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When Mold Runs Amok

Mold growth in buildings and its purported effects on human health have been in the news a lot in recent years. Mold-related litigation and claims against insurance companies for mold and other moisture-related problems in buildings have been on the rise.There is strong scientific and other evidence linking mold and damp conditions in homes and buildings to some health effects. This is one conclusion of a report, titled Damp Indoor Spaces and Health, released at the end of May 2004 by the Institute of Medicine of the National Academy of Sciences.

William Fisk (Photo Roy Kaltschmidt)

The Institute of Medicine’s Committee on Damp Indoor Spaces and Health produced the report, and one of the committee members was William Fisk, head of the Indoor Environment Department in Lawrence Berkeley National Laboratory’s Environmental Energy Technologies Division and a senior staff scientist at Berkeley Lab.

Fisk and eight other committee members, including Committee Chair Noreen Clark, Dean of the School of Public Health at the University of Michigan, conducted an extensive review of the available scientific literature on the subject; they met face to face periodically and communicated over the internet to discuss their findings.

“The committee concluded that there is robust scientific evidence of an association of increases in selected respiratory health effects with building dampness or visible mold,” says Fisk. “These health effects are asthma exacerbation in sensitized individuals, and cough, wheeze, and upper respiratory symptoms in otherwise healthy individuals. The committee also said that building dampness is an important public health problem because dampness and mold problems are present in a significant fraction of buildings, and linked to substantial increases in these health effects.

“However, the committee believes that the existing evidence is insufficient to conclude that there is a causal relationship between dampness or mold and increases in these health effects. For example, moisture itself is not directly causing the adverse health effects and it is not certain whether exposures to molds or to some other pollutants found in damp buildings actually cause the observed increases in adverse health effects.”

Why is dampness a concern?

Dampness in buildings is a concern because it often leads to growth of molds and bacteria and to increased emissions of chemicals. In addition, dampness causes structural degradation on buildings. Building dampness problems have a number of causes. The report argues that the way to reduce these problems and the risk of associated health effects is to improve the design, construction, operation, and maintenance of buildings.

Some molds produce poisonous mycotoxins, although their role in health problems caused by moldy buildings is not known.

“There is considerable existing knowledge about how to make these improvements that is underutilized,” says Fisk. “For example, many dampness problems are caused by simple water leaks in roofs, walls, and plumbing systems that can be prevented or rapidly corrected through building maintenance.”

Another mystery surrounds “toxic molds.” Some molds can produce agents called mycotoxins, under certain conditions. “Cellular and animal studies have shown that mycotoxins can be highly toxic,” says Fisk. “However, we do not know what levels of exposure are necessary to cause health effects in humans, nor the amount to which people are exposed in mold-contaminated buildings.”

The National Academy committee identified a long list of research needs pertaining to damp buildings and mold. One need was for a better method to measure people’s exposures to dampness-related pollutants. “We also need a better fundamental understanding of how people are actually exposed to microbial agents,” says Fisk. “For example, does resuspension of mold spores from floors as people walk over them contribute substantially to exposures? The effects of dampness on several types of health effects needs much further research. The health benefits of mold remediation also need to be better understood.”

Despite the uncertainties, the National Academy of Sciences Committee concluded that dampness is an important public health problem. They provided suggestions regarding the appropriate public health response. Education, training, and incentives for reducing dampness are elements of the suggested public health response.

Berkeley Lab contributions

Most of the dampness and mold research has been performed in homes. Mark Mendell, an epidemiologist in the Lab’s Indoor Environment Department (IED) is analyzing data from office buildings to assess whether dampness in offices increases risks of adverse health effects. A recent analysis performed in collaboration with the California Department of Health Services found that increases in lower respiratory and mucous membrane symptoms were linked to particularly high airborne concentrations of molds and bacteria that grow on damp building materials.

Molds growing in air ducts may contribute to respiratory problems in air conditioned buildings. (Photo Mike McNickle)

The IED has also investigated the relationship between air conditioning systems and health effects. On average, there is a higher prevalence of a variety of health symptoms among occupants of air-conditioned buildings. The explanation is not clear, but one hypothesis is that some air conditioning systems become contaminated with microbial agents that are transported into the occupied spaces. In analyses by Mendell of data from 80 office buildings about which there had been complaints, wet and dirty air conditioning symptoms were associated with increased lower respiratory symptoms such as wheeze and shortness in breath.

In addition to contributing to the related research on causes of health effects, the IED studies how pollutants are transported around buildings, the mechanisms and amounts of pollutant exposure, and the effectiveness of technologies and practices for reducing exposures. At the same time, the IED seeks to maintain or improve building energy efficiency. They are particularly interested in technologies or practices that can simultaneously improve indoor environmental quality and save energy.

A moldy scrapbook: (clockwise from upper right) for security reasons, the tenant in this first floor apartment NEVER opened the windows; this growth was discovered only when cabinets were removed from the kitchen wall; mold caused by a slow leak in a bathroom pipe grew through sheetrock, two layers of wallpaper, a layer of wood paneling, and ate the silver off the back of a mirror; even in the desert, a poorly ventilated closet can sprout mold. (Photos San Francisco Department of Public Health, Mike McNickle, Sandy McNeel)

Advice to homeowners

Fisk offers some suggestions on how to prevent mold from becoming a problem in homes. “The key to prevention,” he says, “is to design, construct, operate and maintain homes in a way that prevents building components and furnishings from becoming unusually damp.”

“Some causes of dampness problems are complex and must be identified and addressed by building experts,” he adds. “If you see evidence of significant dampness such as water stains or water-damaged building materials, you should rapidly take actions to correct the cause of the problem. Often these require the assistance of a building professional — for example, a roofing company for a roof leak.”

Some causes and solutions are obvious. When a plumbing fitting under the sink starts leaking, the homeowner can tighten or replace it. The use of dehumidifiers and bathroom and kitchen fans that exhaust air to the outdoors can help prevent dampness problems in some situations, but these solutions won’t work in other situations such as leaky pipes, roofs, or windows.

When building materials become wet from a sudden leak or spill, Fisk advises that they should be dried as quickly as possible — within hours or days, not weeks — to reduce the risk of mold growth. Outside experts will normally be required to dry buildings after large leaks or floods.

“When visible mold is present,” says Fisk, “it should be removed by cleaning. When cleaning is not possible, the mold-contaminated materials should be removed. Homeowners can use normal cleaning practices to remove small amounts of mold, such as the moldy spots in the shower, but widespread mold contamination should be addressed by professionals.”

“The most important message to remember,” he concludes, “is that controlling building dampness is the key to preventing mold contamination.”

Additional information

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Additional Information