Sequential Extraction Scheme Research Articles

Suitability of four woody plant species for the phytostabilization of a zinc smelting slag site after 5 years of assisted revegetation

Zinc smelting activity generates large volumes of highly toxic waste slags and poses a potential extreme environmental risk for the surrounding areas. The establishment of a vegetation cap for the phytostabilization of abandoned mine tailing heaps using plants is usually considered a beneficial approach. This study aimed to evaluate the suitability of phytostabilization of zinc smelting slag using four woody plants combined with organic amendments, to investigate the distribution of heavy metals in the slag–plant system, and to better understand how the direct revegetation of a zinc smelting slag site can influence the mobility and geochemical fraction of heavy metals. Slags were collected from the areas planted with vegetation (Arundo donax, Broussonetia papyrifera, Robinia pseudoacacia, and Cryptomeria fortunei) and a bare area in a zinc smelting waste slag site using an indigenous method. Physicochemical properties were determined with the usual procedures. The geochemical fraction and bioavailability of heavy metals was determined using the three-step modified European Community Bureau of Reference (BCR) sequential extraction and diethylene triamine pentaacetic acid (DTPA) sequential extraction schemes. Heavy metal concentrations (Cu, Pb, Zn, and Cd) in the slag and plant samples were also measured. Vegetation planted directly in the zinc smelting waste slag significantly enhanced the nutrient accumulation and reduced the bioavailability of heavy metals (Cu, Zn, and Cd) with the exception of A. donax for Zn and Cd. The presence of four woody plants increased the bioavailability of Pb. Sequential extraction revealed that revegetation reduced the acid-soluble extractable fraction and increased the fraction of heavy metals associated with the Fe/Mn oxy(hydr)oxides or organic matter. This is attributed to the establishment of plant-enhanced weathering of minerals in the waste slag that resulted in the formation of an amount of dissolved metals, and the amount of dissolved metals was partly redistributed into the soluble extractable fraction of the zinc smelting waste slag. The final concentration of metals (Cu, Pb, Zn, and Cd) in the soluble extractable fraction is dependent on the dynamics of metals induced by root activity in the rhizosphere. Much lower levels of heavy metals with lower translocation factors accumulated in the four woody plants than in the associated slags. We conclude that the studied four woody plants showed a beneficial vegetation cover and phytostabilization potential within 5 years of revegetation. These woody plants have the potential for high heavy metal tolerance and low heavy metal accumulation. Therefore, these woody plants could be used for revegetation and phytostabilization of zinc smelting slag sites under field conditions.

Fraction-specific rare earth elements enable the reconstruction of primary seawater signatures from iron formations

Rare earth element (REE) abundances in iron formations (IFs) provide key evidence to track the redox evolution of the Precambrian oceans. Deriving information about processes and sources from IFs is complicated by the variable roles of diagenetic dissolution and precipitation that modify primary depositional signals in the rocks. Iron formations are typically mineralogically heterogeneous with varying amounts of carbonate (ankerite + siderite), oxide (predominantly magnetite) and silicate (chert and Fe-silicates). To date, little is known about the respective contributions of these fractions to the bulk-rock REE signal, and which fraction most accurately records primary seawater signals. Here we evaluate an optimized sequential extraction scheme for REE analysis in the ca. 2.46 Ga Asbestos Hills IFs from the Griqualand-West Basin in South Africa. These rocks were deposited immediately before the Great Oxidation Event and are potentially an important archive for large-scale redox changes in the (near) surface environment.To fully evaluate our method, we measured lanthanide elements plus ytrrium (REY) in individual minerals, in bulk rock samples and in three separate fractions using acetate, oxalate and total digestion sequential extractions. The extraction techniques were then verified using a mass balance approach, the first time that this has been comprehensively applied to IFs. Similarities between the carbonate fraction data and modern seawater, coupled with strong measurement reproducibility and systematic stratigraphic variability suggests that carbonate most closely tracks the primary seawater composition. The Asbestos Hills IFs show distinctive REY signatures with strongly variable (Yb/Pr)SN ratios, positive La anomalies, positive and constant Y/Ho, weakly positive Eu anomalies and a lack of Ce anomalies in their carbonate fraction. Stratigraphic variations in these parameters suggest deposition in a stratified fully anoxic ocean, which became shallower over time. The silicate fraction was influenced by various amounts of allochthonous material (detrital and volcanic ash), although some minerals including greenalite, minnesotaite and stilpnomelane may have tracked seawater REE variability. The oxide fraction was found to be the most REY-depleted and therefore susceptible to allochthonous influences as well as diagenetic controls. It shows a systematic MREE enrichment that has not been described in IFs before, but has been seen in sub-oxic, ferrous environments. An increase in the ratio of carbonate to oxide minerals ongoing upwards through the Asbestos Hills IF, from deep to shallow water conditions, most likely reflected an increase in dissimilatory iron reduction close to the margin of the anoxic basin.

