Order Decay Rate Constants Research Articles

Method development for thermal desorption-gas chromatography-tandem mass spectrometry (TD-GC–MS/MS) analysis of trace level fluorotelomer alcohols emitted from consumer products

The scientific foundation for per- and polyfluoroalkyl substances (PFAS) measurements in water, soils, sediments, biosolids, biota, and outdoor air has rapidly expanded; however, there are limited efforts devoted to developing analytical methods to measure vapor-phase PFAS in indoor air. A gas chromatography-tandem mass spectrometry (GC–MS/MS) method coupled with thermal desorption (TD) sorbent tube analysis was developed to quantify trace levels of fluorotelomer alcohols (FTOHs) emitted from consumer products in the indoor environment. Method evaluation included determination of instrument detection limits (IDLs), quality assurance checks of target standards purchased from different vendors, sample loss during storage, and TD sorbent breakthrough with tubes coupled in-series. The IDLs for TD-GC–MS/MS analyses ranged from 0.07 – 0.09 ng/tube. No significant loss of FTOHs was observed during stability tests over 28 days with relative standard deviations (RSDs) of spiked TD tubes ranging from 3.1 – 7.7% and the RSDs of polypropylene copolymer vial storage of standard solutions ranging from 4.3 – 8.4%. TD tube breakthrough was minimal with recovered FTOHs in the second tubes <1% of the spiked concentrations in the first tubes with carrier gas volume up to 20 L. The method has been applied to determine FTOH emissions from three consumer products in micro-scale chambers. A liquid stone cleaner/sealer product contained the highest levels of 6:2, 8:2, and 10:2 FTOHs, while the mattress pad products contained lower levels of 8:2 and 10:2 FTOHs. The emission parameters, including the initial emission factors and first order decay rate constants, were obtained based on the experimental data. The developed methods are sensitive and specific for analysis of all four target FTOHs (4:2, 6:2, 8:2, 10:2 FTOHs) with chamber testing. The methods can be extended to indoor air sampling and could be applicable to ambient air sampling.

Analysis of Growth Inhibition for Microcystis aeruginosa with Periodic Ultrasonic Irradiations

Objectives : To confirm both efficiency and sustainability of algal growth inhibition, various laboratory-scale experiments were conducted and the growth inhibitory effect of Microcystis aeruginosa (M. aeruginosa) was investigated through ultrasonic re-irradiation during the regrowth period after the first ultrasound irradiation.Methods : Experiments with different times of irradiation [i.e., control group A (0 hr), experimental group B (2 hr) applied with only the first ultrasound irradiation, and experimental group C (0.5 hr), D (1 hr), and E (1.5 hr) applied with both first and second irradiations] were performed.Results and Discussion : As a result of both Chlorophyll-a (Chl-a) concentration and cell number of M. aeruginosa, the experimental group (B) with only first ultrasound irradiation (2 hr) displayed rapid regrowth of algae after initial decrease whereas the experimental group (C, D, and E) with both first ultrasound irradiation (2 hr) and second ultrasound irradiation (0.5 hr, 1 hr, and 1.5 hr) confirmed the delay of algae regrowth. Based on the specific growth rate constant (µ) and first order decay rate constant (k), algal growth from the experimental groups (C, D, E) with the secondary ultrasound irradiation was more significantly inhibited due to repetitive inactivation of algae growth. According to the SEM and TEM results, damages to algae cells were clearly observed under the influence of ultrasound, and both decrease in gas vesicles and rupture of cell membrane in M. aeruginosa were also monitored.Conclusion : Through this study, the algae growth inhibitory effect by ultrasonic irradiations was confirmed, and the re-irradiation of ultrasound contributed to the repetitive inactivation of algae growth, indicating that the second ultrasonic irradiation time required to inhibit algal regrowth can be reduced compared to the first irradiation. Therefore, periodic ultrasonic irradiation is required for long-term inhibition of algae growth in stagnant waters, but the appropriate frequency of ultrasonic irradiation may vary depending on the influence of various complex factors such as the size of the stagnant waters, the frequency of algal blooms, water temperature, light irradiation, nutrients, flow rate, etc. Finally, many field studies under various conditions are warranted to establish an optimized ultrasound irradiation protocol.

