Speciation and potential remobilization of heavy metals in sediments of the Taihu Lake, China

The species of Cu, Pb, Zn, Cd and Cr in sediments of the Taihu Lake, China, have been analyzed using the sequential chemical extraction method. Variations in the chemical fractions of these metals and their geographic distributions have also been studied. For all five metals, the residual fraction is highest but the exchangeable fraction is lowest among all the fractions. Compared to other metals, Cd has the highest percentage in the exchangeable fraction, and Cr is associated mainly with the residual fraction. Cu in the organic fraction and Pb in the Fe-Mn fraction are the important species, whereas the lowest percentages are found for Cd in the organic fraction, Cu in the Fe-Mn oxide fraction and Pb in the carbonate fraction. With respect to spatial differences, the total contents in the non-residual fractions of the metals in bay sediments are found to be higher than those in other sediments. The fractions of Cd, Cu and Cr showed significant variations in different regions. The fractions of Pb and Zn, however, did not show significant variations in spatial distribution, suggesting different amounts and different paths of anthropogenic input for the metals. Comparisons of the metal speciation indicated that Cd might be the most bioavailable metal, followed by Pb.     

Quantitative spatial characteristics and environmental risk of toxic heavy metals in urban dusts of Shanghai,China

Associated with the rapid urbanization and industrialization, most of the urban parks and recreational areas in Shanghai are built close to major roads or industrial areas, where they are subject to many potential pollution source, including automobile exhaust and factory emissions. Urban dusts, containing many toxic heavy metals such as Pb, Cr, Cd, Hg and As, are one of main contributors for environmental pollution. In this study, 261 dust samples were collected from two different localities (streets and parks) in the urban area of Shanghai, China. Pb and Cr concentrations of all samples were determined by atomic adsorption spectrophotometer analyzer, and Cd, As and Hg concentrations in 74 samples by atomic fluorescence spectroscopy. The mean concentrations of Pb, Cr, Cd, As and Hg are 287, 157, 1.24, 8.73 and 0.16 mg kg⁻¹, respectively. Each heavy metal shows a wide range of concentration values. In comparison with heavy metal background values of soil in Shanghai, urban dusts have elevated metal concentrations as a whole, except those of As. The concentrations of Pb, Cr, Cd, As and Hg are 11.3, 2.1, 10.3, 0.997, 1.7 times of the soil background values, respectively. Compared with the global mean concentrations, Cr concentration in urban dusts is slightly higher. Pb, Cr and Hg show normal distribution after logarithmic transformation. Pb, Cr, Cd, As and Hg have second-order variation trends of the spatial distribution. The spatial distribution features of five toxic heavy metals, in general, illustrate relatively high levels within the regions of the inner-city ring highway and southwestern Shanghai. Cr and Cd are higher in Baoshan industrial park and the shipbuilding industries regions. The order of environmental risk is Pb > Cd > Cr > Hg > As. Pb and Cd have the highest risk for environment pollution and human health among the five metals. The pollutant sources of toxic heavy metals in Shanghai urban dusts are preliminarily concluded as follows: As may have mainly a natural source. Burning of coal has become the main source of Hg pollution. Pb, Cr and Cd have three sources, traffic, building construction, and weathering corrosion of building materials.     

Speciation and mobility of heavy metals in mud in coastal reclamation areas in Shenzhen,China

