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91.
Sotiriou M Ferguson SF Davey M Wolfson JM Demokritou P Lawrence J Sax SN Koutrakis P 《Environmental monitoring and assessment》2008,137(1-3):351-361
Particles in a dental office can be generated by a number of instruments, such as air-turbine handpieces, low-speed handpieces,
ultrasonic scalers, bicarbonate polishers, polishing cups, as well as drilling and air sprays inside the oral cavity. This
study examined the generation of particles during dental drilling and measured particle size, mass, and trace elements. The
air sampling techniques included both continuous and integrated methods. The following particle continuous measurements were
taken every minute: (1) size-selective particle number concentration (Climet); (2) total particle number concentration (PTRAK),
and; (3) particle mass concentration (DustTrak). Integrated particle samples were collected for about 5 h on each of five
sampling days, using a PM2.5 sampler (ChemComb) for elemental/organic carbon analysis, and a PM10 sampler (Harvard Impactor) for mass and elemental analyses. There was strong evidence that these procedures result in particle
concentrations above background. The dental procedures produced number concentrations of relatively small particles (<0.5 μm)
that were much higher than concentrations produced for the relatively larger particles (>0.5 μm). Also, these dental procedures
caused significant elevation above background of certain trace elements (measured by X-ray fluorescence) but did not cause
any elevation of elemental carbon (measured by thermal optical reflectance). Dental drilling procedures aerosolize saliva
and products of drilling, producing particles small enough to penetrate deep into the lungs. The potential health impacts
of the exposure of dental personnel to such particles need to be evaluated. Increased ventilation and personal breathing protection
could be used to minimize harmful effects. 相似文献
92.
James S. Ferguson Eleanor G. Sheridan 《Journal of the Air & Waste Management Association (1995)》2013,63(12):669-672
The microscope as it has been and is now applied to air pollution work is discussed. A summary of the most common particulate sampling equipment is presented and distinctions as to the area of usage (suspended, or settled particulates) are made in each instance. Actual cases are discussed in which the polarizing microscope was used to determine identities and source of particulate pollutants. Particles from such sources as power plants, feed mills, and combustion sources are discussed and photomicrographs of known samples and unknown particles causing complaints are presented and compared as part of the discussion. References are given which deal with sampling equipment and microscopic analysis of various particulates. 相似文献
93.
Chlorinated aliphatic compounds, notably the chlorinated solvents, are common contaminants in soil and groundwater at hazardous waste sites. While these compounds are often recalcitrant, under favorable conditions they can be transformed and degraded through microbially mediated processes. There is great interest in understanding the transformations that are observed at contaminated sites and in manipulating these systems to achieve remediation. An important class of transformations occurs in anaerobic environments. Many of the transformations are reductive, and many yield useful energy to specific anaerobic bacteria. They include reductive dechlorination, dehydrochlorination and dichloroelemination. Of these, reductive dechlorination is often a growth-supporting reaction, while the others may be abiological or catalyzed by biological molecules. The reactions may result in chlorinated products, but there are often reaction sequences leading to completely dechlorinated products. The behavior of carbon tetrachloride (CT), 1,1,2,2-tetrachloroethane (TeCA) and the chloroethenes, perchloroethylene (PCE) and trichloroethylene (TCE), illustrate the range of anaerobic transformations that are possible, as well as the limited transformation that often is seen in the environment. CT undergoes reductive and substitutive reactions that are catalyzed by biological molecules but do not support bacterial growth. The anaerobic degradation of TeCA, which is a major contaminant at a site near Tacoma, WA, USA, provides examples of each type of transformation, and the products formed are consistent with the chlorinated compounds that are found in groundwater extraction wells. A laboratory study, using anaerobic sludge that had been fed chlorinated compounds, a cell-free extract from the sludge, and killed controls, showed that TeCA was transformed to four products and that these were further transformed, suggesting that it might be possible to degrade TeCA to innocuous products. Reductive dechlorination of PCE and TCE has been studied in many laboratories. Studies with mixed anaerobic consortia and with several dehalogenating bacteria, including strain 195 (. Isolation of a bacterium that reductively dechlorinates tetrachloroethane to ethane. Science 276, 1568-1571) that transforms PCE to ethene, have demonstrated that reductive dechlorination supports growth of the novel bacteria that carry out the reactions. Hydrogen has been shown to be an electron donor for the bacterial dehalogenation reactions, and kinetic and thermodynamic considerations indicate that dehalogenators can compete in some, but not all, anaerobic environments, pointing to applications of in situ bioremediation and to its limitations. Selected field studies of anaerobic transformations help delineate the applications of this type of bioremediation. 相似文献
94.
95.
