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PubMed1999

Antimony speciation in environmental samples by interfacing capillary electrophoresis on-line to an inductively coupled plasma mass spectrometer.

Antimony is a widely distributed trace element of ecotoxicological interest. A pathway via bioalkylation of inorganic Sb species is discussed in the literature, resulting in organically bound Sb species. Therefore, Sb speciation becomes increasingly a matter of interest for risk assessment in the environment. This contribution investigates the possibilities of CE on-line hyphenated to ICP-MS for Sb speciation. Two methods are employed, both highly resolving the species but only one preserving the species stability. The latter used Na2HPO4/NaH2PO4, 20 mM, pH 5.6 as the background electrolyte and NaOH or acetic acid as stacking electrolyte 1 or stacking electrolyte 2, respectively. Detection limits of 0.1 microgram/1-0.7 microgram/1, depending on species, were achieved. When analysing liquid phases from fouling and sewage sludge up to eight antimony species were detected. Sb (V) as well as methylated Sb species were found.

Antimony↗
PubMed1999

Understanding of peak deterioration in hyphenated speciation systems due to gas-liquid separation in the hydride generation interface.

In hyphenated speciation systems with a hydride generation interface one of the processes influencing peak deterioration is gas-liquid separation. A mathematical model was developed to calculate attenuation, signal tailing and resolution loss of HPLC peaks due to gas-liquid separation. It was shown experimentally--using an HPLC-hydride generation-atomic fluorescence spectrometry system for arsenic speciation--that the mathematical model predicts peak deterioration well. This allowed us to study the parameters influencing the deterioration, viz. gas-liquid separation parameters (gas-liquid separator head space volume and purge gas volume flow-rate) and HPLC peak parameters [width (ratio) and resolution] theoretically, simulating HPLC peaks with gaussian functions.

Chromatography, High Pressure Liquid↗
PubMed1988

Ecological speciation by sexual selection.

Quantitative genetic models are used to investigate a mechanism of speciation involving natural and sexual selection on a population with more than one ecological niche available. Female choice of mates, based on ecologically important characters, can initiate a sudden shift into a new niche. Whether males alone or both sexes make the transition depends strongly on the genetic correlation between homologous male and female characters. This mode of speciation rapidly produces premating and postmating isolating barriers, as well as ecological separation, between populations that can then coexist in the same area as distinct species.

Ecology↗
PubMed2001

The uptake and speciation of various Al species in the Brassica rapa pekinensis.

An investigation was carried out on the uptake and speciation of Al species in Al tolerant Chinese cabbage (Brassica rapa L. ssp. pekinensis). Plants were exposed to 10 microg cm(-3) of Al in the chemical forms of Al3+, Al-citrate and Al-malate in a time span from 1 up to 24 h. In each experiment the nutrient solution and stem sap were analysed by a combination of FPLC ICP AES and ES MS MS techniques. Speciation analysis enabled determination of particular chemical forms of Al present in the nutrient solution or in stem sap. The results indicate that Al3+ added to the nutrient solution remained as Al3+ in the solution during the experiments, but in the roots transformation to Al-malate occurred. Al was transported from roots to the upper parts of the plant as Al-malate (70%) and Al3+ (30%). Al-citrate or Al-malate added to the nutrient solution were transferred to the upper parts of the plant without transformation of their chemical forms.

Aluminum↗
PubMed2001

Optimisation of the storage of natural freshwaters before organotin speciation.

The speciation of organotin compounds is essential due to the species-dependent toxicity, especially in natural waters. Precautions have to be taken during sampling and storage of waters in order to prevent degradations and losses. Experimental design methodology has been used to study the conditions of stability of organotins after water sampling in rivers. The modelling of results allows the determination of optimal conditions of preservation. After acidification at pH = 4 with nitric acid, the storage in polyethylene containers at 4 degrees C in the dark is suitable to preserve the most degradable trisubstituted (butyl- and phenyl-) species over 1 month. These conditions of sampling and storage are applied to two different freshwaters. The rate of species decomposition appears to be only dependent on the water nature, whatever the organotin concentrations in the sample. Speciation could be so preserved between 1 and 3 months.

Chromatography, Gas↗
PubMed2001

Physicochemical speciation of molybdenum in rain water.

