Heavy metal speciation and mobility assessment of arid soils in the vicinity of Al Ain landfill, United Arab Emirates

Sixty-four surface soil samples taken in the vicinity of Al Ain landfill were analysed for cadmium, chromium, copper, nickel, lead and zinc by inductively coupled plasma spectroscopy. Extraction techniques were used to establish the association of the total concentrations of the six metals in the soil samples with their contents in the exchangeable, carbonate, iron/manganese oxides, and residual fractions. In the investigated soils, the recorded concentrations were as follows: 0.043 mg kg^-1 for cadmium, 19.1 mg kg^-1 for chromium, 53.3 mg kg^-1 for copper, 60 mg kg^-1 for nickel, 13.7 mg kg^-1 for lead, and 117 mg kg^-1 for zinc. Cadmium, chromium, nickel, lead and zinc concentrations in the investigated soil samples reflect the natural background values in shale, whereas copper is slightly enriched. I-geo (geoaccumulation index) values of the metals in the soils under study indicate that they are uncontaminated with cadmium, chromium, nickel, lead and zinc, but contaminated to moderately contaminated with copper. Heavy metal contents in the sediments were found to be significantly influenced by different physico-chemical parameters. The effect of these parameters can be arranged in the following order: clay fraction > carbonate fraction > silt fraction > organic matter fractions. A sequential extraction procedure showed that the total concentrations of the heavy metals are largely bound to the residual phase (retained 71.4% of cadmium, 77.8% of chromium, 75% of copper, 47% of nickel, 62.8% of lead, and 75.8% of zinc). A likely sequence of mobility in the investigated soils is as follows: chromium > lead > nickel > cadmium > zinc > copper.     

Investigation of heavy metal accumulation in Polygonum thunbergii for phytoextraction

In this study, cadmium (II), lead (II), copper (II) and zinc (II) were determined in Polygonum thunbergii and soil from the Mankyung River watershed, Korea. Soil samples contained detectable lead (<17.5 g g(-1)), copper (<8.4 g g(-1)) and zinc (<24.5 g g(-1)), whereas cadmium was undetectable. Whole plants of P. thunbergii contained detectable lead (<320.8 g g(-1)), copper (<863.2 g g(-1)) and zinc (<2427.3 g g(-1)), whereas cadmium was detectable only in the stem (<7.4 g g(-1)) and root (<10.1 g g(-1)). Whole plant concentrations were very different for each metal, particularly in the case of zinc. The mean content of heavy metal in the whole plants increased in the order of cadmium (8.5 g g(-1))相似文献   

Evaluation of cadmium, copper, zinc, and iron concentrations and tissue distributions in the benthic crab, Dorippe granulata (De Haan, 1841) from Tolo Harbour, Hong Kong

The distributions of copper, zinc, iron, and cadmium among the tissues of Dorippe granulata were determined. The highest copper concentrations were found in the haemolymph (c. 53 microg ml(-1)) while the highest iron concentrations occurred in the gills (c. 720 microg g(-1) dry weight) and the highest zinc concentrations in the exoskeleton (c. 200 microg g(-1) dry weight). By comparison, concentrations of the non-essential metal, cadmium, were low in all tissues (mean = 10 microg g(-1) dry weight). The highest value was recorded from the midgut gland of a female crab (18.5 microg Cd g(-1) dry weight). Concentrations of copper, zinc, and iron were positively correlated with tissue-hydration levels. Such a relationship was not found for cadmium. The findings are discussed with regard to trace-metal levels found in temperate and tropical brachyurans from clean and polluted localities.     

Metal accumulation in arthropods near a lead/zinc smelter in Arnoldstein, Austria. I

This study reports on accumulation of lead, cadmium, copper and zinc in soil, plants and arthropod species in the vicinity of a closed-down lead/zinc smelter with a long history of pollution in Arnoldstein, Austria. Significant site-dependent metal accumulations were measured in most species, increasing in line with site contamination. Within a site, clear species-specific differences were found, even between closely related species. Within some species, developmental-, sex- and/or seasonal-specificities occurred, reflecting individual metal budgeting capabilities. Evidence for copper regulatory mechanisms appeared to be established in most cases, whereas lead, the main pollutant of the region, became heavily accumulated in some organisms. Higher levels of lead than previously reported in field surveys were detected in Carabidae and Caelifera at the most polluted site. It is recommended to take ecological and physiological parameters of species into consideration in interpreting field data on arthropod metal accumulation.     

