5. Health risk assessment of transport-related air pollution

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1 5. Health risk assessment of transport-related air pollution Birgit Kuna-Dibbert and Michal Krzyzanowski Identified health effects The evidence from accumulated research has enabled the assessment of the health effects of ambient air pollution, including quantitative estimates of the burden of the pollution on a global scale (WHO, 2002) and on individual communities (Medina et al., 2002). These estimates indicate that about deaths a year could be linked to ambient air pollution in cities in the WHO European Region, shortening life expectancy by an average of a year. The number of casualties attributed to air pollution is comparable to the number of fatalities from traffic accidents, and its imprint is observed in all age groups, including children (Valent et al., 2004). A large part of the disease burden caused by non-fatal diseases attributable to air pollution is more difficult to quantify, but these diseases probably add substantially to the total burden of pollution-related ill health, especially in children. These analyses of adverse effects on health used exposure to PM10 or PM2.5, measured by monitoring networks or estimated by models, and attributed the effects to the total pollution load generated by all possible sources. Ozone, created in the atmosphere from gases produced largely by transport, also affects mortality, morbidity and the development of the lungs. Traffic contributes substantially to PM and ozone pollution and to population exposure, but precisely quantifying transport s contribution to total exposure and its adverse effects are still difficult tasks. The review presented in this book clearly identifies the hazardous nature of transport-related air pollution, but also presents a variety of factors that may affect exposure and the attribution of the observed adverse health effects to pollution from traffic sources. The effects of transport-related air pollution on health include an increased mortality risk, due particularly to cardiopulmonary causes, and an elevated risk of respiratory morbidity. Further, elevated incidence of non-allergic respiratory symptoms and diseases due to traffic, accompanied by extended non-allergic inflammation in the respiratory tract, has been reported. Exposure can exacerbate 185

2 186 Health effects of transport-related air pollution allergic reactions in asthmatics. As to cardiovascular morbidity, exposure has been shown to increase the risk of myocardial infarction. In addition, evidence implicates air pollution in adverse outcomes of pregnancy, such as premature birth and low birth weight. There is insufficient evidence to draw firm conclusions about the association of transport-related air pollution with elevated incidence of cancer, although certain occupational groups with higher- and longer-than-average levels of exposure (such as professional drivers and railway workers) show an increased incidence of and mortality from lung cancer. The risks are not equally distributed in the population. Children and elderly people and people with preexisting chronic diseases show increased susceptibility to the adverse effects of air pollutants. Needs for further research All this information identifies the hazard sufficiently, but is still too inconsistent to derive a well-based exposure response function, which is needed to quantify precisely the adverse effects of transport-related air pollution. The epidemiological studies available used different exposure and outcome indicators, which limits the possibility of comparing their results quantitatively and estimating a common risk function, as has been done for studies of ambient air pollution (Anderson et al., 2004). Also, it is still difficult to estimate the population s exposure to transportrelated air pollution, which limits the precision with which the effects can be quantified. Estimating this exposure as correctly as possible requires knowledge of where people spend their time and what pollution levels prevail in these microenvironments. The quantity of passing traffic, the distance from a road to a residence, weather conditions and time spent in different traffic modes all contribute to the overall level of exposure. Elevated health risks are expected for people living and working near busy roads or travelling/commuting in heavy traffic, or both. Also, the intake of pollutants varies among such road users as drivers, bicyclists and pedestrians. Most commonly used estimates of levels of population exposure are based on fixed monitoring sites and do not reflect the spatial and temporal variability of personal exposures. Despite the overall improvements in urban air quality in recent ecades, as demonstrated by the results of air-quality monitoring in many urban areas, the trends in population exposure, and particularly exposure to transport-related air pollution, are less clear. The steady increase in the number of vehicles may counterbalance the decrease in emissions per vehicle witnessed in Europe, where conventional diesel and petrol engines will continue to dominate transport patterns in coming decades. Other factors are expected to contribute to transport-related air pollution, such as the large number of short road trips, the increasing share of commuting by passenger vehicles and the increasing amount of time spent on high-volume roads due to increased traffic congestion. Owing to continuing

