A profile of spatial abilities in people with Down syndrome.

BACKGROUND: Spatial abilities are fundamental cognitive abilities, have direct applications in daily life, serve as a cognitive foundation for many other complex skills and are used in many specialty jobs. The current study aimed to systematically and comprehensively evaluate the spatial abilities of individuals with Down syndrome (DS) relative to mental ability-matched typically developing (TD) children based on Newcombe and Shipley's double-dimension theoretical framework for classifying spatial abilities. METHODS: Forty adolescents and young adults with DS and 40 TD children completed a nonverbal intelligence test (Raven's), two measures of static-extrinsic skills (water-level task and cart task), two measures of static-intrinsic skills (figure ground and form completion), two measures of dynamic-extrinsic skills (three mountains task and dog task) and two measures of dynamic-intrinsic spatial skills (mental rotation task and block design task). RESULTS: Participants with DS showed reduced performance on two dynamic-intrinsic tasks and one static-extrinsic task (i.e. cart task) relative to TD children. Performances were similar in two dynamic-extrinsic tasks and two static-intrinsic tasks. Analyses of composite accuracy for each spatial category further confirmed deficits in dynamic-intrinsic and static-extrinsic categories for people with DS relative to TD children. CONCLUSIONS: Our results showed an uneven profile of spatial abilities in people with DS relative to ability-matched TD children with particular weaknesses in comprehending and manipulating dynamic-intrinsic and static-extrinsic spatial relations. Furthermore, our research has important clinical implications for more targeted interventions to improve spatial abilities in people with DS.

Autoclave sterilization and ethanol treatment of re-used surgical masks and N95 respirators during COVID-19: impact on their performance and integrity.

BACKGROUND: An exceptionally high demand for surgical masks and N95 filtering facepiece respirators (FFRs) during the COVID-19 pandemic has considerably exceeded their supply. These disposable devices are generally not approved for routine decontamination and re-use as a standard of care, while this practice has widely occurred in hospitals. The US Centers for Disease Control and Prevention allowed it "as a crisis capacity strategy". However, limited testing was conducted on the impact of specific decontamination methods on the performance of N95 FFRs and no data was presented for surgical masks. AIM: We evaluated common surgical masks and N95 respirators with respect to the changes in their performance and integrity resulting from autoclave sterilization and a 70% ethanol treatment; these methods are frequently utilized for re-used filtering facepieces in hospitals. METHODS: The filter collection efficiency and pressure drop were determined for unused masks and N95 FFRs, and for those subjected to the treatments in a variety of ways. The collection efficiency was measured for particles of approximately 0.037-3.2 µm to represent aerosolized single viruses, their agglomerates, bacteria and larger particle carriers. FINDINGS: The initial collection efficiency and the filter breathability may be compromised by sterilization in an autoclave and ethanol treatment. The effect depends on a protective device, particle size, breathing flow rate, type of treatment and other factors. Additionally, physical damages were observed in N95 respirators after autoclaving. CONCLUSION: Strategies advocating decontamination and re-use of filtering facepieces in hospitals should be re-assessed considering the data obtained in this study.

Concentration gradient patterns of traffic and non-traffic-generated fine and coarse aerosol particles.

The research project described in this article was undertaken to establish baseline information for a Health Impact Assessment (HIA) project of Interstate 75 road construction in Cincinnati, Ohio. The objective of the authors' study was to evaluate the concentrations of elemental and organic carbon (EC and OC), as well as characterize particle number concentrations using devices that measure the fine fraction in the range of 0.02-1 microm and the coarse fraction up to 20 pm. The measurements were conducted at two sites located in the proximity of an interstate highway (at 124 and 277 m) as well as at a remote control site (at >2000 m from any interstate highway). Samples were collected for 24 hours over 12 days in each season (i.e., summer, fall, and winter). Wind data were obtained from the area weather station. Data were analyzed using mixed linear models. Significant increases in concentrations of EC, OC, and fine particles as well as in EC/OC ratios were observed with decreased distance to the highway; this difference was more pronounced in the fall. These results suggest that residents and workers in areas near high-traffic highways may be exposed to elevated levels of airborne fine particles. The results can be used as a baseline for future HIAs of road construction in the area.