Evaluation of 1,4-dioxane attenuation processes at the Gelman Site, Michigan, USA

1,4-Dioxane released at the Gelman Site in Washtenaw County, Michigan, produced a series of contaminant plumes migrating up to 3 km through a heterogenous glacial aquifer system. An analysis of 1,4-dioxane concentrations in the Eastern Area of the Gelman Site between 2011 and 2017 documented a mass balance deficit of 2200 kg in excess of 2100 kg of 1,4-dioxane removed via remediation. Five mechanisms were evaluated to account for the mass deficiency: sorption, matrix diffusion, biodegradation, surface discharge, and bypass of the existing monitoring well network.The mass of 1,4-dioxane sorbed to aquifer and aquitard materials and the mass of 1,4-dioxane diffused into low permeability zones were estimated. However, decreasing aqueous concentrations across most of the contaminated area between 2011 and 2017 are expected to induce desorption and back diffusion during this period. Surface water discharge to a storm drain in the downgradient portion of the site was analyzed using concentration measurements and stream gage data. Results suggest that 1,4-dioxane mass entering the drain during the period between 2011 and 2017 was insufficient to account for the mass deficiency.Although available geochemical measurements indicate predominantly anaerobic aquifer conditions at the Gelman Site, biodegradation of 1,4-dioxane was estimated using first order decay rate constants from other sites where conditions may be more favorable. Results suggest that biodegradation could explain some but not all of the missing mass.Bypass of the downgradient monitoring well network is the most parsimonious explanation for the 1,4-dioxane mass deficit. This conclusion is supported by documented flow path complexity through the aquifer system and the sparse density of monitoring wells in the downgradient Eastern Area. These findings underscore the importance of characterizing aquifer heterogeneity when modeling and remediating persistent groundwater contaminants such as 1,4-dioxane.

Photoinactivation of uncultured, indigenous enterococci.

Enterococci are used to monitor recreational water quality worldwide, so understanding their fate and transport in the environment is essential to the protection of human health. As such, researchers have documented enterococci inactivation under various exposure conditions and in diverse water matrices. However, the majority of studies have been performed using lab-cultured bacteria, which are distinct from indigenous, uncultured bacteria found in the environment. Here we investigate the photoinactivation of indigenous, uncultured enterococci from a range of sources, including wastewater treatment plants (WWTPs), marine beaches, urban streams, and a wastewater-influenced pond. We concentrated indigenous enterococci from their sources using filtration and centrifugation, placed them in a clear buffer solution, and then exposed them to simulated sunlight to measure their photoinactivation rates. First order decay rate constants (k) of indigenous, uncultured enterococci spanned an order of magnitude, from 0.3 to 2.3 m2 kJUVB-1. k values of indigenous enterococci from WWTPs tended to be larger than those from surface waters. The k value of lab-cultured Enterococcus faecalis was larger than those of indigenous, uncultured enterococci from most sources. Negative associations between the fraction of pigmented enterococci and sunlight susceptibility were observed. This work suggests that caution should be taken when extending results on bacterial photoinactivation obtained using lab-cultured bacteria to environmental bacteria, and that enterococci pigmentation may be a useful metric for estimating photoinactivation rate constants.

Can We Swim Yet? Systematic Review, Meta-Analysis, and Risk Assessment of Aging Sewage in Surface Waters.

This study investigated the risk of gastrointestinal illness associated with swimming in surface waters with aged sewage contamination. First, a systematic review compiled 333 first order decay rate constants ( k) for human norovirus and its surrogates feline calicivirus and murine norovirus, Salmonella, Campylobacter, Escherichia coli O157:H7, Giardia, and Cryptosporidium, and human-associated indicators in surface water. A meta-analysis investigated effects of sunlight, temperature, and water matrix on k. There was a relatively large number of k for bacterial pathogens and some human-associated indicators ( n > 40), fewer for protozoans ( n = 14-22), and few for human norovirus and its Caliciviridae surrogates ( n = 2-4). Average k ranked: Campylobacter > human-associated markers > Salmonella> E. coli O157:H7 > norovirus and its surrogates > Giardia > Cryptosporidium. Compiled k values were used in a quantitative microbial risk assessment (QMRA) to simulate gastrointestinal illness risk associated with swimming in water with aged sewage contamination. The QMRA used human-associated fecal indicator HF183 as an index for the amount of sewage present and thereby provided insight into how risk relates to HF183 concentrations in surface water. Because exposure to norovirus contributed the majority of risk, and HF183 k is greater than norovirus k, the risk associated with exposure to a fixed HF183 concentration increases with the age of contamination. Swimmer exposure to sewage after it has aged ∼3 days results in median risks less than 30/1000. A risk-based water quality threshold for HF183 in surface waters that takes into account uncertainty in contamination age is derived to be 4100 copies/100 mL.

Solar Inactivation of Enterococci and Escherichia coli in Natural Waters: Effects of Water Absorbance and Depth.

