The Abbey Newsletter

Volume 23, Number 5

Mold: The Whole Picture
Pt. 2, Assessment of Mold Problems

by Ellen McCrady

Part 1 (v.23 #4) emphasized the preservation community's need for better contact with fields that carry out research and generate information about mold. These fields include medicine, public health, agriculture, indoor air quality, building construction, and historic preservation, in addition to mycology. The history and nature of mold were discussed, and several websites and publications were cited.
The plan for this series does not include a review of preservation literature or procedures on mold, because the scope is so broad already. -Ed.

Defining the Problem

The first signs of a mold problem are often deceptive: a moldy smell in part of a building, tired employees who are said to be suffering from colds or allergies, or visible mold growths on walls or books in certain locations. They are easy to ignore and hard to interpret, so health and building problems may not be investigated right away, although affected items may be cleaned or fumigated. (Note: Mold problems from fire or water disasters are not considered here, because they usually cause explosive mold growth, rather than typically chronic or recurring growth.)

In minor cases, formal inspections are of course not called for. The 1994 edition of the Guidelines on Assessment and Remediation of Stachybotrys Atra [Chartarum] in Indoor Environments says,

"The criteria for conducting an initial inspection include:

  1. presence of visible mold;
  2. evidence of water damage;
  3. symptoms which are consistent with an allergic or toxic response to Stachybotrys atra (e.g., respiratory illness, rashes and chronic fatique) and are severe enough as judged by medical documentation to result in lost work days."

A new edition of this guide, which will apply to more species, is in preparation.

If the smell or visible mold growths are seen as indicators of a health problem, institutions and businesses may call in indoor air quality specialists, who will look for evidence of bacteria, viruses and other microorganisms in addition to mold. They will check for deficiencies in the HVAC (heating, ventilating and air conditioning) system that may be bringing polluted air into the building, or spreading the mold to uninfected areas.

However, indoor air quality people, industrial hygienists and environmental health professionals may not get the whole picture because they are trained mostly to monitor conformity to government standards for work-related exposures, and there are no standards for mold exposure.

Teamwork Recommended

It takes a number of specialists from different fields to do an adequate assessment of a mold problem in a building. The assessment should be thorough enough to justify an expensive remediation, if that is called for (cleaning, restoring, and rebuilding); and the findings have to be credible, if they are intended for possible use in a lawsuit.

Unfortunately, many architects, builders and building engineers do not understand how they are contributing to the modern problem of illness among residents or staff and the decay of building materials. The "tight houses" first built during the oil shortage of the early 1970s do conserve fuel, but they also create ideal homes for mold.

It is no coincidence that the 1993 Workshop on Control of Humidity for Health, Artifacts, and Buildings gave the title "Bugs, Mold and Rot" to both the workshop and the proceedings. The workshop following that one was held last summer during the same week as the 1999 AIC conference. Those proceedings will be available, probably in 2000, from the National Institute of Building Sciences (202/289-7800, fax 202/289-1092).

Almost every writer on this subject recommends a team approach. A health specialist has to be involved, because the effects of exposure to mold are so variable, and reactions to other microorganisms and non-biological agents are also possible. Biological agents often encountered in such investigations include fungi, bacteria, amebae, and viruses; allergens from plants, microorganisms and animals; toxins from bacteria and fungi; and microbial volatile organic compounds (MVOCs). There should be a specialist who knows how to find and identify them, estimate the risk they pose, and do the necessary lab work. Finally, the investigators should include, or be in touch with, someone who knows about building structure and systems, especially of the building in question.

An investigation strategy is outlined on p. 2-3 (ch. 2, p. 3) in Bioaerosols: Assessment and Control, the manual published in 1999 by the ACGIH (American Conference of Governmental Industrial Hygienists). First comes the health assessment of people in the building, then the bioaerosol assessment, and the building assessment. Then hypotheses are formulated about what could be going on, because many factors have to be identified, at least provisionally, before the data can be gathered efficiently. The sampling methods, health precautions, places to look, possible causes, and conditions to correct are all determined or at least influenced by the species of organisms involved.

