Solubility and accumulation of metals in Chinese brake fern, vetiver and rostrate sesbania using chelating agents

Greenhouse experiments were conducted to study the effects of chelating agents on the growth and metal accumulation of Chinese brake fern (Pteris vittata L.), vetiver (Vetiveria zizanioides L.), and rostrate sesbania (Sesbania rostrata L.) in soil contaminated with arsenic (As), Cu, Pb, and Zn. Among the five chelating agents used [ethylenediaminetriacetic acid (EDTA), hydroxyethylenediaminetriacetic acid (HEDTA), nitrilotriacetic acid (NTA), oxalic acid (OA), and phytic acid (PA)], OA was the best to mobilize As, EDTA to mobilize Cu and Pb, and HEDTA to mobilize Zn from soil, respectively. The biomass of vetiver was the highest, followed by rostrate sesbania. All chelating agents inhibited the growth of Chinese brake fern and rostrate sesbania, but HEDTA significantly increased the aboveground biomass of vetiver. Dry weights of both Chinese brake fern and rostrate sesbania decreased with increasing EDTA concentrations amended in the soil, especially in treatments with high EDTA concentrations. EDTA and HEDTA enhanced Cu, Zn, and Pb, but lowered As accumulation in all three plant species, except for As in vetiver, while OA significantly enhanced As accumulation in the aboveground part of vetiver. Concentrations of Cu, Zn, and Pb in the aboveground parts of plants increased significantly with the increase of EDTA concentrations and treatment time. In addition to As, Chinese brake fern also accumulated the highest Cu, Pb, and Zn in its aboveground parts among the three plant species grown in metal-contaminated soil with EDTA/HEDTA treatments. This species, therefore, can be used to simultaneously clean up As, Cu, Pb, and Zn from contaminated soils with the aid of EDTA or HEDTA.     

Identifying the functional groups and the influence of synthetic chelators on Cd availability and microbial biomass carbon in Cd-contaminated soil

Synthetic chelators play an important role in boosting the microbial biomass carbon (MBC), dissolved organic carbon (DOC), and heavy metal solubility in a contaminated soil toward a sustainability of environment for agricultural crops. Castor plant was grown under different levels of Cd contaminated soil (?Cd and +Cd) following adding three chelating agents, ethylenediaminetetraacetic acid (H₄EDTA), nitriloacetic acid (H₃ NTA), and NH₄ citrate (ammonium citrate) to the soil at rates of 10, 15, and 25 mmol in 5 kg of soil per pot. The highest bioavailable Cd concentrations in soil and castor plant were obtained from NH₄ citrate and H₄EDTA treatments in the contaminated soil. Fourier transform infrared (FTIR) analysis showed that NH₄ citrate was the most effective chelator in Cd-contaminated soil. MBC and DOC contents were significantly increased and reached at 81.98–80.37 and 1.96–1.90 mg kg^?1 respectively, in the (H₃ NTA) and NH₄ citrate treatments in Cd-contaminated soil. Further research is needed to investigate the use of chelators in the phytoextraction of Cd-contaminated soils under field conditions and whether it may be beneficial in accelerating the phytoextraction of Cd through hyperaccumulating plants.     

乙二胺四乙酸对孔雀草和一串红铅富集的影响

通过盆栽试验,研究了乙二胺四乙酸(EDTA)对根际土壤Pb的有效性以及孔雀草(Tagetespatula)和一串红(Salviaspendens)富集Pb能力的影响.结果表明:施加EDTA(3mmol.kg-1)7d后,2种花卉根际土壤中乙酸铵溶液(1mol.L-1)可提取的有效态Pb含量极显著提高(P<0.01);孔雀草和一串红叶片中Pb的含量分别达2415.88和1083.68mg.kg-1,为对照处理的61.36和5.37倍;茎中Pb含量也明显增高,而根系Pb含量则略有下降.     

