Mold Testing Methods
Mold in Air: Quantitative Analysis - "Spore counts"
Examining particles on a slide to count Mold spores/Meter3 of air, Mold Spores/M2 of
surface area, or Mold CFU's - colony-forming units is a common practice in Building
investigations. These measures can be used to describe the results of some sampling or
"mold testing" methods in Building.
While there is no fixed (nor fix-able) standard of absolute allowable "spore counts" in air
(we'd need a standard for every genera and species by toxicity, weight, mobility, etc.),
investigators have now seen so many moldy and not-moldy Buildings, and complaint and non-
complaint areas that it's reasonable to have some general guidelines about what levels are
probably a problem and what levels may not be a problem.
Acceptable Mold Levels: While there is no well-established quantitative standard for fungal
spores on surfaces or in air, mold contamination is considered present in a Building when
the total mold spore concentration per cubic meter of air is above 10,000. (Baxter, ETS).
Acceptable levels for individual species vary since species toxicity varies widely as does
spore size, weight, and other features which affect risk to Building occupants. E.g.
Aspergillus/Penicillium in a "clean" residential Building study was at a mean of 230, in
Buildings known to have a moisture or flooding problem it was at 2235 and in mold
contaminated Buildings the figure was 36,037. Surface samples of mold: the presence of
toxic or allergenic mold as a dominant particle in any sample (surface or air) is usually a
cause for further investigation or remediation. The presence of incidental occurrences of
toxic or allergenic material in surface samples requires interpretation in light of other Building
conditions, type of particle (spore chains), and other factors. For example, in a
pre-remediation Building where occupants have Building related complaints and mold
contamination is suspected, even a modest indoor level of 500 spores/M3 of air might
suggest a problem if those spores formed a high percentage of the total indoor spore count
and only a low percentage of the corresponding outdoor spore count taken as a control. our
own field experience is similar to the counts suggested by Baxter. Since indoor
environments in the U.S. and many other parts of the world are similar in conditions and often
in Building materials, it is likely that these levels are not very dependent on region of the
country. Warning: interpret all quantitative data with great caution. Individual samples of
particles in air show tremendous variation from minute to minute, making "ok" test results a
thing to view with care. In situations of particular risk additional or periodic testing should be
considered.
However, because indoor conditions of mechanical disturbance, ventilation, occupancy, and
use vary widely over short intervals of just a few minutes, an indoor "mold spore count" is at
high risk being inaccurate, incoherent, and confounding. Recipients of such reports are may
not realize the distinction between highly precise results (lots of decimal places) and results
which are fundamentally accurate or inaccurate, depending on the design of the sampling
plan and the variation in Building conditions during the sampling interval. Unless there is
good experimental design, quantitative results are precise (lots of decimal places in the
answer) but almost certainly wrong (off by a factor of thousands) as a characterization of a
Building.
Therefore quantitative studies are most useful as part of a more broad qualitative approach,
indicating either relative differences in mold levels between a control area and a problem
area or the relative change in Building conditions before and after cleaning. They are much
less reliable as an absolute pass/fail criteria. Other substantial quantitative report issues
other than accuracy include wide variation among labs in counting and skill levels, and more
interestingly, the lack of and virtual impossibility of establishment of valid quantitative
standards for mold exposure. For example, two different particles have different toxicity,
different air movement; two of the same particle can vary in toxicity depending on supporting
growth surface.
Shortcomings of Quantitative Analysis of Mold Spores in Air
Quantitative Analysis producing low results is unreliable: Building conditions vary
enormously, causing huge variations in what particles may be found in the air at any given
time. our own time-lapse sampling suggests that particle levels vary by a factor of at least
several orders of magnitude due to common variations in Building conditions such as fan on
off, human activity, mechanical disturbance of moldy stuff, etc.
Quantitative results which are superficially similar between indoors and outdoors may be
misleading: An outdoor "Pen/Asp" count of 500 spores/M3 may have captured a genera or
species which is completely different from a corresponding indoor "Pen/Asp" count which
also found 400 spores/M3.
