Publications by authors named "Shohei Hattori"

22 Publications

  • Page 1 of 1

Isotopic evidence for acidity-driven enhancement of sulfate formation after SO emission control.

Sci Adv 2021 May 5;7(19). Epub 2021 May 5.

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Yokohama 226-8502, Japan.

After the 1980s, atmospheric sulfate reduction is slower than the dramatic reductions in sulfur dioxide (SO) emissions. However, a lack of observational evidence has hindered the identification of causal feedback mechanisms. Here, we report an increase in the oxygen isotopic composition of sulfate ([Formula: see text]) in a Greenland ice core, implying an enhanced role of acidity-dependent in-cloud oxidation by ozone (up to 17 to 27%) in sulfate production since the 1960s. A global chemical transport model reproduces the magnitude of the increase in observed [Formula: see text] with a 10 to 15% enhancement in the conversion efficiency from SO to sulfate in Eastern North America and Western Europe. With an expected continued decrease in atmospheric acidity, this feedback will continue in the future and partially hinder air quality improvements.
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http://dx.doi.org/10.1126/sciadv.abd4610DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8099192PMC
May 2021

Development of Microdroplet Generation Method for Organic Solvents Used in Chemical Synthesis.

Molecules 2020 Nov 17;25(22). Epub 2020 Nov 17.

Department of Electronic and Physical Systems, School of Fundamental Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 145-0065, Japan.

Recently, chemical operations with microfluidic devices, especially droplet-based operations, have attracted considerable attention because they can provide an isolated small-volume reaction field. However, analysis of these operations has been limited mostly to aqueous-phase reactions in water droplets due to device material restrictions. In this study, we have successfully demonstrated droplet formation of five common organic solvents frequently used in chemical synthesis by using a simple silicon/glass-based microfluidic device. When an immiscible liquid with surfactant was used as the continuous phase, the organic solvent formed droplets similar to water-in-oil droplets in the device. In contrast to conventional microfluidic devices composed of resins, which are susceptible to swelling in organic solvents, the developed microfluidic device did not undergo swelling owing to the high chemical resistance of the constituent materials. Therefore, the device has potential applications for various chemical reactions involving organic solvents. Furthermore, this droplet generation device enabled control of droplet size by adjusting the liquid flow rate. The droplet generation method proposed in this work will contribute to the study of organic reactions in microdroplets and will be useful for evaluating scaling effects in various chemical reactions.
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http://dx.doi.org/10.3390/molecules25225360DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7697074PMC
November 2020

Temperature control on wastewater and downstream nitrous oxide emissions in an urbanized river system.

Water Res 2020 Dec 19;187:116417. Epub 2020 Sep 19.

Department of Environmental Science and Engineering, Ewha Womans University, Seoul 03760, Republic of Korea. Electronic address:

Although eutrophic urban rivers receiving loads of wastewater represent an important anthropogenic source of NO, little is known as to how temperature and other environmental factors affect temporal variations in NO emissions from wastewater treatment plants (WWTPs) and downstream rivers. Two-year monitoring at a WWTP and five river sites was complemented with available water quality data, laboratory incubations, and stable isotopes in NO and NO to explore how wastewater effluents interact with seasonal changes in environmental conditions to affect downstream metabolic processes and NO emissions from the lower Han River traversing the megacity Seoul. Water quality data from four WWTPs revealed significant inverse relationships between water temperature and the concentrations or fluxes of total N (TN) in effluents. Increased TN fluxes at low temperatures concurred with NO surges in WWTP effluents and downstream rivers, counteracting the long-term decline in TN fluxes resulting from enhanced wastewater treatments. Incubation experiments with river water and sediment, in isolation or combined, implied the hypoxic winter sediment as a large source of NO, whereas the anoxic summer sediment produced a smaller amount of NO only when it was added with oxic water. For both WWTP effluents and downstream rivers, bulk isotope ratios and intramolecular distribution of N in NO distinctly differed between summer and winter, indicating incomplete denitrification in the hypoxic sediment at low temperatures as a primary downstream source adding to WWTP-derived NO. Winter surges in wastewater TN and sediment NO release highlight temperature variability as an underappreciated control over anthropogenic NO emissions from increasingly urbanized river systems worldwide.
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http://dx.doi.org/10.1016/j.watres.2020.116417DOI Listing
December 2020

Isotopic constraints on the formation pathways and sources of atmospheric nitrate in the Mt. Everest region.

