Three-step Sequential Extraction Research Articles

Determination of metal fractions and rare earth anomalies in red mud: the case of bauxite mining district of Seydişehir (Turkey)

A three-step sequential extraction was carried out by modified BCR approach for fractionation of metals, including rare earths in red mud. Acetic acid leaching, hydroxylamine hydrochloride + nitric acid leaching, hydrogen peroxide + acid ammonium acetate leaching, and orthophosphoric + nitric acid digestion in microwave were performed to determine ion exchangeable (F1), reducible (F2), oxidizable (F3), and residual (F4) fractions of metals, respectively. Accordingly, the highest readily soluble phases were obtained for Ca, Na, and K, while the reducible were Al, Zn, Cu, and Li. Rare earth elements (REEs) except for Eu were mostly identified in residual fraction. Most of Eu (88.7%) was detected in the reducible fraction, while the negligible part in residual. Chondrite normalization was implemented for obtaining REE anomalies. The remarkable Eu and Gd negative anomaly differences were determined between the red mud and its origin, Mortaş bauxite. The LREE to HREE ratio and LaN/YbN scores of 8.42 and 7.82, respectively indicated the LREE enrichment to HREE. By performing multivariate analysis, six and five-group clusters were obtained for REEs and non-REE metals in terms of fractional distribution, proving the easier release potential of Eu, La, Gd, K, Na, and Ca.

Accumulation and Risk Assessment of Heavy Metals in Sediments from Dredged Tributaries and Creeks of River Ethiope, South-South, Nigeria

The presence of heavy metals in rivers in the Niger Delta region has become a source of concern due to its associated health challenges. The present study was conducted to assess the risk of heavy metal accumulation in surface sediments obtained from creeks and dredged tributaries of the River Ethiope, Delta State, South-South, Nigeria. Heavy metals in the sediments were extracted using the three-step sequential extraction method of the European Commission Standard Measurement and Testing Program. The heavy metals; magnesium (Mn), iron (Fe), zinc (Zn), lead (Pb), copper (Cu), cobalt (Co), arsenic (As), chromium (Cr), cadmium (Cd) and barium (Ba) were quantified by employing inductively coupled plasma-mass spectrometry (ICP-MS). Assessment of the extent of sediment contamination was carried out by determining the contamination factor (CF), degree of contamination (Cd), modified degree of contamination (mCd), pollution load index (PLI), ecological risk factor (Er), potential ecological risk index (PI) and geo accumulation index (1 geo). Pearson’s correlation coefficient and principal component analysis (PCA) were used to determine the sources and the relationship between pollutants across sediments. The values of heavy metals ranged from 12.5 mg kg–1–116 mg kg–1 and 21.6 mg kg–1–71.1 mg kg–1 in the wet and dry seasons, respectively. The trend of heavy metals for risk index (RI) in this study is Cd > Pb > Cr > Co > Zn > Cu > Mn (wet season) and Cu > Cd > Pb > Zn > Cr > Mn > Co = As (dry season). It showed that heavy metal pollution was a result of Cd for extreme contamination, while moderate to high contamination levels were due to Pb and Cu. The Pearson’s correlation coefficient analysis and PCA displayed strong positive loadings for Mn, Fe, Zn, Pb, Cu and Cd across seasons as a result of high contamination levels in the study sites. The pollution load index revealed that the sediments were polluted by the metals, and the mean and median analyses revealed that the metals datasets were normally distributed, except for Cu with an irregular distribution.

Mixed nitrate and metal contamination influences operational speciation of toxic and essential elements

Environmental contamination constrains microbial communities impacting diversity and total metabolic activity. The former S-3 Ponds contamination site at Oak Ridge Reservation (ORR), TN, has elevated concentrations of nitric acid and multiple metals from decades of processing nuclear material. To determine the nature of the metal contamination in the sediment, a three-step sequential chemical extraction (BCR) was performed on sediment segments from a core located upgradient (EB271, non-contaminated) and one downgradient (EB106, contaminated) of the S-3 Ponds. The resulting exchangeable, reducing, and oxidizing fractions were analyzed for 18 different elements. Comparison of the two cores revealed changes in operational speciation for several elements caused by the contamination. Those present from the S-3 Ponds, including Al, U, Co, Cu, Ni, and Cd, were not only elevated in concentration in the EB106 core but were also operationally more available with increased mobility in the acidic environment. Other elements, including Mg, Ca, P, V, As, and Mo, were less operationally available in EB106 having decreased concentrations in the exchangeable fraction. The bioavailability of essential macro nutrients Mg, Ca, and P from the two types of sediment was determined using three metal-tolerant bacteria previously isolated from ORR. Mg and Ca were available from both sediments for all three strains; however, P was not bioavailable from either sediment for any strain. The decreased operational speciation of P in contaminated ORR sediment may increase the dependence of the microbial community on other pools of P or select for microorganisms with increased P scavenging capabilities. Hence, the microbial community at the former S-3 Ponds contamination site may be constrained not only by increased toxic metal concentrations but also by the availability of essential elements, including P.