Stenotrophomonas, Mycobacterium, and Streptomyces in home dust and air: associations with moldiness and other home/family characteristics.

Respiratory illnesses have been linked to children's exposures to water-damaged homes. Therefore, understanding the microbiome in water-damaged homes is critical to preventing these illnesses. Few studies have quantified bacterial contamination, especially specific species, in water-damaged homes. We collected air and dust samples in twenty-one low-mold homes and twenty-one high-mold homes. The concentrations of three bacteria/genera, Stenotrophomonas maltophilia, Streptomyces sp., and Mycobacterium sp., were measured in air and dust samples using quantitative PCR (QPCR). The concentrations of the bacteria measured in the air samples were not associated with any specific home characteristic based on multiple regression models. However, higher concentrations of S. maltophilia in the dust samples were associated with water damage, that is, with higher floor surface moisture and higher concentrations of moisture-related mold species. The concentrations of Streptomyces and Mycobacterium sp. had similar patterns and may be partially determined by human and animal occupants and outdoor sources of these bacteria.

Streptomycetes in house dust: associations with housing characteristics and endotoxin.

In addition to mold, indoor bioaerosols also contain bacterial components that may have implications for human health. Endotoxin is a cell wall component in Gram-negative bacteria present at varying levels indoors that has been found to have respiratory health implications. Streptomyces is a large genus of Gram-positive bacteria, and some species have been shown to produce inflammatory reactions in vitro and in vivo. The aim of this study was to determine predictors of streptomycetes levels in house dust and to compare the variation in streptomycetes levels with that in endotoxin levels. Dust was collected by floor vacuuming from 178 homes in the Cincinnati metropolitan area. Streptomycetes levels were measured by quantitative PCR, and endotoxin was assayed by the Limulus amebocyte lysate method. Associations between home characteristics and bacterial contaminants, expressed as concentration and load, were investigated through multiple regression analyses. The presence of two or more dogs was a strong predictor of both streptomycetes and endotoxin levels. Season of dust collection and levels of outdoor molds were predictors of streptomycetes but not endotoxin levels. In contrast, number of inhabitants was a significant predictor of endotoxin load only. Neither streptomycetes nor endotoxin levels were associated with metrics of moisture damage.

Removal of viable bioaerosol particles with a low-efficiency HVAC filter enhanced by continuous emission of unipolar air ions.

UNLABELLED: Continuous emission of unipolar ions has been shown to improve the performance of respirators and stationary filters challenged with non-biological particles. In this study, we investigated the ion-induced enhancement effect while challenging a low-efficiency heating, ventilation and air-conditioning (HVAC) filter with viable bacterial cells, bacterial and fungal spores, and viruses. The aerosol concentration was measured in real time. Samples were also collected with a bioaerosol sampler for viable microbial analysis. The removal efficiency of the filter was determined, respectively, with and without an ion emitter. The ionization was found to significantly enhance the filter efficiency in removing viable biological particles from the airflow. For example, when challenged with viable bacteria, the filter efficiency increased as much as four- to fivefold. For viable fungal spores, the ion-induced enhancement improved the efficiency by a factor of approximately 2. When testing with virus-carrying liquid droplets, the original removal efficiency provided by the filter was rather low: 9.09 +/- 4.84%. While the ion emission increased collection about fourfold, the efficiency did not reach 75-100% observed with bacteria and fungi. These findings, together with our previously published results for non-biological particles, demonstrate the feasibility of a new approach for reducing aerosol particles in HVAC systems used for indoor air quality control. PRACTICAL IMPLICATIONS: Recirculated air in HVAC systems used for indoor air quality control in buildings often contains considerable number of viable bioaerosol particles because of limited efficiency of the filters installed in these systems. In the present study, we investigated - using aerosolized bacterial cells, bacterial and fungal spores, and virus-carrying particles - a novel idea of enhancing the performance of a low-efficiency HVAC filter utilizing continuous emission of unipolar ions in the filter vicinity. The findings described in this paper, together with our previously published results for non-biological particles, demonstrate the feasibility of the newly developed approach.