3 Health risk assessment of transport-related air pollution 187 urbanization and expansion of urban areas, an increasing share of the population is likely to be exposed to transport-related air pollutants. The current trend towards the growth of road transport, observed throught the WHO European Region, runs contrary to the intended reduction of pollution levels, mainly because a substantial share of this growth is due to the shift of freight movement away from railways and towards lorries. Although epidemiological evidence for the adverse health effects of exposure to transport-related air pollution is increasing, the associations still need to be adequately quantified. Methods of quantifying the adverse effects on health are available (Box 5.1), but they need to be applied more broadly. More studies, showing consistent results in different study locations and populations, are needed before a comprehensive risk assessment of the health effects of transport-related air pollution can be made. To evaluate the long-term adverse effects, study programmes on repeated exposure which also focus on in-traffic exposures and emphasize the collection of personal exposure data along with population-level Box 5.1. Examples of quantification of the health effects of transportrelated air pollution Using different methods based on epidemiology, an attempt was made to quantify the adverse effects on public health of current levels of transport-related air pollution. To estimate the effects of ambient air pollution and transport-related air pollution on public health in Austria, France and Switzerland, Künzli et al. (2000) used exposure response functions for a 10-µg/m 3 increase in PM10. These functions modelled the exposure of a population to PM10 for each square kilometre and estimated the transport-related fraction, based on PM10 emission inventories. The effect of air pollution on public health was estimated to be 6% of total mortality in adults 30 years of age or older, accounting for more than deaths a year. About half of all mortality caused by air pollution was attributed to motorized traffi c, which also accounted for more than new cases of chronic bronchitis in adults, more than episodes of bronchitis in children, more than asthma attacks and more than 16 million person-days of restricted activity. Using another method, Forsberg et al. (2003) calculated the effect of a system of congestion pricing planned for Stockholm, Sweden, where relatively higher prices would be charged for travel during peak hours. Through the use of traffi c models, a dynamic emission database and an air-quality dispersion model, the effect of congestion pricing on levels of different air pollutants was estimated and combined with a spatial distribution of the population, to obtain population-weighted means and extreme values. For about inner-city residents, the reduction in long-term exposure was estimated to correspond to 47 preventable deaths when nitrogen dioxide is used as the indicator of exposure and 17 preventable deaths when PM10 is used as the indicator per year. The reduction of the population-weighted annual mean pollution level was estimated to be 1.2 µg/m 3 for both nitrogen dioxide and PM10.

4 188 Health effects of transport-related air pollution estimates have to be implemented. Further, exposure to pollution that comes specifically from traffic should be measured, modelled or both (WHO Regional Office for Europe, 2003). Epidemiological studies must take account of human mobility, to be able appropriately to assess health risks. Moreover, emission and exposure hot spots must be thoroughly studied, especially in urban settings, and exposure modelling needs to be linked to emission levels. It is still unclear which constituents of traffic emissions are responsible for the observed adverse effects on people s health. Knowledge of such indicators would be very useful in implementing mechanisms that control air pollutants. Most epidemiological studies have concentrated on the classical air pollutants, such as black smoke, nitrogen dioxide or PM. A few studies have investigated the role of ultrafine particles. The choice of the indicator depends on the application (such as source apportionment, health risk assessment or transportation-flow management). Possible indicators of exposure to PM from traffic in urban areas might include black smoke and ultrafine particles. In addition, studies with new designs are needed adequately to address the role of emissions from diesel-powered vehicles. Some suggest that emissions from vehicles with heavy-duty diesel engines are more relevant to adverse health effects than those from cars with light-duty engines. Specifically differentiating between light-duty and heavy-duty vehicles requires study populations whose exposures differ according to proximity to various diesel sources. Other studies are needed to understand the effects of new pollution constituents, such as trace elements from automobile catalytic converters (specifically, platinum, palladium and rhodium), the emissions of which are rapidly increasing and need to be monitored. There is also an urgent need to assess the benefits to public health of various measures to improve air quality, particularly through interventions that address transport-related air pollution (HEI Accountability Working Group, 2003; National Research Council Committee on Estimating the Health-Risk- Reduction Benefits of Proposed Air Quality Regulations, 2002). Justified action Despite the remaining need for quantitative and qualitative studies, short-term measures to reduce exposure to transport-related air pollution are still well justified. Traffic management is one of the effective instruments for significantly reducing the exposure of residents of urban areas, and the nested adverse effects of the spread of transport-related air pollution to larger areas should be considered. Also, improvements are needed in integrating environmental and health considerations into urban planning, for example, by zoning offices, green areas and non-residential functions around urban highways and separating pedestrians and bicyclists from road traffic. In particular, urban planning may aim for integrative measures that lower emission rates; such measures include the promotion of highly efficient, service-oriented and clean public transport, and the promotion