Environmental bioavailability of arsenic, nickel and chromium in soils impacted by high geogenic and anthropogenic background contents

High arsenic, chromium and nickel in soils can pose a hazard to the ecosystem and/or human health. Large areas can be affected by elevated potentially toxic elements (PTE) background contents, entailing a significant effort for managing the potential risk. Assessing the environmental hazard associated to PTE-contaminated soils requires the determination of soil PTE environmental bioavailability, which reflects the capacity of these elements to be transferred to living organisms. Here we assess the environmental bioavailability of As, Cr and Ni in topsoils from the Liège basin and Belgian Lorraine, two areas in Wallonia, Belgium, affected by elevated As, Cr and Ni background contents. The source of soil As, Cr and Ni differs in Liège and Lorraine: anthropogenic in the former location and geogenic in the latter. The environmental bioavailability of PTE was determined using two complementary approaches: (1) by chemical fractionation with the Community Bureau of Reference (BCR) three-step sequential extraction protocol and (2) by estimating the phytoavailability using a plant-based biotest (Lolium multiflorum as plant model). The results show that total As (6–130 mg·kg−1), Cr (15–268 mg·kg−1), and Ni (8–140 mg·kg−1) contents in the Liège and Lorraine soils frequently exceed the soil clean-up standards. However, no positive correlation was found between the total contents and BCR extraction results or rye-grass contents, except for As in Liège soils. Total As, Cr or Ni contents surpassing soil standards do not necessarily result in elevated mobile, potentially mobilizable and phytoavailable contents. In general, environmental bioavailability of As, Cr and Ni is higher in soils from Liège basin compared to those sampled in Belgian Lorraine. The mobile and potentially mobilizable fractions of As, Cr and Ni account for <30 % of their total contents following the BCR extractions. Our study provides valuable information for sustainable management at the regional scale of soils containing high PTE contents.

Distribution, speciation, and bioaccumulation of potentially toxic elements in the grey mangroves at Indian Sundarbans, in relation to vessel movements

Sundarban is the world's largest mangrove wetland and home of 4.6 million people (Indian part), whose principal mode of communication is motorized boats (ferries). This study shed light on the role played by ferry movement in the speciation (following the BCR three-step sequential extraction method), ecological impact and bioaccumulation of potentially toxic elements (PTEs) in plant tissues (root and lamina) of grey mangrove (Avicennia marina) found near the five ferry ghats (ports). One-way ANOVA showed variation in major soil parameters (silt, clay, organic carbon, pH, Electrical conductivity) and PTEs (As, Cd, Cr, Cu, Hg, and Pb) between sites. Sequential extraction revealed that Cd was present in the ‘exchangeable’ form across the sites, Pb was in the ‘reducible’ form, and the rest of the PTEs were majorly found in ‘residual’ phase. Pollution indices revealed moderate to heavy contamination and considerable potential ecological risk due to Cd. Pearson correlation statistics and concentration variations indicate a relation between Pb and ferry movement frequency in the sites. Higher bioconcentration of Pb in the roots of A. marina, indicates phytostabilization action. Translocation factor for Cd in the leaves, indicates phytoextraction by A. marina. Principal component analysis (PCA) and hierarchical cluster analysis (HCA) showed a close association between vehicle movement and Hg, Pb, Silt fraction, electrical conductivity, Cr, and As. This study recommends regular pollution monitoring across Sundarbans, as the PTEs in sediment-plant matrix can impact the higher trophic levels, human health through possible biomagnification in the detritus food chain, and can adversely impact the existing conservation initiatives.

