Environmental Assay Inc.

IAQ (Indoor Air Quality) Irritants

Pollen

We love plants, or we should, because they provide nutrition, they convert our gaseous exhaust (carbon dioxide, or more commonly CO2) into Oxygen that we consume continuously, and they provide beauty in the form of shapes, colors, etc. However, to propagate, they pollinate. And pollinate they do, partially right into our very noses. Pollen, the small "seedy" part of plant anatomy, is either scattered about by pollinators (bees and other insects) in a long-term fashion, or by wind in a short-term fashion (sometimes only lasting a week or two per year). The latter is a cause of aggravation and suffering for many individuals who on an ongoing basis suffer from congestion, sinusitis, and a reduced ability to breathe. Aside from the destruction of all plant life on the planet (a course of action Not recommended), the only alternative is to be within a filtered enclosure (indoors). Even without inbound filtered air, simply being inside a shelter one is protected from the seasonal onslaught of innumerable and varied kinds of airborne bodies intended to make plants propagate, and their indoor concentration is generally lower than outdoors due to the protection from meandering air currents. For a reduced presence, one can use a stand-alone air filter unit, which will reduce the particulate concentration in one or more rooms. When that shelter is additionally equipped with a central air mover and distribution system, the indoor concentration (when using a good quality filter) is bound to be several magnitudes lower than outdoors. Unfortunately, everyone does not have such equipment, so some are left to their own devices when the pollen season is expected, for certain of the most irritating pollen producers such as ragweed, and to seek appropriate protection indoors. Size-wise these are the heaviest, and produce a layer of fine colored "dust" on horizontal surfaces, until a breeze again lifts them up. Being organic, they form an excellent and diverse food base for bugs small enough to benefit from it.

Animal and Human Dander

We itch, and scratch ourselves, as do animals, and in the process shedding copious amounts of hair and skin cells. Over time these droppings congregate into "tumbleweeds" that locate themselves near wall-to-floor intersections. Over additional time, these acquire names, and seem to follow us around, screaming "It\\'s time to cleeean!" Those who have carpeting have a superficial cover-up. The shed material collects within the matting of the carpet, and gradually provides a dirt layer to complement the carpet matting "forest." As individuals walk over carpeting, each footstep temporarily crushes the matting and forces localized air currents that liberate some of the accumulated dust for us to inhale, and depending on size (as shown below) may remain available for inhalation for hours. We breathe in the particulates we produce and have come full circle!

The idea is not to scratch . . . so try to teach that to a dog, cat, or other animal. But really, the cure is a regular cleaning regimen. It does not need to be extreme, but it needs to be regular and address the areas that are the most prolific sites of collection. Those areas exist underneath every piece of furniture, especially those that get moved the least, and even more especially those whose function causes them to have a recurring forced flow of air around them, such as a refrigerator due to its cooling coil operation, or baseboard radiators. I have many times come to visit and found copious amounts of dust under various pieces of furniture to such a degree, that I am left wondering how many years (decades?) it had been since some of those areas saw a vacuum cleaner hose. I have seen some refrigerator bottoms that appeared to be repositories of a dead cat. Being organic, this is part of the food base for small bugs, such as dust mites.

Dust-mite Debris and . . . Dust

Dust-mites are aptly named because they are mites that live on and in dirt, because it\\'s organic (as from the paragraphs above). They eat it and produce microscopic droppings that are a potent allergen. We humans are not keen on eating bug droppings, but we do it, a lot, and ignorantly, because we do not know where the dirt is, and what lurks on and within it. The dirt gets into our sinuses and lungs by a process akin to that from a leaf blower and vacuum cleaner oprating simultaneously. Previously described herein, at the risk of being redundant, allowing dirt to collect, and then stepping on it, causes it to go airborne. Some have stated that "we are what we eat," but I add that "we eat what we do not pay attention to."

It may be a no-brainer, but more dirt = more problems. Dust mites are opportunistic. Present everywhere, their available concentration cycles with the concentration of organic debris, which can be vegetative remains, degenerative remains, or carnivorous remains, as described above.