Environ Pollut 2020 Dec 15;267:115274. Epub 2020 Aug 15.

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa, 226-8502, Japan; Earth-Life Science Institute, Tokyo Institute of Technology, Meguro-ku, Tokyo, 152-8551, Japan.

Inorganic particulate nitrate (p-NO), gaseous nitric acid (HNO) and nitrogen oxides (NO = NO + NO), as main atmospheric pollutants, have detrimental effects on human health and aquatic/terrestrial ecosystems. Referred to as the 'Third Pole' and the 'Water Tower of Asia', the Tibetan Plateau (TP) has attracted wide attention on its environmental changes. Here, we evaluated the oxidation processes of atmospheric nitrate as well as traced its potential sources by analyzing the isotopic compositions of nitrate (δN, δO, and ΔO) in the aerosols collected from the Mt. Everest region during April to September 2018. Over the entire sampling campaigns, the average of δN(NO), δO(NO), and ΔO(NO) was -5.1 ± 2.3‰, 66.7 ± 10.2‰, and 24.1 ± 3.9‰, respectively. The seasonal variation in ΔO(NO) indicates the relative importance of O and HO/RO/OH in NO oxidation processes among different seasons. A significant correlation between NO and Ca and frequent dust storms in the Mt. Everest region indicate that initially, the atmospheric nitrate in this region might have undergone a process of settling; subsequently, it got re-suspended in the dust. Compared with the ΔO(NO) values in the northern TP, our observed significantly higher values suggest that spatial variations in atmospheric ΔO(NO) exist within the TP, and this might result from the spatial variations of the atmospheric O levels, especially the stratospheric O, over the TP. The observed δN(NO) values predicted remarkably low δN values in the NO of the sources and the N isotopic fractionation plays a crucial role in the seasonal changes of δN(NO). Combined with the results from the backward trajectory analysis of air mass, we suggest that the vehicle exhausts and agricultural activities in South Asia play a dominant role in determining the nitrate levels in the Mt. Everest region.
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http://dx.doi.org/10.1016/j.envpol.2020.115274DOI Listing
December 2020

Constraining the atmospheric OCS budget from sulfur isotopes.

Proc Natl Acad Sci U S A 2020 08 5;117(34):20447-20452. Epub 2020 Aug 5.

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Yokohama 226-8502, Japan.

Carbonyl sulfide (OCS), the most abundant sulfur-containing gas in the atmosphere, is used as a proxy for photosynthesis rate estimation. However, a large missing source of atmospheric OCS has been inferred. Sulfur isotope measurements (S/S ratio and S) on OCS are a feasible tool to distinguish OCS sources from oceanic and anthropogenic emissions. Here we present the latitudinal (north-south) observations of OCS concentration and [Formula: see text]S within Japan. The observed [Formula: see text]S of OCS of 9.7 to 14.5‰ reflects source and sink effects. Particularly in winter, latitudinal decreases in [Formula: see text]S values of OCS were found to be correlated with increases in OCS concentrations, resulting an intercept of (4.7 ± 0.8)‰ in the Keeling plot approach. This result implies the transport of anthropogenic OCS emissions from the Asian continent to the western Pacific by the Asian monsoon outflow. The estimated background [Formula: see text]S of OCS in eastern Asia is consistent with the [Formula: see text]S of OCS previously reported in Israel and the Canary Islands, suggesting that the background [Formula: see text]S of OCS in the Northern Hemisphere ranges from 12.0 to 13.5‰. Our constructed sulfur isotopic mass balance of OCS revealed that anthropogenic sources, not merely oceanic sources, account for much of the missing source of atmospheric OCS.
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http://dx.doi.org/10.1073/pnas.2007260117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7456067PMC
August 2020

Corrigendum to "Isotopic evidence for seasonality of microbial internal nitrogen cycles in a temperate forested catchment with heavy snowfall" [Sci. Total Environ. 69 (2019) 290-299].

Sci Total Environ 2020 Mar 28;710:135552. Epub 2019 Nov 28.

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4529 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan; Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan.

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http://dx.doi.org/10.1016/j.scitotenv.2019.135552DOI Listing
March 2020

Homogeneous sulfur isotope signature in East Antarctica and implication for sulfur source shifts through the last glacial-interglacial cycle.

Sci Rep 2019 08 27;9(1):12378. Epub 2019 Aug 27.

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 226-8502, Yokohama, Japan.

