On July 22, 2007 (go to "Categories"/"Toxic Mold" on the right-hand side of this page), I posted an article on the state of toxic-mold liability in the United States, essentially pointing out that there were as yet no definitive standards to "prove" that mold in any particular situation had caused someone's health problems. In response, one reader sent in a comment that such a standard now exists in the form of the US EPA's "Environmental Relative Moldiness Index", or "ERMI".
I am grateful for the reader's posted comment. However, the ERMI is not a health-based standard but rather simply a method to compare levels of mold in a home environment to a representative sampling of homes across the nation. From this comparison, one can conclude that a home is overburdened (or under-burdened) with mold compared to the average home; but, as even the most ardent proponents of using the standard agree, there is no proven correlation between the level of mold in a home and particular health conditions.
The ERMI approach starts with a highly scientifically accurate sampling of mold, using a specialized vacuum device to scoop up dust particles for mold measurement (as opposed to air sampling, which up until recently was the usual method to collect samples for mold measurement). Whereas air samples reflect a very short duration of measurement in a potentially changing environment (i.e., air currents can vary from time to time), the dust sample is relatively stable, reflecting as the sample does materials that have collected over a relatively long period of time in such media as carpeting.
The dust sample is then analyzed in the laboratory by mold DNA traits, producing conclusive identification of the types of mold in the sample (as opposed to observations of the mold appearance, which observations are apparently prone to more subjective interpretation). 36 types of mold are categorized--26 types which result from historic water damage and 10 types that are associated with common household molds. The quantity (derived at by a "log-transforming" method) of common household molds are subtracted from the quantity of the more dangerous molds to produce a score ranging from -10 to 20. The lower the score, the less of a mold burden is deemed to exist.
The mold-burden score from between -10 to 20 is then compared to a survey of over 1,000 homes done in 2006 by the United States Department of Housing and Urban Development ("HUD"). A mold burden of -10 to -4 places a house in the "low" mold burden category compared to the homes surveyed; from -4 to 5 places the home in the "moderate" burden category; and a score greater than 5 places the home in the "high" burden category.
While the ERMI score is clearly helpful in alerting a homeowner to the possibility of dangerous health conditions being caused by mold, since there remains no definitive correlation between mold exposure and chronic disease the ERMI test is essentially useful only as a warning system that further investigation is required. In a home with a high ERMI score and evidence of health problems (e.g., aggravated asthmatic conditions and other respiratory problems), the high score should sound alarm bells.
However, a low ERMI score does not mean that resident are not suffering apparent symptoms which have been caused by the presence of mold. Nor does a high score where no symptoms are apparent mean there is a definite health problem. The ERMI score is simply one additional indicator of the need for further investigation and interpretation.
Moreover, the ERMI approach has its own methodological limitations. The ERMI test was developed for homes, not commercial buildings. One needs to extrapolate to draw any conclusions in the latter context. Further, the dust sampling used in the HUD survey was done in specific areas of the living room and the bedroom. Varying these sampling areas arguably would introduce some subjectivity in comparison of the dust-burden in any given home with the national sample used for ERMI results.
Thus, the ERMI approach is an important step in ultimately developing a conclusive test of the effects of mold exposure on human health. However, ERMI is just that--a step on the road to such a conclusive test and not the conclusive test which still continues to elude us.
For good website discussions of ERMI, please see http://www.aemtek.com/newsite/?q=node/98, http://www.cleanairlabs.com/media/downloads/ERMI-scores.pdf, http://www.aerotechpk.com/AnalyticalServices/ERMI.aspx, http://www.joem.org/pt/re/joem/abstract.00043764-200708000-00002.htm;jsessionid=H4yTqJLb8G1LSrB0gWQmJv0wLh8bw2hDRXzDKpk4htBKvFJTFn1v!-383192544!181195628!8091!-1 and http://www.mycometrics.com/articles/ERMI_Lin_IEC2007.html