Indoor Air Quality

6. Which chemicals found in indoor air are causing the most concern?

The SCHER opinion states:

3.3. Question 4

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 potential areas of concern in relation to a) specific chemical compounds taking into account the recent outcome of the INDEX report prepared by DG JRC, b) household – chemicals and other products (e.g. decorating materials, cleaners, furnishings, etc.) and c) building dampness/moisture and microbial growth (moulds, bacteria).

Answer to Question 4

3.3.1. Concerns in relation to specific chemical compounds

Indoor environment contains a large number of different chemical compounds. Availability of data on exposures to specific chemicals, their toxicity and associated health risks are highly variable. Therefore, a priority ranking of chemicals and exposures which cause concern is difficult and uncertain. However, the SCHER considers that formaldehyde, carbon monoxide, nitrogen dioxide, benzene, naphthalene, environmental tobacco smoke (ETS), radon, lead and organophosphate pesticides are compounds of concern in indoor environment.

The INDEX project (INDEX 2005) has evaluated health risks of volatile chemicals in indoor air in the European population, as a stepwise procedure, and set up a list of compounds with highest concern on the basis of health impact criteria. After consideration of the quantity and quality of all the data available, 25 compounds were selected for a more detailed analysis and a detailed risk assessment was performed for 14 of them. The highest priority chemicals were formaldehyde, carbon monoxide, nitrogen dioxide, benzene and naphthalene. SCHER agrees that these are compounds of concern because they have caused adverse health effects as indoor pollutants or have a high potential to cause health effects. However, the concern is not similar in all over in Europe due to different exposure levels. For example, limited data on air fresheners indicate that burning of incense may produce abnormally high benzene and formaldehyde emissions in indoor air (Opinion of SCHER on air fresheners, SCHER 2006).

Though active smoking is excluded from this opinion, the SCHER reminds that tobacco smoking is the primary source of several emissions (benzene, fine and ultrafine particles) indoors and associated health effects. In adults, ETS has been associated e.g. with coronary heart disease, sensory irritation and exacerbation of respiratory symptoms, including asthma (IARC 2004). In children, the association with infant sudden death syndrome and middle ear infections and ETS has been observed (Tamburlini et al., 2002, DiFranza et al., 2004). The evidence clearly indicates that ETS requires risk management.

Radon in indoor air has been associated with lung cancer (WHO 1998). According to a recent analysis of European epidemiological studies (Darby et al., 2005) radon may be a common problem in Europe. Radon gas diffuses through soil into residences in areas where bedrock contains in excess uranium. Indoor radon concentrations can be decreased by technical means, even in existing buildings. Data on residential radon concentrations should be obtained by measurements in countries where such data do not yet exist and the associated health risk assessed.

Paint-related lead still exist in indoor environment in old houses in some EU countries though its use has been restricted or banned in indoor paints. Children are especially exposed through non-dietary ingestion of the dust. Exposure from other sources may be significant (TNO 2005)) and the evidence is increasing that already low level exposure of children to lead is harmful (e.g. Lanphear et al., 2005). Therefore, it is essential to evaluate, if the lead level in indoor environment is still a problem in EU countries. The existing data on lead should be compiled, and thereafter, a need for further research considered.

The indoor use of organophosphate pesticides for treatment of cracks and crevices (Byrne et al., 1998) or the use of insect strips (Weis et al. 1998) may lead to high exposures to these compounds by inhalation or ingestion due to accumulation on surfaces including children’s toys (Hore et al., 2005) and house dust (Butte and Heinzow, 2002). This uptake may contribute considerably to the overall uptake of organophosphates by children (Gurunathan et al., 1998). The acute toxicity of organophosphate pesticides is well known (WHO 2004b): however, it is very unlikely that indoor levels can result in acute effects. Recently neuro-developmental effects, have been reported both in experimental animals (Aldridge et al., 2005 ) and humans (Berkowitz et al., 2004) raising concern for possible effects in children from the use of organophosphates in the indoor environment.

