Traffic-related pollution and lung development in children

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The adverse health effects of air pollution are of increasing concern. Many studies show that air pollution causes not only unfavourable respiratory effects in patients with asthma, chronic obstructive pulmonary disease, and other lung conditions, but also cardiovascular effects such as myocardial infarction and stroke. Associations have been recorded for both morbidity and mortality.1 and 2 Of the different air pollutants, particulate matter has emerged as the component most strongly related with health effects, with the size fraction of particles smaller than 2�5 �m being most unfavourable. In urban areas, this fraction is commonly linked to combustion processes, with traffic as a major contributor. In today's Lancet, William Gauderman and colleagues3 provide evidence that living close to motorways (freeways) in California, USA, leads to reduced lung development in children. In a longitudinal study, more than 3600 children were followed up from age 10 to 18 years with measurements of lung function every year. Children living less than 500 m from motorways had reduced lung-function growth, compared with those living more than 1500 m away. This finding is important because it shows that within communities some children are at higher risk than others. Thus environmental equity is an issue of local rather than regional dimensions. Could alternative explanations for Gauderman and colleagues' findings be considered? Other studies from the Los Angeles basin have shown that poor children are more likely to attend schools near busy motorways than those from affluent families,4 and adjustment for social factors is always difficult in this type of study. Although Gauderman did all he could to take socioeconomic status into account, the effect that social factors might have on lung-function growth is difficult to define, and the possibility for residual confounding remains. Another issue is school location: the study covered the age range of 10-18 years-ie, largely those children attending secondary school, and one line of investigation would have been to measure what preceding exposures at younger school ages might have contributed, because associations with school exposures have been reported in some European studies.5 and 6 The density and composition of the traffic could also have been examined, but the study's power would have been insufficient to address these additional questions in detail. However, these questions should not distract from the major achievement of follow-up of such a large group of children through secondary school with repeated lung-function tests. Furthermore, as Gauderman and co-workers discuss, many studies now implicate close residence to busy roads with adverse respiratory outcomes in children. Most investigations have used area monitoring of air pollution to relate to health effects. Few studies specifically accounted for the effects of individuals living close to high emissions from traffic. In their 8-year cohort, Gauderman and colleagues take this context further by showing that poor development of lung function associated with residence within 500 m from a motorway was independent of regional air quality. The quest to identify what traffic-related components are responsible for specific health effects is important. The roles of fuels, engines, exhaust gases, and particles (as well as components of road and vehicle wear) demand much attention to reduce the biomedical consequences of traffic pollution. Gauderman and co-workers point towards diesel emissions as an important cause in the impaired development of lung function in their cohort. Diesel-engine exhaust contains large quantities of nanoparticles with organic hydrocarbon components on the surface. The primary emissions, on the road and in close vicinity, also include organic vapours and nanoparticles in nucleation mode. Indeed, several human experimental studies7 and 8 with dilute diesel-exhaust show extensive inflammatory effects in the bronchial wall with adverse functional consequences. The underlying mechanisms have been associated with oxidative stress and activation of several mitogen-activated protein kinases and transcription factors, and disturbances in cell functions by the physical and chemical characteristics of diesel exhaust.9, 10 and 11 In one study,12 NL Mills, H Tornqvist and SD Robinson et al., Diesel exhaust inhalation causes vascular dysfunction and impaired endogenous fibrinolysis, Circulation 112 (2005), pp. 3930-3936.)12 diesel-exhaust reactions were reported to extend to disturbances in vascular tone and coagulation. Gauderman and colleagues' paper does, combined with previous epidemiological studies on adverse health effects of traffic, focus on traffic emissions and risks of living close to major motorways. This finding leads to important questions for society about the structure of the transportation system, engines, fuels, combustion, and road dust in urban areas. We declare that we have no conflict of interest. 




Sandström, T., & Brunekreef, B. (2007, February 17). Traffic-related pollution and lung development in children. Lancet. Elsevier Limited.

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