Quantitative results which seem "low" and qualify as a "clean Building" may be misleading: a
lab reporting an outdoor "Pen/Asp" count of 700 and an indoor "Pen/Asp" count of 450 may
look like an acceptably "clean" Building - the indoor count is "below the outdoor count." But
suppose in fact the outdoor "Pen/Asp" is actually an unidentified amerospore, or a
basidiomycete mis-classified, or is a common outdoor species of Penicillium, while the
indoor "Pen./Asp" is actually representing Aspergillus niger? This is an argument for doing
some subsequent culture work or better lab microscopy (Aspergillus niger can be identified
by light microscope alone.) In this case the "low" level of 450 spores may in fact be a weak
indicator of a large problem mold reservoir in the Building.
For more about air sampling, spore count methods, and their validity
Spore Counting Methods and Validityinspect-ny.com/sickhouse/sporecounts.htm
Mold Testing: Air samples and their interpretation - a quick
tutorial.inspect-ny.com/sickhouse/tutorial.htm
Mold Levels - how much is bad? http://inspect-ny.com/sickhouse/Mold_Standards.htm
Mold Levels in Mold Test Samples of Surfaces in Buildings
http://inspect-ny.com/sickhouse/moldtapes.htm - how to interpret surface tape samples.
Tape sampling for mold
Clear cellophane tape is pressed into a sampled surface, then removed and affixed to a
clean surface such as a plastic bag or a microscope slide for mailing to a lab. The lab
prepares the tape for microscopic examination. For mold genera and species identification
the tape is examined in the laboratory. Tape samples can also be cultured (see Culture
discussion below). This is the least-expensive collection method available, and is a preferred
tool.
Using clear adhesive tape pressed into a surface to be tested is the first choice
recommended method for identifying mold in a Building, particularly when combined with
visual inspection as part of a mold investigation, per AIHA and other expert sources. This
method permits rapid identification of genera (family name) and very often species
(individual member name), particularly when the mold sampled has uniquely-identifiable
spores or where the sample collects the conidiophore or spore-producing body as well.
In some cases genera determination alone is quite sufficient as the some of the common
problem-genera (Penicillium sp. and Aspergillus sp.) do not have non-problematic members
which grow in Buildings. Speciation is more likely to be needed when doing medical
diagnosis. Tape samples can also be cultured if additional speciation is needed. Since
tapes can collect the conidiophores and hyphae (when tape spot is chosen with some
thought) they give more data than an air or vacuum sample.
For Building where large amounts of mold are found or suspected, tape sampling is a
qualitative approach which is usually quite successful in addressing the basic question: is
there a problematic genera which requires professional remediation? Combined with a
visual inspection to locate target areas of risk and to find visible problems, it is the most
essential component of a Building mold investigation and is the method recommended by
experts writing in the field and by the AIHA's own training materials.
Tape samples are the preferred method of collecting surface samples in Buildings. Tape
pressed into appropriate portions of suspected mold growing on a surface collects the most
material from the surface and often includes sufficient structural material to identify the
dominant problematic genera and species present. A properly collected sample is likely to
contain both fungal conidia, conidiophores, and hyphae, the latter two of which are important
aids for speciation. Tape samples of Building dust and even tape samples of moldy carpet
are also generally useful in this manner but have some limitations discussed below.
Determination of mold genera:
Nearly all Building mold genera can be determined by light microscopic examination of tape
samples. In the majority of Building investigation cases the key question is "is there a
problematic genera (toxic or allergenic) requiring containment and professional
remediation?" This can almost always be completely answered from genera alone. This is
because within the more common troublemakers, their non-problematic member species
may not occur in Buildings. For example, Penicillium notatum, used for the drug penicillin,
does not grow in Buildings! If you find Penicillium sp. in a Building in quantity it needs to be
remediated.