The Removal of Pb and Cd from Heavily Contaminated Soil in Kayseri,Turkey by a Combined Process of Soil Washing and Electrodeposition

In this study, a combined system of soil washing and electrodeposition was designed to remove Pb (16381±643 mg/kg) and Cd (34347±1310 mg/kg) from contaminated soil. 0.05 M Na₂EDTA was used as a chelating agent for the remediation of soil, taken from the nearby city Kayseri, Turkey. As a result of the batch extraction tests, maximum removals were determined as; at the 20:1 liquid: soil ratio for Pb is 60.7%, for Cd at the 30:1 liquid: soil ratio is 67.4%. An electrochemical treatment was applied to the waste washing solution which appeared to be the second pollutant after the Na₂EDTA extraction from the soil. With extraction tests of Pb and Cd, being transformed from the solid phase to the liquid phase. The electrochemical treatment (electrodeposition), performed in three different potential (6 V, 8 V and 10 V) and maximum removal efficiencies, were found 99.7% and 80.3% at 10 V for Pb and Cd, respectively.

Speciation tests (BCR) were carried out, both before and after the soil washing process, to evaluate the redistribution of metal fraction in the soil. The fraction, associated with the organic substance, was found as 10.67% for Pb and 1.81% for Cd. The metal bioavailability factor increased after soil washing, which indicates that EDTA could enhance the mobility of Pb and Cd.     

Effect of high boron application on boron content and growth of melons

Synthetic chelates, such as ethylene diamine tetraacetic acid (EDTA), have been shown to enhance phytoextraction of Pb from contaminated soil but also cause leaching of heavy metal-chelate complexes, posing a groundwater contamination threat. In a soil column study, we examined the effect of EDTA and a biodegradable chelate [S,S] isomere of ethylene diamine disuccinate ([S,S]-EDDS), newly introduced in phytoextraction research, on the uptake of Pb by the Chinese cabbage (Brassica rapa) and Pb leaching through the soil profile. Soil water sorption characteristics were modified by acrylamide hydrogel. The addition of 0.1 and 0.2% (w/w) of hydrogel amendments increased soil field water capacity from initial 24.6% to 28.5% and 31.3%, respectively. The additions of 2.5, 5 and 10 mmol EDTA kg^–1 soil were more effective in enhancing Pb plant uptake than comparable [S,S]-EDDS treatments, but caused (as also 10 mmol kg^–1 [S,S]-EDDS additions) unacceptably high Pb leaching in treatments with any soil water sorption conditions tested. The most efficient level of EDTA (10 mmol kg^–1) enhanced plant Pb uptake by 97 times compared to the control. Shoots Pb concentrations reached 500 mg kg^–1 of dry biomass. However, in this treatment 36.2% of total initial Pb was leached from the soil during the first four weeks after chelate addition. Hydrogel soil amendments were more effective in treatments with [S,S]-EDDS than with EDTA. In treatments with 10 mmol kg^–1[S,S]-EDDS hydrogel amended soils, plant Pb uptake was significantly reduced and Pb leach was as high as 44.2% of total initial soil Pb. At lower [S,S]-EDDS concentrations, the effect of hydrogel soil amendment on Pb leaching was the opposite. The addition of 5 mmol kg^–1 [S,S]-EDDS soil to the soil amended with 0.2% hydrogel increased Pb uptake by 18 times while only 0.2% of total initial Pb was leached. In all treatments, the concentrations of Pb in dry plant biomass were far from concentrations required for efficient soil remediation within a reasonable time span.     

Comparison of EDTA- and Citric Acid-Enhanced Phytoextraction of Heavy Metals in Artificially Metal Contaminated Soil by Typha Angustifolia

