The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Kenny S Crump - One of the best experts on this subject based on the ideXlab platform.
-
manganese exposures in toronto during use of the Gasoline Additive methylcyclopentadienyl manganese tricarbonyl
Journal of Exposure Science and Environmental Epidemiology, 2000Co-Authors: Kenny S CrumpAbstract:Manganese exposures in Toronto during use of the Gasoline Additive, methylcyclopentadienyl manganese tricarbonyl
-
Manganese exposures in Toronto during use of the Gasoline Additive, methylcyclopentadienyl manganese tricarbonyl
Journal of Exposure Science & Environmental Epidemiology, 2000Co-Authors: Kenny S CrumpAbstract:A year-long population-weighted study of personal exposures to particulate matter (PM_2.5) was conducted in Toronto while the manganese-containing Additive, methylcyclopentadienyl manganese tricarbonyl (MMT), was present in Gasoline at an average level of 11.9 mg Mn/l, which was higher than the maximum of 8.3 mg Mn/l allowed in the U.S. In this study, 925 three-day personal samples of PM_2.5 (air concentration of aerosol with an aerodynamic diameter of less than 2.5 µm) were collected, along with a record of participants' occupations, personal habits, surroundings, and activities during sampling. Stationary samples of PM_2.5 were collected indoors and outdoors at a subset of participants' homes over the same 3-day periods. Three-day samples of PM_2.5 were also collected at fixed locations. Personal exposures to PM_2.5 were highly influenced by exposure to tobacco smoke, and were poorly correlated with outdoor levels (Kendall's tau=0.13). The mean concentration of PM_2.5 in homes (21 µg/m^3) was significantly higher than the mean outdoor level (15 µg/m^3). By contrast, the mean PM_2.5 Mn concentration (air concentration of Mn in PM_2.5) was higher outdoors (9.7 ng/m^3) than indoors (5.5 ng/m^3). Other than from tobacco smoke, there were no indications of significant indoor sources of PM_2.5 Mn in homes. The most important predictor of exposure to PM_2.5 was time spent in the subway, and a high level (428 ng/m^3) of PM_2.5 Mn was measured in the subway. The source of this Mn was hypothesized to be friction erosion of subway rails. Small, but statistically significant correlations were present between personal exposures to PM_2.5 Mn and several traffic-related variables (time spent in transit, in a motor vehicle, near a roadway with traffic, and in a parking garage). However, in a stepwise regression that adjusted for weather and personal activities, time in a motor vehicle was the only traffic-related variable significantly associated with PM_2.5 Mn, and it was only the 10th most important personal activity variable in the final model. Concentrations of PM_2.5 Mn were higher at two fixed locations than outside of participants' homes, which were likely further from high traffic areas than the fixed sites. Likewise, outdoor and fixed site samples collected during periods that included weekend days contained lower air concentrations of Mn than samples collected during weekdays when traffic was heavier. On the other hand, the monthly average concentration of Mn in Gasoline was negatively correlated with both outdoor and personal PM_2.5 Mn, which suggests that traffic-related sources of Mn other than MMT may be present. After omitting participants with exposure to Mn from certain identifiable non-MMT sources (subway riders, metal workers and persons exposed to tobacco smoke), the average (median) personal exposure of the remaining 325 participants to PM_2.5 Mn was reduced from 14 ng/m^3 (8.5 ng/m^3) to 8.3 ng/m^3 (7.0 ng/m^3). Potential sources of this residual Mn exposure include, in addition to MMT, naturally occurring Mn in the earth's crust, other occupational exposure, airborne release of Mn from industrial operations, and friction erosion of Mn from steel-containing products. Taken together, these facts (elimination of participants with Mn exposure from known non-MMT sources reduced average exposures by 40%, the existence of multiple non-MMT sources of the remaining Mn exposure, and the negative correlation between MMT usage and PM_2.5 Mn) suggest that the preponderance of personal Mn exposure was from non-MMT sources.
Federica Zaccheria - One of the best experts on this subject based on the ideXlab platform.