Total mercury and methylmercury in garfish (Belone belone) of different body weights, sizes, ages, and sexes

BackgroundGarfish, (Belone belone) is a migratory pelagic fish that inhabits the waters of coastal Europe, North Africa, the North Sea, the Mediterranean Sea. Little information about garfish has been disseminated mainly because of its low abundance and its brief occurrence in various water bodies. Data is lacking on mercury compounds, particularly dangerous the toxic organic form of methylmercury (MeHg), which endangers the health of fish and their consumers. MethodsThe research material was garfish caught off the southern Baltic Sea coast in Puck Bay during the spawning period. Total mercury (THg) content was assayed with the cold vapour atomic absorption method in an AMA 254 mercury analyser. The MeHg extraction procedure was based on three-step sequential extraction method: hydrolysis using of hydrochloric acid, extract by toluene, bind the MeHg by L-cysteine. ResultsThe concentrations of THg and MeHg was determined in the muscle of garfish. The highest concentrations of THg (0.210 mg kg-1) and MeHg (0154 mg kg-1) were detected in the longest specimens (80 cm). The THg and MeHg concentrations in garfish muscles increased with specimens length, weight and age, which was confirmed by positive correlations. Differences were also noted depending on sex. Males accumulated more THg and MeHg than did females. The mercury in garfish from the southern Baltic Sea occurred mainly in its organic form MeHg and accounted for 84.7% of the THg. ConclusionSignificant differences were noted in mercury concentrations depends on length, weight, age and sex. Concentration of MeHg in garfish must be done by length class, and fish sex when selecting this fish for contamination studies and risk assessment. The toxic MeHg in garfish tissues did not pose a threat to the health of consumers, as indicated by the low values of EDI, TWI and THQ indices.

Dynamic sequential extraction procedure using a four-channel circulating flow system for extracting Hg from soil samples

Mercury (Hg) is harmful to the human body. Its physical properties and toxicity differ greatly depending on its chemical form. The quantification of soluble Hg in soils or sediments is crucial for preventing further environmental contamination by Hg sources such as products, processes, and storage. In this study, the risk of leachable Hg that release from soil to the hydrosphere was evaluated by the sequential extraction procedure (SEP), a speciation method of a targeted element based on the solubility of its various compounds. The SEP, which consists of a four-channel circulating flow system (FCFS), was developed to reduce the time and amount of liquid required for SEP of leachable Hg in the Bloom method, which is a conventional SEP for Hg in a solid sample. The SEP with FCFS was optimized by considering the impact of extractant volume, circulation extraction time, and flushing of the extraction line. In the three-step (Fraction 1-3) sequential extraction of leachable Hg in soil samples, the optimized SEP with FCFS required 45mL of extractant and 2.5h, while the common batch SEP required 75mL of extractant and 49h. Furthermore, the combination of the SEP with FCFS for the leachable forms (Fraction 1-3) and the batch method for the insoluble forms (Fraction 4-5) was applied to the five-step SEP of Hg from CRM-JSAC0403. The sum of Hg concentrations that were classified into five fractions was in good agreement with that obtained from the batch method for all extraction, indicating that there are no significant differences in the concentrations extracted from the four channels.

The significance of applying different factors for the evaluation of sediment contamination by toxic elements and estimation of the ecological risk.

The optimized three-step sequential extraction procedure for the fractionation of micro- and macroelements, was conducted to determine fractional characteristics of PTEs (potentially toxic elements) in surface sediments of rivers in the Vlasina watershed. The sequential extraction results, which enable the evaluation of mobility of the studied elements, have indicated that Zn, Ni, Cu, Cr, and As can be considered slightly mobile, whereas Pb, Mn, Cd, and Co were regarded as possibly mobile elements. Lead was dominantly bounded (specifically adsorbed or co-precipitated) to iron and manganese oxides (up to 80%) and may be released by reduction. Since the content of the exchangeable fraction (F1) is an indicator for anthropogenic impact on the aquatic environment, a low percentage (0-8%) of studied toxic elements in this fraction indicated that these elements have lithogenic origin in most sampling locations in the area of study. Except for Pb, the substantial positive correlations between Al and other elements showed that studied elements came primarily from terrigenous sources. Although the values obtained for the risk assessment code (RAC) indicated a slightly increased mobility of some elements (up to 22.44%), the values of the modified risk assessment code (mRAC), which include toxic effects on the environment, showed there is no danger of pollution by studied elements (all values were < 1%). Our recommendation is to use mRAC instead of RAC in ecochemical studies and assessment of the degree of sediment and soil pollution, because mRAC includes toxic effects of elements. Based on ATI values, river sediments show no toxic to a low toxic degree. Even though obtained results indicate that there was no considerable risk for river water contamination, the ecological risk for Fe and Pb should be monitored in the future.