A pot experiment was conducted to study the performance of EDTA and citric acid (CA) addition in improving phytoextraction of Cd, Cu, Pb, and Cr from artificially contaminated soil by T. angustifolia. T. angustifolia showed the remarkable resistance to heavy metal toxicity with no visual toxic symptom including chlorosis and necrosis when exposed to metal stress. EDTA-addition significantly reduced plant height and biomass, compared with the control, and stunted plant growth, while 2.5 and 5 mM CA addition induced significant increases in root dry weight. EDTA, and 5 and 10 mM CA significantly increased shoot Cd, Pb, and Cr concentrations compared with the control, with EDTA being more effective. At final harvest, the highest shoot Cd, Cr, and Pb concentrations were recorded in the treatment of 5 mM EDTA addition, while maximal root Pb concentration was found at the 2.5 mM CA treatment. However, shoot Cd accumulation in the 10 mM CA treatment was 36.9% higher than that in 2.5 mM EDTA, and similar with that in 10 mM EDTA. Shoot Pb accumulation was lower in 10 mM CA than that in EDTA treatments. Further, root Cd, Cu, and Pb accumulation of CA treatments and shoot Cr accumulation in 5 or 10 mM CA treatments were markedly higher than that of control and EDTA treatments. The results also showed that EDTA dramatically increased the dissolution of Cu, Cr, Pb, and Cd in soil, while CA addition had less effect on water-soluble Cu, Cr, and Cd, and no effect on Pb levels. It is suggested that CA can be a good chelator candidate for T. angustifolia used for environmentally safe phytoextraction of Cd and Cr in soils.     

EDTA and Pb—EDTA accumulation in Brassica juncea grown in Pb—amended soil

Previous studies have shown that EDTA is necessary to solubilize soil Pb and facilitate its transport from the soil to the above ground plant tissues. These studies have also suggested that Pb is accumulated in the plant tissue with transpiration as the driving force. We conducted further studies to evaluate the relationship between EDTA soil treatment, plant transpiration, and plant accumulation of Pb and EDTA. Indian mustard (Brassica juncea) plants were grown in soils containing Pb at three different concentrations (1.5, 3.0 and 4.8 mmol/kg) for 5 weeks before being treated with EDTA concentrations ranging from 0 to 10 mmol/kg. Plant shoots and xylem sap were collected and analyzed for Pb and EDTA content using ICP and HPLC, respectively. Water loss was measured for 7 days following EDTA application. Transpiration was not affected at <5 mmol/kg EDTA but, at 10 mmol/kg EDTA transpiration decreased by 80%, whereas accumulation of Pb and EDTA increased. In the Sassafras soil, Pb and EDTA accumulation in the plant shoots continued to increase as the applied EDTA concentration increased, except at the highest level (10 mmol/kg). In soil amended with 4.8 mmol/kg Pb and 10 mmol/kg EDTA, the concentrations of EDTA and Pb in shoots decreased and visible signs of phytotoxicity were observed. The results presented herein support recent studies in hydroponic systems showing that EDTA and Pb are taken up by the plant and suggest that Pb is translocated in the plant as the Pb-EDTA complex. The results also show that the maximum Pb accumulation by plants occurs by maximizing the concentration of the Pb-EDTA complex based on the EDTA extractable soil Pb. This revised version was published online in July 2006 with corrections to the Cover Date.     

Enhanced Phytoremediation of Cadmium-Contaminated Soil by Parthenium hysterophorus Plant: Effect of Gibberellic Acid (GA3) and Synthetic Chelator,Alone and in Combinations

The roles of gibberellic acid (GA₃) and ethylenediaminetetraacetic acid (EDTA) in phytoremediation of cadmium (Cd)-contaminated soil by Parthenium hysterophorus plant was investigated. GA₃ (10^?9, 10^?7, and 10^?5M) was applied as a foliar spray. EDTA was added to soil in a single dose (160 mg/kg soil) and split doses (40 mg/kg soil, four split doses). GA₃ and EDTA were used separately and in various combinations. P. hysterophorus was selected due to its fast growth and unpalatable nature to herbivores to reduce the entrance of metal into the food chain. The Cd phytoextraction potential of the P. hysterophorus plant was evaluated for the first time. Cd significantly reduced plant growth and dry biomass (DBM). GA₃ alone increased the plant growth and biomass in Cd-contaminated soil, whereas EDTA reduced it. GA₃ in combination with EDTA significantly increased the growth and biomass. The highest significant DBM was found in treatment T3 (10^?5M GA₃). All treatments of GA₃ or EDTA significantly enhanced the plant Cd uptake and accumulation compared with control (C1). The highest significant root and stem Cd concentrations were found in the combination treatment T11 (GA₃ 10^?5M + EDTA split doses), whereas in leaves it was found in the EDTA treatments. Cd concentration in plant parts increased in the order of stem < leaves < roots. The combination treatment T9 (GA₃ 10^?7M + EDTA split doses) showed the significantly highest total Cd accumulation (8 times greater than control C1, i.e., only Cd used). The GA₃ treatments accumulated more than 50% of the total Cd in the roots, whereas the EDTA treatments showed more than 50% in the leaves. Root dry biomass showed a positive and significant correlation with Cd accumulation. GA₃ is environment friendly as compared with EDTA. Therefore, further investigation of GA₃ is recommended for phytoremediation research for the remediation of metal-contaminated soil.     

