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PubMed1996

Are bacterial biofilms constrained to Darwin's concept of evolution through natural selection?

Numerous antimicrobial agents have been developed which act at the molecular, cellular, and organismal levels. However, few have been developed which act at the community-level. This results largely from the failure of Darwinian selection theory to envision communities as units of proliferation and evolution. It is thus difficult to conceive of microbial communities as causative agents and to develop antimicrobials which are effective against them. Consequently, we find it necessary to consider a more comprehensive biological paradigm which envisions biofilm communities and other microbial associations (e.g. mixed infections, food spoilage, tooth decay) as units of existence, activity, ecology, proliferation, survival, and evolution. These communities exist in the same sense that organisms exist as units of ecological activity. This is a simpler, more comprehensive, and more unifying theory of ecology. It is simpler in that it no longer requires convoluted explanations of altruistic behavior in terms of individual selection. It is more comprehensive by not constraining evolution to the selection of any single level of biological organization (genes, races, lineages, or groups). It unifies in that it bridges the boundaries between microbial ecology, evolutionary ecology and ecosystem ecology. The basis for this theory lies in recognizing that life consists of various forms of information (order) which evolve not only through genetic recombination and mutation, but also through the recombination of organisms within communities (as well as other mechanisms, some of which are considered beyond the realm of biology). It also involves setting aside the concept of evolution through selection and competition, in favor of evolution through proliferation and association.

Bacteria↗

PubMed2001

Photoinduced hydrogen evolution with peptide dendrimer-multi-Zn(II)-porphyrin, viologen, and hydrogenase.

To construct an artificial photosynthetic system, multi-Zn(II)-mesoporphyrins in peptide dendrimers were equipped as a photosensitizer of photoinduced hydrogen evolution in a four-component system (electron donor, photosensitizer, electron carrier, and catalyst), so that hydrogen was evolved effectively by the dendrimer architecture, for the first time. The hydrogen evolution activity was correlated to the photoreduction ability of viologen by the Zn-porphyrin-peptide dendrimers. Additionally, using positively charged methyl-viologen as an electron carrier, the photoinduced hydrogen evolution function with the positively charged peptide dendrimer was superior to that with the negatively charged peptide dendrimer, despite that the positive dendrimer did not strongly bind the positively charged methyl-viologen with the electrostatic interaction. By contrast, when zwitterionic propylviologen sulfonate was used, photoreduction and hydrogen evolution properties were identical between the positively and the negatively charged dendrimers. These results demonstrated that the dynamic interaction between the positive dendrimer and methyl-viologen was preferable for the photoreduction and hydrogen evolution, and that the three-dimensional assembly of Zn(II)-mesoporphyrins using the peptide dendrimers was effective as a photosensitizer in the artificial photosynthesis.

Amino Acid Sequence↗

PubMed1993

Examples of evolution of microstructure in ceramics and composites.

In this article we describe a number of studies involving the direct observation of microstructural evolution. In general these investigations were carried out to establish the mechanistic paths involved. The materials studied range from fibers being evaluated for use in high-temperature ceramic composites to energetic materials used as propellants. In particular we discuss the room temperature imaging of materials difficult to image by conventional means and the use of the chamber atmosphere to influence microstructural evolution. Imaging of hydroxyapatite formed by chemical means is briefly described as an example of a difficult microstructure. Microstructural evolution during calcium aluminate cement hydration relies on the chamber atmosphere to control moisture loss from the hydrating specimens. In some instances microstructural evolution with heating occurred independently of the chamber atmosphere. Grain growth in PZT films formed by sol-gel processes depends strongly on temperature but does not appear to depend on the chamber atmosphere. This is also the case for the combustion of nitroamine propellants in that their combustion does not depend on access to an external source of oxygen. In other studies, the chamber atmosphere played an indirect role in determining microstructure. However, the mechanistic path driving microstructural evolution in copper-based inks used as conductive paths on electronic substrates is atmosphere dependent. These inks are formulated from copper powder, glass, and an organic binder, and the interaction of the binder with an oxidizing atmosphere allows it to be burned out before significant interaction occurs between the copper powder and the glass. Finally, the microstructural variations during the oxidation of structural composites at high temperature were used to allow assessments of their likely failure mechanisms.

Animals↗

PubMed1996

Classification and phylogeny of the MADS-box multigene family suggest defined roles of MADS-box gene subfamilies in the morphological evolution of eukaryotes.

