S. Zaromb, D. Martell, Zaromb Research Corp., Burr Ridge, IL; N. Schattke, Schattke Chemical Consulting, Yorkville, IL; K. Phelps, Consultant, Perryman, MD; C. Wick, U.S. Army, Aberdeen Provind Ground, MD; B. Christensen, Johns Hopkins University, Baltimore, MD.
Present methods of detecting aerosolized pathogens consist of passing a large volume of air through a “collector” which concentrates airborne particles into a small volume of liquid that can be tested by an appropriate sensor or analyzer. To achieve adequate sensitivity, cyclonic (or other inertial separation) devices sample air at rates of several hundred L/min and achieve collection efficiencies of >50% for particle sizes of about 1 µm or larger. However, for particles of <1 µm, the collection efficiencies of such devices drop off sharply to negligible values. The only airborne viruses that these devices could collect would be those contained in larger droplets or aggregates. Once these dry up or break up, the remaining floating mostly smaller aggregates or single virus particles would be overlooked by the presently available means. Electrostatic precipitation-based devices have been known to capture particles ranging in size from <0.1 µm to >10 µm efficiencies of >90%. A collector based on wet electrostatic precipitation (WEP), recently developed under an Army-sponsored Small Business Innovation Research project, collects 1-µm fluorescent beads at efficiencies of >80% and an airflow rate of 500 L/min. To test its ability to collect single virus particles, we are aerosolizing dilute suspensions of an MS2 phage and collecting the aerosol with a WEP instrument. The collection liquid is then centrifuged down to 0.25 mL and the resulting suspension tested for MS-2 with an integrated virus detection system (IVDS) comprising a virus particle imager and counter developed at the U.S. Army’s Edgewood Chemical Biological Center. The first test yielded a count of 1000 particles 24.1 nm in size in a 50-nL sample, corresponding to a collection efficiency of >15%. The results of continued tests will be evaluated for possible applications to timely discovery of pandemic infections in workplaces, employee cafeterias, and airplanes and other transportation means.
D. Baxter, Environmental Analysis Associates Inc., San Diego, CA.
Indoor air quality and dust complaints can arise with the appearance of “white” or “black” dust on horizontal building surfaces, or heating, ventilation, and air conditioning (HVAC) system supply and return air registers. Identifying the source and origin of the dust can often be more important than determining the chemical or biological composition of the dust. This presentation illustrates the usefulness of analytical microscopy and microanalysis methods to achieve this goal. Over the past 15 years, Environmental Analysis Associates has been compiling aerosol data from complaint buildings, and developing an optical and electron microscopy standards library of common building materials and building generated aerosols. The first step in addressing potential dust complaints is using optical microscopy to evaluate surface samples as well as airborne samples collected by slit impaction sampling. Optical microscopy is used to categorize, quantify, and determine the potential source of large (>3µm in diameter) bioaerosols and aerosols. In many cases, the source can be determined by optical microscopy alone. When results are inconclusive by optical microscopy, scanning electron microscopy and dispersive X-ray analysis can effectively be used to identify indicator particles, fibers, and “small” dust particles that are directly attributed to specific building material sources. This presentation provides examples of common indicator dust particles and identifies their material sources as well as common building conditions associated with their presence.
F. Mirer, Hunter College, New York, NY.
OSHA’s 2004 denial of the 1993 United Auto Workers’ petition for a standard for metalworking fluids (MWF), and the Third Circuit Court of Appeals’ concurrence in that denial, were based on the scientific record in the final report of the OSHA Metalworking Fluids Standards Advisory Committee (SAC) in July 1999. That report heavily relied on the 1998 NIOSH Criteria for a Recommended Standard: Occupational Exposure to Metalworking Fluids. The MWF SAC and NIOSH had recommended an exposure limit of 0.5 mg/M3. OSHA and the court largely concurred that MWF exposure was associated with asthma and hypersensitivity pneumonitis, but argued that evidence for an association with cancer was “equivocal at best.” Published and unpublished studies regarding occupational cancer, respiratory conditions, microbial growth, and composition of MWF will be reviewed, emphasizing knowledge not acted on by the end of 2003, and knowledge that has emerged since. Eleven papers with original results associating cancer with exposure to MWF have been published since 2000, supported by results from an unpublished mortality study. Twelve papers associating respiratory effects with MWF, including laboratory toxicology, have been published. Nine papers have demonstrated that historical methods don’t measure microbial composition. Scientific support for an MWF exposure limit has increased since the NIOSH and Metalworking Fluids SAC conclusions.
N. Esmen, R. Hancock, University of Illinois at Chicago, Chicago, IL.
Before the early to mid-1980s, surface grinding was performed by a method called pendulum grinding. In pendulum grinding, the cooling and lubricating of the work surface was achieved by flooding the work with a metalworking fluid (MWF). In contrast to more recent high-pressure coolant feed grinding, pendulum grinding generates aerosols by two different mechanisms. In one mechanism, the aerosol is generated by mechanically shearing the liquid (MWF) and the metal producing relatively large particles. The particles generated by shear are dominated by the MWF droplets. The particle generation by the other mechanism is an evaporation-condensation process. The model using the analysis of these two mechanisms to describe the generated aerosol suggests that droplet formation can be explained by rotating wheel aerosol generation theory with characteristic particle size of about 20 μm aerodynamic equivalent diameter. Assuming minimal evaporation, the large-particle generation mechanism can be combined with the condensation aerosol generated in the “quenching” stage. Friedlander and Wang’s similarity solution in the continuum region suggests that the submicron aerosol would have a characteristic size of about 0.3 μm. While the analysis suggested a distinct bimodal number based particle size distribution, no confirmatory size distribution data was available. However, there is sufficient total and respirable dust concentration data to roughly confirm the size distribution of the mass dominated droplet mode. Additionally, the aerosols in the accumulation mode, in sufficient concentrations, would produce a blue haze similar to a cloud of tobacco smoke. In a facility where there were in excess of 250 grinders in operation, anecdotal evidence from interviews suggests that such a blue haze was present almost constantly over the area in which these grinders were located. Albeit a qualitative (or subjective) observation, it can, nevertheless, be considered an approximate validation of this model.
