Part 2        

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

 

            In the previous posting I wrote of reliability problems associated with counts involving Aspergillus and Penicillium- type spores.  I indicated that for many mold remediation situations the presence and concentrations of Aspergillus and/or Penicillium species were the most important concern (save maybe Stachybotrys) in clearance sampling.

            The reliability of test results reported by many commercial laboratories may be a more serious problem than their inability to adequately conduct good counts of Aspergillus and Penicillium.   Several  studies have recently been conducted that seriously erode one’s confidence in sample results reported by many commercial laboratories.

Dr. Patricia Heinsohn, an industrial hygienist and indoor air quality consultant at Micro Bios Pacifica, CA, recently reported results of a study at the annual American Industrial Hygiene Conference and Exposition held in Annaheim, CA (May 21-26, 2005).  These studies focused on both inter- and intra-laboratory variability in spore count when a series of samples were analyzed by different analysts within a laboratory and among six different EMLAP certified commercial laboratories.  These studies were not conducted blind and included the cooperation of each laboratory. Reported concentrations for the same sample slides varied in a number of cases by over an order of magnitude.  In some cases more than an order of magnitude differences in reported concentrations were observed among analysts in the same laboratory.

            Inter-laboratory comparison studies that we have conducted at Ball State University confirm the wide variability in concentrations reported among different laboratories.  In our case we sent a series of six samples that were co-located and concurrently collected to 10 commercial laboratories.  Not uncommonly reported results varied by an order of magnitude and when compared to samples analyzed by this investigator some reported results were two orders of magnitude lower.  In a bit of irony, the higher the cost of analysis (i.e. 50-60) samples, the higher the reported concentration.  In one case, a laboratory reported sampling results that were incorrectly calculated in five of six cases.

            At the current time commercial laboratories use no counting protocol that is standardized across the industry and has been evaluated scientifically to provide accurate and reliable results.  Currently the American Industrial Hygiene Association is attempting to establish certification criteria for spore trap analysis similar to those used for culture samples.  Unfortunately, this is going to be a very difficult task because of the heterogeneous nature of particle/mold spore samples and the lack of science published on the significance and variability of particle bounce, percentage of sample to be counted, and what as a countable mold particle.

            As a research scientist and consultant, I have conducted mold spore counts for over twenty years.  I use a magnification of 1000X and typically count 5% of the deposition strip (including deposition associated with particle bounce).  My typical analysis time per sample is 15 to 30 minutes depending on the deposition intensity.

           Commercial laboratories on the other hand commonly report counts that range from 20 to 100% of the deposition trace.  One hundred percent counts are increasingly becoming the norm as some laboratories see this as a competitive advantage.  As a comparison to the analytical time I typically employ for a 5% 1000X count ,some high volume commercial laboratories have an average counting time of 6 to 8 minutes per sample which may be reported as a 20-100% count.

            As can be seen from the information presented above, it hardly makes sense to have clearance guidelines when reported sampling results reported by many commercial laboratories have a high probability of being unreliable.

 

To be continued

 

July 22, 2005