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Dissolved Metals (dissolved + metal)
Selected AbstractsMethods for determining labile cadmium and zinc in soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2000S. D. Young Summary Isotopically exchangeable cadmium and zinc (,E values') were measured on soils historically contaminated by sewage sludge and ones on zinc-rich mine spoil. The E -value assay involves determining the distribution of an added metal isotope, e.g. 109Cd, between the solid and solution phases of a soil suspension. The E values for both metals were found to be robust to changes in the position of the metal solid,solution equilibrium, even though the concentration of dissolved metal varied substantially with electrolyte composition and soil:solution ratio. Concentration of labile metal was also invariant over isotope equilibration times of 2,6 days. The use of a submicron filtration procedure, in addition to centrifuging at 2200 g, proved unnecessary if 0.1 m Ca electrolyte was used to suspend the soils. The proportion of ,fixed' metal, in non-labile forms, apparently increased with increasing pH, although there was considerable variation in both sets of contaminated soil. Zinc and cadmium in the sludged soils were similarly labile. Several possible methods for the measurement of chemically reactive metal were explored for comparison with E values, including single extraction with 1 m CaCl2 and a ,pool depletion' (PD) method. The latter involves comparing solid,solution metal equilibria in two electrolytes with differing degrees of (solution) complex formation, 0.1 m Ca(NO3)2 and CaCl2. Both the single extraction and the PD method gave good estimates of E value for Cd, although the single extraction was more consistent. Neither technique was a useful substitute for determining labile Zn, because of weak chloro-complexation of Zn2+. We therefore suggest that 1 m CaCl2 extraction of Cd alone be used as an alternative to E values to avoid the inconvenience of isotopic dilution procedures. [source] Treatment of Process Water Containing Heavy Metals with a Two-Stage Electrolysis Procedure in a Membrane Electrolysis CellENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 2 2005R. Fischer Abstract The capability of a two-stage electrochemical treatment for the regeneration of acidic heavy-metal containing process water was examined. The process water came from sediment bioleaching and was characterized by a wide spectrum of dissolved metals, a high sulfate content, and a pH of about 3. In the modular laboratory model cell used, the anode chamber and the cathode chamber were separated by a central chamber fitted with an ion exchanger membrane on either side. The experiments were carried out applying a platinum anode and a graphite cathode at a current density of 0.1,A/cm2. The circulation flow of the process water in the batch process amounted to 35,L/h, the electrolysis duration was 5.5,h at maximum and the total electrolysis current was about 1,A. In the first stage, the acidic process water containing metals passed through the cathode chamber. In the second stage, the cathodically pretreated process water was electrolyzed anodically. In the cathode chamber the main load of dissolved Cu, Zn, Cr and Pb was eliminated. The sulfuric acid surplus of 3,4,g/L decreased to about 1,g/L, the pH rose from initially 3.0 to 4,5, but the desired pH of 9,10 was not achieved. Precipitation in the proximity to the cathode evidently takes place at a higher pH than farther away. The dominant process in the anode chamber was the precipitation of amorphous MnO2 owing to the oxidation of dissolved Mn(II). The further depletion of the remaining heavy metals in the cathodically pretreated process water by subsequent anodic treatment was nearly exhaustive, more than 99,% of Cd, Cr, Cu, Mn, Ni, Pb, and Zn were removed from the leachate. The high depletion of heavy metals might be due to both the sorption on MnO2 precipitates and/or basic ferrous sulfate formed anodically, and the migration of metal ions through the cation exchanger membrane via the middle chamber into the cathode chamber. In the anode chamber, the sulfuric acid content increased to 6,7,g/L and the pH sank to 1.7. All heavy metals contained, with the exception of Zn, were removed to levels below the German limits for discharging industrial wastewaters into the receiving water. Moreover, the metal-depleted and acid-enriched process waters could be returned to the leaching process, hence reducing the output of wastewater. The