Mold is a very common concern when dealing with indoor air quality. Many homeowners will believe that an odor or the reason they are feeling sick is due to mold without ever seeing the growth. The truth of the matter is that I find mold in only about 30% of the “unknown odor” cases I investigate! Often, the odor is coming from other sources, or it eventually goes away and the source is never discovered. The percentages are even smaller when it comes to a sickness in the home. Often times, these are truly resulting from work stress, lighting, or other factors in the home.
While it is not as common as it used to be, I still come across scenarios in which the concern has been increased due to the use of a home test kit. These test kits typically consist of two petri dishes that are set out for a period of time. One is used as a control outside, and one is the sample of concern. These tests work off the idea that spores will settle out of the air over a period of time and grow on the auger in the dish.
So you may ask, “Why doesn’t this test work? If there is mold in the dish, doesn’t that mean I have a problem?” Here are some answers for you:
1. Mold is ubiquitous to the environment
Mold is everywhere! Contrary to what many homeowners may believe, there are many spores in your home. These spores are brought in through the air exchanges in the home, on your clothes, the HVAC system, and anything else that has air in or around it. Just because there is mold in the dish does not mean that there is a problem in the home. A control of the outside is needed for comparison. In a normal environment, the indoor sample and the outdoor sample should have a similar composition; spore levels in the indoor sample should be equal to or less than the outdoor one, and any variations from inside should be small or of a type that is not considered a water damage mold. Self-test kits did get one thing right by providing the exterior control, but there are other flaws.
2. A known volume of air must be passed over the samples.
Using petri dishes as a collection media is not a problem, as it is used in viable testing (living specimens are able to grow). However, the issue with the self-test kits is that there is no known volume. You know the time, as the homeowner will write down the hours the dishes were left out, but how much air passed over the dishes? Were fans on in the room, was an HVAC duct blowing on the dish, was there a lot of movement in the room, was the wind blowing outside? All these are factors that will impact the amount of air moving over the dish and the spores it may be exposed to. Some could argue that these are settled dishes and movement of air will lessen the amount of spores; however, this is still an issue with the accuracy of the dishes, as we don’t know the volume of air sampled and therefore do not know if you can accurately compare the interior and exterior sample.
3. Non-viable vs. Viable
This test is only looking for viable or living spores. What about the non-viable ones, or total counts? When looking at the indoor air quality of the home, all spores are of a concern because even non-viable spores can have health effects. While this is a minor concern with the self-test kits, it is still a concern, because looking at only viable samplings can misconstrue findings. Typically non-viable samples are taken first to determine if there is a problem, and then viable are used if further investigation is needed for specific species of mold.
4. Result interpretation
The home test kits are usually interpreted at the lab. While this is not necessarily a bad thing, I have often seen any variation in levels labeled as abnormal. When someone is interpreting results from a lab, they have not seen the home and cannot make assessments based on conditions in the home. I will say that their assessment may not be incorrect; I just caution that there may be other influences in the home that are causing a variation and are not attributed to actual growth. I will often review samples taken by other individuals and make comments on them, but I always caution that in order to make an accurate assessment you have to be at the home at the time of the sampling. I have intentionally taken samples as less than optimum locations in the past to see how sample results vary. A specific one that comes to mind is one I took near a bowl of rotting fruit. The fruit had visible growth on it, and the results showed elevations as compared to the outdoors. Had someone read these in a lab and had not been present in the home, they may have said there was an abnormality – when in actuality, someone just needed to get rid of some fruit!