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Airborne Fungal Sampling Technique … Lemonade from Lemons?

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May/June 2015

Making lemonade out of lemons is an idiom that is often quoted when we attempt to make something good from a difficult situation. In the arena of environmental sampling and analysis, however, it can simply yield to frustration and worse, meaningless results. Consider the following scenarios:

    • Three slit impaction spore trap air samples are taken in the field for the recommended 5 minutes at 15 lpm. The samples are submitted and upon arrival at the laboratory, it’s discovered that for one sample, the loading of debris, both fungal and non-fungal, is so great that the sample must be voided according to the criteria specified in the ASTM Method D7391-09. The remaining samples indicate that mold is present. You wonder if the results are good or bad. No lemonade to be made from sample lemons here.


  • A single tape lift of suspected mold growth is taken from a surface, placed on a glass slide, and placed in a slide box for shipment. At the lab, it’s discovered that the slide broke in transit, with tiny shards of glass stuck in the tape, and that opaque frosted tape was used, rendering the sample unreadable per ASTM Method D7910-14. Why is my lemonade crunchy? Uh-oh…..


In both situations, some elements of sampling were under the sampler’s control (only three airborne samples taken, use of frosted tape), while perhaps other elements were not under the sampler’s control (dusty air thick with debris, package squashed by a careless handler; that never happens!).

The end result is that the analysis is compromised, biased, or impossible due to poor sampling technique. You cry foul! “Wait, how can dirty air or rough package handling be a result of poor sampling technique?” The answer lies not as much in the nuts and bolts of how to sample, but in not having a sampling strategy.

A comprehensive sampling strategy is the foundation of good sampling technique. A strategy will yield answers to the particular questions you have about your project. The first and most important part of a mold sampling strategy is performing a visual inspection to identify a possible mold contamination problem. The next step is to establish criteria for taking samples and interpreting laboratory results. Only in the context of these two steps can air samples and tape lifts be expected to provide meaningful data relevant to the project at hand. A robust sampling strategy should be formulated to help confirm a theory regarding suspected sources of mold and its airborne distribution. Sampling can be used as a tool to help answer the following questions.

Is there mold growing on this surface, and what kind is it? Think tape lift and swab sampling per ASTM D7910-14. Are there airborne mold spores, and what types are present? Think impaction spore trap air sample per ASTM D7391-09.

The answers to these questions should never be used as a basis for building assessment but as a means to test a hypothesis regarding suspected mold contamination.

These peer reviewed and internationally recognized consensus standards from ASTM are powerful protection for you, your laboratory, and your client. Sampling protocol specific to the type of sampler used should be followed, using air cassettes similar to the Zefon or Allergenco design. Detailed notes regarding time of day, weather conditions, location of sampler, etc. should be kept in order to assist in the interpretation of results. A field blank should be submitted with each group of samples to check the field sampling conditions. Samples should be provided in sufficient number and frequency to overcome any unforeseen issue such as overloaded samples, as well as providing a large enough pool of data in light of the fact that air samples are a ‘snapshot in time’ of airborne fungal loading. A single air sample, or even several samples, are not representative of the fungal loading present over time, given the high degree of variability inherent in spore trap sampling.

Tape lift or swab samples also have their own considerations and limitations. Care needs to be taken while sampling to ensure that the suspected growth being lifted or swabbed, is not obscured by underlying paint, varnish or loose debris. Absolutely clear transparent single sided tape is the only material that can be later viewed under a microscope for identification – and then reanalyzed for quality assurance compliance. Tape should be mounted to clear glass microscope slides to minimize possible cross contamination from other samples or mold sources. A tape lift or swab cannot be used to make generalized determinations of suspected mold growth on a surface. A single sample is only representative of the square inch or so that was lifted or swabbed, as similar looking stains and debris only inches apart may yield drastically different results.

Finally, remind yourself that mold is ever present in the air, at greatly varying levels over time, both inside and out. Sampling by itself, cannot answer the question, “Is there mold contamination, and where is it coming from?” Nor can it answer the question, “Is that amount of mold bad?” Recognize the limitations of sampling and take care not to overemphasize laboratory results. There are currently no regulatory bodies which recognize a safe or unsafe level of mold counts. Consequently, the laboratory cannot tell you if your samples are ‘clean’ or ‘high’. Remember that mold is only a symptom of a moisture problem. Therefore, as a sampler, you must know what questions you need answers to and have criteria for interpreting the results before you sample. Having a successful sampling strategy means never having to make lemonade out of lemons!

Author – Ben Reich is a senior analyst at iATL with twenty five years of experience with fungal spore and other environmental laboratory projects. Ben can be reached at mold-lab@iatl.com.

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