ni, Co, Cu, Zn, Pb, Hg, Se, and V in the plants were generally higher than the background levels for forage grasses/legumes, and some of these elements were in the phytotoxic range. Root bioconcentration factor (BCF = root to soil concentration ratio) > 1 was observed for Cu (Oat, Rhodes, Desmodium, and Setaria: Fluvisol), Zn (Setaria: Fluvisol), Cd (Rhodes: Fluvisol; Setaria from both soils) and Hg (Oat and Alfalfa: Fluvisol). Alfalfa and Desmodium displayed translocation factor > 1 (TF = shoot to root concentration ratio) for most heavy metals. Most heavy metals/metalloids may pose a health threat to humans and stock via introduction to the food chain. The plant factors (species and plant part), soil factors (soil type, soil fractions, pH, and CEC), and their interactions significantly (p < 0.05) influenced plant heavy metal and metalloid levels. However, the role of plant part and species emerged as the most important on heavy metal uptake, translocation, sequestration, and ultimately transfer to the food chain. Accordingly, the uptake and distribution of heavy metals/metalloids in the plants reflect the potential environmental and health hazards attributable to the use of fodder grasses, legumes, and cultivation of vegetables in soils with polymetallic and metalloid contamination.     

Spatial Distribution of Heavy Metals in Soil and Flora Associated with the Glass Industry in North Central India: Implications for Phytoremediation

The effect of the glass industry on soil metal characterization was assessed at five test sites at five successive distances in a semi-arid area. A comprehensive profile of Zn, Cd, Pb, Ni, Cu, and As levels in soils was obtained. The spatial distribution patterns of integrated contamination indices for these metals show a similar decreasing trend in distribution as we move further from the industrial cluster. There was significant correlation among individual heavy metal concentrations in the soil samples. Integrated contamination indices indicate that 64% of the sites were in the high contamination range and 28% were in the moderate contamination range. A statistically significant difference (P ≤ 0.001) was obtained for each metal on comparing mean metal content among soil samples. Phytoremedial potential of 12 native plant species was also evaluated. Individual elements displayed remarkably different patterns of accumulation in soils as well as plants. Plants established limited capabilities in mobilizing Zn, Pb, Ni, and Cu in the root zone. While Cd, Cu, As, Zn and Pb were predominantly partitioned in shoots, Ni was equally partitioned between shoots and roots. Interestingly, some plants showed a different partitioning trend at higher concentrations of different metals compared to lower concentrations. Potential species for phytoremediation include Calotropis procera (Milk weed), Chenopodium murale (Goosefoot),Poa annua (Annual bluegrass) and Datura stramonium (Thorn apple). None of the species showed phytoremedial potential for Ni and Cu.     

Fungal Inoculation and Elevated CO2 Mediate Growth of Lolium Mutiforum and Phytolacca Americana,Metal Uptake,and Metal Bioavailability in Metal-Contaminated Soil: Evidence from DGT Measurement

Fungal inoculation and elevated CO₂ may mediate plant growth and uptake of heavy metals, but little evidence from Diffusive Gradients in Thin-films (DGT) measurement has been obtained to characterize the process. Lolium mutiforum and Phytolacca americana were grown at ambient and elevated CO₂ on naturally Cd and Pb contaminated soils inoculated with and without Trichoderma asperellum strain C3 or Penicillium chrysogenum strain D4, to investigate plant growth, metal uptake, and metal bioavailability responses. Fungal inoculation increased plant biomass and shoot/root Cd and Pb concentrations. Elevated CO₂ significantly increased plants biomass, but decreased Cd and Pb concentrations in shoot/root to various extents, leading to a metal dilution phenomenon. Total Cd and Pb uptake by plants, and DGT-measured Cd and Pb concentrations in rhizosphere soils, were higher in all fungal inoculation and elevated CO₂ treatments than control treatments, with the combined treatments having more influence than either treatment alone. Metal dilution phenomenon occurred because the increase in DGT-measured bioavailable metal pools in plant rhizosphere due to elevated CO₂ was unable to match the increase in requirement for plant uptake of metals due to plant biomass increase.     