Water treatment residuals as soil amendments: Examining element extractability, soil porewater concentrations and effects on earthworm behaviour and survival

Drinking water treatment residuals (WTRs), the by-product of water clarification processes, are routinely disposed of via landfill however there is a growing body of research that demonstrates the material has great potential for beneficial use in environmental applications. Application to agricultural land is one option showing great promise (i.e. a low cost disposal route that provides organic matter input to soils and other potential benefits), however questions remain as to the impact such applications may have on earthworm survival and behaviour and also on the potential effects it may have on soil porewater chemistry. This study examined the leachability of elements within two types of WTRs (one Al- and one Fe- based) from England via 0.001 M CaCl2 solution, at varying pH, and via the Community Bureau of Reference (BCR) sequential extraction scheme. Earthworm avoidance, survival, growth, reproduction and element concentrations were examined in WTR-amended sandy soils (0%, 5%, 10%, 20% w/w), while soil porewaters were also recovered from experimental units and examined for element concentrations. The results revealed leachable element concentrations to be very low in both types of WTRs tested and so element leaching from these WTRs would be unlikely to pose any threat to ecosystems under typical agricultural soil conditions. However, when the pH was lowered to 4.4 there was a substantial release of Al from the Al-WTRs (382 mg/kg). Soil porewater element concentrations were influenced to some degree by WTR addition, warranting further examination in terms of any potential implications for nutrient supply or limitation. Earthworm avoidance of WTR-amended soil was only observed for Al-WTRs and only at the maximum applied rate (20% w/w), while survival of earthworms was not affected by either WTR type at any application rate. Earthworm growth and reproduction (cocoon production) were not affected at a statistically significant level but this needs further examination over a longer period of exposure. Increased assimilation of Al and Fe into earthworm tissues was observed at some WTR application rates (maximum fresh weight concentrations of 42 mg/kg for Al and 167 mg/kg for Fe), but these were not at levels likely to pose environmental concerns.

Chemical partitioning of Zn in soil: application of two sequential extraction procedures

The data on the accumulation and distribution of heavy metal (HM) compounds in soils is necessary to assess and predict the ecological situation. The Zn fractional distribution in artificially contaminated soil by the most popular methods of sequential extraction (the well known Miller and Tessier methods) was studied. The sample studied was soil (Haplic Chernozem) artificially contaminated by Zn acetate (2000 mg kg −1 ), a priority pollutant in southern Russia. In order to estimate the role of different soil components in the Zn partitioning, the carbonates, Fe–Mn sesquioxides, and organic matter, were removed from the soil samples, prior to application of each sequential extraction scheme. Results showed a metal absence in the fraction bound to the removed soil component. The Miller method allows better tracing of the HM fractions loosely bound to the soil because of the use of weaker extractants with high complexing capacity, which hampers the reprecipitation of metals from the extract. The Tessier method is more suitable for the separation of the total anthropogenic component from contaminated soils. This is related to the higher extraction capacity of reagents. The differences in the fractional distribution of metal according to each method are most manifested in the contaminated soil.