A combination of a sensitive catalytic determination method with filtration and ultrafiltration has been used for the physicochemical speciation of molybdenum in natural and synthetic rain water samples. The concentration (CL) of labile molybdenum was evaluated by a direct catalytic determination. The total concentration (CT ) of molybdenum was determined after the acid decomposition of the sample to calculate the non-labile concentration (CT-CL). From the speciation results, molybdenum species in the successive rainfall sample were found in a fraction with smaller molecular weights < 10(3) Da and characterized as labile forms, i.e. simple molybdate ions. Non-labile molybdenum existed in particulate matter (> or = 0.45 microm in particle size) and distributed predominantly in the initial rainfall sample. The coprecipitation with Fe(III) hydroxide contributed to the formation of the non-labile molybdenum. In the initial rainfall sample, a small part of molybdenum was labile in the particle fraction (> or = 0.45 microm). This type of molybdenum was associated with the formation of humic iron aggregates.

Air Pollutants↗
PubMed2002

A multi-component numerical leach model coupled with a general chemical speciation code.

A multi-component numerical leach model (SBLEM) was developed by coupling a general chemical speciation code with a modified Crank-Nicolson algorithm to determine the leaching behavior of contaminants in stabillized/solidified (s/s) wastes. The thermodynamic database of the speciation code was modified using batch leaching data. SBLEM was evaluated by simulating a dynamic leaching test of cement-treated combined bottom and fly ash from a municipal solid waste (MSW) incinerator. Simulations used an input composition prepared from acid neutralization capacity (ANC) test data of the ash. The results show that SBLEM can reasonably predict the dynamic leaching behavior of metals from the cement-treated ash when the ANC of the ash and pH-solubility curves of metals are well described. This indicates SBLEM simulations may be able to augment or replace experimental leaching tests that can consume a substantial period of time (> 2 months) and in some cases, provide unreliable results.

Forecasting↗
PubMed2002

The role of colloidal particles in the speciation and analysis of "dissolved" phosphorus.

Colloidal-sized particles (1-1,000 nm) and high molecular mass material play an important, yet poorly understood role in the aqueous speciation of P. This study assessed the size distribution of P in 0.45-microm filtered soil solutions and soil-water extracts from three sandy soils (grassland, arable field and forest) using gel filtration chromatography (GFC) and membrane filtration (0.22- and 0.025-microm pore-size) and evaluated the impact of P speciation on colorimetric and ion-chromatographic methods for orthophosphate analysis. Between 40% and 58% of molybdate reactive P (MRP) and > 85% of molybdate unreactive P in the soil solution from the agricultural soils (pH 5.9-6.3) were associated with high molecular mass material (apparent size > 0.025 microm, or > 600 kDa on Superdex). In solutions from the forest soil (pH 3.2), high molecular mass P (HMMP) compounds were of minor importance (<8% of TP). The GFC elution profiles, composition and spectral characteristics of HMMP-containing solutions as well as the small relevance of HMMP at low pH were all indicative for associations between humic substances, Fe and/or Al, and P. Both MRP and ion chromatographic P measurements overestimated the free orthophosphate concentration (up to 2.3- and 1.4-fold, respectively) in 0.45-microm filtered HMMP-containing solutions. In 0.025-microm filtrates, free orthophosphate was the only MRP species present.

Chromatography, Gel↗
PubMed2003

Study of heavy metal pollution and speciation in Buyak Menderes and Gediz river sediments.

In this study, two economically important rivers of Turkey, Gediz and Buyuk Menderes (BM) are studied to determine their environmental pollution levels. An old analytical procedure involving sequential chemical extraction is improved and used for the partitioning of particulate trace metals (Cu, Co, Cr, Mn, Fe, Zn, Pb and Ni). Cationic and anionic Mn and Cr species with different phases are also determined by using leaching, extraction and ion exchange speciation processes. The sediment samples are analysed using graphic-furnace atomic absorption spectroscopy and differential pulse anodic stripping voltameter. Experimental results obtained on five replicate samples of fluvial bottom surface sediments at the sampling points demonstrate that the relative standard deviation of the sequential extraction procedure is generally better than +/-10%. The accuracy, determined by comparing total metal concentrations with the sum of the five sequential chemical extractions, is proved to be satisfactory. The detection limits established for three standard deviations of blank for different metals are identical and found to be 0.1mg/kg for sediment samples and 1 ppb for water samples. The results show that the pollution levels are significant especially for Pb, Cr, Mn and Zn in the Gediz river and Co, Mn, and Zn in the BM river. Comparison between our results and the measurements outlined before industrialization and the beginning of the intensive pesticide applications in agricultural fields (In: Broekaert et al., editors, Metal speciation in the environment, vol. 23. 1989. p. 601-11; A research on the environmental pollution in the agricultural fields and watering in the Aegean region, Ege University Research Project, No. 127 1988 (in Turkish); DSI Water Analyses Report, Ankara, 1985 (in Turkish)) show that the pollution in these rivers is probably originated from industrial, agricultural and domestic waste discharges.

