Effects of a Combined Amendment on Pb,Cd, and As Availability and Accumulation in Rice Planted in Contaminated Paddy Soil

The objectives of the present study were to investigate the mitigation of lead (Pb), cadmium (Cd), and arsenic (As) in a multi-metal contaminated soil and their accumulation in rice plants (Oryza sativa L., cv II You 93) using a combined amendment (CMF, calcium carbonate + metakaolin + fused calcium–magnesium phosphate fertilizer). The results showed that application of CMF was effective in reducing the acid-extractable concentrations of soil Pb and Cd. The exchangeable concentrations of soil As showed an initial decrease followed by a gradual increase. The application of 0.2% CMF notably reduced the concentrations of Pb, Cd, and As in brown rice by 46.5%, 43.6%, and 32.0%, respectively. The concentration of As in brown rice was 0.179 mg kg^?1 at 0.2% CMF, which met the maximum levels of contaminants in foods of China (MLs) (the ML of Pb, Cd, and As is 0.2 mg kg^?1 according to the China national standard GB 2762-2012). At 1.6% CMF, the concentrations of Pb and Cd in brown rice were 0.002 and 0.185 mg kg^?1, respectively, i.e., reductions of 99.6% and 74.1%, and these values also fell within the MLs.     

Phytoremediation of polycyclic aromatic hydrocarbons (PAH) by cv. Crioula: A Brazilian alfalfa cultivar

This work aimed to evaluate the phytoremediation capacity of the alfalfa cultivar Crioula in soils contaminated with polycyclic aromatic hydrocarbons (PAHs), primary pollutants with mutagenic and carcinogenic potential. Alfalfa was grown from seed for 40 days on soil amended with anthracene, pyrene, and phenanthrene. Soil and plant tissue was collected for biometric assay, dry mass analysis, and PAH analysis by liquid chromatography. Increased total PAH concentration was associated with decreases in plant biomass, height, and internode length. The Crioula cultivar had a satisfactory phytoremediation effect, reducing total PAH concentration (300 ppm) in the experimental soil by 85% in 20 days, and by more than 95% in 40 days. The PAH showed a tendency to be removed in the temporal order: phenanthrene before pyrene before anthracene, and the removal ratio was influenced by the initial soil concentration of each PAH.     

重金属污染的植物修复及相关分子机制

随着近代工业的发展,土壤重金属污染问题日益严重。重金属即使在极低浓度下仍然可以对人畜造成健康上的威胁,因此迫切需要有效的修复方法对土壤进行修复。生物修复,特别是植物修复目前已经成为重金属污染修复的重要手段之一,了解相关植物的重金属解毒和积累分子机制是提高修复效率、解决重金属污染问题的基础。文中以土壤修复方式为起点,结合植物吸收积累重金属以及解毒的相关分子机制研究,探讨了植物修复的发展现状以及趋势。     

重金属污染土壤修复技术中有关淋洗剂的研究进展

淋洗法是修复污染土壤的一种很有效的方法 ,是对污染土壤生物修复的一种补充 ,使污染土壤修复的系统化成为可能。淋洗法就是使用淋洗剂来清洗土壤 ,使土壤中污染物随淋洗液流出 ,然后对淋洗液及土壤进行后续处理 ,从而达到修复污染土壤的目的。而淋洗剂的选择是影响这一技术效率高低的主要因素之一。本文对目前淋洗剂的应用情况 ,作用机制进行了总结和评价。探讨了天然有机酸、生物表面活性剂等对环境影响小的淋洗液的应用前景。并根据“以废治污”的指导思想提出并分析了以柠檬酸废水和味精废水作为淋洗剂修复重金属污染土壤的可行性。     

