Reaction of gallium arsenide with concentrated acids: formation of arsine

Crystalline particles of gallium arsenide (GaAs) (approximately 2 microns in diameter) react with concentrated hydrochloric acid (HCl) (11.6 to 9 M) to form highly toxic arsine (AsH3) gas. None of the other strong acids that were investigated reacted with gallium arsenide to form AsH3. A spectrophotometric method, based on the reaction of AsH3 with silver diethyldithiocarbamate in a chloroform solution containing morpholine, was used to detect AsH3 gas dissolved in aqueous solutions and to determine the AsH3 gas that was liberated by the reaction of GaAs with HCl. Active sites on the gallium arsenide surface initiate the reaction that forms AsH3 gas. Absorption of oxygen or ions from solution on these active sites inhibits the formation of AsH3.     

Aluminium phosphate adjuvants prepared by precipitation at constant pH. Part I: composition and structure

Aluminium phosphate adjuvant was precipitated under constant pH conditions in an effort to characterize materials formed at defined precipitation conditions. A reaction vessel was designed to provide a continuous steady-state process. An aqueous solution containing aluminium chloride and sodium dihydrogen phosphate was pumped into the reaction vessel at a constant rate. A second pump infused a sodium hydroxide solution at the rate required to maintain the desired pH. Precipitations were performed between pH 3.0 and 7.5, at intervals of pH 0.5. The adjuvants were characterized using 27Al NMR, FTIR, Raman and X-ray diffraction methods along with elemental analysis. The results of this study indicate that a continuum of amorphous aluminium hydroxyphosphates were formed having properties that changed as a continuous function of the precipitation pH. The phosphate content decreased as the pH of precipitation increased. 27Al NMR spectra revealed that the majority of the aluminium was octahedrally coordinated, with a small percentage of tetrahedrally coordinated aluminium. The density of the adjuvants was directly related to the pH of precipitation. The most prominent feature of the IR and Raman spectra is the P-O stretching vibration of the structural PO(4) groups. The positions of these bands decreased linearly as the precipitation pH increased. The results of selective deuteration FTIR experiments are consistent with high surface area materials as most of the OH groups were exposed near the surface of the adjuvant.     

Detoxification of endotoxin by aluminum hydroxide adjuvant

Langmuir adsorption isotherms of endotoxin and aluminum-containing adjuvants at pH 7.4 and 25 degrees C revealed that aluminum hydroxide adjuvant has a greater adsorption capacity (283 microg/mg Al) and adsorption coefficient (1.3x10(4) ml/miccrog) than aluminum phosphate adjuvant (3.0 microg/mg Al, 0.20 ml/microg). The difference in endotoxin adsorption was related to two adsorption mechanisms: electrostatic attraction and covalent bonding. The isoelectric point (iep) of endotoxin is approximately 2. An electrostatic attractive force will be present with aluminum hydroxide adjuvant (iep=11.4), and an electrostatic repulsive force will operate with aluminum phosphate adjuvant (iep=4.6). Endotoxin contains two phosphate groups in the lipid A portion. Covalent bonding occurs with surface aluminum in aluminum hydroxide adjuvant but is inhibited by surface phosphate in aluminum phosphate adjuvant. In-vitro desorption experiments using components of interstitial fluid showed that endotoxin adsorbed by aluminum hydroxide adjuvant was not desorbed by interstitial anions (5 mM phosphate or 2.7 mM citrate) or interstitial proteins (25 mg albumin/ml). The effect of aluminum-containing adjuvants on the systemic response of Sprague-Dawley rats to a 15 microg/kg subcutaneous dose of endotoxin was determined by measuring the serum concentration of tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). TNF-alpha and IL-6 were observed in the group which received an endotoxin solution or endotoxin and aluminum phosphate adjuvant. No TNF-alpha or IL-6 was detected in the group that received endotoxin and aluminum hydroxide adjuvant. Aluminum hydroxide adjuvant detoxifies endotoxin by adsorbing it in the vaccine and then not releasing it in interstitial fluid upon administration.     

