Recycling of complexometric extractants to remediate a soil contaminated with heavy metals

Equilibrations were performed with complexing reagent(s) to mobilise Cd, Cu, Mn, Ni, Pb and Zn from a contaminated urban soil. The metal-laden aqueous extract was treated with zero-valent magnesium (Mg0) or bimetallic mixture (Pd0/Mg0 or Ag0/Mg0) to precipitate the heavy metals from solution while liberating the chelating reagent(s). Post precipitation, the pH of aqueous supernatant fraction was readjusted to approximately 5 and the solution was re-combined with the soil particulates to extract more heavy metal pollutants. A sparing quantity of EDTA (10 mmoles) mobilised 32-54% of the 5 mmoles of heavy-metals from the soil with three cycles but only 0.1% of the iron was removed. Three successive extractions with a mixture of complexing reagents (3 mmoles), 1:1 EDTA plus HEDC [bis-(2-hydroxyethyl)-dithiocarbamate], mobilised approximately 49% of the Pb, approximately 18% of the Zn and approximately 19% of the Mn burden but only 7% of the Cu, and 1% of the Fe from this soil. An appreciable fraction of the mobilised Pb and Cu and a portion of the Zn was cemented to the surfaces of the excess magnesium whereas virtually all of the Fe and Mn was removed from solution as insoluble hydroxides.     

湖南省某冶炼厂周边农田土壤重金属污染及生态风险评价

利用野外采样与实验室分析相结合的方法,以湖南省某冶炼厂周边农田土壤(0~20 cm)为研究对象,监测了Cd、As、Pb、Cr、Cu、Zn、Hg等7种重金属的含量,并对重金属污染程度与潜在生态风险进行了评价。结果表明,7种重金属都存在不同程度的超标或污染,其中Cd、As、Pb等的污染较为严重。统计学分析结果表明,Pb、As、Hg、Zn、Cd等来源相同,可能主要都来自于人为污染,即冶炼作业造成的污染。7种重金属化学形态不尽相同:在重金属有效态中,Cd的水溶态和可提取态较高;Pb、Cu、Zn可还原态、可氧化态这两部分含量较高。而Hg、As、Cr的残渣态含量较高。风险评价代码评价结果表明,Cd的生态风险较高,4.5%的样点Cd为极高生态风险,52.8%的样点Cd为高生态风险,42.7%的样点Cd为中度生态风险;100%的样点Zn为中度生态风险;Cu有60.1%的样点属于低生态风险,39.9%的样点属于中度生态风险;As、Pb主要以低生态风险为主(所占比例分别为77.2%、80%);Hg主要以无生态风险为主(所占94.3%)。Hakanson潜在生态风险指数法计算的综合潜在生态风险指数(RI)的范围为46.4~1 627.5,表明研究区域农田土壤存在很高的生态风险。上述各项结果综合表明,研究区农田土壤受到了严重的重金属污染,由此引起的重金属生态风险应引起高度关注。     

Competitive sorption of Cd, Cu, Mn, Ni, Pb and Zn in polluted and unpolluted calcareous soils

The objectives of this study were to investigate competitive sorption behaviour of heavy metals (Cd, Cu, Mn, Ni, Pb and Zn) under different management practices and identify soil characteristics that can be correlated with the retention and mobility of heavy metals using 65 calcareous soil samples. The lowest sorption was found for Mn and Ni in competition with the other metals, indicating the high mobility of these two cations. The Freundlich equation adequately described heavy metals adsorption. On the basis of Freundlich distribution coefficient, the selectivity sequence of the metal adsorption was Cu?>?Pb?>?Cd?>?Zn?>?Ni?>?Mn. The mean value of the joint distribution coefficient (K _dΣsp) was 182.1, 364.1, 414.7, 250.1, 277.7, 459.9 and 344.8 l kg^?1 for garden, garlic, pasture, potato, vegetables, wheat and polluted soils, respectively. The lowest observed K _dΣsp in garden soil samples was due to the lower cation exchange capacity and lower carbonate content. The results of the geochemical modelling under low and high metal addition indicated that Cd, Ni, Mn and Zn were mainly retained via adsorption, while Pb and Cu were retained via adsorption and precipitation. Stepwise forward regression analysis showed that clay, organic matter and CaCO₃ were the most important soil properties influencing competitive adsorption of Cd, Mn, Ni and Zn. The results in this study point to a relatively easy way to estimate distribution coefficient values.     