Environmental Monitoring↗
PubMed2002

Heavy metals in agricultural soils from Piedmont, Italy. Distribution, speciation and chemometric data treatment.

The distribution and speciation of heavy metals in five agricultural soils of Piedmont Region (north-western Italy) were investigated. Ten metals, namely Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Ti and Zn were considered. Analytical determinations were performed by atomic emission or atomic absorption spectroscopy after microwave sample dissolution in acid solution. Total metal concentrations fit in the typical concentration ranges for unpolluted soils, with the exception of cadmium and lead content in some horizons. The effect of sampling depth on concentrations was discussed. Speciation studies were carried out by applying Tessier's procedure, which allows to subdivide the total metal content into five fractions, representing portions bound to different components of the soil. Moreover, the element labilities in two soils were evaluated by extraction with EDTA. Correlations among the variables and/or similarities among the sampling points were identified by principal component analysis and hierarchical cluster analysis.

Agriculture↗
PubMed2000

The impact of Pu speciation on distribution coefficients in Mayak soil.

To assess the long-term consequences when radionuclides are released into the environment, information on the source term, transport and transformation processes, interaction with soils (KD) and biological uptake (CF) is needed. Among the artificial radionuclides released to the environment by nuclear activities, the transuranium elements are a major concern, due to very long half-lives and their accumulation in bone as well as high radiotoxicity. Plutonium has been produced in greater quantity than other transuranic elements, however, environmental assessments are complicated by the complex environmental behaviour. Physico-chemical forms of Pu will determine the interactions with soils and, thus, the degree to which soils can act as a sink or a potential diffuse source of contaminants. In the present work, dynamic tracer experiments have been performed where different Pu-species are added to a 'Mayak soil-rainwater system' to obtain information on KD values. After a defined contact time, the samples where then sequentially extracted and results are used in a dynamic box model to estimate interaction and fixation rates. The interaction of all Pu-species with soils seems to be rapid and follows a two-step reaction. Up to contact times of a few weeks, the KD for Pu(III,IV) (730 +/- 240 l/kg) is approximately one order of magnitude higher than for Pu(V,VI) (90 +/- 20 l/kg) and Pu(III,IV)-organic (40-60 l/kg). After 3 months contact time, the KD in only the two organic-bound Pu-species were significantly lower. This shows that the initial association with the soil is dependent on the Pu-species in the rainwater. After only 1 h of contact, between 33 and 40% of the plutonium was strongly bound to the soil components, i.e. only extractable with strong HNO3. The extraction of soil-bound Pu followed a similar pattern for all the original species, suggesting that the next step of Pu interaction mechanism with soil was rather independent of the original species. For both the Pu(V,VI) and Pu-organic species, the rainwater-desorption extract gave consistently higher KD values than that calculated from the rainwater-sorption data; whereas for Pu(III,IV), desorption KD values were more similar to sorption KD values. This supports the suggestion that the observed difference in Pu adsorption to soils reflects Pu-speciation in the water soluble phase, and that actual soil-Pu interactions are rather independent of the original speciation. Modelling of the extraction data show a different in association rate for the different Pu species, where the Pu(III,IV) has the fastest association rate as expected.

Absorption↗
PubMed2000

Distribution, speciation, and transport of mercury in stream-sediment, stream-water, and fish collected near abandoned mercury mines in southwestern Alaska, USA.