-
new generation biofuels γ valerolactone into valeric esters in one pot
RSC Advances, 2013Co-Authors: Carine E Chanthaw, Marcello Marelli, Rinaldo Psaro, Nicoletta Ravasio, Federica ZaccheriaAbstract:Ethyl valerate and pentyl valerate, suitable as a Gasoline Additive and diesel component respectively, can be obtained in a one pot one step reaction from γ-valerolactone, readily available from lignocellulosic biomass. The reaction takes place in ethanol under H2 through nucleophilic addition of the alcohol to the carboxylic group giving hydroxypentanoate, dehydration to pentenoate and hydrogenation to the saturated ester. The bifunctional catalyst used consists of a non noble metal, namely copper, supported on an amorphous weakly acidic material, therefore representing an interesting alternative to Pt–zeolite catalysts. Pentyl valerate can be obtained in one pot with conversions >90% and selectivity up to 83%.
-
New generation biofuels: γ-Valerolactone into valeric esters in one pot
RSC Advances, 2013Co-Authors: Carine E. Chan-thaw, Marcello Marelli, Rinaldo Psaro, Nicoletta Ravasio, Federica ZaccheriaAbstract:Ethyl valerate and pentyl valerate, suitable as a Gasoline Additive and diesel component respectively, can be obtained in a one pot one step reaction from ?-valerolactone, readily available from lignocellulosic biomass. The reaction takes place in ethanol under H2 through nucleophilic addition of the alcohol to the carboxylic group giving hydroxypentanoate, dehydration to pentenoate and hydrogenation to the saturated ester. The bifunctional catalyst used consists of a non noble metal, namely copper, supported on an amorphous weakly acidic material, therefore representing an interesting alternative to Pt-zeolite catalysts. Pentyl valerate can be obtained in one pot with conversions >90% and selectivity up to 83%. ? 2013 The Royal Society of Chemistry.
G. H. Shahidi Bonjar - One of the best experts on this subject based on the ideXlab platform.
-
Potential Ecotoxicological Implication of Methyl tert-butyl ether (MTBE) Spills in the Environment
Ecotoxicology, 2004Co-Authors: G. H. Shahidi BonjarAbstract:Streptomyceticidal activity of Methyl tert -butyl ether (MTBE) elucidated for the first time. Adverse effect of MTBE, the Gasoline Additive, against 11 soil inhabitant Streptomyces spp. isolates was investigated. MTBE, an octane enhancer is added to Gasoline to reduce atmospheric concentrations of carbon monoxide and ozone. It contaminates soil and groundwater by fuel leaks and spills. Streptomyces spp. are of the major contributors to the biological buffering of soils by exerting beneficial and antagonistic activity against wide range of bacteria and fungi. To evaluate anti-streptomycetidal activity of MTBE, it was tested against 11 soil isolates of Streptomyces isolates and also a plant-root bacterial pathogen, Erwinia carotovora and a plant-root fungal pathogen, Fusarium solani . MTBE did not reveal any growth inhibitory activity against E. carotovora and F. solani , but showed strong inhibitory effect against Streptomyces isolates. The Minimum Inhibitory Concentration (MIC) on Streptomyces isolates was 1/800 of the original MTBE. Fuel leaks and spills have the potential to suppress or eliminate the Streptomyces role in the soil causing alteration in the balance of soil micro flora. This change can promote the domination of microorganisms with adverse biological or ecotoxicological effects.
M. R. Sommerfeld - One of the best experts on this subject based on the ideXlab platform.
-
Liquid-Gas Partitioning of the Gasoline Oxygenate Methyl tert-Butyl Ether (MTBE) Under Laboratory Conditions and Its Effect on Growth of Selected Algae
Archives of Environmental Contamination and Toxicology, 1998Co-Authors: J. M. Rousch, M. R. SommerfeldAbstract:The partitioning of the widely used Gasoline Additive methyl tert -butyl ether (MTBE) between liquid growth media and gaseous phase was measured daily under laboratory conditions to determine how closely dissolved MTBE concentrations matched nominal concentrations. Total (gaseous and dissolved) MTBE averaged across 6 days for 29.6, 503.2, and 1005.7 mg L^−1 MTBE treatments were 89.9, 90.3, and 73.0% of nominal, respectively, and mean dissolved MTBE in these same treatments were 74.6, 73.8, and 69.6% of total MTBE, respectively. This suggests that dissolved MTBE concentrations can vary substantially from nominal. The effect of MTBE on the growth of selected algae was also evaluated under laboratory conditions. Three unicellular algae, Selenastrum capricornutum (Chlorophyta), Navicula pelliculosa (Bacillariophyta), and Synechococcus leopoliensis (= Anacystic nidulans, Cyanophyta = Cyanobacteria), representative of three taxonomic groups, were used as test organisms. Toxicity tests were acute and increase in cell number was used as an indicator of growth. Algal species were exposed by injection of MTBE into sealed vessels containing defined liquid growth media. The growth of N. pelliculosa and S. leopoliensis was negatively affected at nominal 2400 mg L^−1 MTBE, whereas the growth of S. capricornutum was negatively affected at nominal 4800 mg L^−1 MTBE and positively affected at nominal 600 mg L^−1 MTBE. The differential sensitivity of the growth of these representative species suggests that MTBE may alter algal community composition in the natural environment.
