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.     

Dimensional and elemental characterization of suspended particulate matter in natural waters: quantitative aspects in the integrated ultrafiltration, splitt-flow thin cell and inductively coupled plasma–atomic emission spectrometry approach

The present study investigates the quantitative aspects of an analytical procedure for the trace element characterization of suspended particulate matter (SPM) in natural waters. The procedure consists of the following steps: (1) ultrafiltration (UF) concentration; (2) splitt-flow thin (SPLITT) cell fractionation (SF) into different micronic–submicronic dimensional ranges; and (3) inductively coupled plasma–atomic emission spectrometry (ICP–AES) elemental determination on both the separated fractions and the bulk phase. One specific feature of the UF/SF steps is that they are gentle and thus preserve the complexity of the colloidal features of SPM samples as far as possible. The investigation was performed on a real SPM sample (Po River, Italy). Two SF modes were considered: the so called conventional SPLITT fractionation (CSF) mode and the full feed depletion SPLITT fractionation (FFDSF) mode. These differ in terms of resolution, time (both better in CSF as compared to FFDSF) and operating mode (FFDSF does not require a diluting carrier). Quantitative aspects of the UF step recovery and of the CSF and FFDSF modes were investigated in terms of total mass balance proving that only the FFDSF mode is currently satisfactory for quantitative purposes. Mass balance versus the following elements: Cd, Cr, Cu, Mn, Ni and Pb, was performed using ICP–AES over the 0.2–1.5 and 1.5–20 μm FFDSF SPM fractions, proving that the analytical procedure based on UF/FFDSF/ICP–AES is consistent and useful in the investigation of trace element distribution in different SPM dimensional ranges versus that of the bulk phase. The relevance of aggregation–solubility equilibria concerning colloids of SPM phase is emphasized and further improvement of the procedure is discussed.     

Voltammetric methods for speciation analysis of trace metals in natural waters

Trace metals play an important role in the regulation of primary productivity and phytoplankton community composition. Metal species directly affects the biogeochemical cycling processes, transport, fate, bioavailability and toxicity of trace metals. Therefore, developing powerful methods for metal speciation analysis is very useful for research in a range of fields, including chemical and environmental analysis. Voltammetric methods, such as anodic stripping voltammetry (ASV) and competing ligand exchange-adsorptive cathodic stripping voltammetry (CLE-AdCSV), have been widely adopted for speciation analysis of metals in different natural aquatic systems. This paper provides an overview of the theory of voltammetric methods and their application for metal speciation analysis in natural waters, with a particular focus on current voltammetric methods for the discrimination of labile/inert fractions, redox species and covalently bound species. Speciation analysis of typical trace metals in natural waters including Fe, Cu, Zn, Cd, and Pb are presented and discussed in detail, with future perspectives for metal speciation analysis using voltammetric methods also discussed. This review can elaborate the particular knowledge of theory, merits, application and future challenge of voltammetric methods for speciation analysis of trace metals in natural waters.     

Investigations on sample pretreatment for the determination of selected metals and organochlorine compounds in suspended particulate matter of the River Elbe

The River Elbe and some of its tributaries are transporting polluted suspended particulate matter (SPM). Due to the property of SPM to accumulate anthropogenic and nonanthropogenic substances, this matrix is of interest from an analytical point of view. SPM has been collected in 13 sampling devices, placed in monitoring stations along the River Elbe from the Czech border to the North Sea and the embouchures of its tributaries Schwarze Elster, Mulde and Saale. Characterization of the SPM has been carried out by sieving and determining the content of total carbon. Comparative studies with different digestion procedures are presented for the determination of heavy metals and arsenic in the fine grain particle size <20 m of freeze-dried SPM. In a first test the highest concentrations have been found for microwave heating in a closed system when using an acid mixture of HNO₃/HF 3:1. Results of an interlaboratory test show the good practicability of the microwave heating digestion method. The determination of organochlorine compounds in a freeze-dried sample by three different extraction methods including supercritical fluid extraction (SFE) with CO₂ shows that the highest extraction efficiency is found for the conventional Soxhlet method.     

Solution Chemistry of Arsenic Anions in the Presence of Metal Cations

The interaction of arsenic(V) and arsenic(III) oxyanions with metal cations was investigated by potentiometry under temperature and ionic strength conditions approaching those prevailing in natural waters. The selection includes the major metal cations and some other ions of high environmental relevance. Ionic pairs [M(As^VO₄)]^?, [M(HAs^VO₄)] and [M(H₂As^IIIO₃)]⁺ formation is suggested for all +2 metal cations, based on the potentiometric results. These ion-pairs between arsenic anions and other metal cations are hardly ever mentioned or taken into account when arsenic speciation in natural waters is considered. These results provide the basis for studying arsenic speciation in natural aquatic systems, on which environmental fate, bioavailability and toxicity of the element depend. Some extrapolations to the conditions of the natural waters are presented as well as some insights into the adsorption process onto hydrous oxides.     