Sulfate aerosol (SO) preserved in Antarctic ice cores is discussed in the light of interactions between marine biological activity and climate since it is mainly sourced from biogenic emissions from the surface ocean and scatters solar radiation during traveling in the atmosphere. However, there has been a paradox between the ice core record and the marine sediment record; the former shows constant non-sea-salt (nss-) SO flux throughout the glacial-interglacial changes, and the latter shows a decrease in biogenic productivity during glacial periods compared to interglacial periods. Here, by ensuring the homogeneity of sulfur isotopic compositions of atmospheric nss-SO (δS) over East Antarctica, we established the applicability of the signature as a robust tool for distinguishing marine biogenic and nonmarine biogenic SO. Our findings, in conjunction with existing records of nss-SO flux and δS in Antarctic ice cores, provide an estimate of the relative importance of marine biogenic SO during the last glacial period to be 48 ± 10% of nss-SO, slightly lower than 59 ± 11% during the interglacial periods. Thus, our results tend to reconcile the ice core and sediment records, with both suggesting the decrease in marine productivity around Southern Ocean under the cold climate.
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http://dx.doi.org/10.1038/s41598-019-48801-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6711983PMC
August 2019

Isotopic evidence for seasonality of microbial internal nitrogen cycles in a temperate forested catchment with heavy snowfall.

Sci Total Environ 2019 Nov 2;690:290-299. Epub 2019 Jul 2.

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, 4529 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8502, Japan; Earth-Life Science Institute (ELSI), Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550, Japan.

The Hokuriku district of central Japan receives high levels of precipitation during winter, largely in the form of snow. This study aimed to elucidate the internal nitrogen dynamics in this temperate forested region with heavy snowfall using the triple oxygen and nitrogen isotopic compositions of NO. The isotopic compositions of NO in atmospheric depositions (P and Tf), with terrestrial components of the soil layer (A0, S25, S55, and S90), ground water (G), and output (St) were measured from 2015 to 2016 in a forested catchment located in the southern area of the Ishikawa Prefecture, Japan. Seasonal distributions of ΔO(NO) showed a decreasing trend from the inputs to outputs of the ecosystem. We found relatively constant ΔO(NO) values in the output components (G and St), but found highly fluctuating ΔO(NO) values resulting from the seasonal variations in the nitrification activity within soil waters. Specifically, we observed a lower nitrifying activity in the top soil layer throughout cold periods, presumably due to the input of cold melted snow water. The general trend of increasing δN(NO) value from the input to output components, with the changes in denitrification hotspots from shallow to deeper soil layer, can be observed between warm and cold periods. Thus, the seasonal changes of hotspots related to microbial nitrification and denitrification could be noted due to the seasonal changes in the isotopic compositions of nitrate. The estimated ecosystem-scale gross nitrification and denitrification rates are low; however, the output components are relatively stable with low concentrations of nitrate, indicating that the plant uptake of nitrogen most probably occurs at greater rates and scales in this forested ecosystem. Future nitrogen deposition and the vulnerable dynamics of snow melting are likely to have impactful consequences on such localities.
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http://dx.doi.org/10.1016/j.scitotenv.2019.06.507DOI Listing
November 2019

Deep-biosphere methane production stimulated by geofluids in the Nankai accretionary complex.

Sci Adv 2018 06 13;4(6):eaao4631. Epub 2018 Jun 13.

Department of Subsurface Geobiological Analysis and Research, JAMSTEC, Yokosuka 237-0061, Japan.

Microbial life inhabiting subseafloor sediments plays an important role in Earth's carbon cycle. However, the impact of geodynamic processes on the distributions and carbon-cycling activities of subseafloor life remains poorly constrained. We explore a submarine mud volcano of the Nankai accretionary complex by drilling down to 200 m below the summit. Stable isotopic compositions of water and carbon compounds, including clumped methane isotopologues, suggest that ~90% of methane is microbially produced at 16° to 30°C and 300 to 900 m below seafloor, corresponding to the basin bottom, where fluids in the accretionary prism are supplied via megasplay faults. Radiotracer experiments showed that relatively small microbial populations in deep mud volcano sediments (10 to 10 cells cm) include highly active hydrogenotrophic methanogens and acetogens. Our findings indicate that subduction-associated fluid migration has stimulated microbial activity in the mud reservoir and that mud volcanoes may contribute more substantially to the methane budget than previously estimated.
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http://dx.doi.org/10.1126/sciadv.aao4631DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007163PMC
June 2018

A simple and reliable method reducing sulfate to sulfide for multiple sulfur isotope analysis.

