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Dr. Jackson Kung’u (PhD)- Mold Specialist.
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air sampling

Air Sampling

Air sampling is one of the tools used in mold investigation. The primary objective of mold investigation is to determine the extent of mold growth and subsequently its potential effect on indoor air quality. Air sampling helps to termine whether or not visible mold growth has degraded indoor air quality. It may also help to detect the presence of hidden mold growth. Some investigators use air sampling to determine the effectiveness of remediation. This is achieved by taking air samples before and after remediation.

Interpretation of Air Sample Results

Interpretation of air sample results can at times be very difficult. However, having a clear objective, prior to air sampling can make results interpretation easy.

As often stated, fungal spores are present in virtually all environments including indoors. Therefore, presence of some fungal spores indoors is considered normal. Generally, for well maintained mechanically ventilated buildings, airborne spores should be qualitatively similar but quantitatively lower than the outdoors. For naturally ventilated buildings, the airborne spore concentration and their diversity in the indoor air is similar to that of outdoor air.

For both mechanically and naturally ventilated buildings, presence of airborne spores of molds usually found in indoors, in numbers significantly higher than those of outdoors, is an indication of indoors sources of mold growth.

Interpretation of air samples collected primarily to determine whether there was mold growth indoors is therefore based on a comparison of concentrations and categories of spores in outdoor and indoor samples. Significant counts of species present indoors and absent (or in lower counts) outdoors suggest the source for those species is indoors. In the absence of any visible mold growth, further investigation would be required to determine the source and extent of any hidden mold growth.

It’s important to note that the conclusion derived from air sample results should always be backed by visual inspection and the building history.

Monitoring And Documenting Air Quality

Monitoring and documenting air quality, especially in hospitals, pharmaceutical, cosmetics, and food industries environments is very important. Contamination of these environments can originate from nearby or far away sewage plants, landfill sites, and waste separation plants. Therefore, monitoring on a regular basis of air quality in operating rooms, production lines, and other controlled areas is critical.

To assess the level of microbial contamination in the air, air is sampled for analysis by direct microscopy (sometimes referred to as nonviable analyses) or by culture analysis. For direct microscopy, the air is sampled using various cassettes including Air O Cell, Allergenco, Millipore filters and others. The samples are examined at between 600 and 900X magnification.  Fungal spores and mycelial/hyphal fragments are enumerated. Millipore filters are first cleared using acetone and fixed with triacetine and then analysed in a similar manner as the Air-O-Cell or Allergenco samples. The filters have a major advantage over the other spore traps in that, having a large surface area, they can be used in highly contaminated environments, where other spore traps would easily be overloaded with dust thus rendering them difficult to analyse.

Direct microscopic analysis of air samples allows determination of total spore counts regardless of whether the spores were dead or alive. In hospital environments both dead and living spores are of concern because even if the spores were dead, they could be as toxigenic or allergenic just like living spores.

To sample air for culture analysis requires the air to be impacted on suitable agar media. Commonly used types of samplers are the Reuter Centrifugal Sampler (RCS) and the Andersen samplers. However there are many other samplers.  The air is impacted on media such as MEA and DG18. Culturable air samples are incubated for 3-5 days and the resulting colonies counted. The colonies are then transferred onto suitable agar media for identification. In general, number of fungal propagules determined by cultural method is far much smaller (1-50% of total counts in some cases) than the total number of spores and fungal propagules determined by direct microscopic examination.

To assesss air for bacterial contamination, a general purpose media such as Tryptic Soy Agar (TSA) can be used. However, if sampling for a specific type of bacterium such as Legionella spp, then a selective media such as Buffered Charcoal Yeast Extract (BCYE) Agar is recommended.