results indicated that heavy metals could be removed from acidic process waters by two-stage electrochemical treatment to a large extent. However, to improve the efficiency of metal removal and to establish the electrochemical treatment in practice, further work is necessary to optimize the operation of the process with respect to current density, energy consumption, discharging of metal precipitates deposited in the electrode chambers and preventing membrane clogging. [source] Evaluation of sorbent amendments for in situ remediation of metal-contaminated sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2010Seokjoon Kwon Abstract The present study evaluated sorbent amendments for in situ remediation of sediments contaminated with two divalent metals. A literature review screening was performed to identify low-cost natural mineral-based metal sorbents and high-performance commercial sorbents that were carried forward into laboratory experiments. Aqueous phase metal sorptivity of the selected sorbents was evaluated because dissolved metals in sediment porewater constitute an important route of exposure to benthic organisms. Based on pH-edge sorption test results, natural sorbents were eliminated due to inferior performance. The potential as in situ sediment amendment was explored by comparing the sorption properties of the engineered amendments in freshwater and saltwater (10 PPT salinity estuarine water) matrices. Self-assembled monolayers on mesoporous supports with thiols (Thiol-SAMMSÔ) and a titanosilicate mineral (ATSÔ) demonstrated the highest sorption capacity for cadmium (Cd) and lead (Pb), respectively. Sequential extraction tests conducted after mixing engineered sorbents with contaminated sediment demonstrated transfer of metal contaminants from a weakly bound state to a more strongly bound state. Biouptake of Cd in a freshwater oligochaete was reduced by 98% after 5-d contact of sediment with 4% Thiol-SAMMS and sorbed Cd was not bioavailable. While treatment with ATS reduced the small easily extractable portion of Pb in the sediment, the change in biouptake of Pb was not significant because most of the native lead was strongly bound. The selected sorbents added to sediments at a dose of 5% were mostly nontoxic to a range of sensitive freshwater and estuarine benthic organisms. Metal sorbent amendments in conjunction with activated carbon have the potential to simultaneously reduce metal and hydrophobic contaminant bioavailability in sediments. Environ. Toxicol. Chem. 2010;29:1883,1892. © 2010 SETAC [source] Trout density and health in a stream with variable water temperatures and trace element concentrations: Does a cold-water source attract trout to increased metal exposure?ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2009David D. Harper Abstract A history of hard-rock mining has resulted in elevated concentrations of heavy metals in Prickly Pear Creek (MT, USA). Remediation has improved water quality; however, dissolved zinc and cadmium concentrations still exceed U.S. Environmental Protection Agency water-quality criteria. Physical habitat, salmonid density, fish health, and water quality were assessed, and metal concentrations in fish tissues, biofilm, and macroinvertebrates were determined to evaluate the existing condition in the watershed. Cadmium, zinc, and lead concentrations in fish tissues, biofilm, and invertebrates were significantly greater than those at the upstream reference site and an experimental site farther downstream of the confluence. Fish densities were greatest, and habitat quality for trout was better, downstream of the confluence, where water temperatures were relatively cool (16°C). Measures of fish health (tissue metal residues, histology, metallothionein concentrations, and necropsies), however, indicate that the health of trout at this site was negatively affected. Trout were in colder but more contaminated water and were subjected to increased trace element exposures and associated health effects. Maximum water temperatures in Prickly Pear Creek were significantly lower directly below Spring Creek (16°C) compared to those at an experimental site 10 km downstream (26°C). Trout will avoid dissolved metals at concentrations below those measured in Prickly Pear Creek; however, our results suggest that the preference of trout to use cool water temperatures may supersede behaviors to avoid heavy metals. [source] Acute toxicity of heavy metals to acetate-utilizing mixed cultures of sulfate-reducing bacteria: EC100 and