Thermally induced changes in metal solubility of contaminated soils is linked to mineral recrystallization and organic matter transformations

Soils are biogeochemical systems under continual modification by biological and chemical processes. Trace element solid-solution partitioning is thus influenced by long-term changes to these solid phases. We study Pb, Cd, Zn, and Cu solution speciation and solid-phase dynamics in two soils of volcanic origin (Te Akatea and Egmont, high in noncrystalline aluminosilicates), an oxisol from Brazil (Oxisol, high in oxides of Al and Fe), and several sludge-treated soils (labeled NYS soils, high in organic materials). Total soluble (by ICP) and labile (by ASV) concentrations of Pb, Cd, Zn, and Cu were determined after incubation of the soils for about 1.5 yr at room (23 degrees C) and elevated (70 degrees C) temperatures. Changes occurring to the solid phases were monitored by FTIR and extraction with oxalate and pyrophosphate. It is shown that induced hydrolysis or decomposition of organic materials in soils results in increases in both labile and total soluble concentrations of Pb, Cd, Cu, and Zn in solution. Labile and total soluble concentrations of Cu and Zn increase concomitantly with dissolved organic carbon (DOC); the nonlabile soluble fraction also increases with increasing DOC. Similarly, the concentration of Cd and Pb in solution increases with increasing DOC; however, most soluble Cd and Pb is asv-labile. Only in the Egmont soil (mineralogy dominated by proto-imogolite allophane) was reduced Pb solubility observed after prolonged equilibration and heating. Lead solubility increased after partial crystallization of amorphous minerals in the Te Akatea and the Oxisol. Thus, for most of the metal-soil systems studied, prolonged thermal treatment at 70 degrees C increased total soluble and asv-labile metals, suggesting that aging effects on metals in contaminated soils could release metals to labile forms in some cases.     

The effect of storage of canned vegetables on concentration of the metals Fe, Cu, Zn, Pb, Sn, Al, Cd and Ni

The increase in the concentration of Fe, Cu, Zn, Pb, Sn, Al, Cd and Ni over a 2 year's time of strongly corrosive acidic vegetables (pickles) and weakly corrosive vegetables (peas, green beans, haricot beans, mushrooms) has been determined. The results show a considerable increase in Fe, Cu, Pb and Sn content with time, particularly for pickles, while the change in Al, Cd, Zn and Ni content was rather negligible.     

P, As, Sb, Mo, and other elements in sedimentary Fe/Mn layers of Lake Baikal

Distinct layers with accumulated iron and manganese oxyhydroxides are found in the recent sediments of Lake Baikal (Siberia). In the South and Central Basins, these concretions accumulate close to the sediment-water interface. In northern Lake Baikal and the area of Academician Ridge, however, massive Fe/Mn crusts are formed within several thousand years at redox fronts 10 to 15 cm below the sediment surface. In some places, precipitated iron and manganese oxyhydroxides are spatially separated. The patterns are a result of secondary iron and manganese oxide precipitation. This natural long-term experiment allows the analysis of competitive adsorption and coprecipitation of trace elements with iron and manganese oxides in sediments. Background concentrations in the sediment of oxoanions (P, As, Sb, Mo); of trace metals (Cr, V, Cu, Zn, Cd, Pb); and of Mg, Ca, Sr, La, Ce, Pr, Nd, and Sm were analyzed by inductively coupled plasma mass spectrometry. Despite the differences in catchment geology of the many tributaries, they are remarkably uniform in sediment cores from different basins of Lake Baikal. Enrichment factors of P and As within Fe crusts revealed concentrations up to 14 and 58 times higher than the background, respectively. No enrichment of P and As was found in the Mn layers. By contrast, Mo accumulated exclusively in the Mn layer with up to 35-fold enrichment. Sb was only slightly enriched in both the Fe and the Mn layers. Among the trace metals studied, only Cd was found at elevated concentrations with a preference for the Mn layer. Ca and Sr were correlated with both Fe and Mn accumulations. The study quantifies the well-known specific adsorption and coprecipitation of P and As at authigenic iron oxides and of Mo on manganese oxides. In addition, the enrichment of Cd at manganese oxides in contrast to the conservative behavior of Zn and Pb reveals highly selective accumulation processes.     

