Synthesis and Characterization of Vanadium Nitride/Carbon Nanocomposites.

The present work focuses on the synthesis of a vanadium nitride (VN)/carbon nanocomposite material via the thermal decomposition of vanadyl phthalocyanine (VOPC). The morphology and chemical structure of the synthesized compounds were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS). The successful syntheses of the VOPC and non-metalated phthalocyanine (H2PC) precursors were confirmed using FTIR and XRD. The VN particles present a needle-like morphology in the VN synthesized by the sol-gel method. The morphology of the VN/C composite material exhibited small clusters of VN particles. The XRD analysis of the thermally decomposed VOPC indicated a mixture of amorphous carbon and VN nanoparticles (VN(TD)) with a cubic structure in the space group FM-3M consistent with that of VN. The XPS results confirmed the presence of V(III)-N bonds in the resultant material, indicating the formation of a VN/C nanocomposite. The VN/C nanocomposite synthesized through thermal decomposition exhibited a high carbon content and a cluster-like distribution of VN particles. The VN/C nanocomposite was used as an anode material in LIBs, which delivered a specific capacity of 307 mAh g-1 after 100 cycles and an excellent Coulombic efficiency of 99.8 at the 100th cycle.

Synthesis and Characterization of Titanium Nitride-Carbon Composites and Their Use in Lithium-Ion Batteries.

This work focuses on the synthesis of titanium nitride-carbon (TiN-carbon) composites by the thermal decomposition of a titanyl phthalocyanine (TiN(TD)) precursor into TiN. The synthesis of TiN was also performed using the sol-gel method (TiN(SG)) of an alkoxide/urea. The structure and morphology of the TiN-carbon and its precursors were characterized by XRD, FTIR, SEM, TEM, EDS, and XPS. The FTIR results confirmed the presence of the titanium phthalocyanine (TiOPC) complex, while the XRD data corroborated the decomposition of TiOPC into TiN. The resultant TiN exhibited a cubic structure with the FM3-M lattice, aligning with the crystal system of the synthesized TiN via the alkoxide route. The XPS results indicated that the particles synthesized from the thermal decomposition of TiOPC resulted in the formation of TiN-carbon composites. The TiN particles were present as clusters of small spherical particles within the carbon matrix, displaying a porous sponge-like morphology. The proposed thermal decomposition method resulted in the formation of metal nitride composites with high carbon content, which were used as anodes for Li-ion half cells. The TiN-carbon composite anode showed a good specific capacity after 100 cycles at a current density of 100 mAg-1.

Targeting Metal Impurities for the Detection and Quantification of Carbon Black Particles in Water via spICP-MS.

Carbon black (CB) is a nanomaterial with numerous industrial applications and high potential for integration into nano-enabled water treatment devices. However, few analytical techniques are capable of measuring CB in water at environmentally relevant concentrations. Therefore, we intended to establish a quantification method for CB with lower detection limits through utilization of trace metal impurities as analytical tracers. Various metal impurities were investigated in six commercial CB materials, and the Monarch 1000 CB was chosen as a model for further testing. The La impurity was chosen as a tracer for spICP-MS analysis based on measured concentration, low detection limits, and lack of polyatomic interferences. CB stability in water and adhesion to the spICP-MS introduction system presented a challenge that was mitigated by the addition of a nonionic surfactant to the matrix. Following optimization, the limit of detection (64 µg/L) and quantification (122 µg/L) for Monarch 1000 CB demonstrated the applicability of this approach to samples expected to contain trace amounts of CB. When compared against gravimetric analysis and UV-visible absorption spectroscopy, spICP-MS quantification exhibited similar sensitivity but with the ability to detect concentrations an order of magnitude lower. Method detection and sensitivity was unaffected when dissolved La was spiked into CB samples at environmentally relevant concentrations. Additionally, a more complex synthetic matrix representative of drinking water caused no appreciable impact to CB quantification. In comparison to existing quantification techniques, this method has achieved competitive sensitivity, a wide working range for quantification, and high selectivity for tracing possible release of CB materials with known metal contents.

Interactions between silver nanoparticles and other metal nanoparticles under environmentally relevant conditions: A review.

