Fine particle components and health--a systematic review and meta-analysis of epidemiological time series studies of daily mortality and hospital admissions.

Short-term exposure to fine particle mass (PM) has been associated with adverse health effects, but little is known about the relative toxicity of particle components. We conducted a systematic review to quantify the associations between particle components and daily mortality and hospital admissions. Medline, Embase and Web of Knowledge were searched for time series studies of sulphate (SO4(2-)), nitrate (NO3(-)), elemental and organic carbon (EC and OC), particle number concentrations (PNC) and metals indexed to October 2013. A multi-stage sifting process identified eligible studies and effect estimates for meta-analysis. SO4(2-), NO3(-), EC and OC were positively associated with increased all-cause, cardiovascular and respiratory mortality, with the strongest associations observed for carbon: 1.30% (95% CI: 0.17%, 2.43%) increase in all-cause mortality per 1 µg/m(3). For PNC, the majority of associations were positive with confidence intervals that overlapped 0%. For metals, there were insufficient estimates for meta-analysis. There are important gaps in our knowledge of the health effects associated with short-term exposure to particle components, and the literature also lacks sufficient geographical coverage and analyses of cause-specific outcomes. The available evidence suggests, however, that both EC and secondary inorganic aerosols are associated with adverse health effects.

Ambient air pollution: a cause of COPD?

The role of ambient air pollution in the development of chronic obstructive pulmonary disease (COPD) is considered to be uncertain. We review the evidence in the light of recent studies. Eight morbidity and six mortality studies were identified. These were heterogeneous in design, characterisation of exposure to air pollution and methods of outcome definition. Six morbidity studies with objectively defined COPD (forced expiratory volume in 1 s/forced vital capacity ratio) were cross-sectional analyses. One longitudinal study defined incidence of COPD as the first hospitalisation due to COPD. However, neither mortality nor hospitalisation studies can unambiguously distinguish acute from long-term effects on the development of the underlying pathophysiological changes. Most studies were based on within-community exposure contrasts, which mainly assess traffic-related air pollution. Overall, evidence of chronic effects of air pollution on the prevalence and incidence of COPD among adults was suggestive but not conclusive, despite plausible biological mechanisms and good evidence that air pollution affects lung development in childhood and triggers exacerbations in COPD patients. To fully integrate this evidence in the assessment, the life-time course of COPD should be better defined. Larger studies with longer follow-up periods, specific definitions of COPD phenotypes, and more refined and source-specific exposure assessments are needed.

Does outdoor air pollution induce new cases of asthma? Biological plausibility and evidence; a review.

It is widely accepted that air pollution can exacerbate asthma in those who already have the condition. What is less clear is whether air pollution can contribute to the initiation of new cases of asthma. Mechanistic evidence from toxicological studies, together with recent information on genes that predispose towards the development of asthma, suggests that this is biologically plausible, particularly in the light of the current understanding of asthma as a complex disease with a variety of phenotypes. The epidemiological evidence for associations between ambient levels of air pollutants and asthma prevalence at a whole community level is unconvincing; meta-analysis confirms a lack of association. In contrast, a meta-analysis of cohort studies found an association between asthma incidence and within-community variations in air pollution (largely traffic dominated). Similarly, a systematic review suggests an association of asthma prevalence with exposure to traffic, although only in those living very close to heavily trafficked roads carrying a lot of trucks. Based on this evidence, the U.K.'s Committee on the Medical Effects of Air Pollutants recently concluded that, overall, the evidence is consistent with the possibility that outdoor air pollution might play a role in causing asthma in susceptible individuals living very close to busy roads carrying a lot of truck traffic. Nonetheless, the effect on public health is unlikely to be large: air pollutants are likely to make only a small contribution, compared with other factors, in the development of asthma, and in only a small proportion of the population.