Concentration of heavy metals in various children's herbal tea types and their correlations

This investigation was undertaken to determine the concentrations of cadmium, lead, mercury, zinc, copper and magnesium in six tea types used as children's tea. Six types of tea of different herbal composition used for children's consumption (T1, T2, T3, T4, T5 and T6) were analyzed in three subsequent collections. The analysis of cadmium showed that the concentration was very similar in all types of children's tea, ranging from 0.233 to 0.369 mg/kg. Lead concentrations were in the range of 0.340-1.564 mg/kg without any significant differences. The analysis of mercury detected very low concentration of this metal in all samples (0.002-0.004 mg/kg). In zinc, the values ranged from 36.633 to 71.711 mg/kg, with significant differences (p < 0.001) according to tea type. Copper concentration was 10.089-30.178 mg/kg with the highest value in T4. The concentration of magnesium was significantly higher in tea T1 and T2 (102.311 and 129.422 mg/kg) in comparison with other tea types where the level was 19.811-37.411 mg/kg. The maximum tolerable limit determined by Codex Alimentarius was not exceeded in any sample. In general, correlation analysis detected high positive correlation between cadmium and lead (r = 0.89), cadmium and mercury (r = 0.92) and between lead and mercury (r = 0.77).     

Effects of pH on the toxicity of cadmium, copper, lead and zinc to Folsomia candida Willem, 1902 (Collembola) in a standard laboratory test system

EC₅₀s for cadmium, copper, lead and zinc were determined for juvenile production of Folsomia candida at pH6.0, 5.0 and 4.5 in a standard laboratory test system. In contrast to most previous studies where metal toxicity was increased at low pHs, in our experiments there was no clear relationship between soil acidity and EC_{50-reproduction} in this species. The EC_{50-reproduction} values (μg g⁻¹) for cadmium and zinc were similar at all three pHs (pH6.0: Cd 590, Zn 900; pH5.0: Cd 780, Zn 600; pH4.5: Cd 480, Zn 590). In contaminated field sites adjacent to primary zinc smelters, zinc is invariably present in soils at concentrations of at least 50 times that of cadmium Thus deleterious effects of mixtures of these metals on populations of Collembola in such sites can be attributed to zinc rather than cadmium.     

Long-range air pollution and its impact on heavy metal accumulation in dippers Cinclus cinclus in Norway

Heavy metals such as cadmium, lead and zinc are deposited in Norway as long-range transported air pollution, while copper deposition is of mainly local origin. This study examined whether the deposition influences the metal concentrations in dippers Cinclus cinclus. The lead concentration in dippers reflected the deposition pattern of long-range air pollution, with higher concentrations in Southern Norway than Central Norway and a significant decrease (>/=40%) between 1987 and 1994. For cadmium, copper and zinc there were no geographical or temporal variations in metal concentrations. For zinc, this lack of geographic and temporal variation probably reflects the fact that it is a homeostatically regulated metal. For both cadmium and copper, local sources are probably more important than long-range sources. Zinc and copper was at higher level in livers of females than in males during the egg laying period. The concentrations of zinc and copper in livers were positively correlated.     

Mayfly larvae (Baetis rhodani and B. vernus) as biomonitors of trace metal pollution in streams of a catchment draining a zinc and lead mining area of Upper Silesia,Poland

Larvae of two Baetis species were used to investigate spatial and temporal variability in the bioavailabilities of cadmium, copper, lead, zinc and iron in the river Biala Przemsza and its tributaries draining an area of lead and zinc mining in Upper Silesia, Poland. Accumulated metal concentrations were measured in April, May, August and November 2000. Both species indicated significant local geographical variability in availabilities of zinc, iron, lead and cadmium, but not copper. Accumulated concentrations of lead, zinc and cadmium confirmed the high general contamination of the Biala Przemsza system by these three trace metals. Larvae showed little seasonal variation in concentrations of cadmium, copper, lead and iron. Accumulated zinc concentrations were low in Baetis rhodani in August, perhaps as a result of insufficient time for high concentrations to accumulate since hatching of the larvae. Samples collected in August most nearly matched criteria of the greatest availability of larvae for collection and their size homogeneity, minimising the possibilities of any effect of differential larval size and/or age on accumulated metal concentrations. Mayfly larvae are members of a suite of potential stream biomonitors in Central Europe, which together can provide information on the different sources of bioavailable trace metals present in aquatic ecosystems.     

