Professional health practitioners say that mold is present indoors and outdoors during all seasons, in all climates, and in all parts of the world. They further explain that mold should not be allowed to grow and multiply indoors. This does not include the small amounts of mold often seen on shower curtains. Although this mold is unsightly, it is not the cause of mold-related nuisance odors and potential health complaints.
These complaints are associated with exposure to larger quantities of indoor mold growth. Of utmost concern with indoor mold growth is not the nuisance odors, but the potential damage to building materials, finishes and furnishings. In some cases where the mold growth is of a chronic nature, costly structural damage to wood can result (wood rot). Most importantly, though, is that indoor mold growth is 100 percent preventable. But if it does occur and is quickly addressed, nuisance odors and reversible health symptoms diminish and building material damage is generally limited and easily repairable.
The goal of this article is to provide you with scientifically valid information regarding what is known and what is unknown about mold. The hope is that you use the information to help make critical decisions regarding the prevention of mold growth, how to respond if mold growth is discovered, when and how you hire professional assistance, and what information you provide your employees and/or building occupants following the detection of mold growth. The information is presented in a question/answer format. Peer reviewed references are cited and listed at the end of the article.
What is mold and how
does it get indoors?
Molds are a form of fungi. It is the common term for multicellular fungi that grow as a mat of interwoven microscopic filaments (hyphae). Other types of fungi include yeasts, mushrooms, bracket fungi, rusts and smuts. Molds reproduce by making spores, which, if they land on a moist food source, can germinate and begin to grow new hyphae, which may produce a colony that eventually produces another generation of spores.[1] The collection of a mass of hyphae is termed mycelium. When we claim to see mold growth, we are actually viewing the mycelium.
In the outdoors, molds provide a necessary ecological process in the decomposing of organic matter, such as dead wood, plants and animals. Because of this vital function, molds are present in all areas of the planet Earth, including in soils, on plants, in water and on decaying or dead matter. Due to this ubiquitous nature of mold, it is also commonly found indoors. Mold gets indoors through natural ventilation (open windows and doors), and is often carried in by pets and on the shoes and clothing of people.
In the literature, mold is identified using two names. The first name identifies its genus, and the second identifies its species. Aspergillus, like some of the common molds, has 182 accepted species, and Penicillium has 225 accepted species.[2] A very simple way to remember what is meant by genus and species is to think of apples. We all know there are different kinds of apples. Think of the broad name of apple as the genus, and the particular type of apple as the species. It easy to understand that the Jonathan apple is different than the Macintosh apple, just as Aspergillus versicolor is different than Aspergillus flavus.
What makes mold grow
and how can I prevent its growth?
Reproducing molds have temperature, food and moisture requirements that are necessary for survival. The temperature and nutrient sources in our home and business environments are perfect to support mold growth. The third growth requirement is moisture. When organic materials become sufficiently wet, those surfaces become the new germination sites for mold spores that enter through open windows or are carried in on our feet and clothing. If we control the amount of moisture and keep indoor surfaces clean and dry, mold will not grow. If mold does not grow indoors and the only spore types present are from the outside, the indoor spore numbers and types generally remain less than those found outdoors.
Preventing mold growth means preventing the unintentional release of water. The indoor environment should be kept clean and dry. Examples of water or moisture intrusion events include roof leaks, leaking pipes, unventilated humid spaces such as crawlspaces, bathrooms, kitchens and laundry areas, surface condensation, and improperly sealed doors and windows. If you find any of these conditions, or other sources of water intrusion, the improper condition should be immediately corrected, and all excess water should be cleaned up. Materials that stay wet for more than 48 hours are likely to produce mold growth.
How do I know if mold
is growing indoors?
If mold is growing indoors, you may notice a musty or mildew-type odor. You may observe evidence of past or current water damage, and you may see the mold. Often, you may notice an unusual odor, but find no visual evidence to prove that mold is growing indoors. It is then that you must look past the easily viewable surfaces in the space and begin looking for hidden sources of mold growth. Some of these hidden sources include under carpets, behind kitchen, lounge or bathroom cabinets, behind furniture that is placed in front of walls, within wall cavities, humidifier water reservoirs, cooling coils and condensate drip pans, above ceiling tiles and within crawlspaces. Hint: If you are able to identify the source of the water and follow its path through the building, you can use that information to identify spaces were excess moisture may be present, thus potential mold growth.