The MADS-box encodes a novel type of DNA-binding domain found so far in a diverse group of transcription factors from yeast, animals, and seed plants. Here, our first aim was to evaluate the primary structure of the MADS-box. Compilation of the 107 currently available MADS-domain sequences resulted in a signature which can strictly discriminate between genes possessing or lacking a MADS-domain and allowed a classification of MADS-domain proteins into several distinct subfamilies. A comprehensive phylogenetic analysis of known eukaryotic MADS-box genes, which is the first comprising animal as well as fungal and plant homologs, showed that the vast majority of subfamily members appear on distinct subtrees of phylogenetic trees, suggesting that subfamilies represent monophyletic gene clades and providing the proposed classification scheme with a sound evolutionary basis. A reconstruction of the history of the MADS-box gene subfamilies based on the taxonomic distribution of contemporary subfamily members revealed that each subfamily comprises highly conserved putative orthologs and recent paralogs. Some subfamilies must be very old (1,000 MY or more), while others are more recent. In general, subfamily members tend to share highly similar sequences, expression patterns, and related functions. The defined species distribution, specific function, and strong evolutionary conservation of the members of most subfamilies suggest that the establishment of different subfamilies was followed by rapid fixation and was thus highly advantageous during eukaryotic evolution. These gene subfamilies may have been essential prerequisites for the establishment of several complex eukaryotic body structures, such as muscles in animals and certain reproductive structures in higher plants, and of some signal transduction pathways. Phylogenetic trees indicate that after establishment of different subfamilies, additional gene duplications led to a further increase in the number of MADS-box genes. However, several molecular mechanisms of MADS-box gene diversification were used to a quite different extent during animal and plant evolution. Known plant MADS-domain sequences diverged much faster than those of animals, and gene duplication and sequence diversification were extensively used for the creation of new genes during plant evolution, resulting in a relatively large number of interacting genes. In contrast, the available data on animal genes suggest that increase in gene number was only moderate in the lineage leading to mammals, but in the case of MEF2-like gene products, heterodimerization between different splice variants may have increased the combinatorial possibilities of interactions considerably. These observations demonstrate that in metazoan and plant evolution, increased combinatorial possibilities of MADS-box gene product interactions correlated with the evolution of increasingly complex body plans.

Amino Acid Sequence↗

PubMed1987

Basic studies of hydrogen evolution by Escherichia coli containing a cloned Citrobacter freundii hydrogenase gene.

Citrobacter freundii genes that complemented Escherichia coli hyd-(hydrogenase activity) mutation were cloned in plasmids pCBH4 (6.2 kb) and pCBH6(5.7 kb). Hydrogen evolution by the transformant E. coli HK-8(pCBH4 or pCBH6) was investigated. The optimum culture temperature of recombinant E. coli cells for hydrogen evolution from glucose was in the neighborhood of 18 degrees C. The recombinant E. coli cells cultured at this condition showed a several-fold increase of hydrogen evolution, as compared with that of the wild-type cells. The plasmid-retention stability of this recombinant E. coli was extremely high, especially plasmid pCBH4, which was completely retained during 2 wk without any restriction. Hydrogen production by immobilized recombinant E. coli was then investigated using cells cultured at 18 degrees C. The hydrogen evolution rate from glucose and Lennox-broth were about twofold higher than that of E. coli C600, and this high hydrogen evolution rate was maintained for more than 1 mo.

Citrobacter↗

PubMed2004

Time course of CT evolution in traumatic subarachnoid haemorrhage: a study of 141 patients.

BACKGROUND: Evidence of tSAH on an admission CT scan seems to be an early predictor of evolving posttraumatic lesions. Detection of these changes requires serial CT scanners. The goal of our study was to determine the optimal timing of follow-up CT scans in head injured patients with traumatic subarachnoid haemorrhage (tSAH). METHOD: We reviewed the initial and follow-up CT scans in 141 patients with closed head injuries and evidence of tSAH on the initial CT scan. We used the Marshall classification to determine diffuse and focal injuries. The "worst CT scan", defined as the CT examination in which midline shift, cistern compression and/or intracranial focal lesions were greater, was also determined. Any worsening of the admission CT findings, occurring when the "worst CT examination" did not correspond to the initial CT study, was considered as a "CT evolution". Any "CT evolution" associated with a variation from a lower to a higher score in the Marshall classification score was indicated as a "significant CT evolution". FINDINGS: The median time between injury and the first CT scan was 1.3 (IQR 1.5) hours. A CT evolution was found in 83/141 (58.9%) patients in whom the median time between the initial and worst CT scans was 27.7 hours (IQR 69.2 hours). The worst CT studies were seen more often at 12-24 hours and at 24-48 hours after the admission CT scan than in later studies. A similar temporal profile was observed when the timing of the "worst CT scan" was evaluated in 38/83 (45.8%) subjects with a "significant CT evolution". INTERPRETATION: Our findings show that an early admission CT scan did not represent the full extent of the posttraumatic damage in more than half of our patients. They also suggest that to identify these changes in head injured patients with tSAH, CT scans should be repeated at 12-24 and possibly also at 24-48 hours from the admission CT examination to allow early detection and evacuation of evolving intracranial lesions.

