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.

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