Mobility and bioavailability of selected heavy metals in coal ash- and sewage sludge-amended acid soil

A sequential extraction procedure has been used to study the changes in the distribution and mobility of Cd, Cr, Cu, Ni, Pb and Zn in an acid lateritic soil amended with alkaline coal ash and neutral sludge individually and with their mixture of equal proportions at 25, 50 and 75 Mg/ha application rates and grown in a crop with peanuts. A separate set of experiments consisting of the same treatments was repeated with the addition of lime at 2 Mg/ha. Increases in total heavy-metal levels with application of various amendments were mainly associated with increases in the insoluble and less mobile forms of metals except for Cd, which showed an increase in its exchangeable form. An increase in pH of the amended soil restricted the metal mobility in their labile forms and was more pronounced after liming the treatments. Positive yield responses were observed in the amended soil, the magnitude being higher in only sludge-applied treatments. The vegetative plant parts showed maximum accumulation of metals indicating a physiological barrier in the transfer of metals from the root to the kernel. Linear relationships of total concentrations of heavy metals in soil with that in the crop were observed. Lime addition to the treatments further reduced the transfer and accumulation of metals from the soil to the plant, even though the relationship remained linear.     

Competitive adsorption behavior of selected heavy metals in three soil types of India amended with fly ash and sewage sludge

Laboratory batch experiments were carried out to study the competitive sorption behavior of metals in three types of Indian soils, differing in their physicochemical properties: acid laterite (SL1), red alfisol (SL2) and black vertisol (SL3) treated with different proportions of fly ash and sewage sludge mixture. Representative samples were equilibrated with 10 to 200 µM L ^-1 concentrations of metals simultaneously containing Cd, Cu, Ni, Pb and Zn in 5 mM of Ca(NO ₃) ₂ solution. In most of the cases the affinity sequence of metals was Pb>Cu>Zn>Ni>Cd based on their amount of sorption, which varied little with either metal equilibrating concentrations or the soil/mixture type. The observed metal affinity sequences in different soils amended with mixtures were compared to the predicted affinity sequences based on metal properties and a good match was found with those predicted by metal hydrolysis constants. This indicated that formation and subsequent sorption of metal hydrolysis products on soil surface is the predominant mechanism for sorption. In all the cases, Pb and Cu showed higher affinity followed by Zn, Ni or Cd. The increase in the metal additions further enhanced the competition among metals for exchange sites. Adsorption isotherms showed that metal sorption was linearly related to its concentration in the equilibrium solution. The distribution coefficients (K _D) computed from the slopes of linear regression for different metals were higher in SL3 than in both SL2 and SL1. All the mixture amended soils produced higher K _D values than their respective controls. Selectivity between metals resulted in the following affinities based on their K _D values—Pb>Cu>Zn>Ni or Cd—which was in line with the value of the hydrolysis constant of the metals under study.     

Changes in physical and chemical properties of three soil types in India as a result of amendment with fly ash and sewage sludge

The use of coal fly ash and domestic sewage sludge in agriculture is being considered as one of the methods for recycling of these wastes in an environmental beneficial manner. Mixtures with soil were prepared at different proportions of fly ash and sludge, either alone or in combination at a maximum application rate of 52 t ha^-1. The changes in the selected properties and heavy metal contents of three soil types in India were studied after incubating the respective mixtures for 90 days at near field capacity moisture level. Sewage sludge, due to its acidic and saline nature, high organic matter and heavy metals content, had more impact on soil properties than the fly ash. Sludge application produced several changes including an increase in available nitrogen, organic carbon, salinity and water-holding capacity of the soils. The concentrations of major cations and heavy metals also increased because of the sludge application and the pH was decreased. However, the levels of individual metal concentrations in all the mixture types were below the allowable limits prescribed by several environmental agencies. Using fly ash either alone or in equal quantity with sewage sludge had little influence on soil properties and heavy metal content. The relative availability (RA) of heavy metals in three soils amended with 52 t ha^-1 of sewage sludge was observed to be highest in oxisol, followed by alfisol and vertisol.     

