RESUMEN
The conditions that support the simultaneous activity of hydroxyl radicals (OH.) and heterotrophic aerobic bacterial metabolism were investigated using two probe compounds: (1) tetrachloroethene (PCE) for the detection of OH. generated by an iron-nitrilotriacetic acid (Fe-NTA) catalyzed Fenton-like reaction and (2) oxalate (OA) for the detection of heterotrophic metabolism of Xanthobacter flavus. In the absence of the bacterium in the quasi-steady-state Fenton's system, only PCE oxidation was observed; conversely, only OA assimilation was found in non-Fenton's systems containing X. flavus. In combined Fenton's-microbial systems, loss of both probes was observed. PCE oxidation increased and heterotrophic assimilation of OA declined as a function of an increase in the quasi-steady-state H2O2 concentration. Central composite rotatable experimental designs were used to determine the conditions that provide maximum simultaneous abiotic-biotic oxidations, which were achieved with a biomass level of 10(9) CFU/mL, 4.5 mM H2O2, and 2.5 mM Fe-NTA. These results demonstrate that heterotrophic bacterial metabolism can occur in the presence of hydroxyl radicals. Such simultaneous abiotic-biotic oxidations may exist when H2O2 is injected into the subsurface as a microbial oxygen source or as a source of chemical oxidants. In addition, hybrid abiotic-biotic systems could be used for the treatment of waters containing biorefractory organic contaminants present in recycle water, cooling water, or industrial waste streams.
Asunto(s)
Carcinógenos/química , Tetracloroetileno/química , Eliminación de Residuos Líquidos , Xanthobacter/fisiología , Biodegradación Ambiental , Peróxido de Hidrógeno/química , Radical Hidroxilo/química , Hierro , Oxalatos/química , Oxidantes/química , Oxidación-ReducciónRESUMEN
Contaminant degradation, stoichiometry, and role of hydroxyl radicals (OH*) in four Fenton's systems were investigated using trichloroethylene (TCE) as a model contaminant. A standard Fenton's system, a modified soluble iron system with a pulse input of hydrogen peroxide, and two modified mineral-catalyzed systems (pH 3 and 7) were studied. In the standard Fenton's system, which had the most efficient reaction stoichiometry, 78% of the TCE was degraded; however, chloride analysis indicated that no more than two of the three chlorines were displaced per TCE molecule degraded. Although the modified soluble iron system was characterized by 91% TCE degradation, chloride analysis also indicated that no more than two of the chlorines were lost from the TCE. In the goethite system of pH 3, > 99% of the TCE was degraded. Near-complete release of chloride suggested that the TCE may have been mineralized. Only 22% degradation of TCE was achieved in the pH 7 goethite system. and there was minimal release of chloride. The mineral-catalyzed reactions exhibited the least efficient reaction stoichiometry of the four systems. Experiments using hydroxyl radical scavengers showed that the standard Fenton's system degraded TCE entirely by hydroxyl radical mechanisms, while approximately 10-15% of the degradation achieved in the modified soluble iron and goethite-catalyzed systems at pH 3 was mediated by non-hydroxyl radical mechanisms. In the goethite system at pH 7, only non-hydroxyl radical mechanisms were found. The goethite-catalyzed system at pH 3 effectively degraded the parent compound and may have the potential to mineralize contaminants when used for in situ soil and groundwater remediation and ex situ waste stream treatment in packed-bed reactors.
Asunto(s)
Peróxido de Hidrógeno , Hierro , Tricloroetileno/aislamiento & purificación , Contaminantes Químicos del Agua/aislamiento & purificación , Biodegradación Ambiental , Catálisis , Concentración de Iones de Hidrógeno , Radical Hidroxilo , Minerales , Solubilidad , Purificación del Agua/métodosRESUMEN
The relative oxidation of representative aromatic and aliphatic hydrocarbons found in gasoline was evaluated to provide the foundation for risk-based treatment of petroleum-contaminated soils and groundwater using modified Fenton's reagent (catalyzed hydrogen peroxide). Aromatic components of gasoline are considered more hazardous than the aliphatic fractions due to their higher mobility in the subsurface and their higher acute and chronic toxicities. Benzene, toluene, and mixed xylenes (BTX) were selected as aromatic compounds representative of unleaded gasoline, while nonane, decane, and dodecane (NDD) were used as model aliphatic compounds. The effects of hydrogen peroxide (H(2)O(2)) concentration, iron catalyst concentration, and pH on the degree of treatment of the model compounds were investigated using central composite rotatable experimental designs. Oxidation of the aromatic compounds required less iron and less H(2)O(2) than did oxidation of the aliphatic compounds, while proceeding more effectively at near-neutral pH. Greater than 95% of the BTX was treated at near-neutral pH using 2. 5% H(2)O(2) and 12.5 mM iron (III), while only 37% nonane, 7% decane, and 1% dodecane oxidation was achieved under the same conditions. The results show that the more toxic and mobile aromatic fraction was more effectively oxidized using less H(2)O(2) and more economical conditions, including near-neutral pH, compared to the aliphatic fraction. A process design based on treating only the aromatic fraction of petroleum may provide significantly lower costs when using modified Fenton's reagent for the treatment of contaminated soils and groundwater.
