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New oligomers or polymers are prepared by polymerization of arsonium ylides in the presence of boron compounds.
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The case of methylmercury pollution has demonstrated the profound importance of understanding biologically mediated transformation reactions that yield organometallic compounds with a high potential for bioaccumulation and toxicity. Toxic elements that form organometallic compounds, especially the metal-alkyls (e.g., methylmercury), deserve special concern. Most metal-alkyls are poisonous to the central nervous systems of higher organisms, and these compounds do accumulate in cells. Metal-alkyls that are stable in water, and that have been reported to be synthesized biologically, can be formed from the following toxic elements: Hg, Sn, As, Se, Te, Pd, Au, Tl and Pb. In this report we present details of the mechanisms for biological methylation of certain metals and metalloids with special emphasis on those elements that are widely dispersed in the biosphere. In addition we present preliminary results on the use of flourescence quenching techniques to determine cellular diffusion rates and partition coefficients for methylmercuric chloride.
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Arsenic removal from household drinking water has been receiving considerable attention in the field of water supply engineering. To develop the optimal coagulation protocol, the effectiveness of several operation options such as coagulants, coagulant aids and additives, as well as flocs separation systems were investigated in this study through the use of orthogonal array experiment based on Taguchi method. Arsenic removal mechanism during household coagulation (via manual mixing) was also discussed. The results showed that the addition of kaoline and powder activated carbon (PAC) did not enhance arsenic removal efficiency of ferric sulfate or aluminum sulfate. Similarly, mixture of ferric sulfate and aluminum sulfate (MFA) as well as polymeric ferric silicate sulfate (PFSiS) was also unable to improve the overall arsenic removal efficiency. The mechanism of arsenic removal during coagulation was somewhat different from those experienced in conventional processes. Coprecipitation appeared to be the crucial mechanism for arsenic removal. It is noted from this study that arsenic adsorption isotherm under household operation condition could be described by Langmuir equation. An efficient flocs separation system subsequent to coagulation was essential to achieve the effectiveness of overall arsenic removal. The results obtained from field experiment demonstrated that the method of ferric sulfate coagulation/sand filtration for arsenic removal from household drinking water was acceptable and affordable.
Metallothionein (MT) is a sulfhydryl-rich, metal-binding protein that provides protection against metal toxicity. MT is induced by acute stress, hormones, metals, and various organic compounds. Recently, arsenicals have also been shown to induce MT. However, the mechanism and character of MT induction by arsenicals is unknown. Therefore, the effect of various arsenic forms on the tissue concentration of MT was determined. Mice were injected sc with various doses of arsenite [As(III)], arsenate [As(V)], monomethylarsenate (MMAA), and dimethylarsenate (DMAA), and MT content in the liver was measured 24 hr later by the Cd-hemoglobin radioassay. As(III) is a potent hepatic MT inducer in that a 30-fold increase in MT was observed at the dose of 85 mumol/kg. In comparison, it took 3-, 50-, and 120-fold higher molar amounts of As(V), MMAA, and DMAA, respectively to produce a similar effect. MMAA produces the largest increase in hepatic MT (80-fold), followed by As(III) (30-fold), As(V) (25-fold), and DMAA (10-fold). However, none of the arsenicals induced MT in mouse primary hepatocyte cultures. Both MT-I and MT-II were coordinately induced by As(III), As(V), and MMAA. MT induction by As(III) was further characterized following sc administration of arsenite (85 mumol/kg). Hepatic MT induction peaked at 24 hr, and in addition to the liver, As(III) also increased MT in kidney, spleen, stomach, intestine, heart, and lung. MT-I mRNA increased 24-, 52-, and 11-fold at 3, 6, and 15 hr after As(III) administration. This induction profile is similar to that observed after Zn or Cd exposure.(ABSTRACT TRUNCATED AT 250 WORDS)
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Combination of electrodes, such as aluminum and iron in a single electrochemical cell provide an alternative method for removal of arsenic from water by electrocoagulation. The removal process has been studied with a wide range of arsenic concentration (1-1000 ppm) at different pH (4-10). Analysis of the electrochemically generated by-products by XRD, XPS, SEM/EDAX, FT-IR, and Mössbauer Spectroscopy revealed the expected crystalline iron oxides (magnetite (Fe3O4), lepidocrocite (FeO(OH)), iron oxide (FeO)) and aluminum oxides (bayerite (Al(OH)3), diaspore (AlO(OH)), mansfieldite (AlAsO(4).2(H2O)), as well as some interaction between the two phases. The amorphous or very fine particular phase was also found in the floc. The substitution of Fe3+ ions by Al3+ ions in the solid surface has been observed, indicating an alternative removal mechanism of arsenic in these metal hydroxides and oxyhydroxides by providing larger surface area for arsenic adsorption via retarding the crystalline formation of iron oxides.
