Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.23.17 (PCE)
 1,301 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In addition to methane (CH(4)) and carbon dioxide (CO(2)), landfill gas may contain more than 200 non-methane organic compounds (NMOCs) including C(2+)-alkanes, aromatics, and halogenated hydrocarbons. Although the trace components make up less than 1% v/v of typical landfill gas, they may exert a disproportionate environmental burden. The objective of this work was to study the dynamics of CH(4) and NMOCs in the landfill cover soils overlying two types of gas collection systems: a conventional gas collection system with vertical wells and an innovative horizontal gas collection layer consisting of permeable gravel with a geomembrane above it. The 47 NMOCs quantified in the landfill gas samples included primarily alkanes (C(2)-C(10)), alkenes (C(2)-C(4)), halogenated hydrocarbons (including (hydro)chlorofluorocarbons ((H)CFCs)), and aromatic hydrocarbons (BTEXs). In general, both CH(4) and NMOC fluxes were all very small with positive and negative fluxes. The highest percentages of positive fluxes in this study (considering all quantified species) were observed at the hotspots, located mainly along cell perimeters of the conventional cell. The capacity of the cover soil for NMOC oxidation was investigated in microcosms incubated with CH(4) and oxygen (O(2)). The cover soil showed a relatively high capacity for CH(4) oxidation and simultaneous co-oxidation of the halogenated aliphatic compounds, especially at the conventional cell. Fully substituted carbons (TeCM, PCE, CFC-11, CFC-12, CFC-113, HFC-134a, and HCFC-141b) were not degraded in the presence of CH(4) and O(2). Benzene and toluene were also degraded with relative high rates. This study demonstrates that landfill soil covers show a significant potential for CH(4) oxidation and co-oxidation of NMOCs.
 ...
PMID:Atmospheric emissions and attenuation of non-methane organic compounds in cover soils at a French landfill. 1803 20

Concentrations of volatile organic compounds (VOCs) measured outside homes in Houston, TX and Los Angeles, CA were characterized by the effects of source proximity and meteorological factors. Benzene, toluene, ethylbenzene, m,p-xylene, o-xylene (BTEX), methyl tert butyl ether (MTBE), tetrachloroethylene (perchloroethylene, PCE), and carbon tetrachloride (CCl4) were examined. Multiple stepwise regression analysis converged the best-fit models with predictors from meteorological conditions and the proximity to specific point, area, and mobile sources on the residential outdoor VOC concentrations. Negative associations of wind speed with concentrations demonstrated the effect of dilution by high wind speed. Atmospheric stability increase was associated with concentration increase. Petrochemical source proximity was a significant predictor for BTEX and MTBE concentrations in Houston. Ethylbenzene and xylene source proximity was a significant predictor in Los Angeles. Close proximity to area sources such as scrap metal recycling or dry cleaning facilities increased the MTBE, PCE, and CCl4 concentrations in Houston and Los Angeles. Models for ethylbenzene, m,p-xylene, and MTBE in Houston, and benzene in Los Angeles explained that for the median values of the meteorological factors, homes closest to influential highways would have concentrations that were 1.7-2.2 fold higher than those furthest from these mobile emission sources. If the median distance to sources were used in the models, the VOC concentrations varied 1.7 to 6.6 fold as the meteorological conditions varied over the observed range. These results highlight that each urban area is unique and localized sources need to be carefully evaluated to understand potential contributions to VOC air concentrations near residences, which influence baseline indoor air concentrations and personal exposures. Results of this study could assist in the appropriate design of monitoring networks for community-level sampling. They may also improve the accuracy of exposure models linking emission sources with estimated pollutant concentrations at the residential level.
 ...
PMID:Source proximity and meteorological effects on residential outdoor VOCs in urban areas: Results from the Houston and Los Angeles RIOPA studies. 2759 59