Electro-remediation of tailings from a multi-metal sulphide mine: comparing removal efficiencies of Pb,Zn, Cu and Cd

Sulphidic mine tailings characterised by high concentrations of heavy metals (Pb 3532?±?97?mg/kg, Zn 8450?±?154?mg/kg, Cu 239?±?18?mg/kg and Cd 14.1?±?0.3?mg/kg) and abundant carbonate (17%) were subjected to eight lab-scale electrodialytic remediation (EDR) experiments to investigate the influence of current density, treatment time and particle size on removal efficiency. Pb and Cu removal improved when increasing current density, while Zn and Cd removal did not. In contrast Zn and Cd removal improved by grinding the tailings, while Pb and Cu removal did not. At the highest current density (1.2?mA/cm²), 94%, 75%, 71% and 67% removal of Pb, Zn, Cu and Cd could be achieved, respectively, on grinded tailings in 28 days. Sequential chemical extraction made before and after EDR revealed larger oxidisable fractions of Zn, Cu and Cd, representing large fractions of sulphides, which was likely to be the main barrier to be removed as efficiently as Pb. This was in accordance with acid/base extraction tests in which Pb showed high solubility at both high and low pH (up to 65% and 86% of extraction, respectively), while considerable extraction of Zn (55%) happened only at low pH; and very limited extraction (<20%) of Cu and Cd occurred at any pH.     

Geochemical distribution of trace element concentrations in the vicinity of Boroo gold mine,Selenge Province,Mongolia

The environmental impacts of Boroo gold mine project in Mongolia was evaluated by chemical characterization of trace element concentrations in water, soils and tailing dam sediment samples. The results showed that concentrations of B, Cd, Ni and Se in the water samples were within the accepted levels of the Mongolia water quality standard (MNS4586: 1998). However, the concentrations of Al, As, Cu, Mn, Fe, Pb, U and Zn were higher than the maximum allowable concentration especially in the monitoring and heap leach wells. The average concentrations of As, Cd, Cu, Ni, Pb and Zn in the tailing dam sediment were 4419, 58.5, 56.0, 4.8, 20.6 and 25.7 mg/kg, respectively. Generally, arsenic and heavy metals in the soil samples were within the acceptable concentrations of the soil standard of Mongolia (MNS 5850: 2008). The chemical characterization of As solid phase in tailing dam sediment showed that the majority of As were found in the residual fraction comprising about 74% of total As. Assessing the potential risk to humans, simple bioavailability extraction test was used to estimate bioavailability of arsenic and heavy metals, and the concentrations extracted from tailing dam sediment were; 288.2 mg/kg As, 7.2 mg/kg Cd, 41.1 mg/kg Cu, 13.5 mg/kg Pb, 4.7 mg/kg Ni and 23.5 mg/kg Zn, respectively. From these results, the Boroo gold mine project has presently not significantly impacted the environment, but there is a high probability that it may act as a source of future contamination.     

Investigation and risk assessment modeling of As and other heavy metals contamination around five abandoned metal mines in Korea