Investigation of Arbuscular mycorrhizal Fungus and EDTA Efficiencies on Lead Phytoremediation by Sunflower in a Calcareous Soil

Lead (Pb) contamination of soils is a widespread problem. Mycorrhizal inoculation and synthetic chelators such as ethylenediaminetetraacetic acid (EDTA) may be useful for improving phytoremediation efficiency in Pb-contaminated soils. A greenhouse experiment was performed to study the influence of inoculation with arbuscular mycorrhizal fungus (AMF), Glomus mosseae, and addition of EDTA on phytoremediation of Pb by sunflowers (Helianthus annuus) in a calcareous soil. The experiment was a completely randomized design in a factorial arrangement with five levels of Pb, two levels of mycorrhizal treatments, and two levels of EDTA. Inoculation increased root colonization as Pb levels increased, but the addition of EDTA decreased it. Shoot and root dry matter yields increased by inoculation; however, they decreased with EDTA and Pb levels in co-application treatments. Pb concentration in shoots was significantly higher than that in roots, indicating a translocation factor greater than 1. Inoculation or addition of EDTA significantly increased Pb in roots and its translocation to shoots. The uptake index (UI) value increased in co-application of EDTA and AMF and the individual application of them; it is, therefore, concluded that both AMF and EDTA are effective in phytoremediation of Pb by sunflowers in the studied soil.     

EDTA enhanced heavy metal phytoextraction: metal accumulation,leaching and toxicity

Synthetic chelates such as ethylene diamine tetraacetic acid (EDTA) have been shown to enhance phytoextraction of some heavy metals from contaminated soil. In a soil column study, we examined the effect of EDTA on the uptake of Pb, Zn and Cd by Chinese cabbage (Brassica rapa), mobilization and leaching of heavy metals and the toxicity effects of EDTA additions on plants. The most effective was a single dose of 10 mmol EDTA kg^–1 soil where we detected Pb, Zn and Cd concentrations that were 104.6, 3.2 and 2.3-times higher in the aboveground plant biomass compared to the control treatments. The same EDTA addition decreased the concentration of Pb, Zn and Cd in roots of tested plants by 41, 71 and 69%, respectively compared to concentrations in the roots of control plants. In columns treated with 10 mmol kg^–1 EDTA, up to 37.9, 10.4 and 56.3% of initial total Pb, Zn and Cd in soil were leached down the soil profile, suggesting high solubility of heavy metals-EDTA complexes. EDTA treatment had a strong phytotoxic effect on the red clover (Trifolium pratense) in bioassay experiment. Moreover, the high dose EDTA additions inhibited the development of arbuscular mycorrhiza. The results of phospholipid fatty acid analyses indicated toxic effects of EDTA on soil fungi and increased environmental stress of soil microfauna.     

Toxic Effects of Pb on Anatomy and Hypericin Content in Hypericum perforatum L.