EC50ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2001Vivek P. Utgikar Abstract Acid mine drainage from abandoned mines and acid mine pit lakes is an important environmental concern and usually contains appreciable concentrations of heavy metals. Because sulfate-reducing bacteria (SRB) are involved in the treatment of acid mine drainage, knowledge of acute metal toxicity levels for SRB is essential for the proper functioning of the treatment system for acid mine drainage. Quantification of heavy metal toxicity to mixed cultures of SRB is complicated by the confounding effects of metal hydroxide and sulfide precipitation, biosorption, and complexation with the constituents of the reaction matrix. The objective of this paper was to demonstrate that measurements of dissolved metal concentrations could be used to determine the toxicity parameters for mixed cultures of sulfate-reducing bacteria. The effective concentration, 100% (EC100), the lowest initial dissolved metal concentrations at which no sulfate reduction is observed, and the effective concentration, 50% (EC50), the initial dissolved metal concentrations resulting in a 50% decrease in sulfate reduction, for copper and zinc were determined in the present study by means of nondestructive, rapid physical and chemical analytical techniques. The reaction medium used in the experiments was designed specifically (in terms of pH and chemical composition) to provide the nutrients necessary for the sulfidogenic activity of the SRB and to preclude chemical precipitation of the metals under investigation. The toxicity-mitigating effects of biosorption of dissolved metals were also quantified. Anaerobic Hungate tubes were set up (at least in triplicate) and monitored for sulfate-reduction activity. The onset of SRB activity was detected by the blackening of the reaction mixture because of formation of insoluble ferrous sulfide. The EC100 values were found to be 12 mg/L for copper and 20 mg/L for zinc. The dissolved metal concentration measurements were effective as the indicators of the effect of the heavy metals at concentrations below EC100. The 7-d EC50 values obtained from the difference between the dissolved metal concentrations for the control tubes (tubes not containing copper or zinc) and tubes containing metals were found to be 10.5 mg/L for copper and 16.5 mg/L for zinc. Measurements of the turbidity and pH, bacterial population estimations by means of a most-probable number technique, and metal recovery in the sulfide precipitate were found to have only a limited applicability in these determinations. [source] Partitioning of metals (Cd, Co, Cu, Ni, Pb, Zn) in soils: concepts, methodologies, prediction and applications , a reviewEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2009F. Degryse Summary Prediction of the fate of metals in soil requires knowledge of their solid,liquid partitioning. This paper reviews analytical methods and models for measuring or predicting the solid,liquid partitioning of metals in aerobic soils, and collates experimental data. The partitioning is often expressed with an empirical distribution coefficient or Kd, which gives the ratio of the concentration in the solid phase to that in the solution phase. The Kd value of a metal reflects the net effect of various reactions in the solid and liquid phases and varies by orders of magnitude among soils. The Kd value can be derived from the solid,liquid distribution of added metal or that of the soil-borne metal. Only part of the solid-phase metal is rapidly exchangeable with the solution phase. Various methods have been developed to quantify this ,labile' phase, and Kd values based on this phase often correlate better with soil properties than Kd values based on total concentration, and are more appropriate to express metal ion buffering in solute transport models. The in situ soil solution is the preferred solution phase for Kd determinations. Alternatively, water or dilute-salt extracts can be used, but these may underestimate in situ concentrations of dissolved metals because of dilution of metal-complexing ligands such as dissolved organic matter. Multi-surface models and empirical models have been proposed to predict metal partitioning from soil properties. Though soil pH is the most important soil property determining the retention of the free metal ion, Kd values based on total dissolved metal in solution may show little pH dependence for metal ions that have strong affinity for dissolved organic matter. The Kd coefficient is used as an equilibrium constant in risk assessment