Determination of mold species:
Speciation of many mold genera can also be determined from tape sample material alone in
many but certainly not 100% of cases. Some examples of easily speciated molds from
among the most common genera and species found in Buildings: Cladosporium
sphaerospermum, C. cladosporioides, Ulocladium chartarum, Taeoniella rudus, Pithomyces
chartarum, Stachybotrys chartarum, Chaetomium globosum, Chaetomium aureum,
Aspergillus niger are just a few examples. A good tape sample which collects the
conidiophore and hyphae makes speciation possible for many molds. Many other airborne
spores appear in Buildings and can be similarly speciated, but are not Building molds. Other
airborne molds such as the Aspergillus and Penicillium families are probably a sufficient
hazard in Buildings that if they are present in a large reservoir, speciation is not needed to
decide to remediate.
Shortcomings of tape sampling:
Everything depends on where you stick the tape. Investigators and ordinary Building
occupants tend to collect that which is easy to see - "black mold" and may miss more
important, more health-risky light-colored and highly airborne genera (Aspergillus,
Penicillium) which are also present but more difficult to see. An expert looks for
mold-suspect material that seems to represent the dominant presence in an area by color,
texture, and growing surface material. It would be unusual for there to be only a single
genera/species of mold in a mold-problem Building. Looking and taping requires some
guidance and education.
Some smaller airborne mold spores do not settle out of air rapidly and might appear equally
as plated-out on walls as in dust on horizontal surfaces. In Building inspection to search for
an unidentified problem source, samples of surface dust may under-represent the presence
of these molds, though where a substantial airborne presence exists we have always found a
surface dust presence as well. By contrast, properly collected tape samples from visible
mold growing on a surface does not suffer this shortcoming.
Speciation of genera may be needed for special medical diagnostic reasons. From spores
alone in any sample method, two of the most widespread problematic genera can be
speciated only to a few cases. (Aspergillus niger for example.) Therefore for medical use,
tape speciation of some genera is too limited, in particular if the sample collects only spores
- a problem which can occur if tape is pressed into dust rather than into an area of growing
mold, or when tape of a mold colony is pressed into a spore-packed center of a mature
colony instead at the edges where the new colony growth and conidiophores are easier to
find. A little knowledge of mycology is useful to professional Building inspectors.
When growing conditions become unfavorable some molds change form into an encysted or
encapsulated dormant state, forming fungal perithecia, cleistothecia, or pycnidia which may
be collected as "black stuff" from Building surfaces (particularly wood). While often one finds
identifiable material among perithecia that cant' be assured. Culturing of such samples may
produce an identifiable fungus if by luck the right culture media is selected.
Tape sampling is qualitative, not quantitative. Most experts and competent labs will offer a
description of the density of fungal material found in the sample using non-standardized
terms like Level 1-2-3-4 or Light, Medium, Heavy, or Dominant, Present, and Incidental.
These terms lack a standard definition but are of some use provided the lab has and can
provide their own standard and definition.
In sum, the determination of the presence of a Building mold problem (toxic or allergenic) vs.
cosmetic mold can usually be made from tape samples alone.
For more information on tape sampling methods
http://inspect-ny.com/sickhouse/tutorial2.htm about tape sampling
http://inspect-ny.com/sickhouse/bulksamp.htm how to collect and send a tape sample to a
laboratory
Vacuum samples for mold
A collection canister is connected to an air or vacuum pump which is used to draw particles
onto a filter-surface or into a special collection container. The lab clears the filter onto a
microscope slide, washes the filter onto a microscope slide, or uses another method to
transfer particles for examination by microscope for preparation by culture.
Surface vacuuming for mold
Vacuum samples can be useful for testing soft goods (clothing, bedding, curtains, carpets)
for high levels of contaminated spores in a qualitative approach. We particularly like
vacuuming a number of surfaces in an area using a single collection device as a less-costly
way to make a more confident inspection of the level of contamination by moldy dust in
Buildings with a known problem. We also use this method as part of a mold clearance
inspection to evaluate the thoroughness of both the containment system and the general
cleaning effort. For example we may collect a sample of vacuumed surface dust from 10
different surfaces in 5 rooms on a floor of a home, forming a more broad screen for moldy
dust than single tape lifts of surface dust.
