Real-Time Monitoring of Viable Bioaerosols: Capability of the UVAPS to Predict the Amount of Individual Microorganisms in Aerosol Particles

The Ultraviolet Aerodynamic Particle Sizer (UVAPS) is a novel aerosol monitor for enumerating and sizing microbial aerosols. To explore the capability of the method to estimate the number of microorganisms (bacteria) in aerosol particles, and thus to provide information on the concentration of airborne microorganisms, in addition to the total number of microbe carrying particles, a linearity of the UVAPS fluorescent signals with respect to the concentration of the fluorophores was investigated. As the amount of intrinsic fluorophores in bacteria may vary depending on viability status of the cells, the linearity was initially investigated for the non-microbial aerosols (NADH, NADPH, or riboflavin), with preset concentrations of fluorescent material in aerosol particles. The succeeding tests were performed with bacterial aerosols containing carefully washed Bacillus subtilis or Micrococcus luteus vegetative cells. To correlate the fluorescence intensity with particle size, which determines the amount of fluorophores (or cells) in the aerosol particles, the UVAPS data were analysed for each of 64 size-channels individually. The fluorescence intensity was linear with respect to the particle volume at the fluorophore concentrations characteristic to bacterial cells (correlation factors were typically greater than 0.9) and became curvilinear at higher concentrations. As the linearity of the UVAPS signals was confirmed for bacterial aerosols, it was concluded that the UVAPS can be used to estimate the concentration of airborne viable bacterial cells in artificially generated bioaerosols. The predicted concentrations of viable cells in the M. luteus aerosols compared favourably with the results of the AGI-30 sampling for culturable cells

State of Epidemiological Evidence for the Health Impacts of Ultrafine Particles

There has been increasing interest in the effect of ultrafine particles (UFP) on human cardiovascular and respiratory health. The adverse health impacts due to particle exposure are currently attributed to the mass concentration or the chemical composition of particles smaller than 10 μm (PM10) or 2.5 μm (PM2.5) in diameter. However, it has been hypothesised that it is actually UFP (< 0.1 μm) measured in terms of number concentration, as opposed to mass concentration, that might be responsible for the observed health effects. This paper presents the results of a critical literature review aimed at analysing the current state of epidemiological evidence for the effects of UFP on human health. In summary, the array of epidemiological studies conducted thus far suggests that UFP exposure is associated with human mortality, and respiratory and cardiovascular morbidity. This holds true despite the considerable gaps in knowledge that remain, and despite the inconsistencies found between some studies, resulting from some deficiencies in the study designs. The limited number of epidemiological studies conducted thus far indicates that there are comparable health effects of fine and ultrafine particles, which appear to be independent of each other. Fine particles show more immediate effects whilst ultrafine particles show more delayed effects on mortality. However, at present the database is too limited (in terms of both number of studies and number of subjects) and geographically restricted, to allow clear conclusions on the mode of action and/or generalisation to other settings. Consequently, it is recommended that further, better-designed studies be initiated to improve the understanding of health impacts of UFP

Relation Between Particle Mass and Number for Submicrometer Airborne Particles

The relationship between particle mass and the number of ambient air particles for the submicrometer size range was examined using a Tapered Element Oscillating Microbalance to determine the mass concentration, and a Scanning Mobility Particle Sizer to determine the volume concentration and total number of particles. After validating the techniques through their application to the estimation of submicrometer particle density for two laboratory generated aerosols of known bulk density (Sodium Chloride and Di-2-ethylhexyl-sebacate), the submicrometer fraction of laboratory generated Environmental Tobacco Smoke and ambient air were examined and an estimate of the average submicrometer particle densities for these aerosols found to be 1.18 g cm-3 and 1.7 g cm-3 respectively

Dust emissions from a tunnel-ventilated broiler poultry shed with fresh and partially reused litter

Dust emissions from large-scale, tunnel-ventilated poultry sheds could have negative health and environmental impacts. Despite this fact, the literature concerning dust emissions from tunnel-ventilated poultry sheds in Australia and overseas is relatively scarce. Dust measurements were conducted during two consecutive production cycles at a single broiler shed on a poultry farm near Ipswich, Queensland. Fresh litter was employed during the first cycle and partially reused litter was employed during the second cycle. This provided an opportunity to study the effect that partial litter reuse has on dust emissions. Dust levels were characterised by the number concentration of suspended particles having a diameter between 0.5 and 20 μm and by the mass concentration of dust particles of less than 10 μm diameter (PM10) and 2.5 μm diameter (PM2.5). In addition, we measured the number size distributions of dust particles. The average concentration and emission rate of dust was higher when partially reused litter was used in the shed than when fresh litter was used. In addition, we found that dust particles emitted from the shed with partially reused litter were finer than the particles emitted with fresh litter. Although the change in litter properties is certainly contributing to this observed variability, other factors such as ventilation rate and litter moisture content are also likely to be involved

