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PubMed2000

Speciation of dissolved iron(III) and iron(II) in water by on-line coupling of flow injection separation and preconcentration with inductively coupled plasma mass spectrometry.

A method has been developed for the speciation of trace dissolved Fe(II) and Fe(II) in water by on-line coupling of flow injection separation and preconcentration with inductively coupled plasma mass spectrometry (ICPMS). Selective determination of Fe(III) in the presence of Fe(II) was made possible by on-line formation and sorption of the Fe(III)-pyrrolidinecarbodithioate (PDC) complex in a PTFE knotted reactor over a sample acidity range of 0.07-0.4 mol L(-1) HCl, elution with 1 mol L(-1) HNO3, and detection by ICPMS. Over a sample acidity range of 0.001-0.004 mol L(-1) HCl, the sum of Fe(III) and Fe(II), i.e., Fe(III + II), could be determined without the need for preoxidation of Fe(II) to Fe(III). The concentration of Fe(II) was obtained as the difference between those of Fe(III + II) and Fe(III). With a sample flow rate of 5 mL min(-1) and a 30-s preconcentration time, an enhancement factor of 12, a retention efficiency of 80%, and a detection limit (3s) of 0.08 microg L(-1) were obtained at a sampling frequency of 21 samples h(-1). The relative standard deviation (n = 11) was 2.9% at the 10 microg L(-1) Fe(III) level. Recoveries of spiked Fe(III) and Fe(II) in local tap water, river water, and groundwater samples ranged from 95% to 103%. The concentrations of Fe(III) and Fe(II) in synthetic aqueous mixtures obtained by the proposed method were in good agreement with the spiked values. The result for total iron concentration in the river water reference material SLRS-3 was in good agreement with the certified value. The method was successfully applied to the determination of trace dissolved Fe(III) and Fe(II) in local tap water, river water, and groundwater samples.

Fresh Water↗
PubMedDate not supplied

Broad patterns of speciation are correlated with the evolution of new silk proteins in spiders but not in the lepidoptera.

Silk synthesis is an ancestral character of both the Lepidoptera and the Araneae. Araneae evolution is marked by an increased commitment to a silk-producing physiology. At least three major Araneae speciation events are correlated with the evolution of new silk-producing glands and new silk proteins. In contrast, although 98% of the Lepidoptera produce silk, there appears to be no relationship between silk use, protein types, and species numbers. The differences in these two systems, both meeting a need to produce a large volume of protein, may reflect predictable resource availability to herbivorous Lepidoptera larvae but fluctuating resource availability to carnivorous spiders.

Animals↗
PubMed2001

Metal speciation dynamics and bioavailability. 2. Radial diffusion effects in the microorganism range.

The free ion activity model for the biouptake of metals from complex media is limited to cases where mass transfer is not flux determining. This paper follows a previous paper (Van Leeuwen, H. P. Environ. Sci. Technol. 1999, 33, 3743) where speciation dynamics and bioavailability of metals are analyzed in terms of bioconversion kinetics and simultaneous metal transport in the medium coupled with dissociation kinetics. Such analysis shows under what conditions labile complex species contribute to the biouptake process or, equivalently, under what conditions the free ion activity model is not obeyed. The present work addresses the theoretical extension of the expressions for the metal flux in the medium by a radial diffusion term so that these are also applicable in the microorganism size range. The transition from macroscopic to microscopic surfaces affects not only the nature of the flux but also the extent of lability of complex species (Van Leeuwen, H. P.; Pinheiro, J. P. J. Electroanal. Chem. 1999, 471, 55), and this can have a dramatic influence on the rate of biouptake of metal ions. Labilities of metal complexes and the ensuing limiting metal fluxes are therefore systematically analyzed for various dimensions of the uptaking surface. Different conditions of bioaffinities and bioconversion capacities are considered, and a number of examples of metal complexes with specified kinetic features are discussed.

Biological Availability↗
PubMed2001

Atmospheric mercury speciation: laboratory and field evaluation of a mist chamber method for measuring reactive gaseous mercury.

