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    ABSTRACT: Carbon stable isotope (C-13) fractionation in chlorofluorocarbon (CFC) compounds arising from abiotic (chemical) degradation using zero-valent iron (ZVI) and biotic (landfill gas attenuation) processes is investigated. Batch tests (at 25 degrees C) for CFC-113 and CFC-11 using ZVI show quantitative degradation of CFC-113 to HCFC-123a and CFC-1113 following pseudo-first-order kinetics corresponding to a half-life (tau(1/2)) of 20.5 h, and a ZVI surface-area normalized rate constant (k(SA)) of -(9.8 +/- 0.5) x 10(-5) L m(-2) h(-1). CFC-11 degraded to trace HCFC-21 and HCFC-31 following pseudo-first-order kinetics corresponding to tau(1/2) = 17.3 h and k(SA) = -(1.2 +/- 0.5) x 10(-4) L m(-2) h(-1). Significant kinetic isotope effects of epsilon(parts per thousand) = -5.0 +/- 0.3 (CFC-113) and -17.8 +/- 4.8 (CFC-11) were observed. Compound-specific carbon isotope analyses also have been used here to characterize source signatures of CFC gases (HCFC-22, CFC-12, HFC-134a, HCFC-142b, CFC-114, CFC-11, CFC-113) for urban (UAA), rural/remote (RAA), and landfill (LAA) ambient air samples, as well as in situ surface flux chamber (FLUX; NO FLUX) and landfill gas (LFG) samples at the Dargan Road site, Northern Ireland. The latter values reflect biotic degradation and isotopic fractionation in LFG production, and local atmospheric impact of landfill emissions through the cover. Isotopic fractionations of Delta C-13 similar to -13 parts per thousand (HCFC-22), Delta C-13 similar to -35 parts per thousand (CFC-12) and Delta C-13 similar to -15 parts per thousand (CFC-11) were observed for LFG in comparison to characteristic solvent source signatures, with the magnitude of the isotopic effect for CFC-11 apparently similar to the kinetic isotope (abiotic) ZVI degradation.
    Full-text · Article · Dec 2011 · Environmental Science & Technology
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    ABSTRACT: A map of the spatial variation in isotopic composition of a substrate, or isoscape, provides a tool to address a range of research questions, such as the use of isotope fingerprinting to identify the origin of compounds. The focus of this study was to establish a soil S isotope map for Northern Ireland in order to investigate spatial variability within the isotopic composition of total soil sulphur (S). The sample resolution was about one sample every 141km2. δ34S values were grouped based on soil type and soil parent material. Total soil S δ34S data were grouped according to soil type, to evaluate whether a soil’s characteristics affect its isotopic composition. Gleyed soils had a mean δ34S value of +6.3±6.1‰, lower than the means for other soil types. A trend towards higher δ34S values (mean δ34S of+13.8±6.0‰) was observed in soils with a high organic matter content. No trends in δ34S value were observed for other soil types. There were no discernible correlations between total soil S δ34S and soil parent material, with the exception of shale and mudstones. The majority of soils derived from shale and mudstones had δ34S values at or close to the mean of+4.9‰. A spatially coherent pattern of relatively high soil total S δ34S values in the west and north, and low in the SE, is discernible in Northern Ireland. Based on the observed spatial distribution, it has been concluded that the quantity and source (anthropogenic or marine) of wet atmospheric S deposition is a controlling factor on regional variation of soil δ34S in Northern Ireland. This S isoscape will assist studies of S cycling in Northern Ireland and may assist in the creation of an ‘isotopic fingerprint’ for a potential ‘input’ source needed to interpret data in traceability studies.
    Full-text · Article · Aug 2011 · Applied Geochemistry
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    ABSTRACT: The Monkstown zero-valent iron permeable reactive barrier (ZVI PRB), Europe's oldest commercially-installed ZVI PRB, had been treating trichloroethene (ICE) contaminated groundwater for about 10 years on the Nortel Network site in Northern Ireland when cores from the reactive zone were collected in December, 2006. Groundwater data from 2001-2006 indicated that TCE is still being remediated to below detection limits as the contaminated groundwater flows through the PRB. Ca and Fe carbonates, crystalline and amorphous Fe sulfides, and Fe (hydr)oxides have precipitated in the granular ZVI material in the PRB. The greatest variety of minerals is associated with a similar to 1-2 cm thick, slightly cemented crust on top (up-gradient influent entrance) of the ZVI section of the PRB and also with the discontinuous cemented ZVI material (similar to 23 cm thick) directly below it. The greatest presence of microbial communities also occurred in the up-gradient influent portion of the PRB compared to its down-gradient effluent section, with the latter possibly due to less favorable conditions (i.e., high pH, low oxygen) for microbial growth. The ZVI filings in the down-gradient effluent section of the PRB have a projected life span of >10 years compared with ZVI filings from the continuous to discontinuous cemented up-gradient ZVI section (upper similar to 25 cm) of the PRB, which may have a life span of only similar to 2-5 more years. Supporting Information from applied, multi-tracer testing indicated that restricted groundwater flow is occurring in the upper similar to 25 cm of the ZVI section and preferential pathways have also formed in this PRB over its 10 years of operation.
    Full-text · Article · May 2010 · Environmental Science and Technology
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