Determination of the number of individual bacterial cells in aerosol particles with the UVAPS

Intensity of the fluorescent signals detected by the UVAPS was found to be directly proportional to the amount of the fluorophores in the airborne particles, which indicates that the UVAPS data can be used to estimate the number of individual microorganisms in the particles. This study further explored a capability of the UVAPS to provide data on the concentration of airborne bacterial cells, in addition to the concentration of airborne bacterial particles

Investigation of linearity of the UVAPS fluorescent signals

The fluorescence emitted by aerosol particles is registered by the UVAPS in one of 64 channels, depending on the intensity of the signal. The UVAPS does not provide the nominal values for the fluorescence intensity of the particles in arbitrary units such as relative fluorescence units (rfu), as is typically reported by the spectrophotometers. Instead, the intensity of the signals is reported on a scale from 1 to 64, corresponding to the channel numbers. Accordingly to the Beer-Lambert law, the fluorescence intensity should be directly proportional to the amount of fluorophores in the aerosol particles, in the absence of quenching. In order to facilitate interpretation of the UVAPS data in regard to the composition of airborne biological particles, a linearity of the fluorescent signals of the spectrometer was investigated

Size-Selective Assessment of Airborne Particles in Swine Confinement Building with the UVAPS

The Ultraviolet Aerodynamic Particle Sizer (UVAPS) is a novel aerosol counter for realtime monitoring of viable bioaerosols. The previous validation studies on the UVAPS were either laboratory based or were conducted outdoor with the artificially generated aerosols. In this study, the spectrometer was applied to investigate particulate pollution inside a swine confinement building (SCB). Real-time capabilities of the instrument were used to investigate the effect of on-farm-activities, such as an effluent flushing with recycled water, on microbial load inside the SCB. In addition to the UVAPS, monitoring of viable bioaerosols (bacteria and fungi) was simultaneously conducted with the sixstage Andersen microbial impactor and the AGI-30 impingers. The UVAPS measurements showed that the concentrations of both total and biological particles inside the SCB were in order of 106 -107 particles/ m3. These concentrations were approximately seven times the outside concentrations for total particles and up to 12 times for biological particles. Approximately 95 % of both total and biological particles were respirable (< 7mm) and approximately 60 % of total and 50 % of biological particles accounted for the fine particle fraction (<2.5 mm). The concentration of biological particles measured with the UVAPS was at least one order of magnitude higher than the concentration of the viable microorganisms measured with the AGI-30 impingers. Nevertheless, the trends in the concentration changes of bioaerosols measured with the UVAPS followed the trends in the concentration changes of the airborne microorganisms quite adequately. Thus, it was concluded that the UVAPS is an appropriate method for investigating the dynamic of bioaerosols in the SCBs. The results obtained in this study assist in advancing an understanding of the UVAPS performance in the real-life agricultural settings. In addition, the data provide a new insight on the particles size distribution inside the SCB, depending on their nature

Performance Evaluation of the UVAPS in Measuring Biological Aerosols: Fluorescence Spectra from NAD(P)H Coenzymes and Riboflavin

This paper presents the results of the performance evaluation of the Ultraviolet Aerodynamic Particle Sizer (UVAPS, model 3312, TSI Inc., St. Paul, MN), the novel instrument for real-time monitoring of biological aerosols. The main objective of the study was to compare the UVAPS response in measuring aerosols containing the NADH, NADPH, or riboflavin particles. At the excitation and emission wavelengths at which the UVAPS operates, these compounds are the primary intrinsic fluorophores specific to biological particles. In addition, the study was focused on determining the detection limits of the UVAPS for these fluorophores. This information is important for the interpretation of UVAPS data while measuring bacterial aerosols. Fluorescence measurements were initially taken with a Varian Cary Eclipse Fluorescence Spectrophotometer for all three fluorophores. The samples were then aerosolized with the 6-jet Collison nebuliser. Riboflavin was found to be a stronger fluorophore than both NAD(P)H coenzymes. The fluorescence signals were considerably weaker for the NADPH samples compared to the NADH samples. The sensitivity of the UVAPS was found to be sufficiently high to detect the NADH and riboflavin at the concentrations characteristic to bacterial cells. The results of this study are discussed in a context of the results previously reported for the bacterial aerosols. It can be concluded, that the amount of fluorophores detectable in uniformly mixed particles is equal to or less than the fluorophores expected to be present in the individual bacterial particles