Adult↗

PubMed1991

Prognostic importance of delayed Q-wave evolution 3 to 24 hours after initiation of thrombolytic therapy for acute myocardial infarction.

The timing of Q-wave evolution and its prognostic significance was studied in 201 patients who received thrombolytic therapy for a first acute myocardial infarction (AMI). One hundred forty-one patients (70%) had evidence of a Q-wave AMI within 3 hours of the initiation of thrombolytic therapy, 31 (16%) developed Q waves after 3 hours but before hospital discharge, and 29 (14%) were discharged with a non-Q-wave AMI. Laboratory indicators of myocardial damage and in-hospital morbidity and mortality were greater among patients with Q-wave AMIs than with non-Q-wave AMIs. When these indexes were examined with respect to the timing of Q-wave evolution, the prognosis of patients with delayed Q-wave development was similar to that of patients with non-Q-wave AMIs. Thus, compared to patients with early (less than or equal to 3 hours) Q-wave evolution, patients with delayed Q-wave evolution or with a non-Q-wave AMI had a smaller creatine kinase peak (mean 661 to 1,081 vs 1,251 to 1,541 IU; p = 0.005), better preservation of left ventricular function as measured by radionuclide ventriculography before discharge (mean +/- standard deviation 54 +/- 11% vs 47 +/- 13%; p less than 0.01), and a lower incidence of congestive heart failure at discharge (3 vs 15%; p = 0.02). In-hospital mortality was lower among patients with delayed Q-wave evolution or with a non-Q-wave AMI (5 of 141 vs 0 of 60; difference not significant).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

PubMed1985

Karyotypic evolution in patients with myelodysplastic syndromes.

Serial cytogenetic studies were performed in 33 patients with myelodysplastic syndrome in order to establish the frequency of karyotypic evolution and to correlate the chromosome and clinical findings during the course of the disease. Fifteen of the 33 patients (45%) showed abnormalities in the first cytogenetic study and this percentage increased to 57% during the course of the disease. A stable karyotype (normal or abnormal) was found in 19 patients (58%), whereas the rest (42%) showed an unstable karyotype. Trisomy 8, monosomy 7, and del5q were the most frequent abnormalities, not only at presentation, but also during karyotypic evolution. Seven patients (23%) with a known evolution proceeded to leukemia; four of them had stable (22%) and three unstable (25%) karyotypes; however, 33% of patients with unstable karyotypes and only 5% with stable karyotypes died from complications of the disease. Our results suggest that karyotypic evolution is relatively frequent in these patients; this evolution could be related to a poor clinical prognosis, either evolving to leukemia or death.

Acute Disease↗

PubMed1995

Down's syndrome as a model for the decisive role of maternal lineage in human evolution.

The study of human evolution and the mechanism of this process can be approached from physical anthropology, which examines phenotypic expression and molecular evolution, which investigates genotypic change. Alternatively, we suggest that human evolutional process can also be explained using present day examples of abberations in evolution. Thus, from both genotypic and phenotypic perspectives, we address the question of whether Down's syndrome is an instructive example to look into the decisive role of maternal lineage in human evolution.

Animals↗

PubMed2004

Prognostic value of clinical and morphologic findings in short-term evolution of aortic intramural haematoma. Therapeutic implications.

