Pulmonary Evaluation of Permissible Exposure Limit of Syntroleum S-8 Synthetic Jet Fuel in Mice

No current studies have systematically examined pulmonary health effects associated with Syntroleum S-8 synthetic jet fuel (S-8). In order to gain an understanding about the threshold concentration in which lung injury is observed, C57BL/6 male mice were nose-only exposed to S-8 for 1 h/day for 7 days at average concentrations of 0 (control), 93, 352, and 616 mg/m3. Evaluation of pulmonary function, airway epithelial barrier integrity, and pathohistology was performed 24 h after the final exposures. Significant decreases were detected in expiratory lung resistance and total lung compliance of the 352 mg/m3 group, for which no clear concentration-dependent alterations could be determined. No significant changes in respiratory permeability were exhibited, indicating that there was no loss of epithelial barrier integrity following S-8 exposure. However, morphological examination and morphometric analysis of distal lung tissue, by using transmission electron microscopy, revealed cellular damage in alveolar type II epithelial cells, with significant increases in volume density of lamellar bodies/vacuoles at 352 and 616 S-8 mg/m3. Moreover, terminal bronchiolar Clara injury, as evidenced by apical membrane blebs, was observed at relatively low concentrations, suggesting if this synthetic jet fuel is utilized, the current permissible exposure limit of 350 mg/m3 for hydrocarbon fuels should cautiously be applied

Catalytic Dechlorination of Gas-Phase Perchloroethylene Under Mixed Redox Conditions

The validity of a new method to destroy gas-phase perchloroethylene (PCE) is demonstrated at bench scale using a fixed-bed reactor that contains a Pt/Rh catalyst. Hydrogen and oxygen were simultaneously fed to the reactor together with PCE. The conversion efficiencies of PCE were sensitive to H2/O2 ratio and reactor temperature. When the temperature was ≥400 °C and H2/O2 was ≥2.15, PCE conversion efficiency was maintained at ≥90%. No catalyst deactivation was observed for over 2 years, using only mild, convenient regeneration procedures. It is likely that PCE reduction steps precede oxidation reactions and that the importance of oxidation lies in its elimination of intermediates that would otherwise lead to catalyst poisoning. In practice, this catalytic dechlorination method holds potential for low-cost, large-scale field operation

Thermocatalytic Destruction of Gas-Phase Perchloroethylene Using Propane as a Hydrogen Source

The use of propane in combination with oxygen to promote the destruction of perchloroethylene (PCE) over a platinum (Pt)/rhodium (Rh) catalyst on a cerium/zirconium oxide washcoat supported on an alumina monolith was explored. Conversions of PCE were measured in a continuous flow reactor with residence times less than 0.5 s and temperatures ranging from 200 to 600 °C. The presence of propane was shown to increase significantly the conversion of PCE over oxygen-only conditions. Conversions close to 100% were observed at temperatures lower than 450 °C with 20% oxygen and 2% propane in the feed, which makes this process attractive from a practical standpoint. In the absence of oxygen, PCE conversion is even higher, but the catalyst suffers significant deactivation in less than an hour. Even though results show that oxygen competes with reactants for active sites on the catalyst, the long-term stability that oxygen confers to the catalyst makes the process an efficient alternative to PCE oxidation. A Langmuir–Hinshelwood competitive adsorption model is proposed to quantify PCE conversion

Physicochemical Characterization of Mine Tailing Dusts in the US Southwest

Census data reveal that the Southwest is the fastest growing region of the USA, while NOAA GFDL coupled- model results suggest that precipitation is expected to decline in the same region over the coming decades. Besides the obvious impact on water resources, the drier conditions will most likely also result in increased atmospheric dust loads that could impact the health of a rapidly increasing population. This year the US EPA began site assessment and remediation at two mine tailings piles in Arizona contaminated with arsenic, lead, chromium and cadmium. The first is located in the twin towns of Hayden and Winkleman, and the second at the Iron King mine near Humbolt. At a concentration of approximately 0.1 microgram per cubic meter, the level of arsenic in PM10 collected at Hayden/Winkelman sometimes exceeds the Arizona ambient hazardous air pollutant standard (HAPS) by several orders of magnitude. Lead, cadmium and chromium are also sometimes orders of magnitude higher than the HAPS. A top priority is to determine the physicochemical speciation of wind-blown dust as a function of particle diameter because this information can a) help with source apportionment of airborne pollutants (e.g., smelter emissions vs. tailings dust), and b) help to assess the potential health impacts of contaminated dust, since deposition efficiency in human lungs is a strong function of particle diameter. We will present the chemical and physical characteristics of mine tailings dust collected with 10-stage multiple orifice uniform deposit impactors (MOUDI) located at Hayden/Winkleman and Iron King. We will also present scanning mobility particle spectrometer (SMPS) data obtained from the same sites. The MOUDI yields particle composition by size fraction (0.056-18 micrometer aerodynamic diameter) while the SMPS yields particle number by size fraction (0.0025 to 1.0 micrometer diameter). Size selective characteristics such as these have never been previously reported for mine tailings dust, to our knowledge

Mixed Redox Catalytic Destruction of Chlorinated Solvents in Soils and Groundwater

A new thermocatalytic method to destroy chlorinated solvents has been developed in the laboratory and tested in a pilot field study. The method employs a conventional Pt/Rh catalyst on a ceramic honeycomb. Reactions proceed at moderate temperatures in the simultaneous presence of oxygen and a reductant (mixed redox conditions) to minimize catalyst deactivation. In the laboratory, stable operation with high conversions (above 90% at residence times shorter than 1 s) for perchloroethylene (PCE) is achieved using hydrogen as the reductant. A molar ratio of H2/O2= 2 yields maximum conversions; the temperature required to produce maximum conversions is sensitive to influent PCE concentration. When a homologous series of aliphatic alkanes is used to replace hydrogen as the reductant, the resultant mixed redox conditions also produce high PCE conversions. It appears that the dissociation energy of the C–H bond in the respective alkane molecule is a strong determinant of the activation energy, and therefore the reaction rate, for PCE conversion. This new method was employed in a pilot field study in Tucson, Arizona. The mixed redox system was operated semicontinuously for 240 days with no degradation of catalyst performance and complete destruction of PCE and trichloroethylene in a soil vapor extraction gas stream. Use of propane as the reductant significantly reduced operating costs. Mixed redox destruction of chlorinated solvents provides a potentially viable alternative to current soil and groundwater remediation technologies