Rapid Commun Mass Spectrom 2018 Feb;32(4):333-341

School of Materials and Chemical Technology, Tokyo Institute of Technology, 226-8502, Yokohama, Japan.

Rationale: Precise analysis of four sulfur isotopes of sulfate in geological and environmental samples provides the means to extract unique information in wide geological contexts. Reduction of sulfate to sulfide is the first step to access such information. The conventional reduction method suffers from a cumbersome distillation system, long reaction time and large volume of the reducing solution. We present a new and simple method enabling the process of multiple samples at one time with a much reduced volume of reducing solution.

Methods: One mL of reducing solution made of HI and NaH PO was added to a septum glass tube with dry sulfate. The tube was heated at 124°C and the produced H S was purged with inert gas (He or N ) through gas-washing tubes and then collected by NaOH solution. The collected H S was converted into Ag S by adding AgNO solution and the co-precipitated Ag O was removed by adding a few drops of concentrated HNO .

Results: Within 2-3 h, a 100% yield was observed for samples with 0.2-2.5 μmol Na SO . The reduction rate was much slower for BaSO and a complete reduction was not observed. International sulfur reference materials, NBS-127, SO-5 and SO-6, were processed with this method, and the measured against accepted δ S values yielded a linear regression line which had a slope of 0.99 ± 0.01 and a R value of 0.998.

Conclusions: The new methodology is easy to handle and allows us to process multiple samples at a time. It has also demonstrated good reproducibility in terms of H S yield and for further isotope analysis. It is thus a good alternative to the conventional manual method, especially when processing samples with limited amount of sulfate available.
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http://dx.doi.org/10.1002/rcm.8048DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5888127PMC
February 2018

Isotopic Fractionation of Sulfur in Carbonyl Sulfide by Carbonyl Sulfide Hydrolase of Thiobacillus thioparus THI115.

Microbes Environ 2017 Dec 2;32(4):367-375. Epub 2017 Dec 2.

Graduate School of Agriculture, Tokyo University of Agriculture and Technology.

Carbonyl sulfide (COS) is one of the major sources of stratospheric sulfate aerosols, which affect the global radiation balance and ozone depletion. COS-degrading microorganisms are ubiquitous in soil and important for the global flux of COS. We examined the sulfur isotopic fractionation during the enzymatic degradation of COS by carbonyl sulfide hydrolase (COSase) from Thiobacillus thioparus THI115. The isotopic fractionation constant (ɛ value) was -2.2±0.2‰. Under experimental conditions performed at parts per million by volume level of COS, the ɛ value for intact cells of T. thioparus THI115 was -3.6±0.7‰, suggesting that, based on Rees' model, the ɛ value mainly depended on COS transport into the cytoplasm. The ɛ value for intact cells of T. thioparus THI115 was similar to those for Mycobacterium spp. and Williamsia sp., which are known to involve the conserved region of nucleotide sequences encoding the clade D of β-class carbonic anhydrase (β-CA) including COSase. On the other hand, the ɛ value was distinct from those for bacteria in the genus Cupriavidus. These results provide an insight into biological COS degradation, which is indispensable for estimating the COS global budget based on the isotope because of the significant contribution of COS degradation by microorganisms harboring β-CA family enzymes.
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http://dx.doi.org/10.1264/jsme2.ME17130DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5745022PMC
December 2017

Relative Contribution of nirK- and nirS- Bacterial Denitrifiers as Well as Fungal Denitrifiers to Nitrous Oxide Production from Dairy Manure Compost.

Environ Sci Technol 2017 Dec 11;51(24):14083-14091. Epub 2017 Dec 11.

Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Instititute of Technology , 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

The relative contribution of fungi, bacteria, and nirS and nirK denirifiers to nitrous oxide (NO) emission with unknown isotopic signature from dairy manure compost was examined by selective inhibition techniques. Chloramphenicol (CHP), cycloheximide (CYH), and diethyl dithiocarbamate (DDTC) were used to suppress the activity of bacteria, fungi, and nirK-possessing denitrifiers, respectively. Produced NO were surveyed to isotopocule analysis, and its N site preference (SP) and δO values were compared. Bacteria, fungi, nirS, and nirK gene abundances were compared by qPCR. The results showed that NO production was strongly inhibited by CHP addition in surface pile samples (82.2%) as well as in nitrite-amended core samples (98.4%), while CYH addition did not inhibit the NO production. NO with unknown isotopic signature (SP = 15.3-16.2‰), accompanied by δO (19.0-26.8‰) values which were close to bacterial denitrification, was also suppressed by CHP and DDTC addition (95.3%) indicating that nirK denitrifiers were responsible for this NO production despite being less abundant than nirS denitrifiers. Altogether, our results suggest that bacteria are important for NO production with different SP values both from compost surface and pile core. However, further work is required to decipher whether NO with unknown isotopic signature is mostly due to nirK denitrifiers that are taxonomically different from the SP-characterized strains and therefore have different SP values rather than also being interwoven with the contribution of the NO-detoxifying pathway and/or of co-denitrification.
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http://dx.doi.org/10.1021/acs.est.7b04017DOI Listing
December 2017

Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterial method and N O decomposition by microwave discharge.

Rapid Commun Mass Spectrom 2017 02;31(4):396

Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502, Japan.

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http://dx.doi.org/10.1002/rcm.7800DOI Listing
February 2017

Automated system measuring triple oxygen and nitrogen isotope ratios in nitrate using the bacterial method and N O decomposition by microwave discharge.

Rapid Commun Mass Spectrom 2016 Dec;30(24):2635-2644

Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8502, Japan.

Rationale: Triple oxygen and nitrogen isotope ratios in nitrate are powerful tools for assessing atmospheric nitrate formation pathways and their contribution to ecosystems. N O decomposition using microwave-induced plasma (MIP) has been used only for measurements of oxygen isotopes to date, but it is also possible to measure nitrogen isotopes during the same analytical run.

Methods: The main improvements to a previous system are (i) an automated distribution system of nitrate to the bacterial medium, (ii) N O separation by gas chromatography before N O decomposition using the MIP, (iii) use of a corundum tube for microwave discharge, and (iv) development of an automated system for isotopic measurements. Three nitrate standards with sample sizes of 60, 80, 100, and 120 nmol were measured to investigate the sample size dependence of the isotope measurements.

Results: The δ O, δ O, and Δ O values increased with increasing sample size, although the δ N value showed no significant size dependency. Different calibration slopes and intercepts were obtained with different sample amounts. The slopes and intercepts for the regression lines in different sample amounts were dependent on sample size, indicating that the extent of oxygen exchange is also dependent on sample size. The sample-size-dependent slopes and intercepts were fitted using natural log (ln) regression curves, and the slopes and intercepts can be estimated to apply to any sample size corrections. When using 100 nmol samples, the standard deviations of residuals from the regression lines for this system were 0.5‰, 0.3‰, and 0.1‰, respectively, for the δ O, Δ O, and δ N values, results that are not inferior to those from other systems using gold tube or gold wire.

Conclusions: An automated system was developed to measure triple oxygen and nitrogen isotopes in nitrate using N O decomposition by MIP. This system enables us to measure both triple oxygen and nitrogen isotopes in nitrate with comparable precision and sample throughput (23 min per sample on average), and minimal manual treatment. Copyright © 2016 John Wiley & Sons, Ltd.
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http://dx.doi.org/10.1002/rcm.7747DOI Listing
December 2016

Sulfur Isotopic Fractionation of Carbonyl Sulfide during Degradation by Soil Bacteria.

Environ Sci Technol 2016 Apr 25;50(7):3537-44. Epub 2016 Mar 25.

Earth-Life Science Institute, Tokyo Institute of Technology , 2-12-1-IE-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.