Immobilization of Cd,Zn and Pb in sewage sludge using red mud

Sewage sludge is an inevitable end by-product of sewage treatment. Land application provides a cost-effective alternative for sewage sludge disposal. However, sewage sludge contains heavy metals that may limit its application. In this work, red mud was employed for the immobilization of heavy metals in sewage sludge. The effect of red mud amendment on heavy metal immobilization was evaluated using Toxicity Characteristic Leaching Procedure (TCLP) method. The TCLP results showed that the immobilization efficiency of Cd, Zn and Pb was 100, 92, and 82%, respectively, when sewage sludge was mixed with 10% red mud. Tests carried out in leaching columns demonstrated that heavy metal concentrations in the leachate of 10% red mud amended sludge were lower than those of the unamended sludge. Moreover, red mud decreased plant available heavy metal (Cd, Zn and Pb) content from 18.1, 17.2 and 14.6% to 6.9, 11.4 and 7.6%, respectively. Sequential chemical extraction experiments showed that after sludge was amended with 10% red mud, exchangeable fraction was reduced and iron and manganese oxides fraction was increased. Red mud amendment can effectively immobilize Cd, Zn and Pb in sewage sludge before land application.     

Characteristics of heavy metal accumulation on fly ash- and sewage sludge-amended calcific soil

Land disposal of fly ash(FA)and sewage sludge(SS)is a major problem due largely to their potentially harmful constituents.In this paper,a potting experiment was performed to evaluate the effects on the plant growth and to discuss in particular the potential hazard to soils and plants according to the characteristics of heavy metal accumulation and migration when FA and SS are used as the amendments of calcific soil in a limestone mining area. The results showed that the application of FA-SS mixture is capable of accelerating the growth of plants and improving the biomass production at either 1:1 or 1:2 FA-SS mixture:soil(w/w).The highest yields were obtained at 1:1(w/w)mixing ratio.When compared with the Element Background Values of Soils in China,the analysis on heavy metals indicated that the contents of Pb,Cr,Hg,Cd,As,Ni,Cu and Zn in the amended soils came up to the second-class environmental quality standards,only Hg and Cd showed significant accumulation.At the same time, though the metal concentrations in roots were higher than those for the control,the concentrations except Cu,Zn in shoots were lower.And all the heavy metal contents in the plants were substantially lower than the toxicity limits. The results indicated that the combined use of FA and SS at a rational rate of application should pose no danger to both soil and food chain based on the characteristics of the FS and SS,heavy metals and calcific soil.     

Concentrations and solubility of heavy metals in muck sediments from the St. Lucie Estuary,U.S.A.

To evaluate muck sediments as a potential soil amendment, total and Mehlich III-extractable concentrations of Cd, Cu, Cr, Ni, Pb, Zn, and Co in 59 muck sediment samples from the St. Lucie Estuary were analyzed. A seven-step chemical fractionation procedure was used to assess the potential mobility of heavy metals. Except for Cd, the average total concentrations of the metals are lower than the reported average concentrations of these elements in municipal composts in the U.S.A. The concentrations were also below critical levels for the safe use of wastes and byproducts in agriculture, as established by the United States Environmental Protection Agency. The Cd, Cu, Cr, Ni, Pb, Zn and Co in the sediments were predominantly associated with silicate minerals in the residual form. Most metals in the muck sediments occur predominantly in weakly mobile or nonbioavailable forms. Use of mucks in neutral pH upland soils should not pose any significant hazards or risk to the environment. However, Cd, Cu, Cr, Ni, Pb, Zn, and Co, especially Zn, Cu, and Pb, could be more readily released from the muck sediments under acidic soil conditions.     

