Chemical fractionation of heavy metals in urban soils of Guangzhou, China

Knowledge of the total concentration of heavy metals is not enough to fully assess the environmental impact of urban soils. For this reason, the determination of metal speciation is important to evaluate their environment and the mobilization capacity. Sequential extraction technique proposed by the former European Community Bureau of Reference (BCR) was used to speciate Cd, Cu, Fe, Mn, Ni, Pb, and Zn in urban soils from Guangzhou into four operationally defined fractions: HOAc extractable, reducible, oxidizable, and residual. The Cu, Fe, Ni, and Zn were predominately located in the residual fraction, Pb in the reducible fraction, and Cd and Mn within the HOAc extractable fraction. The order of Cd in each fraction was generally HOAc extractable > reducible > residual > oxidizable; Cu and Fe were residual > reducible > oxidizable > HOAc extractable; Mn was HOAc extractable > residual > reducible > oxidizable; Ni and Zn were residual > reducible > HOAc extractable > oxidizable; and Pb was reducible > residual > oxidizable > HOAc extractable. Cadmium was identified as being the most mobile of the elements, followed by Mn, Zn, Ni, Cu, Pb and Fe. Iron–Mn oxides can play an important role in binding Cd, Cu, Ni, Pb, and Zn and in decreasing their proportion associated with the residual fraction in the soils. With total concentrations of Cd, Cu, Ni, Pb, Zn, and Mn increase, these metals more easily release and may produce more negative effects on the urban environment.     

土壤中重金属形态的化学分析综述

土壤中重金属的赋存形态决定其在土壤中的迁移性、生物可利用性以及毒性.土壤中重金属形态的化学分析法是依据不同浸取能力的提取剂分别提取出与土壤颗粒有着不同结合力的化学形态并测定其浓度而建立起来的.文章对土壤重金属形态分析中选用的提取试剂以及分析流程进行了综述,比较了各种试剂和方法的优缺点.同时对形态分析的土壤样品的前处理方式进行了简要概述.     

Total concentrations and speciation of heavy metals in soils of the Shenyang Zhangshi Irrigation Area, China

The Shenyang Zhangshi Irrigation Area (SZIA) was used for the spreading of municipal and industrial waste water, which is an economic way of irrigating crops, recycling nutrients and water treatment. Long-term irrigation resulted in a severe metal contamination of soils. To identify the soil phases implicated in retaining the metals, sequential extractions were performed. The most predominant metal was cadmium which was mainly associated with mobile, easily soluble and easily reducible fractions. Copper was mainly associated with the residual, EDTA extractable and moderately reducible fractions. Lead was bound to organic matter and poorly crystalline Fe-oxides. Nickel and zinc were mainly associated with the residual and strongly reducible fractions. Although copper, lead, nickel and zinc concentrations were of minor importance mobile metal concentrations of these metals as well as of cadmium exceeded German trigger values for plant production and plant growth.     

Concentrations of heavy metals in urban soils of Talcahuano (Chile): a preliminary study

Concentrations of Cd, Cr, Ni, Pb, and Zn in the top-(0–10 cm) and sub-surface (10–20 cm) soils of the Talcahuano urban area were measured. The main soil properties (organic matter, CaCO₃, pH, particle sizes) were determined for a network of representative sampling sites. The mean Cr, Ni, Pb, and Zn contents in the urban topsoil samples from Talcahuano (37.8, 22.6, 35.2, 333 mg kg⁻¹, respectively) were compared with mean concentrations for other cities around the world. The results revealed higher concentrations of heavy metals in topsoil samples than in sub-surface samples. The samples from IS1, IS2, and IS3, located in the Talcahuano industrial park, had higher Cr, Ni, Pb, and Zn contents than did samples from the other sites. This was probably due to local pollution by industrial (metallurgical) dust, although other diffuse pollution throughout the entire port region (shipyards, metallurgy, the dismantling of old ships), and contributions from the wind from adjacent industrial, storage, and vessel areas clearly played a role. Heavy metals were lowest in the sample taken on school grounds (SG).     