Tailings, agricultural soils, vegetables and groundwater samples were collected from abandoned metal mines (Duckum, Dongil, Dongjung, Myoungbong and Songchun mines) in Korea. Total concentrations of arsenic (As) and heavy metals (Cd, Cu, Pb and Zn) were analyzed to investigate the contamination level. Several digestion methods (Toxicity characteristics leaching procedure (TCLP), synthetic precipitation leaching procedure (SPLP), 0.1 N/1 N HCl) and sequential extraction analysis for mine tailings were conducted to examine the potential leachability of As and heavy metals from the tailings. The order of urgent remediation for the studied mines based on the risk assessment and remedial goals was suggested. The Songchun mine tailings were most severely contaminated by As and heavy metals. Total concentrations of As and Pb in the tailings were 38,600–58,700 mg/kg (av. 47,400 mg/kg) and 11,800–16,800 mg/kg (av. 14,600 mg/kg), respectively. Agricultural soils having high As concentrations were found at the all mines. Average concentrations of Cd in the vegetables exceeded the normal value at all mines areas, while As only at the Dongjung, Myoungbong, and Songchun mine area. One groundwater sample each from the Dongil and Myoungbong mines, and 4 groundwater samples from the Songchun mine had values above 10 μg/L of As concentration. The TCLP method revealed that only Pb in the Songchun tailings, 6.49 mg/L, exceeded the regulatory level (5 mg/L). Employing the 1-N HCl digestion method, the concentration of As in the Songchun mine tailings, 4,250 mg/kg, was up to 3,000 times higher than its Korean countermeasure standard. Results from the sequential extraction of As in the tailings showed that the easily releasable fraction in the Myoungbong and Songchun mine tailings was more than 30% and the residual fraction was less than 40%. Based on results showing the exposure health risk employing the hazard quotient and cancer risk of As, Cd and Zn, the Dongil mine needs the most urgent remedial action. The concentration reduction factor (CRF) of As in both soil and groundwater follows the order: Songchun>Dongjung>Dongil>Myoungbong>Duckum mine.     

Selective recovery of Cu, Zn, and Ni from acid mine drainage

In Korea, the heavy metal pollution from about 1,000 abandoned mines has been a serious environmental issue. Especially, the surface waters, groundwaters, and soils around mines have been contaminated by heavy metals originating from acid mine drainage (AMD) and mine tailings. So far, AMD was considered as a waste stream to be treated to prevent environmental pollutions; however, the stream contains mainly Fe and Al and valuable metals such as Ni, Zn, and Cu. In this study, Visual MINTEQ simulation was carried out to investigate the speciation of heavy metals as functions of pH and neutralizing agents. Based on the simulation, selective pH values were determined to form hydroxide or carbonate precipitates of Cu, Zn, and Ni. Experiments based on the simulation results show that the recovery yield of Zn and Cu were 91 and 94 %, respectively, in a binary mixture of Cu and Zn, while 95 % of Cu and 94 % of Ni were recovered in a binary mixture of Cu and Ni. However, the recovery yield and purity of Zn and Ni were very low because of similar characteristics of Zn and Ni. Therefore, the mixture of Cu and Zn or Cu and Ni could be recovered by selective precipitation via pH adjustment; however, it is impossible to recover selectively Zn and Ni in the mixture of them.     

Marble wastes and pig slurry improve the environmental and plant-relevant properties of mine tailings

Poor soil fertility is often the biggest challenge to the establishment of vegetation in mine wastes deposits. We conducted field trials in the El Gorguel and El Lirio sites in SE Spain, two representative tailing ponds of similar properties except for pH, to understand the environmental and plant-relevant benefits of marble waste (MW) and pig slurry (PS) applications to mine tailings. Low pH (5.4) tailings (El Lirio) exhibit reduction of up to fourfold in bio-availability of metals as shown by the DTPA-Zn, Pb, water-soluble Zn, Pb and up to 3× for water-soluble Cd. Tailings in El Gorguel have high pH (7.4) and did not exhibit significant trends in the reductions of water-extractable Zn, Pb, Cd and Cu. Improvements to the edaphic (plant-relevant) properties of tailings after the amendments are not as sensitive to pH compared to the environmental characteristics. The two sites had increases in aggregate stability, organic matter (total N and organic C) although total N is higher in the El Gorguel (up to 212 μg N kg^?1) than the El Lirio (up to 26 μg N kg^?1). However, cation exchange capacities are similar in both sites at 15.2 cmol(+) kg^?1. We conclude that the characteristics, especially pH, of tailing materials significantly influence the fate of metals but not improvements to plant-relevant properties such as cation exchange capacity and aggregate stability 1 year after the application of MW and PS amendments.     