Organometal compounds of arsenic, antimony, and mercury are speciated using supercritical fluid chromatography with inductively coupled plasma mass spectrometric (ICP-MS) detection. The multi-element capability of ICP-MS for transient signals is examined by detecting five compounds containing all three elements in a single chromatographic injection. The results obtained are compared with those obtained from flame-ionization detection (FID). Trimethyl arsine is not distinguished from the solvent peak when FID is used because it coelutes with the solvent, whereas trimethyl arsine is detected when ICP-MS is used because of its element-selective nature. The detection limits obtained by ICP-MS are 2-3 orders of magnitude lower than those obtained by FID. Determination of isotope abundance is also demonstrated for triphenyl antimony and diphenyl mercury compounds.
Pentavalent and trivalent organoarsenic compounds belong to the major metabolites of inorganic arsenicals detected in humans. Recently, the question was raised whether the organic arsenicals represent metabolites of a detoxification process or methylated species with deleterious biological effects. In this study, the effects of trivalent arsenite (AsO(3) (3-); iA(III)), the pentavalent organoarsenic compounds monomethylarsonic acid (CH(3)AsO(OH)(2); MMA(V)) and dimethylarsinic acid ((CH(3))(2)AsO(OH); DMA(V)) and the trivalent compounds monomethylarsonous acid (CH(3)As(OH)(2), MMA(III)) and dimethylarsinous acid ((CH(3))(2)As(OH); DMA(III)) were tested on glutamate receptors and on voltage-operated potassium and sodium channels heterologously expressed in Xenopus oocytes. Membrane currents of ion channels were measured by conventional two-electrode voltage-clamp techniques. The effects of arsenite were tested in concentrations of 1-1,000 micromol/l and the organic arsenical compounds were tested in concentrations of 0.1-100 micromol/l. We found no significant effects on voltage-operated ion channels; however, the arsenicals exert different effects on glutamate receptors. While MMA(V) and MMA(III) significantly enhanced ion currents through N-methyl-D: -aspartate (NMDA) receptor ion channels with threshold concentrations <10 micromol/l, DMA(V) and DMA(III) significantly reduced NMDA-receptor mediated responses with threshold concentrations <0.1 micromol/l; iA(III) had no effects on glutamate receptors of the NMDA type. MMA(III) and DMA(V) significantly reduced ion currents through alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-receptor ion channels with threshold concentrations <10 micromol/l (MMA(III)) and <1 micromol/l (DMA(V)). MMA(V) and iA(III) had no significant effects on glutamate receptors of the AMPA type. The effects of MMA(V), MMA(III), DMA(V) and DMA(III )on glutamate receptors point to a neurotoxic potential of these substances.
The effect of the organic species oxalate, citrate and acetate and the inorganic species silicate and phosphate on release of As(V) from synthetic arsenic-loaded ferrihydrite and Al-ferrihydrite in the pH range 4-8 was investigated. For ferrihydrite, the organic species increased %As(V) extraction in the order: acetate PO4(3-). Competitive adsorption of the investigated organic and inorganic species on ferrihydrite and Al-ferrihydrite could explain the enhanced release of As(V) into solution. However, disproportionate adsorption of other species relative to amount of As(V) release occurs, suggesting that mechanisms other than competitive adsorption are also operative. The results could best be explained in terms of combination of competitive adsorption and processes involving pH-dependent dissolution of ferrihydrite/Al-ferrihydrite, formation of various complex ionic species involving Al(III), Fe(III), As(V), SiO3(2-), PO4(3-), OH-, H+ and organic species: acetate, oxalate and citrate.
