Breaking the Mold

A high school in Illinois is forced to close due to an infestation of mold. In 2001, a Texas court awarded Melinda Ballard $32 million dollars against Farmer's Insurance for mishandling a burst pipe claim. The house is covered with black rot mold (Stachybotrys) and must be destroyed. Lou Ferrigno (the mighty Hulk for heavens sake!) is pictured on a recent CNN television news program evacuating his home due to mold infestation and complaining bitterly over the lack of his insurers' responsiveness to the initial condition caused by the burst water pipe.

Environmental lawyers are holding weekend long seminars on mold litigation. Mold litigation and remediation is the new growth industry, prompting some attorneys to coin the phrase "Mold is Gold." Many states are developing regulations or have passed legislation applicable to fungal growth in indoor environments (New York, Texas, Massachusetts, California and others). On March 13, 2003, Representative John Conyers (D-Mich.) introduced the Toxic Mold Safety and Protection Act in late June (H.R. 1268). The bill has been referred to the House Subcommittee on the Environment and Hazardous Materials. What is going on here?!

Biological Overview
First of all mold, mildew, yeast, mushroom and rust are all names for fungi. Some terms, such as yeast, indicate a particular state of fungus and other terms do not have a clear technical distinction, as is the case between mold and mildew. In this article we will often refer to the various states of fungus, as it affects indoor air quality, as mold. Fungus belongs to the kingdom Mycota. A kingdom is a fundamental grouping of living organisms based on similarities in reproduction and other evolutionary factors. The other major kingdoms include plants, animals, protists and monera. For a long time fungi were considered plants without chlorophyll, but this is not accurate. Fungi have traits in common with plants and animals. Fungi are eukaryotes (possessing a distinct nucleus and nuclear membrane), which separates them from bacteria, as this is a trait common to higher life forms such as plants and animals. Fungi reproduce by spore production with basic cell wall structures, which is a strictly plant-like trait. On the other hand, fungi are heterotrophic (obtaining food from organic material only) and contain no chlorophyll, which are traits held in common with animals. In fact both animals and fungi utilize enzymes (catalase and lignase in the case of fungi) to degrade and absorb food materials, the difference being that animals perform this task internally whereas fungi decompose food stuffs externally and then absorb the nutrients.

Kingdom Mycota is composed of the following phyla:

  • Phylum Zygomycota: tube fungi, including some rusts, bread molds, water molds and others;
  • Phylum Ascomycota: sac fungi, including yeasts, powdery mildews, cup fungi, blue and green molds, some bread molds and others; and
  • Phylum Basidiomycota: club fungi, including most mushrooms, toadstools, bracket fungi, smuts and rusts.

Of these, the major indoor and outdoor contributors to spores are the Ascomycetes and Basidiomycetes. Some examples are: Cladosporium, Penicillium, Aspergillus, Stachybotrys, Candida, Acremonium, Histoplasma, Chrysosporium, Trichothecium, Alternaria, Nigrospora, etc.

The life cycle of fungus is alien to most of us. It is fairly complex and versatile. Fungi can reproduce sexually and asexually producing haploid (produced by mitosis, which is the indirect and more common method of nuclear division of cells) and diploid (produced by meiosis, which is the process of two consecutive nuclear divisions in the formation of spores in plants) spores. The fungus can enter a vegetative state where it primarily obtains and digests food but will often enter a reproductive state when food is depleted. This reproductive state produces spores. There are two basic types of spores, namely dry spores as in Aspergillus and slimy spores as in Stachybotrys. Although this is not an evolutionary distinction, it is an important distinction in regard to filter media performance. Some basic terms applied to fungus are as follows:

  • Hyphae: a filamentous cellular unit of a fungus;
  • Mycelium: a collection of hyphae; and
  • Yeast: a unicellular growth phase of a fungus.

