Characterization and preliminary assessment of a sorbent produced by accelerated mineral carbonation

This study shows that calcium silicate/aluminate-based materials can be carbonated to produce sorbents for metal removal. The material chosen for investigation, cement clinker, was accelerated carbonated, and its structural properties were investigated using X-ray diffraction (XRD), scanning electron microscopy, thermal gravimetric and differential thermal analysis, nuclear magnetic resonance spectroscopy, and nitrogen gas adsorption techniques. The principal carbonation reactions involved the transformation of dicalcium silicate, tricalcium silicate, and tricalcium aluminate into a Ca/Al-modified amorphous silica and calcium carbonate. It was found that carbonated cement had high acid buffering capacity, and maintained its structural integrity within a wide pH range. The uptake of Pb(II), Cd(II), Zn(II), Ni(II), Cr(II), Sr(II), Mo(VI), Cs(II), Co(II), and Cu(II) from concentrated (1000 mg L(-1)) single-metal solutions varied from 35 to 170 mg g(-1) of the carbonate cement. The removal of metals was hardly effected by the initial solution pH due to the buffering capability of the carbonated material. The kinetics of Pb, Cd, Cr, Sr, Cs, and Co removal followed a pseudo-second-order kinetic model, whereas the equilibrium batch data for Cu fitted the pseudo-first-order rate equation. PHREEQC simulation supported by XRD analysis suggested the formation of metal carbonates and silicates, calcium molybdate, and chromium (hydro)oxide. Cesium was likely to be adsorbed by Ca/Al-modified amorphous silica.     

北京市售大米重金属含量监测及膳食风险评估

监测市售大米重金属含量,为北京市食品安全风险评估提供参考和数据支撑,采集了市售大米样品537件,分析其9种重金属(Cd、Cr、Cu、Fe、Mn、Ni、Pb、Sr和Zn)含量。采用内梅罗综合污染指数法评价市售大米的重金属污染水平,采用健康风险评价模型进行食用安全评估。结果如下:大米Cd、Cr、Cu、Fe、Mn、Ni、Pb、Sr和Zn含量平均值分别为0.02、0.02、2.27、2.63、9.10、0.15、0.07、0.17和14.27 mg/kg。大米重金属污染程度依次为:PbZnNiCuCdCr,其风险等级依次为:CuZnCdPbCrNi。结果表明,大米重金属的内梅罗综合污染指数较低,表明当前北京市售大米整体状况较好、处于安全水平;大米重金属对儿童的THQ贡献率高于成人,相关部门应加强有毒重金属监督与相应膳食指导。     

Adsorption of several metal ions onto a low-cost biosorbent: kinetic and equilibrium studies

Sugar beet pulp generated by sugar-refining factories has been shown to be an effective adsorbent for the removal of heavy metals from aqueous solutions. The structural components related to the metallic adsorption being determined, batch adsorption studies were performed for several metal ions, namely, Pb2+, Cu2+, Zn2+, Cd2+, and Ni2+ cations. Two simple kinetic models, that is, pseudo-first- and pseudo-second-order, were tested to investigate the adsorption mechanisms. The kinetic parameters of the models were calculated and discussed. For an 8 x 10(-4) M initial metal concentration, the initial sorption rates (v0) ranged from 0.063 mmol x g(-1) x min(-1) for Pb2+ to 0.275 mmol x g(-1) x min(-1) for Ni2+ ions, in the order Ni2+ > Cd2+ > Zn2+ > Cu2+ > Pb2+. The equilibrium data fitted well with the Langmuir and Freundlich models and showed the following affinity order of the material: Pb2+ > Cu2+ > Zn2+ > Cd2+ > Ni2+. The metal removal was strongly dependent on pH and, to a lesser extent, ionic strength. Ion exchange with Ca2+ ions neutralizing the carboxyl groups of the polysaccharide was found to be the predominant mechanism, added with complexation for Pb2+, Cu2+, and Zn2+ metals.     

Cadmium,lead and some other trace elements in Larch Bolete mushrooms (Suillus grevillei) (Klotzsch) Sing., collected from the same site over two years

The aim of this study was to examine the status of some trace metals accumulated in the flesh of Suillus grevillei mushrooms collected from the same site over two successive years. Total Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Rb, Sr and Zn contents of fruiting bodies were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES) with ultrasonic cross-flow nebuliser. A difference (p < 0.05) was found in the contents of Cd, Cr, Cu, Fe, K, Na, Ni, Pb, Rb and Sr in caps and Fe, Na, P and Rb (p < 0.05) in stipes (Ag, Cd, Co, Cr, Ni and Pb were not determined in stipes). Natural fluctuations in trace elements’ content of Suillus grevillei collected from the same site over time is a variable that needs to be considered when assessing minerals’ nutritional status of mushrooms.     