The decay of sewage-sourced Escherichia coli and enterococci was measured at multiple depths in a freshwater marsh, a brackish water lagoon, and a marine site, all located in California. The marine site had very clear water, while the waters from the marsh and lagoon contained colored dissolved organic matter that not only blocked light but also produced reactive oxygen species. First order decay rate constants of both enterococci and E. coli were between 1 and 2 d(-1) under low light conditions and as high as 6 d(-1) under high light conditions. First order decay rate constants were well correlated to the daily average UVB light intensity corrected for light screening incorporating water absorbance and depth, suggesting endogenous photoinactivation is a major pathway for bacterial decay. Additional laboratory experiments demonstrated the presence of colored dissolved organic matter in marsh water enhanced photoinactivation of a laboratory strain of Enterococcus faecalis, but depressed photoinactivation of sewage-sourced enterococci and E. coli after correcting for UVB light screening, suggesting that although the exogenous indirect photoinactivation mechanism may be active against Ent. faecalis, it is not for the sewage-source organisms. A simple linear regression model based on UVB light intensity appears to be a useful tool for predicting inactivation rate constants in natural waters of any depth and absorbance.

Characterizing the biotransformation of sulfur-containing wastes in simulated landfill reactors

Landfills that accept municipal solid waste (MSW) in the U.S. may also accept a number of sulfur-containing wastes including residues from coal or MSW combustion, and construction and demolition (C&D) waste. Under anaerobic conditions that dominate landfills, microbially mediated processes can convert sulfate to hydrogen sulfide (H2S). The presence of H2S in landfill gas is problematic for several reasons including its low odor threshold, human toxicity, and corrosive nature. The objective of this study was to develop and demonstrate a laboratory-scale reactor method to measure the H2S production potential of a range of sulfur-containing wastes. The H2S production potential was measured in 8-L reactors that were filled with a mixture of the target waste, newsprint as a source of organic carbon required for microbial sulfate reduction, and leachate from decomposed residential MSW as an inoculum. Reactors were operated with and without N2 sparging through the reactors, which was designed to reduce H2S accumulation and toxicity. Both H2S and CH4 yields were consistently higher in reactors that were sparged with N2 although the magnitude of the effect varied. The laboratory-measured first order decay rate constants for H2S and CH4 production were used to estimate constants that were applicable in landfills. The estimated constants ranged from 0.11yr−1 for C&D fines to 0.38yr−1 for a mixed fly ash and bottom ash from MSW combustion.

Deuteration of Perylene Enhances Photochemical Upconversion Efficiency

Photochemical upconversion via triplet-triplet annihilation is a promising technology for improving the efficiency of photovoltaic devices. Previous studies have shown that the efficiency of upconversion depends largely on two rate constants intrinsic to the emitting species. Here, we report that one of these rate constants can be altered by deuteration, leading to enhanced upconversion efficiency. For perylene, deuteration decreases the first order decay rate constant by 16 ± 9% at 298 K, which increases the linear upconversion response by 45 ± 21% in the low excitation regime.

Urban Sediment Transport through an Established Vegetated Swale: Long Term Treatment Efficiencies and Deposition

Vegetated swales are an accepted and commonly implemented sustainable urban drainage system in the built urban environment. Laboratory and field research has defined the effectiveness of a vegetated swale in sediment detention during a single rainfall-runoff event. Event mean concentrations of suspended and bed load sediment have been calculated using current best analytical practice, providing single runoff event specific sediment conveyance volumes through the swale. However, mass and volume of sediment build up within a swale over time is not yet well defined. This paper presents an effective field sediment tracing methodology and analysis that determines the quantity of sediment deposited within a swale during initial and successive runoff events. The use of the first order decay rate constant, k, as an effective pollutant treatment parameter is considered in detail. Through monitoring tagged sediment deposition within the swale, the quantity of sediment that is re-suspended, conveyed, re-deposited or transported out of the swale as a result of multiple runoff events is illustrated. Sediment is found to continue moving through the vegetated swale after initial deposition, with ongoing discharge resulting from resuspension and conveyance during subsequent runoff events. The majority of sediment initially deposited within a swale is not detained long term or throughout its design life of the swale.