AIMS: Intramural haematoma (IMH) forms part of the acute aortic syndrome presenting physiopathologic and evolutive patterns different from those of aortic dissection. The aim of this study was to determine the mortality and predictive factors of IMH in the first 3 months of evolution. METHODS AND RESULTS: Sixty-eight consecutive patients diagnosed of IMH (12 type A, 56 type B) were prospectively studied. Ten patients (eight type A, two type B) were surgically treated for clinical or haemodynamic evolution. Mortality rate was 19% (six type A and seven type B): five surgically treated (three type A, two type B) and eight medically treated (three type A, five type B). No relationship was observed between clinical variables and evolution. Maximum aortic diameter was greater in the group of patients who died (65.5+/-14.4 mm vs 46.0+/-7.6 mm; P<0.0001). Mortality rate in patients with aortic diameter >50 mm was 50% (P<0.0001). Significant periaortic bleeding was mortality-related (47%; P<0.005). Multivariate analysis showed only a significant relationship between mortality and maximum aortic diameter >50 mm (OR=11.33; P<0.005) and ascending aorta involvement (OR=11.18; P<0.05). CONCLUSION: Intramural haematoma mortality in the first 3 months of evolution is high (19%). Maximum aortic diameter >50 mm and ascending aorta involvement are predictive of early mortality.

Aged↗

PubMed2005

Dilated-hypokinetic evolution of hypertrophic cardiomyopathy: prevalence, incidence, risk factors, and prognostic implications in pediatric and adult patients.

OBJECTIVES: This study sought to investigate the incidence, risk factors, and prognosis of dilated-hypokinetic evolution in a large cohort of patients with hypertrophic cardiomyopathy (HCM) followed up at a cardiology center serving both the pediatric and the adult population. BACKGROUND: The available data on this evolution of HCM mainly regards prevalence (rather than incidence) in adults, with very little being known about the pediatric population. METHODS: A total of 222 consecutive HCM patients (65% men, 19% < or =18 years old) were prospectively evaluated for a mean follow-up of 11 +/- 9 years. RESULTS: A diagnosis of dilated-hypokinetic HCM was made in 12 patients at first evaluation (11 without previous septal myectomy surgery; prevalence, 4.9%). Twelve of the 210 patients with classic HCM at first evaluation underwent dilated-hypokinetic evolution (incidence, 5.3/1,000 patient-years). Patients with prevalent/incident dilated-hypokinetic evolution were younger at first evaluation (32 +/- 14 years vs. 41 +/- 21 years, p = 0.04) and more often had a family history of HCM (61% vs. 26%, p = 0.002) or sudden death (43% vs. 19%, p = 0.01) with respect to patients who maintained classic HCM. Moreover, they showed greater interventricular septum (23 +/- 3 mm vs. 19 +/- 6 mm, p = 0.004) and posterior wall (15 +/- 3 mm vs. 13 +/- 4 mm, p = 0.006) thickness. Cardiovascular death-free survival was lower among patients with dilated-hypokinetic HCM (p < 0.04). Cox proportional hazards regression analysis identified left ventricular wall thickness (hazard ratio [HR] = 1.07; 95% confidence interval [CI], 1.01 to 1.14; p = 0.03) and end-diastolic diameter (HR = 1.08; 95% CI 1.04 to 1.11; p = 0.0001) as independent predictors of cardiovascular death. CONCLUSIONS: Dilated-hypokinetic evolution is rare but not exceptional in HCM. Young age at diagnosis, family history of HCM, and greater wall thickness are incremental risk factors for dilated-hypokinetic HCM, which carries an ominous prognosis.

Adolescent↗

PubMed2005

Experimental implementation of local adiabatic evolution algorithms by an NMR quantum information processor.

Quantum adiabatic algorithm is a method of solving computational problems by evolving the ground state of a slowly varying Hamiltonian. The technique uses evolution of the ground state of a slowly varying Hamiltonian to reach the required output state. In some cases, such as the adiabatic versions of Grover's search algorithm and Deutsch-Jozsa algorithm, applying the global adiabatic evolution yields a complexity similar to their classical algorithms. However, using the local adiabatic evolution, the algorithms given by J. Roland and N.J. Cerf for Grover's search [J. Roland, N.J. Cerf, Quantum search by local adiabatic evolution, Phys. Rev. A 65 (2002) 042308] and by Saurya Das, Randy Kobes, and Gabor Kunstatter for the Deutsch-Jozsa algorithm [S. Das, R. Kobes, G. Kunstatter, Adiabatic quantum computation and Deutsh's algorithm, Phys. Rev. A 65 (2002) 062301], yield a complexity of order N (where N=2(n) and n is the number of qubits). In this paper, we report the experimental implementation of these local adiabatic evolution algorithms on a 2-qubit quantum information processor, by Nuclear Magnetic Resonance.