Next the hypotheses are tested by gathering data about the environment, bioaerosols present, and medical aspects, and by consulting experts as needed. If all the data checks out, the investigators are ready to make recommendations on moisture control, cleaning, repair and so on. If it does not check out, then the investigators have to go back to Square One.

A Detective Story

Sometimes the search for the cause of complaints is not easy. One such case was reported at the 1998 Bioaerosols Conference in Saratoga Springs by Joseph Fedoruk, Steven Uhlman and Dean B. Baker ("Microbial Contamination of a Ventilation System Detected by Microbial Volatile Organic Compound [MVOC] Analysis"). A six-story building constructed in 1970 was given an award in 1997 by ASHRAE for its healthy environment; however, in 1995 the HVAC system had been re-engineered to increase the supply of fresh air. By 1997, the year of its award, it was already a sick building. People in one end of the building were feeling ill and complaining periodically of chemical odor.

Fedoruk's company was asked to look at the building, but it appeared to have no problems: they found consistently low counts of viable molds, total spores and atmospheric bacteria, and good temperature and relative humidity. They took samples indoors, outdoors, and in both the complaint areas and non-complaint areas. There was no visible mold growth anywhere, although MVOC concentrations were much higher in the complaint area. In order to get to the bottom of it, Fedoruk (who is a medical doctor) saw the people as a clinician. Perhaps this inspired him to follow the trail of MVOCs upstream to see where they were coming from; he doesn't say so in the abstract of his paper, the source of this story.

Then they inspected the HVAC system and found something that had been overlooked in previous building investigations: mist from a chiller tower that was being drawn into a principal air intake duct only 30' away, along with mist from a condensate pan beneath the chiller tower. The intake duct was damp; still, no mold growth was visible from the outside.

When they opened up the ducts, however, they found mold, yeast and bacteria colonies inside—not on the duct surface, but on the joint adhesive. That was enough to explain the contaminated air inside. (One is reminded of the original incidence of legionnaires' disease, where the hotel's air intake was also located close to the cooling tower. The airborne bacteria from the condensate pan there were also sucked up by the air intake and delivered to the hotel guests inside.)

Fedoruk concludes that MVOC analysis provides a way to detect ventilation system contamination when neither visible mold growth nor measurable bioaerosols (spores, etc.) are present to help the investigator.

Sometimes, if there is no other way to tell where the main source of the mold is, then parts of the walls, ceiling or floors have to be removed to inspect hidden parts of the structure. This is, of course, destructive but sometimes necessary. In England and Denmark, trained dogs called "rothounds" are used to find actively growing dry rot in a nondestructive way. These dogs can detect a certain MVOC that is produced by Serpula lacrymans, the dry rot fungus, from several meters away; they can cover 20-50 rooms an hour and also search small areas inaccessible to humans.

David Miller says the surface area of visible mold is the best measure of exposure, though it is hard to determine accurately. Colony-forming units from airborne samples alone have no value. In order to determine the existence of hidden fungal growth in buildings, the method of taking air samples described in the American Industrial Hygiene Association's Field Guide for the Determination of Biological Contaminants (1996) is valuable, because it provides a comparison of fungal species inside versus species outside. Other tools are being developed to measure individual exposures to fungi for research studies. Aside from the AIHA manual, a recent review of the methods for assessing fungal exposures can be found in: Dillon, H.K., J.D. Miller, W.G. Sorenson, J. Douwes and R.J. Jacobs (1999). "A review of methods applicable to the assessment of mold exposure to children," Environmental Health Perspectives 107 (s.3): 473-480.


Before sampling is done, a plan has to be drawn up specifying which microorganisms will be looked for, where they might be found, likely sources, how the organisms will be located and quantified, and when and where samples will be collected.

