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Indoor Air Quality – Testing For Mold

The health effects of poor indoor air quality are dependent upon several factors including the type of contaminant, concentration, duration of exposure, and individual susceptibility. Indoor air quality can be compromised by a number of contaminants including mold.

Assessing the status of Indoor Air Quality

The status of indoor air quality is assessed by measuring the levels of contaminants indoors. These Contaminants include:
1. Biological contaminants such as mold, bacteria, viruses, etc.
2. Chemical contaminants such as formaldehyde.

This article is focusing on mold as an indoor air contaminant. Contamination of air by mold spores can easily be determined by air testing.

Testing Air for Mold

There are two methods commonly used to test air for mold. These are:
1. Viable or culturing air testing

2. Non-viable or total spore count air testing.

Assessing the Status of Indoor Air Quality by Viable Air Testing.

For viable air testing, air sampling can be conducted in two ways. The first method uses settle plates. This technique involves opening agar plates inside the area being tested and leaving them open for half an hour or more. Airborne mold spores and hyphal fragments settle by gravity onto the agar plates. Any viable spores or hyphal fragments would then grow into visible colonies that can be counted and identified. A high colony count is an indication of poor indoor air quality. This method is cheap since all it requires is agar plates. However, it’s not an efficient way of testing for mold spores in the air. The second method uses an air sampling pump. In this case, air is impacted onto the agar plates by a pump. This method is more efficient since it doesn’t depend on free-falling of spores into the agar. Viable testing for mold has a big disadvantage in that it only detects viable spores/hyphal fragments yet even dead spores are a health hazard.

Assessing the status of Indoor Air Quality by Non-viable Air Testing.

Non-viable air testing samples are collected by impacting air on an inert surface coated with an adhesive. Most of the spores and other particulate in air get stuck on the adhesive surface. The samples are then tested by direct microscopy. The spores and/or other particulates are enumerated and identified. The results are reported as spores per cubic meter of air. This method of sampling requires an air sampling pump such as BioPump and air sampling cassettes such as Air-O-Cell or allergencos. The major advantage of this method is that both viable and non-viable airborne spores and other particulates are enumerated thus giving us a better idea of the status of the indoor air quality.

Evaluating Mold Contamination In A Building

Question: If I want to evaluate mold contamination in a building, should I use air sampling of molds or ergosterol in dust?

Answer: The method to use to evaluate mold contamination in a building depends on the objective of the investigation and the resources available for the investigation. First let’s see what kind of data each method yields.
  • Air sampling For Mold

There are 2 methods currently used for sampling for airborne spores. These are air sampling for total fungal spore count (also referred to as nonviable analysis) and air sampling for culturable airborne fungal propagules (commonly referred to as viable analysis). The data obtained by the nonviable analysis are number of spores (or fungal elements if you include other fungal structures) per cubic meter of air. Viable analysis gives colony forming units (CFU) per cubic meter of air. Each of these 2 methods has it’s advantages and disadvantages. For example since non-viable spore analysis depends on the morphology and sizes of spores alone, identification is limited to only a few groups of fungi that have spores with unique characteristic. A vast majority of spores are reported as unidentified since it’s difficult to tell which group of fungi produced them.

The major advantage of nonviable analysis is that since the analysis does not depend on the viability of the spores, all spores present in the sample can be counted whether they are dead or alive. This brings us to the major disadvantage of analysis. If 95% of fungal structures contaminating the air were dead, this method would detected only 5% of the contamination.

The advantage of culturable sampling is that the recovered molds could be identified to species level. This is important because some important characteristics such as production of mycotoxins or pathogenicity are species (and sometimes strain) specific.

Given the advantages and disadvantages of the 2 air sampling methods, an investigator has to decide which method to use. In some cases, using a combination of the 2 methods is recommended.

  • Dust Sampling For Ergosterol

Ergosterol is the major sterol in the cell membranes of fungi (yeasts and mold). It’s present in mycelia, spores, and vegetative cells. There is a strong correlation between ergosterol content and fungal dry mass. Ergosterol content has, therefore, been widely used as an estimate of fungal biomass in various environments, such as soil and aquatic systems. Ergosterol measurements have been proposed as a new method for determination of total fungal biomass in investigations of indoor environments. One limitation about this method is that the amount of ergosterol in fungal tissue is not constant and varies with fungal species, age of the culture, developmental stage (growth phase, hyphal formation, and sporulation), and growth conditions (growth media, pH, and temperature). Another limitation is that ergosterol measurements cannot be used to determine the species present in the dust sample since it’s not genera or species specific. The method is currently not widely used and very few commercial laboratories have the capability to analyze for ergosterol in dust.

A Useful Ergosterol Reference

ANNA-LIISA PASANEN, KATI YLI-PIETILÄ , PERTTI PASANEN, PENTTI KALLIOKOSKI, AND JUHANI TARHANEN (1999). Ergosterol Content in Various Fungal Species and Biocontaminated Building Materials. APPLIED AND ENVIRONMENTAL MICROBIOLOGY, Vol. 65, No. 1: 138–142.

Bacteria As Contaminants In Indoor Environments

People spend around 80 and 90% of their time in indoor environments (office, school, home, etc) and there is increased awareness of the potential health effects of indoor biological contaminants such as bacteria. Therefore, when considering work or indoor living conditions, the air quality requires special attention.

In indoor environments, biological contaminants are often found in areas that provide conducive conditions for microbial growth. These include damp or wet areas such as cooling coils, humidifiers, condensate pans, draperies, bedding, carpet, and other areas where dust collects.

Bacteria are an important component of indoor biological contaminants. Some of them are pathogenic (that’s they are capable of causing disease) and are involved in respiratory diseases. If the environmental and nutritional conditions are favourable bacteria can colonize and grow on many surfaces (including standing water) from where they and their by-products can become airborne. A number of diverse activities can result in the dispersion and generation of bacterial aerosols indoors, for example, the operation of heating-ventilation-air conditioning systems, hot water systems and water spray devices.

Health Effects Associated With Indoor Bacteria
There are several health effects associated with exposures to bacterial aerosols. Some of them include irritative and nonspecific respiratory symptoms, respiratory infections, and allergic reactions such as alveolitis and chronic bronchitis.

Some of the infectious bacteria include Mycobacterium tuberculosis, Legionella pneumophila, Bacillus anthracis. These bacteria cause pulmonary tuberculosis,  legionellosis (Legionnaire’s disease) and anthrax respectively. Infection is primarily through inhalation.

Bacteria As Causes Of  Bioderioration
Bacteria are rarely thought of as biodeterioration agents. However, they are involved in biodeterioration of various types of materials. Bacillus sp, Nitrosomonas sp, Nocardia sp and Streptomyces are involved in biodeterioration of diverse materials in several regions. They cause physical damage and some are capable of producing acids that cause biochemical deterioration.

Conclusion
In general, several microorganisms including bacteria are present in indoor environments. They can contaminate indoor air and pose health risks especially when certain species are present or when they are in high numbers. Apart from the health effects microorganisms have the ability to cause damage to materials they are growing on.

Contact Information

Dr. Jackson Kung'u, PhD.
Phone: 905-290-9101
Fax: 905-290-0499