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【Es&t_July 7 2007】
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Environ. Sci. Technol., ASAP Article 10.1021/es062536b S0013-936X(06)02536-3 Web Release Date: July 7, 2007 Copyright © 2007 American Chemical Society Positive Matrix Factorization (PMF) Analysis of Molecular Marker Measurements to Quantify the Sources of Organic Aerosols Jeffrey M. Jaeckels, Min-Suk Bae, and James J. Schauer* Environmental Chemistry and Technology, University of Wisconsin, Madison, Wisconsin 53706 Received for review October 22, 2006 Revised manuscript received June 2, 2007 Accepted June 5, 2007 Abstract: One hundred and twenty five particulate matter samples that were collected over a 2 year period at the St. Louis Midwest Supersite were analyzed for 24 hour average organic carbon (OC), elemental carbon (EC), and particle-phase organic compound (molecular markers) concentrations. Over 100 organic compounds along with measurements of silicon and aluminum were analyzed using a factor analysis based source apportionment model, positive matrix factorization (PMF), which has been widely used in the past with elemental data but not organic molecular markers. Four different solutions (7, 8, 9, and 10 factor solutions) to the PMF model were explored to consider the stability of the source apportionment results, which were found to be reasonably stable. The eight-factor solution was further explored and compared to a parallel chemical mass balance (CMB) source apportionment modeling result that used a subset of the PMF data. A base case eight-factor PMF solution resolved two point source factors, two winter combustion factors, a biomass-burning factor, a mobile source factor, a secondary organic aerosol factor, and a resuspended soil factor. An optimized eight-factor case was also examined, which was formulated by removing three extreme point source impacts observed in the base case, to better understand the nonpoint sources. In the optimized case, the daily OC explained by the biomass burning shows good agreement with the corresponding CMB source, with a slope of 0.93 ± 0.03. Likewise, the average OC explained by the optimized PMF resuspended soil factor showed good correlation with the CMB road dust apportionment, but there was a significant bias between the two results. The optimized PMF OC from one of the winter combustion factors showed good correlation with the CMB natural gas combustion apportionment but also has a significant bias. In both cases, PMF analysis factored one mobile source controlled by hopanes and streranes, which did not correlate well with any of the three CMB mobile sources. Although the most of the molecular markers were clustered with the PMF model in a manner consistent with prior knowledge of these organic compounds, one significant deviation was observed. Cholesterol, used in the past as a tracer for meat smoke, was found to largely associate with road dust, which raises questions on the suitability of cholesterol as a tracer for meat smoke in the midwestern U.S. ************************************************************ Environ. Sci. Technol., ASAP Article 10.1021/es070395n S0013-936X(07)00395-1 Web Release Date: July 7, 2007 Copyright © 2007 American Chemical Society Elimination of Mercury by Yellow Perch in the Wild Jillian L. A. Van Walleghem, Paul J. Blanchfield,* and Holger Hintelmann Department of Zoology, University of Manitoba, Z320 Duff Roblin Building, Winnipeg, Manitoba, R3T 2N2, Canada, Freshwater Institute, Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, Manitoba, R3T 2N6, Canada, and Department of Chemistry, Trent University, 1600 West Bank Drive, Peterborough, Ontario, K9J 7B8, Canada Received for review February 15, 2007 Revised manuscript received May 23, 2007 Accepted May 30, 2007 Abstract: The rate of methylmercury (MeHg) elimination by fish is important in determining the extent of bioaccumulation and for predicting recovery times of MeHg-contaminated fisheries. Rates of MeHg elimination remain uncertain in existing bioaccumulation models due to a lack of field studies. We addressed this problem by monitoring fish that had naturally accumulated isotopically enriched MeHg (spike MeHg) during a whole-ecosystem experiment. We transported yellow perch (Perca flavescens) from the experimental lake to an untreated lake and monitored spike total mercury (THg, most of which was MeHg) losses over 440 d. Spike THg was distributed among fish tissues in a similar way as ambient THg (background non-spike THg). We observed rapid loss of spike THg from liver and other visceral tissues (~90 d) followed by a plateau. Subsequently, there was prolonged redistribution of spike THg into muscle (180 d). Loss of spike THg from the whole fish occurred >5 times slower (half-life of 489 d) than in past laboratory studies using this species. We determined that MeHg bioaccumulation models with laboratory-based elimination rates produced faster losses than those observed in wild fish. The present findings provide support for refining elimination rates in MeHg models and show the importance of examining biological processes under natural conditions. ************************************************************ Environ. Sci. Technol., ASAP Article 10.1021/es070531o S0013-936X(07)00531-7 Web Release Date: July 7, 2007 Copyright © 2007 American Chemical Society Insight into Methyl tert-Butyl Ether (MTBE) Stable Isotope Fractionation from Abiotic Reference Experiments Martin Elsner,* Jennifer McKelvie, Georges Lacrampe Couloume, and Barbara Sherwood Lollar Stable Isotope Laboratory, University of Toronto, 22 Russell Street, Toronto, Ontario