Knowledge of atmospheric mercury speciation is critical to modeling its fate. Thus there is a crucial need for reliable methods to measure the fraction of gaseous atmospheric Hg which is in the oxidized Hg(II) form (termed reactive gaseous mercury, RGM). We have developed a novel method for measurement of RGM using a refluxing mist chamber, and we recently reported the results of sampling campaigns for RGM in Tennessee and Indiana. In general, measured RGM levels were about 3% of total gaseous mercury (TGM), and our results support prevailing hypotheses about the nature and behavior of RGM in ambient air. Because its use for RGM is growing, we now report in more detail the development and testing of the mist chamber method. Several styles of mist chambers have been investigated. The most versatile design employs a single nebulizer nozzle and can operate at flows of 15-20 L/min. The water-soluble Hg is collected in ca. 20 mL of absorbing solution, which is then analyzed for Hg(II) by SnCl2 reduction and CVAFS. One-hour samples (ca. 1 m3 of air) generally contain 50-200 pg of RGM. The method detection limit for 1-h samples is approximately 6-10 pg/m3. Thus short sample times can reveal temporal variations in RGM that would not otherwise be observable. The efficiency of collecting RGM in mist chambers is highly dependent on Cl- concentration in the absorbing solution, in keeping with equilibrium calculations. Artifact formation of Hg(II) by oxidation of Hg0 under ozone ambient conditions appears to be sufficiently slow so as to be negligible for the short (ca. 1 h) runs that are typically employed. We observed no significant error from cosampled particles or aerosols in rural nonimpacted air samples. We have developed a simple approach to analyzing mist chamber samples in the field using an automated Hg sampler.

Air Pollutants↗
PubMed2002

Solid-solution speciation and phytoavailability of copper and zinc in soils.

The soil solution speciation and solid-phase fractionation of copper (Cu) and zinc (Zn) in 11 typical uncontaminated soils of South Australia were assessed in relation to heavy metal phytoavailability. The soils were analyzed for pH (4.9-8.4), soil organic matter content (3.5 to 23.8 g of C kg(-1)), total soil solution metal concentrations, Cu8 (49-358 microg kg(-1)) and Zn8 (121-582 microg kg(-1)), and dissolved organic matter (DOM) (69-827 mg of C L(-1)). The solid-liquid partition coefficient (Kd) ranged from between 13.9 and 152.4 L kg(-1) for Cu and 22.6 to 266.3 L kg(-1) for Zn. The phytoavailability of Cu and Zn could be predicted significantly using an empirical model with the solid-phase fractions of Cu and Zn, as obtained from selective sequential extraction scheme, as components. Phytoavailable Cu and Zn were found to significantly correlate with fulvic complex Cu (r= 0.944, P < 0.0001) and exchangeable Zn (r = 0.832, P = 0.002), respectively. The fulvic complex Cu was found to explain 89.2% of the variation in phytoavailable Cu, where as, the exchangeable Zn together with fulvic complex Zn could explain 78.9% of the variation in phytoavailable Zn. The data presented demonstrate the role of solid-phase metal fractions in understanding the heavy metal phytoavailability. The assessment of the role of solid-phase fractions in heavy metal phytoavailability is a neglected area of study and deserves close attention.

Benzopyrans↗
PubMed2001

Speciation of mercury in a fluid mud profile of a highly turbid macrotidal estuary (Gironde, France).

Mercury (Hg) speciation and partitioning have been investigated in a fluid mud profile collected in the high turbidity zone of the Gironde estuary. The formation of the fluid lens generates local and transient oxic-anoxic oscillations following the sedimentation-resuspension tidal cycles under a specific hydrodynamic regime. The total Hg concentration, ranging from 5 to 190 nM, increases with SPM concentration (4-174 g L-1) to a maximum at bottom. Particulate Hg averages 99% of total Hg. Particulate inorganic Hg (IHg(II)P) and monomethyl Hg (MMHgP) exhibit a similar trend: the maximum concentration is observed within the upper layer above the depth of 7 m and the minimum at the bottom layers of the fluid mud. Significant levels of "dissolved" (i.e. filter passing) Hg species (IHg(II)D, HgoD, MMHgD, DMHgD) are observed within the redox transition interface. In the sub/anoxic fluid mud layer, increasing concentrations of IHg(II)D and MMHgD coincide with decreasing concentrations of IHg(II)P and MMHgP, respectively. The distribution coefficient (log Kd) between the "dissolved" and particulate fraction for IHg(II) averages 4.5 +/- 0.2. A Kd minimum for IHg(II) is observed in the surface layer and at the bottom of the fluid mud and coincides with the maximum levels of dissolved Mn and Fe. Log Kd for MMHg averages 3.3 +/- 0.9 and presents the highest values (4.3-4.6) in the surface and the lowest (approximately 2.2) at bottom, corresponding to the particulate carbon profile. These results demonstrate that the fate of IHg(II) and MMHg in the fluid mud system is influenced by the redox cycling of major species such as carbon, Fe, and Mn. It is therefore suggested that the redox oscillations generated by fluid mud formation in the high turbidity zone affect the distribution and transfer of Hg species in macrotidal estuaries.

