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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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.
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.
Shown at left, an example of test results for an airborne mold test. [Click to enlarge any image]
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
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.
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.
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. "
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.
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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Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
(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
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.
Or see these
MOLD LEVEL REPORTING at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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