In Vivo inactivation of nitric oxide in the rat CNS:Quantitative and mechanistic features

Event Abstract Back to Event In Vivo inactivation of nitric oxide in the rat CNS:Quantitative and mechanistic features Ricardo M. Santos1*, Catia F. Lourenco1, Greg A. Gerhardt2, Joao Laranjinha1, 3 and Rui M. Barbosa1, 3 1 University of Coimbra, Center for Neuroscience and Cell Biology, Portugal 2 University of Kentucky, Center for Microelectrode Technology, United States 3 University of Coimbra, Faculty of Pharmacy, Portugal Nitric oxide (NO) is a ubiquitous free radical neuromodulator that conveys information associated with its concentration dynamics in brain tissue. The regulation of its enzymatic production is strongly substantiated but, conversely, the lack of studies regarding NO inactivation in vivo in the brain, largely due to the difficulty of its direct measurement at low concentrations with high temporal resolution, has prevented the elucidation of its neuromodulatory role on mechanistic and quantitative basis. In this study, we experimentally addressed the kinetics of NO inactivation in vivo in the rat brain cortex and hippocampal CA1 region by measuring locally applied NO with home-made NO selective carbon fiber microelectrodes stereotaxically inserted into the selected brain regions.We found that NO is strongly inactivated in the rat brain in vivo, with apparent first order kinetics, for NO concentrations below 2 μM. Apparent first order decay rate constants (k) of NO signals decreased in a sigmoid fashion with increasing NO concentrations in vivo from 0.93 to 0.51 s-1 (EC50 = 16.6 μM) and from 1.05 to 0.57 s-1 (EC50 = 3.2 μM) in the cortex and hippocampus, respectively, suggesting distinct ability of these brain regions to inactivate NO. Based on mathematical modeling of NO signals, we estimate that, below 2 μM, inactivation reactions impose an NO half-life of 0.75 s in the cortex and 0.56 s in the hippocampus.After inducing global ischemia, NO signals amplitude increased and k values decreased to diffusion values (similar to those in agarose gel used as control for NO diffusion). These observations together with our kinetic results suggest a non-saturable mechanism of NO removal and blood flow as determinant for brain ability to inactivate NO in vivo. Moreover, preliminary experiments, concerning the simultaneous measurement of NO and oxygen tension in the brain in vivo, suggest that NO inactivation is largely independent of oxygen tension. Based on our results, we propose hemoglobin as a major contributor for the observed NO decay in vivo in the brain. Conference: 11th Meeting of the Portuguese Society for Neuroscience, Braga, Portugal, 4 Jun - 6 Jun, 2009. Presentation Type: Poster Presentation Topic: Neuronal Communication Citation: Santos RM, Lourenco CF, Gerhardt GA, Laranjinha J and Barbosa RM (2009). In Vivo inactivation of nitric oxide in the rat CNS:Quantitative and mechanistic features. Front. Neurosci. Conference Abstract: 11th Meeting of the Portuguese Society for Neuroscience. doi: 10.3389/conf.neuro.01.2009.11.127 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 11 Aug 2009; Published Online: 11 Aug 2009. * Correspondence: Ricardo M Santos, University of Coimbra, Center for Neuroscience and Cell Biology, Alicante, Portugal, ricardo_dos_santos@hotmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Ricardo M Santos Catia F Lourenco Greg A Gerhardt Joao Laranjinha Rui M Barbosa Google Ricardo M Santos Catia F Lourenco Greg A Gerhardt Joao Laranjinha Rui M Barbosa Google Scholar Ricardo M Santos Catia F Lourenco Greg A Gerhardt Joao Laranjinha Rui M Barbosa PubMed Ricardo M Santos Catia F Lourenco Greg A Gerhardt Joao Laranjinha Rui M Barbosa Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Production and decomposition dynamics of hydrogen peroxide in freshwater

Environmental context. Hydrogen peroxide (H2O2) is the most stable reactive oxygen species (ROS) formed through irradiation of chromophoric dissolved organic matter (CDOM) in freshwater. It can act as a reductant or as an oxidant and decays largely through interaction with microorganisms via unknown mechanisms. In this way it can affect biological and chemical processes in natural waters and thus shape the ecosystem biogeochemistry. Abstract. Hydrogen peroxide (H2O2) is widely recognised as the most stable of the reactive oxygen species produced by solar radiation-driven photochemical reactions in natural waters. H2O2 concentrations were determined in a shallow fresh water system (water of Leith, Dunedin, New Zealand) by flow-injection analysis (FIA) using an acridinium ester chemiluminescent reaction system. Daytime measurements of H2O2 concentration showed a rapid increase from early morning (15 nM) to 1300 hours (491 nM), consistent with photochemical formation, lagging maximum solar irradiance by ~1.5 h. The wavelength dependency of H2O2 formation was studied and it was shown that UV-B, UV-A and PAR contributed 40, 33 and 27%, respectively. The average formation rate was 339 nM h–1 during springtime. The influence of biotic communities on the rate of H2O2 decomposition was also studied and the majority of decomposition was due to particles smaller than 0.22 μm. The overall first order decay rate constant was of the order of 7.1 h–1. The bacterial and algal communities in the water column and on the riverbed were primarily responsible for the decomposition of H2O2.