Arsenic accumulation and toxicity in the earthworm Eisenia fetida affected by chloride and phosphate

Chloride and phosphate (PO4) were added to field soils contaminated with arsenic and heavy metals, and Eisenia fetida were inoculated in these treated soils for 70 d. After 28 d, earthworm survival, body weight, and cocoon production were measured. During the exposure period, the accumulation of As and four metals (Cu, Zn, Cd, and Pb) in E. fetida was analyzed. Bulk soils and soil solutions were characterized for the contents of As, metals, organic matter, and major cations and anions; cation exchange capacity; and pH. Although addition of Cl to the soil did not impact As toxicity, it significantly reduced As uptake. The addition of PO4 induced changes in As toxicity and reduced As accumulation even though the As concentration in the soil pore water increased because of the substitution of As by P at soil sorption sites. These results imply that the addition of Cl induced the formation of an As-Cl complex, thereby resulting in decreased As bioavailability; they also imply that monovalent phosphate (H2PO4(-)) competes with As for uptake through transporter-mediated mechanisms in cells.     

Fast and Considerable Adsorption of Methylene Blue Dye onto Graphene Oxide

The quite efficient adsorption of methylene blue dye from an aqueous solution by graphene oxide was studied. The favorable electrostatic attraction is the main interaction between methylene blue and graphene oxide. As graphene oxide has the special nanostructural properties and negatively charged surface, the positively charged methylene blue molecules can be easily adsorbed on it. In the aqueous solution of methylene blue at 293 K, the adsorption data could be fitted by the Langmuir equation with a maximum adsorption amount of 1.939 mg/mg and a Langmuir adsorption equilibrium constant of 18.486 mL/mg. The adsorption amount increased with the increase of the solution pH (3–11), was not affected significantly by KCl under the examined condition and the adsorption process was exothermic in nature. The fast and considerable adsorption of graphene oxide could be regarded as a potential adsorbent for cationic dye removal in wastewater treatment process.     

Biological monitoring of arsenic exposure of gallium arsenide- and inorganic arsenic-exposed workers by determination of inorganic arsenic and its metabolites in urine and hair

In an attempt to establish a method for biological monitoring of inorganic arsenic exposure, the chemical species of arsenic were measured in the urine and hair of gallium arsenide (GaAs) plant and copper smelter workers. Determination of urinary inorganic arsenic concentration proved sensitive enough to monitor the low-level inorganic arsenic exposure of the GaAs plant workers. The urinary inorganic arsenic concentration in the copper smelter workers was far higher than that of a control group and was associated with high urinary concentrations of the inorganic arsenic metabolites, methylarsonic acid (MAA) and dimethylarsinic acid (DMAA). The results established a method for exposure level-dependent biological monitoring of inorganic arsenic exposure. Low-level exposures could be monitored only by determining urinary inorganic arsenic concentration. High-level exposures clearly produced an increased urinary inorganic arsenic concentration, with an increased sum of urinary concentrations of inorganic arsenic and its metabolites (inorganic arsenic + MAA + DMAA). The determination of urinary arsenobetaine proved to determine specifically the seafood-derived arsenic, allowing this arsenic to be distinguished clearly from the arsenic from occupational exposure. Monitoring arsenic exposure by determining the arsenic in the hair appeared to be of value only when used for environmental monitoring of arsenic contamination rather than for biological monitoring.     

Micellar solubilization of fatty acids in aqueous media containing bile salts and phospholipids.

1. The solubility of fatty acids in aqueous media containing bile salts alone and in admixture with either lecithin (phosphatidylcholine) or phosphatidylethanolamine was determined. 2. Over the pH range 2-0-7-4, the order of fatty acid solubility in aqueous solutions containing bile salts was linoleic greater than oleic greater than elaidic greater than palmitic greater than stearic. The solubility of each fatty acid increased as the pH of the miceus solutions of bile salts greatly increased the solubility of palmitic acid and stearic acid. 4. In the presence of bile salts and lecithin, the solubility of oleic acid and elaidic acid decreased with increasing pH of the micellar solution, indicating a competitive effect between the fatty acid anions and lecithin. The solubility of linoleic acid increased linearly with lecithin concentration. 5. Phosphatidylethanolamine as an additive to bile salts increased the solubility of both saturated and unsaturated fatty acids in the pH range 2-3-7-4. The effectiveness of phosphatidylethanolamine as an amphiphile was similar to that of lecithin, although at pH 3.0 fatty acid solubility was greater in the presence of phosphatidylethanolamine. 6. The significance of these findings is discussed in relation to the intestinal absorption of fatty acids in sheep.     