Relationship between indoor and outdoor bio-aerosols collected with a button inhalable aerosol sampler in urban homes.

This field study investigated the relationship between indoor and outdoor concentrations of airborne actinomycetes, fungal spores, and pollen. Air samples were collected for 24 h with a button inhalable aerosol sampler inside and outside of six single-family homes located in the Cincinnati area (overall, 15 pairs of samples were taken in each home). The measurements were conducted during three seasons - spring and fall 2004, and winter 2005. The concentration of culturable actinomycetes was mostly below the detection limit. The median indoor/outdoor ratio (I/O) for actinomycetes was the highest: 2.857. The indoor of fungal and pollen concentrations followed the outdoor concentrations while indoor levels were mostly lower than the outdoor ones. The I/O ratio of total fungal spores (median=0.345) in six homes was greater than that of pollen grains (median=0.025). The low I/O ratios obtained for pollen during the peak ambient pollination season (spring) suggest that only a small fraction penetrated from outdoor to indoor environment. This is attributed to the larger size of pollen grains. Higher indoor concentration levels and variability in the I/O ratio observed for airborne fungi may be associated with indoor sources and/or higher outdoor-to-indoor penetration of fungal spores compared to pollen grains. Practical Implication This study addresses the relationship between indoor and outdoor concentrations of three different types of bio-aerosols, namely actinomycetes, fungal spores, and pollen grains. The results show that actinomycetes are rare in indoor and outdoor air in Midwest, USA. Exposure to pollen occurs mainly in the outdoor air even during peak pollen season. Unexpectedly high fungal spore concentrations were measured outdoors during winter. The presented pilot database on the inhalable levels of indoor and outdoor bio-aerosols can help apportion and better characterize the inhalation exposure to these bio-aerosols. Furthermore, the data can be incorporated into existing models to quantify the penetration of biological particles into indoor environments from outdoors.

Evaluation of ionic air purifiers for reducing aerosol exposure in confined indoor spaces.

UNLABELLED: Numerous techniques have been developed over the years for reducing aerosol exposure in indoor air environments. Among indoor air purifiers of different types, ionic emitters have gained increasing attention and are presently used for removing dust particles, aeroallergens and airborne microorganisms from indoor air. In this study, five ionic air purifiers (two wearable and three stationary) that produce unipolar air ions were evaluated with respect to their ability to reduce aerosol exposure in confined indoor spaces. The concentration decay of respirable particles of different properties was monitored in real time inside the breathing zone of a human manikin, which was placed in a relatively small (2.6 m3) walk-in chamber during the operation of an ionic air purifier in calm air and under mixing air condition. The particle removal efficiency as a function of particle size was determined using the data collected with a size-selective optical particle counter. The removal efficiency of the more powerful of the two wearable ionic purifiers reached about 50% after 15 min and almost 100% after 1.5 h of continuous operation in the chamber under calm air conditions. In the absence of external ventilation, air mixing, especially vigorous one (900 CFM), enhanced the air cleaning effect. Similar results were obtained when the manikin was placed inside a partial enclosure that simulated an aircraft seating configuration. All three stationary ionic air purifiers tested in this study were found capable of reducing the aerosol concentration in a confined indoor space. The most powerful stationary unit demonstrated an extremely high particle removal efficiency that increased sharply to almost 90% within 5-6 min, reaching about 100% within 10-12 min for all particle sizes (0.3-3 microm) tested in the chamber. For the units of the same emission rate, the data suggest that the ion polarity per se (negative vs. positive) does not affect the performance but the ion emission rate does. The effects of particle size (within the tested range) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria) as well as the effects of the manikin's body temperature and its breathing on the ionic purifier performance were either small or insignificant. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when used inside confined spaces with a relatively high surface-to-volume ratio. PRACTICAL IMPLICATIONS: Ionic air purifiers have become increasingly popular for removing dust particles, aeroallergens and airborne microorganisms from indoor air in various settings. While the indoor air cleaning effect, resulting from unipolar and bipolar ion emission, has been tested by several investigators, there are still controversial claims (favorable and unfavorable) about the performance of commercially available ionic air purifiers. Among the five tested ionic air purifiers (two wearable and three stationary) producing unipolar air ions, the units with a higher ion emission rate provided higher particle removal efficiency. The ion polarity (negative vs. positive), the particle size (0.3-3 microm) and properties (NaCl, PSL, Pseudomonas fluorescens bacteria), as well as the body temperature and breathing did not considerable affected the ionization-driven particle removal. The data suggest that the unipolar ionic air purifiers are particularly efficient in reducing aerosol exposure in the breathing zone when they are used inside confined spaces with a relatively high surface-to-volume ratio (such as automobile cabins, aircraft seating areas, bathrooms, cellular offices, small residential rooms, and animal confinements). Based on our experiments, we proposed that purifiers with a very high ion emission rate be operated in an intermittent mode if used indoors for extended time periods. As the particles migrate to and deposit on indoor surfaces during the operation of ionic air purifiers, some excessive surface contamination may occur, which introduces the need of periodic cleaning these surfaces.