We performed laboratory incubation experiments on the degradation of gaseous phase carbonyl sulfide (OCS) by soil bacteria to determine its sulfur isotopic fractionation constants ((34)ε). Incubation experiments were conducted using strains belonging to the genera Mycobacterium, Williamsia, and Cupriavidus isolated from natural soil environments. The (34)ε values determined were -3.67 ± 0.33‰, -3.99 ± 0.19‰, -3.57 ± 0.22‰, and -3.56 ± 0.23‰ for Mycobacterium spp. strains THI401, THI402, THI404, and THI405; -3.74 ± 0.29‰ for Williamsia sp. strain THI410; and -2.09 ± 0.07‰ and -2.38 ± 0.35‰ for Cupriavidus spp. strains THI414 and THI415. Although OCS degradation rates divided by cell numbers (cell-specific activity) were different among strains of the same genus, the (34)ε values for same genus showed no significant differences. Even though the numbers of bacterial species examined were limited, our results suggest that (34)ε values for OCS bacterial degradation depend not on cell-specific activities, but on genus-level biological differences, suggesting that (34)ε values are dependent on enzymatic and/or membrane properties. Taking our (34)ε values as representative for bacterial OCS degradation, the expected atmospheric changes in δ(34)S values of OCS range from 0.5‰ to 0.9‰, based on previously reported decreases in OCS concentrations at Mt. Fuji, Japan. Consequently, tropospheric observation of δ(34)S values for OCS coupled with (34)ε values for OCS bacterial degradation can potentially be used to investigate soil as an OCS sink.
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http://dx.doi.org/10.1021/acs.est.5b05325DOI Listing
April 2016

Rainwater, soil water, and soil nitrate effects on oxygen isotope ratios of nitrous oxide produced in a green tea (Camellia sinensis) field in Japan.

Rapid Commun Mass Spectrom 2015 May;29(9):891-900

Dept. of Environmental Chemistry and Engineering, Tokyo Institute of Technology G1-17, 4259 Nagatsuta, Midori-ku, Yokohama, 226-8502, Japan.

Rationale: The oxygen exchange fraction between soil H(2)O and N(2)O precursors differs in soils depending on the responsible N(2)O-producing process: nitrification or denitrification. This study investigated the O-exchange between soil H(2)O and N(2)O precursors in a green tea field with high N(2)O emissions.

Methods: The rainwater δ(18)O value was measured using cavity ring-down spectrometry (CRDS) and compared with that of soil water collected under the tea plant canopy and between tea plant rows. The intramolecular (15)N site preference in (β) N(α) NO (SP = δ(15)N(α) - δ(15)N(β)) was determined after measuring the δ(15)N(α) and δ(15)N(bulk) values using gas chromatography/isotope ratio mass spectrometry (GC/IRMS), and the δ(18) O values of N(2)O and NO(3)(-) were also measured using GC/IRMS.

Results: The range of δ(18)O values of rainwater (-11.15‰ to -4.91‰) was wider than that of soil water (-7.94‰ to -5.64‰). The δ(18)O value of soil water at 50 cm depth was not immediately affected by rainwater. At 10 cm and 20 cm depths of soil between tea plant rows, linear regression analyses of δ(18)O-N(2)O (relative to δ(18)O-NO(3)(-)) versus δ(18) O-H(2)O (relative to δ(18)O-NO(3)(-)) yielded slopes of 0.76-0.80 and intercepts of 31-35‰.

Conclusions: In soil between tea plant rows, the fraction of O-exchange between H(2)O and N(2)O precursors was approximately 80%. Assuming that denitrification dominated N(2)O production, the net (18)O-isotope effect for denitrification (NO(3)(-) reduction to N(2)O) was approximately 31-35‰, reflecting the upland condition of the tea field.
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http://dx.doi.org/10.1002/rcm.7176DOI Listing
May 2015

Determination of the sulfur isotope ratio in carbonyl sulfide using gas chromatography/isotope ratio mass spectrometry on fragment ions 32S+, 33S+, and 34S+.

Anal Chem 2015 Jan 23;87(1):477-84. Epub 2014 Dec 23.

Department of Environmental Chemistry and Engineering and ‡Department of Environmental Science and Technology, Tokyo Institute of Technology , Yokohama 226-8502, Japan.

Little is known about the sulfur isotopic composition of carbonyl sulfide (OCS), the most abundant atmospheric sulfur species. We present a promising new analytical method for measuring the stable sulfur isotopic compositions (δ(33)S, δ(34)S, and Δ(33)S) of OCS using nanomole level samples. The direct isotopic analytical technique consists of two parts: a concentration line and online gas chromatography-isotope ratio mass spectrometry (GC-IRMS) using fragmentation ions (32)S(+), (33)S(+), and (34)S(+). The current levels of measurement precision for OCS samples greater than 8 nmol are 0.42‰, 0.62‰, and 0.23‰ for δ(33)S, δ(34)S, and Δ(33)S, respectively. These δ and Δ values show a slight dependence on the amount of injected OCS for volumes smaller than 8 nmol. The isotope values obtained from the GC-IRMS method were calibrated against those measured by a conventional SF6 method. We report the first measurement of the sulfur isotopic composition of OCS in air collected at Kawasaki, Kanagawa, Japan. The δ(34)S value obtained for OCS (4.9 ± 0.3‰) was lower than the previous estimate of 11‰. When the δ(34)S value for OCS from the atmospheric sample is postulated as the global signal, this finding, coupled with isotopic fractionation for OCS sink reactions in the stratosphere, explains the reported δ(34)S for background stratospheric sulfate. This suggests that OCS is a potentially important source for background (nonepisodic or nonvolcanic) stratospheric sulfate aerosols.
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http://dx.doi.org/10.1021/ac502704dDOI Listing
January 2015