5种湿地植物对土壤重金属的富集转运特征

选择芦苇、水葱、千屈菜、扁秆藨草、长苞香蒲5种湿地植物进行盆栽实验,比较它们对土壤中的5种重金属镉、铬、汞、铅、锌的富集特性,分析重金属在各植物体和土壤中的动态分布,以评价所测植物对土壤中重金属的综合富集能力,为利用植物修复金属污染土壤提供理论依据和技术支持。结果表明:(1)种植湿地植物对土壤重金属的富集效果显著高于无植物对照,且随着处理时间的延长,土壤中重金属镉、铬、汞、铅、锌的含量均呈下降趋势。(2)湿地植物对重金属镉、铬、汞、铅、锌的富集效果差异显著,其中水葱根部对重金属镉的富集系数最大,芦苇根部对重金属铬、汞、铅、锌的富集系数均最大,千屈菜、扁秆藨草和长苞香蒲根部对5种重金属的富集系数均较小;芦苇地上部分对金属镉的富集系数最大,千屈菜地上部分对金属铬、汞、铅的富集系数均最大,水葱地上部分对金属锌的富集系数最大。(3)5种湿地植物对重金属镉、铬、汞、铅、锌的转移系数差异显著,其中扁秆藨草对土壤中镉、铬、铅、锌的转移系数均为最大,对铬和锌的转移系数均大于1,长苞香蒲对铬的转移系数大于1,仅次于扁秆藨草。其他3种植物对5种重金属的转移系数均小于1。研究表明,5种湿地植物对重金属Cd、Cr、Hg、Pb、Zn都有富集和转移的能力,但不同植物对不同重金属的富集效果不同。     

强化植物修复重金属污染土壤的策略及其机制

重金属对生态环境、农业生产、人类健康等诸多方面造成重要危害。植物修复因其具有经济有效、绿色生态等优点,已经成为土壤重金属污染修复研究领域的热点。由于植物重金属毒害、修复耗时过长等因素致使植物修复技术受限于研究阶段而不能广泛应用于实践。采用科学合理的强化措施提高植物修复的效率可能是解决该矛盾的关键之一。讨论了根瘤菌、丛枝菌根真菌、溶磷微生物和内生真菌构建的微生物-植物共生系统在强化植物修复过程中的具体应用;概述了EDTA、EDDS等螯合剂在改变土壤中重金属可溶态,促进重金属从土壤向植株转运的重要作用;介绍了植物中编码金属转运蛋白、金属硫蛋白、植物螯合肽等与重金属转运和代谢相关的基因在植物修复领域的实际应用;归纳了上述强化策略主要机制为微生物促进植物生长、缓解重金属植物毒性以及提高了土壤中重金属生物利用度,从而促进重金属在富集植物中积累和植物生物量的增加;最后总结并展望了植物修复强化技术在今后研究的重点及存在的问题。综述植物修复技术采用的主要强化策略及其机制,旨在为利用植物修复技术治理土壤重金属污染提供重要参考。     

Assessment of Metal Uptake Capacity of Castor Bean and Mustard for Phytoremediation of Nickel from Contaminated Soil

The effect of increasing level of nickel (Ni) in soil was studied on biomass production, antioxidants, and Ni bioaccumulation and its translocation in castor bean (Ricinus communis) as well as Indian mustard (Brassica juncea) in similar agroclimatic conditions. The plants were exposed to 25, 50, 75, 100, and 150 mg Ni kg^?1 soil for up to 60 days. It was found that R. communis produced higher biomass during the same period at all the contamination levels than B. juncea, and reduction in fresh and dry weights due to the metal contamination in soil was significantly lower in R. communis than in B. juncea. Proline and malondialdehyde in the leaves increased with increase in Ni level in both the species, whereas soluble protein content was found decreased. A correlation between the protein and MDA contents in the leaves and Ni contamination levels revealed that higher r² values for protein and MDA were found in case of B. juncea, which indicates more toxic effects of the metal in this species. R. communis was found to have enhanced proline accumulation (higher correlation value, r²) at different Ni contamination levels. The bioaccumulation of Ni was higher in B. juncea on the basis of the per unit biomass; however, the total metal accumulation per plant was much higher in R. communis than in B. juncea during the same growing periods. The translocation of Ni from roots to shoots was higher in B. juncea at all Ni concentrations. R. communis appeared more tolerant and capable to clean more Ni from the contaminated soil in a given time and also in one crop cycle.     

