Labile metal content of sediments-fractionation scheme based on ion-exchange resins

The labile metal content of sediments can be evaluated by equilibrating sediment suspensions with ion-exchange resins. By use of a sequence of strong-acid and weak-acid cation-exchangers (H(+)- and Na(+)-form) and chelating resins, extraction can be performed at pH values ranging from 2 to 10. The results allow the total metal content to be subdivided into seven categories designated as (i) low-pH labile, (ii) weak-acid labile, (iii) exchangeable and readily desorbed at sediment-suspension pH, (iv) weak-base labile, (v) high-pH labile, (vi) non-labile soluble forms and (vii) detrital metal content. The sediment suspensions are mixed overnight with the different types of exchanger (held in porous containers) and the cations transferred from the sediment are subsequently back-extracted from the resins into 0.05M EDTA (pH 7.5). The EDTA extracts are analysed for Cu, Pb, Zn, Cd, Ca, Mg, Fe and Al. Analysis of the aqueous phase left in contact with the sediment residue gives the amount of non-labile species released. Eighteen sediments, containing various levels of metal contamination, and an effluent dam sludge have been examined by this technique. All the exchangers released Ca and Mg from the sediments, and the H(+)-form exchangers also released Fe and Al. Some of the Fe, Al and to a lesser extent Zn released by the sediment/exchanger interactions was present as non-labile "soluble" species. The advantages and limitations of this "labile metal" fractionation scheme have been considered.     

Evaluation of "labile" metal in sediments by anodic stripping voltammetry

A procedure for determining the "labile" metal content of contaminated sediments (in different chemical environments) has been critically examined. The sediments were extracted overnight with different chemical solutions and the suspensions were analysed by differential pulse anodic stripping voltammetry. The extractants used have been recommended for soil/sediment speciation schemes, and by examination of the suspensions directly in the ASV cell, errors due to re-adsorption of released metal ion were minimized. The existence of different chemical forms of metal was signified by changes in peak shape and position or by the appearance of additional peaks. With complexing agents present the peak size was pH-dependent. The limitations of the ASV/suspension analysis technique have been carefully evaluated by using ten different extractants and seventeen sediments. The "lability" results obtained have been compared with the values obtained from a cation-exchanger transfer procedure. For characterizing the lability behaviour of the metal contents of sediments, preliminary extraction into a minimum of four base solutions is advisable, e.g., 0.02M nitric acid (low-pH labile); hydroxylamine in acetic acid (reducing conditions); acetic acid/acetate buffer (weakly sorbed and carbonate-bound) and 0.05M calcium chloride (exchangeable fraction at natural system pH), where the terms in parentheses describe the character of the fraction. The results are critically compared with those obtained by atomic-absorption analysis of the extracts and with those obtained by an earlier ion-exchange fractionation scheme. The advantages and limitations of the ASY systems are discussed.     

Effect of soluble calcium on the determination of the labile metal content of sediments with ion-exchangers

Equilibration of sediments with cation-exchangers results in a transfer of loosely bound labile metal species to the exchanger phase. Dissolution of the matrix is also promoted and selectivity rules suggest that some of the cations released (particularly Ca) could effectively compete with metal ions for exchange sites. This potential source of error has been evaluated by studying synthetic mixtures of Ca²⁺ and other metal ions (Cu²⁺, Pb²⁺, Cd²⁺, Zn²⁺) and by analysis of two calcium-rich wastes (a calcine and a jarosite). The ion uptake most influenced by calcium competition was that of zinc; uptake of lead was least affected. For minimum error, i.e., optimum transfer of “available” or “labile” metal ion, the level of free Ca²⁺ introduced into the solution should not exceed 300 mg/l., and the amount of exchanger added must provide an excess of exchange sites relative to the amount of cations released from the sample. By use of exchangers of different types it is possible to attempt some classification of the labile metal content, e.g., acid-displaced, exchangeable, salts of weak acids.     