Environmental Monitoring↗
PubMed2001

Determination of arsenic speciation in poultry wastes by IC-ICP-MS.

The aromatic organoarsenic compounds 4-hydroxy 3-nitrobenzenearsenic acid (Roxarsone, ROX) or 4-aminoben-zenearsenic acid (p-arsanilic acid, p-ASA) are used as feed additives in the poultry industry for disease control and enhanced feed efficiency. While federal regulations govern acceptable As concentrations in edible tissue, elevated As concentrations occur in poultry litter, which raises concerns over repeated land application of poultry litter in agriculture. As a precursor to studying the fate of these organoarsenic compounds in soils, three speciation methodologies were developed to separate ROX and p-ASA from the more common and more toxic As species arsenate, arsenite, dimethyl arsenic acid (DMA), and monomethyl arsenic acid (MMA). The six arsenic species were separated on a Dionex AS14 column using a PO4 eluant, an AS16 column using a OH- eluant, and an AS7 column using a HNO3 eluant. While all three methods provided detection limits below 0.5 microg L(-1) for all species, detection limits were lowest for the AS16 and AS7 columns, where all detection limits were generally < 0.05 microg L(-1). The major arsenic species in a water extract of a poultry litter sample was identified as ROX by all three methods with trace concentrations of DMA and As(V) also detected. The AS14 and AS16 separations also revealed a number of unidentified As species present at low concentrations, presumably metabolites of ROX. This methodology should prove useful in identifying organoarsenic compounds and the more toxic inorganic species in soils subject to poultry litter application.

Animals↗
PubMed2001

Disinfection byproduct relationships and speciation in chlorinated nanofiltered waters.

The formation and speciation of disinfection byproducts (DBPs) resulting from chlorination of nanofilter permeates obtained from various source water locations and membrane types are examined. Specific ultraviolet absorbance and bromide utilization are shown to decrease following nanofiltration. Both dissolved organic carbon (DOC) concentration and ultraviolet absorbance at 254 nm were found to correlate strongly with trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) concentrations in chlorinated nanofilter permeates, suggesting that they can be employed as surrogates for DBPs in nanofiltered waters. Because smooth curves were obtained for individual THM and HAA species as well as bromine and chlorine incorporation into THMs and HAAs as a function of Br-/DOC molar ratio, it is likely that mole fractions of these DBPs are more strongly influenced by chlorination conditions, Br-, and DOC concentrations than NOM source and membrane type. Mole fractions of mono-, di-, and trihalogenated HAAs were found to be independent of Br-/DOC. Even at a very low Br-/DOC of 2.9microM/mM, the mixed bromochloro- and tribromoacetic acids constituted 20% of total HAAs on a molar basis. This increased to approximately 50% as Br-/DOC increased to approximately 25microM/mM or more, proving that a large fraction of HAAs may not be covered under existing federal regulations. Total THM and HAA9 concentrations decreased in permeate waters with increasing Br-/DOC suggesting that nanofilter permeates are limited with respect to DBP precursors.

Absorption↗
PubMed2002

Speciated ambient carbonyls in Rio de Janeiro, Brazil.