Metal accumulation in soil arthropods in relation to micro-nutrients

Nine species of soil arthropod collected at two sites of different pollution levels were compared for concentrations of seven different elements (Ca, Cd, Cu, Fe, Mn, Pb, Zn) and correlations between the different elements were calculated. Significant effects of site on element concentrations of the animals were found for cadmium, iron, manganese and zinc, whereas calcium, copper and lead concentrations showed no significant difference between the sites. Significant differences between the species were found for all metal. The pattern of accumulation was comparable for some of the metals. Correlations were found between calcium, iron, manganese and lead concentrations and between zinc and cadmium concentrations of the species. No significant correlations were found for copper. The study showed that species can not be easily categorised as accumulators or non-accumulators; the pattern depends on the metal.     

The immobilisation and retention of soluble arsenic, cadmium and zinc by biochar

Water-soluble inorganic pollutants may constitute an environmental toxicity problem if their movement through soils and potential transfer to plants or groundwater is not arrested. The capability of biochar to immobilise and retain arsenic (As), cadmium (Cd) and zinc (Zn) from a multi-element contaminated sediment-derived soil was explored by a column leaching experiment and scanning electron microanalysis (SEM/EDX). Sorption of Cd and Zn to biochar’s surfaces assisted a 300 and 45-fold reduction in their leachate concentrations, respectively. Retention of both metals was not affected by considerable leaching of water-soluble carbon from biochar, and could not be reversed following subsequent leaching of the sorbant biochar with water at pH 5.5. Weakly water-soluble As was also retained on biochar’s surface but leachate concentrations did not duly decline. It is concluded that biochar can rapidly reduce the mobility of selected contaminants in this polluted soil system, with especially encouraging results for Cd.     

Ecological risk assessment of arsenic and metals in sediments of coastal areas of northern Bohai and Yellow Seas, China

Distributions of arsenic and metals in surface sediments collected from the coastal and estuarine areas of the northern Bohai and Yellow Seas, China, were investigated. An ecological risk assessment of arsenic and metals in the sediments was evaluated by three approaches: the Sediment Quality Guidelines (SQGs) of the United States Environmental Protection Agency (USEPA), the degree of contamination, and two sets of SQGs indices. Sediments from the estuaries of the Wuli and Yalu Rivers contained some of the greatest concentrations of arsenic, cadmium, copper, mercury, lead, and zinc. Median concentrations of cadmium and mean concentrations of lead and zinc were greater than background concentrations determined for the areas. All sediments were considered to be heavily polluted by arsenic, but moderately polluted by chromium, lead, and cadmium. Current concentrations of arsenic and metals are unlikely to be acutely toxic, but chronic exposures would be expected to cause adverse effects on benthic invertebrates at 31.4% of the sites.     

Transport modeling of copper and cadmium with linear and nonlinear retardation factors

The predictive accuracy of using the one-dimensional advection–dispersion equation to evaluate the fate and transport of solute in a soil column is usually dependent on the proper determination of chemical retardation factors. Typically, the distribution coefficient (K_d) obtained by fitting the linear sorption isotherm has been extensively used to consider general geochemical reactions on solute transport in a low-concentration range. However, the linear distribution coefficient cannot be adequately utilized to describe the solute fate at a higher concentration level. This study employed the nonlinear equilibrium-controlled sorption parameters to determine the retardation factor used in column leaching experiments. Copper and cadmium transportation in a lateritic silty-clay soil column was examined. Through the explicit finite-difference calculations with a third-order total-variation-diminishing (TVD) numerical solution scheme, all results of the theoretical copper and cadmium breakthrough curves (BTCs) simulated by using the Freundlich nonlinear retardation factors revealed good agreement with the experimental observations.     

纳米零价铁颗粒去除污染土壤HCl浸提液中的Pb

主要研究了纳米零价铁颗粒对土壤HCl浸提液中重金属Pb的去除效果。通过批实验探讨HCl浓度、纳米零价铁投入量以及处理时间对Pb去除率的影响。实验结果表明,纳米零价铁颗粒对浸提液中Pb的去除反应符合langmuir和freundlich等温吸附方程;反应遵循准一级反应动力学方程,标准化后的反应速率常数KSA=0.018 mL/(m2.min);反应30 min时,0.5 g纳米零价铁对1.0 mol/L的HCl所提取Pb(51.7 mg/L)的去除率达到91.8%。研究结果表明,纳米零价铁对土壤HCl浸提液中Pb具有良好去除效果,但相对于处理水溶液中的Pb,反应速率偏低。     

Seasonal variations in the concentrations of cadmium, copper, lead and zinc in leaves of the horse chesnut (Aesculus hippocastanum L.)