Global production of engineered nanoparticles (ENPs) continues to increase due to the demand of enabling properties in consumer products and industrial applications. Release of individual or aggregates of ENPs have been shown to interact with one another subsequently resulting in adverse biological effects. This review focuses on silver nanoparticles (AgNPs), which are currently used in numerous applications, including but not limited to antibacterial action. Consequently, the release of AgNPs into the aquatic environment, the dissociation into ions, the binding to organic matter, reactions with other metal-based materials, and disruption of normal biological and ecological processes at the cellular level are all potential negative effects of AgNPs usage. The potential sources of AgNPs includes leaching of intact particles from consumer products, disposal of waste from industrial processes, intentional release into contaminated waters, and the natural formation of AgNPs in surface and ground water. Formation of natural AgNPs is greatly influenced by different chemical parameters including: pH, oxygen levels, and the presence of organic matter, which results in AgNPs that are stable for several months. Both engineered and natural AgNPs can interact with metal and metal oxide particles/nanoparticles. However, information on the chemical and toxicological interactions between AgNPs and other nanoparticles is limited. We have presented current knowledge on the interactions of AgNPs with gold nanoparticles (AuNPs) and titanium dioxide nanoparticles (TiO2 NPs). The interaction between AgNPs and AuNPs result in stable bimetallic Ag-Au alloy NPs. Whereas the interaction of AgNPs with TiO2 NPs under dark and light conditions results in the release of Ag+ ions, which may be subsequently converted back into AgNPs and adsorb on TiO2 NPs. The potential chemical mechanisms and toxic effects of AgNPs with AuNPs and TiO2 NPs are discussed within this review and show that further investigation is warranted.

Use of the sea hare (Aplysia fasciata) in marine pollution biomonitoring of harbors and bays.

Our study evaluated heavy metal concentrations in soft tissues of sea hare, Aplysia fasciata, from the Lower Laguna Madre, Texas. Heavy metals in tissues followed Se>As>Pb>Cd. Concentrations ranged As (BDL-28.08), Cd (BDL-5.50), Pb (BDL-12.85) and Se (4.25-93.43ppm). Median As, Cd, Pb, and Se tissue levels exceeded exposure levels. Significant relationships occurred in metal-metal (AsCd, AsPb, CdPb, CdSe, and PbSe), metal-tissue (significant Se uptake by inhalant and exhalant siphons and As in the hepatopancreas), and metal-metal within tissue (AsPb in the hepatopancreas and CdPb in the digestive cecum) analyses (p<0.05). Bioaccumulation factors (BAF) suggested the inhalant siphon, hepatopancreas, and digestive cecum function as macroconcentrators of Cd, hepatopancreas and digestive cecum as macroconcentrators of Pb, and all tissues were deconcentrators for As and Se. As a bioaccumulator of heavy metals, Aplysia was evaluated as a bioindicator of marine pollution in harbors and bays.

Sorption of Cr(III) and Cr(VI) to High and Low Pressure Synthetic Nano-Magnetite (Fe3O4)Particles.

The binding of Cr(III) and Cr(VI) to synthetic nano-magnetie particles synthesized under open vessel conditions and a microwave assisted hydrothermal synthesis techniques was investigated. Batch studies showed that the binding of both the Cr(III) and Cr(VI) bound to the nano-materials in a pH dependent manner. The Cr(III) maximized at binding at pH 4 and 100% binding. Similarly, the Cr(VI) ions showed a maximum binding of 100% at pH 4. The data from the time dependency studies showed for the most part the majority of the binding occurred within the first 5 minutes of contact with the nanomaterial and remained constant thereafter. In addition, the effects of the possible interferences were investigated which showed some effects on the binding of both Cr(III) and Cr(VI). However, the interferences never completely eliminated the chromium binding. Isotherm studies conducted at room temperature showed the microwave synthesized nanomaterials had a binding capacity of 1208 ± 43.9 mg/g and 555 ± 10.5 mg/g for Cr(VI) and Cr(III), respectively. However, the microwave assisted synthesized nanomaterials had capacities of 1705 ± 14.5 and 555± 10.5 mg/g for Cr(VI) and Cr(III), respectively. XANES studies showed the Cr(VI) was reduced to Cr(III), and the Cr(III) remained as Cr(III). In addition, the XANES studies indicated that the chromium remained coordinated in an octahedral arrangement of oxygen atoms.

