How to Interpret Mold Test Results

aka What do My Mold Test Results Mean?

Any environmental professional performing mold testing, including mold spore trap sampling, mold tape lift sampling, mold swab sampling or mold viable air testing should draft a report defining

1. What testing was performed, where (rooms, indoor/outdoor).

2. Why was testing performed (objective), site conditions (visible mold growth, water damaged area, a background sample location).

3.  Detailed explanation of the results and what the results mean.   

This is the most basic of data that should accompany any testing data.  If you do not have this data, then apparently you did not hire a professional. Professionals do not let clients draw their own conclusions.

What are permissible limits of mold?

There are No Federal or State Agency established Maximum Exposure Limits (MEL) or threshold level values for airborne indoor mold.  So there are no government standards for mold.

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Why are there no standards for mold levels?

The reason is that setting MELs would be difficult for a variety of technical reasons, which include limitations in air sampling techniques, individual variability in sensitivity to microbial exposure among the human population, occurrence of different types of biological and chemical pollutants in indoor environment and limited data on the exposure-response relationship in humans.

If there are no government established mold standards, what do people follow? 

Due to the lack of set government standards, the environmental consulting industry follows general principals when evaluating mold test results.  On basic level mold levels should be higher outside than inside, but the details of the test results when making this comparison is extremely important.  A mold testing report should cover the following topics:

    1. What are the dominant molds present in the sample obtained from the target or complainant room.  Are the molds present  in the control samples?  For examples if Cladosporium is dominating in target or complainant room but is insignificant in outdoor and control sample, we can conclude the source is in complainant room, even though Cladosporium originates from outdoor sources.

    2. Perform an evaluation for the presence of opportunistic types of molds. These so called opportunistic molds (marker) fungi, are frequently found on water damaged building materials.  Their presence can point to a long term moisture issue.  These fungi include Aspergillus and Penicillium species, Acremonium spp., Sporobolomyces spp., Stachybotrys chartarum, Memnoniella echinata, Tritirachium oryzae, Ulocladium botrytis, U. chartarum, Cladosporium spp., and Chaetomium spp.   These are molds that are not typically recovered in the outside air, so when they are found outside, they are in generally low levels. Conversly when they are found indoors these molds typically point to an indoor water issue.


    3. The physical condition of the area sampled (water damaged, odors, and water or past water damage present).  Plain and simple, mold needs moisture, environmental professionals inspect structures for excessive moisture.  Water damaged building materials (basement Sheetrock wall) that was replaced BUT not remediated can hide mold growth and mold spores.
    4. As an example on how mold testing should go, take a project where the client wants to determine if there are elevated mold spore concentrations and/or indoor amplification sources in a complainant room.   In this case, the client suspects that there is an issue pertaining to mold in a specific room.  The sampling objective is to compare total airborne spore concentrations from the complainant room with those from outdoors and non-complaint rooms. This would answer the question whether levels of mold spore concentration were elevated in complainant room compared to outdoor and non-complaint room. 

      How do you compare (interpret) the sampling data from mold  spore trap air samples?  

      You would compare the dominant spore types (and their concentrations) from the target or sampled complainant room with those from control samples (other non-compliant room or an outdoor area). Another objective is to evaluate whether there were amplification sources in the complainant room such as water damage. You do not just want to confirm the presence of mold but also why is the mold present, what created the environment for the mold to grow. In reviewing the test results, evaluation on the following would be performed: Evaluation for species of mold, with special attention to opportunistic spores.

      Evaluation of results when assessing a general complaint area of a structure.   Comparative evaluation of results from the area of compliant to background sample results (non-complaint area).

      You should not expect that any company testing for mold would only provide raw laboratory data.  All lab data must be summarized by the mold consultant explaining the results of the testing performed.  The environmental professional needs to put forth standards for judging what is an acceptable, tolerable, or normal quantity of mold. The results of samples taken in all situations cannot be interpreted without physical inspection of the contaminated area or without considering the building’s characteristics and the factors that led to the present condition.
    5. When evaluating mold test results, the consultant will evaluate patterns among the indoor mold founds, as different molds grow on different organic material and at different moisture levels such as the following:

      Aspergillus/Penicillium are early colonizers of damp building materials.

      Chaetomium or Stachybotrys later colonizers of chronic moisture/wet areas.

      Acsocpores and basidiospores are common outdoor mold, when found inside their presence may be the time of year or poorly filtered outdoor air

      Compare indoor and outdoor mold spore count and species.  You can always find outdoor molds indoors as they can be carried inside by people and by air flow.  You do not expect to find outdoor molds in higher concentrations indoor than outdoors.  When you have this situation then the indoor environment is creating an environment that is beneficial for mold, not an environment that is desirable.phonelady-resized-600The major problem with mold testing is due to the consultant not providing an opinion on the test results and failing to clearly define the sampling objectives prior to testing. In many situations, the consultant fails to clearly define the objectives for taking air samples for microbial analysis. Defined sampling objective helps the develop a scope (sampling strategy) which includes the data required and hence the type of samples to take (i.e., viable or non-viable), the minimum number of samples to take, when to take them and how to interpret the resulting data. 



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