Heavy metal distribution between parent soil and pepper in an unpolluted area,Hainan Island,China

Consuming edible plants contaminated by heavy metals transferred from soil is an important pathway for human exposure to environmental contaminants. In the past several decades, heavy metal accumulation in contaminated soil has been widely studied; however, few researches investigated the background levels of metals in plants and evaluated the difference in plants grown in soils produced from different parent rocks. In this study, a systemic survey of heavy metal distribution and accumulation in the soil–pepper system was investigated in an unpolluted area, Hainan Island, China. Levels of Cu, Pb, Zn and Cd were measured in soils and pepper fruits from five representative pepper-growing areas with different soil parent rocks (i.e. basalt, granite, sedimentary rock, metamorphic rock and alluvial deposits). Average concentrations of Cu, Pb, Zn and Cd in pepper fruits were 11.52, 0.84, 8.77 and 0.05 mg/kg, respectively. The concentrations of heavy metals in soils are controlled by the parent materials and varied greatly from in different areas. Heavy metal contents in all pepper samples were lower than the Chinese maximum contaminant levels. The relationship between heavy metals in soils and biological absorption coefficient (BAC) of pepper fruits suggests that the uptake ability of pepper for soil metals depends mainly on the physiological mechanism, while in some cases, the soil types and supergene environment are also important.     

氨基膨润土对铜镍镉污染土壤的钝化修复研究

采集土壤,加入铜、镍和镉制成重金属污染土壤。以四乙烯五胺改性膨润土和膨润土原土作为修复剂,通过模拟酸雨和混合提取剂提取有效态重金属,评价膨润土和氨基膨润土对土壤中铜、镍、镉的钝化效果。结果表明:p H=3. 5的模拟酸雨对各污染土壤中重金属离子的提取率均在0. 1%以下。混合提取剂对污染土壤中有效态金属的提取能力比模拟酸雨强很多。添加膨润土原土和氨基膨润土均能钝化土壤中的铜、镍和镉,氨基膨润土上嫁接的氨基对金属有络合作用,因而比膨润土原土对铜、镍和镉具有更强的钝化能力。综合评价表明氨基膨润土是一种对铜、镍和镉污染土壤具有应用前景的钝化修复材料。     

Sequential extraction and leaching characteristics of heavy metals in abandoned tungsten mine tailings sediments

The chemical speciation of potentially toxic elements (As, Cd, Cu, Pb, and Zn) in the contaminated soils and sulfides-rich tailings sediments of an abandoned tungsten mine in Korea was evaluated by conducting modified BCR sequential extraction tests. Kinetic and static batch leaching tests were also conducted to evaluate the potential release of As and other heavy metals by acidic rain water and the leaching behaviors of these heavy metals. The major sources of the elements were As-, Zn- and Pb-bearing sulfides, Pb carbonates (i.e., cerussite), and Pb sulfates (i.e., anglesite). The biggest pollutant fraction in these soil and tailing samples consists of metals bound to the oxidizable host phase, which can be released into the environment if conditions become oxidative, and/or to residual fractions. No significant difference in total element concentrations was observed between the tailings sediments and contaminated soils. For both sample types, almost no changes occurred in the mobility of As and the other heavy metals at 7 days, but the mobility increased afterwards until the end of the tests at 30 days, regardless of the initial pH. However, the mobility was approximately 5–10 times higher at initial pH 1.0 than at initial pHs of 3.0 and 5.0. The leached amounts of all the heavy metal contents were higher from tailings sediments than from contaminated soils at pH > 3.0, but were lower at pH < 3.0 except for As. Results of this study suggest that further dissolution of heavy metals from soil and tailing samples may occur during extended rainfall, resulting in a serious threat to surface and groundwater in the mine area.     