Asunto(s)
Gasolina , Hidrocarburos Aromáticos/metabolismo , Contaminantes del Suelo/metabolismo , Peróxido de Hidrógeno/química , Concentración de Iones de Hidrógeno , Modelos Teóricos , Oxidación-Reducción , Medición de RiesgoRESUMEN
Rates of hydrogen peroxide decomposition, hydroxyl radical production, and oxygen evolution were investigated in silica sand-goethite slurries using unstabilized and stabilized hydrogen peroxide formulations. The goethite-catalyzed decomposition of unstabilized hydrogen peroxide formulations resulted in more rapid hydrogen peroxide loss and oxygen evolution relative to systems containing a highly stabilized hydrogen peroxide formulation. Systems at neutral pH and those containing higher goethite concentrations were characterized by higher rates of hydrogen peroxide decomposition and by more oxygen evolution. The stabilized hydrogen peroxide formulation showed greater hydroxyl radical production relative to the unstabilized formulations. Furthermore, hydroxyl radical production rates were greater at neutral pH than at the acidic pH regimes. The results suggest that when stabilized hydrogen peroxide is injected into the subsurface during in situ bioremediation, naturally occurring minerals such as goethite may initiate Fenton-like reactions. While these reactions may prove to be toxic to microorganisms, they have the potential to chemically oxidize contaminants in soils and groundwater.
Asunto(s)
Peróxido de Hidrógeno/farmacocinética , Contaminantes del Suelo/farmacocinética , Biodegradación Ambiental , Concentración de Iones de Hidrógeno , Oxígeno/metabolismo , Administración de Residuos/métodosRESUMEN
Syndecans are a family of heparan sulfate proteoglycans implicated in cell-cell and cell-matrix interactions. To investigate the roles of syndecans in early development, we identified three syndecan family members in Xenopus laevis: Xsyn-1, Xsyn-2, and Xsyn-3. Xsyn-1 and Xsyn-2 are maternal mRNAs localized to the animal pole in blastulae, and are expressed in the ectoderm of gastrulae. In neurulae, Xsyn-1 is restricted to non-neural ectoderm and Xsyn-2 is restricted to neural ectoderm. In tailbud embryos, the three syndecans are expressed in adjacent, non-overlapping patterns. Xsyn-2 is expressed in the heart while Xsyn-1 is expressed in the underlying anterior endoderm. Xsyn-3 is expressed in the hindbrain, midbrain, and forebrain, while Xsyn-2 is expressed in the intervening regions. These results suggest that different members of the syndecan family have distinct developmental roles, perhaps acting as barriers to define tissue boundaries.
Asunto(s)
Glicoproteínas de Membrana/genética , Proteoglicanos/genética , Receptores de Factores de Crecimiento de Fibroblastos/genética , Secuencia de Aminoácidos , Animales , Northern Blotting , Southern Blotting , ADN Complementario/química , Glicoproteínas de Membrana/química , Datos de Secuencia Molecular , Proteoglicanos/química , ARN Mensajero/metabolismo , Receptores de Factores de Crecimiento de Fibroblastos/química , Sindecano-1 , Sindecano-2 , Sindecano-3 , Sindecanos , Xenopus , Proteínas de XenopusRESUMEN
This study characterizes the mRNA expression of the retinoblastoma tumor suppressor gene in regenerating rat liver during 96 hr after 70% partial hepatectomy. A 960-bp BglII-OxaNI fragment of murine retinoblastoma cDNA was used to probe Northern blots of poly(A)(+)-enriched RNA isolated from regenerating liver. Two species of retinoblastoma mRNA, 2.8 kb and 4.7 kb long, were identified in control liver and exhibited an intensity ratio of 5:1, respectively. Expression of the 2.8-kb mRNA was reduced by 50% 1 hr after partial hepatectomy and was less than 10% of control values by 3 hr. The transcript began to reappear at 12 hr and returned to near-baseline levels by 24 hr. In contrast to the rapid disappearance of the 2.8-kb transcript, expression of the 4.7-kb mRNA increased 15-fold by 6 hr and returned to control levels by 18 hr after partial hepatectomy. Pretreatment of the animals with cycloheximide before partial hepatectomy completely stabilized steady-state levels of both mRNA transcripts through 6 hr. Nuclear run-on assays revealed a sixfold increase in transcription by 30 min and a return to near-baseline levels by 6 hr. The in vivo half-lives of the 2.8- and 4.7-kb transcripts in control livers were 39.5 and 41.2 min, respectively. The half-life of the 4.7-kb transcript 6 hr after partial hepatectomy was 39.1 min. Intravenous administration of transforming growth factor-beta 1, a known inhibitor of hepatocyte replication, just before partial hepatectomy caused no significant change in the modulation of the transcripts through 24 hr.(ABSTRACT TRUNCATED AT 250 WORDS)