Assessment of the aerosolization potential for fungal spores in moldy homes.

UNLABELLED: The airborne fungal concentration measured with air samplers during specific time intervals may not adequately represent the indoor air quality because of the sporadic nature of spore release from sources. The conventional source evaluation (e.g. swab and tape sampling) characterizes the mold source but does not relate to the fraction of spores that can be aerosolized from a contaminated material. As an alternative to these methods, we have recently developed and laboratory-tested a novel Fungal Spore Source Strength Tester (FSSST). It allows assessing the potential of aerosolization of fungal spores from contaminated surfaces under the most favorable release conditions. In this study, the FSSST was used to characterize the release of spores from four building materials in mold-problem homes. The spores of different species were efficiently aerosolized by the FSSST, exhibiting a total spore release rate ranging approximately from 10(2) to 10(3) cm2/min. For all tested materials, <2% of the spores on the contaminated surface were released during the tests. The airborne spore concentration estimated from the release rate data was found in most cases to be significantly greater than the concentration actually measured in these environments with simultaneous air sampling. The results suggest that the FSSST can be used for the assessment of maximum potential exposure to airborne spores released from identified sources in homes. PRACTICAL IMPLICATIONS: A recently developed FSSST was found to be suitable to measure the aerosolization potential of indoor fungal sources at the most favorable release conditions. The FSSST generates the data that allows assessing the strength of mold sources in homes with respect to their maximum ability to contaminate indoor air with fungi. The novel approach bridges two conventional methods, the air sampling and the direct source evaluation (e.g. swab sampling), thus providing a better representation of the airborne fungal exposure than these methods individually. The device prototype can be used for evaluating the effectiveness of environmental interventions by taking samples before and after the intervention. As a broader application, the FSSST can be utilized for assessing the release of various hazardous biological and non-biological particles from contaminated surfaces.

Performance of personal inhalable aerosol samplers in very slowly moving air when facing the aerosol source.