印染污泥中重金属形态分析及生物有效性

选取上海某印染厂的印染废水处理后的活性污泥样品,通过盆栽土培试验,用黑麦草对印染污泥进行修复,运用Tessier A连续提取法研究修复后黑麦草根际和非根际印染污泥中铅、铜、镍、锌、镉5种重金属形态的变化,以及重金属的生物有效性与植物中有效态含量之间的关系。结果表明,栽培后根际与非根际环境中各重金属元素具有典型的形态分布特征:铅主要以离子交换态和残渣态存在;铜主要以碳酸盐结合态和残渣态存在;镍由紧结合态(铁锰氧化物结合态+有机结合态)向离子交换态转移;锌的有机结合态和碳酸盐结合态有所增加;镉主要以离子交换态和铁锰氧化物结合态为主,说明镉元素较活泼,具有潜在的环境影响能力,应该给予更多的关注。印染污泥中重金属的生物有效性与重金属元素的性质有关,铜、锌的生物有效性较高,其次是铅,最低是镍、镉。     

粉煤灰污泥添加剂对地下水质影响的模拟研究

通过测定土柱和淋洗液中重金属的含量,研究石灰岩质土壤应用粉煤灰污泥添加剂改良后重金属在土壤剖面上的分布移动特征及对地下水质的影响.结果表明:仅试验层内除As和Ni外,Zn、Cd、Pb、Cu、Cr、Hg含量明显增加,未出现明显向下移动的趋势;同时重金属淋出量明显增加,但未超过地下水Ⅲ级标准.初步认为与添加剂自身、重金属的特性及石灰岩质土壤滤层的截固作用相关.粉煤灰污泥经过合理的配施和预处理应用于石灰岩质矿区退化土壤的改良,短期内不会对地下水的质量产生明显的影响.     

Environmental contamination of Zn,Cd, Ni,Cu, and Pb from industrial areas in Hamadan Province,western Iran

Eleven surface soil samples from calcareous soils of industrial areas in Hamadan Province, western Iran were analyzed for total concentrations of Zn, Cd, Ni, Cu and Pb and were sequentially extracted into six fractions to determine the bioavailability of various heavy metal forms. Total Zn, Cd, Ni, Cu and Pb concentrations of the contaminated soils were 658 (57–5,803), 125.8 (1.18–1,361), 45.6 (30.7–64.4), 29.7 (11.7–83.5) and 2,419 (66–24,850) mg kg⁻¹, respectively. The soils were polluted with Zn, Pb, and Cu to some extent and heavily polluted with Cd. Nickel values were not above regulatory limits. Copper existed in soil mainly in residual (RES) and organic (OM) fractions (about 42 and 33%, respectively), whereas Zn occurred essentially as RES fraction (about 69%). The considerable presence of Cd (30.8%) and Pb (39%) in the CARB fraction suggests these elements have high potential biavailability and leachability in soils from contaminated soils. The mobile and bioavailable (EXCH and CARB) fractions of Zn, Cd, Ni, Cu, and Pb in contaminated soils averaged (7.3, 40.4, 16, 12.9 and 40.8%), respectively, which suggests that the mobility and bioavailability of the five metals probably decline in the following order: Cd = Pb > Ni > Cu > Zn.     

Immobilization of heavy metals in a contaminated soil in Iran using di-ammonium phosphate,vermicompost and zeolite

Fractionation of heavy metals (HMs) in amended soils is needed to predict elemental mobility in soil and phytoavailability to plants. A study was conducted to determine the effects of different amendments on HMs availability and their redistribution among soil fractions. A contaminated soil was selected from around a Zn mine and amended with 0, 2, 4, and 6 g kg⁻¹ of vermicompost (VC), zeolite (ZE), and di-ammonium phosphate (DP) and incubated at field moisture. The amounts of Cd, Pb, Zn, and Cu were determined from the soil after 6 months of incubation time using DTPA and sequential extraction procedures. The total concentrations of Cd, Pb, Zn, and Cu were 41, 3,099, 1,997, and 83 mg kg⁻¹ of soil, respectively. All amendments decreased significantly [probability (p) ≤ 0.05] DTPA-extractable Cd, Pb, and Cu, but not Zn, in the soil. For instance, DTPA-extractable Cd, Pb, and Cu decreased by 40, 290, and 20%, respectively, and that of Zn increased by 18% with DP₁ (2 g kg⁻¹ of di-ammonium phosphate) application. The concentrations of Pb and Cd decreased mainly in the specifically sorbed (SS) but increased in the amorphous Fe oxide (AFeO) fraction with DP application, indicating redistribution of Pb and Cd in the fractions with less mobility. Lead immobilization by DP was mainly attributed to the P-induced formation of chloropyromorphite, which was identified in the DP treatment using X-ray diffraction technique. It was concluded that DP was the most effective amendment in immobilizing Pb and Cd, though it increased Zn mobility.     

