Species In Natural Waters Research Articles

Dispelling the myths: Is the existence of L1 and L2 ligands necessary to explain metal ion speciation in natural waters?

A critical analysis and interpretation of the data published for complexation (conditional stability constants and complexation capacities) of trace metals (copper, Cu(II); zinc, Zn(II); lead, Pb(II); and cadmium, Cd(II)) in whole seawater and freshwater samples over the past 34 yr is presented. We propose that it is not necessary to invoke the presence of any particular classes of ligands (e.g., the so‐called L1 and L2 ligands) to explain the degree of metal complexation observed. Consideration of the presence of a range of many different types of ligands could explain the observed linear relationship between the stability of complexes (log ) and the effective metal ion loading (complexation capacity, ), without the need to assume the presence of any stable specific complexants. Apparently stronger binding sites are utilized at lower metal ion loadings; progressively weaker sites contribute to complexation at higher metal ion concentrations. Taking into account the detection window of the technique employed greatly improves the internal consistency of the overall data. When comparable windows are used, no significant difference is observed between the log relationship for Cu(II) and that for Zn(II), Pb(II), or Cd(II). In natural waters, the complexing material present will be a combination of that derived from terrestrial sources and that formed in situ in the water column. An important observation arising from our analysis is that the binding curves for natural ligands in whole natural‐water samples lie between the binding curves for compounds representative of each these sources, viz. isolated aquatic fulvic acids and biota.

Direct in situ measurements of labile inorganic and organically bound metal species in synthetic solutions and natural waters using diffusive gradients in thin films.

The emerging technique of DGT (diffusive gradients in thin films) is shown to be capable of performing new speciation measurements in situ in natural waters. In DGT, metals are bound to a resin layer after passing through a well-defined diffusion layer. Cd was measured in solutions containing glycine, EDTA, and fulvic (FA) and humic acids (HA) by atomic absorption spectroscopy (AAS), anodic stripping voltammetry (ASV), and DGT. DGT measured similar labile fractions to ASV, with detailed differences being consistent with a thicker diffusion layer allowing more dissociation of labile complexes and a slower diffusion of FA and HA complexes through the gel. When single measurements are made in complex solutions with DGT, precise quantification is impossible due to uncertainties concerning the distribution of species with different diffusion coefficients. A new procedure was proposed based on the advantage of DGT of being able to control the pore size of the diffusive gel layer. Small (inorganic) species diffuse freely through all gels but larger FA and HA (organic) complexes diffuse less freely in more constrained gels. When measurements were made on known solutions of Cu and FA or HA, it was possible to quantify the inorganic and organic species separately. They agreed well with predictions made using the WHAM speciation code. Multiple DGT units were also deployed in situ in a stream with high dissolved organic carbon (14.6 mg/L). The systematic differences between the devices with different gel compositions enabled determination, for the first time, of the in situ concentrations of both labile inorganic and organic species in natural water. A single DGT device with a constrained gel can be used to quantify inorganic species directly, providing absolute accuracy is not required. This ability of DGT to measure well-defined fractions of metals in situ using a simple device gives it considerable potential as a regulatory tool. A direct speciation measurement may be preferable to modeling approaches which require diverse input data that are difficult to determine.

Stability−Charge and Stability−Structure Relationships in the Binding of Dicarboxylic Ligands by Open-Chain Polyammonium Cations

The stability of complexes formed by 5 dicarboxylic ligands with 11 open-chain polyammonium cations (40 systems) was studied potentiometrically, in aqueous solution, at 25 °C. In all the systems ALHr species (A = amine, L = dicarboxylic ligand, r = 1 ... n; diamines n = 3, triamines n = 4, tetraamines n = 4 or 5) were found. Formation constants for the various complexes studied in this work, together with data for the analogous systems previously studied (20 systems), were examined as a function of charges involved in the formation reaction and of the structure of both the dicarboxylic ligand and the polyammonium cation. Structure generally has little effect on stability, while charges play a fundamental role. The most general relationship, valid for all the complexes (the formation constants of 249 complexes were examined), is log K = 0.925(±0.010)ζ2/3 (ζ = |zanionzcation|). The likely role of the formation of these mixed species in the speciation of natural waters and biological fluids is also discussed.