Heavy metal binding fractions in the sediments of the Godavari estuary,East Coast of India

Sequential chemical extraction was used to study the operationally determined chemical forms of five heavy metals (Pb, Cu, Zn, Co and Ni) and their spatial distribution in the sediments. The binding behaviour of heavy metals associating with Fe–Mn oxides showed a good correlation towards Cu, Zn and Co, but moderate linear dependence with Ni and Pb. Among the five metals, correlation between Fe–Mn oxide bound Cu and Fe–Mn oxides (r = 0.95) is highest. The coefficient of determination (r ²) in organically bound heavy metals versus organic matter (OM) ranges from 0.772 to 0.952, which indicates a good linear dependence. The OM fraction in the sediments is more accessible to heavy metals and is the major ligand available for complexation. In particular, Zn and Cu are preferentially bound to OM. In general, Zn co-precipitation with carbonates is the dominant chemical form when Fe–Mn oxide and OM are less abundant. In this study, however, carbonates were less abundant, hence Zn bound to carbonates was less pronounced. Based on the results, even if the excessive binding sites are contained in the sediments, competition of various complexation reactions between sediment phases and heavy metals could dominate metal association.     

Determination of total and EDTA extractable metal distributions in the colloidal fraction of contaminated soils using SdFFF-ICP-HRMS

Newly developed methods involving an on-line combination of sedimentation field-flow fractionation-inductively coupled plasma-high resolution mass spectrometry (SdFFF-ICP-HRMS) have been used to study the distributions of extractable heavy metals in a soil which had been treated with sewage sludge contaminated with Cu or Pb. The relationship of these metals with other elements in the colloidal fraction was also investigated. The colloidal fraction from the soil was obtained by repeated gravitational sedimentation and extracted with 0.11 M acetic acid, 0.1 M hydroxylamine hydrochloride, 0.05 M ethylenediaminetetraacetic acid disodium salt (EDTA) or aqua regia to assess the potential availability of the metals Cu and Pb. Large proportions of the Cu and Pb were extracted by EDTA, approaching that removed by aqua regia, whereas < 10% of the aqua regia extractable metals were removed by acetic acid and hydroxylamine chloride. The distributions of the heavy metals, the major mineral forming element (Al) and the elements forming sesquioxides (Fe and Mn) within different size classes (0.05-1 microm) of the colloidal fraction were measured using SdFFF-ICP-HRMS before and after extraction with EDTA. This information provides an insight into the composition of the colloids and the distributions of metal contaminants. In the contaminated soil colloids, the concentration of Fe, Mn and Pb is greatest in the smaller particles (<0.2 microm). In contrast, the Cu concentration is constant over the size range studied. Iron oxide surface coatings probably play a significant role in Pb adsorption on soil particles, but may be less important for Cu. The combination of selective chemical extraction, SdFFF and ICP-HRMS provides a means of determining the distribution of potentially available heavy metals within the colloidal fraction of contaminated soils.     