Health effects (mainly sensory irritation) of VOCs commonly found in indoor air have been investigated in numerous studies. An extensive evaluation of all available controlled human exposure studies by a group of experts (Andersson et al., 1997) found that effect levels for irritation were usually higher than concentrations in indoor air. These studies would not explain possible health effects at much lower concentrations reported in epidemiological studies; however, the exposure was not adequately measured and cause effect relationship could not be proved due to several confounders, such as temperature, ventilation, exposure from other chemicals, or moulds and mites, as well as psychosocial factors. Anderson et al., (1997) stated that the scientific literature is inconclusive with respect to TVOC as a risk index. This conclusion is still valid, when the publications since this review are taken into account. Recent c omprehensive controlled human studies at VOC concentrations considerably above those in normal homes show no effects (e.g. Fiedler et al., 2005; Laumbach et al., 2005), epidemiological studies give some indication of health effects (e.g. Hutter et al., 2006; Saiijo et al., 2004; Takigawa et al., 2004) but other factors than VOC may play a major role.

Several studies have reported associations between VOCs and asthma symptoms. However, a recent comprehensive review found no consistent association between the commonly measured indoor VOC exposures and onset of new asthma cases (Nielsen et al. 2007a).

Altogether, the available evidence on VOCs in causing health effects in indoor environment is not conclusive; VOCs may also be indicators for the presence of other stressors contributing to health effects.

More recently reaction products formed in indoor air have been investigated. Terpenes may react with ozone to produce secondary reaction products (Wolkoff et al., 2006a). Limonene reacts with ozone and has been reported to produce both gaseous reaction products and fine and ultrafine particles (Wainman et al., 2000, Sarwar et al., 2004). The highest terpene concentrations also produced high particle levels (Sarwar et al. 2004). Several other pollutants react in indoor air and on surfaces producing known and as yet unknown reaction products (Weschler et al., 2006). In some studies, the reaction products have shown irritating properties (Clausen et al., 2001, Nøjgaard et al., 2005) and poor perceived air quality (Tamás et al., 2006) at terpene and ozone concentrations that can be present in indoor air. Adverse health effects have not been observed in all studies (Laumbach et al., 2005, Fiedler et al. 2005). Altogether, the concentrations of VOCs and ozone causing mixture effects are as yet poorly known.

In addition to the compounds emitted from the intact materials in the indoor environment there may also be new compounds formed due to decomposition of the materials. The glue used to fasten PVC flooring can be hydrolysed by water (dampness) from the underlying material, especially if it is concrete with a high pH. The compounds released from decomposing materials should be identified and their potential health effects evaluated.

Phthalates are common contaminants in the indoor environment occurring both in house dust and in indoor air and di(2-ethylhexyl) phthalate (DEHP) is the dominant component (Øie et al., 1997, Rudel et al., 2003, Fromme et al., 2004). The PVC flooring material is an important source for phthalates, but several other sources contribute in indoor environment (Bornehag et al., 2005a). PVC products indoors (different surface materials) have been associated with airway effects in epidemiological studies (Jaakkola et al. 2006) but only in one study has the concentrations of di(2-ethylhexyl) phthalate (DEHP) and butyl benzyl phthalate (BBP) been measured (Bornehag et al., 2004a). In that study DEHP was associated with asthma and BBP with rhinitis in children at the highest exposure quartile (Bornehag et al., 2004a). Long-term exposure to DEHP (Larsen et al 2007) and its metabolite, mono-2-ethylhexyl phthalate (Hansen et al. 2007), together with a model allergen did not show promoting effects on the development of the allergen specific IgE antibodies. Phthalates are not skin sensitizers for humans and there is no evidence of respiratory sensitization (Medeiros et al., 1999, David et al., 2003, European Union Risk Assessment report, 2007). Based on the lack of mechanistic support and taking into account the low exposure level of phthalates by inhalation (Larsen et al., 2007, Nielsen et al., 2007a), the SCHER does not find consistent scientific evidence which indicate that phthalates should be high concern chemicals in indoor air. The RA report on DEHP (European Union Risk Assessment report, 2007) suggests that the MOSs from exposure in indoor air to reproductive effects, which are the basis for risk characterisation, remain large (over 200 for children, over 1000 for adults).

Source & ©: SCHER,  Opinion on risk assessment on indoor air quality (2007),
3.3 Question 4, p.16-19