Robert J. Steffan - One of the best experts on this subject based on the ideXlab platform.
-
biodegradation of methyl tert butyl ether by a pure bacterial culture
Applied and Environmental Microbiology, 2001Co-Authors: Paul B Hatzinger, Kevin Mcclay, Simon Vainberg, Marina Tugusheva, Charles W Condee, Robert J. SteffanAbstract:Methyl tert-butyl ether (MTBE) has been used as a Gasoline Additive since the late 1970s to replace lead and other toxic chemicals and as an oxygenate to meet the vehicle emissions requirements of the 1990 Clean Air Act Amendments (21). Reformulated Gasoline presently contains approximately 11% (vol/vol) MTBE. The widespread use of MTBE in Gasoline has led to accidental spills and its discharge into soils and groundwater. Because it is highly soluble in water (∼43,000 ppm) and has a low tendency to adsorb to soils, it moves rapidly in groundwater (25) and is now often found in groundwater near service stations, fuel storage facilities, and filling terminals throughout the United States. As little as 4 liters of reformulated Gasoline can contaminate >106 liters of groundwater to above its odor and taste threshold of 40 μg/liter. The full extent of MTBE contamination in groundwater in the United States has only recently been under careful assessment. A study performed as part of the U.S. Geological Survey's National Water-Quality Assessment Program revealed that MTBE is the second most commonly detected contaminant in urban groundwater (26). As an example of how widespread this problem has become, Buscheck et al. (5) reviewed groundwater monitoring data from 700 service station sites in the United States and observed that >80% of the active sites and 74% of the inactive sites had MTBE contamination. Approximately 96, 98, and 86% of the service station sites in Texas, Maryland, and California, respectively, where groundwater was analyzed for MTBE had significant MTBE contamination. Of these sites, 63, 82, and 47%, respectively, had MTBE concentrations greater than 1 mg/liter. This widespread contamination has led to increased public and regulatory scrutiny and a need to identify cost-effective remediation technologies. Relatively little work has been done to address the biodegradability of MTBE. In an early study, an aerobic consortium isolated from acclimated sludge was maintained on MTBE as a sole source of carbon (23). MTBE was degraded to tert-butyl alcohol (TBA), which was also degraded by the enrichment culture. This culture has been the focus of a bioremediation demonstration where it was injected directly into an MTBE-contaminated aquifer at the Port Hueneme Naval Station in California (24). MTBE biodegradation has been reported in sewage sludge (20), soils (33), river sediments (3, 4), and a biofilter inoculated with groundwater (7, 8), although the responsible bacteria were not isolated or characterized. At least partial MTBE degradation has been observed in a few pure cultures of bacteria (9, 14, 15, 16, 17, 28) and fungi (12), and recent studies demonstrated growth of a pure culture (strain PM1) on MTBE as the sole carbon source (6, 11). Anaerobic degradation of MTBE has been observed in one aquifer (32), but it was not shown in anaerobic samples from several other sites (18, 30). We previously reported that MTBE is mineralized by propane-oxidizing bacteria and proposed a pathway for MTBE degradation (28). Our initial studies suggested that MTBE is first oxidized to TBA, but more recent studies have demonstrated that the first oxidation product may be tert-butyl formate (16). TBA is subsequently degraded by the strains through the intermediate 2-hydroxy isobutyric acid (HIBA), which accumulates in the culture media. HIBA is not an effective growth substrate for the propane-oxidizing bacteria studied, but it is eventually metabolized to CO2 by the strains. We recently isolated and described a new MTBE-degrading organism, Hydrogenophaga flava strain ENV735, which grows slowly on MTBE but can be grown rapidly on other substrates for research and bioremediation applications (29). In this report, we evaluate MTBE and TBA degradation by strain ENV735 more closely and attempt to identify factors that could account for the persistence of MTBE in the environment. The results of the study suggest that MTBE and TBA are oxidized by separate enzyme systems in this strain.