Coastal reclamation has been carried out along the coastal areas near Shenzhen, China in a large scale since 1980s by dumping fill materials over the marine mud at the sea bottom. Usually the area to be reclaimed is drained first and some of the mud is air-dried for a few weeks before it is buried by fill. After reclamation, the terrestrial groundwater, which is relatively acidic and with high dissolved oxygen, gradually displaces the seawater, which is alkaline with high salinity. The changes in the burial conditions of mud and the properties of the pore water in the mud may induce the release of some heavy metals into the mud. Field survey confirms that the pH and salinity of the groundwater in the reclamation site are much lower than the seawater. Chemical analyses of mud and groundwater samples collected from the reclamation sites reclaimed in different years indicate that most of the heavy metals in the mud decrease gradually with time, but the heavy metals in the groundwater are increased. The release of heavy metals into pore water due to reactivation of heavy metals in the mud is of environmental concern. To understand why some of the heavy metals can be released from the mud more easily than others, a sequential extraction method was used to study the operationally determined chemical forms of five heavy metals (Cu, Ni, Pb, Zn, and Cd) in the mud samples. Heavy metals can be presented in five chemical forms: exchangeable, carbonate, Fe–Mn oxide, organic, and residual. Ni and Pb were mainly associated with the Fe–Mn oxide fraction and carbonate fraction; Zn was mainly associated with organic fraction and Fe–Mn oxide fraction, while Cu and Cd were associated with organic fraction and carbonate fraction, respectively. If the residual fraction can be considered as an inert phase of the metal that cannot be mobilized, it is the other four forms of heavy metal that cause the noticeable changes in the concentration of heavy metals in the mud. On the basis of the speciation of heavy metals, the mobility of metals have the following order: Pb (36.63%) > Cu (31.11%) > Zn (20.49%) > Ni (18.37%) > Cd (13.46%). The measured metal mobility fits reasonably well with the degree of concentration reduction of the metals with time of burial observed in the reclamation site.     

长沙、株洲、湘潭三市土壤中重金属元素的来源

为追踪长沙、株洲、湘潭3个城市表层土壤中Cd、As、Pb等重金属元素的来源,分析了土壤、基岩、大气干湿沉降、水、悬浮物等介质之间重金属元素的质量平衡和土壤自身重金属元素含量随时间变化的特点。结果显示,除As外,区内基岩中的重金属元素含量低于克拉克值;残积物中Cd相对基岩贫化,As、Pb、Cu、Hg等重金属元素相对基岩的富集小于3倍;大气干湿沉降重金属元素相对土壤富集了数倍至数十倍;湘江水体主要向沿江潮土提供As、Cd物源:近50年内土壤重金属元素有较高的增加速率。不同介质间重金属元素的质量变化特点支持长沙、株洲、湘潭三市土壤重金属元素富集的主要物源为大气沉降,地表水及悬浮物是沿江湖土重金属元素的主要物源,基岩对土壤提供的物源有限的结论。     

Assessment of heavy metals contamination in soils of Dexing region, Jiangxi Province, China

Heavy metal contamination has attracted huge concern due to its toxicity, abundance and persistence in the environment, and subsequent accumulation in soil, sediment and water. Mining is one of the most important sources of heavy metals in the environment. Mining-milling operations and disposal of tailings （the finely ground remains of milled ores） in addition to smelting and metal refining provide significant sources of pollution. Mining and mineral processing in the Dexing region of China have been carried out for over forty years and have contaminated the soils with heavy metals, Many studies were conducted to assess and establish the extent of heavy metal contamination in the soils due to mining. The aim of this work was to assess the environmental impact of mining on soils in the Dexing region and to identify the main factors involved in heavy metals dispersion. A 4800 km^2 study area was assessed with respect to its heavy metals on the basis of the current guideline values. In order to assess the extent of heavy metals contamination resulting from past mining activities in the Dexing region, 919 soil samples were collected and analyzed for As, Hg, Cd, Cr, Zn, Cu and Pb, Heavy metals levels were determined using inductively couple plasma-atomic emission spectrometry and X-ray fluorescence spectrometry. Results of soil samples reported concentrations between 1.790-899 mg/kg for As, 0.034-4.980 mg/kg for Hg, 0.043-8.330 mg/kg for Cd, 10-666 mg/kg for Cr, 25-18500 mg/kg for Zn, 6-1825 mg/kg for Cu, and 16-1312 mg/kg for Pb, respectively. The maximum values of As, Hg, Cd, Cr, Zn, Cu and Pb concentration in soils were up to 60, 33, 41, 7, 185, 52 and 37 times higher than the tolerable level, respectively. Meanwhile, the single-factor pollution index and Nemerow pollution index were used to assess the environment quality of heavy metals contamination.     