Journal Article↗

PubMed2005

Quantitative magnetization transfer by trains of radio frequency pulses in human brain: extension of a free evolution model to continuous-wave-like conditions.

A theoretical model of free evolution between repeated magnetic transfer (MT) pulses was extended to continuous-wave (CW)-like conditions showing that only the repetitive "direct" saturation of bulk water changes the transient and stationary behavior. The influence of the pulse repetition period (PR) on progressive saturation was studied in cortical gray matter (GM) and central white matter (WM) under conditions of short periods of free evolution and strong macromolecular saturation. Interpulse delays of 3 ms were achieved in vivo on a 1.5-T MR system with bell-shaped MT pulses of 12-ms duration and nominal flip angles of up to 1440 degrees and single-shot readout by a stimulated echo acquisition mode localization sequence. The frequency offset was chosen between 1 and 3 kHz to avoid excessive direct saturation. The stationary MT ratio (MTR) followed an inverse linear PR dependence, showing a consistent partial saturation of about 90% at zero PR for both WM and GM. Comparison to a relaxation-matched liquid indicated the presence of MT, but not necessarily of direct saturation. The transient behavior indicated considerable direct saturation, but this could also be explained by MT. These inconsistencies showed that the intervals of time evolution in our experiments were too long to be modeled by CW-like conditions. Free evolution takes place during the whole PR rather than during the interpulse delay only. Quantification using the rates of free evolution theory yielded the saturations and rate constants necessary to explain the observed behavior. The theory of rapid CW-like pulsing provides an upper limit for the rate of progressive saturation. This limit is approached at PR below an estimated value of 5 ms. The phenomenological PR dependence of the steady-state MTR may indicate that MT exceeded the direct saturation. Unlike to an idealized CW experiment, the extrapolated value at zero PR is subject to direct effects and not a physically meaningful constant.

Adult↗

PubMed2004

[Evolution study in children with suspected obstructive sleep apnea].

INTRODUCTION: Obstructive sleep apnea syndrome is a common disorder in childhood with an uncertain evolution. OBJECTIVES: Study of children's clinical evolution with suspected diagnosis of OSAS, which was carried out after two years of an overnight polisomnogram. PATIENTS AND METHODS: 73 children were studied. We evaluated if they had been operated and what type of surgery was performed, Brouillete Scale and subjective impressions. We have correlated: age, clinical evolution and surgery. RESULTS: Age was inversely correlated with changes in Brouillete (r=-0.39, p=0.002), standing out that children that underwent surgery were younger (4.1 vs. 7.0 years, Student t: -4.22, p=0.00009). Without the influence of age, the difference between evolution in operated and not operated ones was not significative, statistically speaking, but it was if we analysed the different types of surgery by themselves (Snedecor F: 3.9, p=0.007), tonsillectomy was the larger. CONCLUSION: The middle-term evolution in children with OSAS is good if we use the correct treatment.

Adenoidectomy↗

PubMedDate not supplied

[Characteristics and evolution of cardiopulmonary arrest in children in Spain: comparison between autonomous communities].

INTRODUCTION: In Spain there are many differences between autonomous regions in terms of geography, population distribution and health care organisation. We do not know if these differences could have influenced the characteristics and evolution of cardiopulmonary arrest in children. PATIENTS AND METHODS: A secondary analysis of data from a prospective, multicenter and previously published study, analysing cardiorespiratory arrest in children was made to compare the characteristics and evolution of cardiopulmonary arrest in children depending on the region where the arrest occurred. We studied 283 children aged between 7 days and 17 years who suffered respiratory or cardiopulmonary arrest. Data were recorded according to the international Utstein style recommendations. Patients were classified according to the autonomous region where the cardiac arrest occurred: Catalonia (94 cases), Andalusia (64 cases), Madrid (61 cases) and the rest of the regions (64 patients). A statistical analysis was performed to compare the characteristics of cardiac arrest, resuscitation, evolution and survival between the four groups. RESULTS: Sixty percent of patients initially survived the cardiac arrest episode and 33% (94 patients) were still alive one year later. No significant differences in the characteristics of arrest, resuscitation and evolution were found when the autonomous regions were compared. Even though the differences were not statistically significant, there was a tendency to less than expected survival in Andalusia and higher than expected survival in Catalonia. CONCLUSIONS: There are no important differences in the characteristics of pediatric cardiopulmonary arrest, resuscitation, evolution and survival between the autonomous regions in Spain. Additional studies are needed to analyze the hypothetical influence of health care organization and life support training on survival.

