BRIEF COMMENTS ON AIR SAMPLING AND MOULD DISCOVERY
by George Carroll, Ph.D
Mould Works Chief Scientist Dr. George
Carroll, Ph.D. has taught for over 35 years at the University
of Oregon and has written over 45 publications on mycology.
Mould Work's offices in Portland, Oregon and Golden, Colorado,
are run by his partner, Bob Lanier. Dr. George Carroll, runs
their identification lab in Eugene, OR.
In the last two decades the presence of moulds and mould
spores in interior environments have been recognized as a
cause of allergic reactions and occasional symptoms of more
severe respiratory distress. Homeowners and renters who
suspect mould infestation in their buildings often secure the
services of building inspectors to asses their mould problem.
A common approach involves air sampling. Controlled volumes
of air are sucked through a filter with a vacuum pump, and the
filters are sent to laboratories which specialize in counting
and classifying particulates in air. This direct approach
appeals to occupants of mouldy buildings because it appears to
measure precisely the numbers of mould spores in the ambient
air and thus the allergenic load to which they are exposed.
However, air-sampling is fraught with difficulties. Usually
a single sample from a given room is taken and compared with a
similar sample from outside the building. Unless samples are
replicated, such data are totally meaningless (however
precisely the spores on a single filter are counted) and are a
waste of money. Replication means duplicate samples taken from
exactly the same place in the same room with the same filter
and air pump with the same volume of air. At a minimum three
replicates must be taken. If the differences between inside
and outside are not huge, more replicates (5 or more) may be
required to claim with confidence that the levels of spores on
the inside of the building are greater than those on the
outside. The problems in assessing the actual numbers of rare
spores in a building are even worse. Samples taken from
another room or another floor in a building must also be
replicated. What is the take-home message? Whereas the "mouldiness"
of a building determined by air sampling is usually based on
two filters, 20 might easily be required to generate a
believable, statistically valid conclusion. Few owners of
buildings would agree to cover the cost of such sampling.
The problems with air-sampling extend beyond the
statistical. Many fungi of concern produce spores which are
indistinguishable from each other on an air filter. This is
particularly the case with Aspergillus and Penicillium, but
the problem extends to other common moulds such as Acremonium
and Paecilomyces. To pick an extreme but frequent situation,
spores from Aspergillus sydowii, Aspergillus versicolor, and
Penicillium corylophilum look virtually identical under the
microscope. Aspergillus sydowii can cause invasive infections
of the respiratory tract and Aspergillus versicolor produces a
mycotoxin, while Penicillium corylophilum is a common and
apparently innocuous interior mould of little concern. The
owner of a building deserves to know which mould he has if he
has paid for a mould inspection.
What after all is the point of a mould inspection?
Surely the responsible owner of a building will wish to
locate the source of the mould spores in the air, fix the
leaks or other sources of moisture that have given rise to
the problem and replace the mouldy substrate with clean
materials. In that case air-sampling must be regarded as
inefficient and costly.
The appearance of mould-sniffing dogs is a brilliant
solution to the problem of locating sources of household
mould. Dogs when properly trained are in fact exquisitely
sensitive walking gas chromatographs with a proven record in
locating mouldy substrates even when hidden behind partitions
or on the insides of walls. Once the mouldy areas are located,
the moulds can be identified by optical examination and
culture of tape lifts, which provide a degree of certainty
that can never be attained with filters from air samplers. For
this reason I endorse Mold-Dog Inc with enthusiasm.
Back to Top