Very young children, probably including unborn babies, are particularly sensitive to air pollu-tants, and good evidence suggests a causal relationship between pollutants and a number of health outcomes (11). Particulate air pollution contributes to deaths from respiratory com-plaints in the post-neonatal period, and exposure to ambient air pollutants has been found to have adverse effects on the development of lung function. Both reversible deficits of lung func-tion and chronically reduced lung growth rates and lung funcfunc-tion have been associated with exposure to particulates. There is a causal association between exposure to particulate matter (PM) and the aggravation of asthma, and the increased prevalence and incidence of cough and bronchitis.
Among air pollutants, PM is widely present and people are exposed where they live and work. To a great extent, PM is generated by human activities such as transport, energy pro-duction, domestic heating and a wide range of industries. Concentrations of ambient PM10 (particles with a diameter of up to 10 µm, which are small enough to pass into the lungs) are a good approximation of population exposure to PM from outdoor sources. The value of this is supported by numerous epidemiological studies, conducted in Europe and in other parts of the world, which show links between various indicators of children’s health and out-door PM10. Importantly, effects are seen on health at PM levels currently observed in European cities.
Box 10. Lessons from Germany after unification: respiratory health and ambient air quality
Air quality in the German Democratic Republic (GDR) was very poor compared to the Federal Republic of Germany (FRG) before unification. This, together with changes in respiratory health over time, provides a unique way to exam-ine the potential impact on health of improving ambient air quality. The results need a distinct discussion, and it must not be assumed that changes over time in morbidity rates are exclusively caused by improved air quality levels.
Children and adults in the GDR did not suffer from asthma, allergic rhinitis and allergic sensitization as much as those in the FRG at the beginning of the 1990s (12,13). This was misused as an argument against the assumption that air pollution might cause asthma and allergy. However, in line with the underlying assumption, children in the GDR had significantly more bronchitic symptoms and poor lung function (12,14).
This led to speculation that the development of asthma and allergies was more dependent on lifestyle-related fac-tors than ambient air pollutants, such as sulfur dioxide (SO2) and total suspended particulates. Further, exposure to these pollutants may increase bronchial symptoms and infections in very early childhood, which may have an effect on the response of the immune system and, consequently, reduce the risk of allergic diseases (15).
Not only were air pollution levels different in the two countries at this time, so were the sources, and consequently, the components and distribution. A major source in the GDR was the combustion of surface coal with high sulfur content (up to 4%) for domestic heating, energy production in big power plants, and industry. In the FRG, motor vehicles were much more common and traffic exhausts were a major contributor to ambient air pollution (14). With reunification, what is now the eastern part of Germany saw a shut-down of industry, the introduction of stringent emission controls and the replacement of surface coal with gas and oil. Air quality significantly improved (16,17), although at the same time the number of cars per capita increased three- to five-fold.
In parallel with the improved air quality in eastern Germany, there was a decline in the frequency of bronchitis symp-toms and infectious diseases and improvement in lung function (14,16,18). However, the prevalence of asthma and, even more so, of allergic rhinitis and allergic sensitization, increased (14,16,19).
These findings are strong evidence that a reduction in air pollution from coal combustion could reduce bronchitis symptoms and improve lung function in children. A similar finding in Switzerland showed that air pollution levels had also decreased, without the concomitant social changes seen in eastern Germany (20). Further, the increased preva-lence of atopic diseases in the population in eastern Germany could be due to increased exposure to traffic-relat-ed pollutants, fewer infectious diseases in early childhood and the consequent delaytraffic-relat-ed maturing of immune func-tion, factors related to the adoption of a western lifestyle, or to a combination of these factors.
Fig. 20 shows the population exposure to PM10 (as an average annual concentration) in various European cities in 2004 (or the last available year). This is expected to approximate the exposure in children, assuming children comprise similar proportions of the cities’ populations (21). The average exposure to PM10 varied from 13–14 µg/m3(Finland, Ireland) to 53–56 µg/m3 (Bulgaria, Romania and Serbia and Montenegro (Serbia)). Within some countries, a three-fold variation in the exposure level of children was observed. There have been no substantial changes in average expo-sure levels over the last few years in urban areas of the Region.
Of people living in European cities where PM10is monitored, the vast majority (89%), including children, are exposed to levels exceeding the WHO air quality guideline level of 20 µg/m3(24). This gives rise to a substantial risk to children’s health. For 14% of people, the higher EU limit value of 40 µg/m3is exceeded. Finally, it should be remembered that for 31 countries in the Region – with 43% of the total population – no PM data from regular monitoring are available. However, an approximate assessment indicates that the pollution levels and corresponding health risks may be even higher in many of these countries.