There are many kinds of volumetric air samplers, among which the Andersen sampler is frequently mentioned. They draw in air from the room and discharge it with the bioaerosols onto a filter or sticky surfaces or agar plates.

Air samples can be used to get a count of "colony-forming units" (cfu, which are bacteria and fungi that start growing on the culture media) per cubic meter of air. If the colonies are easy to identify, the counts can be related to individual species. The cfu of mixed species may also be used as a broad index of microbial growth. When species are mixed, however, one or more species may be suppressed on the culture plate by competitors.

A well-known but unreliable way of taking a sample of bioaerosols in an area is to set out culture plates and let the spores and other bioaerosols settle on them. This method is rarely used today, because some organisms do not send out many spores, or have spores that are too light to settle out, or that die soon after they leave the colony.

The mold count can be increased hundreds or thousands of times by "aggressive sampling"—that is, by stirring up the air with a fan, or pounding on the wall. Higher counts are also had when there is traffic through a room, such as a schoolroom at the beginning or end of the day. So a great many facts and observations have to be recorded, and samples have to be taken by several different methods, in order to get reliable data.

There are no standard methods for getting information on airborne microorganisms, according to Brian Flannigan (in his paper," Guidelines for Evaluation of Airborne Microbial Contamination of Buildings," given at the 1994 Saratoga Springs conference). Assessment of only viable microorganisms may reveal as little as 1% of the total microbial airborne load, he says.

Samples of moldy materials (bulk samples) can be taken and pressed directly onto an agar plate, then cultured. Results are counted as colony-forming units per gram of material.

Samples of surface growth can be taken with sticky tape or a sterile swab, then transferred to a plate. This is a useful method for hard surfaces like the inside of an air duct.

An open and multidisciplinary approach is needed to make a complete, fast and efficient diagnosis of hidden mold problems in buildings. ... [In the case of a Stachybotrys chartarum contaminated building], many critically important steps ... are required to make your diagnosis a success story.

First, trust the occupants: if there is a complaint, there is a cause, even if it's not obvious. Find it! Second, a thorough inspection of the premises and their ventilation is mandatory. Keep in mind that mold needs water and porous organic materials that can be hidden in the structures and not directly visible. Almost any building material can harbor fungal growth, if the available water activity is sufficient. Use the proper tools to find it. Third, if sampling is needed, be versatile: no sampling method is perfect. Adapt the sampling strategy to the situation and use an accredited mycology lab to count and identify fungi in your samples. Bear in mind that you are dealing with toxigenic mold and, depending on the extent of the contaminated surface, take proper action to keep occupants away from it and protect their health. Finally, after putting together all the data gathered in the field, always communicate it in a simple, straightforward way, with affordable step-by-step remedial: don't forget that people want to get rid of their problem, not make their lives more complicated.

Claude Mainville, Sr. P. Eng.
President, Natur'air - Kiwatin Inc.
Montreal, QC H2L 1M1, Canada

[Reprinted with the author's permission from the abstract of his paper, "Learning from Stachybotrys chartarum: How to Find Hidden Mold in Buildings,"given at the 1998 Bioaerosols Conference in Saratoga Springs, NY.]

Media and Methods

Opinions differ about which culture media work best.

A common medium used for fungi is malt extract agar. Xerophilic fungi like Aspergillus penicillioides grow better on a medium with a water activity (Aw) reduced by addition of salt, sugar or glycerol. The incubation temperature has to be within a certain range (18°C to 25°C for most fungi and as high as 55°C [99°F] for thermophilic species).

Sometimes, when time is short, polymerase chain reaction (PCR) will be used instead of culturing, because results can be had in hours rather than days or weeks, and identifications are certain and specific. PCR is especially good for identifying hard-to-grow, slow-growing and nonculturable organisms.