A biotic ligand model predicting acute copper toxicity for Daphnia magna: the effects of calcium, magnesium, sodium, potassium, and pH

The extent to which Ca2+, Mg2+, Na+, K+ ions and pH independently mitigate acute copper toxicity for the cladoceran Daphnia magna was examined. Higher activities of Ca2+, Mg2+, and Na+ (but not K+) linearly increased the 48-h EC50 (as Cu2+ activity), supporting the concept of competitive binding of these ions and copper ions to toxic action or transport sites at the organism-water interface (e.g. fish gill, the biotic ligand). The increase of the EC50 (as Cu2+ activity) with increasing H+, however, seemed to suggest cotoxicity of CuOH+ rather than proton competition. Based on the biotic ligand model (BLM) concept, we developed a methodology to estimate stability constants for the binding of Cu2+, CuOH+, Ca2+, Mg2+, Na+, and H+ to the biotic ligand, solely based on toxicity data. Following values were obtained: log K(CuBL) = 8.02, log K(CuOHBL)= 7.45, log K(CaBL) = 3.47, log K(MgBL) = 3.58, log K(NaBL) = 3.19, and log K(HBL) approximately 5.4. Further, we calculated that on average 39% of the biotic ligand sites need to be occupied by copper to induce a 50% acute effect for D. magna after 48 h of exposure. Using the estimated constants, a BLM was developed that can predict acute copper toxicity for D. magna as a function of water characteristics. The presented methodology can easily be applied for BLM development for other organisms and metals. After validation with laboratory and natural waters (including DOC), the developed model will support efforts to improve the ecological relevance of presently applied risk assessment procedures.     

Electrodialytic removal of Cu, Zn, Pb, and Cd from harbor sediment: influence of changing experimental conditions

Electrodialytic remediation (EDR) was used to remove Cu, Zn, Pb, and Cd from contaminated harbor sediment. Extraction experiments were made prior to EDR, and the metal desorption was pH dependent but not liquid-to-solid ratio (L/S) dependent. The desorption order was Cd > Zn > Pb > Cu. Electrodialytic experiments were made with HCl as desorbing agent in a sediment suspension, which was stirred during EDR. Effects of different current strengths and L/S ratios on the heavy metal removal were investigated on wet and air-dried sediment. The effects of drying the sediment were negligible for the removal of Cu, Zn, and Pb, probably due to oxidation of the sediments during stirring. Contrary, Cd removal was lower in the wet sediment as compared to the air-dried. The heavy metal removal was influenced by higher current strengths and varying L/S ratios. The highest removal obtained was in an experiment with dry sediment (L/S 8) and a 70 mA applied current that lasted 14 days. These experimental conditions were thereafter used to remediate more strongly contaminated sediments. Regardless of the initial heavy metal concentrations in the sediments, 67-87% Cu, 79-98% Cd, 90-97% Zn, and 91-96% Pb were removed.     

Experimental measurement of proton, Cd, Pb, Sr, and Zn adsorption onto the fungal species Saccharomyces cerevisiae

Proton, Cd, Pb, Sr, and Zn adsorption onto the fungal species Saccharomyces cerevisiae were measured in bulk adsorption experiments as a function of time, pH, surface: metal ratio, and ionic strength, and we measured the electrophoretic mobility of the cells as a function of pH. We modeled the acid/base properties of the fungal cell wall by invoking a nonelectrostatic surface complexation model with four discrete surface organic acid functional group types, with average pKa values (with 1 sigma uncertainties) of 3.4 +/- 0.4, 5.0 +/- 0.2, 6.8 +/- 0.4, and 8.9 +/- 0.6. The affinity of the fungal cells for the metal ions follows the following trend: Pb > Zn > Cd > Sr. We used the metal adsorption data to determine site-specific stability constants for the important metal fungal surface complexes. Our results suggest that S. cerevisiae may represent a novel biosorbent for the removal of heavy metal cations from aqueous waste streams.     

