Dust sampling can be a good way to assess the health of your environment. The ERMI (Environmental Relative Moldiness Index) test is recommended as a place to begin. Several labs offer this analysis, including EMLab P&K, EMSL Analytical, and Mycometrics.
Below is an interview regarding dust sampling with toxicologist Dr. Jack Thrasher, a leader in the field of indoor air quality.
Why is a dust sample preferable to an air sample when testing your home for mold?
Air sampling is unreliable because the results are too variable. Air sampling only identifies mold spores to the genus level. It is important to know the species of mold. Mold spores are present in the dust and the dust can be examined for species of mold using PCR (ERMI) testing. For example, we did a building in Bermuda. Initial air samples indicated low concentrations of mold spores. We then disturbed the indoor air with an aerosol of sterile fluoroethane. The spore counts went up as high as 250,000 spores per cubic meter. Thus the spores entrained in dust were redistributed into the indoor air.
Do you recommend the ERMI test as a place to begin when testing for toxic mold?
I always recommend the ERMI tests. The moldiness index is not too meaningful, particularly for sensitive and high-risk people. The portion of the ERMI test that is important is the identification of mold species. Often dangerous molds, such as Aspergillus versicolor, fumigatus, and flavus along with certain species of Penicillium are present. These species cannot be determined by spore counts because Aspergillus and Penicillium species have almost identical spore structures. Also, Stachybotrys does not readily shed spores, but can be found in dust and bulk samples by PCR analysis.
When vacuuming for an ERMI test, is it best to vacuum in one spot, or take from a variety of places around the home?
What one must understand is that a single dust sample does not necessarily represent the contamination. I prefer doing a minimum of two samples. The more the better. The species of mold in a contaminated home will vary from room to room. Carpeting can be done - but from one room only, which is usually the most contaminated room. "Historical" dust samples should be included in the testing. Sites for these include the refrigerator coil dust which is a 24/7 collection site, as well as any drop down kitchen cabinets, or return air for heating and air conditioning. If the home has a basement, it should be assessed as well.
Is it best to keep the house closed up for a day or two before taking an ERMI sample?
This is not a necessary requirement. The reason is that certain molds are associated with different substrates. For example, Stachybotrys requires a cellulose source, such as drywall, while others species of mold will be associated with flooring and carpeting.
Do I need to vacuum areas that I don't suspect have been affected by the mold?
If mold is indoors and in wall cavities, all areas of the home are probably affected. Therefore do the dust sampling as discussed above. Some areas may have fewer spores than others; however, the mold spores will drift throughout the house.
What about bacteria?
Both Gram-negative and -positive bacteria are also found indoors. The Gram-negative are producers of endotoxins. The Gram-positive release toxins. The Gram-positive bacteria are Staphylococcus, Streptococcus, and various species of Bacillus that can be pathogenic. In addition, the Gram-positive bacteria includes the Actinobacteria, including species of Streptomyces, nontuberculin Mycobacterium, and Nocardia, to name a few. The Actinobacteria are potential pathogens and release toxins into the indoor environment that are more toxic than the mycotoxins produced by molds.
What is involved with taking bulk samples?
Bulk samples are just what the word means. One cuts out a piece of the contaminated materials, e.g. drywall, carpeting, etc. Put it in a Ziploc bag, date and label the bag, and send it to the testing lab. If litigation is involved, then a chain of custody is needed and a witness to the sampling.
How does one test for bacteria in the home?
Bacteria are tested in buildings and homes the same way. One can use bulk samples (see above) or sterile Q-tips. Take samples of suspected contamination. Culture using sheep blood agar (SBA) and TSA (Trypticase soy agar) at both 35 and 50 degrees centigrade. Have the laboratory identify the bacteria to genus and species. Also, ask them to culture for Actinobacteria. The Actinobacteria bacteria are slow growing and require several days to identify.
If I see visible mold but have no ill health effects, should I still test my home in this way?
Yes. How does one know that they do not have ill health effects? The health effects can range from just sneezing through systemic conditions of not feeling well.
What is important to emphasize about testing for toxic mold?
Too much emphasis is being put on molds. The indoor environment is a complex mixture of biocontaminants (mold, bacteria and their by-products).
For more information on Dr. Thrasher's work, visit his website.