If I see and/or smell
mold indoors, should I get it tested?
Whether or not you test for mold growth depends on your specific circumstances. If your only goal is to find the mold, determine the extent of damage, repair or correct the water source and cleanup the mold growth, then you do not need to test the mold. Cleanup activities are not dependent on the type of mold growing in your space.[3]
Testing for mold is expensive and the testing protocol and strategy should have a clear purpose that answers detailed questions. Some specific instances may exist where testing and sampling is warranted, such as where health concerns are an issue or when litigation is involved. Sampling may also be necessary when the source(s) of mold growth is unknown and testing may assist in the building evaluation.
If I determine that
mold should be tested, who should do the testing, how should the testing be
done, and how will the test results be interpreted?
The building evaluation and any subsequent sampling should
be conducted by a health professional that is competent in mold evaluation and
remediation. The American Industrial
Hygiene Association has a list of industrial hygiene consultants that provide
mold evaluation services at www.aiha.org. You may also find additional consultants in
the yellow pages under Industrial Hygiene
and/or Environmental Services. Before you hire any contractor or health
professional you should ask for and thoroughly check their references. You should also demand that they follow
established guidelines for all testing, laboratory analyses and remediation
activities they recommend.
Testing or sampling actions should follow the guidelines presented in the following documents:
Because
laboratories vary in experience and proficiency, a laboratory that holds a
current AIHA EMLAP accreditation should analyze samples. A listing of accredited labs can be found at
www.aiha.org.
As previously
presented, when sampling is conducted, the sampling strategy should be designed
such that the sampling results answer very specific questions. Unfortunately, there is no accepted national
standard for fungal assessment and acceptable exposure levels. Thus, the sample results have no exposure
standard for comparison. This
assessment limitation stresses the importance of a properly designed sampling
strategy. Prior to the actual
collection of samples, the strategy should address how all sample results will
be interpreted.[4] You, as a client, should request this level
of detail from all contractors or health professionals you hire to collect
samples. The references listed above
provide detailed guidelines (not standards) on how to develop an investigation
strategy, collect and perform sample analysis, how to interpret sample results,
and how to design and oversee the remediation of microbial contamination. The consultant you hire should be competent
in these aspects of mold assessment and remediation, and be able to clearly and
logically communicate their recommended sampling strategy.
Why are there no
standards for mold exposure?
Exposure standards are established to prevent or control the risk of harm to human health. In order to set such standards, the health effect must be thoroughly understood, as well as the exposure level that would lead to that health effect. In the case of molds, understood health effects include allergenic reactions and infections. Less understood associated health effects include irritation and toxicity. One complication is that different mold species may be more or less hazardous with respect to any or all of these health effect categories. A second complication is that specific human responses have not been identified following exposure to defined levels. Simply stated, the science cannot predict what specific health response will result from any given exposure level to mold. If the science cannot predict a health response, it is not able to establish exposure levels to reduce the risk of human’s experiencing that health response.
A third complication is that there is no universally accepted method to detect, enumerate and identify mold exposure. An exposure standard must be compared against a sample concentration that can be measured using a reproducible and scientifically valid method. Such a method does not currently exist.
Once mold is
discovered indoors, what is the next step?
Whether or not testing had been conducted, the surfaces contaminated with mold must be cleaned or the affected materials removed and discarded. The fist step is to identify and correct the cause of water intrusion. If this critical first step is not completed, mold growth will reoccur. The second step is to prepare a remediation plan. The plan should include the following information:
Should I be concerned
about the known or associated health effects from mold exposure?
Unfortunately, there is not an absolute yes or no answer to that question. The medical knowledge is well understood for some health effects and under contentious debate for other presumed, but not proven health effects. Please read on…
Allergic reactions
Of the 40 percent of the population that have high levels of genetically disposed allergic antibodies to inhalant allergens, about 5 percent are predicted to have some allergic airway symptoms from mold exposure throughout their lifetime.[5] Molds are common allergens, but they are not the most dominant allergen. More dominant allergens include plant pollens, dust mites and animal dander. Nearly all allergic reactions are limited to rhinitis or asthma, and sinusitis may occur as a secondary reaction.[6] Preventing or immediately mitigating indoor mold growth can reduce the risk of developing or exacerbating allergies.