Evaluating cadmium bioavailability in contaminated rice paddy soils and assessing potential for contaminant immobilisation with biochar

Cadmium (Cd) contaminated soils from the Mae Sot district in northwest Thailand, a region in which rice Cd concentrations often exceed health limits (0.4 mg/kg) set by the World Health Organisation, were examined for isotopically exchangeable Cd (Cd E values using a 111Cd spike) to determine how this rates as a predictor of rice grain Cd in comparison with soil total Cd and solution extractable Cd (using the commonly applied BCR scheme and, in an attempt to distinguish carbonate bound forms, the Tessier soil sequential extraction scheme reagents). Step 1 of the BCR scheme (0.11 M CH3COOH) and step 1 of the Tessier scheme (1M MgCl2) showed the highest R2 values in regressions with rice Cd (91% and 90%, respectively), but all predictors were strongly linked to rice Cd (p < 0.001) and could be used for prediction purposes. One soil, of the six tested, was an exception to this, where all predictors over-estimated grain Cd by a factor of 2.5–5.7, suggesting that rice grain Cd had been restricted here by the differing flooding regime and subsequent changes to redox conditions. E values and Tessier step 1 extractions were closely related, indicating that these measurements access similar pools of soil Cd. Separately, the isotopic exchangeability (representing bioavailability) of Cd was also assessed in two soils amended with rice husk and miscanthus biochars (0, 1, 5, 10, 15 and 20% w/w) in order to assess the utility of the biochars as a soil amendment for immobilising Cd in situ. One soil showed significant reductions in Cd E value at 5% rice husk biochar addition and at 15% miscanthus biochar addition however, based on the E value-rice grain Cd regression relationship previously established, the E values in the amended soils still predicted for a rice Cd concentration above the health limit. In the second soil, neither of the biochars successfully reduced the Cd E value. This indicates that further work is needed to customise biochar properties to suit specific soil and contaminant situations if they are to be used successfully for remediation of metal contaminated soils.

Immobilization of lead in shooting range soil using biochar from spent mushroomsubstrateImmobilization of lead in shooting range soil using biochar from spent mushroomsubstrate

Spent mushroom substrate (SMS) was pyrolyzed at 450°C for 2 hours and characterized using elemental analyzer and Boehm titration. Shooting range soil was incubated with 2.5% w/w and 5.0% w/w of SMSB for four weeks and the soil were characterized on the elemental composition, pH, electric conductivity (EC) and cation exchange capacity (CEC). The mobility of Pb in the incubated soil were studied using a modified selective sequential extraction (SSE) scheme. Total Pb in shooting range soil is 29385.5 mg/kg. The texture of shooting range soil is loamy sand with an average soil pH of 4.69, EC value 0.17 mS/mand CEC value 6.0 mEq/100g. After treatment with SMSB, the soil pH and CEC were increased and the concentration of exchangeable Pb decreased. Conclusively, this study found that there is potential in using SMSB for remediating Pb contamination in the shooting range soil.

Biorefining of Bilberry (Vaccinium myrtillus L.) Pomace Using Microwave Hydrodiffusion and Gravity, Ultrasound-Assisted, and Bead-Milling Extraction

Bio-refining of bilberry pomace using innovative technologies such as microwave hydro diffusion and gravity extraction (MHG) and ultrasound assisted extraction (UAE) with different concentrations of ethanol/water as the solvent was established. Bead milling was also utilized in this sequential extraction scheme to remove the lipophilic fraction. Solubility index of target polyphenols was predicted using a computational tool (COSMO-RS) and compared to experimental results obtained by in vitro antioxidant activity assessments. MHG extracts obtained using microwave power of 2 W/g had the highest Folin-Ciocalteu reducing capacity (43.46 ± 0.48 mg GAE/g of extract), total flavonoid (4.17 ± 0.04 mg QE/g of extract), total monomeric anthocyanin content (12.19 ± 0.13 mg D3GE/g of extract) and radical scavenging capacity (22.64 ± 2.23 mg TE/g of extract). In UA ethanol/water extracts the highest flavonoid (10.41 ± 0.08 mg QE/g of extract) and anthocyanin content (12.19 ± 0.51 D3GE mg/g of extract) was present in e...