Along with dust, viable (with life) or not, comes a needed cleaning regimen. A vacuum cleaner is a wonderful thing. It collects dust for easy disposal. However, most vacuum cleaners have a collection efficiency limit of about 5 to 10 microns (millionths of a meter), which is about the same efficiency of our noses. Thus they trap the visible and leave most of the invisible go though the filter and become evenly distributed. I have never seen a pollen or mold spore look at me while I was looking at it, because most are too small for the naked eye, which can only discern object larger than about 10 microns. Many central air systems have a filter that is even worse, whose trapping ability may begin around 100 microns (0.1 mm), primarily designed for machine protection, most likely during initial construction, and then replaced with identical ones by the homeowner. High Efficiency Particulate Arrestance (HEPA)  filter equipped vacuum cleaners presently may cost as little as $100, while improved filtration for a central air machine may cost $4. But even with filters, they need to be cleaned or replaced regularly, in order for them to function as intended. With central air systems, a more pressing problem arises, because a poor filter allows easy accumulation of dirt within the air mover blades, the cooling coils, and the subsequent air ducts. When this dirt becomes sufficient, it becomes a haven for the same microbiota previously discussed, and propagation of it through the entire home each time the machine operates. Considering that the air mover causes air turbulence (great for heat transfer), should alert those affected that if they see particulate emissions from the air duct openings (made airborne by the turbulence), there is an immediate and dire need for cleaning the internals, which cleaning might not have been needed, had a better filter been used and regularly replaced.

Mold

Molds are necessary agents of recycling, and exist everywhere. They slowly devour most surfaces they come in contact with, reducing them to their basic chemical constituents. If the surface is inert, as in metal, then they may simply feed off the dirt on its surface, even if vertical. Particularly attractive to mold are surfaces containing cellulose. Cellulose is the main component of wood and its derivatives, such as paper. Cellulose is also a structural rearrangement of simple sugars that gives the assembly great structural strength, and great nutritional value when decomposing due to excessive water content, rendering it easily digestible by mold.

Molds thrive particularly well on moist surfaces. Modern dwellings are outfitted with a plumbing infrastructure that penetrates many structural walls. Any leak (however small) provides the proper environment for mold to colonize. Inattention to the leak(s) for greater than 24 to 48 hours, promotes conditions appropriate for rapid growth (amplification), changing a microscopic presence into macroscopic (visible) mold growth (colonies). Allowing ambient moisture content to rise above about 65% will provide similar favorable conditions for growth. Continued favorable conditions can allow sequentially more aggressive species (whose frequency of occurrence indoors is generally very low) to manifest themselves, possibly feeding off the dead mold colonies they replace. While many species are allergenic, some species are toxigenic, mutagenic, and carcinogenic. When molds colonize a favorable surface they produce a mycelia that penetrates the surface, in many respects similar to a plant\\'s root system. They also produce outcroppings (similar to plant\\'s trunks and branches) that produce spores. When agitated physically or chemically stressed, these spores easily become airborne. You should easily begin to see that simple surface treatment of mold infestation on a porous surface is a cheap and incomplete solution, when the causative factor is not addressed.

In a properly controlled environment, airborne mold spores, available continuously, settle out on clean surfaces and begin to form a microscopic layer of biota. Although inert, because the humidity does not promote growth, they are nonetheless organic, and can form a food base for bugs small enough to benefit from it.

Common Molds

Molds are cosmopolitan, you can find them in your auto, on the bus, at the market, at the library, even at the bank. That aside, they are efficient, ubiquitous, and necessary agents of recycling. That being said, according to some, they lurk around every corner waiting for the unaware and sluggard to make their move, and can fly with the wind to attack. They raise a stink when feasting (and what they feast on, they devour), and release many offspring when feasting. They create effective poisons against their neighbors (Mycotoxins), because they are territorial, and can baffle the best educated. Yet they can be kept in check, and forced to do our bidding (even for the benefit of humanity, would you believe), if we only pay attention. To the right is a listing of Normally Expected Molds, as per the US EPA Environmental Relative Moldiness Index (ERMI). Being that most of the colony fragments, as well as all spores, are microscopic, they can remain suspended in air for hours, rendering them readily available for inhalation, and that we do, with every breath we take. They can become airborne by spore ejection from a growing structure under stress, by a gentle air stream, or by physical agitation such as by human or animal activity.

Food for the asking . . .

If the surface the spores land on is inert, as in metal, glass, or concrete, they have no nutritional value to survive on, but they may simply feed (if only briefly) off the minuscule dirt on its surface. Concrete is peculiar in that it is porous, but due to its PH, repels mold growth. In fact, there is a paint which is cement-based, Caliwel by Alistagen, that is guaranteed to repel mold growth for several years. Particularly attractive to mold are surfaces containing cellulose. Cellulose is the main component of wood and its derivatives, such as paper. Having that in mind, it should easily follow that water or high moisture and paper should not mix. That is, unless you want to invite mold to rapidly proliferate.