Heavy Metals Monitoring using Bivalves from Mediterranean Sea and Red Sea

The concentrations of heavy metals (Cd, Co, Cu, Fe, Mn, Ni, Pd and Zn) were measured in the Bivalves (Modiolus auriculatus and Donax trunculus) collected from the Egyptian coasts of Mediterranean Sea and Brachiodonates sp. from the Egyptian coasts of Red Sea. The average concentrations of the heavy metals analyzed exhibited the following decreasing order: Fe > Zn > Cu > Mn > Ni > Co > Pb > Cd for both Mediterranean Sea and Red Sea. The analyses of Cd, Co, Ni, Pb, and Zn showed higher average concentrations for samples collected from Red Sea than that collected from Mediterranean Sea, while Fe, Cu and Mn showed the reverse results. Fe was used as a normalizing agent for all studied metals and exhibited presence of two locations from each of Mediterranean Sea and Red Sea have anthropogenic inputs of heavy metals. These results suggest that the coastal area in both Mediterranean Sea and Red Sea of Egypt might be considered relatively unpolluted with heavy metal.     

Total concentrations, fractionation and mobility of heavy metals in soils of urban area of Guwahati, India

This work describes the results of assessment of the heavy metals, Cd, Co, Cr, Cu, Mn, Ni, Pb, and Zn in urban soil of Guwahati City, India from 31 sites of five different land use types covering residential, commercial, industrial, public utilities, and roadside. Sequential extraction procedure was used to evaluate the relative distribution of the eight metals in exchangeable, carbonate, reducible (Fe?CMn oxide), organic and sulfide, and residual fractions. Of the eight metals, Cd and Co occur in lower concentrations (Cd <?< Co) in all types of land, and concentration variation from one type of land use to another is not much significant for both the metals. Ni presence is more than Co, and the concentrations show some variation depending on land use status. Average Cr and Cu concentrations are ??100?mg/kg, but Cr has a significantly higher presence in industrial land use. The results are similar in case of Pb. The two metals, Mn and Zn have domination over the other metals, and the values are ??300?mg/kg. Industrial and roadside soil contains much more Mn, while commercial soil is most enriched with Zn. Of the metals, Ni has the largest proportion (~42%) bound to the exchangeable fraction and Co, Cr, and Pb also have appreciable proportion bound to the same fraction. A significant amount of Co is associated with carbonates. The reducible fraction has bound considerable quantity of Mn and Zn, while most of Cu is associated with the organic and sulfide fraction. Both Cd and Pb are dominantly associated with the residual fraction. Computation of the mobility factor of the metals indicates Mn to be the most mobile metal present in the soil samples.     

Assessment of background levels of trace metals in water and soil from a remote region of Himalaya

Selected trace metals were estimated by atomic absorption spectrometry in the water and soil samples collected from the remote region of Himalaya. The soil samples were analysed for soluble and acid extractable fraction of trace metals. In water samples, Ca, Na, Mg and K emerged as dominant contributors, whereas, Ca, Na, K, Mg, Fe and Pb were estimated at comparatively higher levels in the water extract of the soil. In case of acid extract of the soil samples, Ca, K, Fe, Mg, Mn and Na were found at elevated concentrations. Based on mean levels of the metals, following decreasing concentration order was observed in water samples: Ca > Na > Mg > K > Pb > Co > Cu > Zn > Mn > Cr > Fe > Cd > Li, however, in the acid extract of the soil, following order was noted: Ca > K > Fe > Mg > Mn > Na > Pb > Zn > Cr > Li > Cu > Co > Cd. The correlation study revealed appreciably diverse mutual relationships of trace metals in the water and soil samples. The multivariate cluster analyses exhibited divergent apportionment of trace metals in water and soil samples. Among the trace metals, Cd, Pb, Li, Zn, Cr, Cu, Mn and Co exhibited extreme to significant anthropogenic enrichment in the soil samples, while the rest of the metals were mostly contributed by the natural processes.     