While personal aerosol samplers have been characterized primarily based on wind tunnel tests conducted at relatively high wind speeds, modern indoor occupational environments are usually represented by very slow moving air. Recent surveys suggest that elevated levels of occupational exposure to inhalable airborne particles are typically observed when the worker, operating in the vicinity of the dust source, faces the source. Thus, the first objective of this study was to design and test a new, low cost experimental protocol for measuring the sampling efficiency of personal inhalable aerosol samplers in the vicinity of the aerosol source when the samplers operate in very slowly moving air. In this system, an aerosol generator, which is located in the centre of a room-sized non-ventilated chamber, continuously rotates and omnidirectionally disperses test particles of a specific size. The test and reference samplers are equally distributed around the source at the same distance from the centre and operate in parallel (in most of our experiments, the total number of simultaneously operating samplers was 15). Radial aerosol transport is driven by turbulent diffusion and some natural convection. For each specific particle size and the sampler, the aerosol mass concentration is measured by weighing the collection filter. The second objective was to utilize the new protocol to evaluate three widely used aerosol samplers: the IOM Personal Inhalable Sampler, the Button Personal Inhalable Aerosol Sampler and the 25 mm Millipore filter holder (closed-face C25 cassette). The sampling efficiencies of each instrument were measured with six particle fractions, ranging from 6.9 to 76.9 micro m in their mass median aerodynamic diameter. The Button Sampler efficiency data demonstrated a good agreement with the standard inhalable convention and especially with the low air movement inhalabilty curve. The 25 mm filter holder was found to considerably under-sample the particles larger than 10 micro m; its efficiency did not exceed 7% for particles of 40-100 micro m. The IOM Sampler facing the source was found to over-sample compared with the data obtained previously with a slowly rotating, freely suspended sampler in a low air movement environment. It was also found that the particle wall deposition in the IOM metallic cartridge was rather significant and particle size-dependent. For each sampler (IOM, Button and C25) the precision was characterized through the relative standard deviation (RSD) of the aerosol concentration obtained with identical samplers in a specific experiment. The average RSD was 14% for the IOM Sampler, 11% for the Button Sampler and 35% for the 25 mm filter cassette. A separate set of experiments, performed with the Simplified Torso showed that in very slowly moving air a personal sampler can be adequately evaluated even when it is not attached to a body but freely suspended (confirming the data reported previously).

Limitations of monoclonal antibodies for monitoring of fungal aerosols using Penicillium brevicompactum as a model fungus.

Molds are ubiquitous in every environment and many species have been recently associated with an increase in opportunistic infections in immunocompromised patients or the exacerbation of asthmatic episodes in allergic patients. The degree of environmental contamination with fungi thus needs to be monitored and in this study we report the development of a monoclonal antibody (mAb)-mediated enzyme-linked immunosorbent assay (ELISA) for the detection of spores of Penicillium brevicompactum in experimental model aerosols. In addition, we have investigated the influence of different parameters of air sampling and sample recovery on ELISA performance. MAbs were produced with standard hybridoma techniques and cross-reactivities were determined against spores of 53 fungal species by indirect ELISA. Standardized experimental fungal aerosols were collected with the Button Personal Inhalable Aerosol Sampler onto polycarbonate or polytetrafluoroethylene filters (PTFE) and the effects of different extraction buffers and filter agitation methods during sample processing on spore recovery and ELISA detection were investigated. Five mAbs were produced and all of them cross-reacted with several of 31 related Aspergillus, Penicillium and Eurotium species. However, cross-reactivities with 21 non-related fungi were rare. Spores were recovered in much higher numbers from polycarbonate filters (PFs) than from polytetrafluoroethylene filters. Optical densities (ODs) in ELISA were higher for spores collected into carbonate coating buffer (CCB) than phosphate-buffered saline (PBS). Filter bath sonication following filter vortexing had no positive effects on ELISA sensitivity. The cross-reactivity patterns of mAbs suggest that Aspergillus and Penicillium species share multiple antigens. Quantitative ELISA results for fungal aerosols were found to be influenced by differential sample processing and thus method standardization will be essential to maintain the comparability of immunometric monitoring results.

Comparison of filter bag, cyclonic, and wet dust collection methods in vacuum cleaners.

