Part 4

Mold remediation clearance.  What type of air sampling and analysis provides acceptable clearance?  What is an acceptable ratio (percentage of indoor versus outdoor spore counts)?  Should indoor counts be “no more than 50% of outdoor counts or significantly lower indoors as opposed to outdoors”?  This seems to be a grey area everywhere I look.-Matthew, South Carolina          I

Mold Remediation Clearance, Part 4         

          In the previous postings I indicated that the use of spore trap methods for clearance sampling was quite problematic as a result of laboratory analyses reliability issues associated with sample results.   Because of these concerns, I have discussed the desirability of using alternative methods and described the use of volumetric culture plate methods in some detail.  In this posting the use of QPCR analysis for clearance testing is described.

            For some investigators and consultants the use of QPCR is the gold standard for airborne mold analyses.  Some consultants use it for clearance sampling exclusively.

            Because QPCR is a DNA-based method, it can be used to identify mold spore/particles in air, dust and bulk samples.  I have primarily used it to analyze bulk samples to identify species present and their abundance. My use of QPCR for airborne mold levels has been somewhat limited.

            A number of commercial laboratories provide QPCR analysis of samples for panels of 4, 8, 15 & 23 species with price ranges of $100 to $280/ sample for mold types that have been selected as indicators of indoor fungal contamination.  The panel of 23 includes eight Aspergillus and five Penicillium species commonly found indoors on wet or once wet building materials.  It also includes Acremonium, Alternaria, Chaetomium, Cladosporium (Cladosporioides), Memnonulla, Paecilomyces, Stachybotrys, Trichoderma, and Ulocladium.  A number of panel species notably Stachybotrys chartarum,  Chaetomium globosum, Aspergillus  versicolor and Trichoderma arzianium are known to produce potent mycotoxins and are commonly reported to be found on wet building materials.

            As can be seen QPCR includes only target species and as such cannot represent total airborne concentrations present.  These test panels do not include yeasts, basidiomycetes, and Cladosporium hebarum which can often dominate the outdoor mold spectra.  As such, one can expect QPCR results to be in many cases lower than those associated with high quality spore trap analyses and even results from culture methods.  Nevertheless, it provides investigators with the opportunity to quantify species which are of particular importance to indoor mold concerns.  QPCR analyses would be best used by comparing pre and post remediation results to determine the relative effectiveness of remediation.  Indoor/outdoor comparisons may be of less relevance since the outdoor concentrations of most of these species is likely to be low (too date there is little published  science available indicating how such QPCR comparisons differ). 

            QPCR is as one can see much more expensive than sample analyses for spore trap analyses ($25-60/ sample) and this is often a likely deterrent to its use.  This may change as awareness develops in the mold sampling and remediation community that commercial laboratory spore trap analyses are in general unreliable and that knowingly using an unreliable method puts users at a significant risk of legal liability.

August 5, 2005