Photograph of no mold spores, one mite fecal.How to Report Dust Particle or Mold Particle Levels in Test Samples in Buildings
     


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This article discusses how to report levels of mold in buildings in order to promote consistent use of surface particle dust or mold test adhesive tape sample descriptive language among microbiology lab and field investigation professionals.

Here we define levels of significance of mold findings in test results. The definitions that follow are a work in progress and need support by example lab photomicrographs and quantitative study. Our photographs here illustrate three very different densities of mold particles found in a series of indoor environmental samples.

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Useful Definitions of Mold or Other Particle Densities in Indoor Environmental or Dust Samples

Photograph of tape samples of mold on drywall .If collected by an expert during a careful visual inspection, and thus if representative of conditions in a building, surface particle samples collected in buildings provide an important building diagnostic which can be expected to be more reliable than other popular mold testing methods including some which, sadly, may be little more than junk science.

Take a look at our photograph of three adhesive tape sample collections (DUST / MOLD TEST KIT INSTRUCTIONS) on a moldy drywall surface in a laundry room. These samples are collected just one to 1.5" apart. Yet each of them will collect a completely different mold genera and species!

Watch out: in the case of drywall that has become wet from a flooded or wet floor, the moisture gradient in the drywall drops as we check levels higher above the wet floor or flood-water level. At MOISTURE GRADIENTS & MOLD we explain why we find different mold genera/species at different locations on moldy drywall.

A result of these moisture gradients is that completely different mold genera-species, each preferring different moisture levels, may grow at different heights on the drywall - sometimes just inches apart as in this photo.

In a compelling demonstration of the importance of mold sample location selection, for the three samples shown above, collected just an inch or so apart, iIn the lab we confirmed three different mold from the bottom up: Stachybotrys chartarum, Aspergillus sp., and Cladosporium sp.

Of these three molds, the Stachybotrys chartarum is most often the mold which consumers fear and which they ask their "mold expert" to find. But while Stachybotrys is indeed potentially harmful, Aspergillus sp. is far more likely to be airborne, to be breathed deeply into the lungs, and to be hazardous throughout a building where equally-sized reservoirs of the two molds are present. Therefore focusing on testing for "black mold" in buildings is a risky mistake.

Accuracy vs Precision: Nonsensical vs. Reasonable Reports of Mold Levels or Concentrations on Surfaces

Therefore quantitative reporting of mold concentrations found on surfaces (such as spores/M3 or CFU/M2 on a surface) in buildings should not be attempted except for narrow purposes of scientific research under controlled conditions. The variation in tape and other sampling methods is explored at MOLD TESTING METHOD VALIDITY. Once we are informed taht only about 10% of the 1.5 million or so mold genera and species will grow on any culture whasoever, even crazier than spores/M3 is CFU/M2 on a surface - as we elaborate at MOLD CULTURE TEST ERRORS.

If an indoor particle sample is representative of the area being inspected, then the identity of significant or dominant particles present is important information about conditions in the building. If the indoor sample is not collected with intelligence, it is frankly, unreliable as a characterization of what contaminants are actually dominant or important in the building.

So do any mold numbers make sense? In our opinion, yes, as rough approximate counts, not as precise numbers. Experience tells us that there are general guidelines for airborne mold levels that suggest that a building is or is not harboring a signficant, if hidden, problem mold reservoir. See ACCEPTABLE MOLD LEVEL.

Watch out: as we explain below at ENVIRONMENTAL TEST ERROR TYPES, while a high mold or other particle count number almost certainly has meaning, depending on test circumstances and how samples are collected, low numbers may be very unreliable.

Why then do we see these highly precise but inaccurate mold counts or dust counts? Some lab directors explain that such numbers are a response to marketing competition. "If we don't give numbers someone else will". For details see ACCURACY vs PRECISION of MEASUREMENTS.