In this study, methods were developed for comparative evaluation of three primary dust collection methods employed in vacuum cleaners: filter bag, cyclonic, and wet primary dust collection. The dry collectors were evaluated with KCl test aerosols that are commonly used in filter testing. However, these aerosols cannot be used for evaluating wet collectors due to their hygroscopicity. Therefore, the wet collectors were evaluated with nonhygroscopic test particles. Both types of test aerosol indicated similar collection efficiencies in tests with dry collectors. The data show that high initial collection efficiency can be achieved by any one of the three dust collection methods: up to 50% for 0.35 microm particles, and close to 100% for 1.0 microm and larger particles. The degree of dependence of the initial collection efficiency on airflow rate was strongly related to the type and manufacturing of the primary dust collector. Collection efficiency decreased most with decreasing flow rate for the tested wet collectors. The tested cyclonic and wet collectors showed high reentrainment of already collected dust particles. After the filter bag collectors had been loaded with test dust, they also reemitted particles. The degree of reentrainment from filter bags depends on the particulate load and the type of filter material used. Thus, the overall particle emissions performance of a vacuum cleaner depends not only on the dust collection efficiency of the primary collector and other filtration elements employed, but also on the degree of reentrainment of already collected particles.

Particle emission characteristics of filter-equipped vacuum cleaners.

Industrial vacuum cleaners with final high-efficiency particulate air (HEPA) filters traditionally have been used for cleanup operations in which all of the nozzle-entrained dust must be collected with high efficiency, for example, after lead-based paint abatement in homes. In this study household vacuum cleaners ranging from $70 to $650 and an industrial vacuum cleaner costing more than $1400 were evaluated relative to their collection efficiency immediately after installing new primary dust collectors in them. Using newly developed testing technology, some of the low-cost household vacuum cleaners equipped with a final HEPA filter were found to have initial overall filtration efficiencies comparable to those of industrial vacuum cleaners equipped with a final HEPA filter. The household vacuum cleaners equipped with a final HEPA filter efficiently collect about 100% of the dry dust entrained by the nozzle. For extensive cleaning efforts and for vacuum cleaning of wet surfaces, however, industrial vacuum cleaners may have an advantage, including ruggedness and greater loading capacity. The methods and findings of this study are applicable to field evaluations of vacuum cleaners.

Test methods for evaluating the filtration and particulate emission characteristics of vacuum cleaners.

The overall filtration efficiency of a vacuum cleaner traditionally has been tested by placing the vacuum cleaner in a test chamber and measuring aerosol concentrations at the chamber inlet and outlet. The chamber test method was refined and validated in this study. However, this chamber test method shows an overall filtration efficiency of close to 100% for most of the industrial vacuum cleaners and for most of the newly developed household vacuum cleaners of midprice range or higher because all these vacuum cleaners have a high-efficiency particulate air (HEPA) or other highly efficient filter installed at the exhaust. A new test method was therefore developed through which the vacuum cleaner was probed in various internal locations so that the collection efficiency of the individual components could be determined. For example, the aerosol concentration upstream of the final HEPA filter can thus be measured, which permits one to estimate the life expectancy of this expensive component. The probed testing method is particularly suitable for field evaluations of vacuum cleaners because it uses compact, battery-operated optical particle size spectrometers with internal data storage. Both chamber and probed tests gave the same results for the aerosol filtration efficiency. The probed testing method, however, also gives information on the performance of the individual components in a vacuum cleaner. It also can be used to determine the dust pickup efficiency and the degree of reaerosolization of particles collected in the vacuum cleaner.

Release of lead-containing particles from a wall enclosure.

The 1995 Department of Housing and Urban Development (HUD) Guidelines for the Evaluation and Control of Lead-Based Paint Hazards in Housing discusses using interior and exterior wall enclosures for lead hazard control. Leaded dust may be aerosolized inside enclosures and released through gaps and cracks into a room. The effects of airflow and mechanical disturbances on dust release were studied using a laboratory wall enclosure model with dust collected from homes with lead-based paint hazards. Airflows relevant to residences were blown down the enclosure and out a 4-, 6-, or 8-mm horizontal gap at its bottom, simulating potential enclosure failure. Then, low-frequency mechanical vibrations also were applied to the enclosure. No significant dust release was found when blowing air down the enclosure even at 37 cm/sec (representing extremely high flow); release occurred only with this high flow and 3 Hz mechanical disturbances. Dust was released primarily from the floor area immediately adjacent to the enclosure gap; the release rate fluctuated over time. Most dust initially settled near the enclosure. Dust release for 1 hour at extreme conditions (high airflow with vibration) yields lead loading above the 1995 HUD clearance level of 100 microg/ft2 only within 3-4 cm of the wall; for the HUD standard (1 ft2) sampling area, the lead loading does not exceed 30 microg/ ft2. Redistributing dust over the room's 16 m2 floor space yields average extreme-condition loading rate of 2 microg/ft2/hour. At less-than-extreme conditions, dust would have to be released for years without cleaning to yield a hazard.