The water

Molds thrive particularly well on moist surfaces because they need the water to aid their metabolic digestive processes. Most molds thrive particularly well in Relative Humidity (RH) of greater than about 65%. (An inexpensive RH meter can be had for a few shillings, and while not a lab instrument, will be accurate enough to tell you which direction to go on (wintertime RH should typically be higher than 35% and summertime RH at or below 60% for human comfort and to deter mold growth)). That water can come from water intrusion due to shoddy construction, water intrusion due to heavy rains raising the water table and causing indoor flooding, from a leak, and from dog days of summer, to name a few. Inattention to leaks or flooding from whatever source for greater than 24-48 hours, or high RH conditions for a bit longer, is an immediate invitation to highly accelerated mold growth. We may not give it much thought, and that\\'s where we fail, and then end up with expensive repair bills. While dealing with water as from flooding, different categories of severity have been set depending on whether the flooding water is clean, gray, or dirty. Water as from a rising water table, or from a plumbing leak is considered clean. However, the moment that clean water comes in contact with the layer of dirt found in most domestic environments, it is then deemed gray and of higher severity. So do we sterilize our living space in fear of flooding? A better course of action would be to take measures to ensure flooding does not occur.

Microbial Volatile Organic Compounds (mVOCs)

Organic life forms produce gas (in microscopic life forms, this may simply be an aromatization of emitted chemicals). They do so during digestion, and for those trapped into the mindset that gas (as in flatulence) is bad, you may be in for a rude awakening if you get sick, because unless you produce gas, you\\'re not leaving the hospital. Bacteria, and mold are also gas producers. Some aromatics are produced as a byproduct of normal digestion, while some are produced as an offensive or protective mechanism if the colony chemically senses some intruder that may reduce its food base. This latter category (Mycotoxins) can be hazard to humans, when in sufficient quantity (that quantity, from a micoscopic source, implies a severely moldy environment). The variety of all aromatics may resemble a musty smell, or one of rotten eggs, or one of many other varieties. When one enters a home, or goes from one portion to another (as from the upstairs to the basement, or from living spaces to a garage), there should not be any identifiable or offensive aromatics. Although some of these secondary VOCs are toxigenic to humans, not all are bad. One secondary byproduct is Penicillin, which most of us are familiar with.

Cycles abundant

When mold are given an opportunity, they feast. While conditions remain favorable, the mold grows only limited by the extent of the food base. If the food base runs out, or RH begins dropping, or temperature change drastically, the mold may shrivel up and die. In doing so, millions of spores may be produced, which easily go airborne. When conditions become favorable again, some of the established colonies that are still viable may continue to grow. Some of the colonies that had dried up now serve as a secondary food source for other mold types. Since molds have very restrictive taste buds, some mold are expected to always be found (as from a first event). Others are indicators of water damage (as well as indicators of multiple life/growth/death cycles).

Sneaky Mold

By Randall S. Fike, Ph.D.
Chief Technical Officer
Prism Analytical Technologies, Inc.

Every investigator is aware of the less subtle hiding places for mold, like inside air conditioning units, around the standing water in the crawl space, behind the sagging drywall in the dining room, and in the mushroom garden in the basement. But, occasionally, Prism will report a Home Air Check Professional TMVOC result indicating the presence of actively growing mold and the investigator will have great difficulty locating it. This article is a short summary of some of the sneaky hiding places where mold has been found. It also addresses the situation where a mold odor exists but no mold is present. Some remediation and preventive measures are also suggested.

