Tallying the bills of mortality from air pollution
Authors: Douglas W Dockery, John S Evans
Journal: The Lancet (2017)

Since John Graunt's analyses of the Bills of Mortality in London, UK, in 1662, observations of premature deaths have driven public health actions—from John Snow's apocryphal removal of the handle on the Broad Street pump during the 1854 cholera outbreak to the international response to the 2013–16 outbreak of Ebola virus disease in west Africa. The hazard of air pollution episodes was evident in the 4000 excess deaths1Logan WP Mortality in the London fog incident, 1952.Lancet. 1953; 1: 336-338Abstract PubMed Scopus (346) Google Scholar (revised to 12 000 deaths)2Davis DL Bell ML Fletcher T A look back at the London smog of 1952 and the half century since.Environ Health Perspect. 2002; 110: A734-A735Crossref PubMed Scopus (94) Google Scholar during the Great Smog of 1952 in London. However, measuring the cumulative health burden of living with chronically high air pollution is more difficult. As Geoffrey Rose noted, "the cause that is universally present has no influence at all on the distribution of disease, and it may be quite unfindable by the traditional methods".3Rose G Environmental factors and disease: the man made environment.Br Med J (Clin Res Ed). 1987; 294: 963-965Crossref PubMed Scopus (25) Google Scholar Nevertheless, findings from large prospective cohort studies in the USA, Canada, and Europe have consistently shown that fine particle4Hoek G Krishnan RM Beelen R et al.Long-term air pollution exposure and cardio-respiratory mortality: a review.Environ Health. 2013; 12: 43Crossref PubMed Scopus (1281) Google Scholar and, to a lesser extent, ozone5Turner MC Jerrett M Pope III, CA et al.Long-term ozone exposure and mortality in a large prospective study.Am J Respir Crit Care Med. 2016; 193: 1134-1142Crossref PubMed Scopus (437) Google Scholar air pollution are associated with increased mortality. Based on this evidence and air pollution monitoring in the UK, the Committee on the Medical Effects of Air Pollutants estimated that loss-of-life expectancy equivalent to 29 000 deaths was attributable to fine particles in 2008, although, as they pointed out, the uncertainties in estimates of attributable deaths may be substantial.6Committee on the Medical Effects of Air PollutantsThe mortality effects of long-term exposure to particulate air pollution in the United Kingdom. Health Protection Agency, London2010Google Scholar In The Lancet, Aaron Cohen and colleagues7Cohen AJ Brauer M Burnett R et al.Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015.Lancet. 2017; (published online April 10.)http://dx.doi.org/10.1016/S0140-6736(17)30505-6Google Scholar used global population-weighted mean concentrations of particle mass with aerodynamic diameter less than 2·5 μm (PM2·5) and ozone and integrated exposure–response functions to estimate the relative risk of mortality from ischaemic heart disease, stroke, chronic obstructive pulmonary disease, lung cancer, and lower respiratory infections. They report that 4·2 million deaths (95% uncertainty interval [UI] 3·7 million to 4·8 million) globally were attributable to fine particles and another 254 000 (97 000 to 422 000) to surface ozone in 2015. Using the same methods, they computed country-specific deaths and disability-adjusted life-years lost attributable to particulate and ozone air pollution for 1990 through 2015. For example, they estimated 27 200 (20 500 to 34 900) deaths in the UK in 2015 were attributable to fine particles and an additional 1400 (500 to 2500) were attributable to ozone. Cohen and colleagues report that China and India, with the largest populations and commensurately high levels of pollution, had the largest estimated numbers of deaths attributable to air pollution: 1·11 million (95% UI 0·95 million to 1·27 million) and 1·09 million (0·94 million to 1·25 million), respectively, in 2015. Similar numbers have been estimated previously.8Liu J Han Y Tang X Zhu J Zhu T Estimating adult mortality attributable to PM2.5 exposure in China with assimilated PM2.5 concentrations based on a ground monitoring network.Sci Total Environ. 2016; 568: 1253-1262Crossref PubMed Scopus (243) Google Scholar, 9Chowdhury S Dey S Cause-specific premature death from ambient PM2.5 exposure in India: estimate adjusted for baseline mortality.Environ Int. 2016; 91: 283-290Crossref PubMed Scopus (161) Google Scholar Although the numbers of deaths are not as large as in China and India, the proportions of deaths attributable to air pollution were similarly high in neighbouring countries on the Indian subcontinent. Moreover, Cohen and colleagues estimate that the highest mortality rates attributable to fine particles were in countries in central Asia, where air pollution has not been measured. Advances in remote sensing by satellites and air pollution modelling permit estimates of fine particle air pollution at 11 km × 11 km resolution. When coupled with the geographical distribution of the population, these methods can produce reliable estimates of exposure to fine particles.10Brauer M Amann M Burnett RT et al.Exposure assessment for estimation of the global burden of disease attributable to outdoor air pollution.Environ Sci Technol. 