Speciation Of Pb Research Articles

Investigating speciation and toxicity of heavy metals in anoxic marine sediments—a case study from a mariculture bay in Southern China

The pollution of marine sediments by heavy metals is still a major concern, especially in zones affected by industry or mariculture. Toxicity of sediment heavy metal contents may be assessed using sequential extraction (SE) procedures, minding inherent constraints of such approaches. In this study, we investigated heavy metal speciation and toxicity in anoxic marine sediments in Zhelin Bay, a mariculture bay in Southern China, using an SE and acid volatile sulfur-simultaneously extracted metals (AVS-SEM) approach. Speciation of Cd, Cu, Ni, Pb, and Zn were studied by a modified SE of five fractions, adapted to separate organic and sulfidic metal fractions in anoxic sediments: F1 weak acid soluble (readily available), F2 reducible fraction, F3 organic matter-bound fraction, F4 sulfide-bound fraction, and F5 residually bound fraction. Toxicity predictions based on the sum of non-residual (NR) metal fractions from sequential extraction were compared to predictions based on AVS-SEM. Results showed that Cd, Ni, and Pb predominantly occurred in the weak acid soluble fraction (F1), residual fraction (F5), and sulfide-bound fraction (F4), respectively; Cu and Zn were mainly obtained in F4 and F5. Based on the distribution of indicator elements for metal fractions, the SEM from AVS extraction included different yields of non-residual and residual fractions besides the sulfidic fraction. Estimates for potential heavy metal toxicity based on NR metals of the SE procedure were thus based on a better-defined speciation compared to the simplistic approach of the AVS-SEM method. Based on the contents of NR metals and normalizing them by organic matter content, toxic effects are not expected for any of the sampling sites, irrespective of the presence or absence of mariculture. Using Pearson correlation analysis to identify predominant fractions influencing toxicity, we conclude that toxicity of heavy metals in anoxic sediments can be well predicted by their non-residual heavy metal contents.

Effects of paper sludge addition on the bioavailability and distribution of Pb in contaminated soil

Heavy metal contamination of soil poses risks and hazards to environment and human being. Many amendments were used to remediate the contaminated soil. In this report, paper sludge was used to reduce the bioavailability of Pb in soil, and the remediation mechanism was studied by investigating the redistribution of Pb speciation after paper sludge addition. In pot experiments, significantly increased weights of shoots (from 1.6 to 3.3 mg per plant) and roots (from 0.7 to 0.8 mg per plant), as well as significantly decreased Pb content in shoots (from 153.8 to 24.4 mg kg−1) and roots (from 467.1 to 38.0 mg kg−1) of rape were observed after paper sludge was added. The addition of paper sludge resulted in redistribution of Pb from the liable fractions (carbonate-bound Pb from 58.3 to 3.7%) to the Fe–Mn oxide-bound fraction (from 29.2 to 74.9%). Paper sludge addition increased the content of organic matters and pH of soil, and induced Pb redistribution, which ultimately inhibited Pb uptake and improved plant growth.

Speciation and bioavailability of lead in complementary medicines

Complementary medicines have associated risks which include toxic heavy metal(loid) and pesticide contamination. The objective of this study was to examine the speciation and bioavailability of lead (Pb) in selected complementary medicines. Six herbal and six ayurvedic medicines were analysed for: (i) total heavy metal(loid) contents including arsenic (As), cadmium (Cd), Pb and mercury (Hg); (ii) speciation of Pb using sequential fractionation and extended x-ray absorption fine structure (EXAFS) techniques; and (iii) bioavailability of Pb using a physiologically-based in vitro extraction test (PBET). The daily intake of Pb through the uptake of these medicines was compared with the safety guidelines for Pb. The results indicated that generally ayurvedic medicines contained higher levels of heavy metal(loid)s than herbal medicines with the amount of Pb much higher than the other metal(loid)s. Sequential fractionation indicated that while organic-bound Pb species dominated the herbal medicines, inorganic-bound Pb species dominated the ayurvedic medicines. EXAFS data indicated the presence of various Pb species in ayurvedic medicines. This implies that Pb is derived from plant uptake and inorganic mineral input in herbal and ayurvedic medicines, respectively. Bioavailability of Pb was higher in ayurvedic than herbal medicines, indicating that Pb added as a mineral therapeutic input is more bioavailable than that derived from plant uptake. There was a positive relationship between soluble Pb fraction and bioavailability indicating that solubility is an important factor controlling bioavailability. The daily intake values for Pb as estimated by total and bioavailable metal(loid) contents are likely to exceed the safe threshold level in certain ayurvedic medicines. This research demonstrated that Pb toxicity is likely to result from the regular intake of these medicines which requires further investigation.

