Criticality of Seven Specialty Metals

Evaluating metal criticality is a topic that addresses future metals supply and that has inspired research in corporations, academic institutions, and governments. In this article, we apply a comprehensive criticality methodology to seven specialty metals—scandium (Sc), strontium (Sr), antimony (Sb), barium (Ba), mercury (Hg), thallium (Tl), and bismuth (Bi)—at the national and global levels for 2008. The results are presented along with uncertainty estimates in a three‐dimensional “criticality space” comprised of supply risk (SR), vulnerability to supply restriction (VSR), and environmental implications (EI) axes. The SR score is the highest for antimony over the medium term (i.e., 5 to 10 years), followed very closely by bismuth and thallium; for the long term (i.e., a few decades), the highest SR is for thallium, followed very closely by antimony. Strontium and barium, followed very closely by mercury, have the lowest SR over the medium term, and mercury has the lowest SR over the long term. Mercury has the highest EI score. For VSR, thallium is the most vulnerable at both the national level (for the United States) and global level, followed by strontium at both levels. In general, specialty metals are found to possess a unique mix of sparse data, toxicity concerns (in some cases), and inadequate or nonexistent substitutes for a number of specialized uses, a situation that would seem to demand increased effort in acquiring the information needed to characterize specialty metal criticality with more rigor and transparency than is currently possible.     

Criticality of the Rare Earth Elements

Recent constraints on supplies of the rare earth elements (REEs) have led to concerns about their long‐term availability as well as the consequences that shortages would pose for modern technology. To assess this situation, we apply a comprehensive “criticality” methodology to the REE: lanthanum (La); cerium (Ce); praseodymium (Pr); neodymium (Nd); samarium (Sm); europium (Eu); gadolinium (Gd); terbium (Tb); dysprosium (Dy); holmium (Ho); erbium (Er); thulium (Tm); ytterbium (Yb); lutetium (Lu); and yttrium (Y). Assessments are made on national (U.S. and China) and global levels for the year 2008. Evaluations of each indicator are presented and the results plotted in “criticality space” on a 0 to 100 scale. Over the medium term (5 to 10 years), supply risk (SR) for all REEs is moderate with minimal variation (62.8 to 65.1). Over the long term (10 to 100 years), SR is low (42.1 to 49.2). Environmental implications scores, reflecting the economic allocation of environmental burdens, range from 4.2 for La to 34.4 for Lu. Eu, Er, and Dy have the highest vulnerability to supply restriction (VSR) at the global level (50.6, 49.2, and 47.4, respectively), whereas Sm has the lowest (15.1). This is mainly a reflection of their substitution potential. Similarly, at the national level for the United States and China, Eu and Sm have the highest and lowest VSR scores, respectively, although there are notable differences in scores among the REEs and between countries. Although China's export restrictions render REE supplies inadequate to meet demand at present, our analysis indicates a lower criticality for REEs over the longer term than for a number of other industrially used metals.     

Phytoremediation of Cd, Cr, Cu, Mn, Fe, Ni, Pb and Zn from aqueous solution using Phragmites cummunis, Typha angustifolia and Cyperus esculentus

A comparative bioaccumulation pattern and ultra structural changes were studied in Phragmites cummunis, Typha angustifolia and Cyperus esculentus in mixed metals solution of cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn). P. cummunis was observed to be a shoot accumulator for Cr, Fe, Mn, Ni, Pb, and Zn. However, T. angustifolia was found to be a root accumulator for Cd, Cr, Cu, Fe, Ni and Pb. In addition, C. esculentus also accumulated most of the tested heavy metals in the roots, while Mn and Fe were translocated up to leaves. Further, the long term metal treatment showed maximum accumulation of all heavy metals in P. cummunis followed by T. angustifolia and C. esculentus. Among heavy metals, Fe was accumulated maximum, i.e., >1000 microg g(-1) by all three plants. Simultaneously, the adverse effects on biochemical parameters were noted earlier in C. esculentus than T. angustifolia and P. cummunis. Ultra structural observation showed the cellular changes in wetland plants after longer exposure. Results revealed that P. cummunis and T. angustifolia had more potential for tested metals than C. esculentus. This study established that these wetland plants could be used for heavy metals phytoremediation from metal containing industrial wastewater.     

