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PubMed2005

Coexistence of two bifurcation regimes in a closed ferroin-catalyzed Belousov-Zhabotinsky reaction.

The ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction was studied in a batch reactor under anaerobic conditions and was found to evolve through two separated regimes of complex oscillations. Significantly, the two bifurcation regimes exhibited qualitatively different dependence on compositions of the reaction mixture, i.e., initial concentrations of bromate, sulfuric acid, malonic acid, and ferroin. The reaction temperature also showed opposite effects on the two bifurcation regimes, in which complexities of the first bifurcation regime were enhanced while oscillations in the second bifurcation regime became simpler as a result of decreasing temperature. Numerical simulations with a 12-variable model developed specifically for the ferroin-BZ system were able to reproduce transient complex oscillations observed in experiments. These calculations further illustrated that reactions such as ferroin and HOBr, ferroin and HBrO2, and ferriin and Br- were not essential in describing complex dynamics of the ferroin-BZ reaction.

Bromates↗
PubMed2006

Periodic pulses of calcium ions in a chemical system.

By coupling the bromate-sulfite-ferrocyanide oscillating chemical reaction with the complexation of calcium ion by EDTA, we construct a system that generates periodic pulses of free Ca(2+) with an amplitude of 2 orders of magnitude and a period of ca. 20 min. These pulses may be observed either with a calcium ion-selective electrode or with Arsenazo(III) as an indicator. We describe the systematic design procedure and the properties of this first abiotic calcium-based chemical oscillator.

Animals↗
PubMed2001

Monitoring and modeling of disinfection by-products (DBPs).

In the United States, the newly promulgated disinfectant/disinfection by-product (D/DBP) regulations force water treatment utilities to be more concerned with finished and distributed water qualities. In this study, monitoring of DBP formation was conducted from three French water treatment plants trying to assess DBP variations through time and space. Compared to the in-plant total trihalomethanes (TTHM) levels, TTHM levels in the distribution system increased from less than 150% to more than 300%. Significant variations for TTHM and bromate (BrO3-) levels throughout the seasons were also observed; generally higher levels in the summer and lower levels in the winter. Combining chemical DBP models (empirical power functional models) and hydraulic simulations, DBPs including TTHM and BrO3- were successfully simulated from the full-scale monitoring data, indicating that empirical DBP model can be a potential tool to access DBP formation in actual plants. This study also provides the protocols to assess DBP simulations in the water treatment systems.

Bromates↗
PubMed2001

Excitability in chemical and biochemical pH-autocatalytic systems.

Using two different kinds of pH systems--the papain catalyzed hydrolysis of N-benzoyl-L-arginine ethyl ester in a membrane reactor and the bromate-sulfite-ferrocyanide (BSF) reaction in the CSTR--we study the relation among excitability, oscillations and bistability, and the ability of the system to respond to external periodic perturbations. Excitable properties of dynamical systems are examined in terms of a threshold set which is used to characterise dynamics in the reactor subject to external periodic stimuli. A precise definition and a method of calculating the threshold set are formulated. Two kinds of excitability distinguished by either direct or indirect initiation of the activatory process are found in both pH systems. Periodic pulsed perturbations of the BSF system display a nontrivial dependence of an excitation number on the forcing period. We examined this system also in oscillatory mode by looking at the phase shifts caused by single-pulse perturbations and constructing the phase transition curves (PTCs).

Algorithms↗
PubMed2002

High accumulation of oxidative DNA damage, 8-hydroxyguanine, in Mmh/Ogg1 deficient mice by chronic oxidative stress.