Exploring Cd, Cu, Pb, and Zn dynamic speciation in mining and smelting-contaminated soils with stable isotopic exchange kinetics

The exchange kinetics of Cd, Cu, Pb, and Zn in seven mining and smelting-contaminated soils and the other two anthropogenically contaminated soils was investigated by using multi-elementary stable isotopic exchange kinetic (SIEK) method, and the experimental results were successfully interpreted by modelling using a sum of pseudo first order kinetics equations. SIEK results show that in the studied soils the isotopic exchange of Cd is a relatively fast process, and the exchange almost reaches an apparent plateau after 3-d equilibration; whereas for Cu, Pb, and Zn, the exchange is more sluggish, suggesting that it is important to understand the time-dependent metal mobility for risk assessment and management of contaminated soils. In most of the soils, the total isotopically exchangeable pool is divided, for all the metals, into two distinct pools: a fast exchangeable pool (E1) with a kinetic rate constant k1 having values around 1 min−1 and a much slower exchangeable pool (E2) with k2 ranging from 0.0001 min−1 to 0.001 min−1. The distribution of the two exchangeable pools varies significantly among metals. The amount of isotopically exchangeable Cd related to the fast pool is dominant, accounting for on average 60% of total isotopically exchangeable pool in the soils; whereas this pool is smaller for Cu, Zn, and Pb. The sequence of average k1 values is Cd > Pb ≈ Zn > Cu, consistent with the reported sequence of stability constants of metal-humic substances (HS) complexes while the average k2 values follow the order: Cd > Pb > Cu > Zn, probably controlled by the slow desorption of metal ions associated with soil organic matter (SOM) fraction. Our results imply that further study on the exchange kinetics of metals on each individual sorption surface in soils, especially SOM, is critical to help understanding the overall exchange kinetics of heavy metals in whole soils.

Phytoavailability of lead altered by two Pelargonium cultivars grown on contrasting lead-spiked soils

Purpose This study assesses the potential of two contrasted fragrant Pelargonium cultivars to induce pH and dissolved organic carbon (DOC) changes in the soil solution, Pb speciation, and their subsequent effects on rhizosphere phytoavailable Pb.

Tracking the Temporal Dynamics of Intracellular Lead Speciation in a Green Alga.

Organisms have developed metal regulatory mechanisms in response to changes in the bioavailability of trace metals. Just as metal bioavailability dictates cellular uptake, intracellular metal speciation determines the availability of metals to exert biological effects. However, the missing link in understanding the relationship between metal uptake and biological responses is the ability to accurately measure intracellular metal speciation. We conducted Pb exposure studies on the well-characterized model green alga Chlamydomonas reinhardtii and identified temporal changes in intracellular Pb speciation under conditions relevant for fresh water ecosystems using resonant X-ray emission spectroscopy (RXES), which possesses enhanced sensitivity to functional group chemistry relative to X-ray absorption spectroscopy (XAS). Analysis of RXES maps show that only a small fraction of total intracellular Pb was complexed by thiol groups. Initial sequestration of Pb in oxides and inorganic phosphate was followed by binding of Pb to organic phosphate, suggesting potential interference in vital cellular functions. These results contrast proposed detoxification responses involving complexation by thiol groups from peptides.