Heavy-metal loadings related to urban contamination in the Kooloonbung Creek catchment,Port Macquarie,New South Wales

Urbanisation and industrial development lead to contamination of estuaries and streams with dispersed loadings of heavy metals and metalloids. Contributions of these elements also occur from natural sources. This study provides baseline geochemical data on the respective natural and anthropogenic inputs of Cu, Pb, Zn, Cd, As, Sb, Cr, Ni, Mn and S to estuarine, fluvial and wetland sediments, and adjacent soils, in the Kooloonbung Creek catchment that drains the Port Macquarie urban area in north coastal New South Wales. There have been anthropogenic additions of Cu, Pb, Zn and As from dispersed urban sources at Port Macquarie, but they are restricted to the local catchment and do not impact on the adjacent Hastings River estuary. The most contaminated sediments display enrichment factors up to 20 × for Cu and Pb, 9 × for Zn and 5 × for As relative to local background values. However, only one value (for Pb) exceeds National Water Quality Management Strategy interim sediment quality guideline (high) values. On the other hand, sediments and local soils are commonly strongly enriched in Cr, Ni and Mn, reflecting adjacent ultramafic and mafic rock substrate and lateritic regolith. Concentrations of Cr and Ni are commonly well above interim sediment quality guideline (high) values for sediments, but are in mineralogical forms that are not readily bioavailable. Sediment and soil quality guideline values consequently need to recognise natural enrichments and the mineralogical siting of heavy metals. Although dissolved concentrations of heavy metals in stream waters are commonly low, there is evidence for mobility of Cu, Zn, Fe and Al. Parts of the Kooloonbung Creek wetland area lie on sulfidic estuarine sediments (potential acid sulfate soils). Experimental oxidation of uncontaminated and contaminated sulfidic sediments leads to substantial dissolution of heavy metals under acid conditions, with subsequent aquatic mobility. The results warn about disturbance and oxidation of potential acid sulfate soils that have been contaminated by urban and natural heavy-metal sources.     

An experimental study of heavy metal attenuation and mobility in sandy loam soils

Column flow-through experiments reacting wastewater solutions with sandy loam soil samples were performed to study heavy metal attenuation by two soils with different physical and chemical properties. Reacted soil columns were leached with synthetic acid rain to study the mobility of attenuated heavy metals under leaching conditions. This study demonstrates that cation exchange, surface adsorption, chelation with solid organic material, and precipitation were the important attenuation mechanisms for the heavy metals (Cd, Cr, Cu, Mo, Ph, and Zn). Adsorption on soil hydrous oxide surfaces was the primary attenuation mechanism for Cd and Zn in both soils, and for Cu in a soil with low organic matter content. Wastewater solution pH is also an important factor that influences the retention of heavy metals. Cadmium, Cu, Cr, and Zn became mobile after prolonged application of spiked wastewater solution, either through saturation of soil adsorption sites or due to decreasing pH. Only Cr, Pb, and Mo, which are attenuated primarily through precipitation, show significant net retention by soil. Acid rain water removed heavy metals left in the column residual pore solution and weakly sorbed heavy metals in the soils, and has the ability to mobilize some strongly attenuated heavy metals, especially when the soil organic matter content is high. The results have important applications in predicting heavy metal mobility in contaminated soil, the disposal of acid mine drainage, and assessing the risks of landfall leachate leakage.     

Contamination and potential mobility assessment of heavy metals in urban soils of Hangzhou,China: relationship with different land uses

Concentration and distribution of heavy metals (Cd, Cu, Pb and Zn) in urban soils of Hangzhou, China, were measured based on different land uses. The contamination degree of heavy metals was assessed on the basis of pollution index (PI), integrated pollution index (IPI) and geoaccumulation index (I _geo). The 0.1 mol l⁻¹ HCl extraction procedure and gastric juice simulation test (GJST) were used to evaluate the potential mobility and environmental risk of heavy metals in urban soils. The average concentration of Cd, Cu, Pb and Zn in urban soils was measured at 1.2 (with a range of 0.7–4.6), 52.0 (7.4–177.3), 88.2 (15.0–492.1) and 206.9 (19.3–1,249.2) mg kg⁻¹, respectively. The degree of contamination increased in the order of industrial area (IA) > roadside (RS) > residential and commercial areas (RC) > public park and green areas (PG). The PIs for heavy metals indicated that there is a considerable Cd, Cu, Pb and Zn pollution, which originate from traffic and industrial activities. The IPI of these four metals ranged from 1.6 to 11.8 with a mean of 3.5, with the highest IPI in the industrial area. The assessment results of I _geo also supported that urban soil were moderately contaminated with Cd and to a lesser extent also with Cu, Pb and Zn. The IP and I _geo values reveal the pollution degree of heavy metal was the order of Cd > Pb > Zn ≈ Cu. It was shown that mobility and bioavailability of the heavy metals in urban soils increased in the order of Cd > Cu > Zn ≈ Pb. Owing to high mobility of Cd and Cu in the urban soils, further investigations are needed to understand their effect on the urban environment and human health. It is concluded that industrial activities and emissions from vehicles may be the major source of heavy metals in urban contamination. Results of this study present a rough guide about the distribution and potential environmental and health risk of heavy metals in the urban soils.     