Lead (Pb) is one of the most common heavy metal contaminants in the environment. The present study was therefore undertaken to determine the effects of Pb on structural characteristics and hypericin production in Hypericum perforatum. Mature plants were treated with contaminated soil in seven treatments (75, 150, 300, 600, 800, 1000, and 1500 mg/kg Pb in soil) with three repeats per treatment every 14 days. Maximum observed Pb content in shoot parts was observed in the treatments with 600 and 1500 mg/kg Pb. The Pb concentration in roots was higher than in shoot parts, enhanced with increasing Pb concentration in the soil. In this study, Pb treatment significantly influenced the morphology, anatomy, and hypericin content in the plant. Anatomical characteristics of leaf, stem, and root affected by Pb contamination, as well as scanning electron microscopy (SEM) studies, revealed structural changes in stomata and epicuticular waxes. Under Pb toxicity, anatomical symptoms occurred in leaves, including increase in sizes of epidermal cells, mesophyll tissue, and diameter of stems and roots, as well as amplified vascular bundles and pith area. This, therefore, indicated that metal contamination can change the chemical composition of this plant. Maximum hypericin content was observed in the treatment containing 600 mg/kg Pb in soil, which then decreased.     

Induced Phytoextraction of Lead Through Chemical Manipulation of Switchgrass and Corn; Role of Iron Supplement

The effects of combined chemical application of benomyl, ethylenedianinetetraacetate (EDTA), and iron (Fe) (foliar and root) on lead (Pb) phytoextraction by switchgrass (Panicum virgatum) and corn (Zea mays) was examined. Switchgrass was grown in Pb-contaminated urban topsoil with the following treatments: (C) Control, (B) benomyl, (E) EDTA, (F) foliar-Fe, (BE) benomyl + EDTA, (BF) benomyl + foliar-Fe, (FE) foliar-Fe + EDTA, (BFE) benomyl + foliar-Fe + EDTA. Corn was grown in sand-culture supplemented with Pb (500 mg kg^?1) with the following treatments: (C) control, (B) benomyl, (E) EDTA, (F) root-Fe, (BE) benomyl + EDTA, (BF) benomyl + root-Fe, (FE) root-iron + EDTA, and, (BFE) benomyl + root-Fe + EDTA. All treatments were replicated three times and pots were arranged in a completely randomized design. Plants were analyzed for element concentration (Fe, Zn, P, and Pb) using either inductively coupled plasma (argon) atomic emission spectroscopy (ICP-AES) or graphite furnace atomic absorption spectrometer. Iron supplementation (foliar and root) affected Pb-translocation in plants. Foliar-Fe treatment increased translocation ratio of Pb (TF-Pb) significantly compared to other treatments with the exception of plants treated with benomyl and BF. Root-Fe treatment in combination with EDTA (FE) increased TF-Pb significantly compared to other treatments. Phytoextraction was improved by the combined chemical application; plants treated with BFE treatment increased Pb-total-phytoextraction by 424% compared to Control plants.     

Soil microbial activities and heavy metal mobility in long-term contaminated soils after addition of EDTA and EDDS

A 40-day incubation experiment was carried out in order to evaluate the microbial activities and heavy metal availability in long-term contaminated arable and grassland soils after addition of EDTA (ethylenediaminetetraacetic acid) or EDDS ([S,S]-ethylenediaminedisuccinic acid). Soils with similar contamination of heavy metal from the vicinity of a lead smelter were used in the experiment. The soil microbial carbon (C_mic) decreased significantly after addition of EDTA in the arable soil (CM1); lesser effects were observed in the grassland soil (CM2). Addition of EDDS caused a decrease of C_mic during the first 10 days of incubation. In the later phases of the experiment, C_mic increased, and even exceeded the amounts found in the control soils. Respiratory activities and metabolic quotients (qCO₂) increased after the addition of the chelating agents into the soils. Higher respiratory activities and qCO₂ were observed in the EDTA-treated soils. The readily available heavy metal fractions were extracted with NH₄NO₃ solution. Readily mobilizable heavy metal fractions of Cd, Pb, Zn, and (in part) Cu increased during the first 3-10 days of incubation in the presence of EDTA. The addition of EDDS particularly increased concentrations of available Cu. Significant correlations between NH₄NO₃-extractable metals, soil respiratory activities, and qCO₂ were found in both soil treatments with EDTA and EDDS. This indicates that enhanced metal mobility seriously affects the microbial processes in experimental soils. In addition, the relationships between NH₄NO₃-extractable Cd, Cu, and the microbial biomass were found in the CM1 soil amended with EDTA.     

