A bioaerosol (short for biological aerosol) is a suspension of airborne particles that contain living organisms or were released from living organisms. These particles are very small and range in size from less than one micrometer (0.00004") to one hundred micrometers (0.004"). Bioaerosols react to air currents and move quickly or slowly depending on the environment. Bioaerosols are impacted by gravity, but due to their size, air density and air currents play a large role in their movement. The intact cellular component has been given the name primary biological aerosol (PBA), which consists of virus particles, bacteria, fungal spores and plant pollen. PBA can range in size from 10 nanometers (small virus particles) to 100 micrometers (pollen grains). The atmospheric lifetime of PBA particles can range from a near indefinite time frame for some of the smallest virus particles to a few hours for the larger pollen particles.
Air often contains tiny organisms such as fungi, bacteria, mycotoxins, and viruses. It is currently thought that the majority of these airborne microorganisms are not in a viable state while in the atmosphere. However, current research has shown that certain groups of bacteria are capable of performing basic metabolic activity within cloud water. Groups of the small organisms clump up and enhance survival while airborne. Due to evaporation of water, bacterial cells usually die when they become airborne but under high humidity conditions, bioaerosol levels are increased. Fungal cells such as spores, molds, and yeast can be active at low humidity levels and high or low temperatures.
Many techniques are used to collect bioaerosols, such as collection plates, electrostatic collectors, and impactors, although some methods are experimental in nature. Another way to collect or detect bioaerosols is by using a mass spectrometer.
To collect aerosols falling within a specific size range, impactors can be designed for a variety of size cuts, depositing material onto slides, agar plates, or tape. The Hirst spore trap samples at 10 LPM, has a wind vane to always sample in the direction of wind flow. Collected particles are impacted onto a vertical glass slide greased with petroleum. Variations such as the 7-day recording volumetric spore trap (Burkard Air Sampling CO.) have been designed for continuous sampling using a slowly rotating drum that deposits impacted material onto a coated plastic tape. The airborne bacteria sampler (ABS) can sample at rates up to 700 LPM, allowing for large samples to be collected in a short sampling time. Biological material is impacted and deposited onto an agar lined Petri dish, allowing cultures to develop.
Similar to single-stage impactors in collection methods, cascade impactors have multiple size cuts, allowing size resolution of sampled bioaerosols. Separating biological material by aerodynamic diameter is useful due to size ranges being dominated by specific types of organisms (bacteria exist range from 1 um to 20 um, and pollen from 10 um to 100 um). The Andersen line of cascade impactors (Thermo Electron Corporation) are most widely used, available in two and size-stage versions.
Instead of collecting onto a greased substrate or agar plate, impingers have been developed to impact bioaerosols into a liquid, such as deionized water or phosphate buffer solution (PBS). Collection efficiencies of impingers are shown by Ehrlich et al. (1966) to be generally higher than similar single stage impactor designs. Commercially available impingers include the AGI-30 (Ace Glass Inc.) and Biosampler (SKC, Inc).
Methods of Analysis
Following bioaerosol collection, the total concentration and types of bioaerosol are analyzed in a number of different ways. Traditionally, bioaerosol has been analyzed by either performing plate counts or by performing direct counts using biological stains to discriminate between biological and non-biological particles. Plate counting is a very useful method to quantify the number of viable cells in the atmosphere. However, it has been well documented that plate counting methods usually miss approximately 99% of the total microbial diversity found in a given environment. With this in mind, more recent methods are being applied for the identification of bioaerosol. A couple of these methods include mass spectrometry as well as DNA based methods. This shift in methodology will allow for more quantitative studies, which will eventually lead to a more thorough understanding of the biological component of atmospheric aerosol.
- Indoor air quality
- Indoor bioaerosol
- Mold growth, assessment, and remediation
- Mold health issues
- Sick building syndrome
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