At the end of
April the American Industrial Hygiene Association (AIHA)
announced that it would begin to accredit laboratories for counting
airborne mold collected using spore trap methods. This week’s
posting represents a commentary on
AIHA’s protocol for such accreditation.
The idea for accrediting
laboratories that conduct analyses of samples collected using
Air-O-Cell, Burkard, Allergenco and other similar samples is in
theory a good one as such sampling/analyses dominate residential and
non-residential mold testing in the U.S. The question can be asked
as to whether such accreditation will result in accurate and
reliable test results that can be used to determine whether one has
a serious mold exposure problem or not and/or to determine the
effectiveness of a mold remediation?
The AIHA accreditation protocol
focuses on a variety of quality control/assurance guidelines that
have the potential to increase greater uniformity in results
reported for similar airborne mold samples. It requires that
laboratories seeking accreditation provide (1) a description of
sample trace analyses, scope magnification, counting rules, % of
trace analyzed and calculations, (2) the laboratory’s criteria for
identification of reported spore groups/fungal structures, (3)
information on daily microscope alignment, proper microscope use,
and annual calibration, records demonstrating scope performance, (4)
description and documentation of analyst training including the
ability to identify spores, (5) documentation showing the limit of
detection (LOD), (6) documentation on replicate and duplicate
analyses, and (7) documentation of participation in external
proficiency evaluation program with other laboratories.
Under this accreditation program,
any laboratory that meets these criteria can be accredited.
Laboratories are not required to use any specific magnification even
though the most commonly used magnifications (400 and 600X) do not
have the resolution needed to determine the presence of many of the
spores from species of Aspergillus and Penicillium.
These are the most important (in this writer’s opinion) mold spores
in building environments because of their potential to cause
moderate to serious health effects. Our studies show that counts
conducted at 1000X yield count values that are on the order of two
to four times higher than those conducted at 400 and 600X. 1000X
counts result in much higher counts of Aspergillus/Penicillium-type
spores and allow the analyst to distinguish these from yeast cells
that can often dominate outdoor air samples and indoor affected by
outside airflow into a building. Though lower magnifications are
useful for screening for large spores (Stachybotrys, Chaetomium,
Pithomyces, Alternaria, etc.), they are not adequate for
counting small spore species of Aspergillus, Penicillium,
and cells of yeast.
AIHA’s guidelines seem to impose a
requirement for consistency in counting a sample trace.
Unfortunately, this means that analysts will not count beyond a
prescribed limit and as such particle bounce is not taken into
consideration. In some cases particle bounce(responsible for spore
deposition beyond the deposition trace) may result in as much as
60-70% of the spore count. (This is particularly the case with
Penicillium chrysogenum spores which are commonly present as
strings of four or more spores.)
AIHA’s spore trap accreditation
protocol places much emphasis on laboratory quality control
procedures. It unfortunately is not based on the science needed to
assure that reported results accurately reflect airborne mold
levels(and types present) and potential human exposures.
September 23, 2005