Effects of freeze-thaw on characteristics of new KMP binder stabilized Zn- and Pb-contaminated soils

For viable and sustainable reuse of solidified/stabilized heavy metal-contaminated soils as roadway subgrade materials, long-term durability of these soils should be ensured. A new binder, KMP, has been developed for solidifying/stabilizing soils contaminated with high concentrations of heavy metals. However, the effects of long-term extreme weather conditions including freeze and thaw on the leachability and strength of the KMP stabilized contaminated soils have not been investigated. This study presents a systematic investigation on the impacts of freeze-thaw cycle on leachability, strength, and microstructural characteristics of the KMP stabilized soils spiked with Zn and Pb individually and together. For comparison purpose, Portland cement is also tested as a conventional binder. Several series of tests are conducted including the toxicity characteristic leaching procedure (TCLP), modified European Community Bureau of Reference (BCR) sequential extraction procedure, unconfined compression test (UCT), and mercury intrusion porosimetry (MIP). The results demonstrate that the freeze-thaw cycles have much less impact on the leachability and strength of the KMP stabilized soils as compared to the PC stabilized soils. After the freeze-thaw cycle tests, the KMP stabilized soils display much lower leachability, mass loss, and strength loss. These results are assessed based on the chemical speciation of Zn and Pb, and pore size distribution of the soils. Overall, this study demonstrates that the KMP stabilized heavy metal-contaminated soils perform well under the freeze-thaw conditions.

Comprehensive study of Pb (II) speciation in soil by X-ray absorption spectroscopy (XANES and EXAFS) and sequential fractionation

The study is aimed at the analysis of the spatial–structural organization of Pb(II) in Chernozem soils and the relationship between the metal ion and the soil components using X-ray absorption spectroscopy and chemical extractive fractionation. In a model experiment, soil samples were artificially contaminated with elevated rates of Pb(NO3)2 and PbO (2000 and 10,000 mg kg−1). The samples of mineral phases (bentonite, gibbsite, kaolinite, calcite, and hydromuscovite) were saturated with Pb2+ ions. The sequential fractionation of Pb in the soil was conducted by the Tessier method. X-ray absorption near-edge fine structure (XANES) spectra at the Pb LIII-edge (13.040 keV) were obtained on a Rigaku R-XAS Looper spectrometer. Extended X-ray absorption fine structure (EXAFS) LIII-edge Pb was measured at the Structural Materials Science beamline of the Kurchatov Center for Synchrotron Radiation. The results of successive extraction showed that Pb is associated with strongly bound organic substances, Fe and Mn (hydr)oxides, and carbonates. An increase in the portion of exchangeable fraction is observed under extreme loads. At the addition of Pb in the form of oxide and nitrate to the soil, the fractional compositions were similar, which indicates the good transformation of PbO in Chernozem. The features of XANES spectra indicate different orbital transitions in the electron shells of Pb2+ ions for monoxide (PbO) and soluble salt (Pb(NO3)2), which affect the ion properties and determine the individual structure of the coordination sphere. The analysis of XANES revealed that sorption of Pb in the soil samples and in the samples of mineral phases does not change its bond valence. The increased degree of soil contamination with Pb is accompanied by decreasing the stable connection between metal and soil components. Lead ions in bentonite, kaolinite, hydromuscovite, gibbsite, and calcite are incorporated in the positions of the inner-sphere complex replacing some aluminum ions in the octahedral sites. This results in changes the Pb–O distances in Pb-bearing octahedrons. We may suggest that Pb2+ is also sorbed by dimer (Pb–Pb) silicate and/or aluminum groups. The structure of adsorbent surface plays the key role in the sorption of Pb2+ by mineral phases.

Chemical Speciation of Binary Complexes of Pb(Ii), Cd(Ii) and Hg(Ii) with L-Methionine in Propylene Glycol -Water Mixture

Chemical speciation of Pb (II), Cd (II) and Hg (II) complexes of L-methionine in 0.0-60.0 % v/v propylene glycol-water mixtures has been studied pH metrically maintaining an ionic strength of 0.16 M at 303 K. The active forms of ligand are LH3 + , LH2 and LH. The predominant species detected are MLH, ML and ML2. Models containing different numbers of species were refined by using the computer program MINIQUAD75. The bestfit chemical models were arrived at based on statistical parameters. The trend in variation of complex stability constants with change in the dielectric constant of the medium is explained on the basis of electrostatic and non-electrostatic forces.