Adolescent↗

PubMed1981

[Value of quantitative serial EEG analysis during supervision of evolutive cerebral diseases (author's transl)].

The authors emphasize the value of quantitative EEG analysis in patients with acute or subacute evolutive diseases, who have undergone serial EEG records. On the basis of the power spectra, the topographical distribution of the different frequency components and their changes during disease evolution, it is shown (by 142 investigations in 44 patients with various evolutive cerebral diseases) that these analyses (with their immediately interpretable histographic representation) are able: (1) to follow the step-by-step evolution of the disease and to apprehend the (favourable or unfavourable) evolutive tendencies of the cerebral process in a condensed form and often before the appearance of typical clinical and electroencephalographic disturbances; (2) to note a focalisation or lateralisation which does not always clearly appear with the clinical or conventional electroencephalographic data.

Acute Disease↗

PubMed1990

Glu-69 of the D2 protein in photosystem II is a potential ligand to Mn involved in photosynthetic oxygen evolution.

To probe the involvement of amino acid residues of the D2 protein in the water-splitting process in photosystem II, site-directed mutagenesis was applied to identify D2 residues that might contribute to binding the Mn cluster involved in oxygen evolution. Mutation of Glu-69 to Gln or Val in D2 of the cyanobacterium Synechocystis sp. PCC 6803 was found to lead to a loss of photoautotrophic growth. However, in cells of the Gln mutant (E69Q) a significant Hill reaction rate could be observed upon the start of illumination, but the oxygen evolution rate declined with a half-time of approximately 1 min. Addition of 1 mM Mn2+ stabilized oxygen evolution in E69Q thylakoids. Other divalent cations were ineffective in specific stabilization. When the water-splitting system was bypassed, the rate of electron transport remained stable during illumination, indicating that the inactivation of oxygen evolution is localized in the water-splitting complex. We interpret these observations to indicate that Glu-69 is a Mn ligand and that the loss of oxygen evolution in the E69Q mutant upon turnover of PS II is initiated by changes in the Mn cluster, possibly leading to Mn release from the water-splitting complex. The addition of exogenous Mn to E69Q thylakoids may help to keep the Mn cluster active for a longer time, perhaps by providing Mn to rebind in the cluster after release of one Mn and before the Mn cluster had disintegrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗

PubMed2006

Effect of particle age (Fe0 content) and solution pH on NZVI reactivity: H2 evolution and TCE dechlorination.

Subsurface injection of nanoscale zerovalent iron (NZVI) has been used for the in situ remediation of chlorinated solvent plumes and DNAPL source zones. Due to the cost of materials and placement,the efficacy of this approach depends on the NZVI reactivity and longevity, selectivity for the target contaminant relative to nonspecific corrosion to yield H2, and access to the Fe0 in the particles. Both the reaction pH and the age of the particles (i.e., Fe0 content) could affect NZVI reactivity and longevity. Here, the rates of H2 evolution and trichloroethene (TCE) reduction are measured over the lifetime of the particles and at solution pH ranging from 6.5 to 8.9. Crystalline reactive nanoscale iron particles (RNIP) with different initial Fe0 weight percent (48%, 36%, 34%, 27%, and 9.6%) but similar specific surface area were studied. At the equilibrium pH for a Fe(OH)2/H2O system (pH = 8.9), RNIP exhibited first-order decay for Fe0 corrosion (H2 evolution) with respect to Fe0 content with a Fe0 half-life time of 90-180 days. A stable surface area-normalized TCE reduction rate constant 1.0 x 10(-3)L x hr(-1) x m(-2) was observed after 20 days and remained constant for 160 days, while the Fe0 content of the particles decreased by half, suggesting that TCE reduction is zero-order with respect to the Fe0 content of the particle. Solution pH affected H2 evolution and TCE reduction to a different extent. Decreasing pH from 8.9 to 6.5 increased the H2 evolution rate constant 27 fold from 0.008 to 0.22 day(-1), but the TCE dechlorination rate constant only doubled. The dissimilarities between the reaction orders of H2 evolution and TCE dechlorination with respect to both Fe0 content and H+ concentration suggest that different rate controlling steps are involved for the reduction reactions.

Hydrogen↗