models. However, slow dissociation of metal complexes in solution and slow exchange of metals between labile and non-labile pools in the solid phase may invalidate this equilibrium assumption. [source] Heavy metal concentrations during storm events in a rehabilitated industrialized catchmentHYDROLOGICAL PROCESSES, Issue 10 2003W. H. Blake Abstract Water quality data collected on a fortnightly or monthly basis are inadequate for assessment and modelling of many water quality problems as storm event samples are underrepresented or missed. This paper examines the stormflow dynamics of heavy metals (Pb, Cu, Cd and Zn) in the Nant-y-Fendrod stream, South Wales, which has been affected by 250 years of metal smelting, followed by 35 years of landscape rehabilitation measures. For storm events of contrasting (very dry and very wet) antecedent conditions in May 2000 and February 2001, respectively, temporal changes in streamwater heavy metal concentrations above and below an in-line flood detention lake are analysed. At the upstream site, peaks in total metal concentration were recorded on the rising limb for Pb (0·150 mg l,1) and Cu (0·038 mg l,1) but on the falling limb for Zn (1·660 mg l,1) and Cd (0·006 mg l,1) in the summer 2000 storm event, yielding clockwise and anticlockwise hysteretic loops respectively. In contrast, metal concentrations, although high throughout the winter storm event, were diluted somewhat during the storm peak itself. The Pb and Cu appear to be supplied by quickflow processes and transported in close association with fine sediment, whereas Zn and Cd are delivered to the channel and lake by slower subsurface seepage in dissolved form. In the winter 2001 event, antecedent soil moisture and shallow groundwater levels were anomalously high and seepage sources of dissolved metals dominated. Downstream of the lake, Pb and Cu levels and suspended sediment were high in the summer storm, but low in the winter storm, suggesting retention with deposition of fine sediment in the lake during the latter. In the winter storm, Zn and Cd levels were higher downstream than upstream of the lake, perhaps because of additional seepage inputs from the surrounding slopes, which failed to have an impact during summer. An understanding of the complex interplay of antecedent soil moisture and the dynamics of subsurface seepage pathways in relation to the three-dimensional distribution of sources is important in modelling heavy metal fluxes and levels in contaminated urban catchments. Copyright © 2003 John Wiley & Sons, Ltd. [source] 59 Utility of the periphyton index of biotic integrity (PIBI) as an indicator of acid mine drainage impacts in southeastern ohioJOURNAL OF PHYCOLOGY, Issue 2003S. E. Hamsher In the Appalachian region, numerous streams are polluted with acid mine drainage (AMD). These waters are sulfate-rich with elevated amounts of total acidity, low pH, and high levels of dissolved metals. Biotic multimetric indices, such as the Periphyton Index of Biotic Integrity (PIBI) have been employed to determine water quality across a variety of environmental conditions and may prove useful for AMD impacts. This study was initiated (1) to evaluate the PIBI for distinguishing AMD impact in streams and (2) to examine whether PIBI scores are impacted by seasonal differences. Twelve AMD and three reference streams were sampled for periphyton in June, August, and October. Water chemistry was collected at least once during the sampling period. Preliminary results showed that PIBI scores were significantly different (p<0.05) among the seasons. In addition, the seasonal trends in PIBI scores among streams were not consistent. The PIBI scores were correlated with six water chemistry variables in August and with at least one variable indicative of AMD in each season sampled. PCA and UPGMA analyses of water chemistry data grouped the streams into five categories: (1) moderately impacted AMD streams with lower total dissolved solids, sulfate, total aluminum, and alkalinity, and higher sulfate; (2) AMD streams with higher alkalinity and lower total aluminum; (3) AMD streams with lower alkalinity and higher total aluminum; (4) reference streams and (5) an outlier reference stream affected by nutrients. Relationships between the groups based on water chemistry and the groups derived from the PIBI will be discussed. [source] BIOREMEDIATIVE POTENTIAL OF CHROMULINA FREIBURGENSIS IN CULTURE FROM THE BERKELEY PITJOURNAL OF PHYCOLOGY, Issue 2001Article first published online: 24 SEP 200 Dakel, S. M.1 & Mitman, G. G.2 