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Toxic Metal Ions (toxic + metal_ion)
Selected AbstractsBiotic ligand model of the acute toxicity of metals.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2001Abstract The biotic ligand model (BLM) of acute metal toxicity to aquatic organisms is based on the idea that mortality occurs when the metal,biotic ligand complex reaches a critical concentration. For fish, the biotic ligand is either known or suspected to be the sodium or calcium channel proteins in the gill surface that regulate the ionic composition of the blood. For other organisms, it is hypothesized that a biotic ligand exists and that mortality can be modeled in a similar way. The biotic ligand interacts with the metal cations in solution. The amount of metal that binds is determined by a competition for metal ions between the biotic ligand and the other aqueous ligands, particularly dissolved organic matter (DOM), and the competition for the biotic ligand between the toxic metal ion and the other metal cations in solution, for example, calcium. The model is a generalization of the free ion activity model that relates toxicity to the concentration of the divalent metal cation. The difference is the presence of competitive binding at the biotic ligand, which models the protective effects of other metal cations, and the direct influence of pH. The model is implemented using the Windermere humic aqueous model (WHAM) model of metal,DOM complexation. It is applied to copper and silver using gill complexation constants reported by R. Playle and coworkers. Initial application is made to the fathead minnow data set reported by R. Erickson and a water effects ratio data set by J. Diamond. The use of the BLM for determining total maximum daily loadings (TMDLs) and for regional risk assessments is discussed within a probabilistic framework. At first glance, it appears that a large amount of data are required for a successful application. However, the use of lognormal probability distributions reduces the required data to a manageable amount. [source] Chromosomal antioxidant genes have metal ion-specific roles as determinants of bacterial metal toleranceENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Joe J. Harrison Summary Microbiological metal toxicity involves redox reactions between metal species and cellular molecules, and therefore, we hypothesized that antioxidant systems might be chromosomal determinants affecting the susceptibility of bacteria to metal toxicity. Here, survival was quantified in metal ion-exposed planktonic cultures of several Escherichia coli strains, each bearing a mutation in a gene important for redox homeostasis. This characterized ,250 gene,metal combinations and identified that sodA, sodB, gor, trxA, gshA, grxA and marR have distinct roles in safeguarding or sensitizing cells to different toxic metal ions (Cr2O72,, Co2+, Cu2+, Ag+, Zn2+, AsO2,, SeO32, or TeO32,). To shed light on these observations, fluorescent sensors for reactive oxygen species (ROS) and reduced thiol (RSH) quantification were used to ascertain that different metal ions exert oxidative toxicity through disparate modes-of-action. These oxidative mechanisms of metal toxicity were categorized as involving ROS and thiol-disulfide chemistry together (AsO2,, SeO32,), ROS predominantly (Cu2+, Cr2O72,) or thiol-disulfide chemistry predominantly (Ag+, Co2+, Zn2+, TeO32,). Corresponding to this, promoter- luxCDABE fusions showed that toxic doses of different metal ions up- or downregulate the transcription of gene sets marking distinct pathways of cellular oxidative stress. Altogether, our findings suggest that different metal ions are lethal to cells through discrete pathways of oxidative biochemistry, and moreover, indicate that chromosomally encoded antioxidant systems may have metal ion-specific physiological roles as determinants of bacterial metal tolerance. [source] Nanosensor Design Packages: A Smart and Compact Development for Metal Ions Sensing Responses,ADVANCED FUNCTIONAL MATERIALS, Issue 18 2007A. El-Safty Abstract With recent advances in mesostructured materials and nanotechnologies, new methods are emerging to design optical sensors and biosensors, and to develop highly sensitive solid sensors. Here, highly sensitive, low cost, simple nanosensor designs for naked-eye detection of toxic metal ions are successfully developed by the immobilization of commercially available ,,,,,,,-tetrakis(1-methylpyridinium-4-yl)porphine p -toluenesulfonate (TMPyP) and diphenylcarbazide (DPC), and chemically synthesized 4- n -dodecyl-6-(2-thiazolylazo) resorcinol (DTAR) and 4- n -dodecyl-6-(2-pyridylazo) phenol (DPAP) chromophore