Fungal Exposure Assessment
By Dr. Harriet Burge
EMLab Chief Aerobiologist and Director of Scientific Advisory Board
Human Health Effects
Fungi evolved over 400 million years ago and references to mold in buildings suggest that it has always been present in human environments. At present there is growing public concern about the potential health effects of mold in homes and structures that has been heightened by media reports of presumed health effects, clear episodes of illness related to indoor fungal growth, litigation, and requirements for disclosure during real estate transactions.
In addition to health concerns, fungi may cause decay of building materials and contents, occasionally to the extent that the material must be removed from the building. Some of this growth may be hidden inside of attics and walls, making visible diagnostics difficult (Gravesen, Nielsen et. al.). Exposure assessment must then rely on sample collection.
Exposure Assessment vs. Environmental Assessment
We often consider these two topics the same, whereas they may not be. Exposure assessment essentially means that your focus is on human exposure, and you are going to have to interpret your data with respect to the amount of exposure people are experiencing. Environmental assessment, on the other hand, is used to test hypotheses regarding whether or not there is fungal growth, the nature of the growth, and its extent without regard to exposure. Most of the incidental investigations that are done are environmental assessments and the data cannot be interpreted with respect to human exposure. Evaluating human exposure for these studies would require information such as the time each person spends in the environment, what activities he/she performs, and a number of other factors. If you want to do exposure assessment, then you must write hypotheses that ask specific questions about exposure, not just environmental conditions.
Hypothesis Development and Testing
The advantage of generating a hypothesis and writing it down is that you can then focus your investigation on answering that specific question. This focus leads to an investigation structure that produces data that can be interpreted specifically with respect to the question, and you can decide in advance how that interpretation will be done.
Interpreting the Data
So, you have your data as a result of testing a specific hypothesis. You can then ask the question: “Do the data support your hypothesis or not?” If you have not done a hypothesis driven investigation, then you will have to rely on existing guidelines and standards. These simply do not exist for fungi and fungal aerosols in indoor environments. You might be able to make reference to a baseline data set such as the EMLab MoldScore™ (designed for paired indoor/outdoor spore trap data). Otherwise, you might be able to find an appropriate data set in the literature that was collected using the same methods that you used.
Developing a Sampling Strategy
Many studies aim to determine whether or not fungi are growing in an environment, and whether or not aerosols are being produced. In this case, visual assessment, tape or bulk samples, and a limited air sampling protocol are often sufficient for this determination. The most straightforward method for air sampling, the spore trap, is generally used, and data are compared indoors and out. If viability of the airborne organisms is of interest, then a cultural method is used. This type of investigation is most commonly done using a sieve plate impactor (Biocassette™, Andersen, etc.). A good discussion of bioaerosol sampling instruments can be found in the ACGIH Air Sampling Instruments manual.