Determination of Selenium Speciation in High Se-Enriched Edible Fungus Ganoderma lucidum Via Sequential Extraction

Edible fungi are often used as an important selenium (Se) source to improve human daily Se intakes as food or Se supplements because of their strong ability to accumulate Se, in which Ganoderma lucidum was widely accepted in China. However, the existing Se speciation analysis methods such as protease K-based or trypsin-protease XIV-based, have low extraction rate and enzymatic hydrolysis rate (&lt;30%) on the Se-enriched edible fungi, resulting that it is impossible to effectively evaluate Se transformation and safety of Se-enriched edible fungi. In order to improve the extraction rate and enzymatic hydrolysis rates, 12 extraction methods (combination of buffer solutions and enzymes) including 4 two-step extraction methods and 8 three-step extraction methods were applied to extract Se from high Se-enriched Ganoderma lucidum (Total Se content 245.7 μg/g in dry matter (DW)) in the present study. The results displayed that one three-step sequential extraction method as aqueous solution extraction-pepsin extraction-trypsin extraction performed the best, by which the total Se extraction rate could reach 65%, the total Se enzyme hydrolysis rate was 40%, and the Se speciation was revealed as Selenite (63.6%), SeCys2 (20.1%), SeMeCys (14.8%) and SeMet (1.5%) in this high Se-enriched Ganoderma lucidum. This study offers a reliable and efficient method to evaluate the Se transformation and the Se safety in high Se-enriched edible fungi.

Cereal grain mineral micronutrient and soil chemistry data from GeoNutrition surveys in Ethiopia and Malawi

The dataset comprises primary data for the concentration of 29 mineral micronutrients in cereal grains and up to 84 soil chemistry properties from GeoNutrition project surveys in Ethiopia and Malawi. The work provided insights on geospatial variation in the micronutrient concentration in staple crops, and the potential influencing soil factors. In Ethiopia, sampling was conducted in Amhara, Oromia, and Tigray regions, during the late-2017 and late-2018 harvest seasons. In Malawi, national-scale sampling was conducted during the April–June 2018 harvest season. The concentrations of micronutrients in grain were measured using inductively coupled plasma mass spectrometry (ICP-MS). Soil chemistry properties reported include soil pH; total soil nitrogen; total soil carbon (C); soil organic C; effective cation exchange capacity and exchangeable cations; a three-step sequential extraction scheme for the fractionation of sulfur and selenium; available phosphate; diethylenetriaminepentaacetic acid (DTPA)-extractable trace elements; extractable trace elements using 0.01 M Ca(NO3)2 and 0.01 M CaCl2; and isotopically exchangeable Zn. These data are reported here according to FAIR data principles to enable users to further explore agriculture-nutrition linkages.

Comparative studies on the effects of biochar and cow dung amendments on the mobility, bioavailability and toxicity of heavy metals in lead-acid contaminated soil

This study compared the heavy metals remediation potency of biochar and cow dung in soils contaminated by lead-acid batteries. Soil samples were gathered from three different battery charging shops in Benin City at the depth of 0-15cm using systematic grid sampling method. Hardwood was pyrolyzed at 350°C for 80minutes and cow dung was air dried and pound into powder. The soil was characterized using standard methods, and was fractionated using modified European Community Bureau of Reference (BCR) three-step sequential extraction procedure while the concentration of heavy metals was determined using Atomic Absorption Spectrophotometer (AAS). The total metal concentration in the lead-acid contaminated soil was 127.50mg/kg Pb, 0.32mg/kg Cr, 0.03mg/kg Cd, 0.18mg/kg Ni and 135.00mg/kg Fe. The contaminated soil was remediated with biochar and as well with cow dung at 5%, 10%, 15% and 20%. The soil was also amended using biochar-cow dung mixture (1:1, 2:1 and 1:2). The outcome revealed that the metal content in lead-acid contaminated soil remediated with biochar and cow dung were found to generally decrease as the percentage of amenders increases, with biochar being further efficient in lowering the levels of heavy metals in the contaminated soil. However, biochar when mixed with cow dung at 2:1 ratio at 20% amendment gives a better result than when used separately. Pot experiment was designed and the amounts of heavy metals bioavailable to plant were determined. The mobility factors and bioavailability indices of the metals reduced as the percentage of amenders’ increases. The result obtained from this study revealed that although biochar and cow dung were effective amenders, biochar was more potent in lowering the mobility, bioavailability and toxicity of heavy metals in lead-acid contaminated soil. Biochar when mixed with cow dung at 2:1 ratio gave the best result in remediation of lead-acid contaminated soil.