Grant Ferguson Scott St. George 《Journal of the American Water Resources Association》2003,39(5):1249-1259
ABSTRACT: Long term well hydrographs and estimated ground water levels derived from hydroclimatic and biological data were used to evaluate trends within the Upper Carbonate Aquifer (UCA) near Winnipeg, Canada, during the 20th Century. Ground water records from instruments have been kept since the early 1960s and are derived from piezometers in the overlying sediments and in open boreholes in the UCA. Some boreholes extend into an underlying Paleozoic carbonate sequence. Shallow well hydrographs show no obvious long term trends but do exhibit variations on the order of three to four years that are correlated with changes in annual temperature and precipitation at lags up to 24 months. Trends observed in deeper wells appear to be largely related to ground water usage patterns and show little correlation with climate over the past 35 years. Stepwise multiple regression modeled average annual hydraulic head in the shallow wells as a function of regional temperature, precipitation, and tree ring variables. Estimated hydraulic heads had a slightly greater range prior to the 1960s, most prominently during an interval of lowered ground water levels between 1930 and 1942. Regression results demonstrate that moisture sensitive tree ring data are viable predictors of past ground water levels and may be useful for studies of aquifers in regions that lack long, high quality precipitation records. 相似文献
96.
97.
Carol A. Ferguson 《Journal of the American Water Resources Association》1989,25(6):1199-1204
ABSTRACT: Given limited available data and the present state of knowledge on the social aspects of irrigation, there is a need to develop new quantitative methods to measure water management performance in large-scale systems. A qualitative response framework is adapted to formulate a dynamic logit model of weekly field water adequacy and quantify indirectly farmer water utilization. Model parameters are estimated in a weighted least-squares regression using four seasons of data from a Philippine canal system. Estimated coefficients and independent model forecasts indicate greater effective use of rainfall than irrigation in sustaining high levels of water adequacy during the rainy season. Irrigation utilization is two times higher in the dry season, while system location has a much smaller but still significant impact. Utilization rates for both rain and irrigation showed considerable responsiveness to the prevailing scarcity of water. The qualitative response approach is well suited to the aggregated data available for large-scale systems, and allows advances in modeling dynamic water management behavior. Formal evaluation of the model will require further empirical applications. 相似文献
98.
Demokritou P Gupta T Ferguson S Koutrakis P 《Journal of the Air & Waste Management Association (1995)》2002,52(10):1230-1237
This paper presents the design and laboratory evaluation of a personal cascade impactor. The system is compact, lightweight, and uses a single battery-operated sampling pump. It operates at a flow rate of 5 L/min and consists of four impaction stages, each equipped with slit-shaped acceleration nozzles, and a backup filter. The impactor was calibrated using polydisperse particles. The 50% cut points of the four stages were 9.6, 2.6, 1.0, and 0.5 microm, respectively. The backup filter is placed downstream of the fourth stage and is used to collect the particles with an aerodynamic diameter smaller than 0.5 microm (dp < 0.5 microm). The major feature of this novel sampler is its ability not only to fractionate the particles with an aerodynamic diameter smaller than 10 microm to the various size fractions, but also to collect them onto relatively small polyurethane foam substrates without using adhesives. Although the impaction substrates are not coated with adhesives such as grease or mineral oil, particle bounce and re-entrainment losses were found to be insignificant. Interstage losses of particles smaller than 0.5 microm were less than 10%; for fine particles, less than 5%; and for coarse particles, less than 12%. The pressure drop across the four stages and the backup filter were 0.015 kPa (0.153 cm H2O),0.025 kPa (0.255 cm H2O), 0.274 kPa (2.794 cm H2O), 0.323 kPa (3.294 cm H2O), and 0.370 kPa (3.773 cm H2O), respectively. Particles can be easily recovered from the foam substrates using aqueous extraction. 相似文献
99.
Richard Ferguson 《环境质量管理》1992,1(3):261-267
One key development in environmental software is the adoption of a common electronic language for exchanging EH&S data. The ANSIX12-based data management tools offer compatibility across platforms within the company as well as between different companies. The X12 syntax makes it easy for environmental managers to integrate functions more closely with either materials management or quality management systems. 相似文献
100.
OBJECTIVE: Key features of graduated licensing were introduced in 46 states and the District of Columbia between 1993 and 2003. State evaluations consistently have reported positive overall effects and positive effects of nighttime and passenger restrictions. Sixteen year-olds are the main target of graduated licensing, and the present study investigated changes in their fatal crash involvement and crash characteristics that have taken place nationally during 1993-2003. By looking at 16 year-olds nationally, the study does not constitute a direct test of the effect of graduated licensing laws per se. METHODS: Data on fatal crashes were obtained from the Fatality Analysis Reporting System. Sixteen year-olds were compared with older drivers. RESULTS: During these years, the extent to which 16-year-old drivers were in fatal crashes decreased substantially compared with older age groups. The drop in the per capita crash rate for 16 year-olds was 26%. The major change was a reduction in crashes involving transporting young passengers, especially in jurisdictions with restrictions that target these crashes. There was no change in the proportion of fatal late-night crashes even in states restricting this activity. CONCLUSIONS: There has been some progress nationally in reducing the crash problem for 16 year-olds, but this still is a big problem. To achieve further progress, the gaps and weaknesses in present graduated licensing laws will need to be addressed. 相似文献