大型真菌对重金属的生物富集作用及生态修复

大型真菌是一类重要的环境生物资源,对人类的生存具有重要作用.与绿色植物相比,大型真菌能够积累高浓度的Pb、Cd和Hg等重金属.本文论述了大型真菌对重金属的生物富集作用以及利用大型真菌进行重金属生态修复的优势,指出大型真菌种类、生态类型、富集重金属的生物学特性及其遗传潜能、大型真菌菌丝体和子实体的形态、部位、寿命以及结实间隔和环境因子等是影响大型真菌吸收和积累重金属的主要因素.筛选富集重金属功能强大、易于人工栽培、环境适应性强、便于后处理的大型真菌是今后研究的重要方向.     

The influence of pH and chloride on the retention of cadmium,lead, mercury,and zinc by soils

The extent of contamination of soils by toxic heavy metals not only depends on the rate of loading of the metal but also on the nature of the adsorbing surfaces, the degree of alkalinity or acidity of the soil and the presence of aqueous complexant ligands. This work reports on the role of pH on the retention of Cd, Hg, Pb and Zn by two soils and on the influence of the chloride, Cl‐, ion on the chemical speciation and retention of the four metals. Batch adsorption experiments were conducted from pH 3 to 7 in the presence of either 0.1 M LiCl or LiClO₄. The results of the study showed that high concentrations of Cl^‐ ions can greatly decrease the retention of Hg and have an increasingly lesser effect on Cd, Pb and Zn retention. The effect of the Cl^‐ons was directly related to the metal‐Cl formation constants. The results of computer modeling of Cd and Hg retention by goethite and humic acid fractions indicated the relative importance of aqueous vs. surface complexation on metal retention. For organic surfaces, which do not form ternary surface complexes, the presence of aqueous complexant ligands should always decrease the adsorption of the metal. For mineral surfaces, which do form ternary surface complexes, there may be increased or decreased metal retention depending on the formation constant of the aqueous metal‐ligand species, the intrinsic complexation constants for the various binary and ternary complexes of the metal and the concentration of the complexant ligand. Thus for Hg, which forms very strong aqueous species with Cl^‐ ions, reduced adsorption on goethite was predicted in the presence of 0.1 M LiCl, while enhanced adsorption was predicted for Cd and Pb. The results suggest caution in the disposal of Cl‐containing wastes onto metal‐contaminated soils. The deleterious effects of Cl^‐ ion addition would be greatest for soils with relatively high organic matter contents and low contents of hydrous ferric oxides.     

Heavy Metal Contamination in the Brownfield Soils of Cleveland

The results esults of a survey of heavy metal contamination at Cleveland area brownfields and public spaces are presented. Soils were analyzed using a 24?h, 1N HCl extraction procedure. The study was conducted to seek brownfield soils that manifest properties of “old” sequestered contamination and to develop a better understanding of the nature and extent of heavy metal burdens at brownfield sites in the Greater Cleveland area. The results indicated that Cleveland brownfields commonly yield soil burdens well above remediation triggers for residential soils and often yield values above industrial remediation triggers. It was also discovered that public areas in the vicinity of brownfields commonly have heavy metal contamination significantly above background levels and occasionally above residential remediation triggers. These results indicate that brownfields redevelopment initiatives should proceed with caution. The appropriate remediation goals or restrictions must be imposed to control urban exposure to heavy metal contamination.     

Quantification of Heavy Metals in Mining Affected Soil and Their Bioaccumulation in Native Plant Species

Several anthropogenic and natural sources are considered as the primary sources of toxic metals in the environment. The current study investigates the level of heavy metals contamination in the flora associated with serpentine soil along the Mafic and Ultramafic rocks northern-Pakistan. Soil and wild native plant species were collected from chromites mining affected areas and analyzed for heavy metals (Cr, Ni, Fe, Mn, Co, Cu and Zn) using atomic absorption spectrometer (AAS-PEA-700). The heavy metal concentrations were significantly (p < 0.01) higher in mine affected soil as compared to reference soil, however Cr and Ni exceeded maximum allowable limit (250 and 60 mg kg^?1, respectively) set by SEPA for soil. Inter-metal correlations between soil, roots and shoots showed that the sources of contamination of heavy metals were mainly associated with chromites mining. All the plant species accumulated significantly higher concentrations of heavy metals as compared to reference plant. The open dumping of mine wastes can create serious problems (food crops and drinking water contamination with heavy metals) for local community of the study area. The native wild plant species (Nepeta cataria, Impatiens bicolor royle, Tegetis minuta) growing on mining affected sites may be used for soil reclamation contaminated with heavy metals.     