Mercury depth profiles in river and marine sediments measured by the diffusive gradients in thin films technique with two different specific resins

The diffusive gradients in thin films technique (DGT) was used to measure depth profiles of mercury in river and marine sediments in situ to a spatial resolution of 0.5 cm. Agarose gel was used as the diffusive gel in the DGT probes. Two different selective resins—Chelex 100 with iminodiacetic groups and Spheron-Thiol with thiol groups incorporated in the polyacrylamide resin gel—were tested. The different capture efficiencies of the two adsorbents enabled the fractions of mercury bound in different species in sediment pore water to be estimated. Mercury concentrations obtained by DGT with Spheron-Thiol resin were very similar to those obtained after centrifugation. This indicates that DGT with Sheron-Thiol resin reports on total dissolved mercury levels. The concentration of mercury measured by DGT with Chelex-100 resin was much lower (by a factor of 5–20) for the same sediment samples. Chelex-100 does not have such a high affinity to mercury as Spheron-Thiol, and so it only reports on the content of labile mercury species, such as inorganic ions and weak complexes. The content of labile mercury species in the river sediment was approximately 20% of the total dissolved mercury in pore water, whereas in marine sediment only 7% of the mercury was present as labile species.     

Binding and chemical fractionation of heavy metals in typical peat matter

Laboratory batch studies were conducted to evaluate the binding capacity and the mobility of metal species bound to typical humus peat matter. The identification of phase composition of mineral fractions and functional groups in the organic matter was assessed. The results showed generally high, but different retention capacity and binding strength, suggesting distinct diversity in binding mechanisms, phases and chemical nature of binding sites, depending on the metal species and their input concentrations. In general, the binding capacity of peat for the metal ions studied follows the order: Cr(3+) > Cu(2+) > Zn(2+) > Cd(2+) and results in the decrease of pH in the same order, due to displacement of H(3)O(+) from the peat by metal ions. The highest metal enrichment occurs in fractions F1(EXC), F2(CARB), F4(MRO) and F5(OM) of different binding strength adequate to exchangeable, carbonatic, moderately reducible amorphous Fe-oxide and organic/ sulphidic fractions in soils and sediments. In relation to species distribution in peats, the prevailing part of Cr(3+) is strongly bound in oxidizable organic substrate, while Cu(2+) is highly enriched in the moderately reducible F4(MRO) and the most labile F2(EXC) fractions. Cd(2+) and Zn(2+) are predominantly bound in the labile F1(EXC) and F2(CARB) fractions. Diversity of the predominant binding phases for the studied metals suggests rather weak competition for binding sites between chromium and copper ions; the strongest competition between the sorbed metal ions is anticipated for F1(EXC) and F2(CARB) fractions.     

Influence of colloidal charge on response of pH and reference electrodes: the suspension effect

The pH measured in a charged sediment is often very different from that of the supernatant solution. This effect has been studied to determine whether it is caused by an anomalous junction potential at the reference electrode, as commonly thought, or by Donnan partitioning of hydrogen ions. Electrical conductivities in sediments of a strong cation-exchange resin were much higher than predicted by the junction artifact theory; electrode measurements of pH in sediments corresponded to titratable H(+)-content, and pH-changes induced by titration and salt addition were in accord with partitioning theory. These findings suggest that most pH differences observed between colloidal sediments and supernatants are real, not junction artifacts. Guidelines for interpretation of pH measurements on colloids are suggested.     

Mechanism of metal-ion sorption on hydrous metal oxides

A model for treating the sorption of metal ions on hydrous metal oxides was established based on the assumptions that these materials are weakly acidic cation exchangers and have a discrete exchanger phase. The experimental results of the sorption of metal ions on the hydrous niobium(V) and tin(IV) oxides are found to be consistent with the formulas derived from the model by considering that the charge balance and the mass action law hold in the exchanger phase and cations are sorbed by the distribution between this phase and the bulk aqueous phase.     

Sieving of sediments for subsequent analysis of metal pollution: results of a German interlaboratory study

An interlaboratory study was carried out to get information on repeatability and reproducibility of sieving, and how sieving influences the variability of analytical measurements. Thirteen laboratories took part, sieving three marine sediment samples to get particle size fractions (<20/>20 m; <63/>63 m), and determine their percent by weight. Repeatabilities between 2 and 13% and reproducibilities between 25 and 75% were obtained. Differences in the sieving procedures applied by the participants may be proposed as a reason for the high variability in the results. The determination of metals revealed that they accumulated in the below 20 m fraction. These findings support the common practice in German sediment monitoring programmes of using the <20 m fraction of sediments for metal analysis. The reproducibilities of the analyses of metals in sediments were between 5 and 15%, and indicate a significant influence of sieving on the results.     