Risk Element (As,Cd, Cu,Pb, and Zn) Contamination of Soils and Edible Vegetables in the Vicinity of Guixi Smelter,South China

Risk element (As, Cd, Cu, Pb, and Zn) contamination in soils and in two edible vegetables (Solanum melongena L. and Capsicum annum L.) was investigated in the vicinity of Guixi Smelter, South China. Soil As concentrations averaged 23.9 mg/kg. Sites near the smelter tailings recorded the highest levels of As and heavy metals in soils. The concentration order of heavy metals in soils was Cd < Pb < Zn < Cu. Cu and Cd in soils were abundant in the exchangeable and bound to carbonate fraction, while Pb and Zn were in the residual fraction, limiting their potential toxicity as pollutants. The proportions of the metals in the mobile fraction followed the order Pb < Zn < Cu < Cd. In Solanum melongena L. and Capsicum annum L., Zn concentration was the highest, followed by Cu, Cd, and Pb, different from that in soils and in the mobile fraction. Concentrations of heavy metals in the labile fractions in soils and in vegetables presented significant correlation (p < 0.05). Both of the two vegetables are not the Cu and Zn accumulators. As for Cd and As, Capsicum annum L. poses a higher risk to animal and human health than Solanum melongena L., with soil-plant transfer coefficients more than three. Root-stem is the main barrier for most of the heavy metals and As in the two vegetables, resulting in higher metal concentrations in roots relative to other plant tissues. The low stem-fruit transfer coefficients for Zn in Solanum melongena L. and for Pb in Capsicum annum L. suggested that very few of them could reach the fruits.     

吴城鄱阳湖自然保护区鱼体重金属的富集及安全性评价

为研究吴城鄱阳湖自然保护区鱼类重金属的污染情况, 以鄱阳湖吴城6种常见淡水鱼(鲤、鳙、鲢、草鱼、青鱼、鳊)为研究对象, 分别研究鱼心脏、肝脏、鳃丝和肌肉等部位中铜、锌、铅、镉4种重金属的富集情况, 并采用目标危险系数(THQ)评价其健康风险。结果显示, 重金属元素在鱼体不同器官中的富集程度不同, Cd在肝脏中的含量最高, Cu在肝脏和心脏中的含量最高, Pb在肝脏中的富集含量最低, Zn在各器官的总体含量要高于其他3种元素。4种重金属在鱼肌肉中的含量均符合国内外标准。目标危险系数(THQ)分析结果表明, Pb导致的健康风险最高, Cd最低, 单一重金属THQ值和复合重金属TTHQ值均小于1, 说明吴城鄱阳湖自然保护区鱼类重金属的污染程度较低, 不会对消费者健康产生潜在危害。     

Fractionation,mobility and multivariate statistical evaluation of metals in marine sediments of Cape Town Harbour,South Africa

Abstract

Distribution of possible chemical forms of Al, Si, Sn, Pb, Zn, Fe, Hg, Cd and Cu in marine sediments of Cape Town harbour was investigated using a modified Tessier’s sequential extraction procedure and ICP-MS and ICP-AES for heavy metals determination. The mean fractions for all metals at all locations were: 1.5–7196 mg kg^-1 for Si, 7.79–7266 mg kg^-1 for Al, 161-639 mg kg^-1 for Cu, 19–41978 mg kg^-1 for Fe, 2.83–5864 mg kg^-1 for Zn, 1.45–13.26 mg kg^-1for Cd, 9.87–223 mg kg^-1 for Sn, 11.98-979 mg kg^-1 for Pb and 0.13–5.93 mg kg^-1 for Hg. Si, Al and Zn were mostly associated with Fe–Mn oxides, whereas Sn and Hg were mainly bound to residual and organic matter. Pb existed mainly in the residual and iron/manganese oxide phases while Cd was evenly distributed in all the five phases. The loading plots of heavy metals bound to the various chemical forms, as well as Pearson correlation coefficients, enabled the determination binding relationship. Pb, Sn and Hg exhibited similar binding behaviour which indicated an anthropogenic point source from wastes from the ship maintenance workshop, and the presence of Sn in the organic phase can be identified with the use of anti-fouling paints at the harbour, whereas Al, Fe, Si, Cu and Zn would probably be of natural origin. Lastly Cd probably came from a diffuse pollution sources in the harbour due to its unique binding characteristic. The mobility of heavy metals varied depending on location and the heavy metal type. The mobility of metals followed the order: Si > Zn > Fe > Cu> Al> Cd> Pb > Sn > Hg. The high percentage of Cd and Pb in the bioavailable forms suggested the need to keep close surveillance on these metals because of their high toxicity.     