Relative extraction ratio (RER) for arsenic and heavy metals in soils and tailings from various metal mines,Korea

This study focused on the evaluation of leaching behaviours for arsenic and heavy metals (Cd, Cu, Ni, Pb and Zn) in soils and tailings contaminated by mining activities. Ten representative mine soils were taken at four representative metal mines in Korea. To evaluate the leaching characteristics of the samples, eight extraction methods were adapted namely 0.1 M HCl, 0.5 M HCl, 1.0 M HCl, 3.0 M HCl, Korean Standard Leaching Procedure for waste materials (KSLP), Synthetic Precipitation Leaching Procedure (SPLP), Toxicity Characteristic Leaching Procedure (TCLP) and aqua regia extraction (AR) methods. In order to compare element concentrations as extraction methods, relative extraction ratios (RERs, %), defined as element concentration extracted by the individual leaching method divided by that extracted by aqua regia based on USEPA method 3050B, were calculated. Although the RER values can vary upon sample types and elements, they increase with increasing ionic strength of each extracting solution. Thus, the RER for arsenic and heavy metals in the samples increased in the order of KSLP < SPLP < TCLP < 0.1 M HCl < 0.5 M HCl < 1.0 M HCl < 3.0 M HCl. In the same extraction method, the RER values for Cd and Zn were relatively higher than those for As, Cu, Ni and Pb. This may be due to differences in geochemical behaviour of each element, namely high solubility of Cd and Zn and low solubility of As, Cu, Ni and Pb in surface environment. Thus, the extraction results can give important information on the degree and extent of arsenic and heavy metal dispersion in the surface environment.     

Geochemical distribution of trace element concentrations in the vicinity of Boroo gold mine, Selenge Province, Mongolia

The environmental impacts of Boroo gold mine project in Mongolia was evaluated by chemical characterization of trace element concentrations in water, soils and tailing dam sediment samples. The results showed that concentrations of B, Cd, Ni and Se in the water samples were within the accepted levels of the Mongolia water quality standard (MNS4586: 1998). However, the concentrations of Al, As, Cu, Mn, Fe, Pb, U and Zn were higher than the maximum allowable concentration especially in the monitoring and heap leach wells. The average concentrations of As, Cd, Cu, Ni, Pb and Zn in the tailing dam sediment were 4419, 58.5, 56.0, 4.8, 20.6 and 25.7 mg/kg, respectively. Generally, arsenic and heavy metals in the soil samples were within the acceptable concentrations of the soil standard of Mongolia (MNS 5850: 2008). The chemical characterization of As solid phase in tailing dam sediment showed that the majority of As were found in the residual fraction comprising about 74% of total As. Assessing the potential risk to humans, simple bioavailability extraction test was used to estimate bioavailability of arsenic and heavy metals, and the concentrations extracted from tailing dam sediment were; 288.2 mg/kg As, 7.2 mg/kg Cd, 41.1 mg/kg Cu, 13.5 mg/kg Pb, 4.7 mg/kg Ni and 23.5 mg/kg Zn, respectively. From these results, the Boroo gold mine project has presently not significantly impacted the environment, but there is a high probability that it may act as a source of future contamination.     

Mobilization kinetics of heavy metals from contaminated river sediment of northern Taiwan by complexing agents

A laboratory experiment was used to investigate the mobilization kinetics of heavy metals from the sediment of a contaminated river located in northern Taiwan with varied concentrations of NTA and EDTA. We found that there were two stages of desorption in the mobilization of heavy metals from the sediment. As the concentrations of NTA and EDTA ranged 0–3.9 x 10^‐4M (0–100mg/l) and 0–2.7 x 10^‐4M (0–100mg/l) respectively, the mobilization percentages of heavy metals were proportional to the logarithm values of the concentrations of NTA and EDTA. The physical meaning of the multiple first‐order reaction was significant for the actual condition, but occasionally, it had more errors for Cu and Zn in the initial phase. The two‐constant model was most appropriate for describing the rates of mobilization of Pb, Cu, Zn, and Cr. The agreement between the diffusion model and the experimental data was satisfactory for Pb, Cu, Zn, and Cr only in the initial 5 h.     