Trace element speciation by ICP-MS in large biomolecules and its potential for proteomics

Latest studies on the chemical association of trace elements to large biomolecules and their importance on the bioinorganic and clinical fields are examined. The complexity of the speciation of metal-biomolecules associations in various biological fluids is stressed. Analytical strategies to tackle speciation analysis and the-state-of-the-art of the instrumentation employed for this purpose are critically reviewed. Hyphenated techniques based on coupling chromatographic separation techniques with ICP-MS detection are now established as the most realistic and potent analytical tools available for real-life speciation analysis. Therefore, the status and potential of metal and semimetals elemental speciation in large biocompounds using ICP-MS detection is mainly focused here by reviewing reported metallo-complexes separations using size-exclusion (SEC), ion-exchange (IE), reverse phase chromatography (RP) and capillary electrophoresis (CE). Species of interest include coordination complexes of metals with larger proteins (e.g. in serum, breat milk, etc.) and metallothioneins (e.g. in cytosols from animals and plants) as well as selenoproteins (e.g. in nutritional supplements), DNA-cisplatin adducts and metal/semimetal binding to carbohydrates. An effort is made to assess the potential of present trace elements speciation knowledge and techniques for "heteroatom-tagged" (via ICP-MS) proteomics.     

Electrothermal atomic absorption spectrometry in the study of metal ion speciation

The literature on the use of electrothermal atomic absorption spectrometry (ETAAS) in the determination of metals in speciation studies of different samples is comprehensively reviewed. The methods of extraction, preconcentration, etc. in connection with speciation studies have been highlighted. The ETAAS programmes and other details of the developed methodologies are discussed. On critical examination it becomes obvious that chromium is the metal which has been analysed by most workers. Study of other metals falls in the following order: Pb, Sn, Cu, As, Al, Cd, Zn, Fe, Ni and Se. It is clearly evident that the major work on metal ion speciation has been carried out in natural water, followed by biological materials. There are also many reports on the speciation analysis of soil and sediment. Only a few papers have been published on metal speciation in airborne particulates. The analytical details of the developed methodologies have been examined in terms of limit of detection, precision and accuracy. Received: 27 December 1995 / Revised: 20 May 1996 / Accepted: 26 May 1996     

Electrothermal atomic absorption spectrometry in the study of metal ion speciation

The literature on the use of electrothermal atomic absorption spectrometry (ETAAS) in the determination of metals in speciation studies of different samples is comprehensively reviewed. The methods of extraction, preconcentration, etc. in connection with speciation studies have been highlighted. The ETAAS programmes and other details of the developed methodologies are discussed. On critical examination it becomes obvious that chromium is the metal which has been analysed by most workers. Study of other metals falls in the following order: Pb, Sn, Cu, As, Al, Cd, Zn, Fe, Ni and Se. It is clearly evident that the major work on metal ion speciation has been carried out in natural water, followed by biological materials. There are also many reports on the speciation analysis of soil and sediment. Only a few papers have been published on metal speciation in airborne particulates. The analytical details of the developed methodologies have been examined in terms of limit of detection, precision and accuracy. Received: 27 December 1995 / Revised: 20 May 1996 / Accepted: 26 May 1996     

Speciation analysis of heavy metals in natural waters: a review.

Metal speciation in natural waters is of increasing interest and importance because toxicity, bioavailability, environmental mobility, biogeochemical behavior, and potential risk in general are strongly dependent on the chemical species of metals. This paper provides an overview of the need for speciation of heavy metals in natural waters, the chemical and toxicological aspects of speciation, and the analytical procedures for separation and the different techniques for final determination that are used today. The trends and developments of speciation are also discussed. Finally, the case of chromium (Cr) was selected for a detailed presentation because the speciation of this metal has attracted a great deal of interest in view of the toxic properties of Cr(VI).     