1. Refrigerator/Freezers - In refrigerator/freezers, a significant thermal gradient exists between the freezer compartment and the exterior of the unit. Where the unit is not well sealed, condensation will form on the insulation. Eventually spores will get in and mold will proliferate. This is especially true in the freezer door. Fortunately, this is the easiest location in the freezer insulation to check. Also, in frost-free freezers, there is a drain line and a drain pan under the unit. Since there is very significant air movement under the unit and the pan is near the floor where spores and dust are easily kicked up by foot traffic, the condensation pan can quickly spawn mold growth.
   Replacing the door insulation, cleaning or replacing the drain line, and cleaning the evaporation pan are easy fixes; however, if the mold growth is between the compartment and the outer skin, replacement of the unit may be the only option.
2. Empty Beverage Cans - Since nearly everyone is into recycling, bins for empty cans are commonplace. Unrinsed food and beverage cans (especially beer cans) quickly develop mold. Rinsing the cans or returning them more frequently is recommended.
3. Trash cans - From wastebaskets to trash cans, good housekeeping is cheap remediation. Everyone is aware of the kitchen wastebasket but frequently a food item discarded in the den (or, more often, a teenager\\'s bedroom) where the wastebasket may not be emptied for weeks can be a bigger problem. Where severe mold allergies are a problem, placing all items that could spawn mold in a separate container in the freezer until garbage day can be a good suggestion.
4. Potted Plants - This one is rather obvious but it does need to be mentioned. Potted plants with wood chips look appealing but are especially inviting. Replacement with artificial plants is usually the best solution but not using wood chips and watering less frequently can lessen the mold growth. Watering with bleach is not a good idea.
5. Sump Pumps - In the summer, when pump cycling may greatly diminish or even stop, mold can begin to grow in the sump hole. To prevent regrowth after cleanup, pour about a quarter cup (less if the sump hole is small) of hydrogen peroxide in the standing water and stir it around, splashing it up a little on the sides and pipes to thoroughly wet the water line. This should be done every few weeks and an ample supply can be purchased at your local convenience store for about a buck or two.
6. Stand Pipes and Traps - While bacteria-saturated biomass is typically more of a problem than mold, the odor from these hiding places can be offensive. Smells like diaper pail, urine, mold, and rotten meat are all common. Remember, sewers are like life, what you get out of them depends upon what you put into them. The cleanup is very easy though. Simply pour about a quarter cup of hydrogen peroxide in the sink and around the top of the drain (or into the stand pipe). Refrain from using the sink or stand pipe for at least half an hour. Within 24 hours the problem should be gone, however, with heavy buildup, several treatments may be necessary. A monthly treatment thereafter using a tablespoon of hydrogen peroxide should prevent recurrence. While I have never seen any damage to PVC or cast iron pipes or to brass, plastic, and chrome drain rings, caution should be exercised when using this treatment.
7. Books - Newer books with acid-treated paper don\\'t seem to have a problem with mold, but older books, usually pre-1940, can have a problem. The only remediation of which I am aware is to wand the book, page by page, with UV light. Although I have never personally used this treatment and I\\'m not sure about how effective it is, it sounds like a laborious chore, especially if you\\'re doing a full set of encyclopedias or a Tolstoy novel.
8. Mold Outside the Walls - Occasionally, Home Air Check Professional will detect hidden mold in a basement or crawl space where there truly is no mold present. Since this can easily turn into a "gotcha," the first place to check is outside, around the building. Mold will proliferate if wood chips or plant debris are present, especially if the ground is damp or poorly drained or if the wood chips/debris are up against the foundation. The MVOCs from this mold can penetrate the basement wall (especially a block wall) and enter the basement. Because Home Air Check Professional can find mold hidden behind walls, the mold outside will be detected.

These are not the only places that molds hide; they are just some of the less obvious ones. If you know of any other tricky hiding places or you know of any quick and easy remediation or preventative ideas for these hiding places, let us know and we\\'ll pass the word on to our readers.

Article reprinted with permission from Prism Analytical
Technologies, Inc. / Home Air Check Professional
2625 Denison Drive
Mt. Pleasant, MI 48858

For questions pertaining to the indented article content above,
please e-mail support at homeaircheckprofessional dot com

Toxic ("Black?") Mold

So, you\\'ve had a customary house inspection and a mold-like "substance" was pointed out. A lab report returns the verdict of Stachybotris. The structure needs to be demolished, and you\\'re going to die . . . but most likely Not from mold, Or from Stachybotris. There is no single genus that can lay claim to being black, or toxic. All molds are toxic, when in sufficient quantities. Several mold species may appear black. Depending on the outdoor environmental conditions, a residence may be predisposed to having a certain skewed distribution of normal and expected mold types. One type spikes outdoors for several hours after a heavy rain. Other types requires several wet and dry cycles to become manifest. Suffice it to say that describing mold is like describing all the animals in a free ecosystem that shifts with the weather.  To the right is a listing of Abnormal Expected Molds, as per the US EPA Environmental Relative Moldiness Index (ERMI). Many of these are "water damage indicators," as labeled, and when found will usually be in a much greater concentration that the "Normal" molds indicated above. So while several genera are seen in both (some similar), there are more of them in the latter grouping, and the species distribution are also more extensive, which is when health effects can become an issue.