Contamination and distribution of heavy metals in urban and suburban soils in Zhangzhou City,Fujian, China

The urban environment is of growing concern as its continued population increase in China. Due to the urbanization and industrialization, heavy metals have been continuously discharged into the soil recently, and creating the anthropogenic contamination. This study investigated heavy metals contamination in urban and suburban soils in Zhangzhou City, Fujian, China. Multivariate analysis and geographical information system technology were employed in source identification and contamination assessment of heavy metals in the city soils. The survey results indicated that the urban soils were contaminated by heavy metals, especially by Hg, Cd and Pb. The multivariate analysis demonstrated that the distribution of Cu, Zn, Cr and Ni was controlled by pedogenesis, Cd and Pb had been disturbed by industrialization in some urban locations, and Hg was mainly influenced by the hot-spring in some urban park sites. The distribution of heavy metals and soil pollution index suggested the soils of Zhangzhou City have been affected by human activities.     

Capability of vis-NIR spectroscopy and Landsat 8 spectral data to predict soil heavy metals in polluted agricultural land (Iran)

Heavy metals are toxic elements that have hazardous effect on the environment. They cause soil pollution as a result of their toxicity, potential reactivity, and mobility in soils. There are so many methods for the measurement of heavy metal concentrations in soils and aquatic systems. The traditional methods used for detecting heavy metal distribution in soil involve laboratory analysis and raster sampling. Both of them are expensive and time-consuming for large areas. Remote sensing techniques are used for obtaining the earth’s surface information, and these techniques have been used in the investigations of heavy metal distributions in preliminary analysis of soils as a rapid method. Today, near-infrared reflectance spectroscopy (NIRS) of soil characteristics has been of interest as a significant object. The present investigation is focused on the detection of heavy metals in contaminated soils by the application of reflectance spectroscopy in the spectral range of 350 to 2500 nm. This study also discusses the circumstances of the applied current methods for the detection and estimation of arsenic (As), cadmium (Cd), nickel (Ni), and lead (Pb) in contaminated agricultural soils. In the first part of laboratory spectroscopy, estimations were done using heavy metal reflectance spectroscopy and partial least square regression (PLSR) approaches, while in the second part, the heavy metal estimations were done using soil organic carbon reflectance spectroscopy through the PLSR approaches. Similar to the tasks above, estimations of As, Cd, Ni, and Pb by using Landsat 8 images were done in the forms of direct and indirect methods and the distribution of heavy metals in the study area was determined. Finally, the results obtained using direct and indirect methods were compared with the wet chemical measurements of heavy metals and organic carbon. It was found that although the direct detection of heavy metals using the images of Landsat 8 produced more accurate results than the indirect detections, the results obtained from laboratory spectroscopy corresponded more with the results from atomic adsorption spectroscopy. On the other hand, based on the fact that the soil has a complex content, the use of nonlinear methods, such as artificial neural networks in predicting soil heavy metal contents, could be regarded as a trusted method.     

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.     

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

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

Effects of humic acid on heavy metal uptake by herbaceous plants in soils simultaneously contaminated by petroleum hydrocarbons

The effects of humic acid (HA) on heavy metal uptake by herbaceous plants in soil simultaneously contaminated with heavy metals and petroleum hydrocarbons were investigated. The results showed that HA reduced readily soluble and exchangeable forms of heavy metals in the contaminated soil but increased their plant-available forms. Potential bioavailability and leachability factors became larger than 1 after adding HA to the soil, except for those of Ni, suggesting that more heavy metals could be potentially phytoavailable for plant uptake. Furthermore, HA increased the accumulation of Pb, Cu, Cd, and Ni in the shoots and roots of selected plants. The greatest increase in the accumulation of heavy metals was 264.7 % in the shoot of Festuca arundinacea, with the bioconcentration factor (BCF) increasing from 0.30 to 1.10. Humic acid also increased the BCFs of the roots of Brassica campestris for Ni and Pb. These results suggest that HA amendment could enhance plant uptake of heavy metals, while concurrently reducing heavy metal leachability and preventing subsurface contamination, even in soils simultaneously contaminated with petroleum hydrocarbons.     