Effects of tin and lead on organ levels of essential minerals in rabbits

The effect of tin and lead on levels of essential metals (Zn, Cu, Ca, Fe) in rabbit tissues was compared in relation to the route of administration. Animals received intraperitoneally, or per os, SnCl2 (2 mg Sn/kg) or Pb(CH3COO)2 (3.5 mg Pb/kg) every day for 5 d or for 1 mo. Copper, zinc, iron, and calcium were determined by AAS in the liver, kidneys, spleen, brain, bone marrow, and blood; lead and tin concentration were measured in the blood of animals. Tin and lead administered per os caused either no changes or the decreased concentration of endogenous metals in several tissues. The other route of administration (ip) of both metals generally contributed to the increased storage of essential elements. Blood tin levels of tin treated animals were only about less than or equal to 1/10 of blood lead concentrations of rabbits exposed to lead.     

Trace Metals (Cd,Co, Cr,Cu, Hg,Ni, Pb,and Zn) in Food Supplements of Marine Origin

We determined the concentrations of Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn in dietary supplements of marine origin. Four supplement categories were studied; algae, coral, krill, and shark cartilage. A direct mercury analyzer was used for Hg determinations while acid digestions and ICP-AES were used for Cr analysis and ICP-MS for the other trace metals. Algae are the supplements showing the highest concentrations of Pb, Cr, and Ni with respective means of 1.6 mg Pb/kg dry weight (d.w.), 3.2 Cr mg/kg d.w., and 8.0 mg Ni/kg d.w. Krill supplements have the highest levels of Cd, Cu, and Zn with 0.65 mg Cd/kg d.w., 63 mg Cu/kg d.w., and 50 mg Zn/kg d.w., respectively. Shark cartilage supplements show the highest levels of Hg and Co with mean concentrations of 160 μg Hg/kg d.w. and 73 ± 51 μg Co/kg d.w., respectively. No samples in our study exceeded the provisional tolerable daily intakes set by Health Canada, the joint committee of the World Health Organization/Food and Agricultural Organization, or the U.S. Environmental Protection Agency. Nevertheless, Ni and Pb in algae and Hg in shark cartilage may end up contributing to a very significant portion of the allowable daily intake—leaving little room for normal intake through food consumption and other exposure pathways.     

Pollution Assessment and Potential Sources of Heavy Metals in Agricultural Soils around Four Pb/Zn Mines of Shaoguan City,China

A total of 455 agricultural soil samples from four nonferrous mines/smelting sites in Shaoguan City, China, were investigated for concentrations of 10 heavy metals (As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, and Zn). The mean concentrations of the metals were 72.4, 5.16, 13.3, 54.8, 84.5, 1.52, 425, 28.2, 529, and 722 mg kg^?1, respectively. The values for As, Cd, Hg, Pb, and Zn were more than 8 and 1.5 times higher than their background values in this region and the limit values of Grade II soil quality standard in China, respectively. Estimated ecological risks based on contamination factors and potential ecological risk factors were also high or very high for As, Cd, Hg, and Pb. Multivariate analysis (Pearson's correlation analysis, hierarchical cluster analysis, and principal component analysis) strongly implied three distinct groups; i.e., As/Cu/Hg/Zn, Co/Cr/Mn/Ni, and Cd/Pb. Local anomalies for As, Cu, Hg, and Zn by a probably anthropogenic source (identified as mining activity), Co, Cr, Mn, and Ni by natural contribution, and a mixed source for Cd and Pb, were identified. This is one of the few studies with a focus on potential sources of heavy metals in agricultural topsoil around mining/smelting sites, providing evidence for establishing priorities in the reduction of ecological risks posed by heavy metals in Southern China and elsewhere.     

