• Home & Living

Methods Used To Assess Mold Hazards In The Home



In general, visual observation of active or past microbial growth, or measurement of mold in dust or samples of source material, can be used to establish potential for mold exposure. As inhalation is the primary exposure pathway for molds, air sampling for mold can also be used to estimate the likelihood of exposure.

The following section provides the reader with an overview of the range of assessment methods and technologies that are available, from both a and programmatic perspective. The level of rigor involved in assessing mold hazards in a setting surpasses that which is practical or necessary for programmatic or public health use. From a housing or public health perspective, a home assessment is generally constrained by the need for cost effective methods that are sufficient to allow for the identification of mold problems in the home environment. Current guidance generally discourages collecting and analysis of environmental samples for mold analysis in most situations. This is based on factors such as cost, the high variability in sampling results (both spatial and temporal variability), and the fact that remediation decisions are generally not based on sampling results. Significant residential mold problems can usually be identified based on visual observation and/or the presence of odors. Situations where sampling might be conducted include those in which the source of the mold is unclear, litigation is involved, or to test a surface to document adequate cleaning or remediation. Note, however, that some experts recommend that sampling should not be used to verify adequacy of cleaning, because of the high risk of false negatives.

Visual Assessment and Occupant Questionnaires

High humidity levels and excess dampness have clearly been associated with mold growth, as well as increased levels of some environmental allergens, such as those produced by dust mites. Visual inspection for dampness, observable mold growth, and detection of musty odors, often obtained from occupant questionnaires, are the most frequently used methods to assess the potential for indoor mold exposure. Visual observation of mold growth, however, is limited by the fact that fungal elements such as spores are microscopic, and a mold problem may not be apparent until growth is extensive. In some cases, destructive sampling (e.g., the removal of wallboard) is required to assess the extent of fungal contamination. A device called a boroscope, which employs fiber optics technology to make observations in building cavities by inserting the instrument through a small hole drilled in materials such as wall board, can be used by home inspectors to facilitate assessment of hidden mold damage. Although direct observation of visible fungal growth is usually sufficient to warrant a recommendation for mitigation, further air or source sampling (discussed below) may be conducted for documentation purposes and to record the types of fungi that predominate.

Many moisture problems in homes are due to structural deficiencies. Common points of inspection for buildings with dampness problems include: rain leaks (e.g., on roofs and wall joints); surface and groundwater leaks (e.g., poorly designed or clogged rain gutters and footing drains, basement design problems); plumbing leaks; and stagnant water in appliances (e.g., dehumidifiers, dishwashers, refrigerator drip pans, and condensing coils and drip pans in HVAC systems). In addition, assessment is also conducted for water vapor migration and condensation problems, including: uneven indoor temperatures, poor air circulation, air conditioning systems, soil air entry into basements, contact of humid unconditioned air with cooled interior surfaces, and poor insulation on indoor chilled surfaces (e.g., chilled water lines). Portable, hand-held moisture meters, for the direct measurement of moisture levels in materials, may also be useful in qualitative home assessments to aid in pinpointing areas of potential biological growth that may not otherwise be obvious during a visual inspection.

A variety of different protocols exist for assessing water damage in homes; for example, a visual assessment tool for inspecting homes for evidence of mold and moisture has been developed for Cleveland, Ohio, by the Cuyahoga County (Ohio) Board of Health for use in HUD-sponsored research. An overview of additional techniques and issues of concern in conducting visual assessments of homes for mold contamination is presented in Bioaerosols: Assessment and Control . Chapter 3 of the Institute of Medicine report, Damp Indoor Spaces and Health, provides a list of questions used to define dampness used in 25 epidemiological studies. For large-scale assessments, e.g., in multifamily buildings, a sophisticated visual and olfactory inspection tool for moisture and mold developed by a NIOSH team may be useful.

Sample Collection

Quantitative assessment of indoor molds generally involves sampling of a representative environmental medium in the home and quantification of the measure of interest (e.g., allergen concentration, total fungal biomass, or spore count). Because preparation requirements for environmental samples vary with the analysis techniques to be used, investigators should plan a collection procedure accordingly. Standard methods for quantitative sampling of mold or models that would allow for estimates of inhalation or dermal exposure to molds from sampling results are not available.