5 Health risk assessment of transport-related air pollution 189 of improved traffic flow. Revitalizing railways for freight transport, for example, can reduce road travel and the risk of increased air pollution from the expansion of urban areas. Several technologies show promise in lowering the emission levels of conventional vehicles, including particle traps, systems to reduce emissions of nitrogen oxides, preheated catalytic converters and electronic vehicle controls. Their development should be promoted. Effective control mechanisms, such as mandatory car inspections, to eliminate gross polluters and badly maintained vehicles, should be more widely used. Further, alternative vehicle technologies (such as fuel cells, electric drives and hybrid engines) and substitute fuels (such as biofuels, natural gas and hydrogen) have the potential to reduce emission levels of hazardous air pollutants substantially in the future, and should they be further explored and developed. Both research and action should form part of transport policies in the European Region that maximize the benefits to health. References Anderson HR et al. (2004). Meta-analysis of time-series studies and panel studies of particulate matter (PM) and ozone (O 3 ): report of a WHO task group. Copenhagen, WHO Regional Office for Europe (document EUR/04/ ; accessed 4 February 2005). Forsberg B et al. (2003). Predicted air pollution related health impacts of congestion pricing in Stockholm A local assessment. Utrecht, Institute for Risk Assessment Sciences, University of Utrecht ( rome/airnet_poster36_b_forsberg.pdf, accessed 4 February 2005). HEI Accountability Working Group (2003). Assessing health impacts of air quality regulations: concepts and methods for accountability research. Boston, MA, Health Effects Institute (HEI Communication 11; org/pubs/comm11.pdf, accessed 4 February 2005). Künzli N et al. (2000). Public-health impact of outdoor and traffic-related air pollution: a European assessment. Lancet, 356: Medina S et al. (2002). APHEIS health impact assessment of air pollution in 26 European cities. Second year report, Saint-Maurice, Institut de Veille Sanitaire ( accessed 4 February 2005). National Research Council Committee on Estimating the Health-Risk-Reduction Benefits of Proposed Air Quality Regulations (2002). Estimating the public health benefits of proposed air pollution regulations. Washington, DC, The National Academies Press ( accessed 4 February 2005).

6 190 Health effects of transport-related air pollution Valent F et al. (2004). Burden of disease attributable to selected environmental factors and injury among children and adolescents in Europe. Lancet, 363: WHO (2002). The world health report Reducing risks, promoting healthy life. Geneva, World Health Organization ( WHO_WHR_02.1.pdf, accessed 4 February 2005). WHO Regional Office for Europe (2003). Exposure assessment in studies on the chronic effects of long-term exposure to air pollution. Report on a WHO/HEI workshop, Bonn, Germany, 4 5 February Copenhagen, WHO Regional Office for Europe ( accessed 4 February 2005).