Phosphate Treatment of Lead-Contaminated Soil: Effects on Water Quality, Plant Uptake, and Lead Speciation.

Water quality threats associated with using phosphate-based amendments to remediate Pb-contaminated soils are a concern, particularly in riparian areas. This study investigated the effects of P application rates to a Pb-contaminated alluvial soil on Pb and P loss via surface water runoff, Pb accumulation in tall fescue ( Schreb; Kentucky 31), and Pb speciation. An alluvial soil was treated with triple superphosphate at P to Pb molar ratios of 0:1 (control), 4:1, 8:1, and 16:1. After a 6-mo reaction period, rainfall simulation (RFS) studies were conducted, followed by tall fescue establishment and a second set of RFS studies (1 yr after treatment). Results from the first RFS study (unvegetated) demonstrated that the total Pb and P concentrations in the effluents of 8:1 and 16:1 (P:Pb molar ratio) treatment levels were significantly greater ( < 0.05) than the control. One year after P treatment and 6 mo after vegetation establishment, total P and Pb concentrations of the effluents from a second RFS decreased by one to three orders of magnitude. Total and dissolved P concentration in runoff from the 16:1 P:Pb treatment remained significantly greater than all other treatments. However, total Pb concentration in the runoff was comparable among the treatments. Phosphorus treatment also reduced Pb uptake into tall fescue by >55%. X-ray absorption near-edge structure spectroscopy data showed that pyromorphite [Pb(PO)OH,Cl,F] abundance ranged from 0% (control) to 32% (16:1 P:Pb; 1 yr after treatment) of the total soil Pb. Although P treatment stimulated pyromorphite formation, pyromorphite abundance was comparable between the P-treated soils. These findings suggest that a 4:1 (P:Pb molar ratio) P treatment may be a sufficient means of reducing Pb bioavailability while minimizing concerns related to P loss in an alluvial setting.

Speciation and Mobility of Lead, Chromium and Zinc in Soils of Abis Region, Egypt

This study describes the chemical speciation of Pb, Cr and Zn in soils of Abis area in Egypt. The studied area is located at the North Western part of the Nile Delta, which represents soils developed from lacustreine deposits at Abis region south of Mariut Lake and covers about 40000 fed. Total 41 top soil samples (0-35 cm) were collected from the area for analysis. The total contents and fractions of Pb, Cr, and Zn were determined, and the mobility factor and potential mobility were calculated. Small amounts of Pb, Cr, and Zn retrieved from the soluble and exchangeable phases, the readily available for biogeochemical cycles in the ecosystem. Low quantities of Pb, Cr and Zn could be available to plants. Zn is present in negligible amounts lower than those of Pb or Cr. The results also indicate that most of the metals have high abundance in residual fraction indicating lithogenic origin and low bioavailability of metals in the studied soil. The values of average mobility factor for Pb, Cr and Zn in the soils of Abis area were 7.31, 6.74 and 0.51%, respectively which is less than 10%. Therefore, these elements are highly stable in soil. The average potential mobility of Pb, Cr and Zn were 15.05%. 34.79% and 8.25% respectively. The Zn had the least average potential mobility (8.25%). The order of average potential mobility of metals soils agrees with the percentage reduction in concentration of residual heavy metal.