Air and dust sampling, as well as direct sampling of mold colonies where visible mold growth is present, are used to estimate environmental levels of fungi. Generally, indoor environments contain large reservoirs of mold spores and hyphal fragments in settled dust and contaminated building materials. Concentrations of fungi in settled dust generally correlate weakly with those in indoor air. Indoor air fungi levels were strongly associated with outdoor air levels, and the investigators speculated that the two different metrics (air and dust samples) represent different types of fungal exposure, indicating that it may be necessary to collect both air and dust samples. Recent evidence suggests that very fine airborne particles (<1 micrometer aerodynamic equivalent diameter (AED)) can carry fungal fragments and/or metabolites such as allergens. Size characterization is important to detect these particulates, which could be much larger in number than spores. Before the decision is made to sample, there should be a clear justification for the sampling. Sampling is most beneficial when used to augment a visual inspection or survey information, and to help address particular questions that derive from the inspection (e.g., the extent of contamination within a building). Table 2 summarizes several sampling strategies for molds.

Table 2. Selected Mold Sampling Strategies1

Type of Environmental Sample

Sampling Techniques

Advantages/ Disadvantages

Possible/Example Results

Surface

Press collection material (e.g., a contact plate or adhesive tape) against a surface

Wipe small area with a wetted swab, cloth, or filter

Vacuum sample of settled dust.

Non-destructive

Spatially and temporally variable

Settled dust samples expected to be less temporally variable and be a better indicator of exposure over time.

Detection of past mold colonization or active growth

Identification of surfaces/areas where previously airborne mold spores and fragments have settled and accumulated

Bulk

Remove section of building material (e.g., wallboard)

Destructive technique

Detection of past mold colonization or active growth

Bulk

Vacuum or wipe larger area to collect loose bulk material (e.g., settled dust)

Non-destructive

Dust can have inhibitors like salt which can limit growth of some fungal taxa

Spatially and temporally variable

Efficiency of bulk dust collection may be affected by environmental factors (see discussion below)

Identification of surfaces/areas where previously airborne mold spores and fragments have settled and accumulated

Air

Static sampler

Personal sampler

With HVAC off and on

Useful if it is suspected that the ventilation systems are contaminated

Air levels are variable, especially with disturbance

Short-term air samples limit sensitivity

Detection of mold contamination where the presence of mold is suspected but cannot be identified by a visual inspection or bulk sampling

Source Sampling. Source sampling methods used in investigations of mold contamination in homes includes bulk and surface sampling.

In bulk sampling techniques, portions of environmental materials (e.g., settled dust, sections of wallboard, pieces of duct lining, carpet segments, or return air filters) are collected and tested to determine if molds have colonized a material and are actively growing and to identify surfaces areas where previously airborne mold spores and fragments have settled and accumulated. For fixed materials, bulk samples are cut or otherwise removed from the source and thus this technique may be somewhat destructive. For loose materials, such as floor dust, bulk samples are typically collected using wipe sampling or a hand-held vacuum with a special filter. Various factors, including design of the vacuum collector, surface characteristics (e.g., carpet vs. smooth floor), and other environmental characteristics have all been shown to affect the efficiency of dust collection. For example, when collecting dust with a vacuum sampler from a shag carpet surface, lower relative humidity (e.g., around 20 percent, as would be encountered during a dry, cold season) increased the intensity of the electrostatic field on the carpet and thus significantly decreased the collection efficiency of the vacuum.

HUD has developed a recommended “Vacuum Dust Sample Collection Protocol for Allergens” for use by HUD Healthy Homes Initiative grantees. The protocol is adapted from sampling methods used in the National Survey of Lead in Allergens in Housing and the Inner-City Asthma Study, and it is supported by a companion HUD document, “Background and Justification for a Vacuum Sampling Protocol for Allergens in Household Dust”. A hand-held portable vacuum cleaner -electric powered, not battery operated -is recommended, with a filter, sleeve or thimble dust collection device. Most electric powered canister vacuum cleaners are essentially equivalent in their measurement of indoor allergens, but it is necessary to choose a model that can accommodate the dust collection device that will be used. Sampling locations vary with the objectives and resources of the study.