Mobility and potential risk of sediment-associated heavy metal fractions under continuous drought-rewetting cycles

Ecological decline in the water level fluctuating (WLF) zone of the Three Gorges Reservoir (TGR) has been well established over the past decades. However, the effect of heavy metal fractions present in the sediment and their potential ecological risk under the anti-seasonal hydrological regime are still unclear. The Pengxi River is a tributary of the Yangtze River and it has a typical annual water level fluctuation ranging from 145 to 175m above sea level. The current study examined heavy metal fractions in sediments containing Cr, Cd, Cu, Pb and Mn collected along the WLF zone using the Tessier sequential extraction scheme. The total organic carbon (TC), total nitrogen (TN), carbon/nitrogen ratio (C/N), pH, particle size composition and content of nitrate (NO3−-N), and ammonium (NH4+-N) differed dramatically among the sampled altitudes and depths and was significantly correlated with the flooding time of the WLF zone. At lower altitudes of the WLF zone, the amounts of the exchangeable (EXC), carbonate-bound (CA) and total heavy metal contents of the surface sediment were much higher compared to those of higher altitudes of the WLF zone. The risk assessment code (RAC) for Cd and Mn showed an opposite trend to that of Cr, Cu, and Pb and mainly depended on the organic matter-bound fraction (OM). The modified RAC (mRAC) indicated a very high potential adverse effect for the whole WLF zone, although the risk value was much lower at the lower altitudes and upper depths of the WLF zone. Our results showed that the positive response of the loosely bound fractions (LOS) of heavy metals to the drought-rewetting (DRW) process minimizes the risk of heavy metals in the WLF zone sediment.

Fraction-specific controls on the trace element distribution in iron formations: Implications for trace metal stable isotope proxies

Iron formations (IFs) are important geochemical repositories that provide constraints on atmospheric and ocean chemistry, prior to and during the onset of the Great Oxidation Event. Trace metal abundances and their Mo-Cr-U isotopic ratios have been widely used for investigating ocean redox processes through the Archean and Paleoproterozoic. Mineralogically, IFs consist of three main Fe-bearing fractions: (1) Fe-Ca-Mg-Mn carbonates, (2) magnetite and/or hematite and (3) Fe-silicates. These fractions are typically fine-grained on a sub-μm scale and their co-occurrence in varying amounts means that bulk-rock or microanalytical geochemical and stable isotope data can be influenced by cryptic changes in mineralogy. Fraction specific geochemical analysis has the potential to resolve mineralogical controls and reveal diagenetic versus primary precipitative controls on IF mineralogy. Here we adapt an existing sequential extraction scheme for Fe-phases (Poulton and Canfield, 2005) to the high Fe-content in IF and the specific three-fraction mineralogy. We optimized the scheme for magnetite-dominated Archean IFs using samples from the hematite-poor Asbestos Hills Subgroup IF, Transvaal Supergroup, South Africa. Previously commonly-used hydroxylamine-HCl and dithionite leaches were omitted since ferric oxides are quantitatively insignificant in these IF samples. The acetate leach was tested at variable temperatures, reaction times and under different atmospheres in order to ensure that all micro-crystalline Fe-carbonates were effectively dissolved, resulting in an optimum extraction for 48h at 50°C under anoxic conditions. The dissolution of magnetite by NH4-oxalate was also tested, resulting in an optimum extraction for 24h under an ambient atmosphere. Finally, a HF-HClO4-HNO3 leach was used to dissolve the residual silicate fraction which has to date not been considered in detail in IF. Accuracy of the extraction technique was generally excellent, as verified using 1) elemental recoveries, 2) comparison of major and trace element distributions against mineralogy and 3) comparison to results from microanalytical techniques.This study focuses on the distribution of three frequently used geochemical proxies in IF; U, Mo and Cr. Molybdenum abundances in the Kuruman and Griquatown IF are low and show an apparent correlation with mineralogical variability, as determined by the sequential extraction. This suggests that changes in bulk-rock mineralogy, rather than redox chemistry might significantly affect Mo stable isotopes. For Cr, a minor bulk-rock stratigraphic increase can be related to the oxide and silicate fraction. However, a positive relationship with Zr indicates that this was also controlled by detrital or volcanic ash input. Uranium is predominantly bound to the silicate fraction and shows clear correlations with Zr and Sc implying detrital reworking under anoxic conditions. The discrepant behaviour of these three proxies indicate that mineralogy should be taken into account when interpreting heterogeneous bulk-rock samples and that fraction specific techniques will provide new insights into the evolution of atmosphere and ocean chemistry.