SO2 photoexcitation mechanism links mass-independent sulfur isotopic fractionation in cryospheric sulfate to climate impacting volcanism.

Proc Natl Acad Sci U S A 2013 Oct 15;110(44):17656-61. Epub 2013 Feb 15.

Departments of Environmental Chemistry and Engineering and Environmental Science and Technology, Tokyo Institute of Technology, Yokohama 226-8502, Japan.

Natural climate variation, such as that caused by volcanoes, is the basis for identifying anthropogenic climate change. However, knowledge of the history of volcanic activity is inadequate, particularly concerning the explosivity of specific events. Some material is deposited in ice cores, but the concentration of glacial sulfate does not distinguish between tropospheric and stratospheric eruptions. Stable sulfur isotope abundances contain additional information, and recent studies show a correlation between volcanic plumes that reach the stratosphere and mass-independent anomalies in sulfur isotopes in glacial sulfate. We describe a mechanism, photoexcitation of SO2, that links the two, yielding a useful metric of the explosivity of historic volcanic events. A plume model of S(IV) to S(VI) conversion was constructed including photochemistry, entrainment of background air, and sulfate deposition. Isotopologue-specific photoexcitation rates were calculated based on the UV absorption cross-sections of (32)SO2, (33)SO2, (34)SO2, and (36)SO2 from 250 to 320 nm. The model shows that UV photoexcitation is enhanced with altitude, whereas mass-dependent oxidation, such as SO2 + OH, is suppressed by in situ plume chemistry, allowing the production and preservation of a mass-independent sulfur isotope anomaly in the sulfate product. The model accounts for the amplitude, phases, and time development of Δ(33)S/δ(34)S and Δ(36)S/Δ(33)S found in glacial samples. We are able to identify the process controlling mass-independent sulfur isotope anomalies in the modern atmosphere. This mechanism is the basis of identifying the magnitude of historic volcanic events.
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http://dx.doi.org/10.1073/pnas.1213153110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3816419PMC
October 2013

Isotope effect in the carbonyl sulfide reaction with O(3P).

J Phys Chem A 2012 Apr 2;116(14):3521-6. Epub 2012 Apr 2.

Department of Environmental Science and Technology, Tokyo Institute of Technology, Yokohama, Japan.

The sulfur kinetic isotope effect (KIE) in the reaction of carbonyl sulfide (OCS) with O((3)P) was studied in relative rate experiments at 298 ± 2 K and 955 ± 10 mbar. The reaction was carried out in a photochemical reactor using long path FTIR detection, and data were analyzed using a nonlinear least-squares spectral fitting procedure with line parameters from the HITRAN database. The ratio of the rate of the reaction of OC(34)S relative to OC(32)S was found to be 0.9783 ± 0.0062 ((34)ε = (-21.7 ± 6.2)‰). The KIE was also calculated using quantum chemistry and classical transition state theory; at 300 K, the isotopic fractionation was found to be (34)ε = -14.8‰. The OCS sink reaction with O((3)P) cannot explain the large fractionation in (34)S, over +73‰, indicated by remote sensing data. In addition, (34)ε in OCS photolysis and OH oxidation are not larger than 10‰, indicating that, on the basis of isotopic analysis, OCS is an acceptable source of background stratospheric sulfate aerosol.
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http://dx.doi.org/10.1021/jp2120884DOI Listing
April 2012

Isotopomer analysis of production and consumption mechanisms of N2O and CH4 in an advanced wastewater treatment system.

Environ Sci Technol 2011 Feb 21;45(3):917-22. Epub 2010 Dec 21.

Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan.