Besides food, moisture, temperature, oxygen, pH and light can affect the state of fungus. The right combination of the above factors can cause the spore to change from its inactive to active form in the life cycle of the fungus. This process is known as spore germination. Some fungal spores must contact liquid to germinate. Other spores require in excess of 70 percent relative humidity for germination and yet other spores can germinate at extremely low relative humidity. Generally speaking, fungal growth occurs best in warm and wet environments. The most effective way to prevent growth is by keeping material dry. Viable spores can germinate and produce hyphae when appropriate environmental conditions exist. If these conditions are sustained a robust mycelium develops. Once the material is colonized in this way, the organism can usually endure severe environmental conditions and can still survive. The type of fungus present can be indicative of the extent of moisture damage. Primary fungal colonizers, such as Penicillium, require a low water activity constant (aW<0.8, aW is a normalized factor from 0-1, which is an indicator of the available moisture). Secondary colonizers, such as Cladosporium cladosporiorides, require an aW between 0.8-0.9. Tertiary colonizers, such as Stachybotrys, require an aW >0.9.

Fungus degrades cellulose and lignins in order to obtain its energy. Fungus plays an essential role in the carbon cycle by degrading grass, wood, paper and cardboard. To fungus, many housing materials look like food. Humans probably first noticed fungus on the forest floor in the form of mushroom. Since then we have learned to use fungus in baking, brewing, manufacturing pharmaceuticals and in other ways. Until recent times, toxic effects from fungus (mycotoxicosis) were primarily resultant from ingestion of poisonous mushrooms or by exposure to poison produced from mushroom extract (well-documented in history and literature).

Mycotoxins are produced from all fungi in order to ward off predation and competition. Mycotoxins can exist as endomycotoxins (not released from cell or cellular components) and as exotoxins, either volatile and released as a gas or non volatile and released as solid or liquid. Some mycotoxins are the most poisonous substances known. Additionally, fungal spores can act as opportunistic pathogens and actually infect a person with fungus. Although fungal infections are rare, they are very serious and often lethal. Some examples of such infections are Histoplasmosis (bird breeder's disease) and Aspergilliosis, which is one of the most frequently encountered fungal infections and often occurs in hospitals especially in burn wards. Airborne transmission of mold spores and mycotoxins is accomplished through the formation of bioaerosols. Bioaerosols are simply buoyant airborne compounds, solutions, mixtures or solids of biological origin with close to neutral buoyancy in air. Spores, mycotoxins and endotoxins can become aerosolized by air movement, mechanical agitation or through physiochemical processes.

Fungal Levels in Buildings
In recent times, the primary route of entry for fungal infections and mycotoxicosis has changed from ingestion to inhalation (Stachybotrys atra, also known as black rot fungus, is blamed for the recent deaths of infants in Cleveland). What has happened to cause this change? Although the exact cause may be difficult to pinpoint, two events were certainly contributing factors, these being the discovery of freon refrigerant by Thomas Midgley in the 1930s and the energy crisis of the 1970s. These two factors resulted in the tightening up of buildings using synthetic materials, which sealed the structure and reduced air movement resulting in higher available moisture contents in the building materials, a condition favorable for fungal growth. Installation of air conditioning systems without properly considering microorganismal ecology and maintenance of hygiene compounded the problem of fungal growth. When human factors are included, such as the fact that we spend more than 90 percent of our time indoor and the fact that many of us have compromised immune systems from diseases, medications and environmental insult, and add to this the emergence of new and pathogenic organisms, it becomes evident that our relationship with fungus is taking on a new urgency.

What is the extent of the problem and what can be done about it? In recent times, much work has been done in the characterization and quantification of fungi and mycotoxins. Some interesting recent studies are as follows:

  • Airborne levels of culturable molds were sampled in 167 randomly selected schoolrooms in Indiana. Culturable mold levels were low with Basidiomycetes, Penicillium, Cladosporium and yeasts were found to be the most prevalent. Indoor levels were significantly lower than outdoor levels. Higher indoor levels of culturable molds, compared to outdoor levels in the immediate vicinity, is usually a good indicator that there is a problem. Interestingly, significantly higher mold levels were observed in rooms were climate controlled as compared to rooms that did not have operating ventilation systems. Mold levels in particular rooms were found to be high.
  • The biodiversity and concentration of the airborne fungi were monitored over a six-month period in the special care unit of a German hospital. Sampling was performed in a hallway adjacent to a bone marrow transplantation unit. Ninety-eight fungal species were identified including Aspergillus fumigatus as well as 48 other species reported as potential pathogens. Neither the degree of fungal air contamination nor the species composition inside the unit differed from that in the corridor.
  • 12,026 indoor and outdoor samples were taken in 1,717 buildings between 1996 and 1998. In all cases culturable airborne fungal concentrations in indoor air were lower than outdoor air. The fungal levels were highest in fall and summer and lowest in winter and spring. Highest fungal levels were found in the southwest, southeast and the west. The most common species were Cladosporium, Penicillium, nonsporulating fungi, Aspergillus and Stachbotrys chartarum, although these accounted for only six percent of the total.
  • The capability of air filters to retain airborne outdoor microorganisms was examined in field experiments in two heating, ventilating and air conditioning (HVAC) systems. At the beginning of the 15-month investigation period, the first filter stages of both HVAC systems were equipped with new unused filters. The number of airborne bacteria and molds before and behind the filters were determined simultaenously in 14 day intervals. Under relatively dry (relative humidity 60 to 80 percent) and warm (> 12 degrees Celsius) outdoor air conditions, air filters led to a marked reduction of airborne microorganism concentration (bacteria by approximately 70 percent and molds by approximately 80 percent). However, during long periods of relative humidity (> 80 percent) a proliferation of bacteria and mold on air filters with subsequent release into the filtered air occurred. These microorganisms were mainly smaller than 1.1 micron, therefore being a part of the respirable fraction.

Impacts to Human Health
What does all this mean? It is clear that bioaerosols of pathogens including those created by fungi are difficult to avoid and can be very detrimental to human health. The order of precedence for infectious diseases is as follows, beginning with the most serious: virus, bacteria, protozoans, animals-fungi and plants.

Whereas the order of risk to human health from bioaerosols is in the following order of importance, beginning with the most serious: fungi, bacteria, plants and protozoans, animals and viruses.

This is not to say that there are not significant bioaerosol threats from other kingdoms. Legionella, which is known to form in cooling towers and hot water systems and industrial operations such as machining, creates significant anthropomorphic bioaerosol hazards. The extremely complex lifecycle of fungi makes it very difficult to determine whether a toxic condition exists. Many fungal species, including those known to be extremely toxic and pathogenic, seem to coexist peacefully with us. On the other hand, if conditions are right the same fungi can create bioaerosols that can kill us. A good rule of thumb to adhere to order to determine the existence of a potential health problem is fungal and mycotoxin counts inside and outside of the dwelling and the species composition of the air. If counts are higher inside than outside and/or if the species composition of the air is different inside than outside, then you probably have a problem.

It is clear that certain enclosed environments containing high concentration of people, and quite possibly some people with compromised immune response, must do a better job of providing reliable air quality. Two examples that come to mind are hospitals and airlines. In regard to hospitals, it was acceptable in the not too distant past to essentially take no measures in regard to keeping surfaces pathogen free. In present day hospitals, quite a few measures are taken to eliminate surface pathogens as sources of disease. These measures include sterilization, use of biocides, such as chlorhexadiene, and the use of disposable items. Based on the German hospital study as cited above, it appears that measures for providing -free hospital air and the hospital air itself are from a 100 years ago. Approximately 50 percent of hospital deaths are caused by infections acquired during one's hospital stay. Aspergilliosis is a major concern for burn victims. The infection is transmitted through the air. All cases of tuberculosis transmission are traceable to airborne aerosols resulting from human activities such as talking. Hospitals must take much greater measures to ensure that the building is not a source of fungal spores and pathogens. Filtration of introduced spores and pathogens must also be improved. The same general principles apply to airlines, especially in regard to utilization of filtration systems, which are easily cleaned and do not support growth of pathogens.

Regarding prevention and remediation, it is disturbing that air filters and air filtration devices appear to provide a comfortable habitat for fungi especially in high humidity conditions. Recirculation of air without immobilization of spores and toxins probably does more harm than good. In general dust suppression, control of moisture, good ventilation and speed drying of clean surfaces are recommended.