The mobility of thallium from bottom soil of the Silesian-Cracowian zinc-lead ore deposit region (Poland)

Thallium is a nonessential toxic element that may pose an environmental hazard. A crucial factor for the toxic effect of Tl is the mobility of the element. The aim of this work was to investigate Tl mobility in typical soil samples formed over six different lithological backgrounds (glaciofluvial sands and gravel, slope-wash sands and loams, siltstones and conglomerates, loesses, dolomites and ore-bearing dolomites) from the south-eastern part of the Silesian-Cracowian zinc-lead ore deposit region in Poland. Five geochemical fractions (water soluble, ion-exchangeable/carbonates, reducible, oxidizable, and residual) were obtained by using a sequential extraction scheme coupled with flow-injection anodic stripping voltammetry. The results showed that the Tl in most of the soils investigated is mainly entrapped in the parent matter, which is immovable and inert in terms of environmental effects. However, a significant part of the Tl was found in the reducible and oxidizable fractions of the soil formed over ore-bearing dolomites. It highlights that the environmental hazard caused by Tl should be measured by the content of mobile Tl rather than by its total content.

Speciation of Heavy Metals in the Soil and the Mining Residues, in the Zinclead Sidi Bou Othmane Abandoned Mine in Marrakech Area

Mining activity is one of the most important sources of Heavy metals in the environment. In Marrakech region, functioning or abandoned mines represent a great hazard due to huge amounts of waste deposited in waste dumps and tailings often with high concentration of heavy metals pollution. These mining sites located near Marrakesh contain mining residues abandoned for ten to twenty years. They are presently in an agricultural region of the Haouz district (Jbilets- Centrales). The present study was realized for the abandoned mine of Sidi Bou Othmane in order: i) -To determine the total content of heavy metal in soil and mining residues, ii)-To carry out the chemical speciation, of heavy metals in the mining residues and in the samples of soil collected in the vicinity of the mine. The pH, the electrical conductivity, Organic matter content and Total carbonate content in all the samples (soil and mining residues) were measured using the standards methods, heavy metals concentration was determined by atomic spectrophotometery. Therefore, a sequential extraction scheme according to the BCR’s (Community Bureau of Reference) guidelines and total acid digestion were applied to soil and mining residues samples. The results obtained showed that all the abandoned mines still containing very important quantities of solid waste, these sites can thus become potential sources of pollution by releasing heavy metals. In this concern, 4 polluting heavy metals (Cd, Cu, Pb and Zn) were detected with concentrations exceeding those admitted for agricultural soil. For all heavy metals, the most contaminated sites were found in the vicinity of the mines, probably linked to weathering effect, the wind and the topography.