Role of metal speciation in lead-induced oxidative stress to Vicia faba roots

Chemical speciation of metals in soil/solution plays an important role in determining their biogeochemical behavior in soil-plant system. The current study evaluated the influence of applied form of Pb (metal speciation) on its toxicity to metal sensitive Vicia faba L. roots. Lead was applied to young V. faba seedlings alone or chelated by organic ligands (citric acid and ethylenediaminetetraacetic acid). Plants were exposed to all treatments for 1, 4, 8, 12, and 24 h in nutrient solution, and contents of H2O2 and thiobarbituric-acid-reactive substances (TBARS) production were analyzed in V. faba roots. The results showed that Pb toxicity to V. faba roots depended on its applied chemical form and duration of exposure. Lead alone caused two burst of lipid peroxidation and H2O2 induction at 1 h and 12 h. Addition of EDTA dose-dependently inhibited Pb-induced H2O2 and TBARS production, indicating a protective role of this chelator against Pb toxicity during the first 24 h. In contrast, citric acid did not show significant effects on Pb-induced H2O2 and TBARS production, but delayed the induction of these effects. This study suggested that Pb toxicity to V. faba roots varies with Pb speciation in growth medium.

Distribution Characteristics and Risk Assessment of Soil Lead at a Children’s Blood Lead Exceeding Area in Fujian

Taking Pingzhai Village in Sanming City of Fujian Provice as the researching area, the village has already outbroken Children’s blood lead exceeding and cause a lot of damage to local children. In order to reveal the reason for this serious consequence and assess the environmental risk of Pb, 24 soil samples including 12 from parent material layer and 12 from the corresponding surface layer and 4 groundwater samples are collected. The Tessier sequential extraction method is applied to analyze different speciation of Pb in soil, and Risk Assessment Code (RAC) and Ratio of Secondary Phase and Primary Phase (RSP) are both applied to evaluate Pb contamination degree and ecological risks. The results show that: the concentration of Pb in soil samples exceeds the soil Pb background values of Fujian Province, and the overall concentration of Pb shows a rising trend from the surface to parent material layer, then their accumulated pollution index range from 5.4 to 54.9 in surface layer and 4.7 to 68.1 in parent material layer. Coefficients of variation of Pb in surface and parent material layer are 79% and 86%, respectively. The lead in soil can be divided into 3 chemical speciation containing T1 (exchangeable speciation and carbonate bounded form), T2 (potential ecological risk form) and T3 (residual speciation) and Pb in soil mainly exists in T2 and T3. There shows a significant positive correlation between T2 or T3 and the total amount of Pb in soil. Pb concentration in groundwater has exceeded limited value of Standards for Drinking Water Quality. RAC and RSP ecological risk assessment results indicate that: environmental risk level of RSP is higher than it of RAC, and the contamination degree and potential environmental risk level of parent material soil are higher than them of surface soil applied by the two assessment methods.

Effect of dissolved organic matter composition on metal speciation in soil solutions

Knowledge of the speciation of heavy metals and the role of dissolved organic matter (DOM) in soil solution is a key to understand metal mobility and ecotoxicity. In this study, soil column-Donnan membrane technique (SC-DMT) was used to measure metal speciation of Cd, Cu, Ni, Pb, and Zn in eighteen soil solutions, covering a wide range of metal sources and concentrations. DOM in these soil solutions was also fractionated into humic acid (HA), fulvic acid (FA), hydrophilic acid (Hy), and hydrophobic neutral organic matter (HON) by a rapid batch technique using DAX-8 resin. Our results show that in soil solution Pb and Cu are dominant in complex form, whereas Cd, Ni and Zn mainly exist as free ions; for the whole range of soil solutions, only 26.2% of DOM is humic substances and consists mainly of fulvic acid (FA). The metal speciation measured by SC-DMT was compared to the predicted ones obtained via the NICA-Donnan model using the measured FA concentrations. The free ion concentrations predicted by speciation modeling were in good agreement with the SC-DMT measurement. Moreover, we show that to make accurate modeling of metal speciation in soil solutions, the knowledge of DOM composition, especially FA fraction, is the crucial information, especially for Cu and Cd; like in previous studies the modeling of Pb speciation is not optimal and an update of Pb generic binding parameters is required to reduce model prediction uncertainties.