Simultaneous extraction of soil phytoavailable cadmium,copper, and lead by chelating resin membrane

Cadmium, copper, and lead were extracted from suspensions of contaminated soils using metal chelating exchange resin membranes. Nine soils with widely varying properties and Cd, Cu and Pb levels were tested. Soil suspensions made up with 4 g in 40 mL deionized water were equilibrated with 5 cm² Ca-saturated Chelex exchange resin membrane which was retained inside a polypropylene bag and shaken at 150 rpm for 24 hrs. Resin membrane extractable Cd, Cu and Pb of the soils were correlated with Cd, Cu, and Pb uptake by young wheat seedlings grown in these soils and compared with soil Cd, Cu, and Pb extracted by 0.1 M HCl, 0.01 M CaCl₂, and 0.005 M Diethylenetriamine pentaacetic acid (DTPA). The amounts of Cd, Cu and Pb extracted by the Ca-saturated Chelex membrane from all tested soils correlated well with those absorbed by young wheat seedlings. The Ca-saturated Chelex membrane extractable Cd, Cu and Pb of the soil had the strongest correlation with plant uptake Cd, Cu and Pb among the extraction methods we tested. It was demonstrated that the Ca-saturated Chelex membrane extraction is an appropriate method in simultaneously estimating Cd, Cu and Pb phytoavailability of soil and is applicable to a wide range of soils.     

Heavy metal accumulation in iron plaque and growth of rice plants upon exposure to single and combined contamination by copper, cadmium and lead

A pot experiment was conducted to evaluate the bioaccumulation of heavy metals and growth response of rice plants after exposure to single and combined contamination by Cu, Cd and Pb. The results showed that the biomass production was not significantly affected by either single or combined treatment of Cu, Cd and Pb. Adding Cu (Cd, or Pb) separately all increased concentrations of the respective element in root and shoot (p < 0.001). In the combined contamination, Pb promoted both root and shoot absorption of Cu and Cd (p < 0.001), and Cu affected Cd and Pb absorption in the root, but Pb concentrations in both root and shoot were not affected by Cd application. The formation of iron plaques varied obviously with soil types. Heavy metal accumulation in iron plaques was induced by the three elements (p < 0.001). Furthermore, the three heavy metals exhibited an interactive relationship as measured by the Cu, Cd, Pb and Fe concentrations in root surface iron plaques. The iron plaques partially inhibited transfer of Pb to root and shoot, but no such effect was observed for Cu and Cd. This research indicates that the interaction among different heavy metal elements is very complex. It is very important to have a clear understanding on the associated mechanism and the consequential impact on plant growth.     

Heavy metal accumulation in iron plaque and growth of rice plants upon exposure to single and combined contamination by copper, cadmium and lead

A pot experiment was conducted to evaluate the bioaccumulation of heavy metals and growth response of rice plants after exposure to single and combined contamination by Cu, Cd and Pb. The results showed that the biomass production was not significantly affected by either single or combined treatment of Cu, Cd and Pb. Adding Cu (Cd, or Pb) separately all increased concentrations of the respective element in root and shoot (p < 0.001). In the combined contamination, Pb promoted both root and shoot absorption of Cu and Cd (p < 0.001), and Cu affected Cd and Pb absorption in the root, but Pb concentrations in both root and shoot were not affected by Cd application. The formation of iron plaques varied obviously with soil types. Heavy metal accumulation in iron plaques was induced by the three elements (p < 0.001). Furthermore, the three heavy metals exhibited an interactive relationship as measured by the Cu, Cd, Pb and Fe concentrations in root surface iron plaques. The iron plaques partially inhibited transfer of Pb to root and shoot, but no such effect was observed for Cu and Cd. This research indicates that the interaction among different heavy metal elements is very complex. It is very important to have a clear understanding on the associated mechanism and the consequential impact on plant growth.     