基于形态学分析铅锌矿不同功能区土壤重金属元素的分布特征及污染评价

为掌握尤溪铅锌矿区土壤重金属元素分布特征和污染现状,通过采集尤溪铅锌矿不同功能区0~20cm表层土壤样品,测定土壤中Pb、Zn、Cd、Cu、Cr 5种重金属元素的总量及其化学形态,分析不同功能区土壤重金属污染及分布特征,同时采用次生相与原生相比值法(RSP)进行污染评价。结果表明,尤溪铅锌矿不同功能区土壤中Pb、Zn、Cd含量均超过国家土壤环境质量三级标准,废弃冶炼区土壤Cd、Cu、Pb、Zn含量均最高,分别为标准值的14.78、1.13、3.73、1.34倍,采矿区Cr含量最高,但未超过标准限值。重金属形态结果表明,相比其他元素,Cd弱酸提取态所占比例最高,Cu可交换态比例最高,Pb、Zn、Cr以残渣态为主。RSP法评价表明,不同重金属的污染程度表现为:Cu(1.15)Cd(0.80)Pb(0.59)Zn(0.57)Cr(0.54);不同功能区土壤重金属污染表现为:尾矿库区冶炼区废弃冶炼区采矿区。SPEF法评价表明,尤溪铅锌矿区受人为污染明显,采矿区和尾矿库区Zn污染最为严重,冶炼区和废弃冶炼区Pb污染最为严重,功能区污染顺序为:尾矿库区冶炼区废弃冶炼区采矿区。     

Distribution and sequential extraction of some heavy metals in urban soils of Guiyang City,China

Sixty-two soil samples collected from different functional zones of Guiyang were analyzed for total concentrations and sequential extraction of Cr, Cu, Pb, Zn and Cd by ICP spectrometry. The average total concentrations ofCr, Cu, Pb, Zn and Cd in the soils of Guiyang were 92.9, 51.6, 44.1,139.3 and 0.28 mg/kg, respectively. The soils have been polluted by Cr, Cu, Pb, Zn and Cd to some extent in comparison with the background values of Guiyang. Significant differences were recognized in the concentrations of Cr, Cu, Pb, Zn and Cd in different functional zones. As for the sequential extraction, Cr, Cu and Zn were present mainly in the residual fraction, and Pb was present mainly in the oxidizable fraction. The reducible fraction of Cd accounts for 47.5%, and the residual fraction is lowest. The mobility and bioavailability of heavy metals follow the order of Cd〉Pb〉Cu〉Cr〉Zn.     

Spatial distribution,mineralogy, and weathering of heavy metals in soils along zinc-concentrate ground transportation routes: implication for assessing heavy metal sources

We investigated the source of heavy metals in soils at a site in South Korea, where a ground transportation of zinc-concentrates (ZnS, sphalerite) occurs daily. Seventy soil samples were collected at the site and analyzed for residual concentrations of heavy metals, as well as their chemical and mineralogical properties. Enrichment factor was calculated based on local geochemical background level of metals in soils and confirmed the contamination of soils in the area by an anthropogenic source. The concentration data were also subjected to a Pearson correlation analysis to determine the possible influences of anthropogenic sources and identify the primary source. A slight negative correlation between heavy metals and Al, and a weak correlation between heavy metals and Fe implied that the heavy metals originated from anthropogenic inputs rather than a geogenic source. A strong positive linear correlation between Zn and other heavy metals (i.e., As, Cd, Cu, Pb, r ≥ 0.96, p ≤ 0.001) suggested the influence of a single anthropogenic source of zinc-concentrates containing all of these heavy metals. Zinc-concentrate oxidation and leaching experiments, which mimicked physical and chemical weathering in the environment, indicated that zinc-concentrate could be transformed to zinc oxides and release Cd and Pb upon precipitation. The findings in this study provide an insight into the fate of the Zn that the original form of zinc-concentrate would not remain in the soil after long-term weathering, which should be considered when source of heavy metals is identified.     