Effect of pH on cadmium and lead binding by extracellular polymeric substances (EPS) extracted from environmental bacterial strains

Cd and Pb binding by extracellular polymeric substances (EPS) extracted from seven environmental bacterial strains were investigated as a function of pH. The study was carried out by using a polarographic method in the stripping mercury dropping electrode (SMDE) mode which is able to determine labile metal in solution containing soluble ligands such as EPS. The results obtained provide evidence for the presence of a pH-sorption/desorption edge for Cd and Pb by EPS. Kurbatov's model gives information on the mechanisms involved through the determination of "relative complexation constants" (operationally defined) and the number of exchanged protons. This model shows that proton exchange with metals is not the only mechanism involved in metal biosorption by bacterial EPS. The position of the pH-sorption edge curves and the "relative complexation constants" show that Pb displays a greater affinity for EPS than Cd. For a given metal, the seven EPS investigated did not display differences regarding the binding strength. This work suggests that a wide range of products of bacterial species isolated from activated sludge exhibit similar binding behaviours for Cd or Pb, which may potentially simplify the modelling of the distribution and the speciation of metals in bacteria-bearing natural systems.     

Speciation of Cu(II) with a flow-through permeation liquid membrane: discrimination between free copper, labile and inert Cu(II) complexes, under natural water conditions

Metal toxicity is not related to the total metal ion concentration, but to those of some specific Cu(II) species. The Permeation Liquid Membrane technique is based on the carrier-mediated transport of the test metal across a hydrophobic membrane and enables discrimination between various trace metal species in solution. The present work shows how the labile and inert Cu(II) complexes can be determined selectively, by varying the flow-rate of the test solution, in a flow-through cell. A mathematical model of metal flux through the PLM, based on diffusion-limited transport under steady-state conditions, is described. The model and the performance of the technique were studied in well-defined synthetic solutions containing simple organic hydrophilic ligands forming either inert (nitrilotriacetic acid), or labile complexes with Cu(II) (tartaric acid, malonic acid). The results were compared with theoretical predictions of thermodynamic species distribution in solution. Uncertainties on stability constants for copper speciation calculation were taken into account. The detection limits of the device are discussed. This work demonstrates that the flow-through cell is a reliable tool for copper speciation measurements in natural waters.     

Silver binding by humic acid as determined by equilibrium ion-exchange and dialysis

One of the major challenges in environmental analytical chemistry is to develop methods for determining metal speciation in natural waters that contain low metal concentrations and dissolved organic matter (DOM). Because of its complex heterogeneous nature, metal binding to DOM cannot be predicted accurately using equilibrium models. Two independent speciation methods, the equilibrium ion-exchange technique (IET) and equilibrium dialysis (EqD), were used to determine silver binding by standard Suwannee River humic acid. Both approaches gave very similar results, although for a given silver loading, the concentration of free silver obtained by IET was somewhat higher than that determined by EqD. Our results suggest that any high-affinity binding sites present within the humic acid are likely saturated at [Ag(T)] > 10(-9) M. This comparison of free metal ion concentrations with two independent methods provides useful speciation information in the absence of reliable complexation constants for the reaction of silver with humic acid.     

The fractionation and determination procedures for the speciation of Pb and Po in soil samples

A method for speciation and determination of ²¹⁰Pb and ²¹⁰Po in soil samples was developed. The speciation was carried out by fractionating the soil samples into five fractions which are water soluble or exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and bound to residue. After mineralisation, 10% solution of each fraction was used to spontaneously deposit polonium on a silver disk at 85-90 °C and pH 1.5, and ²¹⁰Po was measured by α-spectrometry; the remain solution was used to separate lead by anion-exchange resin and purified by precipitation as PbS and PbSO₄, and ²¹⁰Pb was determined by a low background β-counter. The IAEA-327 reference material (soil) was studied for ²¹⁰Pb and ²¹⁰Po speciation. The results show that: (1) the average yields are 88.7 ± 6.4% for ²¹⁰Pb and 93.8 ± 8.2% for ²¹⁰Po; (2) if compared to the total ²¹⁰Pb activity in the sample, ²¹⁰Pb fractions are 0.95% in exchangeable form, 10.6% bound to carbonates, 14.3% bound to Fe-Mn oxides, 7.0% bound to organic matter and 67.2% bound to residue or acid soluble, and the corresponding values for ²¹⁰Po are 0.17%, 0.97%, 21.0%, 0.47% and 77.4%, respectively; and (3) the obtained ²¹⁰Pb concentration is in good agreement with the recommended value given by the IAEA.     