Ecological adaptation and acclimatization of natural freshwater phytoplankters with a nutrient gradient

Ecological adaptation and acclimatization of natural phytoplankters within a nutrient gradient were studied in an oligotrophic pond with special reference to the diel fluctuations of cell volumes and frequency of dividing cells (FDC) at each season using an in situ gradostat. The predominant phytoplankters ( Cryptomonas ovata in spring and autumn, Crucigenia rectangularis in summer and Chlamydomonas elongus in winter) exhibited moderately phased division during each season. These diel cycles could be regressed onto a sine curve to give a highly significant fit. The diel patterns in all gradostat chambers and periods were almost the same except for slight variations in the FDC. This shows that the diel pattern of cell division was governed mainly by the light:dark cycle during the 24 h, without regard to trophic differences of the aquatic environment. The mean growth rates of most phytoplankters were higher in the mesotrophic zone than in the eutrophic zone during each season. In winter, the growth rate of Chlamydomonas elongus was evidently greater during the seventh day of the experiment (Period III) than during the first day (Period I) in the mesotrophic chamber. As Chlamydomonas species occur as mesotrophic species in natural waters, Chlamydomonas elongus must acclimatize easily from the oligotrophic habitat to the mesotrophic environmental condition.

Mercury speciation in natural waters: Measurement of dissolved gaseous mercury with a field analyzer

Mercury evasion from water is commonly modeled using measurements of dissolved gaseous mercury (DGM). We developed a method using a recently available automated field-ready mercury vapor analyzer to rapidly measure the concentrations of DGM in surface waters. We summarize here results of laboratory tests of the method, field intercomparisons with a manual method, and selected data from recent sampling campaigns in Florida and Michigan. The method uses the 1.5 lpm flow of a Tekran® Model 2537A mercury analyzer to purge and analyze discrete water samples, generating near real time (5-min) data on DGM in samples and blanks. Application of the Tekran allowed for detailed analysis of DGM removal kinetics and short-term diel studies characterizing the influence of sunlight and precipitation on DGM production in surface waters. Gas removal kinetics for dozens of samples indicates a first-order rate constant, and supports a 20-min. purge time for surface water samples from Florida (40-min for Michigan samples). Blanks are measured during a second such purge. Our results indicate that DGMs determined by both automated and manual methods are generally comparable, and that DGM in Florida samples is unstable during storage (loss rate constant ∼0.1--0.2 h-1), probably due to oxidation. This suggests that rapid in-field analysis is preferred to storage with delayed analysis. Our data indicate that DGM at the Florida site is influenced by inputs of reactive Hg in rainwater, and by production of surface DGM during photoreduction of oxidized Hg in the water column.

Field cryofocussing hydride generation applied to the simultaneous multi-elemental determination of alkyl-metal(loid) species in natural waters using ICP-MS detection.

Two hydride generation manifold systems, utilizing flow injection and cryotrapping techniques for alkyl-metal(loid) speciation analysis in natural waters, are described in this paper. They provide shipboard capacity for simultaneous derivatization of analytes with NaBH4 and cryotrapping of the generated products in a field packed column at -196 degrees C. The first system is a large-volume hydride generator, using a reagent-injection flow technique as a flow batch type, that has been fully optimized and applied to the simultaneous detection of alkylated species in estuarine waters. The technique permits the analysis of a large volume sample (0.5-11) at a sampling rate of 3 h-1. The second is an online continuous flow hydride generator. A sampling rate of 3-12 h-1 can be achieved with samples of 0.1-0.51. In addition, shipboard operation eliminates major problems related to sample pretreatment, transport and storage. Ultra-trace multi-element determination is finally performed in the laboratory by cryogenic GC hyphenated with ICP-MS. Routine detection limits of 0.5-10 pg (as metal) for 0.51 water samples were achieved for the selected alkyl-metal(loid) species of arsenic, germanium, mercury and tin. Concentrations of various species, obtained from water samples taken from the Rhine estuary, are also presented. These species include alkylated arsenic compounds, other than methyl derivatives, that have been tentatively identified and are reported here for the first time.