Testing, testing, testing . . .

So how many and how much mold is/are there? So how much can you afford, or are you willing to spend to find out? I have the habit, to the chagrin of analytical labs, of talking myself and my clients out of testing.

1. Testing can be done by capturing mold onto petri dishes with nutrient agar, which is then incubated for about a week, and the growth analyzed. Since most molds are nutrient-selective, there are a variety of different agars to favor isolation and identification of types whose growth may be otherwise overwhelmed by other types. This may mean that to get a real perspective, several or many samples need to be taken, which spells $.
2. Testing can be done by capturing mold onto sticky slides (air grab sample with a spore trap) for direct microscopic observation. Since this is not growth-based, and some types are morphologically similar when airborne, the analytical report may not be helpful, other than for general quantification. Since airborne spore or colony fragment content is location-specific, several or many samples should be taken to eke out relativistic relationships between locations, which spells $.
3. Testing can be done indirectly by sampling the settled dust or VOC content, which involves a variety of equipment and spells $.

When the individual is cost-conscious (and who isn\\'t) testing may be educational but unwarranted. When testing is done to "prove" proper remediation, it needs strict controls to ensure the sampling is of the air space and structures involved, and not associated with, or strongly biased by, exterior open environments. So if a space has been rendered "sterile" by a gung-ho remediation crew, the moment a door is opened for entry or exit, the environmental mold presence is re-established. If that exterior air space contains any trace of molds that are associated with water damage, then sampling of the "properly remediated" space will not indicate it to be so.

What it boils down to is that if RH is controlled, and the structure is relatively water-proof from exterior rain, and there are no interior leaks, there will not be a mold problem. If the airspace has been closed up for some time, as in seasonal homes, then initial entry will display a certain aromatic content that is characteristic of out-gassing / off-gassing of all structures specific to that space. If the structure has been properly controlled for humidity concerns, then introduction of fresh air will remedy this quickly.

Solutions

Flood Control

Flooding requires immediate attention, lest the structure fall down and go boom, and mold issues be of no consequence. Basements and crawlspaces are or particular interest. Contemporary high-density construction requires dewatering as the flooding is happening. This may constitute a sump pump, and / or effective moisture barrier. The detail of the interiors may also dictate if they can withstand soaking without destructive demolition to restore a dry environment.

Leaks require persistent vigilance. Finding the bottom of the kitchen sink cabinet collapsed is too late for simple cleaning. Having the bottom of the kitchen sink cabinet full of many liquids of questionable character is further conducive to staying out of there. Relocate those fluids elsewhere, and keep the bottom of the cabinet clean and observable. 

Air conditioning units in the attic is one of the dumbest ideas by man. The condensate drains from central Heating Ventilation and Air Conditioning (HVAC) cooling coils are subject to recurring flow of pure water out of the drain tube. The recurring flow is conducive to welcoming algae growth, because there are no growth inhibitors, like Chlorine. Algae growth will eventually choke the exit hole altogether and the condensate will leak onto the backup exterior drain pan. This too will eventually fail, causing eventual dripping onto and through the ceiling structure. I have been a first-hand witness to this effect.

HVACs in the attic are definitely, a very, very dumb idea. The air duct manifolds, where all the tubes interconnect, are metallic. When exposed to moist attic air, they become magnets for condensation, due to the cold air within the ducts. It is common for installers to envelop the manifolds in insulation to prevent condensation. It is additionally common for installers to use duct tape. Duct tape used for ducts, get the association?

Duct tape in a sequentially hot and cold attic air space is the second dumbest idea by man. Duct tape under those conditions fails. A colleague and I inspected a manifold in an attic that was dripping from an icy udder that had been created at the bottom of the insulation surrounding the manifold. When the duct tape failed and the moist attic air condensed on the manifold, it dripped onto the bottom of the insulation, forming a watery udder. As winter set in, the watery udder froze. When the weather warmed up, and the ice began to melt, it began dripping onto and through the ceiling structure. When the weather was milder, the colleague and I separated each manifold from the HVAC assembly and brought them to the garage staircase that led out of the attic. Upon tilting one manifold for egress down the ladder, several gallons of water gushed out the insulation. The other manifold displayed similar water content.