Accumulation of zinc, cadmium, and lead in four populations of Sedum alfredii growing on lead/zinc mine spoils

Sedum alfredii Hance is a newly reported zinc (Zn) and cadmium (Cd) hyperaccumulator native to China. In this study,four populations of S. alfredii were collected from Yejiwei (YJW), Jinchuantang (JCT) and Qiaokou (QK) lead (Pb)/Zn mines located in Hunan Province as well as Quzhou (QZ) Pb/Zn mine located in Zhejiang Province for exploring the intraspecies difference of this plant in metal accumulation. Although they grew in the Pb/Zn spoils with relatively similar levels of Zn,Cd and Pb, remarkable differences among the four populations in tissue heavy metal concentrations were observed. The shoot Zn concentration of QZ population (11 116 mg/kg) was highest and nearly five times higher than that of the JCT population (1930 mg/kg). Furthermore, the shoot Cd concentration observed in the QZ population (1 090 mg/kg) was also highest and 144 times higher than that found in the JCT population (7.5 mg/kg). As for Pb concentrations In the shoot of different populations, a fourfold difference between the highest and the lowest was also found. Such difference on metal accumulation was opulation-specific and may be significantly explained by differences in the soil properties such as pH, organic matter (OM), and electrical conductivity (EC). Taking biomass and metal concentration in plants into consideration, the QZ, YJW and QK populations may have high potential for Zn phytoremediation, the QZ population may have the highest potential in Cd phytoremediation, and the QK population may be the most useful in Pb phytoremediation.     

牛组织重金属含量与饲养环境的相关性

通过选择不同污染程度的区域进行取样,分析了贵州地区不同污染水平下牛组织中重金属(Cu、Zn、Pb、Cd)的含量和与饲养环境的相关性.结果表明:贵州不同污染水平下牛组织中的Cu、Zn基本符合国家食品卫生要求,Pb只有污染地区的肝脏和肾脏超过限量标准,Cd污染较严重,除非污染区肝脏外,牛肾脏和肝脏中Cd的平均含量均超过国家肉类制品卫生限量标准,但肌肉组织符合卫生标准;牛组织重金属元素含量与饲养环境中的土壤、饲料和饮用水源的重金属含量和污染程度密切相关,尤其是肾脏组织,其相关系数r＞0.78.饲料向牛组织的重金属迁移系数,随饲料元素含量的增加而逐渐降低,其中Cd的迁移系数最大,Pb的迁移系数最低;必需元素和有害元素在不同组织中的比值,随污染程度的增加而降低.肾脏的Cu/Cd和Zn/Cd值比其它组织低得多,Cd主要在肾脏中蓄积,Cu主要在肝脏组织蓄积,Zn主要在肌肉和肝脏,Pb主要在肾脏和肝脏.     

Metal residues in flesh of edible blue crab,Callinectes amnicola,from a tropical coastal lagoon: Health implications

Metals such as cadmium (Cd), lead (Pb), zinc (Zn), and copper (Cu) were estimated in the flesh of the edible blue crab Callinectes amnicola from selected areas of the Lagos Lagoon, Nigeria (i.e., Makoko, Iddo, Okababa, Ikoyi, and Ajah) for 18 months between March 2011 and August 2012. Estimated average daily intake (EADI) and target hazard quotient (THQ) were used to determine the risk implications for adult and child consumer populations. Range of Cd, Pb, Zn, and Cu across sites was 0.16–0.46, 1.48–3.17, 2.21–3.65, and 9.48–12.76 mg kg^?1 crab flesh wet weight, respectively. Lead concentrations in crab flesh from Makoko (3.16 ± 1.44 mg kg^?1) and Iddo (5.17 ± 1.26 mg kg^?1) exceeded the maximum accepted limits recommended by the Food and Agriculture Organization/World Health Organization for food fisheries. The EADI across sites for the adult consumer population exceeded the reference dose (RfD) recommended by the U.S. Environmental Protection Agency for most metals with magnitude of ≤7-fold while EADI of Pb among child consumer population across sites exceeded RfD by a maximum of 4.5-fold. THQs for adult population were >1 for all metals across all sites, and >1 for Pb and Cd for selected sites for the child consumer population. Findings from this study indicate higher health risks of metal toxicity to adult consumer populations, and risks of lead toxicity to child consumer populations around the Lagos Lagoon, Nigeria.     