Comparison of Pb(II) Immobilized by Bone Char Meal and Phosphate Rock: Characterization and Kinetic Study

Adsorption isotherms and kinetics of aqueous Pb(II) by bone char meal (BM) and phosphate rock (PR) were investigated using batch experiments. Pb removal was characterized and effects of pH and reaction time on Pb removal efficiency by BM/PR were also investigated. Results indicated that Pb removal efficiency by BM and PR is mainly controlled by dissolution of phosphatic components associated with apatite, followed by subsequent precipitation of geochemically stable pyromorphite [Pb₁₀ (PO₄)₆(OH,Cl)₂]. Sorption kinetics results indicated that Pb sorption onto BM or PR was generally biphasic, with initially fast reactions followed by slow and continuous reactions. Pb removal efficiency by BM and PR increased with increasing pH except at a pH higher than 6.15. Sorption isotherms showed that BM has a much higher Pb removal rate than PR in solution; the greater capability of BM than of PR to remove aqueous Pb indicates its potential as another promising way to remediate Pb-contaminated media.     

Geosorption of As(III) from Aqueous Solution by Red Clays: Kinetic Studies

The geosorption of As(III) on red clays from aqueous solution under different environmental conditions (i.e. initial concentration, pH and temperature) was studied. This process reached its equilibrium quickly (<120 min). A decrease of the percentage of adsorption was caused when the initial concentration was increased (0.1–10 mg As(III) L^?1), in all the experimental pH levels (4–10). The optimal pH value for adsorption on red clays at 0.1 mg As(III) L^?1 was 10, while for 10 mg As(III) L^?1 was 4. There wasn’t a significant effect of temperature on the As(III) adsorption. The kinetic pseudo-second order and the isothermal Langmuir were the models that best described the experimental data, suggesting an adsorption process in multistep. Likewise, there are not interactions between neighbor active sites on the red clay surface.     

Systemic uptake and clearance of chloroform by hairless rats following dermal exposure: II. Absorption of the neat solvent.

Blood concentrations of chloroform were monitored after exposing small areas (approximately 5.5 cm2) of the backs of hairless rats to liberal excesses of the solvent for either 1, 3, or 8 min. The amounts absorbed were quantified by comparing areas-under-the-curves (AUCs) of blood concentration versus time plots to the AUC obtained on infusing an aqueous chloroform solution of known concentration for 30 min (positive control). Chloroform penetrated the dermal barrier rapidly, the skin's horny layer and the deeper skin tissues acting as reservoirs for chloroform only for short durations. Evaporative and physiological clearance from these reservoirs was rapid once the chloroform was removed from the surface. Pressure of the template used to confine the exposure affected uptake. For blood levels, the time to reach the maximum blood concentration increased with increased exposure duration. Amounts absorbed also depended on exposure duration. Blood level profiles indicated systemic uptake of chloroform following a 3-min exposure was about 1.3-fold higher than for a 1-min exposure (not significant), while the 8-min exposure produced an AUC roughly 3.8-fold higher than found at 3 min (p = 0.026). Chloroform is rapidly cleared from rat blood (terminal elimination rate constant = 0.009/min). Calculations indicated that its absorption from these area-limited exposures far exceeds that which would be absorbed had the chloroform been presented to the skin as a saturated aqueous solution.     

Toxicity, biotransformation, and mode of action of arsenic in two freshwater microalgae (Chlorella sp. and Monoraphidium arcuatum)