重庆市菜地土壤和蔬菜中Hg、Pb的污染特征及相关性分析

通过对重庆市菜地土壤和蔬菜 Hg、Pb的含量分析 ,发现土壤 Hg含量远远大于背景值 ,并且土壤 Hg的含量与菜地周围的环境密切相关 ;土壤 Pb的含量同背景值相差不大。Hg、Pb在土壤和蔬菜中的污染特征表现为主城区 >近郊区 >远郊区 ;并且不同蔬菜品种中 Hg、Pb的含量差异较大 ,在不同蔬菜种类表现为叶菜类 >果菜类 >根菜类。相关性分析表明同一菜地土壤和蔬菜中 Hg、Pb含量无相关性 ;不同菜地土壤和蔬菜 Hg、Pb含量不具有相关性。     

北京市通州污灌区土壤环境质量监测和蔬菜重金属污染状况研究

通过对北京市通州污灌区土壤现状调查与蔬菜重金属污染监测,结合土壤环境质量标准、食品卫生标准及污灌区污染历史,分析对比该区土壤和蔬菜重金属污染状况及其变化。结果表明,本次监测通州污灌区土壤中重金属平均含量均达到土壤环境质量标准(GB15618-1995)中二级标准限量。对照土壤中的重金属Cu、Pb、Cr、Cd和As均达到土壤一级标准。凉水河两岸和通惠北干渠中重金属含量均高于对照土壤,说明污灌区污水灌溉已使土壤受到一定程度的污染。与二十世纪70年代末监测结果相比,土壤中多数重金属含量处于上升趋势。污灌区蔬菜重金属含量监测结果表明,其含量水平均达到食品卫生标准,说明污灌区蔬菜尚未受到严重污染。     

Competitive Retention of Lead and Cadmium on an Agricultural Soil

Lead and cadmium contamination of an agricultural soil has been studied using batch and column experiments. Thermodynamics of theretention phenomena may be represented by a Langmuir isotherm foran aqueous metal concentration up to 100 mg L^-1. First order kinetics with respect to the solid phase yield good predictabilityfor both batch and column experiments. Kinetics and thermodynamics of lead retention predominate over those ofcadmium. As a consequence, lead is preferentially retainedand can even displace sorbed cadmium. In the event of anspill involving both metals, cadmium would move further inthe soil and its aqueous concentration downstream could beeven higher than that of the influent solution, increasingpotential risks. A two-region model has been used to fit all the experimental results. Satisfactory predictions for column experiments are obtained with parameters which are consistent with those obtained for the batch experiments, for which sorption is described by a Langmuir isotherm including competitive retention.     

Changes in Soil Properties of Abandoned Shrimp Ponds in Southern Thailand

Chemical soil properties between active shrimp ponds andabandoned ones on the Bangkok soil series were compared,at Ranote District, Songkhla Province in southern Thailand.Soil samples were collected at depth intervals of 0–10, 10–20, 20–30, 30–40 and 40–50 cm from pond bottoms at the same ponds used in a former study conducted in 1994, fora total of 6 ponds with 3 sampling sites for each pond. Theseponds were active during the previous study in 1994, abandonedin 1996 and investigated by this study in 1999. All the samples were analyzed for exchangeable Ca, Mg, K and Na electrical conductivity (EC), organic matter, S, P and pH, and statistically compared with the analytical results of theprevious study. An increase in amounts of Ca, Mg, K, Na and EC in the abandoned ponds as compared with the active ones by1.3–3.4, 1.4–2.1, 7.0–30.0, 1.2–6.3 and 1.3–10.9 timesrespectively was observed. That more of these elements weregained than lost each time the seawater was introduced intothe ponds, is explained by the Element Input/Output Consideration as proposed herein. Furthermore, a decreasein organic matter, S and P was also observed in the abandonedpond soils, and attributed to the absence of shrimp food and shrimp excreta following the cessation of shrimp raising activities. An unexpected decline in the soil pH of the abandoned ponds was found as well. Aerobic decomposition of organic matter during the absence of shrimp raising activitiescaused by soil microorganisms triggering SO₂ and H₂SO₄ formation probably played a more significantrole than the increase in the amounts of the basic elements (Ca, Mg, K, and Na) eventually reducing soil pH in the abandoned ponds. The significant depletion of the amounts of organic matter in the abandoned pond soils also supports this observation.     

