Indoor Molds

Characteristics

Fate and Transport in the Environment

Methods for Monitoring in the Environment

Exposure Pathways

Methods for Measuring Human Exposure

Strategies for Preventing or Controlling Mold Exposure


Harmful Effects

Absorption, distribution, metabolism, and sites of toxicity

Biomarkers

Molecular mechanism of action

Risk Assessment

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Harmful effects of molds

The type and severity of health effects that result from molds exposure is widely variable among different locations, from person to person and over time.

Although difficult to predict, exposure to molds growing indoors is most often associated with the following allergy symptoms:

  • Nasal and sinus congestion
  • Cough/sore throat
  • Chest tightness
  • Dyspnea (breathing difficulty)
  • Asthma (or exacerbation of it)
  • Epistaxis (nosebleed)
  • Upper respiratory tract infections
  • Headache
  • Skin and eye irritation

Indoor molds exposure leads mostly to upper respiratory tract symptoms

Long-term exposure to indoor molds is certainly unhealthy to anyone, but some groups will develop more severe symptoms sooner than others, including:

  • Infants and children
  • Elderly people
  • Individuals with respiratory conditions, allergies and/or asthma
  • Immunocompromised patients

Some indoor molds are capable of producing extremely potent toxins (mycotoxins) that are lipid-soluble and readily absorbed by the intestinal lining, airways, and skin. These agents, usually contained in the fungal spores, have toxic effects ranging from short-term irritation to immunosuppression and cancer. (Photo: Mold growing behind wallpaper)

More severe symptoms that could result from continuous human exposure to indoor mycotoxigenic molds include:

  • Cancer (aflatoxin best characterized as potential human carcinogen)
  • Hypersensitivity pneumonitis/pulmonary fibrosis
  • Pulmonary injury/hemosiderosis (bleeding)
  • Neurotoxicity
  • Hematologic and immunologic disorders
  • Hepatic, endocrine and/or renal toxicities
  • Pregnancy, gastrointestinal and/or cardiac conditions

It is important to notice that the clinical relevance of mycotoxins under realistic airborne exposure levels is not fully established. Further, some or much of the supporting evidence for these other health effects is based on case studies rather than controlled studies, studies that have not yet been reproduced or involve symptoms that are subjective.
(Photo: Black mold spores micrography)

Among the indoor mycotoxin-producing species of molds are Fusarium, Trichoderma, and one that, although less commonly isolated, became notorious during the past decade, Stachybotrys atra (aka S. chartarum, black mold). Between 1993 and 1994, there was an unusual outbreak of pulmonary hemorrhage in infants in Cleveland, Ohio, where one kid died. Researchers found that the kids’ homes had previously sustained water damage that resulted in molds contamination, and the quantity of molds, including S. chartarum, was higher in the homes of infants with pulmonary hemorrhage than in those of controls. (Photo: Stachybotrys growing on Potato Dextrose Agar (PDA))

It was this Cleveland event that initiated the headline news of Stachybotrys. The American Academy of Pediatrics produced guidelines in the wake of the outbreak. Other incidents involving kids in Stachybotrys-contaminated water-damaged school buildings have captured headlines as well, with children becoming symptom-free after being removed from those environments.
Article from the Fargo Forum newspaper, North Dakota (5/1/1997)

The role of S. chartarum in pulmonary hemorrhage in the Cleveland incident and in human health in the indoor environment is not clear though. There is not enough evidence to prove a solid causal relationship between S. chartarum and these health problems. Actually, in 2000 the CDC released two reports critical of the study conducted in Cleveland and concluded that the association between S. chartarum and acute pulmonary hemorrhage was not proven.

While case studies certainly indicate the possibility or even the plausibility of an effect from molds exposure, such studies by their nature cannot address whether the effect is common or widespread among building occupants. Results from studies that have not been reproduced may be spurious or have yet to be confirmed by well-designed follow up studies. (Photo: Moldy humid walls in a closet space)

In large epidemiologic studies, general symptoms have been associated with moisture damaged and presumably moldy buildings. Many of the reported symptoms are subjective and difficult to quantify. Results are confounded by the fact that the association is general, and mold is not the only possible cause of the symptoms. Neither condition proves that mold is NOT a cause.

In any case, molds growth in the indoor environment should be considered unacceptable from the perspectives of potential adverse health effects and building performance.

Dose-response

There is almost a complete lack of information on specific human responses to well-defined exposures to molds contaminants. There is currently no proven method to measure the type or amount of mold that a person is exposed to, and common symptoms associated with molds exposure are non-specific, aggravated by the facts that molds are present everywhere in the environment and that responses to exposure vary greatly among individuals. (Photo: Heavy mold growth on the underside of spruce floorboards)

There are no accepted standards for molds sampling in indoor environments or for analyzing and interpreting the data in terms of human health. Most studies are then based primarily on baseline environmental data rather than on human dose-response data. Neither OSHA or NIOSH, nor the EPA has set a standard or PEL for molds exposure.

Mold growth on air diffuser in ceiling
Miller et al. (1988) stated that it is reasonable to assume there is a problem if a single species predominates with >50 CFU/m3, that <150 CFU/m3 is acceptable if there is a mix of benign species, and that there is no problem when up to 300 CFU/m3 of Cladosporium or other common fungi is isolated. There is no source material to support these assertions, as few inhalation studies have been conducted.

References

American Academy of Pediatrics Committee on Environmental Health. 1998. Toxic effects of indoor molds. Pediatrics. 101:712-714. 11/23/03

Centers for Disease Control and Prevention. 2002. State of the Science on Molds and Human Health. 11/15/03

US Environmental Protection Agency – Indoor Air Quality – Molds. 11/15/03

Kuhn, D. M., and M. A. Ghannoum. 2003. Indoor mold, toxigenic fungi, and Stachybotrys chartarum: infectious disease perspective. Clin Microbiol Rev. 16(1):144-172. 11/15/03

Miller, J. D., A. M. Laflamme, Y. Sobol, P. Lafontaine and R. Greenhalgh. 1988. Fungi and fungal products in some Canadian houses. Int. Biodeterior. 24:103-120.

Morbidity and Mortality Weekly Report – Centers for Disease Control and Prevention. 2000. Update: Pulmonary Hemorrhage/Hemosiderosis Among Infants --- Cleveland, Ohio, 1993-1996. 49(9):180-184. 11/17/03

Nelson, B. D. 2001. Stachybotrys chartarum: The Toxic Indoor Mold – APSnet. 11/23/03

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