Toxicity, accumulation, and removal of heavy metals by three aquatic macrophytes

A comprehensive understanding of the uptake, tolerance, and transport of heavy metals by plants will be essential for the development of phytoremediation technologies. In the present paper, we investigated accumulation, tissue and intracellular localization, and toxic effects of cadmium (Cd), lead (Pb), zinc (Zn), and copper (Cu) in three aquatic macrophytes (the angiosperms Lemna minor and Elodea canadensis, and the moss Leptodictyum riparium). We also tested and compared their capacity to absorb heavy metal from water under laboratory conditions. Our data showed that all the three species examined could be considered good bioaccumulators for the heavy metals tested. L. riparium was the most resistant species and the most effective in accumulating Cu, Zn, and Pb, whereas L. minor was the most effective in accumulating Cd. Cd was the most toxic metal, followed by Pb, Cu, and Zn. At the ultrastructural level, sublethal concentrations of the heavy metals tested caused induced cell plasmolysis and alterations of the chloroplast arrangement. Heavy metal removal experiments revealed that the three macrophytes showed excellent performance in removing the selected metals from the solutions in which they are maintained, thus suggesting that they could be considered good candidates for wastewaters remediation purpose.     

Copper,Lead, Cadmium,and Zinc Sorption By Waterlogged and Air-Dry Soil

Competitive sorption of copper (Cu), lead (Pb), cadmium (Cd), and zinc (Zn) was studied in three soils of contrasting chemical and physical properties under air-dry and waterlogged conditions. Competitive sorption was determined using the standard batch technique using six solutions, each with Cu, Pb, Cd, and Zn concentrations of approximately 0, 2.5, 5, 10, 20, and 50?mg L^?1Waterlogged soils tended to sorb higher amounts of added Cu, Pb, Zn and Cd relative to soils in the air-dry condition; however, this increase in sorption was generally not statistically (p<0.05) significant. The magnitude of sorption under both waterlogged and air-dry conditions was affected by the type and amount of soil materials involved in metal sorption processes, and competition between other metals for the sorption sites. Metal sorption was closely correlated with soil properties such as cation exchange capacity, organic carbon, and Fe and Mn hydrous oxides. Exchangeable Al may have markedly reduced metal sorption due to its strong affinity for the sorption sites, while increases in exchangeable Mn may have enhanced Zn and Cd sorption. Heavy metal sorption was best described as a combination of both specific and nonspecific interactions. The extractability of Cu, Pb, Cd, and Zn under waterlogged and air-dry conditions was also studied. Three solutions containing these metals were mixed with each soil to achieve a final concentration of 0, 50, and 500?mg kg^?1. Each soil was extracted every 7 days using 1?M MgCl₂ (pH 7) to determine metal extractability. Metal extractability initially decreased then increased due to waterlogging. The increased extractability of added metals was closely related to increased solubility of Fe and Mn suggesting that dissolution of Fe and Mn, oxides under reducing conditions caused a release of previously sorbed Cu, Pb, Cd, and Zn.     