Arsenic is a toxic element, acting as a nerve poison and proven carcinogen. Its main source for humans is drinking water where the most important are arsenic (V) compounds. With respect to the Slovak standard, in force since 1998, the maximum tolerable value is defined as the important characteristic of drinking water. If the value 0.01 mg.l-1 of arsenic is exceeded, water is not drinkable. The mentioned standard defines criteria for precision of the arsenic determination and the corresponding limit of detection--being 10% of the maximum tolerable value. Arsenic content in the drinking water samples was measured by the AAS method. Internal Quality Control for analysis by the ETA AAS method was based on the harmonised guidelines recommended by IUPAC, ISO and AOAC. The following metrological characteristics were calculated: precision, accuracy, and the yield of the arsenic standard addition to the studied sample--matrix spike and analytical spike. In addition to it, a thorough study of the limit of detection, LOD, and the limit of quantification (determination), LOQ, was performed. The LOD and LOQ values were calculated in the traditional way as well as by the ULA technique, newly recommended by IUPAC. In the latter case, the calculated LOD value was close to the demanded 10% limit of the maximum tolerable value, which is 1 microgram.l-1 As. The repeatability and reproducibility, found at two concentration levels 56.02 +/- 0.73 micrograms.l-1 and 6.0 +/- 0.9 microgramsl-1, were 3.2% and 3.9%, respectively, and 7.1% and 9.8%, respectively. Trueness of the applied AAS method was proven satisfactory on the reference material SRM 1643 Trace Elements in Water.
Different methods for a simultaneous determination of several analytes forming volatile compounds at room temperature are described. The main steps of these methods are: continuous generation, collection in a cryogenic trap, revolatilization, measurement of the volatile compounds by Gas Phase Molecular Absorption Spectrometry and resolution by multi-wavelength methods. Several mixtures containing 2, 3 or 4 components have been studied: 1) elements forming covalent hydrides; 2) arsenic organometallic compounds forming volatile gases with a similar structure to arsine; and 3) sulphur species that can evolve volatile compounds. Under the optimum conditions obtained for each mixture, detection limits range from 0.8 ng/mL (dimethylarsinic acid) to 2 microg/mL (SCN(-)).
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Exposure of splenocytes in vivo or in vitro to gallium arsenide (GaAs) dose-dependently suppresses the ability of these cells to produce antibody after in vitro immunization with sheep red blood cells. In addition, it has been demonstrated that GaAs exerts immunosuppressive effects early (36 hr) in the generation of a primary antibody-forming cell (AFC) response. The objective of this study was to determine if the GaAs-induced suppression was produced as a result of a GaAs-induced alteration in the secretion of soluble mediators. Supernatants from in vivo and in vitro vehicle (VH)-exposed splenocyte cultures time-dependently reversed GaAs-induced suppression of the in vitro-generated primary AFC response produced by both in vitro (50 microM) and in vivo (200 mg/kg) exposure to GaAs. Supernatants from in vitro GaAs-exposed cells suppressed the VH response 40, 89 and 93% at 24, 36 and 48 hr, respectively. Using the arsenic-binding compound meso-2,3-dimercaptosuccinic acid (100 microM), it was determined that the suppression of the VH response by supernatants from in vitro GaAs-exposed cultures was confounded by the presence of free arsenic in the in vitro GaAs-exposed culture supernatant. In contrast, suppression of in vivo VH-exposed AFC responses by supernatants from in vivo GaAs-exposed cells was not seen. The time-dependent reversal of immunosuppression produced by in vivo or in vitro exposure to GaAs, by supernatants from in vivo and in vitro VH-exposed cells mimics the reported kinetics of suppression by addition of GaAs to antibody cultures.(ABSTRACT TRUNCATED AT 250 WORDS)