How should a building be evaluated for mold growth?
Check building materials and spaces for visible mold and
signs of moisture damage indicating a history of water leaks, high humidity
levels, and/or condensation. Any occupant complaints or reported health
problems should be noted as well as any musty or moldy odors.
Components of the building's ventilation system should
also be inspected. A moisture meter is often very helpful in identifying
wet or damp building materials. If mold growth or moisture problems are
found, the air pressure differentials between the area of growth and
surrounding areas should be determined and potential air pathways from the
source should be characterized to determine its impact on the building and
its occupants.
When is sampling necessary in a building evaluation?
Sampling may not be necessary. If visible mold is
present, then it should be remediated, regardless of what species are
present and whether samples are taken. In specific instances, such as cases
where health concerns are an issue, litigation is involved, or where the
source(s) of contamination is unclear, sampling may be considered as part of
a building evaluation. In situations where visible mold is present, and
there is a need to have the mold identified, sampling is needed. Any
sampling must be conducted by professionals experienced with mold issues,
and familiar with current guidelines.
If mold is suspected, but not visibly detectable after an
inspection, then sampling may reveal evidence of mold amplification or
reservoirs indoors. If mold is being removed and there is a question about
how far the colonization extends, then surface or bulk sampling in
combination with moisture readings may be useful. Sampling for airborne
mold spores can indicate whether the mix of indoor molds is "typical" of the
outdoor mix or conversely, "atypical" or unusual, at least at that time. If
samples are taken, regardless of the purpose, there should be a clear
question that the sample results should help answer. Sampling without a
specific purpose greatly increases the chances of generating useless data.
Note that laboratories vary in experience and proficiency; using an AIHA
EMLAC accredited lab is recommended.
Why is there controversy about the health effects of exposure to mold
growth?
Not all health effects of molds are controversial. Fungal
infections are well known. Fungal allergies are also well known and
accepted among medical experts, although the allergens themselves are poorly
characterized. Infections and allergies have objective and well-established
clinical effects. These effects can be measured and reproducibly
demonstrated, and the mechanisms are fully understood. The resulting health
effects caused by eating mycotoxins (from humans and animals consuming moldy
foods or feed) are also well known.
Other health effects have been proposed for mold
metabolites that are irritants or mycotoxins, and plausible mechanisms exist
for health effects due to these mold metabolites. However, the clinical
relevance of these mycotoxins and irritants 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 involves symptoms that are subjective.
While case studies certainly indicate the possibility or
even the plausibility of an effect, such studies by their nature cannot
address whether an 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. 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.
Since much remains unproven, controversy has developed
about the presumed health effects. This controversy is intensified since
the health effects attributed to mycotoxins are often serious and sometimes
are claimed to be permanent. Dampness in buildings is associated with
respiratory effects, but the extent to which mold contributes to these
effects is not known. Some health effects of exposure to mold growth remain
controversial because the potential consequences may be significant; yet
crucial and legitimate scientific questions remain unanswered. Our
incomplete knowledge of non-infectious health effects related to mold
exposure is due as much to limited research support as it is to limited
actual effects. In summary, mold growth in the built environment should be
considered unacceptable from the perspectives of potential adverse health
effects and building performance.
Why are there no standards for mold exposure?
Health hazards of exposure to environmental molds relate
to four broad categories of chemical/ biological attributes of molds and
their metabolites. These materials may be: 1) irritants, 2) allergens, 3)
toxins, and rarely 4) pathogens. Different mold species may be more or less
hazardous with respect to any or all of these categories. However, the
risks from exposure to a particular mold species may vary depending on a
number of factors. This uncertainty is complicated further by the almost
complete lack of information on specific human responses to well-defined
exposures to mold contaminants. In combination, these knowledge gaps have
made it impossible to set simple exposure standards to molds and
mold-related contaminants.
With no standards, how do I interpret my sampling results?