The Adsorption Properties of Agricultural and Forest Soils Towards Heavy Metal Ions (Ni,Cu, Zn,and Cd)

Adsorption of Cu, Cd, Ni, and Zn in single and multi-metal solutions by agricultural and forest soils was investigated in batch sorption experiments. The results showed significant differences in sorption capacities of the studied soils. The selectivity order was as follows: agricultural soil? top forest soil > bottom forest soil. The adsorption sequence Cu > Zn > Ni > Cd was established for the agricultural and bottom forest soil, while the order for the top forest soil was Cu > Ni > Zn > Cd. The experimental isotherms for the metal sorption were described satisfactorily by the Freundlich and Langmuir models. The competitive adsorption experiment indicated a reduction in the amount of metals adsorbed by the soils from the multi-metal solution compared to the single metal solution. Properties of the soils, such as pH, content of clay and organic matter, exchangeable bases and hydrolytic acidity, showed a significant influence on adsorption capacities of the studied soils.     

Arbuscular mycorrhizal contribution to heavy metal uptake by maize (Zea mays L.) in pot culture with contaminated soil

In two pot-culture experiments with maize in a silty loam (P2 soil) contaminated by atmospheric deposition from a metal smelter, root colonization with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were investigated. Soil was -irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatment, whereas in experiment 2 the irradiated soil was inoculated with spores of a fungal culture from P2 soil or a laboratory reference culture, Glomus mosseae. Light intensity was considerably higher in experiment 2 and resulted in a fourfold higher shoot and tenfold higher root biomass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in the mycorrhizal plants than in the nonmycorrhizal plants, suggesting a protection against metal toxicity. In contrast, in experiment 2, biomass did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concentration was significantly increased with the indigenous P2 fungal culture. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treatments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not altered between treatments. Cu and Zn, but not Pb and Cd root-shoot translocation increased with mycorrhizal colonization. The results show that the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be generalized. It is suggested that metal-tolerant mycorrhizal inoculants might be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimized conditions of normal agricultural practice, however, AM colonization even may increase plant metal absorption from polluted soils.     

Eco-service enhancement in peri-urban area of coal mining city of Huaibei in East China

After 50 years of coal mining, Huaibei Mine, located at 50 km southeast of Xuzhou City in East China, has grown to a middle-size city of 600,000 people from a small village of 2000 farmers. The Zhahe Valley, with 400 km² of a built-up area and more than 100 km² of subsided peri-urban wetland at the city center, is surrounded by eight exhausted old mines and communities. In cooperation with the local city government, an ecological landuse change assessment and eco-city planning project has been carried out with a focus on the assessment, restoration and enhancement of the wetland as an eco-service to the community. The assessment includes relationships to Green House Gas emissions and heat island effects, as well as measures for a livable, workable, affordable and sustainable human settlement development through industrial transition, landscape design and capacity building. This paper will briefly introduce the main ecological approaches and results of the assessment, including measures such as changing the car-dominated transportation network to a rail-dominated network, transforming the coal-oriented high-carbon industry to a service-oriented low-carbon industry, the C-shape urban form to an O-shape with a green–blue core at the center, and the fragmentized collapsed land to integrative eco-service land.     