Comparison of NTA and Elemental Sulfur as Potential Soil Amendments in Phytoremediation

The effect of NTA (nitrilotriacetic acid) and elemental sulfur (S), two soil amendments suggested for the enhancement of metal phytoavailability in phytoextraction, on heavy metal uptake by Nicotiana tabacum (tobacco) and Zea mays (maize) were studied and compared in two Zn-, Cu-, Cd -, and Pb-contaminated soils from northern Switzerland. Experiments were performed in the greenhouse with topsoil (0 to 20 cm) material from two locations, Dornach and Rafz. The Dornach soil was calcareous and had been contaminated by dust emissions from a nearby brass metal smelter. The Rafz soil, free of carbonates, had been polluted by former sewage sludge application. Soil amendments with S increased the solubility (NaNO₃ extraction) of Zn and Cd about 10-fold in Dornach soil and up to 30-fold in Rafz soil after 55 days. Zn and Cd removal by N. tabacum and Z. mays, however, increased only about 5.5- and 2.5-fold in these treatments in Rafz soil, respectively, while in the Dornach soil only a slight increase for Cd was found. Repeated NTA application increased soluble Zn, Cu, and Cd about 100-, 20-, and 19-fold in the Dornach soil and 13-, 4-, and 2-fold in the Rafz soil shortly after application. Soluble Pb was increased by NTA up to 50-fold in Rafz soil. After 90 days soluble heavy metal concentrations were only slightly elevated in both soils. Again, however, Zn, Cd, and Cu removal by N. tabacum and Z. mays increased only about 1.5- to 2.5-fold in the two soils, whereas Pb removal by N. tabacum increased about fivefold in the Rafz soil as a result of NTA application     

Phytoremediation of Heavy Metals in Contaminated Water and Soil Using Miscanthus sp. Goedae-Uksae 1

The aim of this study is to characterize the heavy metal phytoremediation potential of Miscanthus sp. Goedae-Uksae 1, a hybrid, perennial, bio-energy crop developed in South Korea. Six different metals (As, Cu, Pb, Ni, Cd, and Zn) were used for the study. The hybrid grass effectively absorbed all the metals from contaminated soil. The maximum removal was observed for As (97.7%), and minimum removal was observed for Zn (42.9%). Similarly, Goedae-Uksae 1 absorbed all the metals from contaminated water except As. Cd, Pb, and Zn were completely (100%) removed from contaminated water samples. Generally, the concentration of metals in roots was several folds higher than in shoots. Initial concentration of metals highly influenced the phytoremediation rate. The results of the bioconcentration factor, translocation factor, and enrichment coefficient tests indicate that Goedae-Uksae 1 could be used for phytoremediation in a marginally contaminated ecosystem.     

Phytoremediation of Wastewater with Limnocharis Flava,Thalia Geniculata and Typha Latifolia in Constructed Wetlands

Phytoremediation is thought to be the most sustainable wastewater treatment option for developing countries. However, its application is often limited by unavailability of suitable candidate species. In the present study, the potentials of Limnocharis flava, Thalia geniculata and Typha latifolia for remediation of heavy metal contaminated wastewater with a constructed wetland system were evaluated. The wetland consisted of three treatment lines each planted with sufficient and equal number of a species. Duplicate plant and water samples were collected bi-monthly and analyzed for Fe, Cu, Zn, Pb, and Hg using the atomic absorption spectrophotometer over a six month period. Bioaccumulation rates generally increased over time and varied among plants for these metals, with Fe (456–1549 mg kg¹ roots; 20–183 mg kg^?1 shoot) being the most sequestered and Pb (1.2–7.6 mg kg^?1 roots; 1.55–3.95 mg kg^?1 shoot) the least. Translocation factors differed among the species but generally remained stable over time. L. flava showed potential for hyperaccumulating Hg. Removal efficiencies varied for the studied metals (～ 20–77 %) and were generally related to metal uptake by the plants. These results demonstrate the suitability of the species for phytoremediation, and the usefulness of the technique as an option for improving irrigation water quality in Ghana.