Determination of selected heavy metals in air samples from the northern part of Jordan

In this work, the atmospheric concentrations of selected heavy metals including lead (Pb), iron (Fe), cadmium (Cd), copper (Cu), nickel (Ni), manganese (Mn), and zinc (Zn) were measured for two different sampling sites (urban and rural) in the northern part of Jordan (Irbid city). Samples were collected according to a certain schedule for 1 year. High volume air samplers and glass fiber filters were used to collect the samples. Collected samples were digested using a mixture of analytical grade nitric acid and analytical grade hydrochloric acid, and analyzed to evaluate the levels of heavy metals by atomic absorption spectrophotometry. Six heavy metals (Pb, Fe, Cu, Ni, Mn, and Zn) were measured in all samples; the concentrations of Cd and Co were not detected in Irbid atmosphere by atomic absorption spectroscopy. The results were used to determine the levels of heavy metal pollutants in air, possible sources, and to compare the levels of selected heavy metals in the two studied sites. Aerosols from the rural site have lower concentrations for all the metals compared to those from the urban site. The daily and monthly variations of the elements were investigated. All heavy metals in urban and rural sites reached maximum concentrations in June, July, and August. This is consistent with the increased activities leading to particulate matter emission during the summer period. The enrichment factors with respect to earth crust and correlation coefficients of heavy metals were investigated to predict the possible sources of heavy metals in air.     

Effects of soil amendments on the bioavailability of heavy metals from zinc mine tailings

A study was conducted to test the effects of soil amendments on the bioavailability of heavy metals in a zinc mine tailings containing soil to plants, using the Indian mustard plant (Brassica juncea) as a test organism. Zinc mine tailing containing soil was amended with humus soil (HS) and phosphatic clay (PC). The zinc mine tailing containing soil (ZMTS) was characterized for heavy metals. It was mixed with PC and HS, and four mixtures were prepared. The first mixture contained ZMTS, and served as a control. The second mixture contained ZMTS and PC in the ratio of 1:1 (w/w). The third mixture contained ZMTS and HS in the ratio of 1:1(w/w). The fourth mixture containing ZMTS, PC and HS in the ratio of (2:1:1) (w/w). A slight increase in the bioavailability of Pb, Cu, Zn and Mn was noticed with increase in the incubation time from 14 to 42 days. The bioavailability of Pb, Cu, Zn and Mn from ZMTS alone in Brassica plant was in the range of 94-99% up to 42 days. Addition of PC and HS to the ZMTS soil reduced the bioavailabilities of Pb by (15%), of Cu by (20%), of Zn by (20%) and of Mn by (25%) in the mustard plant. The data showed that PC in the presence of HS had a high affinity for the heavy metals in the order of Pb, Cu, Zn and Mn.     

Seasonal Variability of Heavy Metals in Surface Sediment of Lake Sapanca, Turkey

Lake Sapanca is exposed to heavy urbanization and industrialization because of its natural beauty and its proximity to the metropolitan İstanbul, Turkey. In this study, it was aimed to investigate seasonal changes of some heavy metals (Pb, Cr, Cu, Mn, Ni, Zn and Cd) concentration of surface sediment. Nine different stations were chosen as sampling points. Samples were taken every three months and the seasonal and annual average concentration of the elements were determined. Seasonal highest values of heavy metals were observed as follows; Cr, Cu, Mn, Ni and Zn in Summer, Cd in Autumn. There was no seasonal difference for Pb, Cr and Cd. It seems that Lake Sapanca has not been polluted yet. However, it was found that Cu and Ni concentrations in surface sediment exceed lowest effect level.     

乌鲁木齐市米东污灌区农田土壤重金属污染评价

对米东污灌区农田土壤重金属含量进行监测分析,利用不同的评价方法和标准对土壤重金属的环境质量进行评价。结果表明:米东污灌区农田土壤重金属含量分别为Cd(0.12±0.06)mg/kg,Cu(40.43±5.30)mg/kg,Zn(78.38±11.04)mg/kg,Pb(11.66±11.79)mg/kg,Ni(20.24±8.05)mg/kg,Cr(75.81±8.05)mg/kg。以国家土壤环境质量标准(二级)为标准评价,各元素的污染指数排序为Cu>Ni>Cr>Zn>Cd>Pb,综合污染指数为0.337,污染程度为安全。以食用农产品产地土壤环境质量要求为标准评价,各元素的污染指数排序为Cu>Ni>Cr>Zn>Cd>Pb,综合污染指数为0.343,污染程度为安全。表明米东污灌区农田土壤重金属含量尚能达到食用农产品产地土壤环境质量要求。Pb、Cu、Zn的平均含量超过乌鲁木齐市土壤背景值,这说明污灌区土壤重金属Pb、Cu、Zn近年来已有所累积,存在一定的污染风险。     