Automatic on-line ultratrace determination of Cd species of environmental significance in natural waters by FI-ETAAS

The ultratrace determination of Cd species in natural waters by using an automatic on-line extraction preconcentration system coupled to a graphite furnace atomic absorption spectrometer is presented. Two operational fractions with environmental meaning (able and not able to be accumulated by aquatic organisms) were determined through kinetic discrimination; a Chelex-100 labile fraction consisting of Cd ions and weak Cd complexes and a silica C18 hydrophobic inert fraction consisting of stable cadmium–organic complexes. The figures of merit for the determination of both fractions are given and the obtained values are fully discussed. The aptitude of different resins for the extraction of each fraction is evaluated taking into account retention capacity, pre-concentration efficiency, ease of elution, type of eluant (i.e., compatible with the graphite furnace operation) and the sample–resin time of contact. Special attention is given to the characterization of humic acids and their Cd complexes and to their sorption and elution capabilities from different extracting materials.

The Free Energies of Reactions of Chlorinated Methanes with Aqueous Monovalent Anions: Application of Ab Initio Electronic Structure Theory

The presence of different anionic species in natural waters can significantly alter the degradation rates of chlorinated methanes and other organic compounds. favorable reaction energetics is a necessary feature of these nucleophilic substitution reactions that can result in the degradation of the chlorinated methanes. In this study, ab initio electronic structure theory is used to evaluate the free energies of reaction of a series of monovalent anionic species (OH{sup {minus}}, SH{sup {minus}}, NO{sub 3}{sup {minus}}, HCO{sub 3}{sup {minus}}, HSO{sub 3}{sup {minus}}, HSO{sub 4}{sup {minus}}, H{sub 2}PO{sub 4}{sup {minus}}, and F{sup {minus}}) that can occur in natural waters with the chlorinated methanes, CCk{sub 4}, CCl{sub 3}H, CCl{sub 2}H{sub 2}, and CClH{sub 3}. The results of this investigation show that nucleophilic substitution reactions of OH{sup {minus}}, SH{sup {minus}}, HCO{sub 3}{sup {minus}}, and F{sup {minus}} are significantly exothermic for chlorine displacement, NO{sub 3}{sup {minus}} reactions are slightly exothermic to the thermoneutral, HSO{sub 3}{sup {minus}} reactions are slightly endothermic to thermoneutral and HSO{sub 4}{sup {minus}}, and H{sub 2}PO{sub 4}{sup {minus}} reactions are significantly endothermic. In the case of OH{sup {minus}}, SH{sup {minus}}, and F{sup {minus}} where there are limited experimental data, these results agree well with experiment. The results for HCO{sub 3}{sup {minus}} aremore » potentially important given the near ubiquitous occurrence of carbonate species in natural waters. The calculations reveal that the degree of chlorination, with the exception of substitution of OH{sup {minus}}, does not have a large effect on the Gibbs free energies of the substitution reactions. These results demonstrate that ab initio electronic structure methods can be used to calculate the reaction energetics of a potentially large number of organic compounds with other aqueous species in natural waters and can be used to help identify the potentially important environmental degradation reactions.« less

Simultaneous Determination and Speciation of Zinc, Cadmium, Lead, and Copper in Natural Water with Minimum Handling and Artifacts, by Voltammetry on a Gel-Integrated Microelectrode Array

The paper reports a new approach based on a gel-integrated Hg-plated-Ir-based microelectrode array (GIME), for measuring Cu, Pb, Cd, and Zn speciation in natural waters. This paper focuses on the quantitative discrimination between mobile and colloidal metal species (size limit of a few nanometers), for which most classical separation techniques present severe drawbacks. Previous papers have shown qualitatively that GIME combined with square wave anodic stripping voltammetry (SWASV) has the basic characteristics required to discriminate between these two fractions directly on the unperturbed sample. In addition, because of the large sensitivity provided by GIME, complexation parameters (equilibrium constants and site concentrations) can be determined in little-perturbed samples, particularly without metal addition or with small addition compared with natural concentrations. The advantages of this procedure are exemplified and the possible artifacts occurring when titrating the sample with metals, in particular intermetallic compound formation and other problems, are discussed in detail. The present paper shows that the characteristics of GIME make it a unique tool to get quantitative information on metal speciation at nanomolar or even subnanomolar levels, with only minor sample handling.

