Pulmonary toxicity of inhaled nanoscale and fine zinc oxide particles: mass and surface area as an exposure metric.

The total surface area is known to be an effective exposure metric for predicting the lung toxicity of low solubility nanoparticles (NPs). However, if NPs are dissolved quickly enough in the lungs, the mass may be correlated with the toxicity. Recent studies have found that the toxicity of zinc oxide (ZnO) NPs was caused by the release of zinc ions. Thus, we hypothesized that mass could be used as an exposure metric for the toxicity of ZnO NPs. Healthy Sprague-Dawley rats were exposed to a low, moderate, or high dose of 35 and 250 nm ZnO particles or filtered air. Bronchoalveolar lavage fluid was collected to determine lung inflammation, injury and oxidative stress. The lung inflammation induced by ZnO particles according to different concentration metrics, including number, mass and surface area, was compared. The mass concentration was significantly correlated with the percentage of neutrophils (R(2) = 0.84), number of neutrophils (R(2) = 0.84) and total cells (R(2) = 0.73). Similarly, surface area concentration was significantly correlated with the percentage of neutrophils (R(2) = 0.94), number of neutrophils (R(2) = 0.81) and total cells (R(2) = 0.76). There was no correlation between the number and lung inflammation. We found that both mass and surface area were effective as metrics for the toxicity of ZnO NPs, although only surface area was previously indicated to be an effective metric. Our results are also consistent with recent study results that ZnO NPs and released zinc ions may play a role mediating the toxicity of NPs.

PCDD/F adsorption and destruction in the flue gas streams of MWI and MSP via Cu and Fe catalysts supported on carbon.

Catalytic destruction has been applied to control polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) emissions from different facilities. The cost of carbon-based catalysts is considerably lower than that of the metal oxide or zeolite-based catalysts used in the selective catalytic reduction (SCR) system. In this study, destruction and adsorption efficiencies of PCDD/Fs achieved with Cu/C and Fe/C catalysts from flue gas streams of a metal smelting plant (MSP) and a large-scale municipal waste incinerator (MWI), respectively, are evaluated via the pilot-scale catalytic reactor system (PCRS). The results indicate that Cu and Fe catalysts supported on carbon surface are capable of decomposing and adsorbing PCDD/ Fs from gas streams. In the testing sources of MSP and MWI, the PCDD/F removal efficiencies achieved with Cu/C catalyst at 250 degrees C reach 96%, however, the destruction efficiencies are negative (-1,390% and -112%, respectively) due to significant PCDD/F formation on catalyst promoted by copper. In addition, Fe/C catalyst is of higher removal and destruction efficiencies compared with Cu/C catalyst in both testing sources. The removal efficiencies of PCDD/Fs achieved with Fe/C catalyst are 97 and 94% for MSP and MWI, respectively, whereas the destruction efficiencies are both higher than 70%. Decrease of PCDD/F destruction efficiency and increase of adsorption efficiency with increasing chlorination of dioxin congeners is also observed in the test via three-layer Fe/C catalyst. Furthermore, the mass of 2,3,7,8-PCDD/Fs retained on catalyst decreases on the order of first to third layer of catalyst. Each gram Fe/C catalyst in first layer adsorbs 10.9, 6.91, and 3.04 ng 2,3,7,8-PCDD/Fs in 100 min testing duration as the operating temperature is controlled at 150, 200, and 250 degrees C, respectively.

Field enhancements of packed-bed performance for low-concentration acidic and basic-waste gases from semiconductor manufacturing process.

Low-concentration acidic and basic-waste gas pollutants contribute significantly in the total emission of a facility. Previous results show that the control of high volumetric flow rate (approximately 500 m3/min), low-concentration acidic (< 1 ppm by vol) and basic (< 3 ppm by vol) gases from semiconductor process vent, by conventional wet scrubbing technique is a challenging task. This work was targeted to enhance the performance of packed beds for high-volumetric flow rate, low-concentration acidic (HF, HCl), and basic (NH3)-waste gases from the semiconductor manufacturing process. The methodology used to meet the goal was the application of fine-water mist over the inlet stream before entering to the packed bed and use of the surfactant with mist/packed-bed liquid in low concentration. An experimental study was carried out in two acid-packed beds to optimize the operating conditions, such as pH of the liquid, circulating liquid flow rate, blow-down cycle, and so forth. The relationship among liquid pH, liquid ionic concentration, and the removal efficiency of the packed bed for the pollutants has been discussed considering chemical equilibrium, two-film theory, and Henry's law. For the potential utilization of scrubbing water, the dependency of the efficiency on blow-down cycle was studied, and a mechanism is suggested. The proposed water-mist surfactant system was installed in two acid-packed beds, and performance of the packed beds was compared. The background efficiencies of the acid-packed beds for HF, HCl, and NH3 were found max to be (n = 11) 53, 40, and 27%, whereas after installation of the system, they increased significantly and became 76 +/- 13% (n = 10), 76 +/- 8% (n = 7), and 78 +/- 7% (n = 7), respectively, for inlet concentrations of HF and HCl < 1 ppm and NH3 < 14 ppm. The mechanism by which the surfactants operate to enhance the removal in scrubbing process is suggested considering the hydrodynamic effect and the interfacial effect with the charge-generating characteristic of surfactants on water surface, when dissolved into water. The results show that a proposed rectification system can effectively reduce the emission rates below the regulatory level (0.6 kg/hr) at the present conditions of the facility.

Axial flow cyclone for segregation and collection of ultrafine particles: theoretical and experimental study.

In this study, an axial flow cyclone was designed, fabricated, and evaluated at different conditions of air flow rates (Q0) and low-pressure environments (P), especially for the segregation and collection of ultrafine particles. An evaporation/condensation type of aerosol generation system consisting of tube furnace and mixing chamber was employed to produce test aerosols. The test aerosol was then classified by a differential mobility analyzer (DMA) and number concentration was measured by a condensation nuclei counter (CNC) and an electrometer upstream and downstream of the cyclone, respectively. The s-shaped curve of the collection efficiency in submicron particle size range was obtained to be similar to the traditional cyclone found in the literatures when the particles were largerthan 40 nm at Q0 = 1.07, 0.455 L(STP)/min, and P = 4.8-500 Torr. The curve was found to be fitted very well by a semiempirical equation described in this paper. For particles smaller than 40 nm, however, the collection efficiency was unusually increased as the particle diameter was decreased due to the fact that the diffusion deposition becomes the dominant collection mechanism in the low-pressure conditions. A model composed of centrifugal force and diffusion deposition is presented and used to fit the experimental data. The cyclone was demonstrated to separate and collect ultrafine particles effectively in the tested vacuum conditions.

The effect of environmental conditions and electrical charge on the weighing accuracy of different filter materials.

Different filter materials and electrical charge elimination methods were used to investigate the weighing accuracy of filter papers under different environmental conditions. The results show that the standard deviations (S.D.) of weight data for glass fiber and MCE filters were substantial without environmental control, whether or not the electrical charge eliminators were used. Values of 0.157 and 0.349 mg were determined for glass and MCE filters, respectively. The accuracy of weighing was substantially improved and the S.D. was reduced to 0.01 and 0.09 mg for glass fiber and MCE filters, respectively, after applying the environmental control conditions. For PVC and Teflon filters, the accuracy of weighing was good, even in the uncontrolled environmental conditions, whether or not the electrical charge eliminators were used. The S.D. values of weighing data of PVC and Teflon filters were 0.007 and 0.011 mg, respectively.