ArticlesPublic-health impact of outdoor and traffic-related air pollution: a European assessment
Introduction
Research during the past 10–20 years confirms that outdoor air pollution contributes to morbidity and mortality.1, 2 Whereas some effects may be related to short-term exposure,3 others have to be considered contributions of long-term exposure.4, 5 Although the mechanisms are not fully explained, epidemiological evidence suggests that outdoor air pollution is a contributing cause of morbidity and mortality.6 State-of-the-art epidemiological research has found consistent and coherent associations between air pollution and various outcomes (eg, respiratory symptoms, reduced lung function, chronic bronchitis, and mortality).6
Relative risks related to air pollution, however, are rather small. For example, for an average adult, the risk of dying may increase on any given day by less than 1% if the concentration of inhalable (> 10 μm diameter) particulate matter (PM10) increases by 10 μg/m3·3 Given the finite resources available to protect health, there is a need to weight different risks and to allocate preventive resources to get the maximum benefit. We present a three-country interdisciplinary assessment of the impact related to air polution on morbidity and mortality. The project has been initiated by WHO Europe as a case study in the framework of the transport environment and health session of the WHO Ministerial Conference on Environment and Health, held in London, UK, in 1999.7
National agencies from Austria, France, and Switzerland assessed the external public-health costs of total air pollution and of traffic-related air pollution. The focus on traffic-related air pollution and on economic valuation is based on the argument that traffic creates costs which are not covered by the polluters (the motorists). Such costs cause economic problems, because they are not included in the market price, which leads to a wasting of scarce and important resources (eg, clean air, silence, and clean water). To stop this wastage, the real price should be put on clean air. With the present study, an important part of the external traffic-related costs, namely the negative impacts of traffic-related air pollution on human health were assessed in terms of attributable number of cases. The quantification of the related external costs are summarised in an Organisation for Economic Cooperation and Development (OECD) report. The full project reports are available from WHO (www.who.dk/london99/transport04.htm, accessed Aug 17, 2000).8, 9, 10
Section snippets
Design and participants
The impact assessment relies on calculating the attributable number of cases.11 We extended the methods of Ostro and colleagues to further specify and standardise influential assumptions and decisions.
Cases of morbidity or mortality attributable to air pollution were derived for the health outcomes listed in table 1. Outcomes were ignored if quantitative data were not available, if costing was impossible (eg, valuing decrement in pulmonary function), and to prevent overlapping health measures
Results
Table 2 summarises for each health outcome the effect estimates, the country-specific health-outcome frequencies at E0, and the respective number of cases attributed to a 10 μg/m3 increase in PM10 (D10). The population exposure distribution is summarised in table 3.
The mean exposure for the population was similar in all three countries with somewhat higher exposures in Austria. Using the Swiss emission-dispersion models for PM, we estimated that the traffic share of the total PM10 exposure
Discussion
By contrast with other projects,14, 15, 16, 17 which each used different assumptions, our results are comparable across the participating countries. Because the whole population is exposed the attributable proportion is substantial, even though epidemiological studies indicate that air pollution imposes on the individual a small risk for morbidity and mortality. The public-health impact, however, depends not only on the relative risk but also on the exposure distribution in the population. Our
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