Cadmium Complexation with Bisulfide

We have used in situ dialysis to measure the solubility of CdS(s) in sulfidic solutions. The solubility product for the reaction CdS(s) + H+ ⇄ Cd2+ + HS- at 25 °C and 1 atm was found to be 10-14.82±0.03 for a crystalline product and to be 10-14.15±0.06 and 10-14.40±0.06 for two precipitates, respectively. We show that the solubility of these three solids at various pH values (4.2−8.6) and sulfide concentrations (10-4.3−10-1.3 M) can be reproduced adequately by the following four bisulfide complexes: CdHS+, Cd(HS)2, Cd(HS)3-, and Cd(HS)42-; the log Kn values for the general equation Cd2+ + nHS- ⇄ Cd(HS)n2-n are 7.38 ± 0.68, 14.43 ± 0.01, 16.26 ± 0.58, and 18.43 ± 0.05, respectively. The species CdOHS-, which has been reported previously, does not explain our experimental results. Calculations using estimated concentrations of organic ligands (humic substances and organic thiols) known to be present in natural waters indicate that sulfide complexes largely dominate Cd speciation in natural waters at ∑S(−II...

Determination of stability constants for the mono- and difluoro-complexes of Y and the REE, using a cation-exchange resin and ICP-MS

Stability constants of the form F β n =[MF n 3− n ][M 3+] −1[F −] − n (where brackets denote the concentrations of complexes MF n 3− n , free metal ions M 3+ and free fluoride F −) were determined for the mono- and difluoro-complexes ( n=1, 2) of yttrium and the rare earth elements (Y+REE). A new method was developed, using equilibration with Bio-Rad AG 50W-X2 cation-exchange resin and analysis of the solution phase using inductively-coupled plasma mass spectrometry (ICP-MS). This method enabled us to measure all stability constants under identical conditions and is, therefore, especially sensitive to subtle inter-element variations in F β 1 and F β 2. The pattern of log F β 1 differs distinctly from the majority of those in the literature and contains more structure. The set of F β 1 values that is commonly used for modeling REE speciation in natural waters appears to be in error for REE heavier than Eu. The pattern of log F β 2 is similar in shape to that of log F β 1, but substantially deviates for Ce. This is reflected in the pattern of stepwise stability constant ratios across the Y+REE series: the average value of K 2/ K 1= F β 2/( F β 1) 2 is 0.07±0.03 for Y+REE excluding Ce, whereas for Ce it is 0.49. While anomalous behaviour of Ce has been reported for many environments and is known to be caused by its unique redox chemistry, only Ce(III) should be present under the conditions of these experiments.

Dissolved phase speciation of zinc in the humber estuary

An established approach to the determination of zinc speciation in natural waters has been applied to samples from a major UK estuary. Data for dissolved zinc concentrations and zinc complexation capacity are reported. The importance of the strength of the metal-ligand complex to the estimation of the predominant forms of zinc in estuaries is discussed. Dissolved zinc in the two major river inputs and low salinity zones appears to be more or less exclusively associated with naturally-occurring organic complexing material. At higher salinities, the assessment of predominant zinc species is dependent on uncertainties in estimates of the metal ligand stability constant.

Chromium speciation in natural waters using serially connected supported liquid membranes

A supported liquid membrane (SLM) method for the speciation of chromium has been developed. The method is based on selective extraction and enrichment of anionic Cr(VI) and cationic Cr(III) species in two serially connected SLM units. Methyltricaprylammonium chloride (Aliquat) and di-(2-ethylhexyl) phosphoric acid (DEHPA), respectively were used as the selective extractants in the membrane liquid. Graphite furnace atomic absorption spectrometry (GFAAS) was utilised for final determination. Optimised conditions for the DEHPA membrane were, sample solution at pH 3, acceptor solution 0.1 M HNO3 and 10% w/w carrier in kerosene. The corresponding values for the Aliquat membrane were pH 7, 0.75 M HNO3 and 6% w/w carrier in di-n-hexylether. This gave extraction efficiencies for Cr(III) and Cr(VI) of 90 and 40%, respectively. The method was used to measure the concentration of Cr III and Cr VI in surface water from an abandoned tannery site. Storage experiments at different pH showed that preservation at neutral pH gave almost constant values over a period of one month. At acidic pH (pH=3.0) the concentration of Cr(VI) decreased rapidly while the concentration of Cr(III) increased. The detection limit, expressed as three times the standard deviation of enriched blank samples was 0.01 μg l−1.