Surface sampling in mold contamination investigations may also be used when a less destructive technique than bulk sampling is desired. For example, non-destructive samples of mold may be collected using a simple swab or adhesive tape. In general, surface sampling is typically accomplished by either pressing a collection material (e.g., a contact plate or adhesive tape) against a surface, or by wiping an area with a wetted swab, cloth, or filter. The size of a collected surface sample is generally much smaller that that of a bulk sample. An overview of procedures and advantages of various contact sampling techniques, including agar plate methods, adhesive tape sampling, and surface-wash sampling, is presented in Bioaerosols: Assessment and Control .

Air Sampling. Air sampling is more technically challenging and has greater opportunity for error than source sampling. For routine assessments in which the goal is to identify possible mold contamination problems prior to remediation, it is usually unnecessary to conduct air sampling because decisions about appropriate remediation strategies can typically be made on the basis of a visual inspection. Air monitoring may, however, be necessary in certain situations, including: 1) if an individual has been diagnosed with a disease associated with fungal exposure through inhalation, 2) if it is suspected that the ventilation systems are contaminated, or 3) if the presence of mold is suspected but cannot be identified by a visual inspection or bulk sampling.

Airborne mold particulates may include spores, fungal fragments, aggregates of spores or fragments, or materials contaminated with fungal product. The most commonly used methods available today for volumetric air sampling (i.e., when a known volume of air is collected) are based on one of the following principles: inertial compaction (e.g., multiple-hole impactors, slit samplers), centrifugal collection (e.g., agar-strip impactors, cyclone samplers), filtration (e.g., cassette filters attached to portable pumps), and liquid impingement (e.g., three-stage impingers). Gravitation or settling techniques (e.g., longer-term collection of settled spores onto a culture plate or microscope slide) can also be used, but they are non-volumetric and, due to large temporal and spatial variations, samples cannot readily be compared to one another or to volumetric samples.

Samplers may be either static or reflective of a personal breathing zone. Static filter samplers used to collect airborne substances are normally placed in a fixed position in a room and do not measure personal exposure . Sampler design and flow rate have been shown to affect the quantity and size of particles sampled and thus can affect the apparent measured levels of a given airborne substance. Both high-volume (60 to 1100 L/min) and lower-volume (6 to 20 L/min) filter samplers have been used, although it has been suggested that the lower-volume samplers may collect a more meaningful sample in relation to exposure because they better approximate breathing volumes of humans. Breathing zone samplers often show much higher levels of collected mold particles than static samplers, likely due to the varying levels of dust that are resuspended in the personal breathing zone as a result of human activity; however, only minor differences in airborne mold levels between personal and static samplers are observed during high levels of dust disturbance. It is generally recommended in the literature that outdoor air samples are collected concurrent with indoor samples for comparison purposes, both for measurement of baseline ambient air conditions (remote from obvious mold sources), and for baseline measurement of air entering a building (samples near outdoor air intakes).

In selecting a type of air sampler for fungal collection, it is recommended that consideration be given to such factors as: the compatibility of the sampler with the analysis method to be used, what type of information is needed (e.g., concentration or identification of species), the concentration (e.g., very high or very low) of the mold at the test site, temperature extremes, the nature of the air stream where the sample will be collected, and possible collection constraints due to the presence of occupants. Comparative assessments of the performance of the different samplers (e.g., filter samplers, Andersen samplers, rotorod samplers, liquid impingers, and cyclone samplers) have been inconclusive, although certain samplers have been observed to perform better for specific purposes (e.g., the Andersen sixstage sampler for viable spore counts and the Burkard 24-hour samplers for total spore counts).

Sample Analysis

Current methods available to analyze environmental samples from the home for mold hazards include:

  • Counting colonies cultured for specific species.
  • Identifying and/or counting spores.
  • Chemical analysis of fungal components and biochemical/immunochemical markers to quantify total fungal loads (biomass).
  • Immunoassays (ELISAs) to measure fungal-specific antigen levels.
  • Genetic probe technologies to identify fungal species.

An overview of selected mold analysis methods and their applicability is presented below.

