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

Ranking air pollutants by risk is difficult because indoor air contains a large number of different substances and because levels vary widely across Europe. Nonetheless, those that raise highest concern because of the adverse health effects they have caused or have a high potential to cause are:

• carbon monoxide (CO)
• formaldehyde (H₂CO)
• benzene (C₆H₆)
• nitrogen dioxide (NO₂)
• naphthalene (C₁₀H₈).

Other pollutants that are of concern in indoor air are:

Environmental tobacco smoke – Tobacco smoking is the primary source of several indoor emissions (benzene, fine and ultrafine particles) and associated health effects. In adults, secondhand tobacco smoke is linked with irritation and coronary heart disease, and it seems to make respiratory symptoms worse. In children, it appears to be linked with sudden death syndrome and middle ear infections.

Radon (Rn) – Radon is a gas that emanates naturally from the ground, particularly in areas where bedrock contains uranium in excess. It can get inside buildings by diffusing through the soil and is a problem in many parts of Europe. Its presence in indoor air can lead to lung cancer.

Lead (Pb) – The use of lead-containing pigments in indoor paints has been banned or restricted. However, some old houses in parts of the EU still have paintwork containing lead. Even low level exposure to lead is harmful for children, for whom the main route of exposure is swallowing dust.

Organophosphate pesticides – These pesticides which are used indoors against insects, are applied to cracks and crevices or present in insect strips. In some studies, they have been shown to affect the development of the nervous system, which raises concern for possible effects on children. Indeed, indoor exposure to these compounds can be high and occurs through inhalation or ingestion due to accumulation on surfaces, including on children’s toys, and in dust. Concentrations in indoor air are unlikely to be high enough to cause short-term effects, but they may contribute considerably to the overall uptake of these pesticides by children.

Other indoor air pollutants that have been studied are volatile organic compounds (VOCs) and phthalates.

Volatile organic compounds (VOCs) are emitted by many consumer products and decomposing materials. Three of the most worrisome are formaldehyde, benzene, and naphthalene.

The total amount of VOCs may serve as a very general indicator of indoor air quality. Because VOCs mixtures can vary a lot in composition, total VOCs are not a useful measure for risk assessment.

Some volatile organic compounds may react with ozone to produce secondary pollutants, including fine and ultrafine particles. Some of these secondary pollutants cause irritation and poor perceived air quality at concentrations that can be found in indoor air. Altogether, the concentrations of VOCs and ozone causing mixture effects are as yet poorly known and evidence of health effects at common indoor concentrations is inconclusive.

Air pollutants can be emitted from intact materials in the indoor environment. In addition, when some materials decompose, they can form and release new compounds. These should be identified and their potential health effects evaluated.

Phthalates are common contaminants in the indoor environment. High exposure to phthalates is linked to asthma and rhinitis. However, it is very unlikely that the low exposure levels of phthalates by inhalation in indoor air will have any harmful effects. From the scientific evidence available, the SCHER does not consider phthalates as high concern chemicals in indoor air. More...