Effectivity of host-Rhizobium leguminosarum symbiosis in soils receiving sewage water containing heavy metals

Disposal of sewage water in cultivated soils often containing considerable amount of potentially toxic metals such as Cu, Zn, Ni, Cd, Pb and Cr can be beneficial or harmful to plant growth, rhizobial survival, nodulation and nitrogen fixation. Soil samples from 14 such locations were collected. Symbiotic effectivity of host-Rhizobium leguminosarum symbiosis in these soils was assessed. The total metal contents of Cd, Cu, Zn and Ni in all the 14 samples collected from farmer's fields receiving sewage water ranged between 1.3 and 6.7, 55.8-353.2, 356.0-1028.0 and 90.0-199.7 mg kg(-1) of soil, respectively. In Rohtak 1 soil, levels of Cd, Cu and Zn were highest while Ni was highest in Sonipat 2 soil. The content of available Cd, Cu, Zn and Ni in these soils ranged from 1.0-29.3; 6.2-47.0; 2.4-13.5, respectively, and was 2-9 percent of their total metal contents. All the N2 fixing parameters in pea and Egyptian clover were adversely affected by the presence of heavy metals. Available Cd and Cu contents significantly affected the N contents of pea and Egyptian clover plants, whereas Ni contents were negatively correlated with the plant biomass of pea and Egyptian clover.     

河北主要土壤中Cd、Pb形态与油菜有效性的关系

当今土壤重金属污染日趋严重而表征土壤污染程度 的指标不够完善、相关性亦较差。为此,采用网室盆栽试验,研究了河北平原主要土壤类型潮土和潮褐土上Cd、Pb的化学形态特征及其与油菜植株干物重、油菜吸收重金属含量的关系。结果表明Cd对油菜的毒害作用大于Pb。总量及各形态Cd、Pb含量与油菜可食部分干物重呈负相关,对油菜干物重影响最大的是交换态Cd、Pb。而对油菜吸收Cd、Pb贡献最大的形态是碳酸盐结合态和铁锰氧化物结合态。深入研究重金属形成与植物有效性间的关系,可为进一步揭示重金属的生物有效性,为更准确评价土壤重金属污染程度提供理论依据,具有重要的理论意义和实际应用价值。     

Effect of Compost and Biochar on Heavy Metals Phytostabilization by the Halophytic Plant Old Man Saltbush [Atriplex Nummularia Lindl]

Remediation of soils is vital to mitigate the negative effects of heavy metals in ecosystems. There is little information available about the metals’ phytostabilization potential of old man saltbush plants [Atriplex nummularia]. A pot experiment in a randomized complete block design was conducted to study the accumulation of heavy metals by old man saltbush plants, as affected by the application of compost and biochar. The cultivation of A. nummularia is an effective tool in immobilizing metals in the contaminated soils. The cultivation of metal-contaminated soil with A. nummularia reduced the availability of Zn, Cu, Cd, and Pb by 20%, 4%, 21%, and 28%, respectively, in comparison to the non-cultivated soil. Zn, Cu, Cd, and Pb concentrations in the aboveground parts of old man saltbush plants were 70–100, 50–80, 4–5, and 50–90 mg/kg of dry biomass. The higher Zn, Cu, Cd, and Pb concentrations were accumulated in the roots, and the lower concentrations were transferred to the shoots of old man saltbush plants. Compost reduced the concentration of Zn, Cu, Cd, and Pb in the shoots by 10%, 19%, 20%, and 6%, respectively, compared to the control soil. Biochar reduced the concentrations of Zn, Cu, and Pb in the shoots by 30%, 38%, and 44%, respectively, compared to the control. Compost had a lower effect in reducing the metals uptake as biochar. Biochar reduced the uptake of Zn, Cu, and Pb in the shoots of the tested plant by 22%, 23%, and 41%, respectively, in comparison to compost. Based on the obtained results, old man saltbush has good characteristics to be a promising candidate for phytostabilization strategies of metal-contaminated soils. Moreover, biochar is a good tool to enhance metals’ phytostablization.     