8-Hydroxyguanine (8-OH-G) is a major pre-mutagenic lesion generated from reactive oxygen species. The Mmh/Ogg1 gene product plays a major role in maintaining genetic integrity by removing 8-OH-G by way of the base excision repair pathway. To investigate how oxidative stress influences the formation of 8-OH-G in Ogg1 mutant mice, a known oxidative agent, potassium bromate (KBrO(3)), was administered at a dose of 2 g/l in the drinking water to Ogg1(+/+), Ogg1(+/-) and Ogg1(-/-) mice for 12 weeks. Apurinic (AP) site lyase activity, measured by the excision of 8-OH-G from synthetic oligonucleotides, remained unchanged in kidney cell extracts isolated from Ogg1 mutant mice when the mice were pre-treated by KBrO(3). The levels of 8-OH-G in kidney DNA tremendously increased in a time-dependent manner following exposure of Ogg1(-/-) mice to KBrO(3). Of particular note, the amount of 8-OH-G in kidney DNA from Ogg1(-/-) mice treated with KBrO(3) was approximately 70 times that of KBrO(3)-treated Ogg1(+/+) mice. The accumulated 8-OH-G did not decrease 4 weeks after discontinuing treatment with KBrO(3). KBrO(3) treatment for 12 weeks gave rise to increased mutation frequencies at the transgenic gpt gene in Ogg1(+/+) mice kidney. Absence of the Ogg1 gene further enhanced the mutation frequency. Sequence data obtained from gpt mutants showed that the accumulated 8-OH-G caused mainly GC-->TA transversion and deletion. Other mutations including GC-->AT transition also showed a tendency to increase. These results indicate that 8-OH-G, produced by chronic exposure to exogenous oxidative stress agents, is not repaired to any significant extent within the overall genome of Ogg1(-/-) mice kidney.

Animals↗
PubMed1995

Combination effects of clastogens in the mouse peripheral blood micronucleus assay.

In order to study how two chemicals interact to induce micronuclei, simple ethylating agents [ethyl methanesulfonate (EMS), ethyl ethanesulfonate (EES) and N-ethyl-N-nitrosourea (ENU)], spindle poisons [vincristine sulfate (VINC) and colchicine (COL)] and an oxidizing agent [potassium bromate (KBrO3)] were used as model chemicals for combination treatments. The frequency of micronucleated reticulocytes (MNRETs) was evaluated in mice treated with two of these chemicals at a time. The combinations of ethylating agents (EMS and EES; EMS and ENU) and of spindle poisons (VINC and COL) induced more micronuclei than those expected on an additive basis. The apparent synergism was due to a 'combined dose' which could be calculated by the dosimetric conversion of one chemical to the other, when damage induced by each chemical was 'equivalent' in the induction of MNRETs. In contrast, no apparent synergism in induction of micronuclei was observed when two chemicals with different modes of clastogenic action (EMS and KBrO3 or EMS and VINC) were combined.

Alkylating Agents↗
PubMed2006

Kinetic spectrophotometric method for the determination of trace amounts of oxalate by an activation effect.

A new, simple and inexpensive kinetic catalytic spectrophotometric method for the determination of oxalate is described. The method is based on an activation effect of oxalate on a catalytic effect of iron(II) on the oxidation of iodide by bromate. The reaction is monitored by measuring the absorbance of triiodide ion at lambda max = 352 nm. A calibration graph was obtained from 0.10 - 7.0 microg cm(-3) of oxalate with a detection limit of 0.080 microg cm(-3). The standard deviations for ten replicate determinations of 0.50, 1.0 and 5.0 microg cm(-3) of oxalate were 4.0, 2.6 and 1.8%, respectively. The applicability of the method was demonstrated by the determination of oxalate ion in real samples.

Bromates↗
PubMed2001

Identification of lactate. Analytical methods of pharmacopoeias with DBH in respect to environmental and economical concern, Part 4.

The identification of lactate according to Ph. Eur. 1997 and DAB 2000 uses the oxidation of lactic acid to pyruvic acid by boiling with bromine water in sulphuric acid. Acetaldehyde arising by decarboxylation is detected according to Legal applying a time consuming and troublesome procedure. 1,3-Dibromo-5,5-dimethylhydantoin (DBH) as well as potassium bromate can replace elemental bromine. Lactic acid and all lactates of Ph. Eur. 1997 and DAB 2000 can be identified better and faster using lactate oxidase (LOD, test strip system Accusport). According to DAB 2000 the base of ethacridine lactate has to be separated. This is no longer necessary, if an enzymatic identification is applied.

