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Dr. Jackson Kung’u (PhD)- Mold Specialist.
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Home | Indoor Air Quality

Indoor Air Quality

Air Pollution and Childhood Respiratory Allergies

A study in the United States suggests that childhood respiratory allergies, which contribute to missed school days and other activity limitations, have increased in recent years, possibly due to environmental factors including air pollution.

The study examined the associations between the reporting of respiratory allergies or hay fever and annual average exposure to particulate matter ? 2.5 µm in diameter (PM2.5), PM ? 10 µm in diameter, sulfur dioxide, and nitrogen dioxide and summer exposure to ozone.

Results showed that increased respiratory allergies or hay fever was associated with increased summer ozone levels and increased PM2.5.

The full version of this article on air pollution and respiratory allergies is available for free in HTML or PDF formats.

Mould Growth

Dampness and mould growth are recognised as major problems affecting a
significant proportion of houses in the North America. Apart from health problems associated with dampness and mould growth, wood decay is also significant problem.

Mould growth in houses is unsightly. But most important, there is considerable evidence to support the view that mouldy housing has a detrimental effect on the health of occupants residing in such environments. This is a cause for concern, considering that many individuals spend most of their time indoors especially during winter. Respiratory problems and allergic reactions are the common health problems associated with mould. Generally, indoor moulds affect people through inhalation of airborne spores. High levels of airborne spores may occur due to growth of mould on walls and furnishings.

Requirements For Mould Growth
Requirements for mould growth in buildings include:

  • nutrients: found in the materials which make up or are deposited on indoor surfaces
  • oxygen. Like most other living things, common indoor moulds require air (oxygen) for growth.
  • suitable temperature (around 25 degrees Celcius)
  • moisture: the relative humidity (RH) at a surface is the best indicator of moisture available for mould growth.

In most cases, mould growth in homes is caused by condensation. Condensation in buildings occurs where moist air meets a cold surface. For example if air meets cold water pipes, window glasses or other cold surfaces and is cooled below its dew point temperature, the vapour close to the surface becomes saturated and excess vapour turns to liquid.

There are two types of condensation:

  • Surface condensation. Surface condensation occurs at the surface of the material.
  • Interstitial condensation. Interstitial condensation occurs inside a material. If vapour passes through porous building materials and the dew point temperature occurs within that material then the vapour will condense. Interstitial condensation is responsible for mould growth in building envelopes.

The major factors influencing condensation in buildings include:

  • Moisture production from sources inside the building. Moisture sources include respiration, cooking, washing and drying of clothes.
  • Air and structural temperatures
  • Ventilation. Proper ventilation helps to reduce condensation. 

Air Sampling

Air sampling is one of the tools used in mold investigation. The primary objective of mold investigation is to determine the extent of mold growth and subsequently its potential effect on indoor air quality. Air sampling helps to termine whether or not visible mold growth has degraded indoor air quality. It may also help to detect the presence of hidden mold growth. Some investigators use air sampling to determine the effectiveness of remediation. This is achieved by taking air samples before and after remediation.

Interpretation of Air Sample Results

Interpretation of air sample results can at times be very difficult. However, having a clear objective, prior to air sampling can make results interpretation easy.

As often stated, fungal spores are present in virtually all environments including indoors. Therefore, presence of some fungal spores indoors is considered normal. Generally, for well maintained mechanically ventilated buildings, airborne spores should be qualitatively similar but quantitatively lower than the outdoors. For naturally ventilated buildings, the airborne spore concentration and their diversity in the indoor air is similar to that of outdoor air.

For both mechanically and naturally ventilated buildings, presence of airborne spores of molds usually found in indoors, in numbers significantly higher than those of outdoors, is an indication of indoors sources of mold growth.

Interpretation of air samples collected primarily to determine whether there was mold growth indoors is therefore based on a comparison of concentrations and categories of spores in outdoor and indoor samples. Significant counts of species present indoors and absent (or in lower counts) outdoors suggest the source for those species is indoors. In the absence of any visible mold growth, further investigation would be required to determine the source and extent of any hidden mold growth.

It’s important to note that the conclusion derived from air sample results should always be backed by visual inspection and the building history.

Spore Trapping And Counting

Spore trapping and counting is extensively used in crop protection to:

  • determine the concentration of pathogenic spores carried by wind
  • forecast a disease outbreak
  • get facts about periodicity of spore showers on crops as one of several infection requirements
  • determine correct timing of protectant sprays and other control measures. 

Spore trapping and counting also provide useful information about airborne spores that cause respiratory allergies such as rhinitis, asthma, and farmers’ lung disease. In building environments, spore counting and trapping can be used for detecting dry rot or other hidden mould. Although there are no acceptable levels of airborne fungal concentration in indoor environment, spore trapping and counting can also help in determining if occupants were potentially exposed to high levels of allergenic fungal spores.

How to collect bacteria samples

Various methods can be used to collect bacteria samples. The procedure will depend on what is being sampled and the type of data required. One may may be interested in a specific bacterium, in which case the method of sampling should be suitable for the recovery of that specific organism.

Sampling from surfaces

Sampling of bacteria from surfaces is usually performed using sterile swabs. Results from this test could be as simple as presence or absense of the bacterium of interest for example E. coli or Legionella. The test could also be detailed to include the amount of the bacterium present. It’s important to know how to collect samples for these different levels of analysis. If quantification is required, it’s important to swab a known surface area, for example 100 cm square. In this case the results would be expressed as “Number of colony forming units” per unit area.

Sampling bacteria samples from the air

To sample bacteria from the air, the air is impacted on some suitable growth media.   The media to use will be determined by the type of bacteria being sampled for. If one is interested on a specific type of bacterium then a media that is selective for that bacterium should be used. To sample for the general population of bacteria in the air, then a media that can support the growth of many types of bacteria such as  tryptic soy agar (TSA) should be used. Results are given as colony forming units per cubic meter of air.

Sampling for bacteria from water

Testing water for bacteria involves collecting a water sample in a sterile container and sending it to the lab for testing. The test results may just indicate the presence/absence of the bacterium of interest or may be detailed to include the amount present in terms of colony forming units per mililitre.