Deep coverage proteome analysis of hair shaft for forensic individual identification

Hair shaft is one of the most common biological evidence found at crime scenes. However, due to the biogenic degradation of nuclear DNA in hair shaft, it is difficult to achieve individual identification through routine DNA analysis. In contrast, the proteins in hair shaft are stable and contain genetic polymorphisms in the form of single amino acid polymorphisms (SAPs), translated from non-synonymous single nucleotide polymorphisms (nsSNPs) in the genome. However, the number of SAPs detected still cannot meet the requirements of practical applications. This paper developed a deep coverage proteome analysis method by combining a three-step sequential ionic liquid-based protein extraction and 2D-RPLC-MS/MS with high and low pH to identify both variant and reference SAPs from 2-cm-long hair shafts. We identified 632 ± 243 protein groups from 10 individuals, with the average number of SAPs reaching 167 ± 21/person. These were further used to calculate random match probabilities (RMPs), a widely accepted forensic statistical term for human identification. The RMPs ranged from 6.53 × 10–4 to 3.10 × 10–14 (median = 2.62 × 10–8) when calculated with frequency of matching nsSNP genotype data from exomes, and ranged from 2.62 × 10–3 to 2.07 × 10–10 (median = 4.88 × 10–6) with SAP genotype frequency. All these results indicate that the deep coverage proteomics method is beneficial for improving SAP-based forensic individual identification in hair shaft, with great potential in crime investigation.

Investigation of metal mobility in gold and silver mine tailings by single-step and sequential extractions

Metal leachate from mine tailings has the potential to release toxic metals into the surrounding environment. A single-step extraction procedure mimicking rainwater and a three-step BCR sequential extraction procedure (acid, reducing and oxidizing conditions) were applied to gold (GMT) and silver (SMT) mine tailings. Major (Al, Ca, Fe, Mg, and Mn) and trace metals were monitored to better understand the mobility and geochemistry of these metals when exposed to various environmental leaching conditions. Rainwater extraction released only small quantities of metals, while the three-step BCR extraction was more effective in mobilizing metals from the tailings. Under the acidic conditions of BCR step 1, Ca, Mg, Cd, Cu, and Mn were released in high concentrations. The dissolution of Fe, Ca, and Mg were dominant along with Pb in step 2 (reducing conditions). In step 3 (oxidizing conditions), Fe was the most dominant species together with Co, Cu, Ni, and Se. A high fraction of Al, Be, Cr, Li, Mo, Sb, Tl, and V remained in the residue. From SMT, larger quantities of As, Ca, Cd, and Zn were released compared to GMT. The BCR extraction could be applied to tailings to predict the potential release of toxic metals from mine wastes; however, excessive amounts of Ca and Fe in the tailings could cause carry-overs and incomplete extraction and carry-overs, resulting in a misinterpretation of results.

Characterization of physicochemical parameters and bioavailable heavy metals and their interactions with microbial community in arsenic-contaminated soils and sediments.

Mobility and toxicity of heavy metal contamination in the environment are highly dependent on its bioavailability. Most of previous studies focused on total heavy metal contents and their influence on microbial community in soils and sediments. Little were concerned about bioavailable fractions. In the current study, soil and sediment samples were collected near an abandoned realgar mine in Shimen County, China. Bioavailable heavy metals including Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Sb, and Pb in the samples were extracted using three-step sequential extraction method. Interactions among physicochemical parameters, total and bioavailable heavy metals, and microbial community in the collected samples were investigated. The study area has been severely contaminated by As with a concentration up to 2158mg·kg-1 detected. The result of principal component analysis showed that the abundance of operational taxonomic units (OTUs) in the soils were obviously different from those in the sediments. In the soil samples, pH made a dominant contribution on the OTU abundance of microbial community. Correlation analyses revealed that the alpha diversity indices and microbial taxon were most correlated with bioavailable fractions of heavy metals in all the samples. That means bioavailable heavy metals rather than total heavy metals or physicochemical parameters played a more important role on richness and diversity of microbial community. Little connections were observed between microbial community and As no matter total concentration or bioavailable fraction. However, bioavailable Fe and Mn were recognized as the major driving force shaping the taxonomic structure of microbial community due to their relatively high concentrations and high affinity to other heavy metal contamination in soils and sediments.