Fig. 20. Percentage of children living in cities with various PM10levels, 2004 (or last available year)
Note. In several countries the assessment is based on one city only.
Source: AirBase for PM10concentration data (22); Eurostat for city population data (23).
The association between mortality and exposure to PM has been described and quantified. For chil-dren, a WHO analysis based on data from the late 1990s indicates that, annually, about 700 deaths due to ARIs in children aged 0–4 years in the Region can be attributed to exposure to PM10(25).
Several studies reviewed by WHO (11) have demonstrated the strong effect of PM on respiratory mor-tality in the post-neonatal period. The review includes a nationwide Czech case-control study which confirmed this effect, with post-neonatal mortality from respiratory causes increasing by 74% (95%
CI 1–198%) for each 50 µg/m3increase in the concentration of total suspended particulates. Further, an increasing evidence base suggests that finer particulates may have even greater effects on respira-tory health, which has led to studies on exposure to PM2.5 (particles with a diameter of 2.5µm).
Recently, Woodruff et al (26) found the risk of respiratory-related post-neonatal mortality more than doubled for each 10 µg/m3increase in PM2.5, after adjustment for other risk factors.
As regards adults, the dominant impact on health of exposure to PM is an increase in mortality from long-term exposure to PM2.5(27). In Europe, current exposures to PM from anthropogenic sources lead to an average of 8.6 months loss of life expectancy. This ranges from around 3 months in Finland up to more than 13 months in Belgium. Around 348 000 premature deaths in the 25 EU countries can be attributed to PM exposure in the period of 1997–2002.
0% 20% 40% 60% 80% 100% Serbia and Montenegro (Serbia) Bulgaria
A recent WHO country assessment (28) of the impact on health of outdoor air pollution in cities with over 100 000 population shows that about 169 000 deaths per year in the Region could be prevented if PM levels were to be reduced to the WHO air quality guideline value of 20 µ/m3.
The quantification of the impact of PM on morbidity is more difficult and gives less precise estimates, but studies show health benefits associated with a reduction of exposure to PM10. For example, a reduction in exposure from the current levels to 20 µg/m3would lead to a 7% decrease in the incidence of coughs and lower respiratory symptoms and a 2% decrease in admissions to hospital of children aged under 15 years with respiratory conditions (29).
While evidence suggests that ambient air pollution is associated with the exacerbation of asthma, an association with the onset of asthma has not been consistently shown (11). However, recent studies, including birth cohort studies, are addressing these limitations, and there is increasing evidence that exposure to traffic-related air pollutants such as fine PM, black smoke and nitrogen dioxide, is associ-ated with an increased risk for the onset of asthma in young children (30,31).
Among the major contributors to urban air pollution, road transport is becoming ever more important.
Traffic contributes to a range of gaseous air pollutants and to suspended PM of different sizes and com-position. Tailpipe emissions of primary particles from road transport account for up to 30% of PM2.5in urban areas. Other emissions, such as those from resuspended road dust or resulting from worn tyres and brake linings, are the most important source of coarse PM. People of all ages experience high levels of exposure to traffic-related air pollutants when they live near busy roads, travel on roads or have to spend a long time on roads (Box 11). Epidemiological and toxicological studies indicate that transport-related air pollution contributes to an increased risk of death, particularly from cardiopulmonary causes, as well as to an increased risk of respiratory symptoms and diseases (32). The exposure of children to traffic-related air pollutants such as PM has a considerable impact on their health and well-being (11).
INDOOR AIR EXPOSURE
As well as exposure to ambient air pollutants, lifestyle-related factors and genetics, indoor fac-tors are known to play a major role in the development and/or exacerbation of asthma and allergies. The incidence of allergic symptoms in children is associated with exposure to aller-gens in indoor environments with poor air quality (36). This includes biomass combustion products, high humidity and moulds, dust mites, pets and ETS (37). Further, the frequency of a child’s exposure to poor indoor air may increase the risk of being affected by outdoor pol-lutants. In asthmatic individuals, exposure to ETS can trigger asthma attacks and make asth-ma symptoms more severe (38). Some evidence suggests it asth-may also lead to the onset of new cases of asthma, although at present there is no scientific consensus on the conclusiveness of this evidence.