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Indoor Air Quality

9. What kind of research on indoor air quality is needed?

  • 9.1 How much information on indoor air quality is available today?
  • 9.2 What questions about human exposure need to be answered?
  • 9.3 What research is needed regarding health effects of indoor air pollutants?
  • 9.4 Are existing measurement standards for indoor air quality adequate?

9.1 How much information on indoor air quality is available today?

The SCHER opinion states:

3.2. Question 2

To provide a basis for assessment of risks to human health from indoor air quality, and a sound scientific basis for the development and implementation of policies, the SCHER is asked to identify the adequacy of current information and data requirements for filling-in gaps on aspects such as exposure/effect and dose/response relationships, existing measurement standards and gaps in knowledge which will help to guide further research and monitoring efforts.

Answer to Question 2

3.2.1. Adequacy of current information

The SCHER notes that, taking into account all the variability and complexity in the indoor environment, the data for risk assessment are scarce and often insufficient. Recently, the THADE-project (THADE-report, 2004) has summarised several aspects on indoor air pollution in dwellings in Europe, including policies and actions taken in different countries. The evaluation indicates large differences between countries, in all aspects, and also lack of relevant data, both in general and member state specific. The PINCHE-project (PINCHE 2006) on children’s health and environment prioritizes risk factors for environmental stressors and gives policy recommendations for research to air pollutants including indoor air.

In relation to exposure, information on concentrations of indoor air pollutants in Europe and information on determinants of personal exposure (e.g. EXPOLIS, 1999, German Environment Surveys (GerES I, GerES II, GerES III), German study on Indoor Factors and Genetics (INGA), the National survey of air pollutants in English homes) is available. These data give indications on the levels for some indoor pollutants and help to identify the compounds with highest concentrations and of highest concern.

Most of this information is on “classical” pollutants, such as carbon monoxide, nitrogen oxide, radon, asbestos, and organic compounds such as VOCs (INDEX 2005). Effects and risks for most of them are known to the extent that strategies to mitigate the problems can be created. But also new sources have emerged for “old” pollutants (e.g. VOCs in air fresheners, lead from candle wicks) and some of them (e.g. terpenes) may react to produce secondary products whose effects are poorly defined (Weschler et al., 2006, Wolkoff et al., 2006a).

Due to privacy of the indoor spaces (e.g. homes), enforceable indoor air standards are not preferred. Their systematic surveillance monitoring would be difficult. Instead, the SCHER supports the development of health-based guideline values and other guidance for key pollutants (as identified in this opinion) to help risk assessment and management. In this context, indicators other than concentrations of the pollutants (i.e. ventilation rate - and CO2 as a related marker-, general cleanliness, signs of dampness) may also be applicable for monitoring. At present, outdoor air quality is monitored for some pollutants (e.g., PM10, nitrogen oxide, ozone) but the data cannot predict the concentration in buildings, and replace measurement, because several local factors contribute to the access of pollutants indoors (e.g. tightness of the building). The variability in indoor levels has been shown for both organic compounds (e.g. Ilgen et al., 2001, Hodgson et al., 2003, Saarela et al., 2003, Gilbert et al. 2005) and particles (e.g. Lazaridis et al., 2006).

Source & ©: SCHER,  Opinion on risk assessment on indoor air quality (2007),
3.2. Question 2, p.14

9.2 What questions about human exposure need to be answered?

The SCHER opinion states:

3.2.2. Data requirements and gaps of knowledge

The SCHER has identified the following requirements for a more comprehensive and reliable health risk assessment of indoor air pollution. The needs range from broad and general to specific ones.

The data needs and gaps of knowledge are compiled into two groups, exposure assessment and health effects assessment. The SCHER considers that the items indicated by “++” should have the highest priority.

Data requirements and gaps in knowledge related primarily to identification and exposure to pollutants:

Need for compilation of existing data:

  • Comprehensive review of the existing data on the indoor air pollutants; definition of the major pollutants and their concentrations range in each Member State of EU, and set up of a pan European database (++). The database could be a part of a relevant existing information source. The process would compile the existing information on indoor pollutants, including allergens, as background for future work, and would facilitate the use of the data at an EU level, to identify differences among member states and data gaps. This information could drive both possible regular monitoring program and future research.
  • Collection and systemization of practical experiences to establish evidence- based risk assessment approaches. Such examples would help to solve similar type problems and decrease the overlapping risk assessment.

Need for more research

  • Exposure patterns (short and long term in different environments) to indoor air pollutants, in quantitative terms, and identification of the most relevant exposure indicators (++). Description of typical exposure patterns would help to assess the typical levels and variability of exposure.
  • Source apportionment of the pollutants in indoor environment, including ambient air, preferably in quantitative terms (++). Identification of the main sources would help their mitigation.
  • Emissions of chemicals from consumer products (++). More data on levels of the emissions in realistic use situations is needed in view of the large part of population handling such products.
  • Existing indoor source and transport/fate models should be identified, evaluated, validated and harmonized (+). Taxonomy of sources consistent data sharing should also be developed.
  • Information on harmful emissions in water damaged buildings, including compounds from decomposing building material, contributing to toxicity (++). See also a detailed answer to question 4c.
  • Evaluation of potentially harmful emissions from indoor combustion processes (e.g. halogenated dioxins). Low burning temperature may favour production of halogenated dioxins.

Source & ©: SCHER,  Opinion on risk assessment on indoor air quality (2007),
3.2.2. Data requirements and gaps of knowledge, p.15

9.3 What research is needed regarding health effects of indoor air pollutants?

The SCHER opinion states:

Data requirements and gaps in knowledge related primarily to health effects of indoor air pollutants:

Need for more research:

  • Effects due to combined exposure to indoor air pollutants and objective methods for their evaluation, including development of validated modelling tools (++).
  • Adverse health effects of microbes and bioaerosols present in indoor air, especially other than respiratory tract effects; responsible microbes and their components and toxins (++).
  • Contribution of indoor air pollutants to childhood respiratory diseases (++).
  • Exposure-effect-relationships especially in vulnerable groups (++).
  • Effects and risks of products which emit indoor air pollutants that can react in indoor air (+). This is, for example, the case with terpenes that can react with ozone. The true role of such reaction products as indoor air pollutants is not clear.
  • Possible effects and risks of man-made nanoparticles in indoor air (+).
  • Contribution of coarse, fine and ultrafine particles from indoor sources to adverse health effects.
  • Controlled clinical studies (including biochemical markers of effect) among persons suffering symptoms in water damaged buildings to clarify the associations and possibly to identify the most harmful microbes.

Source & ©: SCHER,  Opinion on risk assessment on indoor air quality (2007),
3.2.2. Data requirements and gaps of knowledge, p.16

9.4 Are existing measurement standards for indoor air quality adequate?

The SCHER opinion states:

3.2.3. Existing measurement standards

There are some international measurement standards developed for indoor air quality both from CEN and ISO (often identical standards). Some of the standards developed for ambient air measurements can also be applied for the indoor environment, while methods for workplaces often are developed for higher concentrations of the substance. The SCHER does not see development of new measurement standards as a high priority, but recommends the validation and harmonization of the existing ones, in particular those concerned with indoor material emissions (ECA 2005) and biological agents. Development of passive samplers is in a very active phase and has to be followed, but the technique is not ready for standardisation.

Source & ©: SCHER,  Opinion on risk assessment on indoor air quality (2007),
3.2.3. Existing measurement standards, p.16

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