Effect of the addition of gypsum- and lime-rich industrial by-products on Cd,Cu and Pb availability and leachability in metal-spiked acid soils

In situ stabilization of metals in contaminated soils by addition of industrial by-products is an attractive remediation technique. In this work, mixtures of metal-spiked (Cd, Cu and Pb) samples from the Ap horizons of two acid soils and solid samples of 4 industrial by-products (red gypsum, phosphogypsum, sugar foam and dolomitic residue) were incubated in order to assess the efficiency of the by-products for the in situ remediation of contaminated soils. Single (DTPA extraction and TCLP test) and sequential chemical extraction procedures were used to examine the availability and potential mobility of the metals retained as a result of the treatments. Both the sugar foam and dolomitic residue reduced the availability and mobility of Cd, Cu and to a lesser extent, Pb. On the other hand, red gypsum and phosphogypsum proved effective in immobilizing Pb and, to a lesser extent, Cu. However, both gypsum-like by-products were not so effective in reducing Cd availability and mobility.     

Source and remediation for heavy metals of soils at an iron mine of Ulsan City,Korea

Ulsan mine produced the iron ore minerals of magnetite, arsenopyrite, and scheelite in 1992, and serpentine was developed from 1977 to 2002. The soils of the mine were contaminated by heavy metals such as As, Zn, Ni, and Cd. Heavy metals of Ni and Zn came mostly from serpentinite, and As was derived mainly from arsenopyrite in the scan-type iron ore body. As, Zn, and Ni were major contaminants, but Cd was a minor contaminant on a basis of Korean standard. The heavy metals in the deep depth (>?5 m) came from the host rocks, and those in the shallow depth (<?5 m) were derived from the organic–mineral complexation soil. The remediation plan was a soil washing for highly contaminated soils and the containment of clay materials for less contaminated soils. Even though the remediation methods were successful, the continuous monitoring and the analysis of monitoring data are still necessary for the conservation of soil and groundwater around the study area.     

土壤修复过程中重金属形态的研究综述

重金属污染土壤的修复是现阶段污染土壤治理中的难点之一,在土壤修复过程中对重金属的形态研究已在多个领域中开展,并且在重金属形态及其与生物有效性和毒性等研究领域取得了一定的成果。本文综述了现阶段在污染土壤修复过程中对重金属形态研究的主要领域,分析研究重金属形态的必要性,总结出土壤修复过程中重金属形态方面应当从重金属在土壤与植物中的存在形态入手,研究重金属元素在不同界面间的迁移转化规律,通过阻断重金属元素在污染源、土壤、生物之间的传递链条,以阻止重金属对生物体造成危害,从而为土壤重金属污染的治理修复提供理论基础。     

Soil and groundwater pollution of an urban catchment by trace metals: case study of the Addis Ababa region, central Ethiopia

Analysis of the total heavy metal (Cr, Cd, Pb, As, Cu, Ni, Zn, Co) concentration was performed on 33 soil samples taken from different profiles and soil types in a highly urbanized and industrial sector of Addis Ababa, central Ethiopia. They were analyzed using aqua regia extraction coupled with a four-stage sequential extraction (SE) procedure. The objectives of the analysis were to investigate the degree of soil heavy metal contamination, its binding forms, mobility and the implications for the groundwater resource. The results show a relatively high content of the analyzed trace metals in the soil attributed to anthropogenic and geogenic sources. Although most of the trace metals are found in the upper few centimeters of the residual soils, because of churning processes within the black cotton soils, vertical distribution of the trace metals is complex. According to the heavy metal SE analysis, the major heavy metal contribution is from the residual followed by the hydroxide phases. Groundwater heavy metal contamination is present with more than 90 and 50% of the analyzed groundwater samples exceeding WHO guidelines for Cr and Cd, respectively. Since the degree of soil heavy metal contamination has apparently not surpassed the soil’s buffering capacity, it appears that the transport path of these toxic metals to the groundwater is through fractures, joints, and related preferential flow paths.     

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.     