Reasonble & Useful Definitions of Indoor Mold or Dust Particle Levels: Not detected, Incidental, Present, Significant or Dominant

When we examine surface test samples collected in buildings, properly obtained by following a visual inspection of the building and by using a clear, consistent sampling procedure, then we can report the following Non-Quantitative Particle or Mold Levels Based on Samples.

Our mold level terms "Significant/Dominant, Present, Incidental" are defined below. Others may use similar terms such as "heavy, medium, light", or "high, moderate, low. "

  1. Particles not detected in a dust or environmental air or surface sample means that the particle named was below the detection limit of the inspection, sampling, and examination methods used in the field and laboratory. It does not mean that none of these particles are present in the building.

    Watch out: "Particles not detected" does not mean that none of these particles are present in the building. It means that the particles were not detected in the sample. The extent to which we are confident that the particle sample accurately represents building conditions is the extent to which we can generalize from "not detected" to "not present" in a building.
  2. Photograph of no mold spores, one mite fecal.Particles Incidental in a sample means that we found only occasional, or low-levels of fungal spores in the sample provided-below the level we usually find in indoor air samples in buildings where there has been a history of leaks, flooding, or known mold contamination.

    This is a positive description of the quality of indoor air insofar as fungal spores are concerned, but one cannot unequivocally conclude that there is no possible health hazard present because:

    1. individual exposure, sensitivity, and health status vary widely;

    2. even a zero count does not guarantee that a particle is not present in the building.

    It means only that that particle was not in the sample provided. A careful, expert look at the building may disclose particles that an occupant or inspector was unable to recognize and thus did not send to the laboratory for determination.
  3. Photograph of Aspergillus niger spores.Particles Present in a sample means that these particles were frequently present in the sample. They are less likely to be of significance to occupants of the building than "Significant/Dominant" particles except when particles named

    1. are particularly allergenic or toxic

    2. suggest an undiscovered building problem.

    If the building has a history of leaks, water entry, or other hidden moisture problems, the presence of even a few toxic or allergenic spores which are not often found in outdoor air samples may indicate a hidden problem.

    If control samples from outdoors or from non-complaint areas of a building do not show the presence of these particles, further investigation is in order to determine if there is a significant presence elsewhere in the building than from where this sample was taken.
  4. Photograph of Aspergillus niger spores.Particles Significant or Dominant in a sample means that within the sample these particles were the most-frequent particle in the sample or that the particle was present in most or all sample focal fields under the microscope at 400x or higher magnification.

    Problematic mold or allergenic particles listed in this category are likely to be of significance to occupants in the building. Where the particle is a mold genera or species capable of growing indoors a finding at this level makes it likely that there is one (or more) mold reservoir or mold colony in the building. This term refers to the sample content itself.

    A visual inspection of the property is needed to determine if the mold is present in extensive or large areas in the building. When the significant/dominant particle(s) present is/are allergenic or toxic mold or an allergen, building investigation to find and clean/remove the problem source is needed

Guide to Mold and IAQ Investigation Reports

This article explains how to report and understand the significance of the level of particles of mold or other particles found on indoor surfaces. Readers should also see MOLD TESTING USING ADHESIVE TAPE where we provide a quick tutorial on "Mold Testing: Bulk or Tape Surface Samples and their interpretation"

If collected by an expert during a careful visual inspection, and thus if representative of conditions in a building, surface particle samples collected in buildings provide an important building diagnostic which can be expected to be more reliable than other popular mold testing methods including some which, sadly, may be little more than junk science.

If an indoor particle sample is representative of the area being inspected, then the identity of significant or dominant particles present is important information about conditions in the building.

Classes of Testing or Statistical Errors Applied to Mold or Other Environmental Tests, Inspections, Reports

At ENVIRONMENTAL TEST ERROR TYPES we explain in more detail the classes of testing or statistical errors and how in a practical sense they appy to mold or other environmental inspection, testing, lab and reporting procedures. Type 1 and Type 2 errors are defined along with practical examples taken from building inspection and testing for mold contamination.

See MOLD TESTING & SAMPLING MISTAKES for more examples of how mold testing goes wrong.

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