Indoor pollutants and health effects
The Scientific Committee on Health and Environmental Risks (SCHER), one of the independent scientific committees managed by the Directorate-General for Health and Consumer Protection of the European Commission, reported that more than 900 different compounds have been detected in indoor air. Figure 1 shows the main indoor air pollutants and related sources. Most indoor pollutants derive from human activity (anthropogenic pollutants). Carbon dioxide (CO2) is a product of human respiration, and elevated levels may be reached in crowded indoor environments with inadequate air exchange, thus altering indoor air quality. Allergens – mainly related to the presence of dust, damp, pets or insects, but also penetrating from outdoors – and infectious agents play an important role in indoor pollution. Indoor air pollution is the eighth most important risk factor for disease, responsible for an estimated 2.7% of the global burden of disease (4% in low-income countries). Conservative estimates show that 1.5–2 million deaths every year could be attributed to indoor air pollution, and there is consistent evidence that exposure to indoor pollutants increases the risk of several respiratory/allergic symptoms or diseases. The commonest indoor risk factors with related health effects are shown in figure 2.
In indoor environments frequented by smokers, tobacco smoke is the major source of particulate matter (PM), accounting for as much as 50–90% of the total indoor PM concentration (see also chapter 8). It has, for example, been shown in Scotland and Ireland that among homes where solid fuels or gas are burned for heating and cooking, it is only in those where cigarette smoking occurs that the concentrations of fine particles with aerodynamic diameter <2.5 μm (PM2.5) are much higher than those recommended for good indoor air quality. In industrialised countries, few studies of measured indoor PM have been performed and those that do exist relate mainly to children. Positive associations of indoor PM with the risk of respiratory symptoms have been found; for example, an estimated increased incidence of nocturnal symptoms and wheezing in asthmatic children of 6–7% for each 10 μg·m-3 increment in indoor PM2.5. In another study, an increased prevalence of asthma in the previous year was found in schoolchildren exposed to high levels of PM2.5 in the classroom. Further research is needed to clarify whether indoor exposure to particles is associated with the severity of asthma or bronchitis in general populations, as well as with the development of respiratory diseases.