Measuring bioavailable trace metals from freshwater sediments by diffusive gradients in thin films (DGT) in monitoring procedures for quality assessment

An experimental design using passive samplers was set up in our laboratories with the aim of preparing a procedure for the assessment of trace metals bioavailability in freshwater sediments. Trace metal (Cd, Cu, Pb, Ni, and Zn) bioavailability in sediment samples were measured by diffusive gradients in thin films (DGT) devices and compared to those simultaneously extracted (SEM) in 1N HCl with acid-volatile sulfide (AVS). During experiments DGT devices were exposed at various times (from 4 to 336 h) in sediments with different physical and chemical properties and metal content, after equilibration with ambient water (1:2) for 24 h. Trace metal were progressively accumulated in DGT units and after at least 24-48 h metal fluxes became constant. No relation was found between metal available fractions measured by DGTs and total concentrations in sediments or pore waters. On the contrary good relations were found between available metals measured by DGT and metals simultaneously extracted (SEM) in HCl 1N with acid volatile sulfide (AVS).     

Sediment analysis--lability of selectively extracted fractions

Contaminated sediment samples and wastes were extracted with a series of chemical solutions widely used in soil and sediment analyses. The Cu, Pb and Cd contents of the extracts were then determined by both AAS and ASV, and it was found that not all of the metal ion retrieved was "labile". Differences between selected extraction values were compared with the bonding-mode category values obtained by using a well-known sequential extraction procedure, and it was found that the series and sequential approaches yielded different results for Pb and Cu. The advantages and limitations of ASV monitoring in sediment studies are considered and the inappropriateness of some operationally defined fraction categories is indicated.     

A highly selective and sensitive fluorescence "turn-on" probe for Ag+ in aqueous solution and live cells

A naphthalimide-based fluorescent probe, NPQ, that contains a novel receptor was successfully developed. NPQ exhibited "turn-on" fluorescence and excellent selectivity toward Ag(+) in the presence of various other metal ions in aqueous solution. A series of control compounds were designed and synthesized in order to explore the photoinduced electron transfer (PET) quenching mechanism of NPQ and binding mode of NPQ with Ag(+). Moreover, with the NPQ-Ag(+) complex, I(-) was easily selectively recognized by a marked fluorescence quenching. The live cell imaging experiments demonstrate that NPQ can be used as a fluorescent probe for monitoring Ag(+) in living cells.     

Effects of Metal Ion Adduction on the Gas-Phase Conformations of Protein Ions

Changes in protein ion conformation as a result of nonspecific adduction of metal ions to the protein during electrospray ionization (ESI) from aqueous solutions were investigated using traveling wave ion mobility spectrometry (TWIMS). For all proteins examined, protein cations (and in most cases anions) with nonspecific metal ion adducts are more compact than the fully protonated (or deprotonated) ions with the same charge state. Compaction of protein cations upon nonspecific metal ion binding is most significant for intermediate charge state ions, and there is a greater reduction in collisional cross section with increasing number of metal ion adducts and increasing ion valency, consistent with an electrostatic interaction between the ions and the protein. Protein cations with the greatest number of adducted metal ions are no more compact than the lowest protonated ions formed from aqueous solutions. These results show that smaller collisional cross sections for metal-attached protein ions are not a good indicator of a specific metal–protein interaction in solution because nonspecific metal ion adduction also results in smaller gaseous protein cation cross sections. In contrast, the collisional cross section of α-lactalbumin, which specifically binds one Ca²⁺, is larger for the holo-form compared with the apo-form, in agreement with solution-phase measurements. Because compaction of protein cations occurs when metal ion adduction is nonspecific, elongation of a protein cation may be a more reliable indicator that a specific metal ion–protein interaction occurs in solution.      

Synthesis and properties of new N,S-containing fibrous ion exchangers

New N,S-containing fibrous ion exchangers were prepared by polymer-analogous transformations of Nitron fiber, involving amination with polyethylenepolyamines (ethylenediamine and diethylenetriamine), followed by the reaction of the aminated fiber with carbon disulfide. The materials obtained efficiently take up silver ions from multicomponent aqueous solutions of metal ions and from dilute solutions containing calcium ions.     