Prepubertal exposure to arsenic(III) suppresses circulating insulin-like growth factor-1 (IGF-1) delaying sexual maturation in female rats.

Arsenic (As) is a prevalent environmental toxin readily accessible for human consumption and has been identified as an endocrine disruptor. However, it is not known what impact As has on female sexual maturation. Therefore, in the present study, we investigated the effects of prepubertal exposure on mammary gland development and pubertal onset in female rats. Results showed that prepubertal exposure to 10 mg/kg of arsenite (As(III)) delayed vaginal opening (VO) and prepubertal mammary gland maturation. We determined that As accumulates in the liver, disrupts hepatocyte function and suppresses serum levels of the puberty related hormone insulin-like growth factor 1 (IGF-1) in prepubertal animals. Overall, this is the first study to show that prepubertal exposure to As(III) acts peripherally to suppress circulating levels of IGF-1 resulting in delayed sexual maturation. Furthermore, this study identifies a critical window of increased susceptibility to As(III) that may have a lasting impact on female reproductive function.

Spectroscopic determination of the toxicity, absorption, reduction, and translocation of Cr(VI) in two Magnoliopsida species.

Hexavalent chromium is a contaminant highly mobile in the environment that is toxic for plants at low concentrations. In this work, the physiological response of Convolvulus arvensis and Medicago truncatula plants to Cr(VI) treatments was compared. C. arvensis is a potential Cr hyperaccumulator well adapted to semiarid conditions that biotransform Cr(VI) to the less toxic Cr(III). M. truncatula is a model plant well adapted to semiarid conditions with a well studied genetic response to heavy metal stress. The results demonstrated that C. arvensis is more tolerant to Cr toxicity and has a higher Cr translocation to the leaves. The inductively coupled plasma optical emission spectroscopy results showed that C. arvensis plants treated with 10 mg Cr(VI) L(-1) accumulated 1512, 210, and 131 mg Cr kg(-1) in roots, stems, and leaves, respectively. While M. truncatula plants treated with the same Cr(VI) concentration accumulated 1081, 331, and 44 (mg Cr kg(-1)) in roots, stems, and leaves, respectively. Enzymatic assays demonstrated that Cr(VI) decreased ascorbate peroxidase activity and increased catalase activity in M. truncatula, while an opposite response was found in C. arvensis. The x-ray absorption spectroscopy studies showed that both plant species reduced Cr(VI) to the less toxic Cr(III).

Sorption kinetic study of selenite and selenate onto a high and low pressure aged iron oxide nanomaterial.

The sorption of selenite (SeO(3)(2-)) and selenate (SeO(4)(2-)) onto Fe(3)O(4) nanomaterials produced by non microwave-assisted or microwave-assisted synthetic techniques was investigated through use of the batch technique. The phase of both synthetic nanomaterials was determined to be magnetite by X-ray diffraction. The average grain sizes of non microwave-assisted and microwave-assisted synthetic Fe(3)O(4) were determined to be 27 and 25 nm, respectively through use of the Scherrer's equation. Sorption of selenite was pH independent in the pH range of 2-6, while sorption of selenate decreased at pH 5 and 6. The addition of Cl(-) had no significant effect on selenite or selenate binding, while the addition of NO(3)(-) only affected selenate binding to the microwave assisted Fe(3)O(4). A decrease of selenate binding to both synthetic particles was observed after the addition of SO(4)(2-) while selenite binding was not affected. The addition of PO(4)(3-) beginning at concentrations of 0.1 ppm had the most prominent effect on the binding of both selenite and selenate. The capacities of binding, determined through the use of Langmuir isotherm, were found to be 1923 and 1428 mg Se/kg of non microwave-assisted Fe(3)O(4) and 2380 and 2369 mg Se/kg of microwave-assisted Fe(3)O(4) for selenite and selenate, respectively.

Toxicity and biotransformation of uncoated and coated nickel hydroxide nanoparticles on mesquite plants.