We've found wide variety in levels of mold found growing in or on carpets, depending on a
number of variables including even the level of other dirt present in the carpeting. Some
experts question this measure. Carpet vacuuming for mold is interesting as a pre and post
remediation baseline data source for areas out of the remediation/containment area, but for
any carpet this method quickly overloads a particle sampler.
Shortcomings of surface and carpet vacuuming for mold
vacuuming will not collect identifying structural components of mold as well as tape and will
almost certainly damage or destroy the structures which it collects, imposing some limits on
identification
vacuuming will not collect all of the material on a hard surface (which tape handles well).
Particles which are easily lifted by the airflow into the canister will be over-represented
compared with sticky particles which are adhered to the test surface. This problem is
particularly sensitive to the flow rate (LPM) used. A low-flow rate (1LPM) avoids a sample
overload problem (too many particles, can't read the sample) but may fail to collect or
under-collect certain particles. A high flow rate improves particle pick-up but then limits the
number of sample sites (increasing test cost) in order to avoid sample overload. we suspect
that no vacuum method we have tested could reliably pull mold or debris reliably from deep
inside a heavy upholstered couch.
Carpet vacuums and some furniture or drapery vacuums will either be overloaded or
restricted to culture (to which we have already objected).
Shortcomings of vacuuming insulation for mold
We love this method, but one must take care not to overload the sample. If insulation is not
exposed for testing one needs to make a sufficiently large opening to agitate and then
vacuum the insulation - we use a 4" square opening and take care to avoid vacuuming up
simply a collection of drywall dust.
Vacuuming Building cavities for a mold screen
Vacuuming Building cavities is a popular screening practice to look for mold reservoirs. The
investigator is trying to explore wall cavities while doing minimal or no visible damage. A
wall-check system has been marketed for this purpose and several manufacturers have
copied the basic idea: a receiving Air-o-Cel or MCE filter cassette is attached at its inlet
side to a tube which is inserted as a probe into a wall cavity, permitting creation of only a
small hole. The outlet or pump side of the test device is connected to a pump and operated,
typically at 15 lpm. Where we have tested this method we have experimented with both
passive collection (what most investigators use) or aggressive collection (banging on the
wall/ceiling at various points to attempt to dislodge and stir particles).
Short duration samples, 1-2 minutes using an Air-o-Cell permit a comparatively large
number of samples to be collected in a reasonably short interval. Long duration samples,
perhaps for up to two hours, are collected using an MCE filter cassette.
Shortcomings of vacuuming Building cavities through a tube but our testing strongly suggests
that this method is very unreliable for characterizing wall contents. we do not believe that
enough air movement is created in the wall cavity (sucking any lpm flow through a small
diameter tube) to reliably collect what could be a severe mold reservoir that happens not to
be right next to the probe. Further if the cavity is insulated there will be virtually no air or
particle movement except from very close to the probe.
Vacuuming exposed insulation for mold
At many investigations we have found a large hidden mold reservoir in Building insulation,
particularly fiberglass insulation in attics under roof leaks over drywall, and in crawl spaces
which have been damp or wet. we have also found very moldy fiberglass in basement
ceilings after moldy surfaces and debris have been removed (such insulation should have
been removed during the remediation). our method is to agitate the target insulation (simply
poke it with your flashlight or a ruler), followed by holding our vacuum cassette an inch or two
away from the insulation surface. This reliably picks up particles from the insulation without
overloading the sample with fiberglass. (A baseline comparison sample collected in nearby
Building air before any such agitating sampling is also needed.) This method has been
remarkably successful in finding and allowing the removal of several "mystery" problems in
Buildings where severe mold-related complaints were heard.