Interactions between dissolved organic carbon and mercury species in surface waters of the Florida Everglades

An ultrafiltration procedure has been developed to study the interaction between organic C and Hg species in natural waters, and a pilot study was conducted in the surface waters of the Florida Everglades. Compared to total Hg, CH 3Hg shows different distribution patterns in the suspended particulate, colloidal, and truly dissolved phases. Colloidal forms (0.22 μm, 3 kDa) contain the majority of the total dissolved Hg, while the amount found in the truly dissolved fraction (<3 kDa) is small (about 10%). However, CH 3Hg, which shows strong binding capability with low molecular-weight dissolved organic C, is present almost entirely in the lower molecular-weight fraction of the colloids and in the truly dissolved fraction. Quantitative CH 3Hg data correlate well with those for dissolved organic C, an indication that the organic matter present in the system plays an important role in the fate and transport of organomercury. Distribution coefficients between water and the different-sized fractions of the dissolved organic C were determined for both total Hg and CH 3Hg. Results for total Hg were in general agreement with other reports resulting from studies of molecular size distributions of total Hg in freshwater systems. This is, to the best of our knowledge, the first report of such distribution profiles for CH 3Hg between different-sized fractions of dissolved organic C in natural waters.

Arsenic speciation including ‘hidden’ arsenic in natural waters

Recent studies indicate the existence in natural waters of ‘hidden’ arsenic which had previously been undetected by the hydride generation technique. A speciation method for arsenic species has been developed in which hidden arsenic was classified into two fractions by their lability to the photochemical degradation procedure: the ultraviolet-labile fraction and the ultravioletresistant fraction. The ultraviolet-labile fraction was the major fraction of hidden arsenic and comprised 15‐45% and 4‐26% of the total arsenic in Uranouchi Inlet and Lake Biwa (Japan), respectively. The highest concentration of the ultraviolet-resistant fraction was observed in Uranouchi Inlet during the summer, in which dimethylarsinic acid increased in the water column. We discuss the hidden arsenic fraction as the key to explaining arsenic speciation in natural waters. Copyright # 1999 John Wiley & Sons, Ltd.

Application of Pitzer's Equations for Modeling the Aqueous Thermodynamics of Actinide Species in Natural Waters : A Review

A review of the applicability of Pitzer's equations to the aqueous thermodynamics of actinide species in natural waters is presented. This review includes a brief historical perspective on the application of Pitzer's equations to actinides, information on the difficulties and complexities of studying and modeling the different actinide oxidation states, and a discussion of the use of chemical analogs for different actinide oxidation states. included are tables of Pitzer ion-interaction parameters and associated standard state equilibrium constants for each actinide oxidation state. These data allow the modeling of the aqueous thermodynamics of different actinide oxidation states to high ionic strength.

Soluble iron sulfide species in natural waters: Reappraisal of their stoichiometry and stability constants