Monitoring of total and bioavailable heavy metals concentration in agricultural soils

The aim of this paper is to evaluate total and bioavailable concentration of heavy metals in agricultural soils in order to estimate their distribution, to identify the possible correlations among toxic elements and the pollution sources, to distinguish the samples in relation to sampling site or to sampling depth, and to evaluate the available fraction providing information about the risky for plants. In particular, we reinvestigated total concentrations of As, Be, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, V, and Zn and available concentrations of As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, and Zn in soil from Apulia (Southern Italy). Analytical results showed that total concentrations, for all soils, are in the range permitted by regulations in force in Italy, but some soils evidence slight enrichment of Cd, Cr, Cu, Pb, and Zn. All the heavy metals in the available fraction were below the detection limits of the analytical techniques used except Cu, Ni, Pb, and Zn.     

Fractionation and Sequential Extraction of Heavy Metals in the Soil of Scrapyard of Discarded Vehicles

Chemical and physical size fractionation of heavy metals were carried out on 20 soil samples from the scrap yard area. Tessier method was used in sequential extraction. Cadmium showed the highest levels among the other elements studied in the exchangeable fraction (about 33%), while other elements showed low levels in this fraction (≥1%). Lead and manganese were mostly found in the Fe–Mn oxide fraction, zinc and iron were mostly in residual fraction, while copper was mostly found in the organic fraction of the soil. Soil samples were size-fractionated into four sizes: 1000–500, 500–125, 125–53, and less than 53 μm. The highest levels of Fe, Cu, Pb, Mn, and Cd were found in the medium fraction (500–125 μm), while zinc showed its highest levels in the fine fraction (125–53 μm). The order of heavy metal load in the size fractions was found to be medium > fine > coarse > silt for Fe, Mn, Cu, Pb, and Cd, where it was found as fine > medium > coarse > silt for zinc.     

Speciative distribution and bioavailability of metals in agricultural soils receiving industrial wastewater

In order to assess the metal pollution status of agricultural lands of Mandi Bahauuddin receiving industrial wastewater, 35 top soil samples were investigated for the determination of selected metal levels, i.e., Fe, Cu, Cd, Cr, Ca, Ni, and Pb by flame atomic absorption spectroscopy under optimum analytical conditions. The distribution of these metals in different operationally defined chemical fractions was also determined by using the sequential extraction technique. The highest mean total concentration was found for Fe while the least one was observed for Pb. All the studied metals were found to be present at levels much enhanced than national and international standards. Moreover, most of the metals were distributed principally in residual fraction with the exception of Ni which was found to be associated mainly with oxidizable fraction. The significant correlations were observed between Fe-Mn oxide-bound and residual fractions and exchangeable and oxidizable fractions for most of the metals. The highest mobility was exhibited by Ni that evidenced its enhanced bioavailability in the soil. The multivariate statistical analyses in terms of principal component analysis (PCA) and cluster analysis (CA) revealed multiple sources for various geochemical fractions of different metals. CA also revealed that the nonresidual fractions of most of the metals were very closely associated while PCA presented a distinctive behavior of Ca in the soil. It was therefore suggested that in order to avoid the metal contamination arising from industrial wastewater, appropriate remediation strategies must be adopted.     

重金属在贾鲁河表层沉积物中的污染特征及来源分析

采用原子吸收分光光度法、原子荧光法和电感耦合等离子体发射光谱法测定了贾鲁河表层沉积物中6种重金属的含量,用灼烧法测定贾鲁河表层沉积物中有机质含量。运用地累积指数法对贾鲁河流域表层沉积物中重金属污染状况进行评价,并且通过主成分分析法研究贾鲁河重金属污染来源。结果表明：贾鲁河表层沉积物中As、Cu、Ni、Zn的含量比2004年淮河表层沉积物中相应重金属含量明显偏高。重金属污染程度为：As〉Cu〉Zn〉Pb〉Ni〉Cr。通过主成分分析进一步对重金属来源的确定,发现前2个主成分的贡献率分别为58．85％和19．74％,污染来源主要有两类,分别是工农业、生活排污的点源污染,自然变化对沉积物的影响,岩石风化与侵蚀过程和有机质降解矿化的内源污染。     

Transversal immission patterns and leachability of heavy metals in road side soils