M5S 3B1, Canada Received for review March 2, 2007 Revised manuscript received May 29, 2007 Accepted June 3, 2007 Abstract: Methyl group oxidation, SN2-type hydrolysis, and SN1-type hydrolysis are suggested as natural transformation mechanisms of MTBE. This study reports for the first time MTBE isotopic fractionation during acid hydrolysis and for oxidation by permanganate. In acid hydrolysis, MTBE isotopic enrichment factors were C = -4.9” ± 0.6” for carbon and H = -55” ± 7” for hydrogen. Position-specific values were C,reactive position = -24.3” ± 2.3” and H,reactive position = -73” ± 9”, giving kinetic isotope effects KIEC = 1.025 ± 0.003 and KIEH = 1.08 ± 0.01 consistent with an SN1-type hydrolysis involving the tert-butyl group. The characteristic slope of 2Hbulk/13Cbulk bulk,H/ bulk,C = 11.1 ± 1.3 suggests it may identify SN1-type hydrolysis also in settings where the pathway is not well constrained. Oxidation by permanganate was found to involve specifically the methyl group of MTBE, similar to aerobic biodegradation. Large hydrogen enrichment factors of H = -109” ± 9” and H,reactive position = -342” ± 16” indicate both large primary and large secondary hydrogen isotope effects. Significantly smaller values reported previously for aerobic biodegradation suggest that intrinsic fractionation is often masked by additional non-fractionating steps. For conservative estimates of biodegradation at field sites, the largest values reported should, therefore, be used. ************************************************************ Environ. Sci. Technol., ASAP Article 10.1021/es070424u S0013-936X(07)00424-5 Web Release Date: July 7, 2007 Copyright © 2007 American Chemical Society Analysis of Trends in Episodic Acidification of Streams in Western Maryland Kathleen M. Kline,* Keith N. Eshleman, Raymond P. Morgan II, and Nancy M. Castro University of Maryland Center for Environmental Science, Appalachian Laboratory, 301 Braddock Road, Frostburg, Maryland 21532 Received for review February 19, 2007 Revised manuscript received May 15, 2007 Accepted May 29, 2007 Abstract: In this study we report on changes in the magnitude and mechanisms of episodic acidification of a small acid-sensitive stream in western Maryland (U.S.) during the 1990s, a period in which wet sulfate deposition declined by 10-25% due to implementation of the Clean Air Act Amendments (CAAA) of 1990. We observed a relatively minor trend in the magnitude of episodic acidification over this period, as measured by transient changes in acid neutralizing capacity (ANC) and minimum values of ANC (ANCmin) during 22 events sampled prior to and following CAAA implementation. Any relationship to changes in atmospheric deposition appears to be confounded by large hydroclimatological variability between the two sampling periods. Nonetheless, results obtained prior to implementation of the CAAA indicated that the mechanism of episodic acidification was mostly attributable to flushing of accumulated sulfate from the watershed, whereas results obtained post-CAAA indicated domination by base cation dilution. This shift in the mechanism of episodic acidification is qualitatively consistent with hydrochemical theory, as well as with empirical results from surface waters in other regions where dramatic declines in sulfate deposition have taken place. ************************************************************ Environ. Sci. Technol., ASAP Article 10.1021/es0706504 S0013-936X(07)00650-5 Web Release Date: July 7, 2007 Copyright © 2007 American Chemical Society Photodegradation of Perfluorooctane Sulfonate by UV Irradiation in Water and Alkaline 2-Propanol Takashi Yamamoto,* Yukio Noma, Shin-ichi Sakai, and Yasuyuki Shibata National Institute for Environmental Studies, 16-2, Onogawa, Tsukuba, Ibaraki 305-8506, Japan, Kyoto University, Environment Preservation Center, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan Received for review March 15, 2007 Revised manuscript received May 31, 2007 Accepted June 7, 2007 Abstract: Perfluorooctane sulfonate (PFOS) is the environmentally concerned compound because of its persistence and bioaccumulative properties. Since photodegradation of PFOS is not yet experimentally confirmed, photodegradation study of PFOS in water and alkaline 2-propanol solution was conducted. Aqueous and alkaline 2-propanol solution of PFOS (40 M) was irradiated with a low-pressure mercury lamp (254 nm, 32 W) by internal irradiation for 10 d, and then PFOS, fluoride and sulfate ions, and the other degradation products were analyzed. Photodegradation of PFOS was confirmed in both media. PFOS was degraded by 8% after 1 day and by 68% after 10 days irradiation compared to the initial concentration in water. In alkaline 2-propanol, 76 and 92% of PFOS was degraded after 1 and 10 days irradiation, respectively. Photodegradation of PFOS in alkaline 2-propanol was much faster and effective than in water, as the photodegradation rate constants were 0.93 days-1 in alkaline 2-propanol and 0.13 days-1 in water, respectively. Formation of fluoride and sulfate was also confirmed by ion chromatography and X-ray diffraction analysis. From observation of the degradation products, two major degradation pathways of PFOS were considered: via C8HF17 and C8F17OH, respectively, resulting in short-chain fluorinated compounds such as C7HF15 and C7F15OH by stepwise removal of CF2. Formation of short-chain fluorocarbons such as CF4, C2F6, and C3F8 were also confirmed. This is the first study to confirm photodegradation of PFOS in water and alkaline 2-propanol. [ Last edited by duanlin_nk on 2007-7-8 at 00:03 ] |
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