Interaction of tetracycline with aluminum and iron hydrous oxides

The effect of solution chemistry (pH, sorbate-to-sorbent ratio, ionic strength (/)) and reaction time on the sorption of tetracycline to the hydrous oxides of Al (HAO) and Fe (HFO) was examined. Sorption to HAO increased with increasing pH upto pH 7 (no such trend for HFO) above which it decreased at higher pH values for both the hydrous oxides. Experimental results indicate that ligand-promoted dissolution is occurring during tetracycline sorption to these hydrous oxides. Ligand-promoted dissolution was more significantfor HAO than HFO attributable to the difference in labile surface sites between these two sorbents. The ability of tetracycline to form strong complexes with Al and Fe will increase the solubility of these minerals. Sorption of tetracycline was quite rapid and equilibrium was achieved after 8 h. However, soluble metal (Me: Al or Fe) concentrations attained equilibrium only after 24 h. Ligand-promoted dissolution appears to be a two-step process; initially, 1:1 Me-tetracycline soluble complexes are formed and as the reaction progresses 2:1 complexes existed. Increasing / (from 0.01 to 0.5 M) decreased the sorption extent only at higher sorbate-to-sorbent ratios suggesting the dominance of inner-sphere type complexes at low equilibrium tetracycline concentrations. Spectroscopic evidence indicates that tricarbonylamide and carbonyl functional groups of tetracycline could be responsible for sorption to mineral surfaces. Our research findings will increase understanding of the environmental occurrence, fate, and transport characteristics of antibiotics, which are considered as emerging organic contaminants.     

Metal(loid) diagenesis in mine-impacted sediments of Lake Coeur d'Alene, Idaho

Mining activity along the South Fork of the Coeur d' Alene River in northern Idaho has resulted in fluvial mine tailings enriched in Pb, As, Ag, Sb, Hg, Cd, and Zn deposited on the lakebed of Lake Coeur d'Alene, thus serving as a potential benthic source of inorganic contaminants. Our objective was to characterize the dominant solid phase materials and diagenetic processes controlling metal(loid) solubilities, and thus their potential release to the overlying water column. Aqueous and solid concentrations of metal(loid) contaminants were examined along with distinct species of Fe and S within sediments and interstitial water. A gradient from oxic conditions at the sediment-water interface to anoxic conditions below 15 cm exists at all sites, resulting in a dynamic redox environment that controls the partitioning of contaminants. Fluvial deposition from frequent seasonal flood events bury ferric oxides residing at the sediment-water interface leading to reductive dissolution as they transition to the anoxic zone, consequently releasing associated metal(loids) to the interstitial water. Insufficient sulfur limits the formation of sulfidic minerals, but high carbonate content of this mining region buffers pH and promotes formation of siderite. Diagenetic reactions create chemical gradients encouraging the diffusion of metal(loids) toward the sediment--water interface, thereby, increasing the potential for release into the overlying water.     

Removal of cadmium from wastewaters by aragonite shells and the influence of other divalent cations

The effect of dissolved Zn, Co, Pb, Mg, and Ca on the uptake of cadmium by biogenic aragonite was investigated. Experiments were performed in batch-reactors using metal-cadmium-bearing solutions and shell fragments with diameters in different ranges, the solid/liquid ratio being 10 grams per liter. Different initial concentrations of cadmium and metals (1.0-0.005 mM) were used. Uptake takes place via heterogeneous nucleation of metal-bearing crystallites onto the shell surfaces. Cadmium removal occurs by surface precipitation of otavite. Under the conditions used here, Co and Ca as well as Pb < or = 0.3 mM and Zn < or = 0.3 mM do not have a significant effect on the removal of cadmium. At higher concentrations, Pb and Zn outcompete Cd for the dissolving carbonate ions and thus decrease significantly the Cd removal rates. In contrast, Mg has a slight enhancing effect. Pb and Zn are removed faster than Cd, precipitating as PbCO3, Pb3(CO3)2(OH)2, and Zn5(CO3)2(OH)6. Within 24-72 h, the concentrations of lead, cadmium, and zinc decrease until approximately 0.5 microM, and the presence of aragonite buffers the solution to a pH above 8 avoiding redissolution. The study demonstrates the high effectiveness of biogenic aragonite in removing Cd and other metals from polluted waters.     