Even after samples are taken and cultures are grown, the findings have to be interpreted before remediation can begin, even for a small area or building. Interpretation may only consist of an individual's weighing the evidence mentally, or consulting the relevant literature just to be sure. For a large building, however, all possible alternatives to each finding must be considered. There is a whole chapter on it by Harriet Burge et al. in the ACGIH book, Bioaerosols: Assessment and Control, but we will not go into that step here, except to warn that sometimes other microorganisms or even inorganic materials or sources outside the building can be at least partly responsible for symptoms of occupants. And toxins released by mold may greatly increase the effect of toxins from other sources.

Which Mold Species are Most Common? Most Toxic?

Opinion as to the most common species varies. A chapter on indoor mycology in North America (Building Mycology, ch. 11) says the most common fungal genera found in houses (present in 10 to 100% of samples) are Cladosporium, Penicillium, Alternaria, Streptomyces and Epicoccum. Brian Flannigan, who gave a paper, "Guidelines for Evaluation of Airborne Microbial Contamination of Buildings," at the 1994 Saratoga Springs conference, says that the most common indoor molds are likely to be species of Cladosporium, Penicillium, Aspergillus and Eurotium. Fausta Gallo has identified Aspergillus and Penicillium as the most common species in libraries (1986, ICCROM).

Nominations for most toxic species also vary. Aspergillus fumigatus and Stachybotrys are two examples that Flannigan offers of moisture-loving toxic molds that can flourish indoors. He cites a Canadian guide on office buildings, which says that "Pathogenic fungi such as Aspergillus fumigatus, Histoplasma and Cryptococcus should not be present in significant numbers. The persistence of toxigenic molds such as Stachybotrys atra and Aspergillus versicolor in significant numbers requires investigation/action."

Jeffrey Cooper and J. Michael Phillips listed the following five species as most toxic in a recent paper: Aspergillus flavus, A. fumigatus, A. versicolor, Fusarium moniliforme, and Stachybotrys chartarum. They say, "The detection of any toxigenic fungi indoors is considered unacceptable from a human health risk perspective. The confirmed presence of [any of these five species] requires urgent risk management decisions by building owners." ("Assessment and Remediation of Toxigenic Fungal Contamination in Indoor Environments," First NSF International Conference on Indoor Air Health, May 3-5, 1999, Denver, CO)

Several authors have pointed out that each type of building (homes, schools, office buildings) tends to have its own set of typical mold species. This is probably because each building type typically has its own characteristic "amplifiers" or sources and conditions, such as mattress dust and humid bathrooms in homes, leaky roofs and defective plumbing in schools, and poorly maintained HVAC systems in office buildings.

The mold counts found on the weather page of many newspapers have little to do with the indoor exposure to toxic mold spores. Outdoor molds are not normally a threat to human health. Many of them live on plant leaves or in forest litter, and are not found in great concentration except in ooutdoor manmade facilities like compost areas, dumps, and sawmills.

Sources of Information

the Aspergillus Web Site
"This site is designed to provide information on pathogenic Aspergilli for clinicians and scientific researchers. The site includes DNA sequence data, a comprehensive bibliographic database, laboratory protocols, treatment information and discussion groups. The Aspergillus Web Site is sponsored by Alza Corporation and Ortho Biotech Inc. and the sponsors have access to the Web Site address book--as do all other Aspergillus Web Site users. The European Science Foundation has also made a contribution to the maintenance of the site."

Short Courses and Symposia

The Mid-Atlantic Environmental Health Resource Center has planned three courses this spring and summer in Pennsylvania, mainly for representatives of disaster response companies that deal with mold and moisture-related problems. They will be held April 10-11 ("Controlling Chronic Moisture and Microbial Problems in Buildings and Mechanical Systems"); April 12-13, "Damage Mitigation and Building Restoration for a Health Indoor Environment"; and 3 days in July ("Mold Remediation Worker/Supervisor"). MEHRC is at 3624 Market St., First Floor East, Philadelphia, PA 19104 (tel. 215/387-4096; fax 215/387-6321;