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.     

沈阳市新城子区土壤重金属元素的空间变异性

利用地质统计学方法,系统地研究了沈阳市新城子区土壤重金属元素的空间分布及空间变异性特征。研究结果显示,土壤中Cd和Pb的含量明显高于全国平均值和辽宁省土壤背景值。变异函数分析结果表明,Hg具有明显的空间自相关性,Cd、Pb和As均具有中等空间自相关的特征。Cd和Pb含量较高,并呈显著的正相关,主要受灌溉、施肥等外在因素的影响。重金属元素空间变异性的研究对当地土壤环境评价和土地质量评估具有一定的指示和引导作用。     

Spatial distribution of heavy metals in soils: a case study of Changxing,China

Six hundred and sixty-five soil samples were taken from Changxing County in Zhejiang Province, China, to characterize the spatial variability of Hg Cd, Pb, Cu, As and Cr. The geostatistics and geographic information system (GIS) techniques were applied, and the ordinary kriging and lognormal kriging were used to map the spatial patterns of the six heavy metals. Hg, Pb, Cu and As were fitted to the spherical model with a range of 85.75, 82.32, 86.10, and 23.17 km, respectively. Cr was fitted to the exponential model with a range of 6.27 km, and Cd was fitted to the linear model with a range of 37.66 km. Both Pb and Cu had strong spatial dependence due to the effects of natural factors including parent material, topography and soil type. Hg, Cd, Cr and As had, however, moderate spatial dependence, indicating an involvement of human factors. Meanwhile, based on the comparison between the original data and the guide values of the six metals, the disjunctive kriging technique was used to quantify their pollution risks. The results showed that only Cd and Hg exhibited pollution risks in the study area. The pollution source evaluated was closely corresponded with the real discharge of industrial production and the application of organomercury pesticides. The results of this study provide insight into risk assessment of environmental pollution and decision making for agricultural production and industrial adjustment of building materials.     

Evaluation of ecological risk and source of heavy metals in vegetable-growing soils in Fujian province,China

Heavy metal pollution in vegetable-growing soils is of increasing concern due to the potential health risk via food chain. The present study aimed at assessing the potential ecological risk (RI) of heavy metals (HMs) in the vegetable-growing soils collected from Fujian Province, China, and identifying the potential sources with multivariable methods including correlation matrix and principal component analysis (PCA). The concentrations of HMs including Pb, Cd, Hg, Cr, As, Cu, Zn, and Ni in 160 soils collected from 25 sites of vegetable-growing land in Fujian Province, China, are measured with inductively coupled plasma mass spectrometry and hydrogen generation-atomic fluorescence spectrometer, respectively. Results show that most of the soil samples have been seriously contaminated with HMs, especially the metals of Hg, Cd, and Pb, compared with both of the background values of soils in Fujian Province and the limitation of total HMs in soil environmental quality for edible agricultural products set in China (HJ 332-2006). The indexes of RI indicate that only 8% of the 25 sites are environmentally safe, whereas according to the present study 28% of the sampling sites are heavily contaminated with HMs with 628–1,076 of the RI values. Based on PCA analysis, Zn, Cd, and Pb associated with PC1 are found to derive from anthropogenic sources, especially the local industrial activities, such as porcelain plants in Dehua, zinc metallurgical plants in Nan’an, and sewage irrigation from industrial estate in Taijiang. The concentrations of As, Ni, and Cu loaded in PC2 are found to be mainly controlled by natural factors (i.e., the lithogenic process of natural parent soils). Hg in PC3 is also found to originate from the anthropogenic sources, such as local coal combustion in Longhai and industrial activities in Cangshan. However, Cr in PC3 is mainly derived from the lithogenic sources.     

