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Photograph of no mold spores, one mite fecal.Reports of Dust Particle or Mold Levels in Buildings

  • POST a QUESTION or COMMENT about how to report the density or level of mold or other particles found on indoor surfaces or in indoor dust samples

How to report levels of mold contamination in buildings:

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 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!

See details at DUST / MOLD TEST KIT INSTRUCTIONS

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, in 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

Example mold air test report (C) InspectApediaTherefore 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.

Shown at left, an example of test results for an airborne mold test. [Click to enlarge any image]

Why Some Mold Tests Are Not Helpful

OPINION: "air tests" for mold are unreliable: the actual mold spore count detected in an air sample can vary several orders of magnitude depending on just when, where, and how how a test is conducted, so a number of 270 could be 2.7 or 27,000 in actual truth.

Worse, when an air test finds high airborne problem mold spore counts that are high enough that it's very likely that there is an indoor mold problem needing to be addressed, such a report does not really tell us where the mold reservoir is, if there is one that needs action. So it is not telling us what needs to be done. Such a report is not prescriptive.

The building owner may have to pay a similar "mold inspection" fee all over again to actually find out what mold cleanup work is needed.

So the airborne mold count number is not so helpful unless accompanied by a competent, thorough onsite inspection to find the problem mold reservoir OR to tell you that enough looking in the most-suspect areas means that further action isn't justified.

Other types of "mold tests" have accuracy limitations too.

The variation in tape and other sampling methods is explored separately

at MOLD TESTING METHOD VALIDITY.

Once we are informed that only about 10% of the 1.5 million or so mold genera and species will grow on any culture whatsoever, even less credible 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 can we make any use of a mold test report? Yes, maybe.

So do any mold numbers make sense? In our opinion, yes, as rough approximate counts, not as precise numbers.

In particular, very high counts of problem mold types indoors are almost certainly indicative of an indoor mold problem that needs to be addressed.

But low indoor mold counts might simply have missed a significant mold problem because of when, where, and how the test was conducted.

Experience tells us that there are general guidelines for airborne mold levels that suggest that a building is or is not harboring a significant, if hidden, problem mold reservoir.

See AIRBORNE PARTICLE & MOLD COUNT NUMBER GUIDE for general guidelines to what constitutes "high indoor mold counts".

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.

Reasonable & 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 dust or settled dust and airborne debris particles 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.

See DUST / MOLD TEST KIT INSTRUCTIONS

See MOLD TESTING METHOD VALIDITY and also

see MOLD CULTURE TEST KIT VALIDITY.

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 apply 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.

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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: mold cultured from jute carpets

(June 3, 2014) Anonymous said: we have some jute carpets which have been tested and the results are

Microfungi 2% malt --- 34 cfu/ 100cm2

microfungi DG 18 --- about 450 cfu/100 cm2

The mould is not visible to the eye.

Are these acceptable levels for Europe

Or are these dangerous levels

pl advise at my emai - deast123@gmail.com
RAJIV BAHL

Reply:

At page end article links you can find a link to an article on MOLD EXPOSURE STANDARDS that includes the EU.

But your mold culture test is not useful in this application, nor in my opinion valid.

Only about 10 % of molds will grow in culture of any formula, so relying on cultures to screen for mold is potentially 90% wrong from the outset.

See details at MOLD CULTURE TEST KIT VALIDITY


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Continue reading at MOLD TESTING & SAMPLING MISTAKES for more examples of how mold testing goes wrong, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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MOLD LEVEL REPORTING at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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