This is a quick review of home testing for airborne mold.
Bottom line: I’m going to start with some $3-a-pop agar plates (Amazon). Despite numerous drawbacks.
We’ll see what develops.
Note: Results are shown in Post #1898.
Intro
I want to check a few areas of my home for an excess of airborne mold spores. This is a shot in the dark, so I don’t want to spend a lot of money on it, if I can avoid doing that.
I could hire a pro to do that for me. But, cost aside, do I really want my tester to be somebody who’s primarily in the business of selling mold remediation services? Particularly when you can expect to find some level of mold more-or-less everywhere.
So, I’m scoping out the test-at-home market.
Here are my notes. I knew zip about this, as of two hours ago. Here’s what I’ve learned in two hours.
Testing for airborne mold spores.
The first split in the decision tree is whether you are testing for surface mold or airborne mold.
Surface mold is … mold growing on a surface. With those, you swipe a surface, then test the swipe in some fashion.
That’s not what I’m looking for. I want a test for airborne mold.
Airborne mold is mold spores suspended in the air. (For all intents and purposes.) Mold spores are reported to range from about 3 to 30 microns in size, so some of those will float long distances/stay suspended for long times, in air. Some will not. (The cutoff for “airborne” particles is conventionally taken at 5 microns.)
The first thing I learned about airborne mold tests is that the price of the test typically does not include the price of the lab analysis of the test. A typical lab fee is $35-$40 per test, and most places say that you need a minimum of two — one outdoors, one inside — to test for excessive mold.
What, exactly, the “lab test” does, varies from type of test to type of test. For the agar-plate-style tests, they identify the types of mold that are growing. For the air-sample tests, I’m pretty sure they give you a count of spores found.
Three styles of tests
Petri-dish agar tests: Crude, and cheap if read them yourself. (Amazon example) One type of test is a Petri dish coated with sterile growing medium. Take a sterile dish, uncover it for an hour, in a room where the air has been undisturbed for a while. Then cover it up for a couple of days, in a warm place, and see what grows.
These seem to be sold as either read-it-yourself or send-to-the-lab tests. Read-it-yourself boils down to counting the number of mold colonies that have formed, regardless of size. Most common rule seems to be that four and under, for a one-hour exposure, visible after two days, is OK.
So the test is crudely quantitative, in the sense that you may see few mold colonies, or you may see a lot. But there’s no direct link between the number of colonies you see, and the actual amount of mold spores in the air.
As I read it, a lot of factors can partially compromise these tests. Mainly, there are several ways in which you can get false negatives (no mold on agar plate, when unhealthful levels of mold are present). And, based on photos, it’s surprisingly hard to count the mold colonies.
I view agar plates/Petri dishes as a form of one-way testing. If you end up with a plate dotted with mold colonies, after the one-hour-exposure/two-day-incubation routine, then you’ve found something. If you don’t get that, or don’t get it clearly, then it’s not clear what you can conclude. In other words, they may sometimes tell you that you have a mold problem. Plausibly, they are not reliable for indicating that you don’t have a mold problem.
Around $3 a plate if you just buy agar Petri dishes yourself. Around $40 a test if you want ones that you can send to a lab, and have the lab read them. For lab-read tests, it looks like a minimum of two tests — one outside your home, one inside.
Air sample testers: Quantitative, must be lab read, pricey. (Amazon example.) A second type of test uses an air filter and a fan (air pump). This is lab-read-only, but it has two big advantages. First, the in-home portion of the testing is done in under ten minutes. (Versus having an open Petri dish sitting around for an hour). And the test is quantitative — the lab reading will give you some idea of how much mold was in the air.
I only found one on the market, and that rounds to $300 for three usable indoor tests. Minimum of two tests — one outside your home, one inside.
Plus, at the end of it, you’re left with yet another useless battery-powered device to get rid of. In this case, it’s the “air pump” used to draw a known quantity of air through the filter medium.
Dust swab: Like a COVID test. (Amazon example.) Yet a third type of test asks you to swab the dust in a room, and test that for mold. That looks very much like a COVID test, so I assume there’s a reagent there that reacts to some surface compound commonly found on mold spores.
There’s some chance that, like a COVID test, the results are a simple yes/no. Yes, mold is present in the dust. No, it’s not, or not at detectable levels. So I’d call this a non-quantitative test.
Around $40 a test.
PM 10 air quality meter: No. I already own a meter that monitors airborne particulates (so-called PM 2.5 and PM 10). A quick back-of-the-envelope convinced me that a PM 10 air quality meter probably wouldn’t function well as a mold detector. (Independent of the fact that all kinds of non-mold material could be in PM 10). Near as I can tell, there’s just too little mold in the air, at the limit of what’s considered healthy, to trigger a PM 10 meter.
Decision
I bought 10 sterile agar-coated Petri dishes, at $3 each, from Amazon. Unless I want to ship them off to a lab to be “read”, this seems adequate, at least for an initial check.
That, despite their lack of … well, pretty much everything you want in a test. But the bottom line is that, under the right circumstances, this will send up a warning flag if excessive amounts of mold are present.
This whole exercise is a shot in the dark. And I’m not even sure what “normal” mold levels would look like, on any of these tests. So this seems like just about the right place to start.