Supplemental materials are available for this article. Go to the publisher's online edition of International Journal of Phytoremediation to view the supplemental file.     

Chemically Assisted Phytoextraction: A Review of Potential Soil Amendments for Increasing Plant Uptake of Heavy Metals

The contamination of soils by trace metals has been an unfortunate sideeffect of industrialization. Some of these contaminants can interfere with vulnerable enduses of soil, such as agriculture or nature, already at relatively low levels of contamination. Reversely, conventional civil–technical soil-remediation techniques are too expensive to remediate extended areas of moderately contaminated soil. Phytoextraction has been proposed as a more economic complementary approach to deal with this specific niche of soil contamination. However, phytoextraction has been shown to be a slow-working process due to the low amounts of metals that can be annually removed from the soil under normal agronomic conditions. Therefore, extensive research has been conducted on process optimization by means of chemically improving plant availability and the uptake of heavy metals. A wide range of potential amendments has been proposed in the literature, with considerable attention being spent on aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA). However, these compounds have received increasing criticism due to their environmental persistence and associated risks for leaching. This review presents an overview of potential soil amendments that can be employed for enhancing metal uptake by phytoextraction crops, with a distinct focus on more degradable alternatives to persistent compounds such as EDTA.     

Phytotoxicity of Citric Acid and Tween® 80 for Potential Use as Soil Amendments in Enhanced Phytoremediation

Enhanced phytoremediation adding biodegradable amendments like low molecular weight organic acids and surfactants is an interesting area of current research to overcome the limitation that represents low bioavailability of pollutants in soils. However, prior to their use in assisted phytoremediation, it is necessary to test if amendments per se exert any toxic effect to plants and to optimize their application mode. In this context, the present study assessed the effects of citric acid and Tween® 80 (polyethylene glycol sorbitan monooleate) on the development of alfalfa (Medicago sativa) plants, as influenced by their concentration and frequency of application, in order to evaluate the feasibility for their future use in enhanced phytoremediation of multi-contaminated soils. The results showed that citric acid negatively affected plant germination, while it did not have any significant effect on biomass or chlorophyll content. In turn, Tween® 80 did not affect plant germination and showed a trend to increase biomass, as well as it did not have any significant effect on chlorophyll levels. M. sativa appeared to tolerate citric acid and Tween® 80 at the tested concentrations, applied weekly. Consequently, citric acid and Tween® 80 could potentially be utilized to assist phytoremediation of contaminated soils vegetated with M. sativa.     

Characterization of Gaseous Ozone Decomposition in Soil

Laboratory scale batch experiments were performed to investigate the decomposition characteristics of gaseous ozone in porous media. The decomposition rates of gaseous ozone in several solid media were determined, and the relationship of moisture content with sorbed ozone molecules was evaluated. Ozone decomposition in control and glass beads packed columns followed second-order reaction kinetics, while ozone consumption in a sand-packed column demonstrated first-order kinetics with a rate constant of 0.0109 min^?1 and half-life of 1.0 h. The presence of typical metal oxides in the soil resulted in ozone consumption rates in the following order: hematite (Fe₂O₃) > silica-alumina (SiO₂Al₂O₃) > alumina (Al₂O₃) > silica (SiO₂). Ozone decomposition was highly dependent upon soil moisture content. Over 90% of the total ozone mass decomposed in the field soil with moisture content at less than 1 wt%, whereas as low as 5–15% of the total ozone mass degraded with moisture content at more than 2 wt%. In conclusion, ozone decomposition in soils was primarily controlled not only by soil organic matter but also by reactive metal oxides on the soil surface. These two factors were shown to be highly dependent upon soil moisture content.     