The toxicity of As(V) and As(III) to two axenic tropical freshwater microalgae, Chlorella sp. and Monoraphidium arcuatum, was determined using 72-h growth rate-inhibition bioassays. Both organisms were tolerant to As(III) (72-h concentration to cause 50% inhibition of growth rate [IC50], of 25 and 15 mg As[III]/L, respectively). Chlorella sp. also was tolerant to As(V) with no effect on growth rate over 72 h at concentrations up to 0.8 mg/L (72-h IC50 of 25 mg As[V]/L). Monoraphidium arcuatum was more sensitive to As(V) (72-h IC50 of 0.25 mg As[V]/L). An increase in phosphate in the growth medium (0.15-1.5 mg PO4(3-)/L) decreased toxicity, i.e., the 72-h IC50 value for M. arcuatum increased from 0.25 mg As(V)/L to 4.5 mg As(V)/L, while extracellular As and intracellular As decreased, indicating competition between arsenate and phosphate for cellular uptake. Both microalgae reduced As(V) to As(III) in the cell, with further biological transformation to methylated species (monomethyl arsonic acid and dimethyl arsinic acid) and phosphate arsenoriboside. Less than 0.01% of added As(V) was incorporated into algal cells, suggesting that bioaccumulation and subsequent methylation was not the primary mode of detoxification. When exposed to As(V), both species reduced As(V) to As(III); however, only M. arcuatum excreted As(III) into solution. Intracellular arsenic reduction may be coupled to thiol oxidation in both species. Arsenic toxicity most likely was due to arsenite accumulation in the cell, when the ability to excrete and/or methylate arsenite was overwhelmed at high arsenic concentrations. Arsenite may bind to intracellular thiols, such as glutathione, potentially disrupting the ratio of reduced to oxidized glutathione and, consequently, inhibiting cell division.     

一种有机镓化合物对大鼠骨镓,钙及磷含量的影响

目的 探讨接触有机镓对动物骨镓、骨钙和骨磷含量的影响。方法 采用亚急性和慢笥动物染毒实验,将不同剂量的有机镓灌胃,分别偿同时间后大鼠的一般状况及及死后股骨中镓、钙、磷的含量及钙／磷比值。结果 亚急性染毒各剂量组动物股骨中镓及磷含量与对照组判别显著（Ｐ〈０．０１）,而骨钙值只有１２ｍｇ／ｋｇ剂量组与对照组有显著差异。慢性染毒各剂量组骨镓、钙、磷均与对照组差别显著（Ｐ〈０．０５）。而实验组与对照组的骨     

Phosphate inhibition of protein-polysilicic acid complex formation in vitro: a factor in preventing silica urolithiasis

Phosphate concentration and pH were studied as factors influencing the formation of insoluble protein-polysilicic acid complexes of bovine serum albumin (BSA) or urinary proteins (nondialyzable urinary solids, NDUS) with silicic acid under conditions of constant ionic strength (IS) equivalent to 0.1724 N. In the pH range 5.5-7.0, the amount of protein-silicic acid complex measured turbidimetrically increased with decreasing pH. Only a trace of precipitate occurred with use of either of the protein sources at pH 7 or with NDUS at pH 6.5. With BSA at pH 6.5, phosphate supplying the total IS of the solution completely prevented precipitation of the complex. The phosphate effect was linear when it supplied 20-50% of the IS. In this range, there was a 12.3% reduction in the amount of precipitate for each 10% of the IS supplied by phosphate. With NDUS at pH 6.0, the phosphate effect was linear over its full range of concentrations. The phosphate effect resulted in an 8.7% reduction in the amount of precipitate for each 10% of the IS supplied by phosphate. On removal of the precipitated protein-silicic acid complex from the silicic acid solution, dissolution was facilitated by increases in phosphate concentration and pH. It is concluded that phosphate inhibition of protein-polysilicic acid complex formation may play a role in the reduction of silica urolithiasis related to increases in dietary phosphate.     

Inhibition of liver, kidney, and erythrocyte delta-aminolevulinic acid dehydratase (porphobilinogen synthase) by gallium in the rat