C. Lai, S. Lee, W. Lee, Chung Shan Medical University, Taichung, Taiwan; P. Tsai, Q. Chen, National Cheng Kung University, Tainan, Taiwan; D. Tang, Institute of Occupational Safety and Health, Taipei, Taiwan.
The objective of this study is to develop a uniform aerosol deposit sampling holder for quantitatively crystalline free silica analysis by using an X-ray diffraction spectrometer (XRD). In this study, three types of respirable samplers — SKC aluminum cyclone, nylon cyclone, and multiple inlet GS-3 cyclone — were chosen for the comparison. A traditional sampling cassette, asbestos sampling cowl, and newly aluminum holder were compared for the uniformity of collecting aerosol deposits. To determine the uniformity of filter deposits, a vibrating orifice monodisperse aerosol generator and ultrasonic atomizing nozzle were used to generate monodisperse and polydisperse methylene blue particles. Moreover, dioctyl phthalate was generated to measure separation curves of respirable samplers. The aerosols were dried by filtered compressed air and then neutralized by Am-241. An aerodynamic particle sizer was used to measure the number concentration and size distribution of the generated aerosol particles. Meanwhile, the filter deposits were examined via image processing, combined with statistical methods for defining uniformity. The results showed that the SKC cyclone appeared to have higher uniformly sampling results than the nylon and GS-3 cyclones. The uniformity was about 0.6652±0.0157, 0.4050±0.0255, and 0.3842±0.0328, respectively, when assembling with a traditional filter pad and two-piece cassette. However, the uniformity of SKC, nylon, and GS-3 cyclones was increased when assembling with a traditional filter pad and new type of aluminum holder. The uniformity was about 0.7232±0.0166, 0.7697±0.0091, and 0.7642±0.0162, respectively. The uniformity of filter deposits of the new aluminum holder was superior to the traditional sampling cassette. The new holder will need further optimization and will be used for quantitative crystalline free silica analysis by using the Kohyama method.
S. Reynolds, J. Nakatsu, M. Tillery, T. Keefe, J. Mehaffy, Colorado State University, Fort Collins, CO; P. Thorne, K. Donham, P. O’Shaughnessy, University of Iowa, Iowa City, IA; M. Nonnenmann, Southeastern Oklahoma State University, Durant, OK.
New inhalable aerosol samplers offer significant improvement for studies to reduce respiratory disease. However, these devices were not designed for organic dusts. The goals of this field study were (1) to evaluate the performance of two inhalable samplers (IOM, Button) and two traditional samplers (37-mm plastic cassette, cyclone) in agricultural environments, and (2) to determine relationships between these sampling devices to allow comparison with historical measurements. Samples were collected in swine, chicken, turkey, and dairy facilities in Colorado and Iowa. Pairs of each sampling device were attached to the front and back of a rotating manikin. Ten sampling sessions were conducted in each building, n = 20 total, except for dairy, where n = 21. IOM samplers had the lowest, most consistent coefficient of variation (0.042-0.086), followed by the Button. The cyclone had the highest variability. The IOM provided the highest aerosol concentration in all environments (0.20-3.26 mg/m3). The cassette and Button determined similar concentrations in all four environments, and the cyclone determined the lowest levels as expected. Ratios of geometric means for the cassette and Button were closest to 1.00. Ratios for the cassette and Button vs. the IOM ranged from 0.460 to 0.801. The Button and cassette were the most highly correlated (r = 0.70 - 0.93), and this was consistent across environments. The cyclone had the least consistent correlations with the other samplers. The cassette correlated well with the IOM (r = 0.81 - 0.92), except for the dairies (r = 0.08). The relative performance of these four aerosol samplers was dependent on the environment. Aerosol concentration and size distribution may both be important factors. These data suggest that relationships need to be determined for each environment/organic dust type independently before using these new tools to assess risk in occupational and environmental settings.
J. Kesavan, D. Schepers, U.S. Army, Aberdeen Proving Ground, MD.
Aerosol samplers are developed for sampling and detecting bio-aerosols. Aerosol samples collected by a sampler depend on the sampling and retention efficiencies. AGI-30 impingers and SKC biosamplers are used as standard reference samplers for bioaerosol testing. High-volume samplers such as SASS and PHTLAAS are developed for sampling low concentrations of bioaerosols from air. High variability in sampling and retention efficiencies has been seen by many researchers. This study evaluated the sampling efficiencies of AGI-30, SKC biosamplers, and SASS and PHTLAAS aerosol samplers using inert fluorescent polystyrene latex (PSL) microspheres and fluorescent oleic acid particles. Following this the retention efficiency of 0.5, 1-, 2-, 3-, and 10-μm PSL particles over time (up to 1 hr) was measured. The results showed that the SKC biosamplers and AGI 30 impingers have sampling efficiencies ranging from 4% to 100% for particle sizes from 1 µm to 9 μm, and they varied between units tested. The PHTLAAS has sampling efficiencies ranging from 62% to 99% for particle sizes 1 µm to 8 μm and the SASS has the sampling efficiencies ranging from 5% to 65% for particle sizes 1 µm to10 μm. Retention efficiency results showed that one sampler had as low as 6% particle remaining in 60 min. The particle retentions were similar for the SKC biosamplers and impingers tested. The highest particle retention was for 10-μm particles, and the lowest particle retention was for 1-μm particles.