Today there is consensus concerning the road traffic's role as a metal source. However, there are so far only a few studies which focus on the road side immission patterns regarding distance from roads, and especially in combination with the leachability of heavy metals down the soil profile. In this study, the aim was to analyse concentrations of traffic related metals in road side soils, at different depths and distances from roads, both to analyse the immission patterns as well as to explain the importance of the road construction design of the road side terrain. The BCR sequential extraction procedure was performed to be able to address the environmental risk in terms of metal mobility. Approximately 80 soil samples were analysed for seven metals; antimony (Sb), cadmium (Cd), copper (Cu), chromium (Cr), lead (Pb), nickel (Ni) and zinc (Zn). The results showed that, depending on metal, the total metal concentrations in road side soils have increased 3-16 times compared to regional background during the last decades. Each metal had a limited dispersal distance from the roads as well as down in the soil profile and the road construction significantly affected the metal immission distance. Elevated metal concentrations were mostly found for top soils and down to 10 cm in the soil profiles. The labile fractions counted for more than 40% of the total concentrations for Cd, Cu, Ni, Pb and Zn, indicating a potential mobilization of the metals if the road side soils become disturbed. The present soil metal concentration levels are not alarming, but metals with a high accumulation rate might gradually be an upcoming problem if nothing is done to their emission sources.     

Spatial distribution and transport of heavy metals in soil, ponded-surface water and grass in a pb-contaminated watershed as related to land-use practices

The aim of this study was to investigate the spatial distribution of heavy metal in soil and evaluate the dissolution of metal from soil to ponded-surface water, leaching through soil profiles and metal uptake in grass as related to different land-use practices. The data provided a scientific basis for best-management practices for land use in Khli Ti watershed. The watershed has a Pb-contamination problem from the previous operation of a Pb-ore concentrator and abandoned Zn–Pb mine. Sampling sites were selected from a land-use map, with land-use types falling into the following four categories: forest, agricultural land, residential area and road. Soil, ponded-surface water, grass samples and soil profiles were collected. The study related soil characteristics from different land-use practices and locations with observed metal concentrations in ponded-surface water and soil. High enrichment factors of Pb and As in soil were found. Partitioning coefficient, K_d values were in the order: Cr > Pb > Ni > Cu > Cd > Zn. Soil disturbance from land-use activities including tillage and traffic increased leaching of trace metal from soils. Pb in soil was significantly taken up by grass even though the Transfer Factor, TF values were rather low. Agricultural activities in the watershed must be limited. Moreover, land encroachments in the upper and middle part of the watershed which have high potential of Pb must be strictly controlled in order to reduce the Pb contamination from non-point sources.     

洪泽湖溧河洼水生植物体内重金属调查

对洪泽湖溧河洼区域的水生植物进行了Cu、Zn、Pb、Cr和Cd等重金属元素的污染调查与监测分析,结果表明:水生植物对重金属元素的吸收与积累反映了环境中的重金属污染水平,不同水生植物对各种重金属元素的吸收富集状况具有相对一致性,即Zn>Cu>Cr>Pb>Cd。水生植物对各种重金属元素的平均富集系数大小顺序为:Cd>Cu>Zn>Cr>Pb,这与各元素迁移性强弱的顺序也是相一致的,Cd、Cu、Zn等各元素较易为植物所吸收,而Pb的移动性较差。大部分水生植物根部的重金属含量比茎叶部分高。研究表明:可以从中筛选出具有高富集作用的植物,作为修复水体或土壤重金属污染的实验植物,为植物修复作用的研究提供参考。     

Determination and speciation of heavy metals in sediments of the Juru River,Penang, Malaysia

The Juru River flows through largely urbanized areas and is grossly polluted by domestic wastes and discharges from pig farms. Other than carrying highly polluting organic materials, these wastes are also contaminated with heavy metals. To ascertain the extent of heavy metal pollution in the river, total and non-residual concentrations of Cu, Pb, Zn, Mn and Fe in sediment samples collected along the river were determined. The results indicate that both the total and non-residual metal concentrations in sediments can successfully be used to identify heavy metal pollution sources. The speciation of Zn, Mn and Fe in the sediment samples were investigated using a sequential leaching technique which identifies the elements among six operationally defined host fractions: (1) exchangeable, (2) carbonate and surface-associated, (3) easily reducible, (4) moderately reducible, (5) bound to organic matter and sulphides and (6) residual. The results indicate that Zn is mainly associated with the reducible fractions. Zn and Fe found in the moderately reducible fraction are significantly correlated, indicating that iron oxides is the preferred host phase by Zn.     