Evaluates the chemical fractions of arsenic bounded to solid matrixes of thar coalfield of pakistan by sequential extraction method

The main objective of this work was to evaluate the bounded fractions of arsenic (As), physicochemical parameters, and mineral composition of solid matrices of coal mining area of Pakistan. Clay, sand, and soil samples were collected from different depths of blocks 3 and 5 of Thar coalfield. The As bounded with different chemical fractions of solid matrices was extracted by sequential extraction scheme, proposed by the Community Bureau of Reference protocol (BCR). Certified reference material and spiking tests were performed to check the accuracy of methodology. Extracted As fractions from all studied solid material by sequential extraction method were measured by hydride generation atomic absorption spectrometry. Mineral composition has been determined by scanning electron microscopy and X‐ray diffraction. All the three solid samples obtained from both blocks varied in their physicochemical parameters and As contents in different chemical forms. The total As and extractable As concentration in block 3 was higher as compared to block 5. The recovery and standard deviation between total As and ∑(1–4) fractions in all studied samples were obtained as &gt;95% and &lt;5%, respectively. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1667–1675, 2017

Silicon fractionation in Mollic Fluvisols along the Central Elbe River, Germany

Quantification of Si in its different forms in soil is a prerequisite to understand the geochemical distribution and fate of Si along with their driving biogeochemical processes. However, different Si fractions in floodplain soils have not been quantified yet, and little is known about the biogeochemical processes driving Si fractionation in these soils. Therefore, we applied for the first time a sequential Si extraction scheme to three floodplain soils (Mollic Fluvisols) to separate six Si fractions: mobile Si, adsorbed Si, Si bound to organic matter, Si included in pedogenic oxides and hydroxides, biogenic as well as minerogenic amorphous silica. Residual Si was calculated. The highest Si proportion apart from the residual fraction (Si bound in primary and secondary silicates) was found in minerogenic amorphous silica (up to 5.6% of total Si), followed by Si occluded in pedogenic oxides and hydroxides (up to 0.7% of total Si). Silicon from biogenic amorphous silica amounted to 0.02–0.6% of total Si. The smallest proportion of Si was found in the mobile Si fraction and made up about 0.01% of the total Si. The results of this study demonstrate the importance of the soil water budget (here periodic flooding with prolonged water saturation) on the accumulation of easy-to-mobilise Si, Si occluded in pedogenic oxides and hydroxides and amorphous minerogenic as well as biogenic silica. Reductive dissolution of Fe and Mn oxides may induce Si release into the soil solution, subsequent oxidizing conditions may induce Si accumulation by adsorption, co-precipitation and occlusion of Si on/with newly formed Fe and Mn oxides. These processes are more pronounced in floodplain than in terrestrial soils, thus implying different distributions of Si among soil fractions.

An improved sequential extraction method to determine element mobility in pyrite-bearing siliciclastic rocks

ABSTRACTA sequential extraction method was developed for pyrite-bearing (FeS2) siliciclastic rocks. The focus of this study was to enhance the procedure by an improved oxidation step to completely dissolve not only organic matter but also microcrystalline pyrite. In the first experiment, four oxidation procedures were compared for pure pyrite at extraction temperatures of 25°C and 85°C with hydrogen peroxide (H2O2) as the main oxidant. It was found that pyrite dissolution was most effective by using a mixture of H2O2, ammonium acetate (NH4OAc) and nitric acid (HNO3) at 25°C. This procedure dissolved >90% pyrite, and detected >75% using solute iron measurements. The difference between these two results was explained by reprecipitation of secondary iron minerals. The procedure worked best at 25°C, since solvent evaporation at 85°C amplified iron oversaturation and precipitation. For the pyrite-bearing siliciclastic rocks, two sequential extraction schemes were compared to optimise solid–solvent ratio, extraction step order and type of solvent. Eventually, the most effective step order identified for siliciclastic rocks containing pyrite and little organic matter was to first (1) remove the exchangeable fraction, followed by (2) dissolution with acid and afterwards (3) with a reducing agent. The (4) oxidation step was performed last.