Concentrations of total Hg, Hg (II), and methylmercury were measured in stream-sediment, stream-water, and fish collected downstream from abandoned mercury mines in southwestern Alaska to evaluate environmental effects to surrounding ecosystems. These mines are found in a broad belt covering several tens of thousands of square kilometers, primarily in the Kuskokwim River basin. Mercury ore is dominantly cinnabar (HgS), but elemental mercury (Hg degrees) is present in ore at one mine and near retorts and in streams at several mine sites. Approximately 1400 t of mercury have been produced from the region, which is approximately 99% of all mercury produced from Alaska. These mines are not presently operating because of low prices and low demand for mercury. Stream-sediment samples collected downstream from the mines contain as much as 5500 microg/g Hg. Such high Hg concentrations are related to the abundance of cinnabar, which is highly resistant to physical and chemical weathering, and is visible in streams below mine sites. Although total Hg concentrations in the stream-sediment samples collected near mines are high, Hg speciation data indicate that concentrations of Hg (II) are generally less than 5%, and methylmercury concentrations are less than 1% of the total Hg. Stream waters below the mines are neutral to slightly alkaline (pH 6.8-8.4), which is a result of the insolubility of cinnabar and the lack of acid-generating minerals such as pyrite in the deposits. Unfiltered stream-water samples collected below the mines generally contain 500-2500 ng/l Hg; whereas, corresponding stream-water samples filtered through a 0.45-microm membrane contain less than 50 ng/l Hg. These stream-water results indicate that most of the Hg transported downstream from the mines is as finely-suspended material rather than dissolved Hg. Mercury speciation data show that concentrations of Hg (II) and methylmercury in stream-water samples are typically less than 22 ng/l, and generally less than 5% of the total Hg. Muscle samples of fish collected downstream from mines contain as much as 620 ng/g Hg (wet wt.), of which 90-100% is methylmercury. Although these Hg concentrations are several times higher than that in fish collected from regional baseline sites, the concentration of Hg in fish is below the 1000 ng/g action level for edible fish established by the US Food and Drug Administration (FDA). Salmon contain less than 100 ng/g Hg, which are among the lowest Hg contents observed for fish in the study, and well below the FDA action level.

Alaska↗
PubMed2001

Speciation patterns of heavy metals in tropical estuarine anoxic and oxidized sediments by different sequential extraction schemes.

The speciation patterns of Cu, Cd, Zn, Pb, Fe and Mn in sediment samples under anoxic and oxidized conditions were investigated using three-stage, four-stage and five-stage sequential extraction schemes. All the extraction schemes identify the non-residual metal among three basic operationally-defined host fractions, namely, exchangeable, reducible and organic/sulfide bound. The anoxic sediment samples were found to have been oxidized during the extraction stage for the reducible fraction under the three-stage and four-stage schemes and the moderately reducible fraction under the five-stage scheme despite the maintenance of an oxygen-free environment. This artifact has resulted in an over-representation of the reducible fraction and an under-representation of the organic/sulfide fraction in the heavy metal speciation patterns of anoxic sediment samples. For Cd, Zn and Pb which had > 70% associated with the acid volatile sulfide in the organic/sulfide fraction, this artifact has resulted in the observation of a decrease in the reducible fraction and, in some cases, an increase in the organic/sulfide fraction upon oxidation of the anoxic sediment samples.

Journal Article↗
PubMed2002

Role of microbes in controlling the speciation of arsenic and production of arsines in contaminated soils.

The influence of microbes on the speciation of arsenic and production of arsines in contaminated soils was investigated under laboratory conditions. Microbes were able to carry out reactions that resulted in changes in the speciation of arsenic in soil. The transformation of soil dominating species, arsenate [As(V)], under both aerobic and anaerobic conditions to arsenite [As(III)], monomethylarsonic acid [MMAA], dimethylarsinic acid [DMAA] and to volatile trimethylarsine [TMA] was, however, less than 0.5%, of which the production of TMA represented 0.02-0.3%. The volatilization process was also verified in the field, in the soil of a dumping area. The 'life-time' of arsines in air was, however, short and they were rapidly converted back to water soluble species, As(V) and trimethyl arsine oxide (TMAO).

Arsenic↗
PubMed2002

Arsenic speciation and distribution in an arsenic hyperaccumulating plant.

Arsenic-contaminated soil is one of the major arsenic sources for drinking water. Phytoremediation, an emerging, plant-based technology for the removal of toxic contaminants from soil and water, has been receiving renewed attention. Although a number of plants have been identified as hyperaccumulators for the phytoextraction of a variety of metals, and some have been used in field applications, no hyperaccumulator for arsenic had been previously reported until the recent discovery of Brake fern (Pteris vittata), which can hyperaccumulate arsenic from soils. This finding may open a door for phytoremediation of arsenic-contaminated soils. Speciation and distribution of arsenic in the plant can provide important information helpful to understanding the mechanisms for arsenic accumulation, translocation, and transformation. In this study, plant samples after 20 weeks of growth in an arsenic-contaminated soil were used for arsenic speciation and distribution study. A mixture of methanol/water (1:1) was used to extract arsenic compounds from the plant tissue. Recoveries of 85 to 100% were obtained for most parts of the plant (rhizomes, fiddle heads, young fronds and old fronds) except for roots, for which extraction efficiency was approximately 60%. The results of this study demonstrate the ability of Brake fern as an arsenic hyperaccumulator. It transfers arsenic rapidly from soil to aboveground biomass with only minimal arsenic concentration in the roots. The arsenic is found to be predominantly as inorganic species; and it was hypothesized that the plant uptakes arsenic as arsenate [As(V)I and arsenate was converted to arsenite [As(III)] within the plant. The mechanisms of arsenic uptake, translocation, and transformation by this plant are not known and are the objectives of our on-going research.