黑土中几种重金属的化学形态

在自然界中,重金属元素的总浓度不能正确反映出它们对生物的效应和地球化学的过程。重金属的毒性在很大程度上取决于它们存在的化学形态。重金属进入土壤这个有机、无机复合体后,通过溶解、沉淀、凝聚、络合、吸附等各种反应,形成重金属的不同化学形态,并表现出不同的活性。东北地区的黑土,其主要特征是富含有机质,为了探索土壤有机质含量与土壤重金属的亲合力及其在土壤中存在的各种形态,我们用A.Tesser等提出的连续浸提法,作了重金属元素在黑土中存在形态的研究,这对进一步研究土壤净化功能与土壤环境容量具有一定意义。     

Effect of Organic Residues and Liming Materials on Metal Extraction from a Mining-Contaminated Soil

Incubation tests were used to assess the effectiveness of three different organic residues and three different liming materials, alone or in combination, in the remediation of a mine contaminated soil. The organic residues tested were sewage sludge from a municipal wastewater treatment plant (SS), compost from the organic fraction of unsorted municipal solid waste (MSWC), and garden waste compost (GWC), applied at 100 and 200 Mg ha^{? 1}. The liming materials tested were agriculture limestone (6.4 Mg ha^{? 1}), calcium oxide (3.7 Mg ha^{? 1}), and sugar beet sludge (12.2 Mg ha^{? 1}) from the sugar manufacturing process. The soil and mixtures of soil and amendments were adjusted to 70% of the maximum water holding capacity and incubated for 28 days in a controlled-temperature room at 20°C ± 1°C. At the end of the incubation, samples were analyzed for pH, electrical conductivity, organic matter content, CaCl₂-extractable, and' NH4Ac/HAc+ EDTA–extractable metal fractions (Cu, Zn, and Pb). Correlations among the variables and/or similarities among the treatments were identified by principal component analysis and hierarchical cluster analysis. The amendments tested decreased the CaCl₂-extractable Cu and Zn fractions, considered as mobile metal fractions, to below analytical detectable limits, providing organic matter to the soil with levels between 1% and 2% at the end of the experiment, significantly different relatively to the original soil. pH and electrical conductivity reached high values when using 200 Mg ha^{? 1} SS or 200 Mg ha^{? 1} MSWC, with any of the liming materials tested, making these application rates excessive for this particular situation. Furthermore, the treatments using MSWC increased the NH4Ac/HAc+ EDTA–extractable Cu, Pb, and Zn fractions, considered as mobilizable metal fractions, as did the 200 Mg ha^{? 1} SS for Pb and Zn. Considering the overall results, the compost made from garden waste decreased metal solubility in the soil and increased soil pH and organic matter content, without the addition of large amounts of soluble salts, and without increasing the mobilizable metal content. Of the organic materials tested, this was the only one that can be considered adequate for remediation of the contaminated soil under study, at the application rates tested.     

Characterization of Nickel Tolerant Bacteria Isolated from Heavy Metal Polluted Glass Industry for its Potential Role in Bioremediation

Heavy metal contamination of the environment is a serious concern because of their deleterious effects on biological systems. To the best of our knowledge, this is the first investigation on isolation of heavy metal resistant bacteria from contaminated sites of glass industrial area.

The study focused on isolation and characterization of Ni²⁺ resistant bacteria from these sites and analysis of their Ni²⁺ accumulation potential. Out of 38 different bacterial isolates 3 bacteria were able to tolerate up to 24 mM Ni²⁺ concentration. These bacterial strains were identified as E. coli (AS17b), Escherichia coli (AS21) and Microbacterium sp. (AS33) by 16S rRNA (16S ribosomal RNA) sequencing and their basic local alignment search tool search analysis. Growing cell of E. coli and Microbacterium sp. revealed accumulation of 0.12, 0.08 and 0.06 µg, of Ni²⁺/mg dry weight of cells, respectively, by 72 hr. Similarly resting cell of these strains showed accumulation of 0.27, 0.11 and 0.08 µg of Ni²⁺/mg dry weight of cells by 150 min, respectively. These results reveal that strain E. coli (AS21) shows maximum accumulation efficiency for Ni²⁺ among different isolates studied under shaking as well as starving conditions. Hence, E. coli (AS21) could serve as an efficient and promising bacterium for bioremediation of nickel-contaminated sites.