Any of several types of vacuum cassettes are used to collect dust from a surface. we use
Air-o-Cel cassettes and MCE filter cassettes. we am experimenting with vacuum cassettes
loaded with high-adhesive tape. The contents of the cassette may be examined by light
microscope or may be used for preparation of cultures. One special (and costly) cassette
method collects dual samples permitting both direct examination and culturing. This method
may be used for both qualitative and quantitative analysis, depending on collection method
details. It is best suited for sampling dust from surfaces and from soft goods such as
carpeting or upholstered furniture. It's strength is its use in examining multiple hard surfaces
with relatively low levels of debris (avoiding sample overload) or individual soft surfaces
where tape may not collect particles imbedded in the surface, and in collecting dust from
multiple locations in a single cassette as a Building dust scan for mold.
Cultures to "Test for Mold"
Mold cultures involve the collection of particles by air sampling pump, by gravity settlement,
or by lift from a surface using a swab or tape. Some sampling equipment (Anderson spore
traps) can collect spores directly into a petri dish of culture medium, and are used for "viable
spore sampling in air." The sample by pump, gravity, tape or swab is in any case applied to
one or more petri dishes of culture media for incubation and subsequent examination of the
growth product. Mold Culturing is useful for genera speciation once you have collected a
single or dominant sample whose importance (frequency in the Building) you already know.
As a "home test kit" for the presence of problematic mold in a Building this is an unreliable
method, as we describe below at "shortcomings."
Mold Cultures are useful for:
Identifying the genera/species of a mold which was not readily named by (faster, cheaper)
light microscopy
Identifying a problem genera to the species level for medical diagnostic purposes - i.e. pass
this (possibly accurate) data along to your doctor if you're sick
Distinguishing apparently similar outdoor mold counts from indoor mold counts of
"look-alike" spores that may really be different genera/species
Shortcomings of culturing mold samples
While this is an important tool which has a place in our arsenal, mold culturing is
questionable as a means to characterize a mold risk in a Building, particularly if it reports the
absence of a mold problem. The objections listed below mean that field investigators must
collect samples with some care and interpret lab reports with some caution.
Roughly 90% of all molds on earth will not grow on any culture under any condition. Others
are quite difficult to coax into growing on culture, even with careful methods. So if you buy a
"home test kit" that uses a single culture plate, you're 90% wrong when you open the
container. To be fair, it might be that many common indoor problem-molds will show up in
certain cultures, but these numbers still hold.
The toxicity or allergenicity of a specific mold (genera/species/strain) may vary widely
depending on what it's growing on. So even a "toxic" Building mold might be low or non-toxic
when growing on certain substances. Molds that grow on cultures may produce very different
structures and have different medical characteristics than when growing in nature or in a
Building.
Cultures may name the wrong mold as "the problem": Cultures have a high risk of both
missing the problematic spore and of indicating that some other spore is the dominant or
problem in a Building. For example, to speciate one of the more than 100 members of the
Aspergillus genera requires culturing the sample on four different media, simultaneously,
comparing subtle things like growth rate among morphologically similar species. we believe
that virtually no lab uses that troublesome procedure outside of university research and
medical laboratories.
Settlement plate cultures (such as "home test kits") rely on gravity, making any comparison of
"spore counts" dead wrong - different spores are of different sizes and masses, and settle
out of the air at different rates. This over-states the presence of big heavy spores (like
Stachybotrys chartarum) and under-states the presence of small light spores (like Aspergillus
versicolor) in a given sample. These small spores (2-3u) tend to stay airborne due to very
slight indoor convection currents (e.g. heat from lighting and natural Building stack effects).
Swab and tape samples for cultures may collect the wrong mold. Swab or tape samples
used for culture for identification of what's on a surface have the same viable-non-viable
question we have already raised. Everything depends on where you collected the swab or
tape sample. Moving a tape or swab over as little as one inch on a surface, and certainly
moving it a few feet, can collect a completely different mold genera and species! An "expert"
should know what's probably representative of the Building and should know where the
important genera/species are likely to be growing. Many investigators are quick to sample
the highly-visible "black" mold on a surface and under-sample very important but hard to see
light colored molds often found higher on a wall, for example, where the surface was less wet.