Nanomaterials are of particular interest in environmental chemistry due to their unknown toxicity to living organisms. Reports indicate that nanoparticles (NPs) affect seed germination, but the uptake and biotransformation of metal nanoparticles is not well understood. The present study investigated the toxicity and biotransformation of Ni(OH)2 NPs by mesquite plants (Prosopis sp.). Three sets of plants were treated for four weeks with 0.01, 0.05, or 0.10 g of either uncoated or sodium citrate coated NPs before and after synthesis. Nickel concentrations in plants were determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and the form and oxidation state of Ni was determined using X-ray absorption spectroscopy (XAS). Results showed that uncoated NPs had an average size of 8.7 nm, whereas coated NPs before and after synthesis had an average of 2.5 and 0.9 nm, respectively. The ICP-OES results showed that plants treated with 0.10 g of uncoated and coated NPs before and after synthesis had 803, 764, and 400 mg Ni kg dry weight, in the leaves, respectively. The XAS analyses showed Ni NPs in roots and shoots of plants treated with uncoated NPs, whereas leaves showed a Ni(II)-organic acid type complex. However, plants treated with coated NPs before or after synthesis showed Ni NPs only in roots and a Ni(II)-organic acid complex in shoots and leaves. Results also showed that none of the treatments reduced plant size or chlorophyll production. To the authors' knowledge, this is the first time that the biotransformation of nanoparticles by a plant system is reported.

X-ray absorption spectroscopy as a tool investigating arsenic(III) and arsenic(V) sorption by an aluminum-based drinking-water treatment residual.

Historic applications of arsenical pesticides to agricultural land have resulted in accumulation of residual arsenic (As) in such soils. In situ immobilization represents a cost-effective and least ecological disrupting treatment technology for soil As. Earlier work in our laboratory showed that drinking-water treatment residuals (WTRs), a low-cost, waste by-product of the drinking-water treatment process exhibit a high affinity for As. Wet chemical experiments (sorption kinetics and desorption) were coupled with X-ray absorption spectroscopy measurements to elucidate the bonding strength and type of As(V) and As(III) sorption by an aluminum-based WTR. A fast (1h), followed by a slower sorption stage resulted in As(V) and As(III) sorption capacities of 96% and 77%, respectively. Arsenic desorption with a 5mM oxalate from the WTR was minimal, being always <4%. X-ray absorption spectroscopy data showed inner-sphere complexation between As and surface hydroxyls. Reaction time (up to 48h) had no effect on the initial As oxidation state for sorbed As(V) and As(III). A combination of inner-sphere bonding types occurred between As and Al on the WTR surface because mixed surface geometries and interatomic distances were observed.

The extraction of gold nanoparticles from oat and wheat biomasses using sodium citrate and cetyltrimethylammonium bromide, studied by x-ray absorption spectroscopy, high-resolution transmission electron microscopy, and UV-visible spectroscopy.

Gold (Au) nanoparticles can be produced through the interaction of Au(III) ions with oat and wheat biomasses. This paper describes a procedure to recover gold nanoparticles from oat and wheat biomasses using cetyltrimethylammonium bromide or sodium citrate. Extracts were analyzed using UV-visible spectroscopy, high-resolution transmission electron microscopy (HRTEM), and x-ray absorption spectroscopy. The HRTEM data demonstrated that smaller nanoparticles are extracted first, followed by larger nanoparticles. In the fourth extraction, coating of chelating agents is visible on the extracted nanoparticles.

Accumulation, speciation, and coordination of arsenic in an inbred line and a wild type cultivar of the desert plant species Chilopsis linearis (Desert willow).

This study investigated the absorption of arsenic (As), sulfur (S), and phosphorus (P) in the desert plant Chilopsis linearis (Desert willow). A comparison between an inbred line (red flowered) and wild type (white flowered) plants was performed to look for differential responses to As treatment. One month old seedlings were treated for 7 days with arsenate (As(2)O(5), As(V)) at 0, 20, and 40 mg As(V)L(-1). Results from the ICP-OES analysis showed that at 20mg As(V)L(-1), red flowered plants had 280+/-11 and 98+/-7 mg As kg(-1) dry wt in roots and stems, respectively, while white flowered plants had 196+/-30 and 103+/-13 mg As kg(-1) dry wt for roots and stems. At this treatment level, the concentration of As in leaves was below detection limits for both plants. In red flowered plants treated with 40 mg As(V)L(-1), As was at 290+/-77 and 151+/-60 mg As kg(-1) in roots and stems, respectively, and not detected in leaves, whereas white flowered plants had 406+/-36, 213+/-12, and 177+/-40 mg As kg(-1) in roots, stems, and leaves. The concentration of S increased in all As treated plants, while the concentration of P decreased in roots and stems of both types of plants and in leaves of red flowered plants. X-ray absorption spectroscopy analyses demonstrated partial reduction of arsenate to arsenite in the form of As-(SX)(3) species in both types of plants.

