July 25, 2002

Mold: Getting a grip on the fuzzy stuff

URS Corp.


How much mold in a building is too much mold?

As a consultant who works in the mold investigation and removal/remediation industry, I hear this question often.

Like so many questions in life, there is no simple answer. Some questions — like “Is mold the same thing as mildew?” and “Are molds and fungi the same?” — are easier to answer: yes and yes. Because molds are so ubiquitous in our environment, I’ll address the basic issues first: What is mold? What are its health effects? What are the guidelines on mold remediation? Why are there no current regulatory limits for how much mold is too much?

Fungi are chlorophyll-free plants that come in a variety of shapes, sizes and growth types. They are usually found in moist organic environments and grow well at a variety of temperatures. Molds (which are a fungus) produce spores so that they can survive during times of poor growth conditions (i.e., no water or no food source). Spores are generally a thick-walled seed-like structure produced by the mold.

Mold can adversely affect human health in a variety of ways. Some fungi can cause serious medical problems, particularly in health care facilities and among immune-suppressed individuals.

Health concerns

Exposure to molds indoors has been linked to a number of adverse health effects resulting from allergy/asthma, infection by pathogenic fungi, mucous membrane irritation (i.e. hypersensitivity pneumonitis), sensory irritation (i.e. dermatitis) and toxicity alone, or in combination.

Significant secondary effects may also be related to mycotoxins produced by the fungi, including pulmonary hemosiderosis (bleeding in the lungs), organic dust toxic syndrome (produces flu-like symptoms), cytotoxicity (toxic to cells of the body), cognitive impairment, encephalopathies (diseases of the brain usually affecting motor function), suppression of the immune system, and even cancer.

Standards are set by health agencies to prevent harmful exposures to airborne concentrations of contaminants. For most other widely-used constituents of concern, such as lead and asbestos, concentration levels are established for conditions at which it is believed that nearly all workers may be repeatedly exposed day after day without adverse health effects.

These are usually based on epidemiology, and studies of adverse health effects at various levels of exposure. This is called a “dose-response” relationship.

Why then are there no relevant or permissible exposure limits for toxic molds set by the National Institute for Occupational Safety and Health, Occupational Safety and Health Administration, or the American Conference of Governmental Industrial Hygienists (ACGIH)?

According to the American Industrial Hygiene Association (AIHA), “health hazards of exposure to environmental molds relate to four broad categories of chemical/biological attributes of molds and their metabolites: irritants, allergens, toxins and pathogens. Different mold species may be more or less hazardous.... Risks vary depending on a number of factors. Uncertainty is complicated by 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.”

Essentially, there is no single dose-response relationship.

Because of these gaps in knowledge, no mandatory limits exist which investigators can compare their results against when assessing a building for mold hazards. Much of the mold investigation and remediation work currently being done is based on past experience, opinion and guidance documents.

Current guidance is provided by a variety of sources, including the New York City Department and Health, Bureau of Environmental and Occupational Disease Epidemiology, which produced a major document on mold sampling and remediation. Guidance can also be obtained from Web sites with documents produced by the U.S. Environmental Protection Agency, the U.S. Federal Emergency Management Agency, from environmental microbiology laboratories, from abatement companies, and from health and safety consultants with mold abatement experience.

How much is too much?

But despite all the existing information and guidance, it’s still not known exactly “how much mold is too much mold?”

The answer to this question is up to interpretation, but much research is now being performed to provide recommended exposure limits to mold spores. Currently, consultants performing mold sampling and analysis are basing their results on a range of variables. As a result of research, groups such as Health Canada, AIHA, the International Society of Indoor Air Quality and Climate, and the ACGIH agree that the concentration of airborne fungi should be lower indoors than outdoors and that the presence of pathogenic fungi and/or the presence of indicator species whose presence indicate excessive moisture or a health hazard should not typically be present in healthy indoor environments.

Several groups are working on developing exposure limits for exposures to mold. The California Legislature has introduced a bill that directs its Department of Health Services to adopt mold remediation standards, based on permissible levels of exposure which will need to be developed based on the “latest scientific data.”

Legislation coming

Representative John Conyers (D-Mich.) plans to introduce legislation shortly that will direct the EPA to issue guidelines specifying what levels of toxic mold are dangerous and what levels are acceptable. Conyers wants government oversight over what he characterizes as an unregulated industry of inspections and cleanups. There is pressure from industry and insurance companies to additionally require states to license and monitor mold inspectors and mold remediators.

In the scientific community, the ACGIH Advanced Bioaerosols Committee is working “to compile and disseminate information on biologically derived airborne contaminants, to develop recommendations for assessment, control, remediation, and prevention of such hazards, and to establish criteria for bioaerosol exposure limits.”

The National Academy of Sciences Institute of Medicine, sponsored by the Centers for Disease Control and Prevention, will conduct a comprehensive review of the scientific literature regarding the relationship between damp or moldy indoor environments and the manifestation of adverse health effects. The review will make recommendations or suggest guidelines for public health research in these areas.

With more data on how molds can cause adverse health effects, more information on airborne concentrations of molds that may produce adverse health effects, and with further experience in mold remediation in combination with pressure from Congress and the insurance industry, some exposure standards may soon be developed to help determine “how much mold is too much mold?”

Gail Gislason, MS, CIH, is a senior industrial hygiene consultant at URS Corp. She can be reached at (206) 438-2120.

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