An assessment of the utilization of waste resources for the immobilization of Pb and Cu in the soil from a Korean military shooting range

Military shooting range soils contaminated by heavy metals have been subjected to remediation efforts to alleviate the detrimental effects of exposure on humans and the surrounding environment. Waste materials can be used as cost-effective soil amendments to immobilize heavy metals in contaminated soils. In this study, naturally occurring lime-based waste materials including egg shells, oyster shells, and mussel shells were assessed for their effectiveness toward heavy metal immobilization in military shooting range soil in Korea. Soil was treated in batch leaching experiments with 0, 2.5, 5, 10, and 15% of each lime-based waste material. The results showed that the lime-based waste materials effectively reduced water-soluble Pb at an application rate of 2.5% by weight of the soil. Increase in soil pH from 6.6 to 8.0 was considered to be the main chemistry of Pb immobilization, which was supported by the formation of insoluble Pb species at high pH values as confirmed by the visual MINTEQ thermodynamic model. In contrary, water-soluble Cu was increased in the lime-based waste material-treated soils when compared to the untreated soil. This was likely attributed to the formation of soluble Cu?CDOC (dissolved organic carbon) complexes as all lime-based waste materials applied increased DOC contents in the soil. Therefore, care must be taken in selecting the appropriate amendment for immobilizing metals in shooting range soils.     

Heavy-metal contaminated soils associated with drained fenland in Lancashire,England, UK,revealed by BGS Soil Geochemical Survey.

Areas showing anomalously high levels of heavy metals (eg. Cu, Pb, Sn, Zn) in both peri-urban and rural soils in parts of western Lancashire (UK) were indentified during a regional geochemical survey. The sites were identified as areas of former peat fenland that had been filled in with a variety of domestic and industrial wastes including furnace slag, as well as inert rubble. The very high levels of heavy metals present in the soil raises concerns about possible translocation into food crops, as this is an important market gardening area. There is no direct evidence of a health risk, and the high-pH soils will limit metal mobility and bioavailability, but these soils are worthy of further multidisciplinary scientific investigation.     

Geo-environmental study of heavy metals of the agricultural highway soils,NW Jordan

This study investigated the status and distribution patterns of selected heavy metals in roadside soils along Irbid-North Shooneh Highway, Jordan. This highway has experienced a growing number of vehicles that are likely to influence the levels of heavy metals in the surrounding agricultural lands. The average concentrations of Cr, Co, Cd, Cu, Pb, Zn, and Ni were 16.0, 36.0, 11.0, 4.0, 79.0, 122.0, and 60.0 mg/kg, respectively. Cd, Pb, and Co showed average levels that are higher than the average world soil background values. Elevated levels of heavy metals were measured in surface soil layer which decreased with depth, and with distance from the roadway. The contamination factor (CF), pollution load index (PLI), single ecological risk (Ei), potential ecological risk index (PERI), and geo-accumulation index (Igeo) generally indicated that the roadside soils are contaminated with Cd, Pb, and Ni. Heavy metals in soils are of geogenic and anthropogenic origins. Weathering of parent rocks in Wadi Al-Arab catchment is the primary natural source, whereas agrochemicals, vehicle exhausts, degradation of surface wear and paint of vehicles, vehicle wear debris of tire, and brake lining are the main anthropogenic sources of heavy metals.     

Effect of red mud on the mobility of heavy metals in mining-contaminated soils

The mobility of Cu2+, Zn2+, Ni2+, and Cd2+ in soils treated with red mud was experimentally studied to explore the feasibility of remediation of smelter-contaminated soils. Red mud samples were collected with the Bayer process (BRM) and confederate process (CRM) in the Aluminous Plant of Guizhou Province. Two farmed soil samples were collected from the Niujiaotang mining area, Guizhou Province, Southwest China. One sample was weakly polluted by fly ash; and the other was polluted severely by waste water from the smelter. For evaluating the potential of remediation, the concentrations of free metal ions and the distributions of metals in the soil were determined. The concentrations of free metal ions were measured by using the Donnan Membrane Technique, and the contributions of soil sorbents to the heavy metals adsorptions were calculated with Equilibrium Calculation of Speciation and Transport (ECOSAT). BRM reduced the concentrations of free metal ions in two kinds of soils, while CRM only favored the decrease of the concentrations of free metal ions in seriously contaminated soils. The experimental data also showed a tendency that the concentrations of free metal ions decreased proportionally with the amount of added red mud, which resulted from the increasing adsorption of heavy metal ions in the form of metal ion hydroxides.