Carbonyls in urban air continue to receive scientific and regulatory attention as toxic air contaminants and for their important role in photochemical smog. However, few data are available for speciated carbonyls in urban air. Ambient concentrations of up to 61 carbonyls have been measured in Rio de Janeiro, Brazil. The most abundant carbonyls were formaldehyde and acetaldehyde (study-averaged concentrations of 10.8 +/- 4.1 and 10.4 +/- 4.6 microg m(-3), respectively, in samples of 3-h duration collected from May to November 2000 at a downtown location during the morning vehicle commute) followed by acetone, 2-butanone, and benzaldehyde. Ambient concentrations of other carbonyls (except acetophenone) correlated well with those of acetaldehyde and of formaldehyde. This study examines the ambient acetaldehyde/ambient formaldehyde concentration ratio in Brazilian cities since the mid-1980s in the context of changes in Brazil's reliance on ethanol as a vehicle fuel. This ratio has begun to decrease in recent years due to fleet turnover and is likely to decrease further as older cars fueled with ethanol are replaced by lower-emitting models that run on a gasoline-ethanol blend. The carbonyls measured are ranked with respect to ozone formation potential (using MIR coefficients) and reaction with OH (using carbonyl-OH reaction rate constants). Ozone formation is dominated by formaldehyde (43% of total) followed by acetaldehyde (32%) and methylglyoxal (8%); other carbonyls each contributed < or = 4% of total. For reaction with OH, acetaldehyde ranks first closely followed by formaldehyde.

Air Pollutants↗
PubMed2002

Natural organic matter affects arsenic speciation and sorption onto hematite.

Arsenic mobility in natural environments is controlled primarily by sorption onto metal oxide surfaces, and the extent of this sorption may be influenced strongly by the presence of other dissolved substances that interact with surfaces or with arsenic itself. Natural organic matter (NOM), a prevalent constituent of natural waters, is highly reactive toward both metals and surfaces and is thus a clear candidate to influence arsenic mobility. The objectives of this study were therefore to reveal the influences of diverse NOM samples on the sorption of arsenic onto hematite, a model metal oxide, as well as to reveal influences of arsenic on the sorption of NOM, using conditions and concentrations relevant to natural freshwater environments. Of the six NOM samples tested, four formed aqueous complexes with arsenate and arsenite. The extent of complexation varied with the NOM origin and, in particular, increased with the cationic metal (primarily Fe) content of the NOM sample. In addition, every NOM sample showed active redox behavior toward arsenic species, indicating that NOM may greatly influence redox as well as complexation speciation of arsenic in freshwater environments. When NOM and As were incubated together with hematite, NOM dramatically delayed the attainment of sorption equilibrium and diminished the extent of sorption of both arsenate and arsenite. Consistent with this result, when NOM and As were introduced sequentially, all NOM samples displaced sorbed arsenate and arsenite from hematite surfaces, and arsenic species similarly displaced sorbed NOM from hematite in significant quantities. Competition between NOM and As for sorption thus appears to be a potentially important process in natural waters, suggesting that NOM may play a greater role in arsenic mobility than previously recognized. In addition, in all sorption experiments, arsenite was consistently desorbed or prevented from sorbing to a greater extent than arsenate, indicating that interactions with NOM may also partially explain the generally greater mobility of arsenite in natural environments.

Adsorption↗
PubMed2002

Chemical speciation and toxicity of nickel species in natural waters from the Sudbury area (Canada).

Metal complexation properties of dissolved organic carbon (DOC) in freshwaters are recognized but poorly understood. Here, we investigated the release of free nickel from Ni-DOC complexes using nickel-polluted freshwaters from Sudbury (Canada). We used the Competing Ligand Exchange Method with Chelex-100 as the competing ligand to measure the rate of free Ni2+ ion released by the dissociation of Ni-DOC complexes. The kinetic studies showed that the fastest kinetically distinguishable component representing approximately 30-95% of the total nickel had a dissociation rate coefficient similar to that reported for [Ni(H20)6]2+. High concentrations of Ca2+ and Mg2+ caused a larger amount of the DOC-bound nickel to be released as free Ni2+ ion. Growth inhibition of the freshwater alga Pseudokirchneriella subcapitata was highly correlated with the Ni/DOC ratio, the free plus labile nickel concentration, and the dissociation rate coefficient. While the levels of metals were not sufficient to kill Daphnia magna, these test organisms were immobilized in the same samples that showed algal growth inhibition. Only one sample caused 22% death of Hydra attenuata. The algal toxicity tests were consistent with the kinetic speciation results and are consistent with the hypothesis that dissolved [Ni(H20)6]2+ plus other labile nickel species are toxic forms of Ni present.