Estimate of heavy metal contamination in soils after a mining accident using reflectance spectroscopy

The possibility to adapt chemometrics approaches for the quantitative estimation of heavy metals in soils polluted by a mining accident was explored. In April 1998, the dam of a mine tailings pond in Aznalcóllar (Spain) collapsed and flooded an area of more than 4000 ha with pyritic sludge contaminated with high concentrations of heavy metals. Six months after the end of the first remediation campaign, soil samples were collected for chemical analysis and measurement of visible to near-infrared reflectance (0.35-2.4 microm). Concentrations for As, Cd, Cu, Fe, Hg, Pb, S, Sb, and Zn were well above background values. Prediction of heavy metals was achieved by stepwise multiple linear regression analysis (MLR) and an artificial neural network (ANN) approach. It was possible to predict six out of nine elements with high accuracy. Best R2 between predicted and chemically analyzed concentrations were As, 0.84; Fe, 0.72; Hg, 0.96; Pb, 0.95; S, 0.87; and Sb, 0.93. Results for Cd (0.51), Cu (0.43), and Zn (0.24) were not significant. MLR and ANN both achieved similar results. Correlation analysis revealed that most wavelengths important for prediction could be attributed to absorptions features of iron and iron oxides. These results indicate that it is feasible to predict heavy metals in soils contaminated by mining residuals using the rapid and cost-effective reflectance spectroscopy.     

Observation of surface precipitation of arsenate on ferrihydrite

X-ray diffraction and Raman spectroscopy were used in this study to characterize arsenate phases in the arsenate-ferrihydrite sorption system. Evidence has been obtained for surface precipitation of ferric arsenate on synthetic ferrihydrite at acidic pH (3-5) underthe following experimental conditions: sorption density of As/Fe approximately 0.125-0.49 and arsenic equilibrium concentration of <0.02-440 mg/L. Surface precipitation occurred under apparently undersaturated (in the bulk solution phase) conditions, and probably involved initial uptake of arsenate by surface complexation followed by transition to ferric arsenate formation on the surface as indicated by XRD analysis. At basic pH (i.e., pH 8), however, no ferric arsenate was observed in arsenate-ferrihydrite samples at a sorption density of As/Fe approximately 0.125-0.30 and an arsenic equilibrium concentration of 2.0-1100 mg/ L. At pH 8, arsenate is sorbed on ferrihydrite predominantly via surface adsorption, and the XRD patterns resemble basically that of ferrihydrite.     

Simultaneous application of dissolution/precipitation and surface complexation/surface precipitation modeling to contaminant leaching

This paper discusses the modeling of anion and cation leaching from complex matrixes such as weathered steel slag. The novelty of the method is its simultaneous application of the theoretical models for solubility, competitive sorption, and surface precipitation phenomena to a complex system. Selective chemical extractions, pH dependent leaching experiments, and geochemical modeling were used to investigate the thermodynamic equilibrium of 12 ions (As, Ca, Cr, Ba, SO4, Mg, Cd, Cu, Mo, Pb, V, and Zn) with aqueous complexes, soluble solids, and sorptive surfaces in the presence of 12 background analytes (Al, Cl, Co, Fe, K, Mn, Na, Ni, Hg, NO3, CO3, and Ba). Modeling results show that surface complexation and surface precipitation reactions limit the aqueous concentrations of Cd, Zn, and Pb in an environment where Ca, Mg, Si, and CO3 dissolve from soluble solids and compete for sorption sites. The leaching of SO4, Cr, As, Si, Ca, and Mg appears to be controlled by corresponding soluble solids.     