Impacts of wet thermal treatment on heavy metals speciation in contaminated waste activated sludge using a modified sequential extraction scheme

The mobility and the bioavailability of heavy metals in waste activated sludge were determined according to their total content and chemical speciation. A modified three-step sequential extraction procedure was used to determine the total content and metal speciation distribution pattern of various heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) pretreated at a temperature of 100 °C to 200 °C. It was found that the organics solubilization was enhanced at higher temperature, increased by 1.75, 183 and 3.03 folds over the soluble chemical oxygen demand (SCOD) at 100 °C. The total contents of Cd, Pb and Zn exceeded the threshold value established in GB/T standard 23486 (2009), as a function of pH, due to the pollution from the local nonferrous metals industry. For most cases, the impacts of thermal pretreatment on the species distribution were limited and obscure. Cr was the only element showing a potential risk of metal mobilization, such that its residual fraction shifted towards oxidizable fraction at higher treatment temperature. The speciation distribution pattern of Ni, Cr, Cu, and Zn showed potential risks of contamination due to their bioavailability, mobility, or toxicity.

Preliminary analysis on roles of metal\u2013organic compounds in the formation of invisible gold

The paper comprises new analytical data on the nature and occurrence of gold in solid pyrobitumen, closely associated with the main gold-bearing sulfide arsenic ores of the Bakyrchik gold deposit (Kazakhstan), related to post-collisional magmatic-hydrothermal origin. Gold mineralization of the deposit occurs mainly in the form of an “invisible” type of gold in the structures of arsenian pyrite and arsenopyrite, and the form of gold-organic compounds of pyrobitumen in carbonaceous-terrigenous sequences of Carboniferous formation. Microscopic and electron microscopic analysis, Raman and FT-Infrared analysis, mineralogical and three-step sequential extraction analysis (NH2OH·HCl, H2O2, HNO3 + HCl) has been carried out using 9 ore samples (from 3 different types of ores) for a comprehensive study of pyrobitumen and sulfide arsenic ores focusing mainly on organic matter. The sequentially extracted precious metal content of pyrobitumen reaches up to 7 ppm gold and other metals like Ag 4 ppm, Pt 31 ppb, and Pd 26 ppb, forming metal–organic compounds, while arsenic sulfide minerals incorporate 11 ppm gold, 39 ppm Ag, 0.49 ppm Pt. The enrichment of gold associating with organic matter and sulfide ore minerals was confirmed in this study. Organic matter was active in the migration of gold and the capture of gold by pyrobitumen. Moreover, the reductive organic matter agent released gold, most likely for the sulfide arsenic ore minerals. Pyrobitumen was a decisive factor in the concentration, transportation, and preservation of gold in the deposit.

Microwave-assisted single-step extraction method for determination of heavy metals in saline soil and compare with conventional sequential extraction method

The present research assesses the chemical fractionation of cadmium (Cd), chromium (Cr), and lead (Pb) detected in saline soil samples of Hyderabad Pakistan. Based on the reagents used in the BCR three-step conventional sequential extraction (CSE) for partitioning Cd, Cr, and Pb in saline soil samples, a Microwave induced single-step extraction (MSE) method was developed. The validity of the method was confirmed using certified reference material (CRM) BCR-483 and the standard method of addition (recoveries 96–102%). The data provided by the BCR- CSE method for Cd, Cr and Pb partition were compatible with MSE using the same operating conditions applied and checked in BCR fraction by the Certified Reference Material (CRM) BCR-483. Using compromised sonication and microwave conditions steps 1–3 of the sequential extraction (excluding hydrogen peroxide digestion in step 3) could be accomplished with ultrasonic bath between 15 and 30 min, whereas 60–120 s needed for MSE. The total concentrations of Cd, Cr, and Pb extractable metals produced by three separate extractions ranged 1.02–3.30, 5.02–9.95 and 3.97–8.01 μgg−1, respectively. The accuracy of the proposed BCR single extraction methods (expressed as RSD %) for all metals was found within the range of (4.99–8.61%).