Metal exposure among abrasive blasting workers at four U.S. Air Force facilities.

Button Aerosol Samplers were used to monitor the personal exposure of workers performing abrasive blasting operations at four U.S. Air Force facilities. Inhalable aerosols containing 25 metals, including cadmium, lead, and chromium, were investigated. The Button Aerosol Sampler was chosen because of its ability to successfully withstand mechanical stress, prevent very large particles from collection, and protect the filter from overloading and shredding by rebound particles. In addition, previous studies have shown that the sampling efficiency of this personal Aerosol Sampler exhibits low sensitivity to the ambient air conditions and that it adequately follows the inhalability convention. Inductively coupled plasma (ICP) was used to analyze the collected samples for all 25 metals. In addition, visual absorption spectrophotometry (VAS) was used to analyze for hexavalent chromium because of the presence of strontium chromate. The collected samples yielded 8-hr time-weighted average (TWA) concentrations that were up to 250, 6, and 5 times higher than the permissible exposure limits (PELs) for cadmium, lead, and hexavalent chromium, respectively. Also, the chromium levels measured by the ICP and VAS exceeded the strontium chromate threshold limit value (TLV) by up to 640 and 950 times, respectively. No correlation was found between the ICP and VAS hexavalent chromium concentrations. The likely reasons of this were the presence of Cr (II) and (III) that cannot be detected by the VAS, and the chemical interference from iron and some other metals in the samples. The Button Aerosol Sampler was shown to be useful for the monitoring of workers' exposure to heavy metals during abrasive blasting operations.

Performance characteristics of the button personal inhalable aerosol sampler.

The button inhalable aerosol sampler with a curved porous inlet recently was developed and evaluated as a stationary sampler in the laboratory and in the field. The present study focused on investigating its suitability for personal inhalable aerosol sampling. The button sampler was tested at two wind velocities (0.5 and 2.0 m/sec), three particle sizes (7, 29, and 70 microm) and three orientations to the wind (0, 90, and 180 degrees). The performance characteristics of the button sampler were compared with those of three other personal samplers--the IOM (Institute of Occupational Medicine), GSP, and 37-mm closed-face filter cassette. The experiments were conducted in a wind tunnel with the samplers mounted on a full-size manikin. The direction-specific sampling efficiency of the button sampler was found to be essentially independent of the wind direction and dependent on the wind velocity to a much smaller degree than that of the three other samplers. When direction-averaged, the fit of its sampling efficiency curve to the inhalability curve was found to be better than that of the 37-mm closed-face cassette, comparable with that of the GSP sampler, and less than that of the IOM sampler. The precision of the button sampler was found to be generally equal to or better than the precision of the comparison samplers. It was concluded that the button sampler can be successfully used as a personal inhalable aerosol sampler.

Particle settling after lead-based paint abatement work and clearance waiting period.

