World Health Organisation (WHO) has long recognised indoor air quality as an important health determinant. Most of us spend majority of time indoors whether it is in the workplace or at home and therefore the quality of the indoor air plays in important role in our health. It is estimated that we spend up to 90% of our time indoors. Naturally our major exposure source is the indoor environment itself which can be polluted by many biological and non-biological pollutants. The major sources of indoor pollutions are the chemical compound released from modern building materials, combustion gasses from heating systems and fireplaces, chemical fumes from paints, solvent, deodorants, air fresheners etc, gasses such as radon and methane seeping through the foundations of the building, cleaning products and outdoor pollutants.
Indoor spaces can be contaminated by a whole range of biological contaminants from which the most prevalent are bacteria followed by fungi, protozoa, algae, pollen from outdoors, house dust components (skin cells, fibres, mineral particles etc), microbial organism such as dust mites, insects (ant, cockroaches etc) and pet related allergens. Microbiological grown indoors is essentially controlled by the availability of water and nutrients, also other factors may play role they are not significant.
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WHO reports that more than 50% of buildings in northern Europe are affected by moisture at some point in the life-cycle. Moisture related problems are most likely cause lying behind steadily increasing rate of asthma affecting children. The prevalence of asthma in children reaches and in some cases exceeds 20% in some of the European counties. The highest prevalence of asthma symptoms in children aged 6–7 years (>20%) and 13–14 years (>25%) were found in Ireland and the United Kingdom. The lowest asthma rates for both age groups were found in Albania (<5%).
Biological contamination of indoor areas is almost exclusively linked to sources of moisture. Although temporary dampness may not usually present a problem prevalent and persistent moisture leads rapidly to the growth of micro-organisms. Besides from the acceleration of microbial growth excessive moisture in building materials leads to chemical and physical degradation resulting in emissions (off gassing) of organic and inorganic pollutants while at the same time causes physical damage to the structures.
Health risk to occupants is not only cause by microorganism directly but also by production of various allergens such as mycotoxins, betaglucans, endotoxins and microbial volatile organic compounds (MVOC).
WHO has carried out a review of scientific evidence on health effects of microbial contamination in indoor spaces was conducted in three sections: (1) epidemiological, (2) toxicological and (3) clinical studies.
- The reviewed epidemiological studies are based on large human populations and realistic, existing exposure levels however accurate data interpretation is a very challenging process.
- The research into toxicological studies offers more accurate results because of better control of exposure levels and microorganisms involved. But toxicological studies are limited to use of in-vitro studies involving non human organism and unrealistically high exposure levels in comparison to typical indoor situations.
- One of the most important aspects in evaluating the health risk from indoor organisms remain clinical studies based on evidence where data on human patients is studied in relationship with their exposures and, more importantly, exposure reductions achieved by renovation is needed. The clinical evidence collected by the WHO working group shows that exposures to moulds and other dampness-related microbial agents increase also the risk of rare conditions, such as hypersensitivity pneumonitis/allergic alveolitis, chronic rhinosinusitis and allergic fungal sinusitis (WHO 2009b).
“Based on the systematic review of the scientific evidence, the WHO working group concluded in October 2007 in Bonn that there is sufficient epidemiological evidence from studies in different countries and climatic conditions showing that occupants of buildings affected by dampness or mould, both homes and public buildings, are at increased risk of experiencing respiratory symptoms, respiratory infections and exacerbations of asthma (WHO, 2008a). Non-comprehensive evidence suggests an increased risk of developing allergic rhinitis and asthma. “
Although the WHO Guidelines are neither standards nor legally binding criteria, they are designed to offer guidance in reducing the health impacts of air pollution based on expert evaluation of current scientific evidence. They are intended to be relevant to the diverse conditions of all WHO regions, and to support a broad range of policy options for air quality management.
The guidelines are intended to inform policy-makers and to provide appropriate targets for a broad range of policy options for air quality management in different parts of the world.
By Tomas Gabor