1Department of Environmental Engineering; 2Department of Biological Sciences, Montana Tech of The University of Montana, Butte, MT 59701 USA The Berkeley Pit, part of the largest Superfund site in the United States, is an open-pit copper mine that operated from 1955 through 1982. Today, the Berkeley Pit contains approximately 1200 billion liters of metal laden water with an average pH of 2.7, and 12 grams/liter of dissolved solids. The principle dissolved ions include aluminum, arsenic, calcium, cadmium, copper, iron, potassium, magnesium, manganese, sulfates, and zinc. A species from Division Chrysophyta,Chromulina freiburgensis Dofl. was isolated from this extreme environment. This species has been tested in the laboratory through a series of controlled experiments to determine bioremediative potential. Optimal temperature was determined by monitoring growth with cell counts at temperatures ranging from 5°C to 40°C . The optimal nutrient ratio was determined by varying nitrogen (NaNO3) and phosphorus (Na2HPO4) levels. An experimental matrix varying nutrients was developed to test for bioremediative potential which included: initial and final pH measurements; initial and final Ion Chromatography Pairing,Atomic Emission Spectrometry (ICP-AES) for dissolved metals; and examination of final samples under Transmission Electron Microscopy (TEM). From these experiments, Chromulina freiburgensis was found to grow optimally in Berkeley Pit surface water with cell densities reaching ten million cells per milliliter at 10°C with additions of 50 mg NaNO3/L and 5 mg Na2HPO4/L. This large biomass was also found to increase diversity and abundance of heterotrophs. At the optimal nutrient level, this species was found to increase pH from 2.21 to 2.47 over 90 days. Significant removal of calcium, iron, nickel, and silica was observed. [source] Remedial options for chlorinated volatile organics in a partially anaerobic aquiferREMEDIATION, Issue 4 2004Xiujin Qiu A laboratory study was conducted for the selection of appropriate remedial technologies for a partially anaerobic aquifer contaminated with chlorinated volatile organics (VOCs). Evaluation of in situ bioremediation demonstrated that the addition of electron donors to anaerobic microcosms enhanced biological reductive dechlorination of tetrachloroethene (PCE), trichloroethene (TCE), and 1,1,1-trichloroethane (1,1,1-TCA) with half-lives of 20, 22, and 41 days, respectively. Nearly complete reductions of PCE, TCE, 1,1,1-TCA, and the derivative cis-dichloroethene were accompanied by a corresponding increase in chloride concentrations. Accumulation of vinyl chloride, ethene, and ethane was not observed; however, elevated levels of 14CO2 (from 14C-TCE spiked) were recovered, indicating the occurrence of anaerobic oxidation. In contrast, very little degradation of 1,2-dichloropropane (1,2-DCP) and 1,1-dichlorethane (1,1-DCA) was observed in the anaerobic microcosms, but nutrient addition enhanced their degradation in the aerobic biotic microcosms. The aerobic degradation half-lives for 1,2-DCP and 1,1-DCA were 63 and 56 days, respectively. Evaluation of in situ chemical oxidation (ISCO) demonstrated that chelate-modified Fenton's reagent was effective in degrading aqueous-phase PCE, TCE, 1,1,1-TCA, 1,2-DCP, etc.; however, this approach had minimal effects on solid-phase contaminants. The observed oxidant demand was 16 g-H2O2/L-groundwater. The oxidation reaction rates were not highly sensitive to the molar ratio of H2O2:Fe2+:citrate. A ratio of 60:1:1 resulted in slightly faster removal of chemicals of concern (COCs) than those of 12:1:1 and 300:1:1. This treatment resulted in increases in dissolved metals (Ca, Cr, Mg, K, and Mn) and a minor increase of vinyl chloride. Treatment with zero-valent iron (ZVI) resulted in complete dechlorination of PCE, and TCE to ethene and ethane. ZVI treatment reduced 1,1,1-TCA only to 1,1-DCA and chloroethane (CA) but had little effect on reducing the levels of 1,2-DCP, 1,1-DCA, and CA. The longevity test showed that one gram of 325-mesh iron powder was exhausted in reaction with > 22 mL of groundwater. The short life of ZVI may be a barrier to implementation. The ZVI surface reaction rates (ksa) were 1.2 × 10,2 Lm,2h,1, 2 × 10,3 Lm,2h,1, and 1.2 × 10,3 Lm,2h,1 for 1,1,1-TCA, TCE, and PCE, respectively. Based upon the results of this study, in situ bioremediation appeared to be more suitable than ISCO and ZVI for effectively treating the groundwater contamination at the site. © 2004 Wiley Periodicals, Inc. [source] | |||||||||||||