Assessment of solid waste and dumpsite leachate and topsoil

Dumpsite leachate contains different hazardous substances, some of which threaten the environment. In this study, municipal solid waste, dumpsite leachate and topsoil from seven different dumpsites in Lagos and Ibadan, Nigeria were analysed using standard methods. The parameters analysed in the composite leachate samples collected are pH, solids, alkalinity, chloride, nitrate, sulfate, phosphate, biochemical oxygen demand, chemical oxygen demand turbidity, heavy metals (e.g. Zn, Pb, Co, Ni, Cd) and some persistent organic pollutants (e.g. polyaromatic hydrocarbons [PAHs] and polychlorinated biphenyls [PCBs]). Total organic carbon, heavy metals (e.g. Zn, Pb, Co, Ni, Cd) and organic pollutants (e.g. PAHs, PCBs) were analysed in the dumpsite topsoil and the control samples. The samples for heavy metal determination were digested using concentrated nitric acid and the digestate was analysed using atomic absorption spectrometry, whereas organic pollutants were extracted using cold extraction and quantified by gas chromatography-mass spectrometry (GC-MS). The study revealed that dumpsites in Ibadan have ～90% domestic and 10% industrial waste, whereas the figures for Lagos are 80% and 20%, respectively. In the leachate samples, concentrations of PAHs and PCBs ranged from 0.85 to 1.47 mg/L and 0.01 to 0.08 mg/L, respectively; the values were 0.94–2.79 mg/kg and 10.0–412 μg/kg in the topsoil. If not properly managed, dumpsite leachate can seep into groundwater and surface water via run-off, and can have adverse effects on human health and the entire ecosystem.     

Geochemical investigation of potentially harmful elements in household dust from a mercury-contaminated site,the town of Idrija (Slovenia)

A comprehensive geochemical investigation of potentially harmful elements (PHEs) in household dust from the town of Idrija (Slovenia), once a world-famous Hg mining town that is now seriously polluted, was performed for the first time. After aqua regia digestion, the content of mercury (Hg), arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), molybdenum (Mo), nickel (Ni), lead (Pb) and zinc (Zn) was measured. PHE-bearing particles were recognised and observed by scanning electron microscopy and energy-dispersive spectrometry before and after exposure to simulated stomach acid (SSA). Mercury binding forms were identified by Hg thermal desorption technique and gastric bioaccessible Hg was estimated after SSA extraction by ICP-MS. With regard to rural and urban background values for Slovenia, high Hg content (6–120 mg/kg) and slightly elevated As content (1–13 mg/kg) were found. Mercury pollution is a result of past mining and ore processing activities. Arsenic content is potentially associated with As enrichment in local soils. Four Hg binding forms were identified: all samples contained Hg bound to the dust matrix, 14 samples contained cinnabar, two samples contained metallic Hg (Hg⁰), and one sample assumingly contained mercury oxide. After exposure to SSA, Hg-bearing phases showed no signs of dissolution, while other PHE-bearing phases were significantly morphologically and/or chemically altered. Estimated gastric Hg bioaccessibility was low (<0.006–0.09 %), which is in accordance with identified Hg binding forms and high organic carbon content (15.9–31.5 %) in the dust samples.     

Long-term geochemical evolution of acidic mine wastes under anaerobic conditions

A nearly 5-year anaerobic incubation experiment was conducted to observe the geochemical evolution of an acidic mine waste. Long-term storage of the mine waste under strict anaerobic conditions caused marked increase in aqueous sulfur, while aqueous iron showed no remarkable change. Co-existing oxidation and reduction of elemental sulfur appeared to play a central role in controlling the evolutionary trends of aqueous sulfur and iron. Addition of organic matter increased the aqueous Fe concentration, possibly due to enhanced iron mobilization by microbial iron reduction and increased iron solubility by forming organically complexed Fe species. Further addition of CaCO₃ resulted in immobilization of aqueous iron and sulfur due to elevated pH and gypsum formation. The chemical behaviors of environmentally significant metals were markedly affected by the added organic matter; Al, Cr, Cu, Ni and Zn tended to be immobilized probably due to elevated pH and complexation with insoluble organic molecules, while As and Pb tended to be mobilized. Jarosite exhibited high stability after nearly 5 years of anaerobic incubation and even under circumneutral pH conditions. Long-term weathering of aluminosilicate through acid attack raised pH, while continuous reaction between the added CaCO₃ and mine waste-borne stored acid decreased pH.     