Speciation of Cr, Fe, Cu, Pb in the surface and under water sediment of Trans–Ekulu river, Enugu State, Nigeria

This study investigated the distribution and speciation of Cr, Fe, Cu and Pb between the surface and bottom sediments of Trans-Ekulu river Enugu, Nigeria, using flame atomic absorption spectrometric technique. The results showed that the concentrations of Fe vary significantly in the two sediment samples. Iron was observed at elevated concentrations in exchangeable, carbonate bound and Fe-Mn oxide bound fractions (76.04 to 81.03 µg/g). Very low concentration in comparison was recorded at the organic matter bound fraction (5.01 µg/g). This observation was in contrast to bottom sediment where Fe recorded an elevated concentration at the organic matter bound fraction (73.01 µg/g) and reduced concentrations at the exchangeable and carbonate bound fractions (2.01 µg/g and 4.02 µg/g) respectively. The result also indicated an increase in Cr concentrations at Fe-Mn oxide fraction of the bottom sediment (14.04 µg/g) compared to the surface sediment where Cr was not detected at the Fe-Mn oxide phase. Copper and Pb were generally not detected in the fractions studied. However, Cu was observed at Fe-Mn oxide phase for the bottom sediment (25.01 µg/g) and reduced phase for the surface sediment (7.01 µg/g). These results indicate an objectionable values in the concentration of the parameters analysed. Keywords : Speciation, metals, Enugu, sediments, AAS.

Heavy Metal Speciation in Some Selected Farms Treated with Urban Solid Waste, in Jos South, Plateau State, Nigeria

The speciation of metals in environmental samples is a serious factor in appraising the potential environmental impacts, before their disposal. The six step extraction procedure pre vi ously proposed by Obasi et al. was used with modification to systematically study the speciation of Cd, Cu, Mn, Pb, Zn, Fe and Cr in a farm treated with the dumpsite soils. The speciation study revealed higher distribution of the metals in the residual fractions except Cd which had 70.18% in the exchangeable fraction. The results also showed that there were low tendency of bioavailability and reactivity in the environment. The results of the newly introduced extractants (BeCl 2 , mixture of BeCl 2 /BaCl 2 and CaCl 2 /NH 4 Cl), revealed that these reagents could be used for the leaching of the exchangeable fraction in speciation analysis. BeCl 2 extracted 0.6499 mg/kg of the exchangeable Cd while the conventional MgCl 2 extract 0.010 mg/kg (Cd). The results also reve aled that the mixture BeCl 2 /BaCl 2 extracted 0.4384 mg/kg of Cd. The use of the mixture of BeCl 2 /BaCl 2 and Original Research Article

Photo-transformation of pedogenic humic acid and consequences for Cd(II), Cu(II) and Pb(II) speciation and bioavailability to green microalga

Humic substances (HS) play key role in toxic metal binding and protecting aquatic microorganisms from metal-induced stress. Any environmental changes that could alter HS concentration and reactivity can be expected to modify metal complexation and thus affect metal speciation and bioavailability to microalgae. The present study explores the influence of increased solar irradiance on the chemical structures and molecular weight of Elliott soil humic acid (EHA) and the associated consequences for Cd(II), Cu(II) and Pb(II) complexation and intracellular metal content in microalga. The results demonstrate that high radiance doses induce an oxidation of EHA with a formation of low molecular weight acids, an increase of –OH and –COOH group abundance, and a drop in EHA hydrodynamic size and molecular weight. The photo-induced structural changes are accompanied with a release of metal from M–EHA complexes and narrowing their size distribution, which in turn results in an increase of the intracellular Cd, Cu and Pb contents in microalga Chlamydomonas reinhardtii in agreement with the measured free metal ions concentrations.

Does Biochar Alter the Speciation of Cd and Pb in Aqueous Solution?