Animals↗
PubMed2002

Speciation of aqueous chromium by use of solid-phase extractions in the field.

Here the fate and mobility of chromium in an organic-rich wetland area was studied through a field investigation in which chromium speciation in aqueous samples was estimated by use of solid-phase extraction resins that removed the cationic, anionic, and hydrophobic organic species from solution. Results show that aqueous chromium concentrations in the surface and pore waters at this site are higher than would be predicted by simple thermodynamic equilibrium with solid chromium hydroxides. Hexavalent chromium was not observed and therefore could not explain these higher than expected chromium concentrations. Aqueous chromium in concentrations greater than 30 microg/L was found to be slightly correlated with total dissolved organic carbon (R2 = 0.66), thus suggesting enhanced chromium concentrations because of complexation with organic ligands. The results of the solid-phase extraction performed show that aqueous chromium in the wetland pore water and surface water exists primarily as an anion (96%). It is concluded that the solubility and mobility of chromium are controlled, at least in part, by complexation with dissolved organic carbon and that this may be a thermodynamically controlled process.

Carbon↗
PubMed2003

Selenium speciation, solubility, and mobility in land-disposed dredged sediments.

Pilot-scale tests for the land disposal of Se-enriched sediments from the San Luis Drain were performed in the San Joaquin Valley, California. Three test plots were instrumented and monitored on a dirt-road embankment near the sediment source area, providing an opportunity to measure Se oxidation and solubilization rates over a period of 2-3 yr. Soil, soil water, and groundwater data indicated that the amendment did not cause movement of dissolved Se below a depth of 15 cm. The low permeability of underlying sediments and the overall low Se solubility limit Se movement toward the groundwater table. Selenium remained in reduced forms and largely immobile at this site, although in-situ Se oxidation was measurable. Soluble Se concentrations increased from less than 0.5% to approximately 2.5% in the first 207 d following sediment application. Minor Se solubilization occurred after 439 and 704 d. Changes in Se fractionation measured using sequential extractions and Se speciation based on X-ray spectroscopy (XANES) results were in qualitative agreement. XANES results indicated initially rapid oxidation of organo-Se and/or elemental Se to selenite during the first 207 d, followed by minor oxidation after 439 d. Further solubilization of the Se inventory is anticipated, but at a low rate of 1-2% per year, comparable to rates measured in other studies.

Geologic Sediments↗
PubMed2002

Solid-state speciation of natural and alum-amended poultry litter using XANES spectroscopy.

While alum amendments have shown to be effective in lowering water-soluble phosphate levels in poultry litter, the mechanism by which this occurs is not fully known. To determine the solid-state speciation of phosphate in litter samples, experiments were conducted with X-ray absorption near edge structure (XANES) spectroscopy. XANES analysis reveals that, in unamended samples, phosphate is present as weakly bound inorganic as well as some organic phosphate, with some dicalcium phosphate-type calcium phosphates also present. When alum is applied in the houses, XANES results suggest that it precipitates out as amorphous Al(OH)3 and then reacts with phosphate via an adsorption mechanism. No evidence was found of aluminum phosphate precipitation in any samples.

Alum Compounds↗
PubMed2003

Kinetic speciation of Co(II), Ni(II), Cu(II), and Zn(II) in model solutions and freshwaters: lability and the d electron configuration.

The kinetic speciation of Co(II), Ni(II), Cu(II), and Zn(II) in model solutions of a well-characterized fulvic acid (Laurentian fulvic acid), freshwater samples from the Rideau River (Ottawa, Ontario), and freshwater samples from the Sudbury (Ontario) area were investigated by the competing ligand exchange method using Chelex 100 as the competing ligand and by inductively coupled plasma-mass spectrometry to measure the dissociation kinetics. The metal species were quantitatively characterized by the rate coefficient for the first-order dissociation of metal complex to free metal ion. This technique can be applied to almost all elements and represents an important advance in our ability to investigate the kinetic availability of metal species in the freshwater environment. The order of the lability of the metal complexes, Co(II) > Ni(II) > Cu(II) < Zn(II), follows the reverse order of the ligand field stabilization energy with the exception of Cu(II); the behavior of Cu(II) is also due to the Jahn-Teller effect, which shortens the equatorial bonds and lengthens the axial bonds of a tetragonally distorted Cu(II)-L6 complex. This study has demonstrated a relationship between the lability of metal-DOM complexes of the 3d transition metals in freshwaters and their d electron configuration. This is the first time that the importance of the d electron configuration on the lability of metal complexes in the freshwater environment has been demonstrated. The slow complexation kinetics of both Ni(II) and Cu(II) suggestthatthe usual equilibrium assumption for freshwaters may be invalid.