Trace elements and metals in farmed sea bass and gilthead bream from Tenerife Island, Spain

The aim of this study was to determine the levels of metals (Ca, K, Na, Mg) and trace metals (Ni, Fe, Cu, Mn, Zn, Pb, Cd) in two fish species (gilthead bream [Sparus aurata] and sea bass [Dicentrarchus labrax]) collected from fish farms located along the coast of Tenerife Island. Ca, K, Na, Mg, Fe, Cu, Zn, and Mn were measured by flame atomic absorption spectrometry, whereas Pb, Cd, and Ni were determined using graphite furnace atomic absorption spectrometry. Mean Fe, Cu, Mn, and Zn contents were 3.09, 0.59, 0.18, and 8.11 mg/kg (wet weight) in S. aurata and 3.20, 0.76, 0.24, and 10.11 mg/kg (wet weight) in D. labrax, respectively. In D. labrax, Ca, K, Na, and Mg levels were 1,955, 2,787, 699.7, and 279.2 mg/kg (wet weight), respectively; in S. aurata, they were 934.7, 3,515, 532.8, and 262.8 mg/kg (wet weight), respectively. The Pb level in S. aurata was 7.28 ± 3.64 μg/kg (wet weight) and, in D. labrax, 4.42 ± 1.56 μg/kg (wet weight). Mean Cd concentrations were 3.33 ± 3.93 and 1.36 ± 1.53 μg/kg (wet weight) for D. labrax and S. aurata, respectively. All Pb and Cd levels measured were well below the accepted European Commission limits, 300 and 50 μg/kg for lead and cadmium, respectively.     

Contribution to the study of avocado honeys by their mineral contents using inductively coupled plasma optical emission spectrometry

Avocado honey samples were analyzed by inductively coupled plasma optical emission spectrometric. First, the botanical origin of the honeys was confirmed by melissopalynological analysis. Twenty-four minerals were quantified for each honey sample. The elements Al, Ba, Ca, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, P, Pb, S, Se, Si and Zn were detected in all samples; seven elements were very abundant (Ca, K, Mg, Na, P, S and Si), six were not abundant (Al, Cu, Fe, Li and Zn) and 11 were trace elements (As, Ba, Cd, Co, Cr, Mo, Ni, Mo, Pb, Se, Sr and V).     

Concentrations and bioconcentration factors of minerals in yellow-cracking bolete (xerocomus subtomentosus) mushroom collected in noteć forest, poland

Abstract: Yellow‐cracking Bolete (Xerocomus subtomentosus) mushrooms and soil were collected from Note? Forest–a large forested enclave in western part of Poland. Mercury was determined by cold vapour atomic absorption spectroscopy and the other elements by inductively coupled plasma atomic emission spectroscopy. K, P, and Mg were particularly abundant, with mean values of 46000, 8400, and 1100 mg/kg dry weight (dw) in caps followed by Na, Rb, Zn, and Ca with mean concentrations of 580, 350, 200, and 170 mg/kg dw, respectively. In descending order, the mean concentrations of Fe, Al, Cu, and Mn were 52, 49, 46, and 14 mg/kg dw, while the mean for the remaining elements was around 1.0 mg/kg dw or less. The elements such as Ca, Cu, Hg, K, Mg, Na, P, Rb, Zn, Ag, Cd, and Ni were accumulated (with bioconcentration factor (BCF) > 1), while Al, Ba, Fe, Mn, Sr, Co, Cr, and Pb were excluded (BCF < 1) in the fruiting bodies. The Pb and Cd content did not exceed the maximum levels set by the EU for cultivated mushrooms. Mercury in a conventional meal (300 g) portion of Yellow‐cracking Bolete was far below the provisionally tolerable weekly intake of 0.004 mg/kg body weight (bw) as reevaluated recently by WHO. Practical Application: The method presented in this study allows one to determine the content of 20 elements (Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, P, Pb, Rb, Sr, and Zn) in caps and stipes of Yellow‐cracking Bolete (Xerocomus subtomentosus) mushrooms and soil samples collected from Poland. This study has revealed that the total Cd, Hg, and Pb dose provided to human body due to consumption of Yellow‐cracking Bolete does not pose threat to a consumer's health.     

Minor and trace elements in different honey types produced in Siena County (Italy)

The concentrations of 23 chemical elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Ni, Pb, Sb, Se, Sr, Th, Tl, U, Zn) were determined in 51 honey samples of different botanical origin produced in Siena County (Italy). K, Ca, Na and Mg were the most abundant elements, with mean contents of 1195, 257, 96.6 and 56.7 mg/kg, respectively. The Fe, Zn and Sr contents generally ranged from 1 to 5 mg/kg. Except for Ba, Cu, Mn and Ni, the trace element contents were below 100 μg/kg. The analytical data indicated a good level of quality of the honeys, especially with regard to the concentrations of toxic trace elements, such as As, Cd, Pb and Sb, and suggested a significant influence of the botanical origin on the element composition. Some local geological and geochemical features also seemed to affect the chemistry of the honey.     