Selected Methods for Analyzing Home Environmental Samples for Mold 1

Analysis

Test Applicability

Method (units)

Advantages/Limitations

Important Species

Data Obtained 2

Allergen immunoassays, ELISA 3 (micrograms/g or pg/m3)

Not currently reliable for fungi (e.g., Alternaria counts must be very high or germinating)

Aspergillus, Alternaria, Cladosporium

Allergen levels (Asp f 1 and Alt a 1)

Spore Count

Intact spores may not account for total allergen load

All (Aspergillus, Penicillium, Trichoderma and yeasts difficult to identify)

Concentration of spores; spore identification

Culture

Viable fungi may not account for total allergen load

All

Species identification; Estimates of fungal concentrations

Chemical biomarkers (ergosterol, extracellular polysaccharides (EPS), Bglucan, VOCs, mycotoxins)

Ergosterol and EPS are good indicators of total biomass (components in all fungal hyphae and spores, cannot identify species)

Not species specific; Nonfungal sources can affect Bglucan and VOC results; Methods not well developed for fungal VOCs or mycotoxins in indoor environments.

Concentration of chemical biomarker; Estimates of fungal biomass

Polymerase chain reaction (PCR) based technologies (i.e., genetic probes)

Accurate: Based on targeting species-specific sequences of DNA. Identifies both viable and nonviable fungal elements, but is prone to amplifying sample contaminants.

Species specific, including but not limited to Alternaria, Aspergillus, Cladosporium and Penicillium

Mold identification to the species level

No single method provides a complete assessment of the exposure hazard associated with an environmental sample. The quality of environmental microbiology laboratories performing analyses on samples for molds and other microbiological agents is monitored under an external peer review program sponsored by the American Industrial Hygiene Association (AIHA). This program, which includes the Environmental Microbiology Proficiency Analytical Testing (EMPAT) Program and the Environmental Microbiology Laboratory Accreditation Program (EMLAP), is specifically for labs identifying microorganisms commonly detected in air, fluids, and bulk samples during indoor studies. EMPAT is a performance evaluation program that uses proficiency testing to score participating laboratories. Proficiency in EMPAT is mandatory for labs seeking EMLAP accreditation. In the absence of standard methods, using laboratories with an accreditation, such as from the EMLAP, is particularly important. When a laboratory is accredited by AIHA, the laboratory and its clients have the assurance that the laboratory has met defined standards for performance based on examination of a variety of criteria. As of this writing, AIHA’s website lists 87 accredited laboratories nationwide, including five in Canada, that are accredited under AIHA’s EMLAP. Additional information on the EMPAT and EMLAP programs is available online at www.aiha.org….

Culture Methods and Spore Examination. The growth of fungal colonies on specially prepared nutrient media (culture) from spores contained in air or dust samples is a common method used to assess mold populations. Following culture, identification of fungal species can often be accomplished with a dissecting or light microscope via examination of colony morphology or spore bearing structures. Culture results can also be reported in terms of colony forming units (CFU) per m3, g, or cm2. The type of isolation media used to culture the fungal spores, however, can introduce substantial variability into the types and relative magnitudes of mold species that are cultured. Bias in culture measurements may be introduced because a highly nutritionally rich substrate favors the growth of fast-growing species, or because one species present in the sample may not compete well with another on the culture plate. For example, some genera such as Penicillium grow well and quickly on most media and thus may be over-represented in a culture sample, while others such as Stachybotrys grow slowly or not at all on commonly used substrates.

Many types of fungi are identifiable to the genus or species level, depending on the type of fungi sampled, via microscopic examination of spores in collected air and source samples. Spore counts can also be reported, typically in units of spores per m3, g, or cm2. This method is relatively inexpensive, but timeconsuming, and can give a general indication of atypical indoor mold growth.

Chemical Analyses. Methods using chemical analysis can be used to quantify total fungal loads (biomass), although, generally, these methods do not allow for identification of species. These methods can be based on chemical components (biomarkers) common to a particular group of organisms (e.g., ergosterol in the membranes of fungal hyphae and spores).. These markers can indicate the relative extent and presence of fungal growth, but do not measure fungal allergen exposure. Furthermore, their use in quantitating fungal exposure and relationship to human allergic disease is highly investigational. Results of dust analysis are typically expressed as concentration in units of weight of analyte per weight of settled dust. Results of air sample analysis are usually expressed volumetrically (e.g., micrograms/m3).