Lead uptake and the effects of EDTA on lead-tissue concentrations in the desert species mesquite (Prosopis spp.)

Experimental results have shown that the desert plant species mesquite (Prosopis spp.) is capable of accumulating high levels of lead in the roots, translocating it to the aerial portion of the plant. One-week-old mesquite seedlings were treated for 7 d in a hydroponic culture using a modified Hoagland solution. Six treatments were used; three treatments contained only Pb [as Pb(NO3)2] at 25-, 50-, and 75-mg L(-1) levels and three treatments contained the same levels of Pb, but with equimolar concentrations of disodium ethylenediamine tetraacetic acid (EDTA). Our results showed that the plants exposed to 25-, 50-, and 75-mg Pb L(-1) treatments without EDTA concentrated in stems 524, 3726, and 1417 mg kg(-1), respectively. However, the plants treated with Pb-EDTA concentrated in stems 480-, 607-, and 1247-mg Pb kg(-1) for the 25-, 50-, and 75-mg Pb L(-1) treatments, respectively. Results for the roots followed a similar trend; without EDTA the Pb levels ranged from 16,055, 89,935, and 63,396 for the 25-, 50-, and 75-mg Pb L(-1) treatments, respectively, and with EDTA these levels were 9,562, 49,902, and 39,181 mg kg(-1) for the three treatments. However, the addition of EDTA increased lead movement to the leaves. The levels of Pb without EDTA were 20, 35, and 51 mg kg(-1) for the 25-, 50-, and 75-mg Pb L(-1) levels, respectively. Treatments with EDTA showed uptake levels of 105, 124, and 313 for the 25-, 50-, and 75-mg Pb L(-1) treatments. Further, the percent Pb in dry leaf tissues for all EDTA treatments were greater than 0.1%. However, only the 25-mg Pb L(-1) treatment was greater than 0.1%, compared to 0.04 and 0.08% for the 50- and 75-mg Pb L(-1) treatments, respectively. Preliminary transmission and scanning electron microscopy corroborate the presence of lead.     

淹水条件下控释氮肥对污染红壤中重金属有效性的影响

采用淹水培养方法研究了不同氮水平(100、200和400 mg/kg,分别记为1、2、3)下普通尿素(PU)、硫包膜尿素(SCU)、树脂包膜尿素(PCU)和硫加树脂双层包膜尿素(SPCU)对污染红壤中Cd、Pb、Cu、Zn有效性的影响.结果表明,不同包膜尿素对土壤pH值和水溶性SO42-含量有较大影响.各施氮处理红壤pH值随着施氮量的增加(除5d时PU和60 d时SCU)而增加,不同包膜尿素对土壤中水溶性SO42-含量有较大影响,在同一施氮水平下不同包膜尿素处理间土壤pH值和土壤中水溶性SO42-含量差异较大.60 d培养期间PU、SCU、PCU和SPCU处理pH值比对照分别升高0.17-0.38、0.08-0.27、0.07-0.36和0.10-0.21;水溶性SO42-含量PU、SCU和PCU处理比对照分别升高39.5％-157.3％、40.9％-94.5％和7.55％-55.8％,而SPCU处理降低5.67％-90.7％.不同尿素类型和氮肥的施用量对红壤Cd、Pb、Cu和Zn有效性的影响均存在显著差异.60 d培养期间红壤有效态Cd含量以树脂包膜尿素100 mg N/kg下最低,其有效态Cd含量比对照显著降低20.7％-69.8％;有效态Pb、Cu和Zn含量以普通尿素400 mg N/kg下最低,其有效态Pb、Cu和Zn含量比对照分别显著降低17.0％-54.2％、18.5％-34.6％和15.6％-59.5％.随施氮量提高,PU处理有效态Cd含量先升高后降低,有效态Pb、Cu和Zn含量逐渐降低;SCU处理有效态Pb含量逐渐降低,有效态Cd、Cu和Zn含量变化规律不一致;PCU处理有效态Cd含量逐渐升高,有效态Pb、Cu和Zn含量变化规律不一致;SPCU处理有效态Cd、Pb、Cu和Zn含量逐渐降低.有效态Pb和Zn含量与pH值和水溶性SO42-含量呈显著负相关,有效态Cd与水溶性SO42-含量呈显著正相关.在多重金属污染红壤中,可考虑不同控释氮肥的配合使用,降低土壤中重金属的有效性.     