Cultures are probably not really being done with full accuracy in some labs, especially for
Aspergillus: Culturing on one or even two media risks that the important genera/species in
the sample does not grow at all on the medium, that it grows in a different form and is
identified differently than it appears in the Building, or that it is overgrown by another
genera/species present which likes the culture more than the target species. we have
demonstrated this culture-media variation in a study we am pursuing about mold in tea. In a
problem-tea sample cultured on the most commonly used culture media, MEA, the culture
produced an overwhelming growth of Cladosporium sp., while a parallel culture (from the
identical sample) made on DG-18 produced a single Cladosporium colony and grew an
overwhelming collection of Aspergillus niger!
Non-viable spores, that don't grow on culture may still be toxic or allergenic particles which
are a problem for some people exposed to them.
While we enjoy growing mold cultures in our lab (it makes for nice, photogenic mold
colonies), it is less often useful than direct microscopic examination of a field-collected
surface or vacuum sample. Without the added step of mold culturing, from a good surface
sample using adhesive tape, a trained microscopist can identify mold genera and mold
species as well in many cases. In many instances, knowing the mold genera is enough to
decide on a course of cleanup action without further expense. For example, if we agree that
there are no harmless Aspergillus species or Penicillium species that grow indoors, then for
purposes of deciding on the need for remediation, only the size of the reservoir is important.
P. notatum, used for making the drug Penicillin, has not to our knowledge been found
growing on Building materials.
For more discussion about mold cultures from settlement plates or swabs see "The Validity
of Cultures at InspectAPedia.com/sickhouse/cultures.htm
Swab sampling
Swab samples can be used to pull particles for microscopic exam but destroy the identifying
conidiophores and hyphae; They are more often used to prepare cultures which have the
shortcoming cited above. We make use of swabs to sample for bacteriological
contamination.
A sterile swab is wiped across a sampled surface, the inserted into a sterile tube for mailing
to a lab.
Swabs are processed in one of two ways:
Direct examination: The lab can lift particles from the swab using tape or other methods to
make a direct particle examination similar to tape sampling above.
Culturing: The lab rolls the swab across a culture plate to culture the sample for identification.
Shortcomings of swab sampling for mold
Direct examination: determination of species by direct examination is nearly impossible as
the collection method destroys or fails to collect identifying structures such as conidiophores
and hyphae. "Rubbing" and possibly even "rolling" the swab on a surface to collect a sample
will often destroy key structural components (the conidiophores and hyphal details) which
would have been more easily preserved using adhesive tape.
Culturing from swabs (or tape): risks misidentification of the dominant species present and
may completely miss species which are present due to choice of culture media and growing
conditions, as stated above about mold cultures.
Swabs used to collect particles from insulation, fabric, upholstery, carpets, may fail to collect
representative material as they only touch surface particles. Vacuuming such surfaces is
more representative of what particles are aerosolized by human activity in a Building.
Swabs are great for testing for bacteriological contamination testing but in our opinion they
are of less use in fungal work.
PCR methods for Mold Identification
Polymerase chain reaction (PCR) can be used to identify individual genera/species with
good accuracy and fairly quickly. The method requires costly equipment and is not available
at most laboratories. Perhaps more important is that the data base of PCR identification
information is limited to a small set of species compared with the wide range of
genera/species which occur. At least one excellent national laboratory offers this service for
mold speciation. Depending on how rapidly technology drives down the cost and how rapidly
the identification data base is expanded, I suspect that this method will see increased use.
The limitations of this tool are currently two: first, it is quite costly to perform per sample, and
second, it is excellent at identifying the presence or absence of a specific mold you're
looking for. It is less useful as a broad spectrum scan expected to pop up with a result of
what's present out of the 1.5 million possible candidates - of which only a few are yet even in
the PCR database.
The Usefulness of Mold Testing vs. Mold Identification
Are Mold Home Test Kits Useful? Accurate? Worth the cost?