Vertical and Horizontal Distributions of Zn,Cd, Pb,Cu, and Hg in Uncultivated Soil in the Vicinity of a Zinc Smelter at Odda,Norway

In the present work the extent and variation of Zn, Cd, Pb, Cu, and Hg loading in undisturbed surface soil (0–5 cm) and the vertical transport of the metals in soil profiles are studied in the vicinity of a zinc smelter in Norway. Three major controlling factors on the metal concentrations in soil have been assessed: 1) distance from the anthropogenic point source; 2) organic matter content (O.M.); and 3) the prevailing wind directions. Moreover metal distributions in proximal soil profiles in 1972 and 2003 are compared. Current concentrations of Zn, Cd, Pb, Cu, and Hg in surface soil reach 14000, 60, 980, 430, and 7.0 mg·kg ^{? 1} , respectively, near the smelter and decrease regularly with distance in the northerly direction according to the regression model (y = ax^{? b} ). The Zn concentrations are significantly different from the background range up to 30 km from the smelter, whereas the other metals approach background at only 10 km distance. Subsurface concentration peaks of Pb, Cu, and Hg are found at greater depth in soil profiles than peaks of Zn and Cd. Levels of Zn, Cd, and Pb in surface soil seem to have decreased from 1972 to 2003, whereas for Cu the levels appear not to be significantly different.     

The ATP hydrolytic activity of purified ZntA, a Pb(II)/Cd(II)/Zn(II)-translocating ATPase from Escherichia coli

ZntA, a soft metal-translocating P1-type ATPase from Escherichia coli, confers resistance to Pb(II), Cd(II), and Zn(II). ZntA was expressed as a histidyl-tagged protein, solubilized from membranes with Triton X-100, and purified to homogeneity. The soft metal-dependent ATP hydrolysis activity of purified ZntA was characterized. The activity was specific for Pb(II), Cd(II), Zn(II), and Hg(II), with the highest activity obtained when the metals were present as thiolate complexes of cysteine or glutathione. The maximal ATPase activity of ZntA was approximately 3 micromol/(mg x min) obtained with the Pb(II)-thiolate complex. In the absence of thiolates, Cd(II) inhibits ZntA above pH 6, whereas the Cd(II)-thiolate complexes stimulate activity, suggesting that a metal-thiolate complex is the true substrate in vivo. These results are consistent with the physiological role of ZntA as mediator of resistance to toxic concentrations of the divalent soft metals, Pb(II), Cd(II), and Zn(II), by ATP-dependent efflux. Our results confirm that ZntA is the first Pb(II)-dependent ATPase discovered to date.     

Leaching of Zinc,Cadmium, and Lead in a Sandy Soil Due to Application of Poultry Litter

Dissolved organic matter in poultry litter could contribute organic ligands to form complexes with heavy metals in soil. The soluble complexes with heavy metals can be transported downward and possibly deteriorate groundwater quality. To better understand metal mobilization by soluble organic ligands in poultry litter, soil columns were employed to investigate the movement of zinc (Zn), cadmium (Cd), and lead (Pb). Uncontaminated soil was amended with Zn, Cd, and Pb at rates of 400, 8, and 200 mg kg ^{? 1} soil, respectively. Glass tubes, 4.9-cm-diameter and 40-cm-long, were packed with either natural or metal-amended soil. The resulting 20-cm-long column of soils had bulk density of about 1.58 g cm ^{? 3} . Columns repacked with natural or amended soil were leached with distilled water, 0.01 M EDTA, 0.01 M CaCl ₂ , or poultry litter extract (PLE) solutions. Low amounts of Zn, Cd, and Pb were leached from natural soil with the solutions. Leaching of Zn, Cd, or Pb was negligible with distilled water. In the metal-amended soil, EDTA solubilized more Zn, Cd, and Pb than CaCl ₂ and PLE. The breakthrough curves of Zn and Pb in the PLE and CaCl ₂ were similar, indicating they have similar ability to displace Zn and Pb from soils. Compared with Zn and Cd the PLE had a small ability to solubilize Pb from metal-amended soil. Thus, the application of poultry litter on metal-contaminated soils might enhance the mobility of Zn and Cd.     

