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Photograph of a mold culture plate home test kit for mold. Validity of Mold Culture Tests

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Mold culture test kit accuracy:

Are culture plates a reliable method to screen buildings for indoor mold contamination? This article discusses building mold tests that rely only on settlement plates or swabs to find toxic mold in buildings. Before you buy any "mold home test kit" for mold you should read this article.

This article explains the limited accuracy of mold cultures when used as "mold test kits" to examine indoor air quality as an investigation methodology in searching for possible causes of respiratory illness, asthma, immune system disorders, rashes, skin disease, psychological and neurological disorders, eye infections, or other symptoms that may have a physiological and environmental component.



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Problems With Relying on cultured mold samples to evaluate a building

Ulocladium and other molds in culture (C) D FriedmanWhy don't we use readily-available mass-marketed cultures, settlement plates, and swab kits such as those available at the local hardware store?

While all "mold tests" and "mold test kits" or mold sampling methods have their limitations, the usefulness of mold culture plates as a general screen for harmful indoor mold contamination is particularly limited.

OPINION: because most mold genera / species simply will not grow in any culture. So even if the culture does successfully grow mold we don't know if this accurately represents what mold contaminants are in the building tested.

The underlying methodology of this test may be seriously flawed if you're relying on the results of culturing to characterize just what problematic fungal spores are present in a building.

Mold cultures, typically taken using settlement plates, Anderson-type samplers, and sterile swabs, can be quite unreliable as indicators of what's really present in an indoor environment. This is especially true if the test does not detect a mold problem (one may be present but was not detected by this method) and it might be true even if the test does seem to detect a problem as it may detect molds other than the largest or most serious mold contamination reservoir that's present.

As another test limitation example, a dead spore in the air may be toxic but may not grow at all in a culture medium.

In addition, variations in building indoor air movement, activity, humidity, temperature, and other conditions causes an enormous variation in the level in air of all sorts of indoor particles. I have found as much as four orders of magnitude in the level of airborne mold spores as these conditions in buildings were changed.

And individual mold spores, varying by size, mass, toxicity, and preference for mold culture, find very different rates of first settlement out of the air onto any building surface (including a culture plate) and second rates of growing within any given culture medium (including a range of growth from abundant to zero).

In our mold culture photo at above right you see a "home test kit" for mold collected in a Washington DC apartment in the Watergate. Apparently there are about seven different mold genera/species appearing on this "overgrown" culture plate.

But the fastest growing molds (those who most like the media) will of course overgrow and hide other mold spores that may have landed on the media. And then, heavier larger spores tend to settle out of air sooner than smaller lighter spores. So the culture plate may over-represent heavy large molds compared with the actual molds present in the building.

Use of cultures as building screens for the presence or absence problematic mold is unreliable - only 10% of all molds of any genera will grow on any culture under any circumstances, so a mold culture screening test for mold is 90% wrong at the outset. More so if one considers that certain molds that can be grown in culture only respond to specific culture media.

Even if a mold is grown on a culture, given these constraints one cannot reliably infer that the mold grown is the problem material in a building. Therefore no screening test by air or culture is an adequate substitute for nor superior to the value of a careful visual inspection by an experienced inspector who knows where mold is likely to grow and what it looks like on or in building surfaces and cavities.

Other serious flaws include inconsistent presence of problematic particles in building air, variations in particle settling rate out of air, variations in growth rates on different media of different mold species (fast growing spore A over-grows and hides the presence of slow growing spore B) and the fact that some problematic spores which could be hazardous to building occupants simply do not grow at all in the culture medium. There is indeed a valid place for cultures (air or swab) in the arsenal of building investigation tools (cross check on visual inspection and bulk sampling, cross check on clearance inspection and sampling, and elaboration of dormant particles).

Culture methods for fungal spore determination are an important tool, but these methods should not be relied-upon as the principal means for determining what problematic particles are in indoor air.

Relying on over-the-counter home test kits for mold to evaluate a building

Stachybotrys spores (left) and structure (right)

Home test kits for mold are inexpensive, easily available, and easy to use. Therefore we wish we could say they could be an OK place to start, but we don't think this is the most accurate approach to screening a building for mold.

In a recent field experiment we used an over-the-counter "mold test kit" according to its instructions while we also performed a professional inspection of the building.

Among problems which our inspection discovered in the building the settlement-plate culture "toxic mold test kit" successfully found an Aspergillus sp. presence. It also found some nice Alternaria sp. spores, as well as the usual other collection of common Cladosporium species found in air.

What the mold test kit failed to find was what was probably making the occupants in the building sick. Our visual inspection identified various area of mold on surfaces and in the building cavities.

We collected bulk (tape) samples (as well as vacuum samples (such as vacuum samples of fiberglass building insulation) and we also collected some air samples used as a cross-check screen).

A strategic examination of these samples identified a very extensive Stachybotrys chartarum infection in the building, Penicillium, and an extensive Chaetomium globosum colony as well as the Aspergillus and the less troublesome Alternaria and its buddies.