molecules into spherical nanosized cavities and surfaces. A rational strategy was crucial to develop optical nanosensors that can be used to control accurate recognition and signaling abilities of analyte species for ion-sensing purposes. This is the first reported evidence of the significant key factors of the development of receptors as ,indicator dyes' and surface-confinement materials as ,carriers' to broadening the applicability of optical chemical sensors for selective discrimination of trace levels of toxic analytes. In all the nanosensor design techniques presented here, a dense pattern of immobilized hydrophobic ,neutral' and hydrophilic ,charged' chromophores with intrinsic mobility, as a result of extremely robust constructed sequences on nanoscale structures, is a key to enhancing the sensing functionality of optical nanosensors. These nanosensor designs can be used as cage probe sinks with reliable control, for the first time, over the colorimetric recognition of cadmium ions to low levels of concentration in the range of 10,9 to 10,10M. Optimization of control sensing conditions is established to achieve enhanced signal response and color intensities. These chemical nanosensors are reversible and have the potential to serve effectively in on-site field analysis of environmental samples, which eliminates the necessity for instrument-dependent analysis. Moreover, these new classes of optical cage sensors exhibit long-term stability of signaling and recognition functionalities that in general provide extraordinary sensitivity, selectivity, reusability, and fast kinetic detection and quantification of various deleterious metal ions in our environment. [source] Preconcentration and matrix elimination for the determination of Pb(II), Cd(II), Ni(II), and Co(II)by 8-hydroxyquinoline anchored poly(styrene-divinylbenzene) microbeadsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2008Hakan A Abstract Poly(styrene-divinylbenzene), PS-DVB, microbeads were modified with 8-hydroxyquinoline (8-HQ) following nitration, reduction of NO2 to NH2, and conversion of NH2 to diazonium salt. Characterization of pristine, NO2, NH2, NN+Cl,, and 8-QH functional groups modified microbeads was made by Fourier transform-infrared spectrometry (FTIR) and porosimetry. Total reflectron-X-ray florescence spectrometer (TXRF) was used to test the affinity of the 8-HQ modified microbeads to toxic metal ions. 8-HQ-modified microbeads were used to examine the adsorption capacity, recovery, preconcentration, and the matrix elimination efficiency for Pb(II), Cd(II), Ni(II), and Co(II) ions as a function of changing pH, initial metal-ion concentrations, and also equilibrium adsorption time of the studied metal ions. Preconcentration factors for the studied toxic metal ions were found to be more than 500-fold and recovery between 93.8% and 100.6%. Ultratrace toxic metal-ion concentrations in sea water were determined easily by using modified microbeads. Reference sea-water sample was used for the validation of the method, and it was found that recovery, preconcentration, and the matrix elimination were performed perfectly. For the desorption of the toxic metal ions, 3M of HNO3 was used and desorption ratio shown to be more than 96%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Removal of toxic metal ions from aqueous systems by biosorptive flotationJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2002Anastasios I Zouboulis Abstract Biosorptive flotation was used as a combined operation for the simultaneous abstraction of nickel, copper and zinc ions from aqueous streams. Laboratory-scale batch experiments, as well as pilot-scale continuous experiments, have been conducted. Grape stalks, a by-product of the winery industry, were used as sorbent material. The experimental procedure consisted of two consecutive stages: (i) biosorption, and (ii) flotation. The possibility of reusing biomass, after appropriate elution, was also examined. The main parameters examined were biomass concentration, particle size of sorbent, surfactant concentration, pH and flocculation. Flotation removals, following laboratory-scale experiments, were found to be in the order of 100, 85 and 70% for copper, zinc and nickel, respectively. In pilot-scale experiments, biomass sorption capacities were determined as 25 for copper, 81 for zinc and 7,µmol,dm,3 for nickel. The order of biomass affinity regarding the studied metals was Cu,>,Zn,>,Ni. Short retention time and high effectiveness suggest that biosorptive flotation is a promising treatment process for the removal of toxic metals from contaminated aqueous solutions. © 2002 Society of Chemical Industry [source] | |||||||||||||