The effect of traffic on levels,distribution and chemical partitioning of harmful metals in the street dust and surface soil from urban areas of Tehran,Iran

Due to the explosive industrialization and rapid expansion of the population in many parts of the world, heavy metals are released into the environment continuously and pose a great risk on human health. Street dust and surface soil samples from very heavy, heavy, medium and low traffic areas and a natural site in Tehran, Iran, were analyzed for some physicochemical features, total and chemical fractionating of selected metals (Zn, Al, Sr, Pb, Cu, Cr, Cd, Co, Ni and V) to investigate the influence of traffic on their mobility and accumulation in the environment. The pH, electrical conductivity (EC), carbonates and organic carbon contents were similar in soil and dust samples from the areas with same traffic. The traffic increases EC contents in dust/soil matrixes, but has no effect on concentrations of metals in soil samples. Rises in metal levels with traffic were found in dust samples. Moreover, the traffic increases the percentage of both acid-soluble and reducible fractions, which are related to Pb and Zn. The mobilization of Cu, Zn, Pb, Cr in dust samples was easier than in soil. The speciation of metals except Cd is mainly affected by physicochemical features in soil, though total metals affected the speciation in dust samples (except chromium and nickel).     

福建龙海土壤重金属含量特征及影响因素研究

为有效预防土壤重金属生态风险,以福建龙海市表层土壤为研究对象,应用经典统计分析、随机森林等方法,研究重金属元素含量特征及其影响因素。结果表明：(1)第四纪冲洪(海)积成因水稻土中多数重金属元素含量较高;(2)燕山期中酸性岩风化形成的残坡积红壤中重金属元素活动态含量较高;(3)As、Cu、Ni形态含量与全量相关性较好,而Cd、Cr、Hg的多数形态含量与全量相关性较差;(4)除元素全量外,土壤有机质对弱有机结合态重金属(不包括Ni、Pb元素)以及离子交换态、碳酸盐结合态Cd、Zn有重要影响,阳离子交换量对各形态Ni,(Fe×Al)/Si对各形态Cu具有重要影响,而土壤成因、土壤类型对重金属形态组成的影响较小。研究表明土壤重金属形态组成及其富集区与其全量不尽一致,土壤重金属生态风险评价应考虑土壤重金属形态分布特征。     

Assessing the bioaugmentation potentials of individual isolates from landfill on metal-polluted soil

Heavy metals from leachate are persistent pollutants in soil, especially when landfills lack liners and basic structural system that prevents overflow of leachate beyond restricted areas. It is not ideal to rely only on physical and chemical options for the reclamation/restoration of such contaminated soil. Therefore, it is imperative to adopt bioremediation through the enhancement of microbial potentials. The present study investigated the use of individual isolates for the remediation of soil contaminated by leachate-metals. This is a way to understand the discrete potentials of the gram-positive bacteria species. Environmental isolates taken from contaminated soil were used to remedy soil characterized with various concentrations of metals (Al, Cd, Cr, Fe, Ni, Pb and Zn). Treatments A, B, and C amended with Bacillus sp., Lysinibacillus sp., and Rhodococcus sp., respectively, demonstrated better metal reduction potentials than the control experiment (Treatment D; zero microbial amendment) that depended solely on natural attenuation. With the exception of Ni, the degree of reduction of other metals was less than 50% for all treatments. This study suggests that such result reflects the potential ability of the microbes to metabolize selectively in the presence of metal pollution. However, it is difficult for the individual microbes to attain higher metal reduction efficiency (above 50%) except when blended in the appropriate formulation.     