Modeling of microbial dynamics and geochemical changes in a metal bioprecipitation experiment

A biogeochemical transport modeling study was carried out to analyze large-scale laboratory column experiments in which ethanol was used as an electron donor to create favorable conditions for the immobilization of selected trace metals (Zn and Cu) in groundwater. Microbial activity was explicitly simulated to capture the dynamic changes of the redox zonation within the column (i) in the early phase of the experiment (microbial lag) and (ii) in response to a significant decrease in the pH of the feed solution introduced after 188 days. The simulated redox dynamics agreed well with the observations after the pH-dependency of microbial growth was incorporated into the microbial model. The study showed that residual minerals may have buffered the pH for a period after the pH of the feed solution was decreased. Where the buffering capacity was exhausted, the pH decreased, leading to a successive downstream movement of the redox boundaries. The simulations reproduced the Zn immobilization within the sulfate-reducing zone as well as its partial remobilization after this zone moved further downstream. The immobilization of Cu within the denitrifying zone could also be well explained by incorporating malachite (Cu2(OH)2CO3) precipitation in the simulations.     

岩藻聚糖中重金属元素脱除方法的研究

研究采用螯合剂及超滤技术脱除岩藻聚糖中重金属元素的方法。在提取岩藻聚糖工艺中添加不同浓度的EDTA 二钠和植酸溶液,对所制备的岩藻聚糖采用电感耦合等离子体- 质谱技术(ICP-MS)及氢化物- 原子荧光光谱法(HGAFS)检测其Mg、Ca、Fe、Mn、Cu、Zn、Ag、Cd、Ba、Pb、As、Hg 元素的含量。研究表明,在提取工艺中加入1.0 × 10-2mol/L EDTA 二钠可以有效地降低岩藻聚糖中Mg、Ca、Mn、Zn、As、Ag、Cd、Pb等元素的残留量,但没有减少Hg、Fe、Cu、Ba 元素的残留量;而提取工艺中加入0.10mol/L 植酸仅对减少Ag、Cd 和Zn 元素的残留量有一定的效果。通过对岩藻聚糖进行As、Hg 富集处理,研究在酸处理后采用超滤脱除重金属元素的效果,结果表明,各实验组均未检出As 元素,但对Hg 元素没有效果。因此,在提取岩藻聚糖的工艺中添加一定浓度的EDTA 二钠或在纯化过程中经酸处理后采用超滤脱除技术均可显著减少岩藻聚糖制品中重金属元素的残留量,从而制备高质量的岩藻聚糖。     

Characterization of zinc, lead, and cadmium in mine waste: implications for transport, exposure, and bioavailability

We characterized the lability and bioaccessibility of Zn, Pb, and Cd in size-fractionated mine waste at the Tar Creek Superfund Site (Oklahoma) to assess the potential for metal transport, exposure, and subsequent bioavailability. Bulk mine waste samples contained elevated Zn (9100 +/- 2500 ppm), Pb (650 +/- 360 ppm), and Cd (42 +/- 10 ppm), while particles with the greatest potential for windborne transport and inhalation (< 10 microm) contained substantially higher concentrations, up to 220 000 ppm Zn, 16 000 ppm Pb, and 530 ppm Cd in particles < 1 microm. Although the mined ore at Tar Creek primarily consisted of refractory metal sulfides with low bioavailability, sequential extractions and physiologically based extractions indicate that physical and chemical weathering have shifted metals into relatively labile and bioaccessible mineral phases. In < 37 microm mine waste particles, 50-65% of Zn, Pb, and Cd were present in the "exchangeable" and "carbonate" sequential extraction fractions, and 60-80% of Zn, Pb, and Cd were mobilized in synthetic gastric fluid, while ZnS and PbS exhibited minimal solubility in these solutions. Our results demonstrate the importance of site-specific characterization of size-fractionated contemporary mine waste when assessing the lability and bioavailability of metals at mine-waste impacted sites.     