Selective inhibition of enzymes in the heme biosynthesis pathway with concomitant urinary excretion of heme precursors serve as potentially important biological markers of chemical exposure and cell injury. Intratracheal administration of gallium arsenide particulate suspensions has been shown to result in inhibition of delta-aminolevulinic acid dehydratase (ALAD) in several tissues and increased excretion of the heme precursor aminolevulinic acid (ALA). This study was undertaken to evaluate in vivo the role of gallium alone in ALAD inhibition and increased urinary excretion of ALA. Male CD rats received a single ip injection of Ga2(SO4)3 at doses of 12.5, 25, 50, 100, and 200 mg Ga/kg. A dose-dependent inhibition of ALAD was observed 24 hr later in liver, kidney, and erythrocytes. After injection of 25 mg Ga/kg, maximal inhibition (42 to 49% of control) of ALAD occurred between 6 and 24 hr in liver and kidney with full recovery of activity at 96 hr. In erythrocytes, maximal inhibition (48% of control) occurred between 24 and 48 hr with recovery of activity at 96 hr. Mild to moderate renal proximal tubular necrosis in the pars recta was observed 24 hr after administration of 100 and 200 mg/kg, but no histopathologic changes were evident at lower doses. No consistent changes in urinary excretion of ALA were observed. Lineweaver-Burk analyses of renal and hepatic ALAD activities in the absence and presence of gallium indicated that the inhibition of ALAD by this element is noncompetitive (same Km, decreased Vmax). Gallium was shown to possess an inhibition constant (Ki) of approximately 3 microns for ALAD, similar to the Ki obtained for lead in other studies. Incubation of ALAD in vitro with gallium and lead, an active thiol group inhibitor, resulted in a greater inhibition of the enzyme. Further in vitro studies demonstrated the attenuation of gallium inhibition of hepatic and renal ALAD by zinc, suggesting that the mechanism of gallium action may involve competition for or displacement of zinc from the sulfhydryl group of the enzyme active site. Since ALAD inhibition occurred at doses at which no histopathologic changes were evident, the determination of ALAD activity in various tissues, including blood, may be of potential value as a biomarker of exposure/toxicity to metals such as gallium. The effect of chemical form and route of exposure of gallium and effects of other Group III metals on inhibition of ALAD and excretion of ALA is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)     

辽宁省一般人群血中镓、铟、 铊水平研究

目的调查辽宁省一般人群血中镓、铟、铊水平,分析其人群分布特点。方法将辽宁省划分为东、中、西部地区,采用多阶段分层整群随机抽样的方法,于2009—2010年从辽宁省东、中、西部地区抽取2105名对象进行问卷调查,并采集血液样品。用电感耦合等离子体质谱法对血样进行镓、铟、铊含量的检测,通过统计分析研究一般人群血液中镓、铟、铊的分布水平。结果辽宁省一般人群血中镓、铟、铊几何均数均小于检出限。结论辽宁省一般人群血中镓、铟、铊几何均数均小于检出限,与全国水平一致。     

Effect of microenvironment pH of aluminum hydroxide adjuvant on the chemical stability of adsorbed antigen

The rate of acid-catalyzed hydrolysis of glucose-1-phosphate (G1P) when adsorbed to aluminum hydroxide adjuvant was significantly slower than the rate of hydrolysis of a solution of G1P at the same pH. It was concluded that the positively charged aluminum hydroxide adjuvant (iep 11.4) electrostatically attracted anions including hydroxyls to form a double layer surrounding the adjuvant particles. Thus, the pH of the microenvironment surrounding the aluminum hydroxide adjuvant was higher than the bulk pH. Adsorbed G1P hydrolyzed at a rate associated with the pH of the microenvironment of the surface of the adjuvant rather than with the pH of the bulk solution. Comparison of the rate constant for the hydrolysis of adsorbed G1P to the pH-stability profile of G1P in solution revealed that adsorbed G1P hydrolyzed at a rate associated with a pH that was approximately two pH units higher than the bulk pH. The results suggest that the chemical stability of antigens that degrade by pH-dependent mechanisms can be optimized by modifying the surface charge of the aluminum-containing adjuvant to produce the pH of maximum stability in the microenvironment of the adjuvant.     

Calcium and magnesium enhance arsenate rhizotoxicity and uptake in Triticum aestivum