Infections
Exposure to indoor molds commonly associated with moist environments is generally not a risk factor for fungal infections. Fungal infections with deep tissue invasion are primarily restricted to severely immunocompromised patients.[7] A limited number of fungi (Histoplasma, Cryptococcus) can infect normal subjects, but these molds do not generally grow indoors.
Irritation
Molds produce volatile organic compounds (VOC) through normal metabolic processes. The process can be equated to the sometimes pungent or unpleasant metabolic products that are generated through human food consumption. The microbial VOCs have distinctive odors and low odor thresholds. Some of these metabolic gases give the distinctive musty or moldy smells associated with the presence of growing mold. Some researches have postulated that these compounds may be responsible for some non-specific building related symptoms (i.e., poor indoor air quality). The science to date has not defined the role of fungal VOCs in clinically evident disease.[8]
Toxicity
Another metabolite produced by molds are mycotoxins. The antibiotic penicillin is one example of a fungal mycotoxin that has been used beneficially by humans. For those molds found indoors, the amount and type (if any) of mycotoxins produced is dependent on a complex and poorly understood interaction of factors. Some of those factors may include available nutrition sources, quantity of moisture, and maturity of the fungal colony.[9]
Mycotoxins are not volatile, thus an airborne exposure requires that the toxin adhere to an aerosol (particulate) that is airborne.[10] In order for a toxic response, the concentration and duration of exposure must be sufficient to deliver a toxic dose. Currently, a mycotoxin exposure concentration that constitutes a toxic dose is unknown.
Given the current state of knowledge, the American College of Occupational and Environmental Medicine states that, “Levels of exposure in the indoor environment, dose-response data in animals, and dose-rate considerations suggest that delivery by the inhalation route of a toxic dose of mycotoxins in the indoor environment is highly unlikely at best, even for the hypothetically most vulnerable subpopulation.”[11]
Am I required to inform my employees or building occupants if mold is found in my building? If yes, what should I tell them?
It can be argued that the presence of active mold growth constitutes a potential occupational exposure. Thus, under OSHA’s Hazard Communication Standard, you must inform your employees of its presence, its potential hazards and how they can protect themselves from exposure. If you require your employees to conduct remediation activities, you must certainly adhere to the provisions under the Hazard Communication Standard. For those individuals that are not conducting the cleanup, but are in the general area, you may consider following the suggestions the EPA has published in the document titled, Mold Remediation in Schools and Commercial Buildings, www.epa.gov/iaq/molds/index.html. It states that the status of the building assessment and remediation be openly communicated, including information on any known or suspected health risks. You may wish to communicate the information in this article as well.
[1] Levetin, Estelle. Fungi, in Bioaerosols, Ed. H. Burge, CRC Press, 1995.
[2] American Industrial Hygiene Association. The Facts About Mold, Fairfax, VA 2003.
[3] Shaughnessy, R. and P. R. Morey, Remediation of Microbial Contamination, in Bioaerosols: Assessment and Control. American Conference of Governmental Industrial Hygienists, 1999.
[4] Bioaerosols: Assessment and Control, Chapter 7: Data Interpretation. American Conference of Governmental Industrial Hygienists, 1999.
[5] American College of Occupational and Environmental Medicine, Adverse Human Health Effects Associated with Mold in the Indoor Environment, JOEM Vol. 45(5): May 2003, pp 470-478.
[6] Ibid.
[7] Ibid.
[8] Burge, H., Fungi, in Bioaerosols: Assessment and Control. American Conference of Governmental Industrial Hygienists, 1999.
[9] Burge, H. and H. M. Ammann, Fungal Toxins and β-(1 à 3)-D-Glucans, in Bioaerosols: Assessment and Control. American Conference of Governmental Industrial Hygienists, 1999.
[10] American College of Occupational and Environmental Medicine, Adverse Human Health Effects Associated with Mold in the Indoor Environment, JOEM Vol. 45(5): May 2003, pp 470-478.
[11] Ibid.