Performance Evaluation of the UVAPS: Influence of Physiological Age of Airborne Bacteria and Bacterial Stress

This study evaluated the effect of bacterial physiology, such as physiological age and stress, on the performance of the Ultravioloet Aerodynamic Particle Sizer (UV-APS, model 3312, TSI Inc., St. Paul, MN). Intensity of the fluorescent signals was measured for three bacteria having various sensitivities to environmental stresses, Bacillus subtilus (spores and vegetative cells), Pseudomonas fluorescens, and Micrococcus luteus. The performance of the UVAPS was found to depend on the type of airborne bacteria. In addition, the fluorescence signals for stationary-phase bacteria were generally stronger than for their log-phase counterparts. These results indicated that bacterial injury due to environmental stresses has a strong influence on the measured fluorescence signals. This hypothesis was confirmed by obtaining a linear relationship between the percentage of fluorescent particles and the proportion of injured bacteria in the total population of cultivable bacteria in samples simultaneously collected with the AGI-30 impingers. This indicates that the amount of fluorophors (specifically NADH) within injured bacteria is below the UVAPS sensitivity level. The practical implications of these findings are discussed in the paper. The reported results contribute to broadening our understanding of the method and may assist in developing sampling strategies for the application of the UVAPS to various bioaerosol studies

Measuring Intrinsic Fluorescence Of Airborne Particles For Real-Time Monitoring Of Viable Bioaerosols

Development of the advanced, real-time methods for monitoring of bioaerosols is becoming increasingly important. At present, the Ultraviolet Aerodynamic Particle Sizer (UVAPS, Model 3312, TSI, St. Paul., MN) is the only commercially available method for in-situ, continuous measurements of viable airborne microorganisms. Research included in this thesis aimed towards comprehensive evaluation of the method over a wide range of operating conditions, linking the experimental results to the theoretical basis of its design and operation, and to developing a scientific basis for its application to real-time monitoring of bioaerosols. Specifically, due to a growing concern in the general community about the environmental and health aspects of biological aerosols originated from various types of agricultural operations including animal farming, this research was focussed on developing a research methodology/strategy for applying the method to the investigation of bioaerosols in the swine confinement buildings (SCB). Investigations under controlled laboratory conditions were primarily concerned with selectivity, sensitivity, counting efficiency, and detection limits of the spectrometer. This study also examined the effect of physiological state (metabolic activity) of bacteria on the performance characteristics of the method. The practical implications of the research findings are discussed in this thesis. Further field investigations undertaken on a pig farm advanced understanding of the UVAPS performance in the real-life environmental settings. The research also provided a new insight on the particle size distribution and the effect of on-farm-activities on aerosol load inside the SCBs, for both biological and non-biological aerosols. This study has proved that the UVAPS is a powerful tool for investigation of viable bioaerosols in the environment. However, this method is limited to detection of active metabolising bacteria that excludes dormant bacterial spores. In addition, the method is very sensitive to physiological state of bacteria and to the effect of adverse environmental conditions on metabolic activity of airborne bacteria, which may decrease the amount of the intrinsic fluorophores in the cells below sensitivity level iv of the monitor. Possible limitations of this technology include also the lack of selectivity and thus interferences from the non-microbial organic components of airborne particles. In addition, the sensitivity of the method is insufficient for monitoring viable bacteria in the environments with relatively low concentrations of bioaerosols. In order to increase sensitivity of the method, it would be desirable to concentrate the bioaerosols into a smaller volume with the aim of high-volume virtual impactors (aerosol concentrators) prior to the monitoring. Therefore, in the indoor environments where an application of the concentrator is not feasible, the utilisation of the UVAPS may be problematic. Due to the intrinsic limitations, the method is not recommended for the direct measurements of viable bioaerosols and should be used in conjunction with the conventional biosamplers for obtaining more realistic insights into the microbial air quality. Nevertheless, the UVAPS has been found to be an adequate method for the investigation of the dynamics of biological aerosols in real-time. Overall, this thesis contributes to the advancing of the understanding of the method and may assist in developing new, more advanced technologies for the real-time monitoring of viable bioaerosols, as well as in developing sampling strategies for the application of the method to various bioaerosol studies