Accelerated fractionation of heavy metals in contaminated soils and sediments using rotating coiled columns

A new approach to performing an accelerated sequential extraction of trace elements from solid samples has been proposed. It has been shown that rotating coiled columns (RCC) earlier used in counter-current chromatography can be successfully applied to the dynamic leaching of heavy metals from soils and sediments. A solid sample was retained in the rotating column as the stationary phase under the action of centrifugal forces while different eluents (aqueous solutions of complexing reagents, mineral salts and acids) were continuously pumped through. The procedure developed is time saving and requires only 4-5 h instead of the several days needed for traditional sequential extraction (TSE), complete automation being possible. Losses of solid sample are minimal. In most cases the recoveries of readily bioavailable and leachable forms of Pb, Zn, and Cd are higher, if a dynamic extraction in RCC is used. Since naturally occurring processes are always dynamic, continuous extraction in RCC may help to estimate the contents of leachable forms and their potential risk for the environment more correctly than batch TSE. The Kersten-Foerstner and McLaren-Crawford leaching schemes have been compared, the former has been found to be preferable.     

The occurrence of heavy metals in irrigated and non-irrigated arable soils,NW Albania

The study analysed the content of heavy metals in surface soil and sediment samples from the Bregu i Matit Plain in NW Albania in relation to irrigation in order to evaluate the soil pollution and the potential risk to human health. Evaluation of soil pollution was performed using the enrichment factor and geo-accumulation index. Contents of cadmium, chromium and nickel of irrigated soils were significantly higher than those of non-irrigated soil, while contents of lead (in three of the irrigated locations), zinc and arsenic (in one of the irrigated locations) were significantly lower. Correlation analysis (CA) and principal component analysis (PCA) indicated that the primary source of the first three metals was irrigation, and the last three metals were originated from other anthropic sources, like the use of chemicals, etc. Enrichment factor (E _f) calculation showed that irrigated soils were most enriched in cadmium, chromium, copper and nickel. Index of geo-accumulation (I _geo) revealed that arable soils of Bregu i Matit are unpolluted to moderately polluted with cadmium, chromium, copper and zinc and moderately to strongly polluted with nickel and arsenic. The presence of heavy metals in the studied soils indicates a potential risk of transfer of these elements in the food chain. Therefore, further studies on the speciation of heavy metals in the studied soils in order to evaluate their mobility are needed.     

Natural concentrations and reference values of heavy metals in sedimentary soils in the Brazilian Amazon

The soils of the Brazilian Amazon exhibit large geochemical diversity reflecting the different soil formation processes in an area covering 49% of the Brazilian territory. Soil contamination by heavy metals is one of the threats to the sustainability of this Biome but establishing quality reference values (QRVs) for the region is a challenging owing to the immense territorial area of the Amazon. This study aimed to determine the natural background of heavy metals in soils from the southwestern Brazilian Amazon in order to propose QRVs for Ba, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Sb, and Zn for alluvial sedimentary soils. One hundred and twenty-eight soil samples were collected at a depth of 0.0–0.2 m in sites with minimal anthropogenic interference. Soil sample digestion was based on the EPA 3051A method and metal concentrations were determined by ICP-OES. QRVs calculated for the southwestern Brazilian Amazon are among the lowest recorded in Brazil (mg kg^?1): Ba (16.5), Cd (0.1), Cr (6.9), Cu (2.8), Fe (15.4), Mn (13.4), Ni (1.7), Pb (4.4), Sb (0.9), and Zn (5.7). The low metal concentration is likely a result of the sedimentary origin of the soils. The results of this study can serve as a basis for defining public policies to investigate the environmental impacts resulting from changes in land use in areas of the Brazilian Amazon.     

Comparison between availability of heavy metals in dry and wetland tailing of an abandoned copper tailing pond

Wetland sediments are generally considered as a sink for metals and, in the anoxic zone, may contain very high concentrations of heavy metals in reduced state. A comprehensive study was carried out to compare the differences of total, environmentally available (Env-Av), HOAC, EDTA and DTPA available heavy metal fraction in tailing of the marshy area of a copper tailing pond and the dry tailing. The average concentrations of all the seven metals in the wetland tailing were found higher than dry tailing. Regarding pH, organic carbon, availailable N, P and K also found higher in marshy wetland tailing compare to the dry tailing. This information is needed in order to understand wetland system and to assure that wetlands do not themselves eventually become sources of metal contamination to surrounding areas. But as levels of pollutants increases, the ability of a wetland system to incorporate waste can be impaired and the wetland can become a source of toxicity.