Fungal Contamination in Public Buildings: Health Effects and Investigation Methods

3. Investigation of Fungal Contamination of the Non-Industrial Workplace (Continued)

3.4.4 Documentation of visually moldy area

Within the informed inspection component of the overall investigation, detailed notes of the amounts of mold visible should be noted on the appropriate perspective of the building plans. The moldy areas should be drawn on the plan with sufficient accuracy to permit an estimation of the number of square metres of mold.

Bulk samples might be collected from the visibly moldy building materials to delimit the affected areas by examining the materials for fungal growth. A small amount of material can be scraped off the surface and examined under the microscope and/or plated on agar media. Usually, the colour of visibly moldy material comes from conidia, ascocarps, pycnidia and, in the case of melanized fungi, the mycelia. Conidia that are not visible to the naked eye, but present on building materials may still have the potential to affect the air quality of the occupied space.

Where there is probable cause to believe that there is appreciable mold behind wall cavities, physical inspections should be performed by opening up the hidden area. Factors to consider include whether there is insulation in the walls and what kind of water damage has occurred. For example, if there has been a pipe burst, flood, fire storm or evident problems with the cladding or windows, all affected areas can be reasonably suspected of having been affected and need to be examined for mold damage. The informed inspection and/or air samples can be useful in determining whether destructive testing is required. Methods range from sawing the bottom 0.3 metre off one side of interior walls to using a keyhole saw and a boroscope (AIHA 2001). Such destructive testing should be done with source control HEPA vacuums (e.g. near the saw) or under simple containment, using all appropriate respiratory protection required (ACGIH 1999).

3.4.5 Mycological analysis of bulk samples

Bulk samples refer to physical, destructive samples of building materials. Dilution plating methods are selective and do not provide direct information on the fungi growing on the damaged material versus dormant organisms that might have settled out from the air. Dilution plating involves taking an amount of a powered material (e.g. ground wallboard, settled dust) and suspending it in an appropriate diluent. This is then further diluted in 10-fold steps and aliquots are plated on agar media at least in triplicate, followed by spreading the liquid evenly over the surface, incubating and counting the colonies that emerge. Representative colonies are then transferred to agar media appropriate to identify the species present. The strength of this method is that a picture of the diversity of species present can be obtained.

In the absence of regular HEPA vacuum cleaning, mycological analysis of settled dust samples has value in identifying a problem that might be seasonal or due to factors not present at the time of the investigation (ACGIH 1999). For example, condensation around perimeter induction units, which leads to wet carpets, occurs only in the summer. Investigation of occupant complaints may occur when the carpet is not wet. As is the case for air samples, interpretation of dust samples is appropriately made by analysis of the fungal diversity, but is less straightforward (Dillon et al. 1996; ACGIH 1999).

Small pieces of building materials collected (ca. 0.5 g) can be plated on different agar media. These are incubated and the colonies that grow out are counted and transferred for identification. The advantage of this method is that the colonies that first emerge from moldy building material are likely to be the most reflective of those active in the damaged material.

3.4.6 Microscopic techniques

Samples of moldy building materials that are plated by either method should also always be mounted in lactophenol cotton blue or other appropriate stain and examined by microscopy to determine the presence of organisms that might not be viable. This allows a comparison to be made between viable and non-viable cultures. This will provide information on the dead fungi present on damaged material to be obtained, thus helping prevent false negative results. (Dead fungal spores still contain allergens and toxins.) If the majority of the fungi are found to be dead on a moldy item, the water event probably occurred months to years ago.

There are two basic techniques to examine moldy surfaces by microscopy: tape samples and mounting scrapings of the mold-damaged area collected in small plastic bags or vials. Tape samples are made by pressing the affected surface with good quality cellophane tape. If scrapings are available, they can be mounted on slides and examined; they can also be cultured whereas the tape samples cannot. As with all microscopic methods, large dark spores are easier to see and, depending on the skill of the microscopist, small hyaline spores are often overlooked. The taxonomic information obtained is limited.