4种草对铅锌尾矿污染土壤重金属的抗性与吸收特性

盆栽试验的结果表明,高羊毛、早熟禾、黑麦草、紫花苜蓿在纯尾矿污染土壤或经处理的尾矿污染土壤上都能生长,但在处理的土壤上生长的植物长势明显优于对照,其中紫花苜蓿的生物量所受影响比其他几种草坪草更大,说明其重金属抗性低于其他几种植物。单位面积上 4 种植物体内重金属质量分数高低均为 w(Zn)>w(Pb)>w(Cu)>w(Cd),但每种植物对 Cd、Pb、Zn 和 Cu 的吸收质量分数和分布均不相同,一般为根系质量分数大于茎叶。加入改良剂(CaCO3)和有机肥(菜枯)使生长在铅锌尾矿污染土壤上的 4 种草坪草生物量显著增加,植物体中的 Cd、Pb、Zn 质量分数下降,但 Cu 质量分数反而上升,结果单位面积上草坪草吸收各重金属元素的量均有所增加,可见利用改良措施与草坪草相结合的方法来修复重金属污染土壤具有可行性。     

Effect of acid rain on the fractionation of heavy metals and major elements in contaminated soils

Acid rain is a serious environmental problem worldwide. In the present study, we investigated the effect of acid rain (1:1 equivalent basis H₂SO₄:HNO₃) at pH values of 2.0, 4.0 and 7.0 on the fractionation of heavy metals (Cd, Cu, Fe, Mn, Ni, Pb and Zn) and major elements (K, Na, Ca, and Mg) in contaminated calcareous soils over a 2084 h period. Heavy metals and major elements in soil samples were fractionated before and after 2084 h kinetic release using a sequential extraction procedure. Before kinetic studies the predominant fractions of K, Na, Ca, Mg, Cd and Ni were mainly associated with carbonate fraction (CARB), whereas Fe, Mn and Zn were associated with the Fe–Mn oxide fraction (Fe–Mn oxide). The highest percentage of Pb and Cu were found in the exchangeable (EXC) and organic matter (OM) fractions, respectively. After kinetic study using different simulated acid rain solutions, the major fractions of heavy metals (expect of Cu) and Na was the same as before release. Upon the application of different acid rain solutions, K and Mg were found dominantly in Fe–Mn oxide fraction, whereas Ca was in the EXC fraction. The results provide valuable information regarding metal mobility and indicated that speciation of metals (Cu and Zn) and major elements in contaminated calcareous soils can be affected by acid rain.     

Contamination and vertical distribution of As,Cd, Cr,Cu, Pb,Tl, and Zn in paddy soil irrigated with untreated leachate from tailings retention ponds

The contamination and vertical distribution of As, Cd, Cr, Cu, Pb, Tl, and Zn in paddy soil irrigated with untreated leachate from the tailings retention pond were investigated. As, Cr, Cu, and Zn were slightly contaminated in the surface soil and hence their vertical distribution was not obvious. However, Cd and Pb were highly contaminated in the surface soil, while their concentrations decreased with depth, being negatively correlated with pH and positively with total organic matter. Tl was considerably contaminated in the surface soil and a V-shaped vertical distribution was observed where the concentration increased to a maximum at about 30 cm depth and decreased thereafter. The findings revealed that the regular irrigation with untreated leachate from the tailings retention ponds could cause considerable contamination of Cd, Pb, and Tl, and thus tailings should be stringently treated before disposal to minimize their potential environmental impacts on the surroundings.     