Remediation of mold is becoming a hot area. Remediation of mold looks like it will become the next asbestos. Currently there are a variety of recommended procedures for remediation, including use of oxidizers, fungicides and bactericides and shielding compounds, which seal the antimicrobial agents within the treated surface. Much work remains to be done regarding determination of an effective means for eliminating mold. It is uncertain whether cleaning procedures improve or exacerbate the problem. In the meantime the best course of action is to eliminate any conditions favorable for the growth of the most toxic fungi. Fortunately most of these are secondary or tertiary colonizers and require a fair amount of moisture for spore initiation.


  • Shelton, B.G et al, "Profiles of Airborne Fungi in Buildings and Outdoor Environments in United States," Journal of Applied and Environmental Microbiology, Vol.68, pp. 1743-1753.
  • Chao, H.J.; Schwartz,J. et al., "Population and Determinants of Airborne Fungi in Large Office Buildings," Journal of Environmental Health Perspectives, Vol. 110, pp. 777-782.
  • Anon, "Mold and Indoor Health: Improving Health by Controlling Molds," Soplan Review, Vol.98, pp. 3-5.
  • Rainer, J.; Peitner, U. et al., "Biodiversity and Concentration of Airborne Fungi in a Hospital Environment," Journal of Mycophathologia, Vol.149, pp. 87-97.
  • King, N.; Augur, P., "Indoor Air Quality, Fungi and Health. How Do We Stand?," Canada Family Physician, Vol.48, pp. 298-302.
  • Langvad, Finn., "Moulds and Indoor Air Quality -- a Man Made Problem," Naturen, Vol. 126, No.3.

Additional References

1. Populations and determinants of airborne fungi in large office buildings.

Chao, H. J.; Schwartz, J.; Milton, D. K.; Burge, H. A. Environmental Health Perspectives, Vol. 110, No. 8, 2002. PP. 777-782. 45 notes and reference(s). ISSN- 0091-6765

Bioaerosol concentrations in office environments and their roles in causing building-related symptoms have drawn much attention in recent years. Most bioaerosol studies have been cross-sectional. We conducted a longitudinal study to examine the characteristics of airborne fungal populations and correlations with other environmental parameters in office environments. We investigated four office buildings in Boston during one year beginning May 1997, recruiting 21 offices with open workstations. We conducted intensive bioaerosol sampling every six weeks resulting in 10 sets of measurement events at each workstation, and recorded relative humidity, temperature, and CO2 concentrations continuously. We used principal component analysis (PCA) to identify groups of culturable fungal taxa that covaried in air. Four major groupings (PCA factors) were derived where the fungal taxa in the same groupings shared similar ecological requirements. Total airborne fungal concentrations varied significantly by season (highest in summer, lowest in winter) and were positively correlated with relative humidity and negatively related to CO2 concentrations. The first and second PCA factors had similar correlations with environmental variables compared with total fungi. The results of this study provide essential information on the variability within airborne fungal populations in office environments over time. These data also provide background against which cross-sectional data can be compared to facilitate interpretation. More studies are needed to correlate airborne fungi and occupants' health, controlling for seasonal effects and other important environmental factors.CAB 02-09 20023122059 NDN- 191-0672-2577-9

Author Affiliation: Department of Environmental Health, Harvard School of Public Health, Building 1 Rm. G28, 665 Huntington Ave., Boston, MA 02115
Publisher: Public Health Service, U.S. Department of Health and Human Services, Research Triangle Park

2. Profiles of airborne fungi in buildings and outdoor environments in the United States.

Shelton, B. G.; Kirkland, K. H.; Flanders, W. D.; Morris, G. K. Applied and Environmental Microbiology, Vol. 68, No. 4,2002. PP. 1743-1753. 27 reference(s). ISSN- 0099-2240

We examined 12 026 fungal air samples (9619 indoor samples and 2407 outdoor samples) from 1717 buildings located across the United States; these samples were collected during indoor air quality investigations performed between 1996 and 1998. For all buildings, both indoor and outdoor air samples were collected with an Andersen N6 sampler. The culturable airborne fungal concentrations in indoor air were lower than those in outdoor air. The fungal levels were highest in the fall and summer and lowest in the winter and spring. Geographically, the highest fungal levels were found in the Southwest, Far West, and Southeast. The most common culturable airborne fungi, both indoors and outdoors and in all seasons and regions, were Cladosporium, Penicillium, nonsporulating fungi and Aspergillus. Stachybotrys chartarum was identified in the indoor air in 6 percent of the buildings studied and in the outdoor air of 1 percent of the buildings studied. This study provides industrial hygienists, allergists and other public health practitioners with comparative information on common culturable airborne fungi in the United States. This is the largest study of airborne indoor and outdoor fungal species and concentrations conducted with a standardized protocol to date. CAB 02-06 20023058665 NDN- 191-0666-4950-0