Mycotoxins. Methods currently available for detecting mycotoxins in environmental samples were designed for testing agricultural products and generally do not translate well to residential testing requirements (e.g., air samples with very low mycotoxin concentrations). Thin layer chromatography has been used to measure mycotoxins in some studies, although the usefulness of this technique is limited due to lack of sensitivity and susceptibility to interference. High performance liquid chromatography (HPLC) and gas chromatography with mass spectrometric detection (GC-MS) have also been used for mycotoxin quantification, although these techniques are also limited due to specialized laboratory requirements and associated expense. Various researchers have measured cell toxicity of particulate air samples and inferred the presence of mycotoxins. For example, Vesper used a protein synthesis inhibition assay to evaluate the toxicity of air particulate samples during a Stachybotrys chartarum remediation study. Protein synthesis inhibition is an activity characteristic of trichothecene mycotoxins typically produced by Stachybotrys. Field sample extracts were assayed for trichothecene toxicity by comparison to a known sample, with the results expressed as toxin equivalents per cubic meter of air. Mycotoxin analysis can be used to detect the presence of certain fungi in the environment, but, more commonly, mycotoxin levels are only measured after the fungal species has been identified.

Other Chemical Components of Fungi. Ergosterol, which is a component of fungal cell membranes, has been used as an index of fungal mass in house dust and air samples, and can be analyzed using gas chromatography with mass spectrometric detection. Ergosterol is not present in vascular plants, and therefore, in most indoor environments can be used as a specific measure of total fungal biomass. Ergosterol measurement has been applied in assessments of house dust and air, although, as with mycotoxin analysis, this highly specialized technique may have resource limitations for home assessments. There are about 15 volatile organic compounds (VOCs) produced by fungi that may also be used as markers of fungal growth, although some are also emitted by bacteria. VOCs can be collected on solid sorbents, extracted, and quantified using gas chromatography with mass spectrometric detection. Measurement of fungal VOCs may be particularly useful in some home assessments for detection of hidden mold growth because the compounds can permeate porous walls in buildings. However, the uncertainties currently associated with accuracy of these methods preclude using this approach for routine investigations. For example, significant questions remain regarding reliable “signature” VOCs for a particular fungus, and how to deal with the variability in VOCs produced under different conditions.

Immunoassays. To measure mold allergen levels in collected dust and air samples, enzymelinked immunosorbent assays (ELISAs, a specific type of immunoassay) have been developed for some indoor mold allergens and some mold components such as (1→3) ß-D-glucan and extracellular polysaccharides. An immunoassay is a laboratory technique that makes use of the specific binding between the antigen associated with an allergen and its homologous antibody in order to identify and quantify a substance in a sample. However, although immunoassays have been developed for some major fungal allergens to date, this technology is not as highly developed or well standardized as that for house dust mite, cat, or cockroach allergens. Currently, monoclonal antibody ELISAs for Alternaria (Alt a 1) and Aspergillus (Asp f 1) are available from commercial laboratories (e.g., see Indoor Biotechnologies website at www.inbio.com…).

(1→3) ß-D-glucan, a component of some fungal, bacteria and plant cell walls has also been used as a surrogate measure of total fungal biomass in house dust and air. To date, only a few laboratories test environmental samples for glucan, and its utility in large-scale epidemiologic studies is hampered by its large “within-home variation”. A new assay has been developed for (1→3, 1→6) β-D glucans which is more specific for fungi, but the glucan levels were not associated with decrements in lung function. Further research into the role of (1→3, 1→6) β-D glucans in is warranted.

Mold extracellular polysaccharides (EPS) have potential usefulness as fungal measures, as they are produced in mycelia cell walls under almost all growth conditions. Douwes examined the relationship between measured EPS from Aspergillus and Penicillium species (EPS-Asp/Pen) and culturable fungi, reported home dampness, and respiratory . EPS-Asp/Pen levels were significantly correlated with total culturable fungi, and levels in living room floor dust were positively associated with home dampness and respiratory symptoms. EPS can be measured using a specific enzyme inhibition assay (EIA), and has been studied in residential and occupation environments . The within-home variability appears to be smaller than that of (1→3) β-D glucans.

Genetic probes. Polymerase chain reaction (PCR) based technologies (i.e., genetic probes), unlike other non-culture methods, can be used to identify certain biological particles such as fungi to the species level. The technology is based on targeting short, species-specific sequences of DNA, and allows for the rapid identification and quantification of molds in a matter of hours, eliminating the need for plating and culturing or identifying and counting. Genetic probes could prove particularly useful in situations where fungi are not otherwise easily differentiated on the basis of morphology (e.g., Aspergillus and Penicillium) or where culture methods are not useful because spores have lost their viability.

