Air pollution—time to address the silent killer

Abstract

On Sept 21, 2021, WHO published their new Air Quality Guidelines—a welcome update on the previous report from 2005—where they recommend new air quality levels for the six main pollutants (CO, lead, NO2, O3, PM, and SO2). Meeting these new levels is likely to be a challenge without substantive buy-in from governments globally, especially as pollutant projections worldwide are set to increase. As one of the biggest environmental contributors to poor health, air pollution has led to 7 million premature deaths globally each year. In 2017, it was reported that more than 90% of the global population lived in areas where the concentration of particulate matter (PM)2.5 was higher than the WHO recommended (2005) annual mean of 10 μg/m3—accounting for 12% of all deaths that same year. If the 2021 guidelines had been implemented in 2016, it is estimated that 3·3 million deaths in the WHO European region alone could have been prevented. If the levels proposed in the latest update of the guidelines are met, the burden of disease related to air pollution could be reduced by 80%. Emerging evidence of the health effects of air pollution is not only increasing in quality, but is also becoming more inclusive, with a wider array of countries represented and more low-income and middle-income countries (LMICs) contributing to the body of research. When it comes to the harms of air pollution, the lungs are first line of defence. Studies have shown associations of high levels of air pollutants with poor lung growth in early life, development of asthma, inflammation of airways, increased respiratory infections, and impaired lung function. Pollutants cause production of reactive oxygen species (oxidative stress) and reactive nitrogen species in the body, which in turn promote pathogenic pathways leading to inflammation, cell death, and mitochondrial dysfunction, among others. Sustained exposure to air pollutants bombards the lung's natural defences and culminates in lung injury and disease. Damage from pollutants does not stop at the lungs; direct or indirect damage to other organs can also occur. For example, acute myocardial infarction is associated with increased pollutant concentrations in the previous few days or hours. In Europe, steps are being taken to tackle the issue of pollution. The European Commission has agreed to a deal—the European Green Deal—which states that Europe will aim to be the first climate neutral continent in the world. The deal, made in December, 2019, revised the European Commission's air quality standards to align more closely with the 2005 WHO guidelines; however, the new WHO guidelines show that current European standards will not be enough to improve air quality to levels that have a meaningful impact on health. Only when the new, evidence-based guidelines are followed—and are legally binding—will Europe be able to meet its goal. Although ambient air pollution affects both developed and developing countries, LMICs have the highest burden in terms of adverse effects on health. WHO Western Pacific and South-East Asia regions bear the brunt of this burden. If there is to be a truly global commitment to reduce the burden of air pollution, the differing threats between regions need to be taken into account, and approaches must be adaptable and sustainable to best suit these regions and the people living there. Health inequalities must also be considered in any policies put in place. Governments and policy makers should be encouraged to agree to legally binding standards to facilitate responsibility and accountability. Without such measures, air quality and health could be deprioritised, as happened with the 2005 standards set by WHO. Campaigns that educate on the connection between air pollution and health and that mobilise people to make change will encourage individuals to consider steps that they can take to improve their health via improving air quality—whether that be decisions on a personal level or putting pressure on their governments to meet standards set. The health sector can also help to raise awareness. Respiratory clinicians could be at the forefront of educating their patients on the risks of air pollution. Although personal steps are welcome, government- and corporate-level change is needed to make significant inroads into climate change and air pollution. The WHO Air Quality Guidelines have been published at an appropriate time, just before COP26. With an opportunity to implement real change as world leaders meet, we hope that the new guidelines will be carefully considered, and air pollution and its associated respiratory health burden pushed to the forefront of health policy agendas. The silent killer can no longer be ignored.