A useful method for interpreting microbiological results
is to compare the kinds and levels of organisms detected in different
environments. Usual comparisons are indoors to outdoors or complaint areas
to non-complaint areas. Specifically, in buildings without mold problems,
the qualitative diversity of airborne fungi indoors and outdoors should be
similar. Conversely, the dominating presence of one or two kinds of fungi
indoors and the absence of the same kind outdoors may indicate a moisture
problem and degraded air quality. Also, the consistent presence of fungi
such as Stachybotrys chartarum, Aspergillus versicolor, or
various Penicillium species over and beyond background concentrations
may indicate the occurrence of a moisture problem that should be addressed
and a potential atypical exposure. Generally indoor mold types should be
similar and levels should be no greater than outdoor and non-complaint
areas. Analytical results from bulk material or dust samples may also be
compared to results of similar samples collected from reasonable comparison
areas.
Comparisons of total bacterial levels indoors versus
outdoors may not be as useful as with fungi, since natural reservoirs exist
in both places. Comparisons of specific taxa of bacteria present, excluding
those of known human origin, can help determine building-related sources.
Does mold remediation always require isolation / containment?
Mold remediation should always require some level of
isolation of materials or containment. The lower level of containment or
isolation would involve sealing removed moldy materials in a plastic bag for
disposal. Local area or full area containment decisions should be made
based upon the size of the area of growth and the potential for occupant
exposure or building contamination without containment. These decisions
should be based on an understanding of the full scope of mold contamination,
including visible and hidden mold sources.
Are biocides required or useful in remediation projects?
Biocides are disinfectant chemicals used to kill germs in
order to prevent infections resulting from contact with these materials. In
most mold remediations, biocides are not a substitute for thorough
cleaning. Biocides are of limited use in remediation of indoor mold
contamination for two main reasons:
1) The adverse effects caused by mold (other than
infection) are due to metabolites present in their spores and secreted
into the materials upon which molds have grown. The application of
biocides may kill mold spores but it does not necessarily eliminate these
metabolites. The only sure way to do this requires the physical
elimination of mold and moldy materials by thorough cleaning or removal of
the affected materials.
2) Most commonly used biocides do not kill molds
effectively. Active fungal growth on a surface may produce a spore
density of one million spores per square inch. Treating an active mold
growth site with a spore density of one million spores per square inch
with a biocide with an effectiveness of 99.999% would then leave an
estimated 10 viable spores per square inch. As such, if the underlying
moisture problem is not resolved, mold growth may re-occur.
The only situation where biocidal treatments are indicated
is where the contaminant is one of the few fungi that are known to cause
human infection. This is particularly important in health care facilities
or other places with occupants who have impaired immune systems or who may
be more susceptible than the general population to infection.
What are the gaps in our knowledge about mold exposure and the health
effects of mold exposure?
The etiology of infectious fungi is relatively well
understood. Conversely, mechanisms responsible for allergic sensitization,
contact dermatitis, hypersensitivity pneumonitis, and inhalation fevers vary
from incompletely characterized to entirely unknown. Predisposing host
factors, presumably under genetic control, influence individual
susceptibility to environmental exposures. The psychogenic/psychosocial
contribution to mold-related illness remains elusive. Chief among our
knowledge gaps are: (1) defining how mycotoxins affect human health and (2)
the health risks associated with mycotoxin, microbial volatile organic
compound, allergen, and glucan exposures, particularly the proposed response
to Stachybotrys mycotoxins associated with hemosiderosis.
The lack of meaningful threshold limit values for most
indoor air quality contaminants is a major obstacle to establishing
regulatory standards for individual exposure to airborne contaminants. The
same is certainly true for molds. Until microbiological methods for
demonstrating mold concentrations in the environment are standardized and
reproducible, epidemiological studies necessary to determine dose-response
can only suggest association, not cause and effect, with respect to mold
exposures and health effects.
List of Guidance Docs
Consult other fact sheets from AIHA on mold: The
Facts About Mold: For Everyone, and
The Facts About Mold: A Glossary.
Listings of indoor air quality consultants can be obtained
from the American Industrial Hygiene Association (AIHA). See consumer
brochure "How
to Select an Indoor Air Quality Consultant" or call (703) 849-8888.
Additional technical information is included in these
sources.
CDC "Draft Guideline for Environmental Infection Control
in Healthcare Facilities" (especially sections I.C.3, I.C.4, I.F, II.C.1 and
Appendix B)
http://www.cdc.gov/ncidod/hip/enviro/env_guide_draft.pdf
This Fact Sheet is a joint effort by the following AIHA Technical
Committees:
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