Settlement plates, culture media, or swabs which are later cultured, used alone for Building
mold risk analysis are invalid methods which risk both false positive results (saying there's a
problem when there is not) and false negative results (missing an important problem). More
about this is in this article and you can read in greater depth at The Validity of Cultures.
http://inspect-ny.com/sickhouse/cultures.htm
What about other do-it-yourself tests? Amateur mold "testing" by a homeowner, using a tape
lift of visible mold, perhaps with some good advice on where to look, might be an
inexpensive way find out that the "black mold" on the floor joists is a "cosmetic-only" mold,
thus avoiding the cost of a more expert professional Building investigation/remediation.
However anyone using this approach should understand that it is incomplete and superficial:
you might collect your sample from a spot which is not representative; you will not address
the risk of hidden mold in Building cavities; you will not have expert mold remediation advice;
you will not have baseline data to support a later clearance test after cleanup, finally, you risk
leaving another problem in the Building. These warnings should be considered carefully
where large areas of mold are already visible or at-risk occupants are involved.
Of the mold samples sent to our lab by owners who have had no collection advice, we find
that "black molds" seem to be over-represented and I suspect these are often not the real
problem in the Building. The mold the owner sees may be simply the indicator of moldy
conditions. Lighter, harder-to see molds in the Penicillium sp. and Aspergillus sp. families,
for example, are under-represented in owner-collected samples (based on our field
experience and on our review of statistics of samples sent to Dr. J. Haines at the N.Y. State
Museum for identification) because these genera are often more difficult to see.
Mold "Testing" vs. Mold "Problem Identification"
We are making up this temporary distinction to make clear an important point.
Mold Testing a Building for the presence or absence of a problematic level of mold is
unreliable if by "testing" one means a simple air test, an arbitrary surface or vacuum test, a
swab test, or any culture method used alone and without a careful and complete inspection of
the property. In particular, failure to detect problem levels of problem mold with an air, culture,
swab, PCR or similar test (used alone) is not sufficient to conclude that there is no problem.
1. Airborne particle levels vary widely over short time intervals. What's in the air in a Building
varies enormously, possibly by a factor of thousands, over just a few minutes, depending on
things like the level of activity, mechanical disturbance of dust, fans being turned on or off, hot
air heat or central air being on or off, and more subtle changes in humidity, etc.
2. Cultures whether from a "home test kit" culture plate or a swab are unreliable as a
characterization of presence or absence of mold because first, only about 10% of all of the
1.5 million mold species on earth will grow in any culture under any condition, second
because what grows on a particular culture may be what likes that culture not what is the
dominant problem, and third, because accurate speciation of some of our problem groups
such as Penicillium sp. and Aspergillus sp. require arduous multiple cultures under very
controlled conditions for reliable results.
3. PCR tests are highly accurate in identifying individual molds, if you know what you're
looking for. PCR is not reliable as a broad spectrum scan to find what's in a Building.
Mold Problem Identification, as I'm speaking here, is an important part of a Building
investigation for mold (or other allergen) problems. By this we mean, an investigator should
be charged to identify the presence of problematic mold, including no less than the following:
first, the evidence that problematic levels of mold are present and that the predominant
genera/species are ones which can be expected to be toxic or highly allergenic; second, the
evidence that a large problem reservoir exists; third, the location(s) of the problem reservoir;
fourth, the underlying causes for the presence of the problem reservoir. This information
permits preparation of a remediation plan to specify the cleanup needed and the Building
repairs needed to avoid simply producing more mold.
Key in a Mold Problem Identification investigation is the actual visual examination of the
Building, its history, its leaks, and other physical evidence. As a part of such an investigation,
samples are collected of visible mold to distinguish cosmetic from problematic material, and
other samples might be collected to examine the level of moldy dust settled in Building areas
where mold is not present. Additional samples may be collected for comparison baselines
such from outdoor areas or from non-complaint areas in the problem Building.
A thorough Building investigation will include sampling or "tests" to identify the presence of
mold and to identify the dominant problem molds by genera and often species. By contrast, a
quick and simple "mold test," particularly a random spot check, is of little value by itself:
grabbing a 90 liter air sample or putting a settlement plate in a closet for an hour is not a
reliable Building characterization for mold, and a tape sample of the single square foot of
mold in a Building is unnecessary.
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