Metals in tidal flats colonized by microbial mats within a South-American estuary (Argentina)

In this study, we measured the concentrations of metals (Cd, Cu, Pb, Ni, Cr, Zn, Hg, Mn, and Fe) and assessed the characteristics of tidal flats (grain size and organic matter content) in sediments and their overlying microbial mats fractions to evaluate the anthropogenic impact within the Bahía Blanca Estuary (BBE). Puerto Rosales (PR) and Almirante Brown (AB), located in the middle and inner zone of the estuary, respectively, were used as sampling sites. Sediments were composed mainly of silt–clay in AB, whereas first fine-grained particles were coarser in depth in PR. Regarding the concentration of metals in both fractions, we found differences between sites: There were higher concentrations of overall metals in AB relative to PR. In addition, higher concentrations of Cu were recorded in the first centimeters of AB tidal flats, whereas higher concentration of Cd were recorded in microbial mats of PR. Considering that the grain size was similar between sites, these results are consistent with the high concentration of organic matter found in AB, probably because this site is close to a former municipal dump and sewage discharges. Also, the higher Cd content found in PR site would highlight both the influence of untreated urban discharges and port anthropogenic activities. In conclusion, this study allowed identifying high values of some metals in the presence of microbial mats in the BBE, thus suggesting a possible interaction between both, at least for metals like Cu or Cd.     

某矿区土壤重金属分布特征及来源解析

为探究赣南某矿区土壤重金属污染状况及来源,以该矿区内40个土壤样品为研究对象,分析了土壤中Cu、Pb、Zn、Cr、Ni、Cd、As和Hg等8种重金属元素的含量,并采用频率直方图、相关性分析、主成分分析等多种统计方法探究了土壤重金属含量的分布特征及来源。研究结果表明:(1)研究区8种重金属中有7种不同程度地超过了江西省土壤重金属元素背景值;(2)Pb、Zn、As和Hg的含量接近正态分布,而Cu、Cr、Ni和Cd的含量则呈现出右偏分布的趋势,这可能与研究区矿山开采活动及土地利用类型等因素有关;(3)矿区土壤重金属相关性分析表明,Cu、Cr、Ni的同源性较高,可能具有相同的污染源,而Pb、Zn、Cd等元素与Cu、Cr、Ni相比,其来源可能存在一定的差异;(4)主成分分析结果显示,矿区内土壤中8种重金属元素含量可以由2个主成分来解释,所代表的实际意义按贡献率排序分别是成土母质和人为采矿活动;(5)矿区内土壤重金属污染物主要为Pb、Zn、Cd,人为采矿活动是这三种重金属污染的主要来源。     

Ecotoxicological assessment of heavy metals in sewage sludge amended soils

Contamination of soils by potentially toxic elements (PTEs) (e.g. Zn, Cu, Ni, Cr, Pb, Cd) from amendments of sewage sludge is subject to strict controls within the European Community in relation to total permissible metal concentrations, soil properties and intended use. This paper highlights the need for ecotoxicological data for the assessment of PTE impacts in addition to geochemical data alone. The soil microflora plays an essential role in determining levels of soil fertility, being intimately associated with the biogeochemical cycling of essential plant nutrients and the turnover of organic carbon. The measurement of soil microbiological parameters can provide insight into the impact of PTEs upon soil fertility, where geochemical analysis alone can often be inadequate to assess contaminant effects on essential components of the soil ecosystem. Microbial investigations were conducted on soils sampled from a well-controlled field experiment previously amended with specific types and rates of sewage sludge. Key microbiological parameters measured included the activity of the dehydrogenase enzyme and the presence and number of effective nitrogen fixing cells of Rhizobium leguminosarum biovar trifolii capable of nodulating the host plant, white clover (Trifolium repens). Results were evaluated with respect to maximum permissible concentrations of PTEs in sludge amended soils, as stipulated under UK limit values and the European Directive 86/278/EEC. Important effects on the size of the Rhizobium population and dehydrogenase activity were apparent in soils samples in relation to the soil pH, sludge type, addition rates and the concentrations of PTE present.     

