Photograph of a mold culture plate home test kit for mold. Validity of Cultures (settlement plates or swabs) to find toxic mold in buildings

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Mold culture test kit accuracy: 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?

The underlying methodology is 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. As an example, a dead spore in the air may be toxic but may not grow at all in a culture medium.

Also see our MOLD CULTURE PHOTOS. The use, accuracy, and reliability of mold culture test kits for screening buildings for mold contamination are discussed at MOLD CULTURE TEST KIT VALIDITY and MOLD CULTURE SAMPLING METHOD and see Mold Culture Plate Test Errors.

Before you buy a "home test kit" for mold you should read this very article about the limitations of cultures, swabs, settlement plates. After reading this paper you may want to see our tape sampling procedures

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 Introductory Comments on Air Movement in buildings.

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.

Frequently Asked Questions (FAQs) about do-it-yourself mold tests

Question: Where Can I Buy Mold Test Kits for do-it-yourself testing?

I will be calling one of the testing inspectors that you list at MOLD & ENVIRONMENTAL INSPECTORS . In addition, is there any device I can purchase which would allow me to make an independent test? - Thanks J.O.


Do-it-yourself mold tests are widely available at hardware stores and building suppliers as well as online. The tests usually fall into one of two groups:

Adhesive tape collection surface particles: particle or surface debris or suspected mold on a surface - see for detailed procedures on how this test sort is used (to avoid any conflict of interest, or even an apparent conflict, don't sent your sample to us)

Mold culture kits: a plastic petri dish of growth medium is exposed to air, re-sealed, and you or the lab gets to see what grows. Since 95% of molds won't grow on any culture, this is an unreliable way to screen a building for problem mold, though cultures do have widespread and valid use in the lab. MOLD CULTURE TEST KIT VALIDITY has details.

Airborne tests for mold are not usually performed by a building owner as special equipment is needed. See AIR TEST FOR MOLD: ACCURACY and for more detail, AIR TEST SAMPLING CASSETTE STUDY and AIRBORNE MOLD SPORE COUNT ACCURACY.

And frankly, for serious mold or water damage investigation cases, using any of these "mold test" methods to produce useful results needs to be combined with an expert building inspection and case history as well as occupant interview.

At ACCURACY OF VARIOUS MOLD TEST METHODS we provide details about the accuracy of various mold test methods.

The reliance on mold "tests" without a thorough, expert onsite inspection, history taking, etc. is simply unjustified. And that may be why whomever you paid to do these tests can't be more helpful to you.

Properly, and providing an onsite investigation was justified in the first place (see MOLD / ENVIRONMENTAL EXPERT, HIRE ?- when to hire a mold expert) then the person who inspected the site, took its history, understands the building, its occupants, its environment, should be able to make a meaningful interpretation of various tests done in the building that supplement the more thorough site investigation.

Relying on a mold "test" is profitable for the test company and lab but by itself, can be misleading, especially where low numbers or low mold-level findings were the results found in the test. Even high mold level findings can be misleading as the test may not have detected the most problematic mold present.

All of that said, you can hire someone to read and interpret and discuss your report, and then to suggest further investigative steps that could be helpful. (See MOLD & ENVIRONMENTAL INSPECTORS)

Bottom line: in our experience and opinion, relying on mold tests alone to diagnose a building is a risky proposition.


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