Assessment of human health risks from heavy metals in outdoor dust samples in a coal mining area

Jharia (India) a coal mining town has been affected by the consequences of mining and associated activities. Samples of outdoor fallen dust were collected at different locations of Jharia covering four different zones: commercial, petrol pump, high traffic, and residential areas. The dust samples were analysed for different trace elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, and Zn). The highest concentration of the elements in the dust samples are Mn (658 mg/kg), Zn (163.6 mg/kg), Cr (75.4 mg/kg), Pb (67.8 mg/kg), Ni (66 mg/kg), Cu (56.8 mg/kg), Co (16.9 mg/kg), As (4.1 mg/kg), and Cd (0.78 mg/kg). The concentration of selenium was below detection limit. Except Cd, contents of all the other elements in the dust samples were significantly lower in the residential area. High amount of Ni (145 mg/kg) and Pb (102 mg/kg) was observed in the high traffic and petrol pump areas, respectively. The exposure risk assessment strategies are helpful in predicting the potential health risk of the trace elements in the street dust. Selected receptors for risk assessment were infants, toddlers, children, teens, and adults. The calculated hazard quotient (HQ) for lifetime exposure was <1.0 for all the elements studied, indicating no risks from these elements for adults Among the receptors, toddlers were found to be more vulnerable, with HQ for Co, Cr, and Pb > 0.1. The finding predicts potential health risk to toddlers and children.     

橡胶园土壤若干微量元素含量 ——以海南省胶园土为例

胶园土壤微量元素含量有一定的特征。海南省胶园土个别样点Ｃｄ偏高,Ｃｕ偏低,其它样点Ｃｄ、Ｃｒ、Ｐｈ、Ｚｎ、Ｃｕ、Ｎｉ、Ｍｏ、Ｈｇ含量正常。土壤母质、质地、化学组成、耕作等对微量元素含量有一定影响。玄武岩上的胶园土微量元素较丰富。质地粘重的土壤微量元素含量往往较高。由于铁的水合物吸附固定作用,Ｃｕ、Ｚｕ、Ｃｄ、Ｈｇ含量与Ｆｅ含量有一定关系。Ｃｕ、Ｚｎ、Ｃｄ、Ｈｇ的许多化学性质相似,它们的含量有一定的相关性。     

Health risk assessment through consumption of vegetables rich in heavy metals: the case study of the surrounding villages from Panasqueira mine,Central Portugal

Panasqueira mine is a tin–tungsten mineralization hosted by metasediments with quartz veins rich in ferberite. The mineralization also comprises wolframite, cassiterite, chalcopyrite, several sulfides, carbonates and silver sulfosalts. The mining and beneficiation processes produce arsenic-rich mine wastes laid up in huge tailings (Barroca Grande and Rio tailings). The contents of As, Cd, Cr, Cu, Pb and Zn were estimated in rhizosphere soils, irrigation waters, road dusts and in potatoes, cabbages, lettuces and beans, collected on local gardens of four neighborhood Panasqueira mine villages: S. Francisco de Assis (SFA) and Barroca suffering the influence of tailings; Unhais-o-Velho and Casegas considered as non-polluted areas. The mean concentrations of metals in rhizosphere soils and vegetables exceed the reference guidelines values and seem to be linked to the sulfides. The rhizosphere ecological risks were ranked in the order of Cd > As > Cu > Pb > Zn > Cr and SFA > Barroca > Casegas > Unhais-o-Velho. Metal concentrations, in vegetables, were found in the order of lettuce > cabbage > potatoes and SFA > Barroca > Casegas > Unhais-o-Velho. For cabbages and lettuces, the tendency of contamination is roots > leaves and for potatoes is roots > leaves > tubers. The risk for residents, due to ingesting of metals/metalloid, by consuming vegetables grown around the sampling area, was calculated and the result indicates that the inhabitants of these villages are probably exposed to some potential health risks through the intake of heavy metals and metalloids via consuming their vegetables.     