Author Affiliation: PathCon Laboratories, 270 Scientific Drive, Suite 3, Norcross, GA 30092

3. Biodiversity and concentration of airborne fungi in a hospital environment.

Rainer, J.; Peintner, U.; Poder, R. Mycopathologia, Vol. 149, No. 2, 2001. PP. 87-97. 53 reference(s). ISSN- 0301-486X

The biodiversity and concentration of airborne fungi were monitored over a period of six months in a special-care unit of a hospital in Austria √Ědate not given¬®. Air sampling was performed in a corridor that was also accessible to visitors and in an adjacent bone-marrow transplantation (BMT) unit using an air sampler and 2 isolation media. Altogether, 98 fungal species were identified, among them Aspergillus fumigatus and A. terreus, as well as 48 other species reported as potential pathogens. The mean contamination values of the corridor air ranged from 124 to 485 colony forming units (cfu)/m3. Neither the degree of fungal air contamination nor the species composition inside the special care unit differed from those found in the corridor. By means of data obtained with a light-activated sensor, a possible influence of human activities on diurnal changes of fungal propagule concentration was shown.CAB 01-04 20013036969 NDN- 191-0646-1058-5

Author Affiliation: Institute of Microbiology (N.F.), Leopold-Franzens-University Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria.

4.Moulds and indoor air quality -- a man-made problem; Muggsopp i inneklima - et menneskeskapt problem. Language -- Norwegian

Langvad, Finn. Naturen., Vol. 126, No. 3, 2002-07-01, 7 figs. ISSN- 0028-0887

In the 1970s and 1980s, many house owners in Norway, in order to save energy, insulated their houses by injecting torn-up mineral wool into the entire cavity of the wall. This made the house warmer to live in, but it also created serious condensation problems followed by rot and mould. The extensive use of gypsum boards is also alarming. If gypsum becomes really wet because of a water leakage, it becomes a ticking bomb from the micro-biologic point of view as it provides growth conditions for some of the most dangerous indoor mould fungi known, the Stachybotrys chart arum. The article discusses the danger of this fungus and surveys some of the ways that mould affect human health. There is at present no definition of a normal number of fungus spores per unit volume of air. But the following principles can be taken as guidelines: (1) The concentration of spores indoor must be lower than outdoors. Otherwise extra spores have been generated in the house. (2) The species composition of the air must be approximately the same indoors and outdoors. EDB 02-16 20269934 NDN- 108-0706-0591-2

Contract/Grant Number: NTUNA9 ; TRN: NO0205221

5. Mould and indoor health: improving health by controlling moulds.

Anon. Solplan Review, No. 98, 2001-05. PP. 3-5. ISSN- 0828-6574

High concentrations of moulds in building environments, and the serious risks that moulds pose for those living or working in the building are discussed, with useful suggestions as to how to deal with mould contamination within a building. Prompt clean-up and repair of contaminated material is the primary response to mould contamination, although the main emphasis should be on preventing contamination through proper building and mechanical system maintenance and prompt repair of water damage. Specific methods of assessing and remediating fungal contamination are discussed, including the use of various detergents, bleaches for wood and tri-sodium phosphate and water for concrete. Dust suppression, the control of moisture sources and the need for good ventilation to speed drying of cleaned surfaces are stressed. Guidelines for evaluating likely health effects of fungal contamination and remediation, developed by the City of New York, are reviewed as an example of potential regulation. EDB 01-14 01:061667 20173431 NDN- 108-0693-9814-1

6.Indoor air quality, fungi, and health. How do we stand?

King, N.; Auger, P.Can Fam Physician, Vol. 48, 2002 Feb, PP. 298-302. 25 reference(s). ISSN- 0008-350X

This article originally appeared in the 06/01/2003 issue of Environmental Protection.

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