Beneficial attributes of PCR are: (1) it is species specific, which may allow assessment for certain mold species suspected to be associated with health effects or ; (2) unlike live culture analysis, it reports non-viable as well as viable molds, which is important because non-viable molds are potentially allergenic; (3) it results in fewer “non-detects” than live culture analysis; (4) it is apparently more reliable than live culture analysis because not all species may grow on the media used and because fast-growing species may overtake the slowgrowing species; (5) it finds higher concentrations than culture analysis, sometimes by orders of magnitude; and (6) it is quicker and easier. In recent studies, the cited investigators found that results of PCR-analyzed settled-dust samples did not correlate with PCR-analyzed short-term air samples (five minutes or less). Also, PCR results did not correlate with culture-analysis results. Perhaps the main limitation of PCR is that it does not measure whether the mold is growing. The best established health effect of mold relates to the presence of mold growth.

In May of 2002, EPA’s Office of Research and Development was granted a patent for this technology as applied to describing mold DNA sequences. The technology is available for licensing on a non-exclusive basis by laboratories, indoor air quality specialists, or other environmental professionals. As a result, the technique is becoming more widely available as several commercial labs have begun offering analysis of indoor samples (preferably dust, but can be applied to any medium) using genetic probes. As of October 2005, 13 companies have a license to utilize the EPA technology (available online: www.epa.gov…).

Interpretation of Results

Methods for assessing human exposure to fungal allergens and mycotoxins are relatively poorly developed and interpretation of results is difficult. This is due, in part, to the fact that fungal allergens and toxins vary widely across mold species and because the traditional methods of mold population assessment (e.g., spore counts) do not have consistent relationships with levels of mold allergens or toxins. Furthermore, because viable mold measures do not include particles that are not culturable (non-viable spores or non-reproducing vegetative fragments) but that may have toxic or allergenic properties, investigations of moldaffected houses that focus only on assessing the number of culturable organisms may underestimate actual allergenic or toxic potential. Conversely, total measures of a fungal component (e.g., ergosterol or glucan) in a sample do not allow for identification of mold species, or provide information about the biologically active portion of the sample. Therefore, neither measure provides a complete assessment of the potential allergen or mycotoxin exposure hazard associated with an environmental sample. The accuracy of substituting measures of exposure to fungi for exposure to fungal allergens or toxins has not been determined, and direct measurement of allergens and toxins is limited by the current development and standardization of immunoassays for specific allergens and reliable, affordable techniques for mycotoxin analysis.

Further complicating the exposure assessment is variability associated with the collection of samples. The accuracy of quantifying air samples is complicated by large variations in airborne concentrations from room to room and temporally over relatively short periods of time, as well as outdoor concentrations with season. The release of molds from carpets and walls or other surfaces has also been cited as an important factor in introducing variability into the magnitude and nature of indoor air spora collected. In addition, due to the ubiquitous presence of mold spores in the outdoor environment (often in concentrations far higher than indoors), it can be difficult to establish the presence of indoor mold growth using air sampling.

Dust sampling for molds is sometimes used to circumvent this temporal variability, although dust samples sometimes show differences in the relative abundance and types of mold in comparison to air samples.

Professional inspectors frequently compare the types and levels of fungal organisms detected in various environments, e.g., outdoors vs. indoors, as a way of interpreting microbiological results. The qualitative diversity of airborne fungi outdoors should be similar to that measured indoors in the absence of mold contamination. Conversely, if one or more types of fungi dominates the indoor environment but is not detected outdoors, the sampled building may have a moisture problem and fungal contamination. However, that may not always be true. Spores of some outdoor fungi may infiltrate a house and persist under normal conditions long after outdoor sources are no longer present. In addition, levels of spore counts can vary by region and season. Another common indicator of indoor moisture problems is the consistent presence of fungi such as Stachybotrys chartarum, Aspergillus versicolor, or various Penicillium species at levels well above background concentrations.