宁波市回龙河表层沉积物重金属的形态分析及风险评价

为了解回龙河表层沉积物中重金属的污染状况,采集了表层沉积物样品,测定了重金属Zn、Cu、Pb、Cr、Cd和Ni的总量及其化学形态,并采用潜在生态风险指数法对重金属进行了生态风险评价。结果显示,回龙河表层沉积物中Zn、Cu、Pb、Cr、Cd和Ni均有一定程度的累积,总量分别为286.4～1277.9mg/kg、21.71～146.0mg/kg、10.33～44.20mg/kg、25.13～90.40mg/kg、0.07172～0.3901mg/kg、13.27～157.2mg/kg,其中Cu、Cr、Pb与Ni 4种重金属具有一定的同源特性;形态分析表明,Cu的形态分布以有机结合态为主,最容易迁移释放,Zn、Cr和Ni除残渣态外,铁锰氧化结合态和有机结合态占一定比例,具有潜在风险;潜在生态风险指数法分析表明,沉积物中重金属元素的单一潜在生态风险指数顺序为Cd〉Cu〉Ni〉Zn〉Pb〉Cr,潜在生态危害指数RI均小于150,总体上回龙河处于轻微的生态风险等级。     

EDTA and citric acid mediated phytoextraction of Zn, Cu, Pb and Cd through marigold (Tagetes erecta)

Phytoextraction is an emerging cost-effective solution for remediation of contaminated soils which involves the removal of toxins, especially heavy metals and metalloids, by the roots of the plants with subsequent transport to aerial plant organs. The aim of the present investigation is to study the effects of EDTA and citric acid on accumulation potential of marigold (Tagetes erecta) to Zn, Cu, Pb, and Cd and also to evaluate the impacts of these chelators (EDTA and citric acid) in combination with all the four heavy metals on the growth of marigold. The plants were grown in pots and treated with Zn (7.3 mg l(-1)), Cu (7.5 mg I(-1)), Pb (3.7 mg l(-1)) and Cd (0.2 mg l(-1)) alone and in combination with different doses of EDTA i.e., 10, 20 and 30 mg l(-1). All the three doses of EDTA i.e., 10, 20 and 30 mg l(-1) significantly increased the accumulation of Zn, Cu, Pb and Cd by roots, stems and leaves as compared to control treatments. The 30 mg l(-1) concentration of citric acid showed reduced accumulation of these metals by root, stem and leaves as compared to lower doses i.e., 10 and 20 mg l(-1). Among the four heavy metals, Zn accumulated in the great amount (526.34 mg kg(-1) DW) followed by Cu (443.14 mg kg(-1) DW), Pb (393.16 mg kg(-1) DW) and Cd (333.62 mg kg(-1) DW) in leaves with 30 mg l(-1) EDTA treatment. The highest concentration of EDTA and citric acid (30 mg l(-1)) caused significant reduction in growth of marigold in terms of plant height, fresh weight of plant, total chlorophyll, carbohydrate content and protein content. Thus EDTA and citric acid efficiently increased the phytoextractability of marigold which can be used to remediate the soil contaminated with these metals.     

Bioaccumulation and regional distribution of trace metals in fish of the Tibetan Plateau

There are limited data on trace metals in the fishes of the Tibetan Plateau. In this study, 62 fish samples were collected from six alpine lakes and a river to investigate the levels and spatial variations of trace metals across the Tibetan Plateau. The concentrations of nine trace elements in fish samples were measured using an inductively coupled plasma mass spectrometer after microwave digestion. Results showed the metal concentrations in the fish muscles had the following ranges: Cr 0.09–0.74 mg/kg, Mn 0.38–4.49 mg/kg, Ni 0.06–0.91 mg/kg, Cu 1.00–32.2 mg/kg, Zn 13.1–102.5 mg/kg, As 0.12–3.10 mg/kg, Pb 0.46–3.22 mg/kg, Ba 0.60–4.93 mg/kg, and Se 0.77–9.38 mg/kg on a dry weight basis, respectively. All the lake-averaged metal concentrations in the fish muscle were below the maximum permissible levels set by the Chinese food health criterion (GB2762-2012). The results were analyzed by multivariate statistical techniques to identify the major factors explaining the variance of metal concentrations in the alpine lakes. This work provides baseline data on metal pollution in common fish species of the Tibetan Plateau, contributing to the effective evaluation of both the environmental quality and health status of organisms in the aquatic ecosystem.