Overview – Culturable Air Sampling
Culturable air sampling is one of the most common methods of volumetric air sampling, and Andersen Instruments manufactures the most commonly used culturable air sampling devices. The Andersen sampler works by drawing measured volumes of air through an instrument that contains a petri dish (or dishes) with culture media. Spores that impact onto the plate are then allowed to incubate and grow, after which the colonies may be counted and identified. An alternative to the Andersen sampler is the BioCassette, developed by EMLab P&K. The BioCassette avoids high capital expense and is less prone to contamination issues during the air sampling process
Our philosophy regarding the interpretation of biological air samples is formed primarily by two guiding principles. First, an effective interpretation is based on the comparison of indoor and outdoor samples. There are currently no guidelines or regulations to indicate "safe" or "normal" spore levels, however, we typically expect indoor counts to be 30 to 80 percent of outdoor spore counts, with the same general distribution of spore types present. And second, variation is an inherent part of biological air sampling. The presence or absence of a few genera in small numbers should not be considered abnormal.
Culturable air sampling allows for the differentiation of Aspergillus and Penicillium (speciation when required). It also provides counts indicative of how many spores are viable and present in the air. It can also be used to provide a bacterial count.
Culturable air sampling methods require that the spores in the air are alive, survive the sampling process, germinate on the sampling media, and compete well with other species present on the growth media. Culturable air sampling does not indicate the presence of non-viable spores, which may also be capable of producing allergies or irritation. Culturable air sampling also requires five to seven days for incubation after the sampling has taken place.
A few tips...
A three-minute sampling time for Andersen samples is a good starting protocol. Sampling times should be reduced if visible mold growth is present, if dust is excessive, or if semi-aggressive sampling techniques are utilized. Sampling locations should include problem areas, an indoor non-problem area if available, and an outdoor sample (or samples) for interpretation. Samples should be sent to us (with volumetric data) within 24 hours using overnight courier services, and should be packed with care to prevent breakage and contamination. Cold packs or cooling chambers are unnecessary since cold surfaces attract moisture, and excessive moisture during transit is not good. Please remember that air sampling data represents a specific moment in time, and that field observations are of equal importance. Sampling at multiple times may be helpful.
The recommended industry practice for the number of field blanks is to provide two field blanks for every 10 samples with a maximum of 10 field blanks for each sample set.
Reference: Jensen, Paul A., Ph.D., PE, CIH, and Schafer, Millie P., Ph.D., NIOSH/DPSE "Sampling and Characterization of Bioaerosols", NIOSH Manual of Analytical Methods, Chapter J, 1/15/98.