The concentrations of cadmium, copper, lead and zinc have been measured in the leaves of a deciduous tree the horse chestnut (Aesculus hippocastanum L.) over the period of their lifetime (7 months). The average concentrations for the total sample based on ash weight are: (microg g(-1)) cadmium, 0.197; copper, 129; lead, 294; and zinc, 299. The temporal trends in the concentrations of the metals can be related to their dominant source. Copper and zinc concentrations are highest in the new leaves and decrease with time, suggesting the main source of the elements are uptake from the soil. The decrease occurs partly because of dilution by leaf material as it increases over the growing period. In the case of zinc, however, aerial deposits appear to be also a significant source. Lead concentrations, on the other hand, show an increase with time, which can be related to increasing deposits from aerosol lead arising from the combustion of petrol lead. The increase is enough to offset the dilution effect. For cadmium there is no significant trend, but the tendency is a decrease with time. It is not possible, however, to distinguish between soil uptake and aerial deposit as both are small compared with increase in leaf material.     

Concentration of heavy metals in various children's herbal tea types and their correlations

This investigation was undertaken to determine the concentrations of cadmium, lead, mercury, zinc, copper and magnesium in six tea types used as children's tea. Six types of tea of different herbal composition used for children's consumption (T1, T2, T3, T4, T5 and T6) were analyzed in three subsequent collections. The analysis of cadmium showed that the concentration was very similar in all types of children's tea, ranging from 0.233 to 0.369 mg/kg. Lead concentrations were in the range of 0.340–1.564 mg/kg without any significant differences. The analysis of mercury detected very low concentration of this metal in all samples (0.002–0.004 mg/kg). In zinc, the values ranged from 36.633 to 71.711 mg/kg, with significant differences (p < 0.001) according to tea type. Copper concentration was 10.089–30.178 mg/kg with the highest value in T4. The concentration of magnesium was significantly higher in tea T1 and T2 (102.311 and 129.422 mg/kg) in comparison with other tea types where the level was 19.811–37.411 mg/kg. The maximum tolerable limit determined by Codex Alimentarius was not exceeded in any sample. In general, correlation analysis detected high positive correlation between cadmium and lead (r = 0.89), cadmium and mercury (r = 0.92) and between lead and mercury (r = 0.77).     

Influence of initial pH on bioleaching of heavy metals from contaminated soil employing indigenous Acidithiobacillus thiooxidans

Bioleaching of heavy metals from contaminated soil was carried out employing indigenous sulfur oxidizing bacterium Acidithiobacillus thiooxidans. Experiments were carried out to assess the influence of initial pH of the system on bioleaching of chromium, zinc, copper, lead and cadmium from metal contaminated soil. pH at the end of four weeks of bioleaching at different initial pH of 3-7 was between 0.9 and 1.3, ORP between 567 and 617mV and sulfate production was in the range of 6090-8418mgl(-1). Chromium, zinc, copper, lead and cadmium solubilization ranged from "59% to 98%" at different initial pH. A. thiooxidans was not affected by the increasing pH of the bioleaching system towards neutral and it was able to utilize elemental sulfur. The results of the present study are encouraging to develop the bioleaching process for decontamination of heavy metal contaminated soil.     

Metal accumulation in the earthworm Lumbricus rubellus. Model predictions compared to field data

The mechanistic bioaccumulation model OMEGA (Optimal Modeling for Ecotoxicological Applications) is used to estimate accumulation of zinc (Zn), copper (Cu), cadmium (Cd) and lead (Pb) in the earthworm Lumbricus rubellus. Our validation to field accumulation data shows that the model accurately predicts internal cadmium concentrations. In addition, our results show that internal metal concentrations in the earthworm are less than linearly (slope<1) related to the total concentration in soil, while risk assessment procedures often assume the biota-soil accumulation factor (BSAF) to be constant. Although predicted internal concentrations of all metals are generally within a factor 5 compared to field data, incorporation of regulation in the model is necessary to improve predictability of the essential metals such as zinc and copper.     