Coordination and speciation of cadmium in corn seedlings and its effects on macro- and micronutrients uptake.

The effect of cadmium (Cd) on both the absorption of important nutrients and the synthesis of low molecular weight thiols (LMWTs) was investigated in corn plants. The inductively coupled plasma-optical emission spectroscopy results demonstrated that the concentration of Cd in tissues (mainly in roots) increased as the concentration in the medium increased. In addition, the concentration of phosphorus increased in roots of Cd treated plants but remained at normal concentration in shoots. On the other hand, the uptake of sulfur (S) followed a similar trend as the Cd uptake. The concentration of S and the production of LMWT were found to increase significantly upon exposure to Cd. The results of the X-ray absorption spectroscopy analyses indicated that Cd within tissues was bound to S ligands with interatomic distances of 2.51-2.52 A. These results confirm a strong linkage between S uptake and the production of LMWT upon exposure to Cd.

EFFECT OF INDOLE-3-ACETIC ACID, KINETIN, AND ETHYLENEDIAMINETETRAACETIC ACID ON PLANT GROWTH AND UPTAKE AND TRANSLOCATION OF LEAD, MICRONUTRIENTS, AND MACRONUTRIENTS IN ALFALFA PLANTS.

Alfalfa plants germinated and grown for 15 d in soil containing 80 mg Pb kg-1 were treated with ethylenediaminetetraacetic acid (EDTA) at 0.8 mM and indole-3-acetic acid-kinetin (IAA-KN) at 100 µM. Fifteen days after the treatment application, the concentration of lead (Pb), macronutrients, and micronutrients was determined using inductively coupled plasma/optical emission spectroscopy. The chlorophyll content and plant growth were also measured. Roots of plants exposed to Pb alone, Pb-EDTA, and Pb-EDTA-IAA-KN had 160, 140, and 150 mg Pb kg-1 DW, respectively. Pb was not detected in the stems of plants exposed to Pb alone; however, stems of plants treated with EDTA and EDTA-IAA-KN had 78 and 142 mg Pb kg-1 DW, respectively. While the Pb concentration in leaves of plants treated with EDTA and EDTA-IAA-KN was 92 and 127 mg kg-1 DW, respectively. In addition, EDTA and EDTA-IAA-KN significantly increased the translocation of zinc and manganese to leaves. The x-ray absorption spectroscopic studies demonstrated that Pb(II) was transported from roots to leaves without a change in the oxidation state.

Use of synchrotron- and plasma-based spectroscopic techniques to determine the uptake and biotransformation of chromium(III) and chromium(VI) by Parkinsonia aculeata.

In this study, a combination of inductively coupled plasma optical emission spectroscopy and X-ray absorption spectroscopy (XAS) was used to study the uptake and speciation of chromium in Parkinsonia aculeata, commonly known as Mexican Palo Verde. Plants were treated for 14 days in a modified Hoagland solution containing chromium(III) or chromium(VI) at several concentrations. The results showed that plants treated with 70 mg Cr(III) L(-1) and 30 mg Cr(VI) L(-1) had similar Cr concentrations in leaves (∼200 mg kg(-1) dry weight, DW). The results also showed that neither Cr(III) nor Cr(VI) affected the uptake of phosphorus and sulfur. However, the concentration of calcium in the stems of plants treated with Cr(VI) at 40 mg L(-1) (about 6000 mg Ca kg(-1) DW) was significantly higher compared to the Ca concentration (about 3000 mg kg(-1) DW) found in the stems of plants treated with 150 mg Cr(III) L(-1). However, no differences were observed in potassium and magnesium concentrations. The iron concentration (about 1000 mg kg(-1) DW) in roots treated with 40 mg Cr(VI) L(-1) was similar to the iron concentration found in the roots of plants treated with 110 mg Cr(III) L(-1). The XAS data showed that Cr(VI) was reduced to Cr(III) in/on the plant roots and transported as Cr(III) to the stems and leaves. The XAS studies also showed that Cr(III) within plants was present as an octahedral complex.