Cations such as calcium (Ca) and magnesium (Mg) alleviate toxicities of cationic toxicants and increase those of anionic toxicants such as arsenic (As) present as arsenate under aerobic conditions. Increasing evidence exists that these phenomena are related to the outer surface electrical potential (ψ?0°) of the root cell plasma membrane (PM). Short-term (48-h) nutrient culture experiments with wheat (Triticum aestivum L.) seedlings investigated Ca and Mg effects on arsenate rhizotoxicity and uptake. Increased Ca and Mg in solution from 0.2 to 3.5 mM equally reduced the negativity of ψ?0° from -45 to -15 mV. This increased arsenate activity at the PM surface from 0.3 to 0.9 μM at the same bulk concentration of 2.0 μM NaH(2) AsO(4) consequently increased arsenate uptake and rhizotoxicity. However, increased Mg was more effective than Ca in enhancing As uptake by roots, especially with the activity of As in the range of 0.5 to 1.5 μM in the bulk medium. This was explained by a modified electrostatic uptake model which indicated a mechanism other than through an effect on ψ?0°. Subcellular fractionation of roots indicated that > 95% of As was associated with cellular debris and heat-stable protein (HSP). The results of the present study show that Ca and Mg reduce the negativity of ψ?0°, increasing arsenate uptake and rhizotoxicity, and suggest that Mg is more efficient than Ca in enhancing the uptake of As due, in large part, to inducing greater As binding by peptides in the HSP fraction.     

The comparison of aluminium effects and its uptake by Escherichia coli in different media

The investigation of the toxic effects and the uptake of aluminium by Escherichia coli in growth medium (GM) and in physiological solution (PS) have been studied. The toxicity was quantitatively determined according to the decrease of the colony forming units (CFU) in the physiological solution, that is its growth inhibition in the growth medium, vs. the aluminium concentration and incubation time, at pH 5.2, 6.2 and 7.2. The uptake of aluminium was investigated by determining the intracellular aluminium in dry weights (DW), by graphite fumace atomic absorption spectrophotometry, considering that aluminium adsorbed to the cell surface was removed by washing with EDTA solution. The results show that toxicity and accumulation increase with the increase of the aluminium concentration and incubation time. However, the linearity of these functions was lost at higher values, which indicate dependence on time and concentration saturation. The effect of pH was specific, and correlated with the form of aluminium in solution. The increase in toxicity as the pH decreases, suggests that the Al(H2O)6(3+) ion is the major toxic form, among the remaining present ones aluminium in aqueous media. The results also show that the aluminium in a concentration range from 0.10 to 10.0 mg/l toxic to E. coli in PS, was significantly less toxic for bacteria in the GM, mainly because of living conditions and the accessibility of free Al.     

Bio-Separation of Toxic Arsenate Ions from Dilute Solutions by Native and Pretreated Biomass of <Emphasis Type="Italic">Aspergillus fumigatus</Emphasis> in Batch and Column Mode: Effect of Biomass Pretreatment

The sorption of As(V) from aqueous solution onto live and pretreated biomass of Aspergillus fumigatus was studied. The studies on optimization of contact time, adsorbent dosage and pH showed that the FeCl(3) treated and FeSO(4) treated biomass had the maximum capacity to adsorb As(V) while acid treated biomass was found to be minimum. Adsorption parameters were determined using both Langmuir and Freundlich isotherm models. The maximum adsorption capacity of 0.054 mg/g was observed in FeCl(3) treated and FeSO(4) treated biomasses. Column mode studies were conducted using FeSO(4) treated biomass to compare its efficacy with batch mode to adsorb As(V). Batch mode experiments proved to be efficient. Desorption studies were also carried out with dilute sodium hydroxide to recover both the adsorbent and adsorbate.     

Quantitative Study of As (V) and As (III) Interaction with Mangrove DNA by Molecular Fluorescence Spectroscopy

This study describes the in vitro study of (1:1) one step nucleophilic displacement ( \({\text{S}}_{\text{N}}^{1}\) ) of phosphate by heavier anion arsenate and arsenite in the DNA of arsenic ridden Sundarban mangroves. Mangrove DNA was found to give rise to a broad fluorescence and its integrated fluorescence intensity was enhanced on addition of As (V) and As (III), respectively. Analyses of the fluorescence parameter showed adequacy of 1:1 model to describe substitution of phosphate of mangrove DNA chain exiplex by arsenate and arsenite with equilibrium constant (log K_c) ranging between 4.19 and 4.32 for As (V), and between 3.77 and 3.89 for As (III) at pH 7 and 25°C. In the cases, the melting temperature (T_m) and reassociation rate constant of mangrove DNA was increased on treatment with As (V) and As (III). It is suggested that heavier ion arsenate and arsenite may substitute phosphate in natural DNA.