Biological nitrification/denitrification of high sodium nitrite (navy shipyard) wastewater

In the hydroblasting of ships' boiler tubes, a wastewater high in nitrite (as high as 1200 mg litre(-1)) is produced by the US Navy. This research has evaluated the use of a suspended-growth biological system to treat this wastewater by denitrification. Two biological treatment configurations were evaluated (direct denitrification versus nitrification/denitrification) with nitrification/denitrification producing better nitrite removal efficiencies (54 to 62% versus 40%, respectively). The introduction of metals (cadmium, chromium, lead, copper and iron) in concentrations typical for this wastewater did not inhibit the nitrite removal efficiencies. The influent metal concentrations ranged from 0.02 mg litre(-1) for cadmium to 22 mg litre(-1) for iron and the metal removal efficiencies ranged from 4.8% for cadmium to 50% for copper. Increasing sludge age resulted in improved nitrite removal efficiencies (52%, 57% and 74% for sludge ages of 4, 6 and 8 days, respectively). The resulting biokinetic constants were similar to those reported by others for lower influent concentrations of nitrite or nitrate (Ygs=0.02 mg/mg; Ygn=0.16 mg/mg; Yb=0.8 mg/mg; and b=0.006 h(-1)).     

Sorption-desorption of cadmium in aqueous palygorskite, sepiolite, and calcite suspensions: isotherm hysteresis

Sorption isotherms have been widely used to assess the heavy metal retention characteristics of soil particles. Desorption behavior of the retained metals, however, usually differ from that of sorption, leading to a lack of coincidence in the experimentally obtained sorption and desorption isotherms. In this study, we examine the nonsingularity of cadmium (Cd) sorption–desorption isotherms, to check the possible hysteresis and reversibility phenomena, in aqueous palygorskite, sepiolite and calcite systems. Sorption of Cd was carried out using a 24-h batch equilibration experiment with eight different Cd solution concentrations, equivalent to 20–100% of maximum sorption capacity of each mineral. Immediately after sorption, desorption took place using successive dilution method with five consecutive desorption steps. Both Cd sorption and desorption data were adequately described by Freundlich equation (0.81 < r² < 0.99). The sorption and desorption reactions, however, did not provide the same isotherms, indicating that hysteresis occurred in Cd sorption–desorption processes. The extent of hysteresis was quantified based on the differences obtained from sorption and desorption isotherms regarding the amount of Cd sorbed, the Freundlich exponent, and the Cd distribution coefficient. The results revealed that, sepiolite possessed the most hysteretic behavior among the minerals studied. Calcite showed much smaller hysteresis compared to the other two silicate clays at low Cd surface load, but its hysteresis indices significantly increased, and exceeded that of palygorskite, as the amount of Cd in the systems increased. The average amount of Cd released after five desorption steps, was 13.8%, 2.2% and 3.6% for the palygorskite, sepiolite and calcite, respectively, indicating that a large portion of Cd was irreversibly retained by the minerals.     

Performance evaluation of intermediate cover soil barrier for removal of heavy metals in landfill leachate

This pilot-scale study evaluated the use of intermediate cover soil barriers for removing heavy metals in leachate generated from test cells for co-disposed fly ash from municipal solid waste incinerators, ash melting plants, and shredder residue. Cover soil barriers were mixtures of Andisol (volcanic ash soil), waste iron powder, (grinder dust waste from iron foundries), and slag fragments. The cover soil barriers were installed in the test cells' bottom layer. Sorption/desorption is an important process in cover soil bottom barrier for removal of heavy metals in landfill leachate. Salt concentrations such as those of Na, K, and Ca in leachate were extremely high (often greater than 30 gL(-1)) because of high salt content in fly ash from ash melting plants. Concentrations of all heavy metals (nickel, manganese, copper, zinc, lead, and cadmium) in test cell leachates with a cover soil barrier were lower than those of the test cell without a cover soil barrier and were mostly below the discharge limit, probably because of dilution caused by the amount of leachate and heavy metal removal by the cover soil barrier. The cover soil barriers' heavy metal removal efficiency was calculated. About 50% of copper, nickel, and manganese were removed. About 20% of the zinc and boron were removed, but lead and cadmium were removed only slightly. Based on results of calculation of the Langelier saturation index and analyses of core samples, the reactivity of the cover soil barrier apparently decreases because of calcium carbonate precipitation on the cover soil barriers' surfaces.