Evaluation of Heavy Metals in Soil Using Modified BCR Sequential Extraction

Recent studies have shown that strong acid digestions for the determination of heavy metals in soils and sediments can be misleading when assessing environmental effects. Therefore, this study adopted the use of modified community bureau of reference (BCR) sequential extraction scheme in order to overcome the limitation. The physicochemical properties of the soil such as pH, cation exchange capacity (CEC) and soil organic matter (SOM) were determined. The pH, CEC and SOM were found to be 5.90, 0.0023 cmol/kg and 99.8% respectively. The concentrations of the heavy metals in the solution were also measured using atomic absorption spectrophotometry. Pseudo total metal content in the soil (aqua-reqia digestions) for cadmium, lead, chromium, nickel, zinc and copper were 0.12, 0.74, 0.48, 0.26, 15.9 and 11.0 mg/kg respectively. These concentrations are within the World Health Organization (WHO) permissible limit in agricultural soils. The heavy metals were partitioned into four fractions (exchangeable, reducible, oxidizable and residual fractions) in the soil using modified BCR sequential extraction. Cd, Zn and Cu were predominantly in the first two fractions, thus, mobile and bioavailable for plant uptake, while Pb, Cr and Ni were found in the last two fractions (less mobile and immobile residual fractions). Thus, Cd, Zn and Cu may pose high environmental risk. The results indicate the reliability of the Modified BCR scheme in risk assessment of heavy metals in soils.

Modelling the concentrations of dissolved contaminants (Cd, Cu, Ni, Pb, Zn) in floodplain soils.

Central European floodplain soils are often contaminated with potentially toxic metals. The prediction of their aqueous concentrations is a prerequisite for an assessment of environmental concerns. We tested the aqueous concentrations of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) derived from multi-surface adsorption modelling (on hydrous iron, aluminum and manganese oxides, clay and soil organic matter) against those analyzed in situ in the soil solution of four horizons of floodplain soils at the Elbe River, Germany. The input data for the reactive metals were derived from a seven-step sequential extraction scheme or from extraction with 0.43M nitric acid (HNO3) and evaluated in four modelling scenarios. In all scenarios, measured and modelled concentrations were positively related, except partially for Pb. Close reproduction of the measured data was obtained using measured data of accompanying cations and anions together with amounts of reactive metals from both the sequential extraction or from 0.43M HNO3 extraction, except for Cu, which was often strongly overestimated, and partially Cd. We recommend extraction with 0.43M HNO3 to quantify reactive metals in soil because the modelling results were metal-specific with better or equal results using the single extractant, the application of which is also less laborious. Approximations of ion concentrations and water contents yielded similar results. Modelled solid-phase speciation of metals varied with pH and differed from that from sequential extraction. Multi-surface modelling may be an effective tool to predict both aqueous concentrations and solid-phase speciation of metals in soil.

An optimised sequential extraction scheme for the evaluation of vanadium mobility in soils

Reviewing the current state of knowledge about sequential extraction applied for soil vanadium (V) fractionation, we identified an urgent requirement of an sequential extraction (SE) specified for V. Namely, almost all previous SE extracted only 8.4%-48% of total V in soils (excluding residue). Thus, we proposed an eight-step SE for V fractionation in soils according to the knowledge gained from literature and our own dissolution experiments with model minerals. After extracting the mobilisable and adsorbed V with de-ionised water and 5mmol/L phosphate, 1mol/L pyrophosphate was applied to gather organic matter bound V which minimised the artefact dissolving Al and Fe (hydr)oxides occurred when using HNO3-H2O2 for extraction. Extraction with 0.4mol/L NH2OH⋅HCl was highly selective toward manganese oxides. Fractionation of different crystalline Al and Fe (hydr)oxides associated V with 1mol/L HCl, 0.2mol/L oxalate buffer and 4mol/L HCl at 95°C especially improved the extractability of V incorporated with crystalline phase associated V. The suitability of our new SE scheme was confirmed by its higher selectivity against the target phases and higher extraction efficiencies (55%-77% of total V) with model minerals and 6 soils of different properties than previous SE.