Heavy metal in sediments and bioaccumulation in the bivalve Corbula gibba in a drilling discharge area

The longterm bioavailability of heavy metals in sediments of a Northern Adriatic Sea shelf area affected by drilling mud and cutting discharges was discussed. Levels of Mn, Cu, Cr, Zn and Pb in different geochemical phases of the sediment and in soft tissues of the bivalve Corbula gibba were recorded and the relationships between biological and geochemical metal investigated. Total metal content, acetic acid extractable-, exchangeable-, carbonate-, easily reducible-, moderately reducible-, oxidable- and residual-fractions were determined on sediment samples. Corbula gibba was collected from wet sediments at the same times and sites, and the soft-tissue metal contents were determined. Correlations show that the fractions with greatest bioavailability are the exchangeable and carbonate for Cr and the exchangeable, carbonate, easily and moderately reducible fractions for Zn. Data also show a possible bioavailability of Pb only from the residual fraction, consisting of very resistant matter of more recent anthropogenic origin. Near the platform, total Mn content in sediments and in C. gibba tissues show a strong correlation suggesting that this organism is sensitive to variations of the Mn-oxi-hydroxides superficial film. No relationships were found between biological and sediment-bound Cu, however the discharged muds did not cause Cu enrichment. The metal fraction determined by weak acetic acid extraction at no point seems related to metal levels in Corbula gibba.     

Melting behavior of lamellae of isotactic polypropylene studied using hot-stage atomic force microscopy

The α- and β-form lamellae of isotactic polypropylene were developed at different temperatures. The melting behaviors of the lamellae were observed in real time at elevated temperatures using a hot-stage atomic force microscopy. The melting behavior of the α-form lamellae was determined by the lamellar defects. For the α-form lamellae developed at different undercoolings, the larger the undercoolings, the relatively higher amount of defect in the lamellae was observed. The lamellae with defects were melted into lamellar segments, and recrystallization took place during the heating process. The β-form lamellae had lower thermal stability, and they melted firstly and separately from that of α-form.     

Characteristics of Novel Types of Substituted Cerium Phosphates

The disodium, dilithium, dipotassium and distrontium forms of cerium phosphate were prepared from their corresponding mono-forms. The chemical content of these inorganic ion exchangers have been characterized by inductively coupled plasma (ICP) spectroscopy. The ion exchange properties of these cation exchangers, their chemical stability and selectivity for certain ions were investigated. It was found that, by introducing different salts into the reaction mixture used to prepare cerium phosphate, robust cation exchange materials of reproducible composition with a good cation capacity, and suitable for column use, are produced. All the ion exchangers with the exception of CeP (dipotassium) show excellent selectivity towards certain cations, thereby increasing the potential practical applications of these inorganic exchangers.     

Determination of Elemental Sulfur in Bottom Sediments Using High-Performance Liquid Chromatography

A procedure for determining elemental sulfur in bottom sediments by microcolumn reversed-phase high-performance liquid chromatography was developed. The analytical range was 4–1200 g/g (in terms of the dry weight of a sediment). The procedure is based on the direct injection of acetone extracts of sediments into a chromatographic column. The detection limit was 5 ng/peak (signal-to-noise ratio of 3 : 1); the relative standard deviation was 5.6%. Errors introduced at particular stages of analysis and the total errors were evaluated for different sampling techniques. The results of determining elemental sulfur in the core samples of bottom sediments from Lake Baikal are presented.     

Preparation of poly(glycidylmethacrylate‐divinylbenzene) weak acid cation exchange stationary phases with succinic anhydride,phthalic anhydride,and maleic anhydride for ion chromatography

In this work, poly(glycidylmethacrylate‐divinylbenzene) microspheres were prepared and applied for the preparation of weak acid cation exchange stationary phases. Succinic anhydride, phthalic anhydride, and maleic anhydride were selected as carboxylation reagents to prepare three weak acid cation exchangers by direct chemical derivatization reaction without solvent or catalyst. The diameters and dispersity of the microspheres were characterized by scanning electron microscopy; the amount of accessible epoxy groups and mechanical stability were also measured. The weak acid cation exchangers were characterized by Fourier transform infrared spectroscopy; the content of carboxyl groups was measured by traditional acid base titration method. The chromatographic properties were characterized and compared by separating alkali, alkaline earth metal ions and ammonium and polar amines. The separation properties enhanced in the order of succinic anhydride, phthalic anhydride, and maleic anhydride modified poly(glycidylmethacrylate‐divinylbenzene) cation exchangers.     

