Find Mold

How To and How Not To Find, Molds in Indoor Proliferations?

Scientific ideals die hard. For at least four decades, there existed a scientific ideal that went more or less as follows: in order to determine the significance of indoor molds, first build a perfect air sampling device. Then use it to count either the total spores and conidia, for direct microscopic techniques, or the colony forming units (CFU), for culturing techniques, of molds in the building where excessive mold growth was suspected. Compare the numbers of molds you detected with a pre-existing standard threshold level above which the number of mold propagules is known to be unacceptable. This standard benchmark will have been calculated by comparing problem buildings with non-problem buildings. In buildings exceeding the air sampling benchmark, go looking for the mold sources and remediate them.

The problems with this doggedly pursued strategy were many. Here are a few - there was no possibility of building a perfect air sampler. Non-viable samplers, depending on direct microscopy, rendered impracticable the accurate counting of small, nondescript propagules such as Aspergillus conidia. Yet some research studies showed that up to 50% of the mold propagules in air were dead, so that viable samplers tended to underestimate numbers. This was especially true with Stachybotrys, for which often 3% or fewer of the conidia in indoor air were viable in culturing techniques. Yet, dead conidia appeared to be just as irritating as live ones.

Outdoor air mold counts fluctuated drastically over the year, making the setting of threshold benchmark mold count levels for indoor environments very difficult. The techniques used had no way of separating material produced indoors from that produced outdoors unless laborious identification studies were conducted on dozens or hundreds of fungal colonies, and species on the outdoor list were subtracted from the indoor list. In the decades where the air sampling/counting ideal was pursued, benchmarks that were proposed were highly arbitrary, and the need for further research was cited routinely.

Often the mold colonies could be seen growing on the wall (or in the air system, or other places). This posed a quandary. If the number of colonies in indoor air sampling were below the published benchmark, should these molds simply be dismissed as insignificant and left to keep on growing? Could spending money cleaning such an insignificant problem be justified? If workers or tenants still complained that the molds were bothering them, were such people just being combative or neurotic? What if new workers or tenants also began to voice the same complaints?

The ideal was rather dependent on all molds being more or less of the same significance, so that they could all be counted together. But there was increasing evidence that some molds were far more irritating than others. Each mold was a biological species with its own array of allergenic proteins and potentially irritating toxins. When it became clear that a single Stachybotrys colony from indoors (which probably represented the presence of an additional 30 or more dead conidia in the same sample, and signaled, for example, a biochemically irritating forest of mold in the basement derived from a water leak) was actually more indicative of an air quality problem than 200 Cladosporium colonies which came into the house from the park across the street, it became pretty obvious that simply counting CFU was inadequate.

Viable air sampling, especially with the more accurate machines, tended to take only a brief "snapshot" of the molds present in the air. The length of exposure was limited by need not to have colonies overgrowing one another. (With bacterial sampling, this problem was diminished by using liquid impingers that air could be bubbled through. These were of dubious efficacy, however, with highly water-repellent mold conidia.) But the actual presence in the air of mold conidia or spores was highly dependent on room activity, air currents, humidity, whether the door to the basement (or crawlspace, or attic hatch, or moldy closet) was open or closed, etc., not to mention the weather outdoors, time of day, wind speed, degree of maturity of nearby vegetation, occurrence of spore-mobilizing disturbances such as crop harvesting or compost turning, and so on.

Different individual people vary in their responsiveness to molds. Even if testing people's responses to different levels of molds were possible (lab experiments along these lines would be considered experimenting on humans, and would likely be regarded as ethically inadmissible), it would be difficult to decide what kind of person to use as a standard for devising benchmark levels:

• The most sensitive? This might be someone claiming sensitivity to almost everything in the environment, binding everyone else to an unlivable standard.
• The least sensitive? That would please almost no one except the occasional curmudgeon who had smoked off most of his/her airway epithelium.
• The average person? That ought to, in theory, leave about half the population dissatisfied, assuming a bell curve of mold response. This sort of strategy reaches the acme of difficulty when you incorporate the possibility that different people might have different levels of reaction to different mold species.

Finding the ideal benchmark population for Cladosporium cladosporioides proliferation might not help at all in assessing Stachybotrys chartarum proliferation.

An alternative strategy?

Mold amplifiers (proliferation sites) indoors are often eminently findable by room inspections or other simple techniques (e.g., sticky tape examination of dust from within heating ducts.) If not, air sampling can be used as an exploratory device to detect which molds are unusually well represented in indoor but not outdoor samples. This usage makes air sampling an auxiliary tool which can be used in the effort to physically locate indoor amplifiers, rather than an arbiter of the acceptability of mold propagule levels.

Some molds are more irritating than others. Recognition of species involved in amplification is often important, whereas overall aerial counts are unlikely to be.

Despite the differences in significance of different mold species, it is hard to justify allowing any mold amplifiers to persist indoors. Usually they indicate a moisture control problem that is also causing other damage or economic loss: for example, mold around a window sill in an area of temperate climate often indicates poor heat seal and condensation, meaning that energy is being lost and the support for the window frame is probably rotting; mold on a poorly insulated wall in winter in a chilly climate indicates voluminous energy loss; mold in the basement indicates either leaks or floods that are causing active destruction of structural materials, or foundation cracks/porosity that threatens every biodegradable item in the basement, whether clothing, shoes or suitcases, with destruction through excess humidity; Mold on water-stained ceiling tiles or on rippled wallboard under the window indicates major leaks damaging the building, and so on.

Now here's another key piece of logic: if the mold amplifier is quite large, clearly it may be a major irritation or allergy problem, and it probably indicates a major underlying building problem as well. For the sake of the building, as well as for the human sufferers, it's worth the remediation efforts. But if the mold amplifier is small, it may be of negligible health significance, but then again, if it's that small, it probably is very easy to clean up. And most likely any underlying problem it represents is minor in scale and easy to remedy. These principles came together in the following recommendation, taken from Health Canada's "Fungal Contamination in Public Buildings: A Guide to Recognition and Management".

The visible presence of fungi on moldy ceiling tiles, humidifiers, diffusers, air supply ducts or other surfaces (including microscopically visible fungi in humidifiers) requires investigation and remedial action regardless of the airborne spore load. People working in actual cases - for example, industrial hygienists and public health inspectors - have reported that this recommendation is very effective in solving problems in the field. If the occasional building owner is recommended to clean up a mold amplifier even though its connection to health complaints is uncertain, he or she can have the satisfaction of knowing that following the recommendation will solve a problem of some kind. Even if a significant respiratory health problem is not solved, at least some sort of pernicious building maintenance problem is resolved, one that otherwise probably would have gotten worse. After all, leaving moldy materials around a building is rather like leaving moldy materials at the back of your refrigerator. It is negligence slowly giving rise to filth. And it's very hard to defend.