Fractionation and Mobility of Thallium in Volcanic Ashes after Eruption of Eyjafjallajökull (2010) in Iceland.

Volcanic ash contains thallium (Tl), which is highly toxic to the biosphere. The aim of this study was to determine the Tl concentration in fractions of volcanic ash samples originating from the Eyjafjallajökull volcano. A sequential extraction scheme allowed for a study of element migration in the environment. Differential pulse anodic stripping voltammetry using a flow measuring system was selected as the analytical method to determine Tl content. The highest average content of Tl in volcanic ash was determined in the fraction entrapped in the aluminosilicate matrix (0.329 µg g−1), followed by the oxidizable fraction (0.173 µg g−1). The lowest content of Tl was found in the water soluble fraction (0.001 µg g−1); however, this fraction is important due to the fact that Tl redistribution among all the fractions occurs through the aqueous phase.

Lead redistribution in a mine soil treated with three manures and incubated at two different temperatures

ABSTRACTThe study of heavy metals’ redistribution between different fractions allows to know their bioavailability and mobility in soils. Soil samples were collected from a lead mine in Hamadan provinces, NW Iran. In a factorial experiment soil was treated with cow, sheep and poultry manures (20 g kg−1 soil) separately and incubated near field capacity at 10°C and 37°C. An untreated soil (as control) was also incubated at the same temperatures. After 0 and 120 days, a sequential extraction scheme was used to fractionate Pb of incubated samples into soluble-exchangeable (Sol-Exch), organic matter associated (AOM), carbonates associated (ACar), and residual (Res) forms. Soil Pb in Sol-Exch and AOM fractions were increased by manure application significantly. The AOM and ACar forms of Pb were higher in soils treated with the manures and incubated in lower temperature. In contrast, the Sol-Exch and Res chemical forms of Pb were higher in the soils incubated at 37°C. These results may be related to the higher calcium carbonate dissolution and organic matter decomposition because of better biological activity in the soils incubated in higher temperature. The increase of the Res fraction (stable form) in this condition may resulted in lower toxicity and mobility in soil environment.

Thallium dispersal and contamination in surface sediments from South China and its source identification

Thallium (Tl) is a non-essential element in humans and it is considered to be highly toxic. In this study, the contents, sources, and dispersal of Tl were investigated in surface sediments from a riverine system (the western Pearl River Basin, China), whose catchment has been contaminated by mining and roasting of Tl-bearing pyrite ores. The isotopic composition of Pb and total contents of Tl and other relevant metals (Pb, Zn, Cd, Co, and Ni) were measured in the pyrite ores, mining and roasting wastes, and the river sediments. Widespread contamination of Tl was observed in the sediments across the river, with the highest concentration of Tl (17.3 mg/kg) measured 4 km downstream from the pyrite industrial site. Application of a modified Institute for Reference Materials and Measurement (IRMM) sequential extraction scheme in representative sediments unveiled that 60–90% of Tl and Pb were present in the residual fraction of the sediments. The sediments contained generally lower 206Pb/207Pb and higher 208Pb/206Pb ratios compared with the natural Pb isotope signature (1.2008 and 2.0766 for 206Pb/207Pb and 208Pb/206Pb, respectively). These results suggested that a significant fraction of non-indigenous Pb could be attributed to the mining and roasting activities of pyrite ores, with low 206Pb/207Pb (1.1539) and high 208Pb/206Pb (2.1263). Results also showed that approximately 6–88% of Tl contamination in the sediments originated from the pyrite mining and roasting activities. This study highlights that Pb isotopic compositions could be used for quantitatively fingerprinting the sources of Tl contamination in sediments.