Question: I am seeking information for a community hall regarding mold sampling. This hall is used for meetings and occasionally food is prepared and served. There has been a multi-year history of clean water seepage but the source has not been identified yet. Walls and surfaces have large areas of primarily black coloured mold, some green and some a peachy colour.
There is a musty odour too. My questions are:
- With the limited exposure most people have to the environment, can mold sampling give us information as to health risks for public and for the cleaning staff?
- If we send samples, and worst case scenario: mold is toxic, do you provide info on proper cleanup procedures?
- Would tape method of mold sampling be adequate for assessing the above?
- Areas mentioned have recently been bleached/washed and none are visible today; how long should we wait to do mold sampling?
Thanks for your help.
Answer: Mold Sampling on its own cannot provide information as to the health risks for public and the cleaning staff. This is because there are no exposure limits for airborne mold spores. Health Canada states that “in the absence of exposure limits, results from tests for the presence of fungi in air cannot be used to assess risks to the health of building occupants”. That does not mean mold sampling is not necessary. Read the article “Is Sampling and Testing for Indoor Mold and Bacteria Necessary?” Regardless of the type of mold, i.e., whether toxigenic or not, the procedures for cleanup are the same. A mold cleanup procedure is determined by the amount of mold growth in square footage. You’ve mentioned that the contaminated area had recently been bleached and no mold is visible. Since the source of water has not been identified and corrected, mold growth will reoccur. I would suggest you consult a professional knowledgeable in building science to help in identifying the source of water and assess the extent of mold growth. It’s possible there could be more hidden mold growth than what was visible before bleach was used.
If you have further questions regarding mold sampling please contact us at 604-435-6555 in British Columbia or 905-290-9101 in Ontario.
The problem of using a single type of media is that some molds may not grow well (or may not grow at all) in the selected media. Hence, although such molds may be the dominant contaminants in the air, they may end up being missed or underestimated. The solution, therefore, is to use more than one type of mold sampling media or select one that is known to support a wide range of environmental molds. A good example is Malt Extract Agar (MEA). The problem with this media is that it also supports the growth of bacteria to some extent. 
If the environment sampled is contaminated with bacteria, the bacteria grow faster than molds and interfere with mold growth. This problem can be overcome by incorporating a suitable antibiotic or other suitable compounds (e.g., Rose Bengal) into MEA to suppress bacterial growth. Rose Bengal not only suppresses the growth of bacteria but also restricts the spread of fast growing molds thus making it easy for colony counting.
Direct microscopy allows identification of the dominant contaminant (at least to genus level) regardless of whether the mold is dead or cannot grow on media used.
After plating onto DG18 and MEA and incubation (see petridishes marked “B”), Stachybotrys appeared on MEA but not on DG18. These observations clearly indicate how wrong conclusions can be made if the right type of media is not used either in air sampling or culturing of bulk samples.