含铜有机肥对土壤酶活性和微生物群落代谢的影响

以猪粪和麦秆为原料,向原料中添加不同浓度硫酸铜溶液模拟原料铜污染堆制有机肥,通过小白菜盆栽试验施用堆制腐熟的有机肥,研究其对土壤酶活性及群落功能多样性的影响。结果表明,与CK处理(Cu质量分数10.35mg/kg)相比,L处理(Cu质量分数300.00mg/kg)的脱氢酶活性下降了64.75%,H处理(Cu质量分数900.00 mg/kg)的脱氢酶活性下降了90.66%。在Biolog生态测试板(ECO Microplate)温育过程中,CK处理的AWCD值(Average Well Color Development)始终大于L处理和H处理。与CK处理相比,L处理和H处理96h的AWCD值分别下降了3.55%、36.59%,CK处理显著高于H处理(P<0.01)。多样性指数对含Cu有机肥有不同的响应,L处理的shannon指数最高,H处理的simpson指数最高,CK处理的Mclntosh指数及Mclntosh均匀度最高。主成分分析结果表明,对3个处理起分异作用的碳源主要是糖类和羧酸类。     

The Combined Effect of Cu,Zn and Pb on Enzyme Activities in Soil from the Vicinity of a Wellhead Protection Area

Heavy metals are known to have adverse effects on soil ecosystems, while soil enzyme activities are sensitive to soil pollution. This study investigated the combined effects of Cu, Zn and Pb on the activities of invertase (IN), urease (U) and alkaline phosphatase (ALP) in soil obtained from the vicinity of a wellhead protection area via an orthogonal array (OA) design method. The experimental results showed the following: (1) Cu showed higher inhibition on the activities of all three enzymes than Zn and Pb when three metals were all present in the soil sample. IN activity, U activity and ALP activity decreased as the levels of Cu increased, and ranged from 15.9% to 55.7%, 3.57% to 78.6%, and 3.23% to 75.3%, respectively. Their lowest values were found in samples at 35 days with 400 mg/kg Cu. (2) Zn and Pb had different influences on the activities of the three enzymes. The lowest IN activity (the highest reduction 58.0%) and U activity (76.8%) were observed when Zn was at the concentration of 100 mg/kg after 35 days, whereas the highest inhibitory function of Zn on ALP activity (75.3%) was at 300 mg/kg after 7 days. When the concentration of Pb increased from 35 to 350 mg/kg, the activities of IN (62.5%) and U (69.6%) were most inhibited at 35 days and 14 days, respectively. However, when Pb was at the concentration of 500 mg/kg after 14 days, ALP activity (72.0%) showed the lowest value. (3) With respect to the three hydrolases in this study, ALP was the most sensitive to the two-variable interactive effects of Cu, Zn and Pb, especially Cu?×?Pb. It is concluded that the soil ALP activity may be a sensitive tool for assessing additive toxic effect on soil biochemical parameters. To provide more information about the potential ecological risk of chemicals on soil ecosystems, much more should be done to clearly determine the mechanisms of the combined effects of heavy metals in soil.     

Enhanced uptake of soil Pb and Zn by Indian mustard and winter wheat following combined soil application of elemental sulphur and EDTA