HVACs are not designed for installation in seldom accessed (and uncontrolled) air spaces.

Moist spaces in contact with structural lumber should NOT be vented to outdoors. I visited a crawlspace where the ceiling fiberglass insulation was glistening. It was so saturated as to be a mini rain forest. Throwing a dehumidifier therein will be of no use if the vents are open, as that is equivalent to trying to dry the planet. No human can claim that success. The same dehumidifier not set up for unattended operation is a similarly wasted effort, as once the tank fills, the unit shuts off until the tank is emptied. Uncontrolled crawlspaces are the reason for many homes failing structurally because the continued high RH will cause the floor lumber to rot. A properly applied moisture barrier, and a dehumidifier are a necessity, and very cheap insurance to preclude structural failure.

For seasonal homes, an unattended dehumidifier is essential. All closet doors should remain open to prevent cold exterior walls dropping below the dew point and causing condensation on the walls, and subsequent visible mold growth on the wall, albeit minimal. When molds colonize a favorable surface they produce a mycelia that penetrates the surface, in some respects similar to a plant\\'s root system. They also produce outcroppings (similar to plant\\'s trunks and branches) that produce spores. When the surface is painted, the mold may not be able to penetrate the surface readily, and what growth there is, may be simply cleaned off with a slightly damp towel. For unpainted gypsum wallboard, simple surface treatment of mold growth is no longer possible, as the wallboard will need to be cut out and discarded.

While not a flood, high RH produces the same effects as far as mold growth is concerned. So RH control should take equal importance as flood control or prevention.

Another idiotic application is a structure with a central HVAC unit in the basement, without any air supplies or returns in the basement. Hello! It seems the lights are on, but nobody\\'s home! I visited a newly built structure, only three months out of the builder\\'s hands, with heavy condensation on metallic piping in the basement, dense mold growth on basement ceiling beams, and an HVAC unit in the same basement without air access to the same basement. It would only seem logical, since the HVAC unit serves to dehumidify, that air access should be provided for the basement, as that is the area most likely to have elevated moisture content, due to the floor and wall surfaces in contact with the soil being at typically 55 degrees.

Food Control

If you can\\'t stop the water, take out the food. From easiest to least digestible order, Paper is the easiest to digest because it is thin and water can soak it with minimal effort. Then gypsum wallboard, cardboard, particleboard, plywood, and structural lumber. Mold growing on lumber can simply be scraped off and vacuumed with a High Efficiency Particulate Arrestance (HEPA) vacuum unit. There should be no newspapers in crawlspaces . . . ever!

A note about HVAC Filters. I encountered a client who had developed a persistent cough that would not go away. A visit to the attic-located HVAC identified a filter that was about three inches too short, and had lots of various color mold colonies. The filter was removed and replaced with an appropriate one, and the cough went away. When inquiring of the husband, he did not know the HVAC had a filter, and that it needed changing regularly. It had been in place, gathering dust and mold growth for about five years!

Food (mold food, that is) containers should be cleaned on a timely basis.

Bacteria

Bacteria, as most other particulates are ever-present. They, like mold, appreciate surfaces that have been made wet from leaks. Their food base requirements vary depending on the genus (similar with molds), and their propensity to cause trouble is mainly evidenced by leaks that go untended, maybe because "it\\'s the landlord\\'s problem," or because "it\\'s somebody else\\'s job." They may produce aromatics that are telltale, or not, depending on the many variables necessary to foster massive growth spurts. As with Molds, These growth spurts are known as "Amplification." Since the factors favoring amplification may not be constant, the cyclic chemical and physical stresses forced onto the opportunistic biota forces them to cast off portions of their structures, which then become airborne.

Identification of problem areas associated with viable particulates should be focused on the cause, not the effect. A leak or high moisture is the cause. Excessive mold, dust-mites, or bacteria is the effect. Removing the mold and leaving the cause will allow the mold to reoccur, similarly with bacteria.

Viruses

Some of the smallest particulates, viruses have a very limited lifetime outside a host. Their existence, however, can be lengthened somewhat if they find a receptive surface rich in nutrients. Surfaces rich in mold, dust-mites, and / or bacteria, may provide such a surface. The solution centers, as before, on a regular cleaning regimen.

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