Antioxidant and radioprotective effect of the active fraction of Pilea microphylla (L.) ethanolic extract

The ethanolic extract of Pilea microphylla (L.) was defatted, successively fractionated with acetone and the residue so obtained was found to be most potent when subjected to detailed free radical scavenging and in vivo radioprotection studies. The most active fraction reacts with free radicals, such as DPPH (50 microM), ABTS(.)(-) (100 microM) and (.)OH (generated by Fenton reaction) with IC(50) value of 23.15 microg/ml, 3.0 microg/ml and 310 microg/ml, respectively. The most active fraction inhibited iron-induced lipid peroxidation in phosphatidyl choline liposomes with an IC(50) of 13.74 microg/ml. The kinetics of scavenging of DPPH and ABTS(.)(-) radicals were followed at different concentrations of the fraction by employing stopped-flow studies. The observed first order decay rate constants at 200 microg/ml and 50 microg/ml of fraction with DPPH (50 microM) and ABTS(.)(-) (50 microM) were found to be 0.4s(-1) and 2.1s(-1), respectively. The fraction when screened for in vivo radioprotection in Swiss albino mice showed 80% protection at a dose of 900 mg/kg and with a DRF of about 1.12. The fraction was also found to protect livers of irradiated mice from depletion of endogenous antioxidant enzymes like glutathione, GST, SOD, catalase and thiols. The fraction also protected the villi height, increased the number of crypt cells while offering general protection to the intestine from acute radiation effects. The fraction also protected the hematopoietic system as assessed by endogenous spleen colony assay, contributing to the overall radioprotective ability.

A Laser Flash Photolysis Study of Electron Transfer Processes of [Ru(bpy)3]2+ in High Magnetic Field

Abstract The effect of high magnetic fields (≤13 T) on the charge transfer reaction between Ru(II) tris(2,2′-bipyridine) and methylviologen is studied by laser flash photolysis in a pulse magnet. The initial yield of the methylviologen radical decreases by about 20% at 13 T and the second order decay rate constant of the escaped radicals increases as the magnetic field increases. These effects of high magnetic field are interpreted in terms of the Δg mechanism with strong spin-orbit coupling proposed by Steiner et al.

ChemInform Abstract: External Heavy‐Atom Effects on First and Second Order Decay Rate Constants of Anthracene Triplets.

AbstractSecond‐order rate constants for quenching of anthracene triplets, 3A*, by methyl iodide in benzene and ethyl iodide in methylcyclohexane are determined flash kinetically.

External heavy-atom effects on first and second order decay rate constants of anthracene triplets

External heavy-atom effects on first and second order decay rate constants of anthracene triplets

THE PHOTOREDUCTION OF METHYLENE BLUE BY ARYLAMINOMETHANE‐SULFONATES

Abstract— The photoreduction of methylene blue in the presence of arylaminomethanesulfonates (RAMS = RC6H4NHCH2SO3Na) was studied by laser and conventional flash photolysis. These compounds quenched the methylene blue triplet deviating from a normal Stern‐Volmer behaviour. For low quencher concentrations, a Rehm‐Weller relationship was found between the kq's and the DLG's obtained for the electron transfer reactions. The lack of further quenching at higher [RAMS] is ascribed to the formation of a ground state ion pair between the dye and the anionic quencher which, on excitation, forms a triplet state unable to under go electron transfer for steric reasons. A second order decay rate constant was found for the semireduced species (MB') (ca. 5 × 109M‐1 s‐1, independent of the RAMS used) and is attributed to a proton transfer from the radical zwitterion (RC6H4NH CH2SO3−) to MB. The overall dependence on the substituent of the bleaching observed by continuous irradiation follows the triplet behaviour.

Laser flash studies of thioindigo and indigo dyes. Evidence for a trans configuration of the triplet state

The triplet-triplet absorption spectra of thioindigo, 5,5′-di-t-amylthioindigo, 5,5′-di-neopentylthioindigo, and N,N′-diacetylindigo in glycerol triacetate (GT) and in EPA were found to be practically the same in fluid and rigid media. The logarithms of the first order decay rate constants depend linearly on T−1. In GT and 2-methyltetrahydrofuran (MTHF) temperature and viscosity cause a strong decrease of φt-c, whereas the right yield remanis constant. The results indicate that the lowest triplet state of the thioindigo dyes has predominantly a planar trans configuration (tr3). The twisted configuration (p3) is suggested to be in thermal equilibrium with tr3 at room temperature. Triplet decay in liquid solution occurs via intersystem crossing from p3 to the twisted ground state (p3 - p0).