Survey on the quality of commercial Nigari (crude magnesium chloride [sea water])

Contents of minerals (Mg, Ca, Na and K), anions (SO4(2-), Br- and Cl) and heavy metals (Pb, Cd, Zn, Hg and As) were determined in 17 commercial samples of Nigari, 15 samples of crude magnesium chloride (sea water) products as a food additive and 2 magnesium-containing foods. Obtained values were compared with the specifications proposed in a draft of the eighth edition of Japan's Specifications and Standards for Food Additives. Out of 15 food additive samples, only 5 samples satisfied the specification. Since the Joint FAO/WHO Expert Committee on Food Additives (JECFA) proposed to lower the limits of heavy metals in food additives, a simple method was developed for the determination of low levels of Pb and Cd by extracting chelates of these metals with organic solvents. The quantification limits for Pb and Cd were 0.5 microg/g and 0.05 microg/g, respectively. It was estimated from the SO4(2-)/Ca ratios that 15 samples were sea water evaporation products, and the remaining 2 were ion-exchange membrane process products. No pollution with heavy metals was found in any of the samples.     

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.     

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.     

Daily intake of trace metals through coffee consumption in India

The trace element contents of five varieties of instant coffee powder available in the Indian market have been analysed. Ca, Cr, Fe, K, Mg, Mn, Ni, Sr, Zn and Pb, Cd, Cu have been determined using atomic absorption spectrophotometry and differential pulse anodic stripping voltammetry, respectively. The metal levels in the coffee powders observed in this study are comparable with those reported for green coffee beans (Arabica and Robusta variety) reported worldwide with the exception of Sr and Zn, which were on the lower side of the reported values. Concentrations of these metals have been converted into intake figures based on coffee consumption. The daily intakes of the above metals through ingestion of coffee are 1.4mg, 1.58 mu g, 124 mu g, 41.5mg, 4.9mg, 17.9 mu g, 2.9 mu g, 3.8 mu g, 12.5 mu g, 0.2 mu g, 0.03 mu g and 15.5 mu g, respectively. The values, which were compared with the total dietary intake of metals through ingestion by the Mumbai population, indicate that the contribution from coffee is less than or around 1% for most of the elements except for Cr and Ni which are around 3% .     

Elemental Composition of Various Sour Cherry and Table Grape Cultivars Using Inductively Coupled Plasma Atomic Emission Spectrometry Method (ICP-OES)

Three sour cherry and three table grape cultivars were analyzed using inductively coupled plasma optical emission spectrometry. The elements: Na, K, Ca, Mg, Fe, Cu, Zn, Mn, Cr, Cd, Co, Pb, and Ni were detected in all samples; four elements are very abundant (K, Na, Ca, and Mg), and four are not abundant (Cu, Fe, Mn, and Zn). Five of them are trace elements (Cr, Cd, Co, Pb, and Ni) at <0.1 mg/kg. Among the 13 elements analyzed, potassium was the most abundant element distributed throughout all categories of fruits. Iron was the predominant minor element constituents. Manganese concentration was the highest in table grape cultivars. The accuracy of the results was evaluated by spike recovery tests. Analysis of variance was used to establish the metals with significant difference in mean content between the cultivars from sour cherries and between table grapes. Principal component analysis was used to evaluate the distribution of metals.     

Uptake of metals during chelant-assisted phytoextraction with EDDS related to the solubilized metal concentration

The use of chelants to enhance phytoextraction is one method being tested to make phytoextraction efficient enough to be used as a remediation technique for heavy metal pollution in the field. We performed pot experiments with sunflowers in order to investigate the use of the biodegradable chelating agent SS-EDDS for this purpose. We used singly and combined contaminated soils (Cu, Zn) and multimetal contaminated field soils (Cu, Zn, Cd, Pb). EDDS (10 mmol kg(-10 soil) increased soil solution metals greatly for Cu (factor 840-4260) and Pb (factor 100-315), and to a lesser extent for Zn (factor 23-50). It was found that Zn (when present as the sole metal), Cu, and Pb uptake by sunflowers was increased by EDDS, butin multimetal contaminated soil Zn and Cd were not. EDDS was observed in the sunflower roots and shoots at concentrations equal to metal uptake. The different metal uptake in the various soils can be related to a linear relationship between Cu and Zn in soil solution in the presence of EDDS and plant uptake, indicating the great importance of measuring and reporting soil solution metal concentrations in phytoextraction studies.     