Using mold specific quantitative polymerase chain reaction (MSQPCR), certain molds, labeled Group I molds, are found in higher concentrations in water-damaged homes than in other homes, while other molds (labeled Group II molds) are found in all homes. Group I molds included, but were not limited to: Apergillus restrictus, Penicillium brevicompactum, Aspergillus niger, Paecilomyes variotii, Aspergillus ochraceus, and Trichoderma viride. One way this information may be useful is in identifying homes that have suffered water damage but do not display easily identifiable signs of it. Another may be in narrowing the list of molds for which PCR analysis is necessary. Also, the investigators compared PCR-analyzed dust sample results from water-damaged homes of asthmatic children with those from control-group homes and found (1) that only Group I molds had higher concentrations in the water-damaged, asthmatic-occupied homes compared to the control homes, and (2) that certain Group I mold species had significantly higher concentrations. The authors concluded that “if Group I molds are discovered, water-damaged remediation and mold removal might be considered as part of the total prevention plan in an asthmatic child’s home.”

Finally, there is the issue of comparison of results to standards that indicate potential hazard. The major limitations with existing quantitative guidelines for fungi are the lack of human dose/response data, reliance on short term grab samples analyzed only by culture methods, and the lack of standardized protocols for data collection, analysis, and interpretation. For example,a review of peer-reviewed literature through 1995 identified nine population based studies that examined the relationship between allergy and the presence of fungi in the home environment. All of the studies included quantitative measures of fungal presence in either air or dust. Evaluation of the studies indicated that although the existence of positive associations between fungal levels and health outcomes was supported in the literature at that time, inconsistency and inadequate validation of the measures used to evaluate exposure and health effects made determination of guidelines for fungi in home environments based on health risk assessment impossible.

The Institute of Medicine recommends that the evaluation of testing results “should, whenever possible, be based on:

  • Comparison of exposure data with background concentrations or, better, a comparison of exposures between symptomatic and non-symptomatic subjects.
  • Multiple samples, because space-time variability in the environment is high.
  • Detailed information about sampling and analytic procedures (including quality control) and knowledge of the potential problems associated with those procedures.”

In general, types of molds found inside buildings without mold problems should be similar to those found outdoors, and concentrations should also be similar inside and out.

Currently, there are no standard numerical guidelines for assessing whether there is a mold contamination problem in an area. In the U.S., there are no EPA regulations or standards for airborne mold contaminants. Various governmental and private organizations have, however, proposed guidance on the interpretation of fungal measures of environmental media in indoor environments (quantitative limits for fungal concentrations).

Legislators in more than a dozen states and one federal legislator have introduced bills directed at the indoor mold problem. Legislation has been enacted in Arizona and California to study and review mold contamination of indoor environments. States, such as Texas, Louisiana, and California, have enacted legislation requiring the licensing of contractors conducting mold abatement activities.

Organizations that have produced guidelines on mold prevention and/or remediation include the ACGIH, the U.S. Occupational Safety & Health Organization (OSHA), the American Industrial Hygiene Association (AIHA), the Canada Mortgage and Housing Corporation (CMHC), the Commission of the European Communities (CEC), and the World Health Organization (WHO), as well as numerous smaller and/or local organizations like the New York Department of Health.

Recommendations vary widely, with quantitative standards/ guidelines ranging from less than 100 CFU per m3 to greater than 1000 CFU per m3 as the upper limit for airborne fungi in non-contaminated indoor environments. Indoor spore counts equal to or greater than 1000/m3 and colony counts on the order of 1000 to 10,000 CFU per m3 likely represent indoor fungal contamination. In a review article, it was concluded that, “it seems reasonable to expect that total airborne spore counts attributable to indoor sources greater than 1,000 spores/m3 indicate a concern and those greater than 10,000 spores/m3 indicate a definite problem.”

Such guidelines based on total spore counts are only rough indicators, however. Other factors in addition to indoor spore counts should be considered. For example, the University of Minnesota Department of Environmental Health and Safety recommends consideration of several factors in addition to total spore counts when attempting to assess the severity of a mold contamination problem, including: the number of fungi indoors relative to outdoors, whether the fungi are allergenic or toxic, if the area is likely to be disturbed, whether there is or was a source of water or high relative humidity, if people are occupying the contaminated area or have contact with air from the location, and, whether there are immune compromised individuals or individuals with elevated sensitivity to molds in the area.

Given evidence that young children may be especially vulnerable to certain mycotoxins and in view of the potential severity or diseases associated with mycotoxin exposure, some organizations support a more precautionary approach to limiting mold exposure. For example, the American Academy of Pediatrics recommends that infants under 1 year of age are not exposed at all to chronically moldy, water-damaged environments.