Mycological Aspects of Indoor Air Quality

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Mycological Aspects of Indoor Air Quality

Fungal interpretation

Initially a walk through evaluation is made to attempt to identify potential

sources of fungal amplification. Fungi need a source of moisture, a source

of carbon, and proper temperature. Because fungi grow well at room

temperature, control is achieved through adequate filtration and control of

moisture. Areas which have poor filtration and a source of moisture are

likely to be sources for fungal amplification.

A walk through investigation will look for possible sources for fungal

amplification. These include: visible filamentous fungal growth, water

damage, poor housekeeping, poor ventilation, and inadequate filtration.

Bulk samples are taken from the suspect material. These may be swab samples,

bulk dilution samples, or Rodac plate samples. For duct insulation, the

following numbers are rough rules of thumb used to assess fungal

contamination using a dilution sample.

Concentration Qualitative Assessment of Contamination

Colony forming units/gram

less than 10,000 low

10,000 to 100,000 medium

100,000 to 1,000,000 medium to heavy

>1,000,000 heavy

The organisms present in the sample have a bearing on whether or not an area

is considered a problem.

Interpretation of Results

Attempts to link bulk sources to airborne concentrations of fungal organisms

are often problematic. The levels of fungal organisms vary by several orders

of magnitude during the course of a day due to activity levels in an area

and other factors such as fluctuations in temperature or humidity which

cause the release of spores. The spores may no longer be viable and though

allergenic and possibly toxigenic it will not grow on any media. Rapidly

growing fungi may crowd out slower growing fungi. The wrong media may be

used for viable sampling.

There are at present no strict numerical guidelines which are appropriate

for assessing whether the contamination in an area is acceptable or not.

Further investigation of contamination sources is warranted in the following

circumstances.

Total indoor counts are greater than outdoor fungal counts (compare indoor

and outdoor ratios). This comparison is not valid when the outdoor sample

was taken during or immediately after precipitation. It probably is not

valid during some winter months where outdoor fungal counts are usually

below that indoors.

Comparison of indoor and outdoor levels of fungal organisms show one of the

following:

Organisms are present in the indoor sample and not in the outdoor sample.

The predominant organism found in the indoor sample is different than the

predominant organism in the outdoor sample.

A monoculture of an organism is found in the indoor sample. The organism may

be present in a mixed outdoor sample. It may be absent from samples taken in

other areas of the building.

If the criteria in #2 are met and the organism is capable of producing a

carcinogen (e.g., aflatoxin produced by Aspergillus flavus). The spores may

be toxic by inhalation (e.g., satratoxin H in the case of Stachybotrys

atra). The production of the toxin is very dependent on the source of

nutrition for the organism.

In some cases, to comply with the American's With Disabilities Act, efforts

will be taken to further reduce levels even though they are not identified

as a problem in section 1, 2 and 3. This would be the case where an

individual has been diagnosed by a physician to be allergic to a specific

fungal organism. Efforts may then be made to further reduce exposure through

increase filtration of the air. There are often problems linking an

environmental exposure to an allergy test. The antigenic material produced

by a fungus of a particular genus will vary according to species or a strain

within the species and vary with the source of nutrition for the organism.

Other factors also influence the antigenicity of the fungal spore. Thus,

establishing a direct link between environmental exposure and the results of

an allergy test is often problematic. Removal of the person from the area is

often the most successful approach.

An opportunistic fungal pathogen is found in an area which houses

individuals who are immune compromised.

A

ggressive sampling and sampling of suspected sources of fungal organisms is

often warranted. The amount of fungi present in an air sample is highly

variable. Changes in airflow, humidity, light level and temperature can all

trigger a spore release. A single air sample will often underestimate the

fungal contamination in the air.

A general rule of thumb:

If the numbers are high (air or bulk)

Fungi indoors are different from outdoors or noncomplaint controls

The fungi are allergenic or toxic,

The area is likely to be disturbed,

There is or was a source of water or high relative humidity, and

There is or was a source of water or high relative humidity, and

People are occupying this area or have contact with air from this location.

There are immune compromised individuals or individuals with elevated

sensitivity to molds - there may be a problem.

Note: If A through G are not true, then there probably is not a fungal

related problem.

The preceding guidelines are not meant to be all inclusive but should aide

in interpreting the sampling results. The findings listed for each group,

genera or species represent a document in progress.

N. Carlson 9/92; Rev. 4/93, 7/93, 9/93, 1/94, 2/94,2/95,4/95

last updated 4-29-96