A wide range of stoichiometries has been previously proposed for soluble iron sulfide species and there is no general agreement on their importance in natural waters. The solubility of Fe(II) in 0.1 M NaClO4 equilibrated at 20 ± 0.1°C with various partial pressures of H2S (0.1, 0.001, 0.0001, 0.00001 MPa) was measured in the pH range 3.1-7.9. Equilibrium was established within 1-6 h when amorphous FeS was the solid phase. The results could all be fitted using values for the solubility product constant (I = 0) of p*Ks = 3.00 ± 0.12 and of the stability constant for a soluble Fe(HS) 2 species (I = 0) of pβ 2 = -6.45 ± 0.12 where *Ks = aFe2+· aHS-/aH+ and β 2 = aFe(HS) 2/aFe2+· (aHS-)2. Any soluble species of the form Fex (HS) 2x where x = (1 ?∞) would fit the data equally well. Measurements at different partial pressures are inconsistent with labile species of the form FexSx. There was no evidence for a Fe(HS) + species. When a solution is saturated with respect to amorphous FeS, Fe(HS) 2 will only be a significant proportion of Fe(II) when S(-II) is higher than 0.2mmoll-1. The constants for Fe(HS) 2 or Fex (HS) 2x (x ≥ 2) are consistent with all freshwater data where constant values of measured ion activity products provide no evidence for soluble complex formation. For marine waters with high sulfide concentrations (≥ 6mmol l-1), measured concentrations of Fe(II) are consistent with there being negligible soluble iron sulfide. The data are better fitted if the dissolved species are polymeric as predicted concentrations of the monomer Fe(HS) 2 are significant. These findings suggest that rather than the dissolved species being Fe(HS) 2, it is probably polymeric, that is Fex (HS) 2x (x ≥ 2).

Flow analysis of micro amounts of chromium(III) and (VI) in natural water by solid phase spectrophotometry using diphenylcarbazide

Specific determination of chromium(III) and chromium(VI) in natural water samples was performed without mutual separation. The chromium in sample solution was concentrated on cation-exchange resin packed in a flow-through cell as a reaction product of chromium(VI) with diphenylcarbazide. The absorbance increase caused by the accumulation of the complex on cation-exchange resin was continuously measured. By using peroxodisulfate as an oxidizing agent, the chromium(III) in sample solution was completely oxidized to chromium(VI). The chromium(III) concentration was calculated by the difference between the values of the total chromium and chromium(VI). The detection limit for chromium(VI) and total chromium was 70 pg and 120 pg, respectively. This method was applied to the specific determination of chromium in several natural water samples. The results of the total chromium obtained by the proposed method show moderate agreement with that obtained with ICP-MS. Unlike the previous results reported in chromium speciation studies, the predominant chromium species in natural water was chromium(VI).

Chromium speciation in natural waters draining contaminated land, Glasgow, U.K.

Historically, solid waste from chromite ore processing has been disposed of at a number of sites in Glasgow, Scotland. Leachate from these sites has been implicated as a source of chromium (Cr) contamination to both groundwaters and stream waters in the south east area of the city. In this study, chromium speciation has been determined in ground-, stream-, river- and pore waters, to assess the extent of contamination and the associated risk. The speciation of chromium is important, as the trivalent species of chromium (Cr(III)) is an essential form of the element, while hexavalent chromium (Cr(VI)) is a known carcinogen to humans via inhalation. Concentrations of total chromium have also been determined in sediments from the River Clyde, to assess the significance of local concentrations relative to those elsewhere in the catchment. High concentrations of Cr(VI) were found in groundwaters and streamwaters in the area immediately surrounding the contaminated sites, and high concentrations of chromium were also found in River Clyde sediments downstream of these sites. However, these concentrations rapidly decrease away from the chromium-contaminated south eastern side of the city. Data from porewaters suggest that some reduction of Cr(VI) occurs naturally in the sediments, indicating that the risk posed by high concentrations of Cr(VI) should be decreased over the longer term.

The speciation of (CH3)2Sn2+ in electrolyte solution containing the major components of natural waters

Hydrolysis constants of dimethyltin(IV) cation, in different salt solutions (CaCl2: 0.15 ≤ I ≤ 0.90; MgCl2: 0.30 ≤ I ≤ 0.60; NaCl-–NaClO4, NaCl-–NaNO3 mixtures: I = 3; NaCl-–Na2SO4 mixtures: I = 1 mol dm-3) were determined by potentiometric ([H+]-glass electrode) measurements. These data, together with previous data (De Stefano et al., 1996b) were interpreted in terms of DHT (Debye–Huckel type) and Pitzer equations. The mixed electrolyte solution results also allowed us to obtain Θ and Ψ parameters for the Pitzer equation. Calorimetric measurements were made at different ionic strengths in order to find the temperature dependence of hydrolysis constants and of the relative interaction parameters. The body of results allows us to determine the speciation of natural waters in a wide range of ionic strengths and temperatures.