Synthesis of plant-mediated gold nanoparticles and catalytic role of biomatrix-embedded nanomaterials.

Growth of Sesbania seedlings in chloroaurate solution resulted in the accumulation of gold with the formation of stable gold nanoparticles in plant tissues. Transmission electron microscopy revealed the intracellular distribution of monodisperse nanospheres, possibly due to reduction of the metal ions by secondary metabolites present in cells. X-ray absorption near-edge structure and extended X-ray absorption fine structure demonstrated a high degree of efficiency for the biotransformation of Au(III) into Au(0) by planttissues. The catalytic function of the nanoparticle-rich biomass was substantiated by the reduction of aqueous 4-nitrophenol (4-NP). This is the first report of gold nanoparticle-bearing biomatrix directly reducing a toxic pollutant, 4-NP.

A novel class of metal-directed supramolecular DNA-delivery systems.

The bis-complexes [Cu(L(dt))(2)](OTf)(2) (1) and [Cu(L(ot))(2)](OTf)(2) (2), where L(dt) = 1-dodecyl-1,4,7-triazacyclononane, L(ot) = 1-octadecyl-1,4,7-triazacyclononane and OTf = trifluoromethanesulfonate, formed a novel class of metallo-liposomes in water that transfect pEGFP-N1 plasmids into HEK 293-T cells at 38% and 4% efficiency, respectively.

Surface arsenic speciation of a drinking-water treatment residual using X-ray absorption spectroscopy.

Drinking-water treatment residuals (WTRs) present a low-cost geosorbent for As-contaminated waters and soils. Previous work has demonstrated the high affinity of WTRs for As, but data pertaining to the stability of sorbed As is missing. Sorption/desorption and X-ray absorption spectroscopy (XAS), both XANES (X-ray absorption near edge structure) and EXAFS (extended X-ray absorption fine structure) studies, were combined to determine the stability of As sorbed by an Fe-based WTR. Arsenic(V) and As(III) sorption kinetics were biphasic in nature, sorbing >90% of the initial added As (15,000 mg kg(-1)) after 48 h of reaction. Subsequent desorption experiments with a high P load (7500 mg kg(-1)) showed negligible As desorption for both As species, approximately <3.5% of sorbed As; the small amount of desorbed As was attributed to the abundance of sorption sites. XANES data showed that sorption kinetics for either As(III) or As(V) initially added to solution had no effect on the sorbed As oxidation state. EXAFS spectroscopy suggested that As added either as As(III) or as As(V) formed inner-sphere mononuclear, bidentate complexes, suggesting the stability of the sorbed As, which was further corroborated by the minimum As desorption from the Fe-WTR.

Gibberellic acid, kinetin, and the mixture indole-3-acetic acid-kinetin assisted with EDTA-induced lead hyperaccumnulation in alfalfa plants.

There are a few plant species considered potential hyperaccumulators for heavy metals, particularly lead (Pb). In this study, alfalfa plants grown in hydroponics were exposed to Pb at 40 mg/L, ethylenediaminetetraacetic acid (EDTA) equimolar to Pb, and 1, 10, and 100 microM concentrations of the phytohormones indole-3-acetic acid (IAA), gibberellic acid (GA), and kinetin (KN) and a mixture of IAA and KN at 100 microM each. Metal quantification by inductively coupled plasma/optical emission spectroscopy demonstrated that plants treated with Pb/EDTA plus KN at 1, 10, and 100 microM increased the Pb concentration in alfalfa leaves (compared to Pb alone) by factors of 17, 43, and 67, respectively, and by factors of 2, 5, and 8, respectively, compared to the Pb/EDTA treatment. The correlation coefficient between the Pb concentration in leaves and the concentrations of KN in the medium was 0.9993. In addition, the leaves of plants exposed to a Pb/EDTA/100 microM IAA-KN mixture had approximately 9500 mg of Pb/kg of dry weight, demonstrating that non-Pb hyperaccumulating plants could hyperaccumulate Pb when treated with EDTA and a mixture of IAA-KN. The X-ray absorption spectroscopic studies demonstrated that the absorption and translocation of Pb was in the same oxidation state as the supplied Pb(II).