Fungi are naturally occurring and widespread in the environment, and the air we breathe naturally contains fungal spores and structures. Airborne fungal levels may vary over time due to spatial, temporal, and seasonal variations, environmental and meteorological conditions and nearby activity that may cause airborne fungal levels to fluctuate.
In the indoor environment, fungal growth occurs when there is sufficient moisture. Fungi are most likely to grow when conditions are damp or wet such as in bathrooms and basements. Fungal growth can also be observed on windowsills when there is condensation. Additionally, fungi proliferate indoors when the building has been water-damaged through a flooding event or a prolonged leak, for example.
Fungal growth indoors can be a serious problem because of the potential health risks associated with exposure and inhalation of fungal spores and structures. One of the most widely accepted methods of assessing indoor air quality and its effects on building occupants is the analysis of indoor air samples. Sampling for airborne fungi can also detect hidden mould growth in indoor areas and determine how effective remediation procedures are. Hidden mould is defined by the American Industrial Hygiene Association (AIHA) as “concealed fungal growth on building materials or contents that is within the building envelope but concealed from view during a normal walk-through inspection”.
The collection of air samples is performed using a sampling pump calibrated to a specific flow rate per minute to take in a known volume of air. The air that is taken in through the sampling pump is then impacted onto a cassette containing a gel coated slide. Fungal spores and other particulate matter are deposited onto the gel surface. Using direct microscopy, the sample is then analysed for the quantification and categorisation of fungal structures. Fungal structures are categorised by morphological type from the genus level (eg. Cladosporium) to the phylum level (eg. Basidiospores). The major advantage is that mould is observed and identified whether it is viable (alive) or non-viable (dead). Both live and dead mould can contain toxins that can be harmful to people.
Currently, there are no widely accepted standards or regulations regarding microbial contamination in indoor air. There are also no recommended health-based exposure limits for mould. Without any standards or guidelines available, a common strategy is to collect an outdoor baseline sample. Fungal spore types and levels detected indoors are compared to the types and levels found outdoors.
Focus Analytics conducts analysis to ASTM D 7391-20 ‘Standard Test Method for Categorization and Quantification of Airborne Fungal Structures in an Inertial Impaction Sample by Optical Microscopy’.