Bioaccessibility of metals in dust from the indoor environment: application of a physiologically based extraction test

A physiologically based extraction test, simulating sequential digestion in the stomach and intestine, has been applied to dust samples collected from various domestic and working settings to define bioaccessible concentrations of metals (Al, Ca, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sn, U, Zn) in the indoor environment. With the exception of Ca, Cd, and Zn in the stomach phase, mean bioaccessibilities (relative to respective total metal concentrations) were less than 50%. For a given metal, bioaccessibility in either phase was variable among samples but, in many cases, displayed an inverse dependence on total concentration. This suggests that, to a good approximation, variations in both metal contamination and accessibility in the indoor environment arise from variable proportions of metal-rich particulates of low digestibility. Compared with accessibility in the stomach, accessibility in the more alkaline, carbonate-rich intestine was either lower (Al, Ca, Cd, Mn, Ni, Sn, Pb, Zn), similar (Co, Cu, Fe) or greater (Cr, U). We attribute these observations to precipitation and/or readsorption in the intestine, stabilization by complexation, or anion-like adsorption of negatively charged, polyatomic species, respectively.     

Heavy metal levels in leafy vegetables and some selected fruits

The aim of this study was to determine the levels of Cu, Zn, Fe, Pb and Cd in various fruits (tomato, cherry, grape, strawberry) and vegetables (parsley, onion, lettuce, garlic, nettle, peppermint, rocket, spinach, dill, broad bean, chard, purslane, grapevine leaves) grown in Manisa region. Flame and Graphite Furnace Atomic absorption spectrometry was used to estimate and evaluate the levels of these metals. Detected levels ranged from 0.56 to 329.7, 0.01 to 5.67, 0.26 to 30.68, 0.001 to 0.97 and 0 to 0.06 μg/g for Fe, Cu, Zn, Pb and Cd, respectively. While the highest mean levels of Cu and Zn were detected in grapevine leaves, the lowest mean levels of Fe and Pb were detected in nettle. Cd was not detected in most of the fruits and vegetables studied. The estimated daily intakes of Cu, Zn, Fe, Pb and Cd through fruits and vegetables were found to be below the maximum tolerable levels recommended by FAO/WHO. The element concentrations of fruits and vegetables analyzed in this study were within safety baseline levels for human consumption.     

Heavy metal levels in leafy vegetables and some selected fruits

The aim of this study was to determine the levels of Cu, Zn, Fe, Pb and Cd in various fruits (tomato, cherry, grape, strawberry) and vegetables (parsley, onion, lettuce, garlic, nettle, peppermint, rocket, spinach, dill, broad bean, chard, purslane, grapevine leaves) grown in Manisa region. Flame and Graphite Furnace Atomic absorption spectrometry was used to estimate and evaluate the levels of these metals. Detected levels ranged from 0.56 to 329.7, 0.01 to 5.67, 0.26 to 30.68, 0.001 to 0.97 and 0 to 0.06 μg/g for Fe, Cu, Zn, Pb and Cd, respectively. While the highest mean levels of Cu and Zn were detected in grapevine leaves, the lowest mean levels of Fe and Pb were detected in nettle. Cd was not detected in most of the fruits and vegetables studied. The estimated daily intakes of Cu, Zn, Fe, Pb and Cd through fruits and vegetables were found to be below the maximum tolerable levels recommended by FAO/WHO. The element concentrations of fruits and vegetables analyzed in this study were within safety baseline levels for human consumption.     

pH dependence of Fenton reagent generation and As(III) oxidation and removal by corrosion of zero valent iron in aerated water

Corrosion of zerovalent iron (ZVI) in oxygen-containing water produces reactive intermediates that can oxidize various organic and inorganic compounds. We investigated the kinetics and mechanism of Fenton reagent generation and As(III) oxidation and removal by ZVI (0.1m2/g) from pH 3-11 in aerated water. Observed half-lives for the oxidation of initially 500 microg/L As(III) by 150 mg Fe(0)/L were 26-80 min at pH 3-9. At pH 11, no As(III) oxidation was observed during the first two hours. Dissolved Fe(III) reached 325, 140, and 6 microM at pH 3, 5, and 7. H2O2 concentrations peaked within 10 min at 1.2, 0.4, and < 0.1 microM at pH 3, 5, and 7, and then decreased to undetectable levels. Addition of 2,2'-bipyridine (1-3 mM), prevented Fe(II) oxidation by O2 and H2O2 and inhibited As(III)oxidation. 2-propanol (14 mM), scavenging OH-radicals, quenched the As(III) oxidation at pH 3, but had almost no effect at pH 5 and 7. Experimental data and kinetic modeling suggest that As(III) was oxidized mainly in solution by the Fenton reaction and removed by sorption on newly formed hydrous ferric oxides. OH-radials are the main oxidant for As(III) at low pH, whereas a more selective oxidant oxidizes As(III) at circumneutral pH.     