Arsenic↗
PubMed1998

Modelling the chemical speciation of trace metals in the surface waters of the Humber system

Calculations have been performed to estimate the chemical speciation at equilibrium of six divalent trace metals (Co, Ni, Cu, Zn, Cd, Pb) in riverine, estuarine and marine surface waters of the Humber system. The Windermere Humic Aqueous Model (WHAM) was used to compute distributions of dissolved metals. In the rivers, the free aquo ion (M2+) is a major part of dissolved Co, Ni, Zn and Cd, but accounts for less than 1% of Cu and Pb. The main complexes are formed with carbonate ligands and dissolved natural organic matter, represented by fulvic acid. In the low-salinity region of the estuary and in seawater, complexation with fulvic acid is less significant, although most of the Cu is still in this form, while the speciation of Cd is dominated by chloride complexes. Adsorption of metals by suspended particulate matter was calculated with a simple model involving the concentrations of the free aquo ions (M2+) and H+, together with a constant for each metal estimated from laboratory adsorption data. Calculated adsorbed concentrations were used to predict the partition coefficient (KD) for each metal under different circumstances. The values can vary by an order of magnitude or more, depending upon solution conditions. Typical values for rivers, low-salinity water and seawater are within one order of magnitude of observations. However, there is a general tendency to underestimate KD, possible reasons being (1) neglect of electrostatic enhancement of adsorption at low ionic strengths; and (2) analytical overestimation of particulate metal in equilibrium with the solution phase. There is a strong case for the development of a more sophisticated adsorption model.

Journal Article↗
PubMed2000

Evaluation on speciation and removal efficiencies of mercury from municipal solid waste incinerators in Taiwan.

Two large-scale municipal solid waste incinerators (MWIs) located in Taiwan were selected for conducting flue gas sampling to determine the chemical speciation of mercury by both USEPA Method 29 and Ontario Hydro Method (OHM). In addition, the emission characteristics and removal efficiencies of mercury were evaluated via isokinetic sampling of flue gas upstream and downstream of APCDs. Results indicated that the average removal efficiencies of Hg for MWI-A and MWI-B were 29.56 and 44.70%, respectively. In terms of mercury speciation by USEPA Method 29 and Ontario Hydro Method (OHM), oxidized mercury (Hg2+), in the flue gas was predominant at the inlet of APCD for both incinerators. Less than 30% of mercury in the flue gas existed in the elemental form (Hg0) at APCD inlet. Mercury emitted from the stack also predominated as a form of Hg2+ in MWI-A. Approximately 90% of total mercury emission from the stack existed in the form of Hg2+ for MWI-A. Due to the higher removal efficiency of soluble mercury (Hg2+) in wet scrubber, less total Hg was actually emitted from MWI-B than MWI-A. Regarding the removal efficiency of Hg0 in the flue gas, the APCDs of MWI-A (DSI + FF) had a higher removal efficiency than that of MWI-B (ESP + WS) possibly due to the reduction of Hg2+ which occurred in the wet scrubber.

Air Pollution↗
PubMed2002

Speciation of chromium in the presence of copper and zinc and their combined toxicity.

Speciation of chromium has attracted a great deal of interest in view of the toxic properties of Cr(6+) compared with the much less toxic Cr(3+). A freshwater plant, duckweed which is uniquely suitable for aquatic toxicity tests is utilized to study the growth responses and accumulation of chromium in the presence of copper and zinc. Speciation analysis was carried out by using differently activated alumina. Metal ion concentrations in the plant were determined by FAA spectrometry. Results of the present study revealed that the oxidation state of chromium as well as its concentration in media controlled the growth and the metal accumulation in duckweed. Regarding this, Lemna minor (common duckweed species) accumulated Cr(3+) in smaller quantities and it resulted in relatively larger growth responses, whereas Cr(6+) was accumulated in larger quantities and it yielded relatively smaller growth responses. Different types of metal interactions among chromium, copper, and zinc ions were evident. These interactions were classified as synergistic, antagonistic, and additive and they were strictly dependent on the oxidation state of the chromium ion.

Araceae↗