Bioavailability of heavy metals in urban particles

Urban particles, as one of the toxic air pollutants, are important issues concerning air quality and public health, especially in large cities like Guangzhou （China）. Toxicological studies implicated heavy metals （particularly water-soluble metals） as a health hazard of particles. Once absorbed into human lung tissues, heavy metals are likely released from the particles and do harm to human body even in low concentrations. Thus, evaluating the bioavailability of heavy metals in urban particles is quite necessary. The particle samples used in this study were collected from a building roof in Guangzhou. Three different methods, sequential extraction procedure and two leaching tests, were employed to investigate the bioavailability of heavy metals in the particles. The sequential extraction scheme is specific for analyzing the chemical speciation of metals in particles, which consists of four fractions： F1： soluble and exchangeable metals; F2： carbonates, oxides and reducible metals; F3： bound to organic matter, oxidisable and sulphidic metals; and F4： residual metals. Leaching tests, GB 5086.2-1997 and TCLP, are standard methods developed by China-EPA and US-EPA and widely used in evaluating the toxicity of solid wastes. They were applied to gain additional information about more easily mobilized form of metal. Heavy metals in extraction solution, including Cu, Zn, Pb, Cd, Cr, and Ni, were analyzed by ICP-MS. According to the data from the total concentration analysis, the relative contents of 6 heavy metals in particles follow the order of Pb〉Zn〉Cu〉Cr〉Ni〉Cd. The results of sequential extraction showed that more than 50% of Cu, Zn and Cd were distributed in the F1, F2, and F3. This indicated that the bioavailability of Cu, Zn and Cd in the particles is much higher than that of Pb, Cr, and Ni. Leaching tests revealed that the concentrations of heavy metals in leachate are relatively lower than the regulatory level. The results of TCLP are much higher than those of GB 5086.2-1997, mainly due to the low pH value of the extraction fluid.     

雄安新区土壤重金属和砷元素空间分布特征及源解析

研究雄安地区土壤重金属和砷元素空间分布特征及其来源,对于支撑新区土地资源和环境管理具有重要意义。基于雄安新区土壤环境调查,运用地统计学方法和ArcGIS 技术分析模拟了土壤中As、Hg、Cd、Cu、Pb、Zn、Ni、Cr等8种元素空间分布特征,综合运用空间分析、多元统计学方法和正定因子矩阵模型解析这些元素的主要来源。结果表明：（1）区内土壤质量总体良好,4.35 %的土壤样品Cd和Cu含量超过农用地土壤污染风险筛选值,但均低于农用地土壤污染风险管控值;与河北省背景值相比,Cd、Cu、Pb、Zn和Hg存在不同程度中度和显著富集。（2）As、Cd、Cu、Pb、Zn、Ni、Cr含量呈现出由北部向南部逐渐增高的趋势,高值区主要分布在新区西南部;Hg元素分布分散,高值区主要分布在城镇及工业企业周边。（3）不同土地利用类型土壤剖面重金属和砷元素垂向分布受pH值、有机碳和铁铝氧化物等理化性质影响显著。（4）研究区土壤重金属和砷元素富集受人类活动影响明显,人为来源贡献率达67.12 %,Hg元素主要来源于人为排放的大气沉降富集,As元素富集受到废渣堆放和利用的影响,Cd、Cu、Pb和Zn元素富集受工业生产、污水灌溉以及尾气排放等活动影响。研究成果可为雄安新区合理制定土地资源开发利用和生态保护措施提供技术支撑。     

都柳江上游沿岸喀斯特地区土壤重金属污染特征及风险评价

采集都柳江上游沿岸喀斯特地区62个土壤样品,利用地累积指数法、潜在生态风险指数法、克里金插值方法综合研究Sb、Cd、As、Cr和Pb五种重金属元素累积污染特征和潜在生态风险。结果表明,研究区土壤中Sb和Cd元素平均含量分别超过贵州省土壤环境背景值4.085倍和1.876倍。空间分布上,Sb元素严重污染面积占研究区总面积37.87%,主要受区内赋矿层位望城坡组、尧梭组和鸡窝寨组的影响。而Cd元素轻度累积污染面积为59.76%,其与碳酸盐岩分布密切相关。研究区土壤重金属污染潜在生态风险属于低风险等级,但是Cd和Sb元素单项污染潜在生态风险概率较大,Cd污染最高概率风险地层主要是石牛栏组和邦寨组,而Sb污染最高概率风险地层为邦寨组、鸡窝寨组和独山组。因此,研究区应重点防控石牛栏组、邦寨组、鸡窝寨组和独山组土壤Cd与Sb污染的潜在生态风险。      

