You have previously commented that mold sample analysis reports are difficult to interpret by homeowners, and even by some professionals.  Can you provide a guide for when the “counts” of the most common indoor fungi (such as Penicillium and Aspergillis) are sufficiently high to require remediation efforts?-Tim , California 

            This is probably one of the most difficult questions to answer, with the answer being actually useful to those concerned about what their test results mean.

            The mold spore category described as Aspergillus/Penicillium by commercial laboratories may include spores of Aspergillus and Penicillium.  Also, depending on the analyst, it may include any spore that is round or ovoid and in a certain size range.  It may include cells/spores such as those of yeast species, Aureobasidium, Trichoderma, Paecilomyces, Mucor, Verticillium, Acremonium, and even young spores of Cladosporium.  As such, in some cases, a high count of Aspergillus/Penicillium may not mean a high count of these two very important (from a health a health perspective) mold genera.

            When I do counts of outdoor mold, they are typically dominated by Cladosporium and yeast with lesser concentrations of typical Aspergillus and Penicillium-type spores.  No commercial laboratory to my knowledge reports yeast concentrations save for the  genus Torula.  Yeast are easily recognized by shape, their thin cell walls and propensity to take up aniline blue stain.  These features can only be seen clearly under 1000X magnification. 

Magnification used by the analyst is also a significant factor in conducting so-called Aspergillus/Penicillium-type counts.  There are many Aspergillus and Penicillium spores mas well as yeast and Acremonium, that cannot be seen clearly at the two most commonly used magnifications of 400 and 600X.  Those magnifications are too low and do not have the resolving power to adequately detect, identify and count many of the smaller Aspergillus and Penicillium-type spores.  Since most laboratories use either 400 or 600X magnifications concentrations of Aspergillus/Penicillium are likely  to be significantly under reported.  When I compare my counts to those conducted concurrently in the same environment or in the same building but at different times it is striking how commercial laboratory counts under- report actual concentrations compared to 1000X magnification counts. The lower magnifications  are simply not good enough for the task of counting spores in the 2-3 µm range.

            Aspergillus/Penicillium counting is further confounded by the fact that these two genera often release their spores in strings.  This changes their aerodynamics and collection on sample media.  They often bounce and then  deposited up to several millimeters away from the deposition trace.  Most if not all commercial laboratories count the deposition trace and no more.  As such, particle bounce with subsequent deposition is not taken into consideration.  In some cases (particularly when Penicillium chrysogenum is abundant) two thirds of my count at 1000X is spores not found on the deposition trace.

            So what does an Aspergillus/Penicillium count mean?  How much is too much?  If the laboratory does not conduct counts at 1000X and take particle bounce into consideration reported Aspergillus/ Penicillium concentrations in most cases are not reliable enough to make important mold-related decisions.

 

September 2, 2005