Vertical distribution of heavy metals in soil profile in a seasonally waterlogging agriculture field in Eastern Ganges Basin

The accumulation of heavy metals in soil and water is a serious concern due to their persistence and toxicity. This study investigated the vertical distribution of heavy metals, possible sources and their relation with soil texture in a soil profile from seasonally waterlogged agriculture fields of Eastern Ganges basin. Fifteen samples were collected at ～0.90-m interval during drilling of 13.11 mbgl and analysed for physical parameters (moisture content and grain size parameters: sand, silt, clay ratio) and heavy metals (Fe, Mn, Cr, Cu, Pb, Zn, Co, Ni and Cd). The average metal content was in the decreasing order of Fe?>?Mn?>?Cr?>?Zn?>?Ni?>?Cu?>?Co?>?Pb?>?Cd. Vertical distribution of Fe, Mn, Zn and Ni shows more or less similar trends, and clay zone records high concentration of heavy metals. The enrichment of heavy metals in clay zone with alkaline pH strongly implies that the heavy metal distributions in the study site are effectively regulated by soil texture and reductive dissolution of Fe and Mn oxy-hydroxides. Correlation coefficient analysis indicates that most of the metals correlate with Fe, Mn and soil texture (clay and silt). Soil quality assessment was carried out using geoaccumulation index (I _geo), enrichment factor (EF) and contamination factor (CF). The enrichment factor values were ranged between 0.66 (Mn) and 2.34 (Co) for the studied metals, and the contamination factor values varied between 0.79 (Mn) and 2.55 (Co). Results suggest that the elements such as Cu and Co are categorized as moderate to moderately severe contamination, which are further confirmed by I _geo values (0.69 for Cu and 0.78 for Co). The concentration of Ni exceeded the effects-range median values, and the biological adverse effect of this metal is 87 %. The average concentration of heavy metals was compared with published data such as concentration of heavy metals in Ganga River sediments, Ganga Delta sediments and upper continental crust (UCC), which apparently revealed that heavy metals such as Fe, Mn, Cr, Pb, Zn and Cd are influenced by the dynamic nature of flood plain deposits. Agricultural practice and domestic sewage are also influenced on the heavy metal content in the study area.     

Heavy metals in urban ambient PM10 and soil background in eight cities around China

The ambient PM₁₀ and background soil samples were collected and analyzed with ICP-AES in eight cities around China to investigate the levels of ten heavy metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and Pb). The mean concentrations of ten heavy metals in PM₁₀ of the eight cities of China followed the order of Zn?>?Pb?>?Mn?>?Cu?>?Ni?>?Cr?>?Co?>?V. The metals in the ambient PM₁₀ and soil were compared in each city to evaluate the heavy metal mass fraction from anthropogenic sources in ambient air. The CD values in these cities were all above 0.2, indicating that the ingredients spectrums of PM₁₀ and soil vary markedly. Most heavy metals were enriched in PM₁₀, except Fe and Ti. The results showed that almost all the cities suffer important heavy metal pollution from anthropogenic sources. The eight cities were also grouped according to their similarity in heavy metals of ambient PM₁₀ by cluster analysis to investigate the relationship between the heavy metals and the pollution sources of each city. The conclusion was that the eight cities were divided into three clusters which had similar industrial type and economy scale: the first cluster consisted of Shenzhen, Wuxi, and Guiyang; followed by Jinan and Zhengzhou as the second grouping; and the third group had Taiyuan, Urumqi, and Luoyang.     