Bromates↗
PubMed2000

[Study on the determination of trace ions in the presence of high concentration of matrix by simplified column-switching ion chromatography].

A simplified column-switching technique for the determination of trace ions in the presence of high concentration of matrix is established. A binary eluent mechanism is developed to study the effect of matrix on the shift of the analyte retention time. According to this mechanism, eluent of high concentration is preferred to suppress the peak shift of trace analyte caused by large amount of matrix. Since the peak shift has been effectively suppressed, the procedures for determining the column-switching time windows were greatly simplified. According to the different samples, different strategies should be employed in this technique. In this work, three typical samples were analyzed by this technique and the strategies for these three samples were studied to show the principles of choosing the proper separation conditions. Results showed that by this simplified technique analysis for trace analytes in the presence of complicated matrix was accurate and precise. The successful use of this method to the determination of trace bromate in drinking water, and nitrate, ammonium and iodide in sea water indicates that the application of this versatile technique to quantify analytes of low concentration in a wide range of sample matrices is promising.

Bromates↗
PubMed2004

[Catalytic kinetic spectrophotometric determination of trace ascorbic acid].

In this paper, a new catalytic kinetic spectrophotometric method for the determination of trace amounts of ascorbic acid has been studied. The method is based on the activation effect of ascorbic acid on vanadium (V) catalyzed oxidation of deoxidized rhodamine B by potassium bromate in weak acidic medium at pH 4.5. The optimal experimental conditions have been discussed. The absorbance was measured at 555 nm. The linear range of the method was 0-7.0 microg x mL(-1). The detection limit for ascorbic acid was 2.5 x 10(-7) g x L(-1). The method has been applied to the determination of ascorbic acid in vitamin C tablet and tomato with satisfactory results.

Ascorbic Acid↗
PubMed2004

[Inhibitory kinetic-synchronous fluorimetric determination of trace aniline].

A novel kinetic-synchronous fluorimetric method is reported for the determination of trace aniline. The method is based on the inhibitory effect of aniline on the oxidation of fluorescein by potassium bromate in the presence of surfactant -CTMAB in the acid medium. Fluorescein's oxidized product produces strong fluorescence. But its excitation and emission spectra overlap seriously. So this article adopted synchronous fluorimetric spectra to diminish spectra overlap and obtained very good sensitivity and selectivity. The detection limit for aniline is 0.3 microg x L(-1), and the linear range is 0-10 microg x L(-1). The proposed method has been applied to the determination of trace aniline in waste water and laboratory water with satisfactory results.

Aniline Compounds↗
PubMed1985

Risk evaluation of tumor-inducing substances in foods.

Carcinogenic risk assessment of chemicals consists of four phases, namely, 1) hazard identification, 2) exposure assessment, 3) hazard assessment or dose-response assessment, and 4) risk characterization. The third phase of risk assessment is the evaluation of both hazard and exposure information to estimate the mathematical probability that the carcinogenic potential associated with an agent will be realized in the human population under defined conditions of exposure. The estimation of virtually safe dose (VSD) is regarded as a component of the third phase. Carcinogenic risk assessment is still at an embryonal stage of development, and there remains a number of problems to be clarified. With regard to the estimation of VSD, it is an important task to establish the principle for selection of appropriate mathematical models. The intention of this paper is to illustrate the estimation of VSD of two tumor-inducing chemicals, N-ethyl-N-nitrosourea and potassium bromate based on the dose-response data in animals and to discuss the biological implication of the estimated VSD in relation to the risk assessment of the chemicals in humans.

Animals↗
PubMed1982

New considerations on hydrogen peroxide and related substances as food additives in view of carcinogenicity.

