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Validity of Cultures (settlement plates or swabs) to find toxic mold in buildings MoldAPedia © Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• Are indoor air quality "mold test kits" that rely on culture plates accurate?
• Advice on how to test or screen for problem mold indoors

This document provides information about 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 which may have a physiological and environmental component. 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 © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Relying on cultured mold samples to evaluate a building

Why 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. 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.

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

Home test kits for mold are inexpensive, easily available, and easy to use. Therefore I wish I could say they could be an OK place to start, but I don't think this is the most accurate approach to screening a building for mold. In a recent field experiment I used an over-the-counter "mold test kit" according to its instructions while I also performed a professional inspection of the building. Among problems which my 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. My visual inspection identified various area of mold on surfaces and in the building cavities. I collected bulk (tape) samples (as well as vacuum samples (such as vacuum samples of fiberglass building insulation) and I 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 species are toxic, the last, allergenic. They were totally missed by the "test kit." Why?

In addition to my bulk samples (which found the mold missed by the "home test kit") I 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. Spores may appear or fail to appear because of variations in particle disturbance during activity in the building, though there is a huge number of factors which affect air and particle movement inside. I say more about air movement in buildings at my 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. I am 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.

More Mold Test Validity Articles

• Review more discussion of the Shortcomings of cultured mold samples - which lists a number of detailed concerns about viable spore traps and culture media for building problem detection
• Validity of air samples for mold and their interpretation is at my Air Sample Tutorial.
• Validity of Bulk Surface or Tape Sampling is at my Tape Sampling Tutorial

See our main website (below) for very important additional information such as mold testing, cleanup and mold remediation guideline resources.

More Information on Building Diagnostic Inspections and Repairs

• Mold Classes: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
• Mold Levels: How Much toxic or allergenic mold is Bad? counts in air or by visual inspection
• Mold Spore Counts: are indoor fungal spore counts valid?

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