The first two mold species are toxic, the last, allergenic. They were totally missed by the "test kit." Why did the home test kit for mold fail to find the actual problem in the building?

In addition to our bulk samples (which found the mold missed by the "home test kit") we also used two different types of air sampling machines as well as pulling some vacuum samples of suspect carpeting in an area which looked pretty clean.

Remarkably, our air samples confirmed the Stachybotrys chartarum presence, a spore not so easily found in air, despite the fact that we did nothing more than walk across a carpeted room during the test.

Mold spores may appear or fail to appear in an air test or "spore trap" for mold because of significant variations in particle disturbance during activity in the building, though there is a huge number of other factors which affect air and particle movement inside.

We provide more details about air movement in buildings at ACCURACY OF VARIOUS MOLD TEST METHODS

In this building the owner had begun a do-it-yourself demolition and repair of a water-damaged bathroom. Extensive mold contamination was on the exposed side of bathroom drywall and more extensive mold was growing on the cavity side of these walls.

As the owner used a hammer and hatchet to smash and remove drywall, considerable levels of airborne mold were produced - a condition probably more hazardous to the occupants than when the mold was simply growing on and in surfaces and cavities.

We are often able to spot a building where there has been a previous demolition of moldy materials by examining dust from remote surfaces. The actual exposure level of the building occupants to this mold is not something one can immediately infer from finding leftover traces in a building, but if professional containment and remediation measures were not followed, there is at least a risk that for a time the occupants may have been breathing some pretty moldy air.

In the case described here, the owner who performed the demolition developed a rather ugly skin rash that appeared to be mold-related, and which abated after a combination of treatment and some proper housecleaning.

Personal Field Experience Finds Wide Variation of Airborne Mold Spores over Short Time Intervals

Really? While Pasanen (1991) found that

The relative humidity of air had no direct influence on the growth of fungi.

By repeated measurements of airborne mold levels of a species of Aspergillus sp. at the same location on successive days during a process of dehumidification in a moldy library basement, I found that the level of airborne Aspergillus sp. spores ranged from barely detected (counts in the tens of spores per liter of air) to very high (tens of thousands of spores per liter of air) as the indoor relative humidity fell.

I posit that the very thick mold visible on books in this historically very damp space consisted in, among others, Aspergillus sp. that began to release its spores at dramatically increased levels as the area began to dry.

Most mold species have not been named nor studied

Fuligo septic  (C) Daniel FriedmanOf over 5 million mold genera/species currently estimated to be growing away on earth, less than 100,000 individuals have been named and studied at all.

Less than two percent of all molds have been studied. (Blackwell 2011)

And mold is everywhere, even inside the U.S. Laboratory module of the International Space Station, (Vesper 2008).

Happily for people cleaning up a mold problem or diagnosing a medical or allergenic mold problem, we can do a little better.

There are probably about 200 common mold genera/species that are often found indoors growing in or on building materials.

While there are many others who may make an occasional appearance, even as a large area of mold growth, most often it's one of these 200 or so molds.

Surface Dust & Tape Sampling: An Alternative to Mold Cultures & Speciation for Building Screening Tests

We prefer collecting physical samples of representative settled dust as that will collect both viable and non-viable mold spores. We cannot perform accurate quantitative analysis of a surface or tape sample but we can recognize when there is an unusual level of a particular problem particle, mold or otherwise.
See TAPE SAMPLING PROCEDURES

Keep in mind that except for special circumstances (medical need, need to prove that other building dust is due to improper dust containment during a mold remediation) we do not need to know the mold's name to clean it up. Except for cosmetic (harmless) black mold that we sometimes find on framing lumber, we want the indoor mold to be cleaned-up (removed) and we want the cause for its growth to be corrected.
See also COSMETIC MOLD, RECOGNIZE

Research on Accuracy of Mold Culture Testing for Indoor Mold Contamination

Mold Culture Test Articles


Continue reading at MOLD CULTURE SAMPLING METHOD or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see ACCURACY OF VARIOUS MOLD TEST METHODS - pitfalls of various methods for testing or screening for building mold contamination

Or see COSMETIC MOLD, RECOGNIZE - mold that you can safely ignore

Or see HIDDEN MOLD, HOW TO FIND

Or see MOLD TEST REASONS Three cases in which mold tests are useful

Or see MOLD / ENVIRONMENTAL EXPERT, HIRE ? where we discuss how to decide when building or occupant conditions appear to warrant hiring an expert.

Or see MOLD TEST vs. PROBLEM DIAGNOSIS where we explain the limitations of mold testing.

Or see TAPE SAMPLING PROCEDURES for settled dust or mold in buildings

Suggested citation for this web page

MOLD CULTURE TEST KIT VALIDITY at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

INDEX to RELATED ARTICLES: ARTICLE INDEX to MOLD CONTAMINATION & REMEDIATION

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