Metal retention in a thin karstic soil, Christian County, Missouri

 The response of a Wilderness cherty loam series soil to repeated dosages of metals (as sewage sludge) using a two-step sequential extraction procedure was investigated. Variations in metal content between amended and control soils were related to organic matter, clay content, and clay mineralogy. Of the four metals investigated, Cu was found to accumulate in the top 20 cm of amended soils; Pb and Zn were present in even smaller amounts with respect to the control soils, and Cr concentrations were unaffected with respect to both depth and amendment. None of the metals indicated accumulation in deeper (>20 cm) parts of the soil profile. Overall, results suggest that the metals remobilize in the top 20 cm, being readily uptaken by the fescue grass growing in this lot. Precipitation of insoluble forms of metal into deeper parts of the soil profile was proven unlikely based on the distribution of metal concentrations throughout the profile. Received: 15 December 1997 · Accepted: 23 March 1998     

Study on effective species of heavy metals in lacustrine sediment core from Xijiu Lake,Taihu Lake catchment,China

The BCR sequential extraction procedure is applied to probe into the speciation distribution of heavy metals (Cd, Cr, Zn, Cu and Pb) in lake sediments of Core XJ2 in Xijiu Lake, Taihu Lake catchment, China. The results showed that the effective species concentration of this five heavy metal elements increased obviously during the past century, the proportions of organic/sulphide fractions of Zn, Cu and Pb decreased while the Fe–Mn oxide fractions increased, and the proportion of Fe–Mn oxide fractions of Cd decreased while the exchangeable and carbonate fractions increased. The concentrations of exchangeable and carbonate fractions of these five elements were increased in the past century, especially the proportions of these fractions of Cd, Zn, Cu and Pb increased prominently. These changes could be attributed to the anthropogenic pollution. Since the changes of the heavy metal concentrations were corresponding to the history of human activities, especially the industry development, within the catchment.     

Comparison of extractability of Cd, Cu, Pb and Zn with sequential extraction in contaminated and non-contaminated soils

Various extraction procedures were employed for measuring extractable concentrations of potential toxic elements in soil. The extractability of Cd, Cu, Pb and Zn in four contaminated and four non-contaminated soils of Japan, was compared by single extraction (CaCl₂, DTPA, NH₄Cl, 0.1 M HCl and 1 M HCl ) and sequential extraction procedures [(six operationally defined chemical phases, viz. water soluble (Fl), exchangeable (F2), carbonate (F3), oxide (F4), organic (F5) and residual (F6) fractions)]. Extractability of metals from soils samples varied depending on metals and/or extradants used. Among the extradants, 1 M HCl extracted the largest proportion of Cd (79 to 96% of total), Cu (61 to 83%), Pb (51 to 99%) and Zn (23 to 52%) from soils followed by 0.1 M HCl, NH₄Cl, DTPA and CaCl₂. In all the extradants, the proportion of extractability of metals was higher in the contaminated soils than the non-contaminated soils. Regardless of soils and extradants, relative extractability was higher for Cd as compared to other three metals. The use of 1 M HCl may be recommended for first-level screening of soil contamination with heavy metals. The other four weak extradants are believed to provide a better assessment of bioavailable/mobile metals content in soils than 1 M HCl extradant. However, 0.1 M HCl mobilized all four metals irrespective of soil types, therefore, might be the best choice if only one extradant is to be used. The sequential extraction procedures showed 22 to 64% of total Cd was in the mobile fraction (sum of Fl to F3), while the corresponding values for Cu, Pb and Zn in this fractions were 2 to 23% suggesting higher mobility of Cd than other three metals. The single extraction procedures are simple and easy to perform and obtained results are comparable with sequential extraction procedure.     

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.