Enhancement of Pb and Zn uptake by Indian mustard (Brassica juncea (L.) Czern.) and winter wheat (Triticum aestivumL.) grown for 50 days in pots of contaminated soil was studied with application of elemental sulphur (S) and EDTA. Sulphur was added to the soil at 5 rates (0–160 mmol kg^?1) before planting, and EDTA was added in solution at 4 rates (0–8 mmol kg^?1) after 40 days of plant growth. Additional pots were established with the same rates of S and EDTA but without plants to monitor soil pH and CaCl₂-extractable heavy metals. The highest application rate of S acidified the soil from pH 7.1 to 6.0. Soil extractable Pb and Zn and shoot uptake of Pb and Zn increased as soil pH decreased. Both S and EDTA increased soil extractable Pb and Zn and shoot Pb and Zn uptake. EDTA was more effective than S in increasing soil extractable Pb and Zn, and the two amendments combined had a synergistic effect, raising extractable Pb to ¿1000 and Zn to ¿6 times their concentrations in unamended control soil. Wheat had higher shoot yields than Indian mustard and increasing application rates of both S and EDTA reduced the shoot dry matter yields of both plant species to as low as about half those of unamended controls. However, Indian mustard hyperaccumulated Pb in all EDTA treatments tested except the treatment with no S applied, and the maximum shoot Pb concentration was 7100 mg kg^?1 under the highest application rates of S and EDTA combined. Wheat showed similar trends, but hyperaccumulation (1095 mg kg^?1) occurred only at the highest rates of S and EDTA combined. Similar trends in shoot Zn were found, but with lower concentrations than Pb and far below hyperaccumulation, with maxima of 777 and 480 mg kg^?1 in Indian mustard and wheat. Despite their lower yields, Indian mustard shoots extracted more Pb and Zn from the soil (up to 4.1 and 0.45 mg pot^?1) than did winter wheat (up to 0.72 and 0.28 mg pot^?1), indicating that the effects of S and EDTA on shoot metal concentration were more important than yield effects in determining rates of metal removal over the growth period of 50 days. Phytoextraction of Pb from this highly contaminated soil would require the growth of Indian mustard for nearly 100 years and is therefore impractical.     

Chemically enhanced phytoextraction of lead-contaminated soils

The effects of the combined application of soil fungicide (benomyl) and ethylenediaminetetraacetic acid (EDTA) on lead (Pb) phytoextraction by ryegrass (Lolium perenne) were examined. Twenty-five pots of Pb-contaminated soil (200 mg Pb kg(-1)) were seeded with ryegrass and randomly arranged into the following treatments: (1) Control, (2) benomyl, (3) EDTA, (4) benomyl and EDTA (B+E), and (5) benomyl followed by an application of EDTA 14 days later (B .. . E). Chemicals were applied when plants had reached maximum growth. Plants were analyzed for foliage Pb concentration using inductively coupled argon plasma (ICAP) spectrometry. The synergistic effects of the combined benomyl and EDTA application (treatments 4 and 5) were made evident by the significantly (p < 0.05) highest foliage Pb concentrations. However, the foliage dry biomass was significantly lowest for plants in treatments 4 and 5. The bioaccumulation factor (BF) and phytoextraction ratio (PR) were highest for plants in treatment 5 followed by plants in treatment 4.     

Enhanced accumulation of Cd in castor (Ricinus communis L) by soil-applied chelators

Phytoextraction has been identified as one of the most propitious methods of phytoremediation. This pot experiment were treated with varying amounts of (ethylenediamine triacetic acid) EDTA 3–15, (Nitriloacetic acid) NTA 3–10, (Ammonium citrate) NH₄ citrate 10 – 25 mmol and one mg kg^–1Cd, filled with 5 kg soil. The addition of chelators significantly increased Cd concentration in soil and plant. The results showed that maximum Cd uptake was noted under root, shoot and leaf of castor plant tissue (2.26, 1.54, and 0.72 mg kg^–1) under EDTA 15, NTA 10, and NH₄ citrate 25 mmol treatments respectively, and in soil 1.08, 1.06 and 0.52 mg kg^–1 pot^–1 under NH₄ citrate 25, NTA 10 and EDTA 15 mmol treatments respectively, as against to control (p < 0.05). Additions of chelators reduction biomass under the EDTA 15 mmol as compared to other treatments, However, Bioconcentration factor (BCF), translocation factor (TF) and remediation factor (RF) were significantly increased under EDTA 15 and NH₄ citrate 25 mmol as against control. Our results demonstrated that castor plant proved satisfactory for phytoextraction on contaminated soil, and EDTA 15 and NH₄ citrate 25 mmol had the affirmative effect on the Cd uptake in the artificial Cd-contaminated soil.