Trace metal speciation by adsorptive stripping voltammetry of metal chelates of solochrome violet RS

Adsorptive stripping voltammetry has become one of the most sensitive methods for trace metal determinations. The growing application of the method to natural water systems prompted an investigation into the fraction of the metal concentration that contributes to the adsorptive stripping response. Recent procedures for trace measurement of iron, titanium and gallium, based on chelation with solochrome violet RS (SVRS) are coupled to systematic ligand competition experiments. Tannic acid, EDTA, NTA, glycine, cysteine, carbonate and chloride ions are used as model natural ligands. It is shown that adsorptive stripping voltammetry measures the free ion and metal displaced from complexes by the “analytical” ligand. The exact fraction of the metal measured thus depends on the thermodynamic stability of the metal-SVRS chelate (compared to that of natural complexes), and on the relative concentrations of the competing ligands. The method offers possible distinction between metal complexes, based on their thermodynamic stabilities. The use ofa large excess of the “analytical” ligand can lead to measurement of the total metal content. Implications of these results relative to the use of this procedure for studying the speciation of trace elements in natural waters are discussed.     

Research on Electroanalytical Chemical Methods for Trace Metal Speciation in Sea Water Samples

Since bioavalability of a trace metal in natural waters is affected by its chemical forms, the speciation of a trace metal becomes more and more important in environmental chemistry. Differential pulse anodic stripping voltammetry (DPASV) titration procedures are developed and applied to identify organic trace metal species of copper (Cu), lead (Pb) and zinc (Zn) in sea water and to determine their complexing capacity.     

Organometallic species of the elements tin, mercury and lead in sediments of the longitudinal profile of the River Elbe

In 1992, for the first time, a whole longitudinal sediment profile of the River Elbe from the Czech Republic to the North Sea has been sampled within the framework of the project Registration and assessment of harmful substances in the River Elbe: Heavy metals and heavy metal species. Organometallic species of the elements tin, mercury and lead have been determined. The species have been extracted together from the wet sediments using hexane after an in-situ ethylation with sodium tetraethylborate (NaBEt₄). Gas chromatography-inductively coupled plasma-mass spectrometry (GC-ICP-MS), a very sensitive hyphenated technique for multielemental speciation analysis, has been used for their separation and detection.     

Identification,characterization and determination of metal-binding proteins by liquid chromatography. A review

The use of liquid chromatography in the separation and determination of metal-binding proteins is reviewed. Advantages and drawbacks of different chromatographic techniques based on various principles: size exclusion, ion exchange (cationic and ionic), reversed phase and affinity, are presented and discussed. The topic "metal-binding proteins" is considered and presented from two different points of view. The first one regards metal speciation in biological samples (serum and blood). In metal speciation studies, the exact identity of the protein to which the metal is bound often remains unknown. The second point of view is that, frequently, the interest of analyzing metal-binding proteins is not related anymore to the metallic fraction of the protein, but to other chemical structures attached to the protein, such as carbohydrates, which indirectly determine how good the function of the protein is. In this review, special attention is paid to studies dealing with the glycosylation of transferrin, and with the glycated isoform of haemoglobin.     

Speciation of copper and zinc in natural freshwater: comparison of voltammetric measurements, diffusive gradients in thin films (DGT) and chemical equilibrium models

In situ measurements of copper and zinc using diffusive gradients in thin films (DGT) in two distinct natural water systems were compared to metal speciation assessed by competitive ligand exchange (CLE) and voltammetric measurements. In a dynamic river system, where dissolved metal concentrations vary significantly over short-time periods, DGT technique provided averaged values of the metal concentrations over time. In microcosms, at different total dissolved concentrations of copper and zinc, DGT technique measured a similar fraction as measurements of labile metal performed by voltammetry. The proportion of DGT and voltammetric-labile zinc to dissolved zinc was 61±4% and, respectively, 76±9%. DGT technique was measuring 81±8% of exchangeable copper (by exchange with catechol). These two fractions were similarly influenced by the addition of NTA. In the absence of NTA, copper measured by DGT represented 34±4% of dissolved copper whereas in the presence of NTA, this proportion raised to 57±2%. These measurements were compared to calculations performed with speciation programs using several models for the complexation by humic and fulvic substances, namely Model VI (WHAM), NICA-Donnan and SHM. The predicted speciation by these three models was similar. The prediction of free zinc ion and labile zinc concentrations were in agreement with experimental data. Calculated concentrations of free copper ion were overestimated because these models are not considering strong specific copper-binding ligands probably present in natural water.     

Speciation analysis — why and how?

Summary The different aspects of speciation analysis are reviewed. Species-specific instrumental techniques as well as various speciation schemes are considered for the determination of species of metals and metalloids, including organometallic compounds. The application of the methods are discussed in some detail for the analysis of natural waters, air, soil, sediment and biological samples. The relationship between metal species and bioavailability is also briefly dealt with.     

化学形态分析

本文综述了金属元素的化学形态分析,包括:形态分析的方法与技术,形态分析在水、土壤、空气和生物样品中的应用,样品的处理方法等。