The US EPA Region 8 and the University of Tulsa's Center for Environmental Research and Technology (CERT) will be giving a short course in Denver, Mar. 8-9, 2000, entitled "Indoor Air Quality: Asthma and Allergen Control." It will cover indoor air basics, public health issues, cleaning, remediation and indoor air solutions; the emphasis will not be on mold. Registration for people from the public sector is $190. Contact the University of Tulsa, Chemical Engineering Department, Attn: Indoor Air Program, 600 S. College Ave., Tulsa, OK 74104-3189 (918/631-3290; fax 918/631-3289 or 631-3268;

The University of Tulsa will also give a longer course with a broader scope, for doctors and the medical community, in Dallas May 11-13. Announcements have not been sent out yet.


Fungi and Bacteria in Indoor Air Environments: Health Effects, Detection and Remediation. (Proceedings of the International Conference, Saratoga Springs, NY, Oct. 6-7, 1994). Editors: Eckardt Johanning and Chin S. Yang. Eastern New York Occupational Health Program, 1 CHP Plaza, Latham, NY 12110. 1995. 228 pp. This is the volume that includes the 7-page "Guidelines on Assessment and Remediation of Stachybotrys Atra in Indoor Environments." It also includes "Legal Aspects of Indoor Air Quality," by Guy Keith Vann.

Bioaerosols, Fungi and Mycotoxins: Health Effects, Assessment, Prevention and Control. Eckardt Johanning, ed. (Proceedings of the Third International Conference on Fungi, Mycotoxins and Bioaerosols, 1998, Saratoga Springs, NY) 638 pp. Available for $25.00 to participants (and $45 or 45 Euros to others, + $6 shipping). U.S. and Canada: order from Boyd Printing, 49 Sheridan Ave., Albany, NY 12210 (fax 518/436-7433). The last six papers, which are in a "Special Section" at the end, contain some material on assessment. "Learning from Stachybotrys Chartarum: How to Find Hidden Mold in Buildings," by Claude Mainville et al. (see sidebar above), is an eminently readable narrative concerning a Montreal office building that had suffered water intrusion during the January 1998 ice storm. (He says, by the way, that the way to find hidden mold is to open up the structure.)

Bioaerosols: Assessment and Control. Janet Macher, ed. American Conference of Governmental Industrial Hygienists, 1999. [Full reference on p. 60 of the last issue.]

Building Mycology: Management of Decay and Health in Buildings, by Jagjit Singh. 326 pp. E & F Spon, An Imprint of Chapman & Hall, 1994. About $122. Most of the text has to do with mold problems in England, but there is one chapter that describes North American problems. Well illustrated with color photographs and photomicrographs, drawings of building structure, graphs, and ordinary photographs of buildings—and of "rothounds" searching for dry rot. Cost: about $122, from Preservation Resource Group in Rockville, MD (301/309-2222; fax 301/279-7885).

The Preservation Resource Group book catalog lists 10 books under the heading "Building Pathology," including Building Mycology, Dampness in Buildings, and The Growing Fungus. The company also sells borate based wood preservatives to treat decayed wood. It serves the needs of the historic preservation community, and also of homeowners who want to decontaminate and rebuild moldy parts of their houses.

"A Search for Moisture Sources," by Jeffrey E. Christian, p. 71-81 in Bugs, Mold & Rot II: Workshop Proceedings, Nov. 16-17, 1993. William B. Rose and Anton TenWolde, eds. Building Environment and Thermal Envelope Council of the National Institute of Building Sciences, Washington, DC. 1993. Every conceivable source of water in a house is identified and its output quantified. Example: In a typical new house, a concrete basement will release 6.4 liters of moisture per day.

Proceedings of the First NSF International Conference on Indoor Air Health: Impacts, Issues and Solutions. May 3-5, 1999, Denver. ISSN # 1523-6080. NSF International, 789 Dixboro Road, Ann Arbor, MI 48105.

 [Contents]  [Search]  [Abbey]

[Search all CoOL documents]