Effect of multi-walled carbon nanotubes on extractability of Sb and Cd in contaminated soil

The interaction between multi-walled carbon nanotubes (MWCNTs) and soil heavy metals was rarely studied. With the convenience of detecting multiple metal elements by ICP-AES, this paper examined the potential effectiveness of MWCNTs on extractability of antimony (Sb) and cadmium (Cd) in contaminated soil. Three-step sequential extraction procedure, toxicity characteristic leaching procedure, bioaccessibility and CaCl2 single extraction were employed to evaluate Sb and Cd speciations and their extractabilities. According to our results, only at low Sb content level of 100 mg/kg, antimony bioavailability reduced with MWCNTs addition of 0.3% and 0.9% by 22.97% and 20.74%, respectively, which might due to the increase of adsorption point, nevertheless, the excess Sb(OH)6- was not adsorbed more efficiently. Secondly, due to the difference in effective specific surface area, only under the condition of high content level and MWCNTs addition of 0.1%, the mild acid-soluble fraction increased at most by 15.40% for Sb and 9.40% for Cd, respectively. However, in terms of TCLP-extractable Sb and Cd and CaCl2-extractable Sb and Cd, no significant, continuous, regular extractability pattern were found. Overall, MWCNTs were selective on extractability of soil heavy metals due to mechanisms of physical adsorption. This paper provides data reference for the interaction between MWCNTs and soil heavy metals extractability.

Toxicity of soil antimony to earthworm Eisenia fetida (Savingy) before and after the aging process

Information on soil antimony (Sb) toxicity to earthworm Eisenia fetida (Savingy) is limited. This ecotoxicology study was designed to quantify the soil Sb toxicity to earthworm E. fetida before and after aging process, establishing dose-effect relationship between Sb content and mortality. Results of the avoidance test and acute test showed that the values of net avoidance response, escape rate and mortality were generally decreased in aged treatment compared to that in fresh treatment, respectively from 93.33% to 66.67%, 36.67% to 13.33% and 100% to 53.33% (15 d) taking TL800 (treatment level of 800 mg/kg) for example, meanwhile the values of median lethal content (LC50) at 72 h, 7 d and 15 d were respectively increased from 355.27 mg/kg to 2324.55 mg/kg, 322.19 mg/kg and 1743.19 mg/kg and 282.74 mg/kg to 745.94 mg/kg, indicating that aging process could reduce the Sb acute toxicity to earthworm. According to a three-step sequential extraction procedure, the bioavailable Sb ranged from 24.45% to 43.24% and 16.97% to 27.70% in fresh treatment and aged treatment, respectively, and the mortality of earthworm for 24 h decreased with the decrease of the content of mild acid-soluble antimony (which decreased averagely from 23.09% to 14.00%), which was more suited to assess Sb toxicity. This is the first report that confirms the toxicity of soil Sb to earthworm E. fetida as well as the considering of aging process and speciation.

Evaluation of mobility, fractionation, and potential environmental risk of trace metals present in soils from Struibult gold mine dumps

This study reports the fractionation of trace metals such as As, Bi, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sb, Se, Tl and Zn in soils collected from Struibult gold mine dump, Gauteng, South Africa using a modified three-step BCR sequential extraction procedure. The extractable fractions such as exchangeable, easily reducible and oxidizable fractions were used assessed to the mobility and potential bioavailability of each investigated metal. Fractionation results revealed that As (55.4–80.6%), Bi (16.8–42.2%), Cr (83.3–94.8%), Cu (0–51.5%), Mo (0–80.4%), Ni (13.2–100%), Pb (55.6–79.6%), Sb (61.9–93.3%), Se (47.3–77.9%), Tl (58.8–100%) and Zn (8.7–100%) predominant metals in the residual fraction (F4) of soil samples. Individual contamination factors (ICF), geo-accumulation index (Igeo), contamination factor (CF), risk assessment code (RAC) and enrichment factor (EF) were used for assessment of the environmental impacts of trace metals in soil samples. The RAC and ICF values showed that Co, Ni and Zn have high environmental risk. The bioaccumulation of trace metals in the plants (Chrysopogon zizanioides) growing at the foot of the mine dump was assessed. Chrysopogon zizanioides was found to accumulate most of the studied metals that were available for uptake, with bioaccumulation factor (BAF>1). These results suggested that this plant species is a good accumulator for toxic metals in mining areas.