Wastewater treatment processes are believed to be anthropogenic sources of nitrous oxide (N(2)O) and methane (CH(4)). However, few studies have examined the mechanisms and controlling factors in production of these greenhouse gases in complex bacterial systems. To elucidate production and consumption mechanisms of N(2)O and CH(4) in microbial consortia during wastewater treatment and to characterize human waste sources, we measured their concentrations and isotopomer ratios (elemental isotope ratios and site-specific N isotope ratios in asymmetric molecules of NNO) in water and gas samples collected by an advanced treatment system in Tokyo. Although the estimated emissions of N(2)O and CH(4) from the system were found to be lower than those from the typical treatment systems reported before, water in biological reaction tanks was supersaturated with both gases. The concentration of N(2)O, produced mainly by nitrifier-denitrification as indicated by isotopomer ratios, was highest in the oxic tank (ca. 4000% saturation). The dissolved CH(4) concentration was highest in in-flow water (ca. 3000% saturation). It decreased gradually during treatment. Its carbon isotope ratio indicated that the decrease resulted from bacterial CH(4) oxidation and that microbial CH(4) production can occur in anaerobic and settling tanks.
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http://dx.doi.org/10.1021/es102985uDOI Listing
February 2011

Microbial methane production in deep aquifer associated with the accretionary prism in Japan.

ISME J 2010 Apr 3;4(4):531-41. Epub 2009 Dec 3.

Department of Geosciences, Faculty of Science, Shizuoka University, Shizuoka, Japan.

To identify the methanogenic pathways present in a deep aquifer associated with an accretionary prism in Southwest Japan, a series of geochemical and microbiological studies of natural gas and groundwater derived from a deep aquifer were performed. Stable carbon isotopic analysis of methane in the natural gas and dissolved inorganic carbon (mainly bicarbonate) in groundwater suggested that the methane was derived from both thermogenic and biogenic processes. Archaeal 16S rRNA gene analysis revealed the dominance of H(2)-using methanogens in the groundwater. Furthermore, the high potential of methane production by H(2)-using methanogens was shown in enrichments using groundwater amended with H(2) and CO(2). Bacterial 16S rRNA gene analysis showed that fermentative bacteria inhabited the deep aquifer. Anaerobic incubations using groundwater amended with organic substrates and bromoethanesulfonate (a methanogen inhibitor) suggested a high potential of H(2) and CO(2) generation by fermentative bacteria. To confirm whether or not methane is produced by a syntrophic consortium of H(2)-producing fermentative bacteria and H(2)-using methanogens, anaerobic incubations using the groundwater amended with organic substrates were performed. Consequently, H(2) accumulation and rapid methane production were observed in these enrichments incubated at 55 and 65 degrees C. Thus, our results suggested that past and ongoing syntrophic biodegradation of organic compounds by H(2)-producing fermentative bacteria and H(2)-using methanogens, as well as a thermogenic reaction, contributes to the significant methane reserves in the deep aquifer associated with the accretionary prism in Southwest Japan.
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http://dx.doi.org/10.1038/ismej.2009.132DOI Listing
April 2010

Biomass production and energy source of thermophiles in a Japanese alkaline geothermal pool.

Environ Microbiol 2010 Feb 29;12(2):480-9. Epub 2009 Oct 29.

Department of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan.

Microbial biomass production has been measured to investigate the contribution of planktonic bacteria to fluxations in dissolved organic matter in marine and freshwater environments, but little is known about biomass production of thermophiles inhabiting geothermal and hydrothermal regions. The biomass production of thermophiles inhabiting an 85 degrees C geothermal pool was measured by in situ cultivation using diffusion chambers. The thermophiles' growth rates ranged from 0.43 to 0.82 day(-1), similar to those of planktonic bacteria in marine and freshwater habitats. Biomass production was estimated based on cellular carbon content measured directly from the thermophiles inhabiting the geothermal pool, which ranged from 5.0 to 6.1 microg C l(-1) h(-1). This production was 2-75 times higher than that of planktonic bacteria in other habitats, because the cellular carbon content of the thermophiles was much higher. Quantitative PCR and phylogenetic analysis targeting 16S rRNA genes revealed that thermophilic H2-oxidizing bacteria closely related to Calderobacterium and Geothermobacterium were dominant in the geothermal pool. Chemical analysis showed the presence of H2 in gases bubbling from the bottom of the geothermal pool. These results strongly suggested that H2 plays an important role as a primary energy source of thermophiles in the geothermal pool.
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http://dx.doi.org/10.1111/j.1462-2920.2009.02089.xDOI Listing
February 2010
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