Evaluation of trace metals in sediment,water, and fish (Mugil cephalus) of the central Black Sea coast of Turkey

In this study, concentrations of trace metals such as As, Cd, Cu, Cr, Fe, Pb, Ni, Sn, Se, and Zn were determined in sediments, water, and a kind of fish (Mugil cephalus) of the central Black Sea coasts by employing Inductively Coupled Plasma Mass Spectrometry and microwave digestion technique. Gill, muscle, liver, and other tissues were analyzed separately for each sample. The accuracy of the results were checked by using a certified reference material (DORM-4). In water samples, the metal determined at highest concentrations was Cu (1645.44 µg/L). In sediment samples, the metal determined at highest concentrations was Fe (12223.50 mg/kg). The levels of trace metals found in the different parts of the fish were: Zn in muscle tissue (30393.28 mg/kg), Sn in gill tissue (5140.08 mg/kg), and Cu in liver tissue (289.31 mg/kg). These results were also compared with various relevant guidelines and literature.     

Heavy metals in wetland soils along a wetland-forming chronosequence in the Yellow River Delta of China: Levels,sources and toxic risks

Surface soil (0–20 cm) samples were collected from four chronological sequences of wetlands (i.e., >50-yr-old wetlands, 40-yr-old wetlands, 30-yr-old wetlands and 10-yr-old wetlands) in the Yellow River Delta of China in May and June of 2007. Total contents of Al, As, Cd, Cr, Cu, Ni, Pb and Zn were determined using inductively coupled plasma atomic absorption spectrometry (ICP-AAS) to investigate the levels, sources and toxic risks of heavy metals in these wetlands. Our results showed an increasing trend for Pb, Cu and Zn along the wetland-forming chronosequence although their pollution levels were low. Both As and Cd exhibited significant enrichment due to their high enrichment factor (EF) values (EF > 5), especially in older wetlands (i.e., >50-yr-old and 40-yr-old wetlands), whereas other heavy metals were minimally or moderately enriched in this region. The results of principal component analysis showed that 83.09% of total variance based on eigenvalues (eigenvalue > 1) could be explained by three principal components (PCs) in four wetlands. The source of Al, Cu, Pb and Zn was different from Cd, Cr and Ni. According to the sediment quality guidelines (SQGs) of China, soil samples in the younger wetlands, especially the 10-yr-old wetlands, were moderately polluted by As, Cd and Ni. According to the SQGs of US EPA, all soil samples were heavily polluted by As and moderately polluted by Ni and soil samples in the older wetlands were moderately polluted by Cr. However, with the exception of As and Ni, the contents of other heavy metals in the four wetlands did not exceed the probable effect level (PEL) values. As, Cd and Ni were identified as heavy metals of primary concerns in four wetlands, Cr were of moderate concern in older wetlands, and Pb, Cu and Zn should be paid more attention in younger wetland (i.e., 10-yr-old and 30-yr-old wetlands). A new and sensitive toxic risk index (TRI) is developed for the accurate assessment of toxic risk for heavy metals in wetland soils compared with the sum of the toxic units (∑TUs), and As, Cr, Ni and Cd showed higher contributions to TRI.     

芜湖钢铁厂周边土壤及油菜籽中镉、铜、锌、铅含量和形态分布研究

研究了污染土壤、油菜籽中Cd、Cu、Zn、Pb含量、形态分布特征和重金属富集状况及可能存在的生物毒性.结果表明,土壤中Cd、Zn、Pb以铁锰氧化物结合态、Cu以残留态占5种形态最高比例,分别为31.1%、39.3%、53.79%、46.24%;Cd、Pb交换态比例较高,为23.47%、16.32%,Cu、Zn的交换态比例较小,为3.14%、0.54%;土壤中不同重金属与各重金属形态相关关系有差别,5种重金属形态转化为有效态重金属难易程度不同;油菜籽和油菜籽壳中不同重金属累积趋势有差异,Cu易在油菜籽壳中累积,Cd、Zn、Pb易在油菜籽中累积;油菜籽中不同重金属累积率不同,Cd累积率最高,为0.56.油菜籽中重金属累积率与土壤中重金属总量呈显著负相关关系(P＜0.05),土壤中重金属的形态、转化差异是此种负相关关系的主要原因;油菜籽中Cd、Cu、Pb以氯化钠态为主,分别为32.50%、22.94%、34.69%,Zn以EDTA态为主,为45.97%.油菜籽中重金属形态可能影响其毒性,但其毒性的人类膳食风险还需进一步研究证实.油菜籽中重金属形态与油菜中重金属总量相关性不好.