First we have to look at the differences between viable and nonviable sampling:
Viable Sampling – Viable sampling only documents mold that is alive and able to grow and produce spores. Nonviable sampling documents all spores, alive and dead. The advantage of viable sampling is that the mold is actually grown out on a Petri dish and mycologists are able to identify the mold down to the species level, and viable sampling can differentiate Aspergillus and Penicillium. The disadvantage of viable sampling is that it takes 7-10 days to culture the sample, and the dead spores, which can also contribute to poor indoor air quality, are not counted. Another disadvantage of viable sampling is that some mold species grow better on specific media, so the standard PDA or MEA Petri dishes may not allow all species to grow.
Nonviable Sampling – Nonviable sampling documents all spores. The main advantage of nonviable sampling is the quick turn-around time. Pacific IAQ can get results next-day at no additional charge. The disadvantage of nonviable sampling is that molds are reported at the genus level, and Aspergillus and Penicillium cannot be differentiated and are therefore reported together as “Penicillium/Aspergillus”.
The most common samples collected are:
- Tape-Lift Surface Sample – Tape-lifts are a nonviable method of sampling where surface material is “lifted” off on a piece of clear tape. The tape is fixed to a microscope slide and analyzed through direct microscopy. Tape-lifts are quick and reliable, with very few cons. This is the most common type of surface sample collected.
- Spore-Trap Air Sample – Spore-traps are small cassettes that trap particles on an adhesive slide inside. The cassettes are attached to a pump, which pulls a specified volume of air across the interior slide. The particles that are stuck to the slide are analyzed through direct microscopy. The advantage of spore-traps is that they are quick. The disadvantage is that they document conditions at a specific place, at a specific time, and conditions can change rapidly, especially in the outdoor air. This is the most common type of air sample collected.
- Swab Sample – Sterile swabs are used to collect surface material. The swabs are sent directly to the laboratory where they are used to inoculate a Petri dish. The Petri dish is cultured for 7-10 days and the resulting mold growth is analyzed through direct microscopy. This type of sampling is commonly used for legal documentation.
- Anderson Sampling – An Anderson sampler is used to move air through 400 small holes, directly onto a Petri dish. The Petri dish is cultured for 7-10 days and the resulting mold growth is analyzed through direct microscopy. This type of sampling is commonly used for legal documentation.
- Bulk Sampling – Bulk sampling is the collection of bulk material for analysis. This material may include carpet samples, drywall, wood, or any other material suspected of containing mold growth. Analysis can be either viable or nonviable. This type of sampling is rarely used.