Development of a new bioaerosol sampler employing the impingement process

Status:

completed 12/2006

Aims:

A range of methods, based upon different measurement principles, exist for the collection of bioaerosols. None is equally well suited to the collection of all bioaerosols. The collection of gram-negative bacteria which are sensitive to desiccation poses particular problems. For many years, impingement methods were preferred for this purpose, owing to the absence of drying stress in the collection phase; such methods include collection by means of the AGI 30 All-Glass-Impinger.
The AGI 30, which has been employed since the 1960s for the measurement of bioaerosols, does not satisfy the criteria for collection set out in EN 481, "Workplaces atmospheres; size fraction definitions for measurement of airborne particles". In addition, it must be operated at a volumetric flow of 12.7 l/min. This prevents the use of manageable pumps which in turn would permit the use of personal samplers. For this reason, manageable pumps which would also permit personal collection cannot be used. Thus, the AGI 30 and other bioaerosol samplers employing the impingement method (separation of particles in liquids) have not been employed routinely to date for the detection of vegetative bacteria in working areas. The objective of the project was thus the development and validation of a sampling system for vegetative bacteria based upon an established method employing a defined collection characteristic to EN 481 and a volumetric flow of 10 l/min.

Activities/Methods:

A preliminary sub-project was launched in which an impinger with a defined collection characteristic to EN 481 and a volumetric flow of 10 l/min was developed (BS-10). For this purpose, measurements were conducted on the existing AGI-30 and the dimension adjusted to the modified reference volumetric flow. Several prototypes were manufactured, measurements conducted, and the physical properties of the devices tested, such as the pressure difference. The optimized version was tested for its intake efficiency and penetration properties.

For the second phase of the project, a test was planned of the BS-10's suitability for use as a sampling system for particles of biological origin, such as vegetative bacteria.

Results:

As yet, it has not proved possible to attain a satisfactory pressure difference across the capillary of the bioaerosol collector with the use of personal sampling pumps operating at a volumetric flow of 10 l/min. This pressure difference is required in order to ensure the function of the device as an impinger. The intake efficiency of the newly developed bioaerosol collector, averaged over the wind velocity and wind direction, closely follows the definition curve of the inhalable dust. In the configuration tested, however, a large part of the aerosols passing through the inlet are retained within the sampling line before they reach the collection medium.
The same can be assumed to be true for other impingers available on the market.
The new collector is not suitable for bioaerosol measurement in accordance with the definition of the inhalable dust fraction. The use of the sampling system for workplace measurements of biological agents was not therefore studied further. The design of the impinger may be suitable for the collection of very small bioaerosols (such as viruses).
These findings, concerning the drawbacks of impingement methods for measurement of bioaerosols in general, emphasize the benefits of the standard method employed at the BGIA for the measurement of bacteria in workplace atmospheres (filtration over short sampling times), which satisfies the criteria of EN 481.

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