The use of hydrogen peroxide as a labile and safe food preservative in fish cake and boiled noodles has recently been restricted by the Japanese government, since hyperplasia has been found in the duodenum of mice after long-term peroral study. The action of compounds with resembling mode of action, potassium bromate as an improving agent in bread, and sodium chlorate as a weed killer are discussed in this paper in view of developmental and environmental pharmacology.

Animals↗
PubMed2002

Determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater by capillary zone electrophoresis with artificial seawater as the background electrolyte using transient isotachophoresis.

We describe a combination of selected ions as a terminating ion which is useful for transient isotachophoresis (ITP) in capillary zone electrophoresis (CZE) for the determination of nitrite and nitrate in seawater. In addition to 150 mM sulfate as the principal terminating ion, 10 mM bromate was added to a sample solution as the additional terminating ion. Artificial seawater containing 3 mM cetyltrimethylammonium chloride (CTAC) was adopted as a background electrolyte (BGE). The limits of detection (LODs) for nitrite and nitrate were 2.2 and 1.0 microg/L (as nitrogen), respectively. The LODs were obtained at a signal to noise ratio (S/N) of 3. The values of the relative standard deviation (RSD) of peak area for these ions were 1.9 and 1.4%. The RSDs of peak height were 1.7 and 1.9%, the RSDs of migration time 0.11%. The proposed method was applied to the determination of nitrite and nitrate in a proposed certified reference material for nutrients in seawater, MOOS-1, distributed by the National Research Council of Canada (NRC). The results almost agreed with the assigned tolerance interval.

Calibration↗
PubMed2002

Mammalian cell cytotoxicity and genotoxicity analysis of drinking water disinfection by-products.

Cytotoxicity and genotoxicity assays were used to analyze drinking water disinfection by-products (DBPs) in Chinese hamster ovary (CHO) AS52 cells. The DBPs were chosen because they are common in drinking water, resulting from conventional disinfection using chlorination and chloramination. Data were also available to compare these results with cytotoxicity and mutagenicity studies in Salmonella typhimurium. The rank order in decreasing chronic cytotoxicity measured in a microplate-based assay was bromoacetic acid (BA) >> 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX) > dibromoacetic acid (DBA) > chloroacetic acid (CA) > KBrO(3) > tribromoacetic acid (TBA) > EMS (ethylmethanesulfonate, positive control) > dichloroacetic acid (DCA) > trichloroacetic acid (TCA). The induction of DNA strand breaks by these agents was measured by alkaline single-cell gel electrophoresis (SCGE, comet assay) and the rank order in decreasing genotoxicity was BA >> MX > CA > DBA > TBA > EMS > KBrO(3), while DCA and TCA were refractory. BA was more cytotoxic (31x) and genotoxic (14x) than MX in CHO cells. BA was over 400x more genotoxic than potassium bromate. The brominated haloacetic acids (HAAs) were more cytotoxic and genotoxic than their chlorinated analogs. The HAAs expressed a statistically significant inverse relationship in CHO cell cytotoxicity and genotoxicity as a function of increased numbers of halogen atoms per molecule. A quantitative comparison was conducted with results from a previous study with cytotoxicity and mutagenicity in S. typhimurium. There was no correlation between chronic CHO cell and bacterial cell cytotoxicity. DBP-induced CHO cell cytotoxicity was not related to mutagenic potency in S. typhimurium. Cytotoxicity in CHO cells was statistically significant and highly correlated to CHO cell genotoxicity. Finally, we determined that the DBP genotoxic potency in CHO cells and the mutagenic potency in S. typhimurium were not related. This suggests that toxicity data in S. typhimurium did not quantitatively predict the toxic effects of DBPs in mammalian cell systems. The microplate CHO cell cytotoxicity and genotoxicity assays were well suited for the analysis of DBPs, especially when the quantity of test material is limited.