Metal ion distribution between water and river sediment: speciation model and spectroscopic validation

Natural sediments show sequestering properties that can lead to a process of self-purification of aquatic environment from metal pollution. The study of the interaction between metal ions and sediment particles enhances what is known about the distribution and bioavailability of heavy metals in natural systems. Our contribution concerns the characterisation of the sequestering ability of a River Po sediment with regard to calcium(II), magnesium(II), cadmium(II), nickel(II) and copper(II), in fixed experimental conditions, through pH-metric and spectrometric measurements. A batch titration procedure was adopted and, in each solution, after equilibration, both pH and pM (M = Ca(II), Mg(II), Cd(II), Ni(II), Cu(II)) (via Inductively Coupled Plasma - Optical Emission Spectroscopy, ICP-OES) values were measured. The experimental data were first processed with a specific software to evaluate the concentration and protonation constants of the sediment ligand site(s). The speciation model was then assessed, together with the values of complexation constants, for the different sediment/metal cation systems. In order to better characterise the copper(II)-sediment interaction and to obtain more information about the nature of ligand site(s) involved, EPR (Electronic Paramagnetic Resonance) measurements were also made on the dry sediment before and after reaction with copper(II) ions.     

Theorization on ion-exchange equilibria: activity of species in 2-D phases

Ion-exchange reactions are naturally occurring at soil and sediment/water interphases, determining soil fertility and water quality. These ion-exchange reactions with inorganic and organic exchangers are applied to chemical analysis, recovery of useful ions from low-grade ores (potentially from sea water), water purification including the preparation of "ultrapure" water, production of foods and medicines, therapy, and other uses. It is important to theorize about or to model ion-exchange reactions for quantitative explanations of ion-exchange phenomena and for efficient operation of ion-exchange processes. This paper describes the modeling of ion-exchange equilibria for hydroxyl sites on metal oxides and carboxyl sites in resins with monovalent cations (alkali metal ions), a monovalent anion (nitrate ion), and divalent heavy metal ions. The procedure of modeling is as follows: the stoichiometry and material balance equations of the respective ion-exchange reactions were established based on findings here and by others. The equilibrium conditions were given by the Frumkin equation, where the mass-action relation is modified with lateral interactions between species at the interphase. The model equations were fitted to the measured data and model parameter values were determined by nonlinear regression analysis. The formation of bonds between ions and exchanger sites was evaluated by the equilibrium constant and the suppression of bond formation by electrostatic, geometric, and other lateral interactions was evaluated by the interaction constant. It was established that the properties of ions are determined by the valence, size, and hydration state of the ions. Monovalent ions (anions and cations) react with oxide surface hydroxyl and resin carboxyl sites as hydrated ions and form loose ion-site pairs by a weak electrostatic bond (nonspecific adsorption). However, the lateral interactions are large because of a large polarization of the ion-site pairs. When the monovalent cations are dehydrated to react with carboxyl sites in narrow resin nanopores, the bond formation is difficult because energy for dehydration is necessary. The suppressive lateral interactions here are small because of a small polarization of the dehydrated ion-site pairs that are in direct contact. Divalent heavy metal ions react with oxide hydroxyl sites by replacing their hydrated water molecules and form ion-site pairs in direct strong contact (specific adsorption). The bond formation becomes easier with increasing charge density of the ions evaluated by the charge/radius ratio, agreeing with the order of these ions to form hydroxo complexes in solution. The suppressive lateral interaction is, however, small for ions with large charge densities, because a strong contact bond reduces the polarization of ion-site pairs by neutralization. The properties of exchangers are functions of the molecular and pore environments around the functional groups. The acid-base nature of oxide surface-hydroxyl groups is determined by the electronegativity of surrounding lattice metal ions, and that of resin carboxyl groups by the electron-repelling effect of adjacent methyl groups. Pores in oxides have diameters sufficient to accommodate hydrated ions, and the suppression is large because of repulsion from ions adsorbed on opposite pore walls (across-pore interaction). Pores in resins differentiate ions that can access or not access sites on the internal surfaces of the pores. Narrow nanopores with diameters less than those of the hydrated ions require ions to dehydrate before they can enter. The ion-exchange reactivity here is small, as described above for dehydrated monovalent ions. In wide nanopores where hydrated ions can enter, bond formation is easier, but suppression is greater because of a larger polarization of hydrated ion-site pairs and also of the across-pore interaction. Macropores have diameters much larger than those of the hydrated ions and the bond formation is the same as that in wide nanopores, but the suppression is smaller because of the absence oe of the absence of the across-pore interaction. Finally, this paper attempts a formulation of activity coefficients of exchanging sites and adsorbed ion-site pairs and compares the proposed activity coefficients of interphase species with that of solution species given by the Debye-Hückel equation.