Biological Availability↗
PubMed2002

Speciation of Cu and Zn in drainage water from agricultural soils.

Inputs of copper and zinc from agricultural soils into the aquatic system were investigated in this study, because of their heavy agricultural usage as feed additives and components of fertilizers and fungicides. As the mobility and bioavailability of these metals are affected by their speciation, the lipophilic, colloidal and organic fractions were determined in drainage water from a loamy and a humic soil treated with fungicides or manure. This study therefore investigates the impact of agricultural activity on a natural environment and furthers our understanding of the mobility of metals in agricultural soils and aquatic pollution in rural areas. Marked increases in the total dissolved metal concentrations were observed in the drainage water during rain events with up to 0.3 microM Cu and 0.26 microM Zn depending on the intensity of the rainfall and soil type. The mobile metal fractions were of a small molecular size (<10 kD) and mainly hydrophilic. Lipophilic complexes originating from a dithiocarbamate (DTC) fungicide could not be observed in the drainage water; however, small amounts of lipophilic metal complexes may be of natural origin. Cu was organically complexed to > 99.9% by abundant organic ligands (log K 10.5-11.0). About 50% of dissolved Zn were electrochemically labile, and the other 50% were complexed by strong organic ligands (log K 8.2-8.6). Therefore very little free metal species were found suggesting a low bioavailability of these metals in the drainage water even at elevated metal concentrations.

Agriculture↗
PubMed2003

XAS speciation of arsenic in a hyper-accumulating fern.

The coordination environment and the redox speciation of arsenic in a newly discovered arsenic hyper-accumulating fern (Pteris vittata L) were investigated by X-ray absorption spectroscopy. This method allowed us to probe arsenic directly, i.e., with minimal sample preparation. The results indicate that arsenic is predominantly accumulated as As(III) in the leaves. XANES and EXAFS results show that As(III) in the leaves is primarily present as aqueous arsenite species. The plant actively maintains arsenic in this reduced oxidation state, because after sample collection and subsequent aging and drying of the plant material, As(III) is gradually oxidized to As(V). We think that these arsenite species are sequestered in vacuoles. At extremely high As concentrations (ca. 1% As per dry weight) arsenic in the fern leaves is coordinated to a significant degree by sulfur in addition to oxygen. This spectral signature indicates that thiol-rich compounds are implicated in the biochemical transformations of arsenic within the plant.

Arsenic↗
PubMed2003

Importance of chlorine speciation on de novo formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans.

The role of chlorine speciation on de novo formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) has been studied thoroughly in an entrained flow reactor during simulated waste combustion. The effects of gas-phase chlorine species such as chlorine (Cl2), hydrogen chloride (HCl), and chlorine radicals (Cl*), as well as ash-bound chlorine, on PCDD/F de novo formation were isolated for investigation. The ash-bound chlorine alone was observed to be a sufficient chlorine source for PCDD/F formation. The addition of HCl to the system did not influence the yields of the PCDDs/Fs nor the degree of chlorination due to its poor chlorinating ability. Addition of 200 ppm of Cl2 to the ash-feed system resulted in increased PCDD/F yields, especially for the octa- and hepta-chlorinated congeners. Altering the reaction temperature to enable the presence of only Cl2 to the system did not change the yields of PCDD/F compared to those when both Cl2/Cl* were present. However, comparison between ash-bound and gas-phase chlorine, the latter at a concentration typical of a realistic combustion process, revealed ash-bound chlorine to be the more important chlorine source for de novo formation of PCDD/F in a full-scale incinerator.

Air Pollutants↗