Animals↗
PubMed2005

Exposure of human lymphocytes and lymphoblastoid cells to simulated microgravity strongly affects energy metabolism and DNA repair.

Exposure of freshly drawn lymphocytes and lymphoblastoid cells (LB and COR3) to simulated microgravity decreased the intracellular ATP concentration to 50%-40% of the value found in normal growth conditions. The decrease was reversible although recovery to normal values occurred only slowly both in lymphocytes and in lymphoblastoid cells. Poly(ADP-ribose) polymerase (PARP ) activity was increased indicating that cells exposed to conditions of reduced gravitation experience stress. Exposure to microgravity forces cells into a condition of metabolic quiescence in which they appear to be particularly sensitive to subsequent exposures to a genotoxic agent. Thus, treatment of cells with the strong redox agent potassium bromate under microgravity conditions, indicated an impairment in repair of DNA 8-hydroxy-2'-deoxyguanosine (8-OHdG), an oxidized derivative of deoxyguanosine. We conclude that gravitational modulation of the kind routinely obtained under laboratory conditions and during spaceflights is a stressful process to which cells appear to be extremely sensitive. These effects may reflect the physiological alterations observed in astronauts and in animals following spaceflights or exposure to conditions of simulated microgravity.

Adenosine Triphosphate↗
PubMed2002

Ionizable drugs and pH oscillators: buffering effects.

It has been proposed that chemical pH oscillators may form a basis for periodic, pulsed drug delivery of weak acids and bases across lipophilic membranes. However, drugs have been shown to interfere with the ability of the chemical systems to oscillate, and rhythmic delivery of drugs by this means has been demonstrated only under constrained circumstances. Herein, we provide evidence that low concentrations of acidic drugs can attenuate and ultimately quench chemical pH oscillators, by a simple buffering mechanism. A model system consisting of the bromate-sulfite-marble pH oscillator in a continuous stirred tank reactor is used, along with acidic drugs of varying concentration and acid dissociation constant, pK(D). A published kinetic model for this oscillator is modified to account for the presence of acidic drug, and the results of this model are in qualitative agreement with the experimental results.

Acetic Acid↗
PubMed2002

Analysis of the cytotoxicity and mutagenicity of drinking water disinfection by-products in Salmonella typhimurium.

We analyzed the cytotoxicity and mutagenicity of the drinking water disinfection by-products (DBPs) bromoform (BF), bromoacetic acid (BA), dibromoacetic acid (DBA), tribromoacetic acid (TCA), chloroform (CF), chloroacetic acid (CA), dichloroacetic acid (DCA), trichloroacetic acid (TCA), 3-chloro-4-(dichloromethyl)-5-hydroxy-2[5H]-furanone (MX), and potassium bromate (KBrO3) in Salmonella typhimurium strains TA98, TA100, and RSJ100 +/- S9. Solvent controls of DMSO and ethanol and a positive control of ethylmethanesulfonate (EMS) were also analyzed. We developed a rapid microplate-based method to determine the cytotoxicity of the DBPs and we determined their mutagenic potencies. The distributions of the rank order for the cytotoxicity and mutagenicity of these DBPs were compared and the structure-function relationships were identified. TA100 -S9 was the most sensitive strain for these DBPs. The rank order of the mutagenic potency adjusted with a cytoxicity factor was MX > BA > EMS > DBA > DCA > CA with TBA, TCA, BF, and CF not mutagenic. From a structure-function perspective, the brominated acetic acids were more cytotoxic and mutagenic than their chlorinated analogs. BA was 150x more mutagenic than CA. The mutagenic potency of the haloacetic acids was inversely related to the number of halogen atoms of the molecule. BA was 36x more mutagenic than DBA. The differential cytotoxicity expressed by the DBPs indicated that a cytotoxicity analysis enhanced the sensitivity of the mutagenicity data, which resulted in an enhanced precision for comparing their relative mutagenic strengths. This information is critical when conducting quantitative structure-function analysis of these hazardous agents.

Disinfectants↗