2012; 46: 652-660Crossref PubMed Scopus (551) Google Scholar Therefore, estimation of the disease burden of air pollution is feasible in countries or even cities with few or no direct measurements of air pollution. Such estimations also require extrapolation of epidemiological evidence from developed countries to the higher air pollution exposures in the developing world. Borrowing information from studies of analogous fine particle exposures to household air pollution, second-hand smoke, and active smoking provides a framework for extrapolation that is internally consistent across a range of inhaled doses.11Burnett RT Pope III, CA Ezzati M et al.An integrated risk function for estimating the global burden of disease attributable to ambient fine particulate matter exposure.Environ Health Perspect. 2014; 122: 397-403Crossref PubMed Scopus (1221) Google Scholar The non-linear shape of the integrated exposure–response function used by Cohen and colleagues means that the smallest benefits from incremental reductions in pollution would be expected in the most polluted countries. Because of the profound implications for air pollution control, this hypothesis needs to be tested in mortality studies and, wherever possible, by assessing the health benefits of interventions to reduce pollution in highly polluted communities. Until the results of such studies become available, the uncertainty in the shape and marginal slopes of the integrated exposure–response function (especially at high concentrations) must be fully acknowledged and, to the extent possible, quantified. Cohen and colleagues also estimate high rates of deaths attributable to particulate air pollution in Egypt, Iraq, Libya, United Arab Emirates, and Yemen. Fine particle pollution in these arid countries includes substantial fractions of resuspended crustal material. Assuming all fine particles have the same toxicity, the estimates of the effect of air pollution on mortality are quite large. The evidence from developed countries has not yet identified a specific component of fine particles to be responsible for the reported mortality effects; therefore, this assumption needs to be tested in countries with particle characteristics that differ from those in developed countries. Again, until the results of such studies become available, the uncertainty in estimates due to the assumption of equal toxicity must be acknowledged and quantified. Tallying counts of deaths attributable to air pollution on a national scale identifies the health problem, but does not pinpoint the sources of pollution. The chemical transformations that produce ozone and a major portion of the fine particle mix are complex, and the populations exposed are often far downwind of the pollution sources. Calling attention to the tens of thousands or hundreds of thousands of deaths attributable to air pollution each year in developing countries is not sufficient. We in the public health community must provide the methods to identify the pathways of exposure and the approaches to reduce those exposures. The challenge falls to risk assessors, atmospheric chemists, and meteorologists to provide the methods to back calculate the sources of fine particles and ozone air pollution, even in the parts of the world with few data.12Silva RA Adelman Z Fry MM West JJ The impact of individual anthropogenic emissions sectors on the global burden of human mortality due to ambient air pollution.Environ Health Perspect. 2016; 124: 1776-1784Crossref PubMed Scopus (120) Google Scholar Furthermore, we must be honest about the strengths and weaknesses of the estimates we make from even the best methods now available. Scientists will need time to resolve these uncertainties. However, decision makers must resist the temptation to wait for perfect information before they act, because the costs in loss of life to be expected while waiting will be substantial. Providing the capacity to reduce air pollution in each part of the world will have immediate, local health benefits. To the extent that these actions reduce emissions of carbon dioxide and other greenhouse gases, the long-term health risks associated with global climate disruption will be ameliorated in the entire global population.13Bell ML Davis DL Cifuentes LA Krupnick AJ Morgenstern RD Thurston GD Ancillary human health benefits of improved air quality resulting from climate change mitigation.Environ Health. 2008; 7: 41Crossref PubMed Scopus (110) Google Scholar We declare no competing interests. We thank Virgi Hepner for editorial help in preparing this Comment. Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015Ambient air pollution contributed substantially to the global burden of disease in 2015, which increased over the past 25 years, due to population ageing, changes in non-communicable disease rates, and increasing air pollution in low-income and middle-income countries. Modest reductions in burden will occur in the most polluted countries unless PM2·5 values are decreased substantially, but there is potential for substantial health benefits from exposure reduction. Full-Text PDF Open Access