Heavy metal content in different types of smoked meat in Serbia

Concentrations of Fe, Cu, Ni, Cr, Pb, Mn, Zn and Cd in pork, beef, turkey and chicken samples were determined using inductively coupled plasma-optical emission spectrometry (ICP-OES). The mean concentration ranges in milligrams per 100?g of the studied metals in all samples were 0.6924–1.2154 for Fe, 0.6492–0.9831 for Cu, 0.0012–0.0027 for Pb, 0.041–0.0510 for Ni, 0.1186–0.1481 for Mn, 0.7257–5.2726 for Zn and 0.0042–0.0050 for Cd. The levels of analysed elements were in accordance with European standards for all metals except for manganese in all samples and for nickel in a certain number of samples. Zn level in beef was significantly higher compared to other samples, and Pb and Cd were found in concentrations well below the recommended daily intake.     

The effect of natrojarosite addition to mine tailings

An increasingly common practice for metallurgical plants is to discard their wastes by combining them with mine tailings prior to disposing the blended material to a containment facility. This practice has occurred since 1985 at the Kidd Creek tailings impoundment where natrojarosite, a waste produced from the adjacent Zn refinery, is combined with mine tailings and is deposited in a single impoundment. To assess the environmental impact of the co-disposal, a laboratory column experiment was conducted. The column material was flotation tailings from the Kidd Creek site containing 3 wt % natrojarosite residue. Dilute sulfuric acid was passed through the column to simulate the acid generated in the unsaturated zone of the tailings impoundment. The results of this experiment were compared to the results of a previous experiment conducted on unamended flotation tailings. The results showed that the effluent from the column containing the natrojarosite-bearing mixture had a faster decrease in pH, earlier increases in the concentrations of dissolved metals such as Pb and Cd, and a greater persistence in effluent metal concentrations such as Pb, Zn and Ni. To prevent the observed enhanced release of dissolved metals from mine waste disposal areas, natrojarosite should not be co-disposed with tailings.     

Market Survey and Risk Assessment for Trace Metals in Edible Fungi and the Substrate Role in Accumulation of Heavy Metals

Levels of cadmium (Cd), arsenic (As), mercury (Hg), lead (Pb), iron (Fe), and zinc (Zn) were investigated in 285 samples of 9 species of edible fungi (Lentinus edodes, Auricularia auricula, Pleurotus ostreatus, Tremella fuciformis, Flammulina velutipes, Agrocybe chaxinggu, Armillaria mellea, Agaricus bisporus, and Pholiota nameko), which were collected from markets in Beijing, China. In addition, edible fungi and culture substrates were collected from 7 cultivation bases to examine the role of the substrate in trace metal accumulation. Trace metal concentrations were determined on a dry weight basis. Data showed that all the edible fungi contained trace metals, the levels of which varied among species, and there were significant positive correlations between trace metal (Cd, Pb, and As) concentrations in mushrooms and their substrates. The concentrations of Cd, As, Hg, Pb, Fe, and Zn in the tested fungi ranged from 0.005 to 13.8 mg/kg, nd to 1.62 mg/kg, nd to 0.506 mg/kg, 0.011 to 22.1 mg/kg, 46.3 to 2514 mg/kg, and 14.6 to 289 mg/kg, respectively. In general, concentrations of Cd, As, Hg, Pb, Fe, and Zn were relatively high in L. edodes, whereas Tremella fuciformis and P. nameko had relatively low levels of trace metals. Furthermore, the estimated weekly intake of trace metals was calculated and compared with the WHO/FAO provisional tolerable weekly intake. The estimated weekly intake of Cd, As, Hg, Pb, Fe, and Zn from consuming edible fungi was lower than the provisional tolerable weekly intake.