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Indoor Air Quality

10. Conclusions and recommendations

    The SCHER opinion states:


    Indoor environment is a complex issue in terms of toxicology and health risk assessment. There are many different types of pollutants which may give rise to combined effects. The exposed population is the general public including vulnerable groups. Many different factors influence air quality, e.g. ventilation, cleaning conditions, properties of buildings, products used in house-holds, cultural habits, climate, outdoor air etc. Thus, large variations in indoor environments can be expected across the EU.

    The SCHER considers that the health risk assessment of the pollutants in indoor environments should be done according to the principles used in the EU for risk assessment of chemicals as this is an evidence based approach. Those principles should be applied on the data available and the specific features related to indoor environment taken into account. The risk assessment paradigm should be used flexibly, taking into account that complaints and diseases related to indoor exposures may have a complex cause-effect relationship.

    The SCHER considers that the data base for indoor air risk assessment is in general limited. Frequently, there are more data available for risk assessment of “classical” indoor air pollutants such, as organic pollutants as compared to particles and microbes. Especially, more data on exposure, in quantitative terms, are required. Available dose-response data seldom cover vulnerable groups. The SCHER has identified several gaps of knowledge, presented in answer to Question 2, which should be addressed by European-wide multidisciplinary research.

    As to single known compounds, SCHER considers carbon monoxide, formaldehyde, benzene, nitrogen oxides and naphthalene to be compounds of concern because they have caused adverse health effects as indoor pollutants or have a high potential to cause them. Environmental tobacco smoke, radon, lead and organophosphates are also of concern. For most other pollutants the data available are yet limited for risk assessment as indoor air pollutants.

    Consumer products, one source of chemicals in indoor environment, emit mostly volatile organic compounds. Lack of data on true exposure for emissions in consumer products has hampered evaluation of the associations with possible health effects most of which are also caused by other factors. The recent data suggest that some of the emitted products may react further in air and on surfaces producing secondary products, including fine and ultrafine particles. The health effects of those reaction products are poorly known.

    Association of adverse health effects with dampness, water damage and mould in buildings is repeatedly shown in epidemiological studies but the causative factors and all health effects and consequences are not known. This is potentially a serious indoor air problem in EU. More research is needed to understand the associations to health effects and seriousness of the problem in EU countries.

    Combined and mixture effects of indoor air pollutants can so far only rarely be assessed. There are not enough data on combined effects and also the methodology is limited. The SCHER recommends the production of data in order to make the evaluation of combined effects of indoor air pollutants feasible. In addition, the SCHER recommends taking into account routes of exposure other than inhalation (dermal, oral) in risk assessment and contribution of indoor environment exposure to total exposure from other sources. The risk assessment should be transparent to allow the evaluation of its strengths and weaknesses.

    The SCHER recommends the development of health based guideline values for key pollutants and other practical guidance in general to help risk management. The SCHER also recommends that practical experiences are collected and systematized to establish evidence-based risk assessment approaches. Such examples help to solve similar type problems and decrease the overlapping risk assessment.


    Indoor air may contain over 900 chemicals, particles, and biological materials with potential health effects. Since their concentrations are usually higher than outdoors and people spend more time indoors than outdoors, the SCHER recommends that any studies to correlate outdoor air concentration with health effects need to consider the impact of indoor exposure.

    The composition and concentrations of the different components in indoor air vary widely and are influenced by human activities. Since it is not feasible to regulate all possible scenarios, prevention from possible health effects and protection of sensitive populations is best achieved by reducing exposure. As a consequence the SCHER recommends that all relevant sources that are known to contribute should be evaluated. Such sources include tobacco smoke, any open fires including candles, building materials, furniture, pets and pests, use of household products, as well as conditions that lead to the growth of moulds. Constructers, maintenance personnel and inhabitants should also be aware that appropriate humidity avoids annoyances and sufficient air exchange reduces accumulation of pollutants.

    Source & ©: SCHER,  Opinion on risk assessment on indoor air quality (2007),
    4. Conclusion &5. General Conclusions and recommendations, p.21-22

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