Could you
please tell me how to determine 1) limit of detection and 2)
acceptance criteria for mold?-R.,Michigan
The limit of detection for a sampling
is determined from the minimum count and sampling volume used. In the
case of an Andersen sampler, if one samples for two minutes at a flow
rate of 28.3 L/min and expresses the concentration in CFUs/m3,
the multiplication factor that converts the colony count to CFU’s/m3
is determined by dividing the sample volume (in this case 2 X 28.3 =
56.6 L/min) into 1000L (1000L = 1m3). The multiplication
factor in this example is 17.6. If one has a count of one
Penicillium, the limit of detection is 17.6 CFU/m3. If
one has only one colony total, then the detection limit for all
culturable-viable spores is 17.6.
In the case of spore trap sampling,
the limit of detection is determined from the volume of air sampled ,
the % of the deposition trace analyzed and the minimum count. Let us
assume that a 75 L/sample was collected using an Air-O-Cell cassette
and that 20% of the deposition area was counted. Let us further
assume that one Alternaria spore was observed on such a count.
The multiplication factor used to express concentration in S/m3
or counts per cubic meter must take into account both the volume of
sample collected and the % of sample counted. The multiplication
factor to correct for volume is 1000 divided by 75 that is 13.3. The
correction factor for % of deposition area counted is 100 divided by
20, that is 5. The combined multiplication factor is 5 X 13.3 =
66.7. If one spore of Alternaria is observed on 20% of the
deposition area the limit of detection is 66.7.
Acceptance criteria refers to what
is an acceptably low concentration. Because of the different sampling
and analytical methods used, acceptance criteria will vary from one
technique to another and one investigator to another. For Andersen
culturable airborne mold sampling, I use levels < 300 CFU/m as
acceptable. For spore trap sampling counted at 1000X, I use 5000 S/m3
as acceptable. Samples counted at 400 or 600X will result in lower
numbers and thus acceptance values will be lower. These can be based
on the total spore count (i.e. < 1000 S/m3, individual mold
types (i.e. Aspergillus/Penicillium < 500 S/m3), and
Stachybotrys (0).
An extensive review of mold
exposures guidelines has been recently published by Robert Brandys
Ph.D. and Gail Brandys. It is entitled Worldwide Exposure Standards
for Mold and Bacteria-Historical and Current Perspectives. It is
available for sale at
www.safety-epa.com.
May,2004
Indoor Environmental Quality (2000), Thad Godish Ph.D.,
C.I.H
Direct E-mail
00tjgodish@bsu.edu