基于Hakanson潜在生态风险指数的某垃圾填埋场土壤重金属污染评价

将Hakanson提出的潜在生态风险指数法应用于垃圾填埋场及周边土壤重金属污染评价,扩充了评价因子,确定了各重金属的毒性系数及参比值。研究结果表明,评价区土壤中Hg的潜在生态风险较重,其后依次为Cd、As、Ni、Cu、Pb、Co、Cr、Mn和Zn。对污染场地的风险评估及生态修复有一定的指导意义。     

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.     

渭河陕西段表层沉积物重金属污染特征及潜在风险

为了解渭河陕西段表层沉积物重金属的污染特征,采用ICP-MS分析了13个采样断面表层沉积物中As、Cd、Cr、Cu、Mn、Ni、Pb和Zn 8种重金属的含量,并对其来源和生态风险进行了评价。结果表明：渭河陕西段8种重金属的平均含量顺序依次为Mn > Zn > Cr > Cu > Ni > Pb > As > Cd;除Ni外的其余7种重金属的平均含量均超过陕西省A层土壤背景值。各断面表层沉积物重金属的潜在生态风险指数（RI）介于111.4~7 043.7,其中23.1%的断面有极强生态风险,46.2%的断面为中等生态风险,其余为轻微生态风险。Cd污染最为严重,对各断面的潜在生态风险介于较强生态风险与极强生态风险之间,对RI的贡献平均为85.2%;其余7种重金属在所有断面均属于轻微生态危害。渭河陕西段表层沉积物As、Cd、Cu和Zn主要为工业与农业来源;Cr和Ni主要为自然来源;Pb和Mn与城市污水和交通污染来源有关。     

太原市大气颗粒物中重金属的污染特征及来源解析

为了解太原市采暖期大气颗粒物不同粒径中重金属的污染特征及其来源,于2012年10月—2013年2月对环境空气中颗粒物采样,用原子吸收分光光度法测定样品中Fe、Pb、Cu、Ni、Cr、Cd、Mn、Zn等8种元素的含量。结果表明,太原市采暖期重金属浓度从高到低依次为FePbMnZnCrCuNiCd。重金属Pb、Mn、Zn、Ni、Cd主要富集在PM2.5中;Cr主要富集在PM10中;Cu主要富集在PM5中;Fe主要在粒径大于2.5μm的粗粒子中富集。除Zn外,其他7种元素浓度均表现为灰霾期采暖期采暖前。通过主因子分析表明,太原市大气颗粒物中重金属主要来源于冶金、有机合成工业、燃煤、汽车尾气、土壤尘等。     

水稻重金属含量与土壤质量的关系

根据“淮安市绿色食品基地调查以及相关研究”课题资料 ,分析了水稻中重金属含量与其土壤质量的关系。结果表明 ,重金属含量在水稻中的分布是 :根 >茎叶 >籽粒 ;水稻籽粒对重金属的吸收特点因其元素不同而差异较大 ,重金属元素被水稻糙米吸收的程度为 :砷 <镉 <汞 <铅 <锰 <铬 <铜 <锌 ;在糙米中检出的重金属铜和铬的含量与土壤中铜和铬的含量呈显著性相关关系 ,铅、锌、锰的含量与土壤中铅、锌、锰的含量相关关系不显著     

Speciation and assessment of heavy metals in surface sediments of Jinjiang River tidal reach, southeast of China

The concentration and speciation of heavy metals (Cr, Ni, Cu, Zn, Cd, Pb) in surface sediments (??≤ 63 μm) of Jinjiang River tidal reach are determined to evaluate the metal behavior. A modified BCR three-step sequential extraction procedure is carried out, and the residual fraction is undertaken by microwave-assisted acid digestion. The index of geo-accumulation indicates that Cd appeared highest among all these heavy metals in surface sediments, Cr, Cu, Zn lower, and Ni, Pb the least. The percentage of Zn, Cd is comparatively higher in the acid soluble fraction, Pb and Cu higher in the reductive fraction, indicating larger potential danger to the environment. So it is essential for developing the future remediation plans and pollution control strategies.