This study investigated the evolution of airborne particle concentration and size distribution following abatement work in a controlled environment utilizing direct real-time particle monitoring and used it to project potential lead loadings as those particles settle. An 860 ft3 environmental test chamber with sophisticated ventilation and air purifying systems was built. Wooden doors with lead-based paint were dry sanded or scraped to generate the highest feasible airborne lead concentrations. Size-fractional airborne particle concentrations decreased exponentially with time in all tests, even with no air exchange, consistent with the stirred model of constantly mixed air, which predicts longer settling than for tranquil settling. Very low levels of air mixing generated by temperature gradients and initial room air turbulence affected particle settling. About 90% of airborne lead mass settled within 1 hour after active abatement, before final cleaning began. During the second waiting period of 1 hour, which followed cleaning of the floor, additional dust settled so that the additional potential lead loading from remaining airborne lead was less than 20 microg/ft2. For this worst case scenario, the underestimate of the lead loading done by the clearance sampling did not exceed about 30%. For more realistic conditions, the underestimates are projected to be much lower than the new 40 microg/ft2 Housing and Urban Development (HUD) clearance standards for floor dust lead. These results were obtained for the first waiting period (between the end of active abatement and the beginning of cleaning) of 1 hour, as recommended by HUD guidelines. Thus, this study demonstrates no need to increase either the first or second waiting period.

Performance of Air-O-Cell, Burkard, and Button Samplers for total enumeration of airborne spores.

Performance of three devices used for the total enumeration of airborne spores-the Air-O-Cell sampling cassette, the Burkard personal volumetric air sampler, and the Button Aerosol Sampler--was evaluated under controlled laboratory conditions. The first two are glass-slide impactors; the third collects spores on a filter. The samplers were challenged with 0.44-5.10 microm polystyrene latex particles and five microorganisms of 0.84-3.07 microm mean aerodynamic diameter: Streptomyces albus, Bacillus subtilis, Cladosporium cladosporioides, Penicillium brevicompactum, and Penicillium melinii. An optical particle counter measured the particle concentrations upstream and downstream of each sampler, and thus determined the physical collection efficiency of the three samplers. Collection efficiency of the Button Aerosol Sampler was close to 100% for the entire particle size range studied. The cut-off size of each impactor was 2.3-2.4 microm. Acridine orange (with epifluorescent microscopy) and lactophenol cotton blue (with bright light microscopy) staining techniques were used for the microscopic enumeration of spores. No significant difference in microscopic counts was found (at the 95% significance level) when using these two techniques with the Button Aerosol Sampler filters. When the lactophenol cotton blue staining was used to compare total microbial counts yielded by all three samplers, the Button Sampler showed significantly higher counts for the smaller size microorganisms (B. subtilis and C. cladosporioides). For the larger microorganisms (P. brevicompactum and P. melinii) all three samplers yielded similar results. Uniformity of particle deposition on the collection surface was highest for the Button Aerosol Sampler due to the design of its inlet. Thus, the filter collection method used with the Button Aerosol Sampler is suitable and can be advantageous for the enumeration of total airborne spores.

Survival of mycobacteria on N95 personal respirators.

OBJECTIVES: The overall aim of this study was to investigate the survival and possible growth of Mycobacterium tuberculosis simulant bacteria on respirator filters. METHODS: Mycobacterium smegmatis was used as a biochemical simulant for M tuberculosis. Bacterial survival was tested on National Institute for Occupational Safety and Health-certified N95 respirators from three manufacturers. The first experiments simulated one-time respirator use and subsequent storage for 1 to 9 days under ideal conditions for the growth of mycobacteria: 37 degrees C and 85% relative humidity. The bacteria were loaded on the respirator filters under three different nutritional conditions: in the absence of nutrients; in the presence of human saliva (simulating conditions when the respirator is worn); and in the presence of nutrient broth (for ideal growth potential). The subsequent experiments simulated respirator wear for 2 hours under medium work-load conditions at a breathing rate of 56 L/min. RESULTS: It was found that M smegmatis did not grow on the tested respirators, even when the respirators were stored at temperature, humidity, and nutrition conditions most favorable for microbial growth. However, these bacteria could survive on respirators for up to 3 days during storage. The culturability of M smegmatis was not affected by airflow that simulated the breathing rate associated with medium work-load conditions for 2 hours. CONCLUSIONS: This study shows that M tuberculosis surrogate bacteria collected on a respirator are not able to grow and are able to survive only in ideal (ie, not clinically relevant) conditions. Based on these experiments, we conclude that M tuberculosis is unlikely ever to become an infectious problem in the air again, once it is removed by a respirator.