Cadmium and lead contamination in bodies of water has been a serious concern because of risk to the environment. A laboratory experiment was initiated to investigate the efficacy of biochar (BC) in removing cadmium and lead (Cd and Pb, respectively) from solution. After absorption by BC, the fractions of Cd and Pb at different solution temperatures were measured. The adsorption data were described by Langmuir isotherm with maximum adsorption capacities of 6.36, 6.47, and 6.74 mg Cd g-1 and 50.05, 55.86, and 63.09 mg Pb g-1 at 25, 35, and 45 °C, respectively. The adsorption capacities were affected by Cd/Pb initial concentration, pH, BC particle size, BC dosage, and reaction time. Biochar adsorbed the Cd and Pb mainly as species bound with carbonate (> 50%) and organic compounds (~40%). Exchangeable and residual fractions of Cd and Pb were less than 10%. Results from this study indicate that BC is highly effective in the adsorption of the heavy metals Cd and Pb through binding with carbonates.

Content, speciation and pollution assessment of Cu, Pb and Zn in soil around the lead–zinc smelting plant of Baoji, NW China

The concentration and speciation of Cu, Pb and Zn in soil samples collected around the lead–zinc smelting plant of Baoji, NW China, were determined using X-ray fluorescence spectrometry and the modified European Community Bureau of Reference sequential extraction procedure. The single pollution index (PI) and the integrated pollution index (IPI) were calculated to evaluate the contamination levels of Cu, Pb and Zn in the soil. The mean concentrations of Cu, Pb and Zn in the topsoil samples are 31.8, 41.3 and 102.6 mg kg−1, respectively, higher than their concentrations in the control sample. The concentrations of Cu, Pb and Zn decreased significantly with depth from 0 to 35 cm, while they were relatively constant for depths between 35 and 100 cm. The concentrations of Cu, Pb and Zn in topsoil north of the lead–zinc smelting plant decreased exponentially with distance from the plant. Cu and Zn in the soil are mainly associated with the residual fraction, while Pb is dominated by the reducible and residual forms. The mobile fractions of Cu, Pb and Zn in topsoil are Pb (60.1 %) > Cu (20.1 %) ≈ Zn (20.6 %). The PI for Cu, Pb and Zn varies from 1.1 to 1.4, 1.0 to 2.5 and 1.1 to 2.0, with means of 1.2, 1.4 and 1.4, respectively, indicating that Cu, Pb and Zn are all moderately polluted in the topsoil around the lead–zinc smelting plant. IPI values range from 1.1 to 2.0 with an average of 1.3, showing that the topsoil samples are moderately contaminated by Cu, Pb and Zn.

A Study on Distribution and Chemical Speciation of Lead in Corn Seed Germination by Synchrotron Radiation X-ray Fluorescence and Absorption Near Edge Structure Spectrometry

Synchrotron radiation X-ray fluorescence analysis technology (SRXRF) can effectively reduce the detection limit for the determination of heavy metal elements. The technique is especially suitable for in situ nondestructive analysis of biological samples with low contents. By corn seed germination test, and combining with SRXRF technique, the effects of Pb on corn seed germination and Pb micro-distribution in the corn seed were studied. X-ray absorption near edge structure (XANES) technique was also used to analyze the Pb chemical speciation in different parts of corn seed. The above experiments were carried out for understanding the absorption and transformation mechanism of Pb by corn seeds. The results showed that the germination rate, bud length and root length decreased with the increasing contents of Pb. The analysis of variance showed that P-value of the germination rate, bud length and root elongation of corn seeds which were exposed to different concentration of Pb were 2.0 × 10−3, 1.4 × 10−4 and 2.4 × 10−8 respectively, suggesting there were highly significant differences during this three indicators and the content of Pb. In addition, the inhibition effect on root growth was greater. The results of SRXRF analysis showed that Pb was mainly enriched in episperm and embryo, which would inhibit embryonic develop into bud and root. Moreover, the results showed that all samples including root, shoot and the different part of seed had the same Pb-LIII (13035 eV) XANES spectra and Pb speciation. The linear combination fitting results indicated that the lead phosphate chloride and lead stearate accounted for 74.3% and 24.2% respectively, suggesting that the main Pb speciation in corn was lead phosphate chloride which deposited inside of corn, and a few combined with carboxylic to form organic lead.