Removal of heavy metals from mine waters by natural zeolites

In this study, we investigated the removal of Fe, Pb, Cd, and Zn from synthetic mine waters by a natural zeolite. The emphasis was given to the zeolite's behavior toward a few cations in competition with each other. Pb was removed efficiently from neutral as well as from acidic solutions, whereas the uptake of Zn and Cd decreased with low pH and high iron concentrations. With increasing Ca concentrations in solution, elimination of Zn and Cd became poorer while removal of Pb remained virtually unchanged. The zeolite was stable in acidic solutions. Disintegration was only observed below pH 2.0. Forward- and back-titration of synthetic acidic mine water were carried out in the presence and absence of zeolite to simulate the effects of a pH increase by addition of neutralizing agents and a re-acidification which can be caused by subsequent mixing with acidic water. The pH increase during neutralization causes precipitation of hydrous ferric oxides and decreased dissolved metal concentrations. Zeolite addition further diminished Pb concentrations but did not have an effect on Zn and Cd concentrations in solution. During re-acidification of the solution, remobilization of Pb was weaker in the presence than in the absence of zeolite. No substantial differences were observed for Fe, Cd, and Zn immobilization. The immobilization of the metals during pH increase and the subsequent remobilization caused by re-acidification can be well described by a geochemical equilibrium speciation model that accounts for metal complexation at hydrous ferric oxides, for ion exchange on the zeolite surfaces, as well as for dissolution and precipitation processes.     

Trace metal concentrations in distilled alcoholic beverages and liquors in Nigeria

The concentrations of 12 metals (Cd, Pb, Ni, Cr, Cu, Co, Fe, Mn, Zn, Ca, Mg and K) in 13 classes of alcoholic beverages were determined by atomic spectrometry after HNO₃/H₂O₂ digestion. The mean concentrations of metals (µg mL^?1) in these alcoholic beverages varied in the ranges 0.01–0.04, 0.02–0.24, 0.04–0.13, 0.01–0.28, 0.01–0.77, <0.001–0.12, 0.28–1.48, 0.004–0.33, 0.10–1.02, 1.43–162.86, 0.26–25.46 and 0.49–322.58 for Cd, Pb, Ni, Cr, Cu, Co, Fe, Mn, Zn, Ca, Mg and K respectively. The concentrations of metals found in these particular alcoholic beverages were below the International Statutory Limits for metals in alcoholic beverages. The estimated daily intake of the metals based on a per capita consumption of 3.6 L per annum pure alcohol was <3% of the tolerable daily intake of each metal. The individual and combined target hazard quotients of the metals were <1, indicating no long‐term health concerns from the consumption of these alcoholic beverages based on their metal content alone. Copyright © 2014 The Institute of Brewing & Distilling     

Extracellular polymeric substances from Bacillus subtilis associated with minerals modify the extent and rate of heavy metal sorption

Extracellular polymeric substances (EPS) are an important source of organic matter in soil. Once released by microorganisms, a portion may be sorbed to mineral surfaces, thereby altering the mineral?s ability to immobilize heavy metals. EPS from Bacillus subtilis were reacted with Ca-saturated bentonite and ferrihydrite in 0.01 M KCl at pH 5.0 to follow the preferential uptake of EPS-C, -N, and -P. The sorption kinetics of Pb(2+), Cu(2+), and Zn(2+) to the resulting EPS-mineral composites was studied in single and binary metal batch experiments ([metal](total) = 50 μM, pH 5.0). Bentonite sorbed much more EPS-C (18.5 mg g(-1)) than ferrihydrite (7.9 mg g(-1)). During sorption, EPS were chemically and size fractionated with bentonite favoring the uptake of low-molecular weight components and EPS-N, and ferrihydrite selectively retaining high-molecular weight and P-rich components. Surface area and pore size measurements by N(2) gas adsorption at 77 K indicated that EPS altered the structure of mineral-EPS associations by inducing partial disaggregation of bentonite and aggregation of ferrihydrite. Whereas mineral-bound EPS increased the extent and rate of Pb(2+), Cu(2+), and Zn(2+) sorption for bentonite, either no effect or a decrease in metal uptake was observed for ferrihydrite. The extent of sorption always followed the order Pb(2+) > Cu(2+) > Zn(2+), which also prevailed in binary Pb(2+)/Cu(2+) systems. In consequence, sorption of EPS to different minerals may have contrasting consequences for the immobilization of heavy metals in natural environments by inducing mineral-specific alterations of the pore size distribution and, thus, of available sorption sites.