Selenium and heavy metals content in some Mediterranean soils

The study of metal contents in industrial, agricultural or/and polluted soils compared with natural or unpolluted soils is currently necessary to obtain reference values and to assess soil contamination. Nonetheless, very few works published appear in international journals on elements like Se, Li and Sr in Spanish soils. This study determines the total levels of Se, Li, Sr, As, Cd, Co, Cr, Cu, Ni, Pb, V, Zn, Fe, Mn and Ba in 14 natural (unpolluted) soils (Gypsisols, Leptosols, Arenosols and Acrisols), 14 agricultural soils (Anthrosols, Fluvisols and Luvisols), and 4 industrial–urban affected-surface soil horizons (Anthrosols and Fluvisols) of Eastern Spain. The geochemical baseline concentrations (GBC) and reference values (RV) have been established, and the relationships among elements and also between soil properties and elemental concentrations have been analysed. The RV obtained in this study were (mg kg⁻¹): Se 2.68, Li 115, Sr 298, Cd 0.97, Co 35, Cr 217, Cu 46, Ni 50, Pb 137, V 120, Zn 246, Fe 124,472, Mn 2691, and Ba 743. The RV for Se and Li were used as a preliminary approach to assess soil contamination in Spanish soils. The results confirm human impact on Sr, As, Cd, Cr, Cu, Ni, Pb and Zn soil concentrations, but evidence no deviation from natural Se, Li, Co, V, Fe, Mn and Ba concentrations. The results obtained from the statistical analysis reveal significant correlations between some elements and clay and soil organic matter (SOM) contents, indicating that metal concentrations are controlled by soil composition. One particularly interesting finding is the high correlation coefficients obtained between SOM and Se, Cd, Cr, V, Fe, and Mn, and between clay and Cd, Zn, V, Fe and Mn. Once again, these facts confirm the role of SOM and clay minerals in soil functions and that soil is an ecosystem element responsible for maintaining environmental quality.     

湖南株洲市土壤重金属分布特征及污染评价

对株洲市土壤重金属Cu、Pb、Zn、Cd、Cr、Hg、As污染现状进行了调查与评价。结果表明:①株洲市60个样品中Cd已达到重度污染程度,污染严重;Cu、Hg、As处于中度污染;Pb、Zn、Cr属于轻度污染。内梅罗综合污染指数也已达重污染。②不同土地利用类型土壤中各重金属含量由高到低变化如下:Cu、Zn、Cr为水田→菜地→旱地;Pb、Hg、As为旱地→水田→菜地;Cd为菜地→旱地→水田。③不同土壤类型中各重金属含量由高到低变化如下:Zn、Cd、As为潮土→粘土→红壤;Pb、Hg为粘土→潮土→红壤;Cr为红壤→潮土→粘土;Cu为潮土→红壤→粘土。     

Risk assessment of heavy metals in topsoil along the banks of theYangtze River in Huangshi,China