Impact of Humin on Soil Adsorption and Remediation of Cd(II), Pb(II), and Cu(II)

In situ immobilization constitutes a promising technology for the mitigation of contaminants, through the reduction of metal bioavailability and mobility. This study investigated the adsorption isotherms and kinetic characteristics of humin extracted from peat soils. We also studied the influences of the pH, ionic strengths, and soluble organic matter concentrations of soil solutions on the adsorptive properties of humin, and compared its ability to detoxify potentially toxic metals in both actual and simulated soil solutions. The study results indicated that humin contains a massive population of oxygen-containing functional groups. Its adsorption capacity for Pb(II) was greater than that for Cu(II), which exceeded that for Cd(II). The adsorption of humin for Pb(II) conformed to the Freundlich model, while the adsorption of humin for Cd(II) and Cu(II) followed the Langmuir model. The adsorption kinetics of humin with respect to potentially toxic metals aligned well with second-order kinetics equations. As the pH was elevated, the potentially toxic metal adsorption by humin increased rapidly. Electrolyte ions and tartaric acids in solution both inhibited the adsorption of potentially toxic metals by humin, and its ability to inactivate potentially toxic metals. This was shown to be improved in actual field soil solutions in contrast to simulated soil solutions.     

A field lysimeter study of heavy metal movement down the profile of soils with multiple metal pollution during chelate-enhanced phytoremediation

The agricultural soils near a copper smelter in southeast China were found to be highly contaminated with Cu, Pb, Zn, and Cd. Metal migration from the soil to groundwater presents an environmental risk that depends on the physicochemical properties of the contaminated soils. Soil solution samples were obtained using lysimeters from a loam soil with multiple metal pollutions over a period of about 1 yr. A field lysimeter study was also conducted to examine the potential use of (S, S')-ethylenediamine-N, N'-disuccinic acid trisodium salt (EDDSNa3) in chelate-enhanced phytoremedation and to evaluate the leaching of heavy metals. The average heavy metal concentrations in the soil solution (without the addition of EDDS) were high (e.g., 0.15 mg Pb L(-1) at a 50-cm depth) compared to the upper limit for protection of groundwater in China, but varied during the sampling period. Cu concentrations were not correlated with pH or dissolved organic carbon (DOC), but Zn and Cd concentrations were related to soil solution pH. EDDS enhanced metal solubility in the soil, but plant metal uptake by Elsholtzia splendens Nakai did not increase accordingly. There may be an increasing risk of groundwater pollution by Cu and the EDDS enhanced phytoremediation technique needs to be carefully applied to minimize this side effect.     

Phytoextraction of zinc, copper, nickel and lead from a contaminated soil by different species of Brassica

In a pot culture experiment, five different species of Brassica (Brassica juncea, Brassica campestris, Brassica carinata, Brassica napus, and Brassica nigra) were grown for screening possible accumulators of heavy metals, viz. Zn, Cu, Ni, and Pb. The plants were grown to maturity in a soil irrigated with sewage effluents for more than two decades in West Delhi, India. The soil analysis showed enhanced accumulation of Zn, Cu, Ni, and Pb in this sewage-irrigated soil. Among all species, B. carinata showed the highest concentration (mg kg(-1)) as well as uptake (microg pot(-1)) of Ni and Pb at maturity. Although B. campestris showed a higher concentration of Zn in its shoots (stem plus leaf), B. carinata extracted the largest amount of this metal due to greater biomass production. However, B. juncea phytoextracted the largest amount of Cu from the soil. In general, the highest concentration and uptake of metal was observed in shoots compared to roots or seeds of the different species. Among the Brassica spp., B. carinata cv. DLSC1 emerged as the most promising, showing greater uptake of Zn, Ni, and Pb, while B. juncea cv. Pusa Bold showed the highest uptake of Cu. The B. napus also showed promise, as it ranked second with respect to total uptake of Pb, Zn, and Ni, and third for Cu. Total uptake of metals by Brassica spp. correlated negatively with available as well as the total soil metal concentrations. Among the root parameters, root length emerged as the powerful parameter to dictate the uptake of metals by Brassica spp. Probably for the first time, B. carinata was reported as a promising phytoextractor for Zn, Ni, and Pb, which performed better than B. juncea.