High concentrations of heavy metal in farmland threatens food production and human health. Our study assesses soil quality and the distribution of Cd, Cr, Cu, Zn, Pb and Ni, to identify possible sources of heavy metals along the banks of the Yangtze River in Huangshi. Heavy metal concentrations of 22 topsoil samples were measured using the inductively coupled plasma mass spectrometry instrument and data was analyzed by multivariate statistic approaches. Heavy metal contamination risk assessment was performed using a combination of the Nemerow multi-factor index method, the Hakanson potential ecological risk index method and the Muller index of geo-accumulation method. These methods determined similar results indicating that cadmium (Cd) poses a health risk to residents at the study site while Cr, Cu, Zn, Pb and Ni do not. The Nemerow multi-factor index method demonstrated that 18 samples were heavily polluted, three moderately polluted and one lightly polluted. The Muller index of geo-accumulation method found ten samples were moderately to strongly polluted by Cd, five were moderately polluted, six were lightly to moderately polluted and one was lightly polluted. The Hakanson potential ecological risk index method proved six samples were strongly polluted, seven were moderately polluted and nine were lightly polluted. Since our sampling sites were all in agricultural lands, we recommend the potential ecological risk index method as the most effective given it not only considers the range of pollutants contributing to soil pollution but factors in heavy metals toxicity. We are apt that the source of the high concentrations of Cd found in topsoil is derived from alluvial sediments upstream of the Yangtze River with a high percentage of residual speciation and a low percentage of exchangeable speciation distribution of Cd. This in turns indicates that a high concentration of Cd in soil had little impact on the natural environment. However, 31.9% of the iron-manganese oxides bound speciation indicating that such levels of Cd in soil would be potentially hazardous to the crops, particularly if exposed to a reductive condition.     

Spatial variability of heavy metals in soils across a valley plain in Southeastern China

An investigation was carried out to survey the magnitude and spatial distribution of heavy metals, as well as their relation with soil series, in a valley plain in Southeastern China. Soil was sampled at 159 sites by combining a squared grid and nested sampling strategies along the transect perpendicular to the Qujiang River in Zhejiang Province, China. Total concentrations of six metals, namely Cu, Fe, Mn, Ni, Pb and Zn, were measured. Classical statistics and geostatistics were used to quantify their spatial characteristics. There was a considerable variation in many of these parameters. The total concentrations ranged from 6.8 to 29.3 mg kg⁻¹ for Cu, 6,784 to 18,678 mg kg⁻¹ for Fe, 94 to 385 mg kg⁻¹ for Mn, 6.1 to 20.3 mg kg⁻¹ for Ni, 25.0 to 49.5 mg kg⁻¹ for Pb, and 12 to 160 mg kg⁻¹ for Zn. Pearson correlation coefficients among total metal concentrations and selected soil properties showed a number of strong associations. By virtue of analysis of variance, a predominant influence of soil series on the spatial variability of metal concentrations was observed. All metals were spatially correlated. The semivariograms of Cu, Fe, Mn, Ni and Zn were dominated by short range correlation (600 or 700 m), and that of Pb by long range (1200 m). Block kriging maps of total metal concentrations and soil properties showed strip distributions, perpendicular to the river, in the manner similar to the soil series. Principal component analysis was run to identify common distribution patterns of heavy metals and soil properties. These results illustrate that soil series information of valley plain may be useful for developing management zones for site-specific agriculture.     

太湖MS岩芯重金属元素地球化学形态研究

采用BCR三步提取法对太湖MS岩芯沉积物中Cu、Fe、Mn、Ni、Pb和Zn等6种重金属元素的化学形态进行了研究.结果表明,有效结合态的Cu、Ni和Pb主要以有机物及硫化物结合态、Fe-Mn氧化物结合态存在,Fe和Zn主要以Fe-Mn氧化物结合态存在,Mn主要以可交换态及碳酸盐结合态存在;Fe-Mn氧化物结合态的Ni、Pb和Zn与可还原态的Mn有较好的正相关关系,有机物及硫化物结合态的Cu、Mn、Ni、Pb和Zn与有机碳含量有较好的正相关关系;重金属形态分布体现了重金属元素地球化学性质的差异,以及重金属形态含量与沉积物理化性质的关系.沉积岩芯重金属元素形态垂向变化规律及次生相富集系数表明,Cu、Mn、Ni、Pb和Zn在沉积岩芯13～4 cm有效结合态含量较稳定,为自然沉积;4～0 cm有效结合态含量明显升高,存在一定程度的人为污染.根据137Cs测年结果判断,沉积岩芯Cu、Mn、Ni、Pb和Zn等重金属污染开始于20世纪70年代末期,主要污染元素及污染历史与太湖流域污染工业类型及经济发展阶段相吻合.