Communicating the health effects of air pollution

To the Editor: Air pollution causes 3000 deaths each year in Australia.1 To put this in perspective: the national road toll in 2014 was 1153. Deaths from air pollution are due to both acute and chronic effects, and the principal diagnoses are of cardiac and respiratory disease. Reform of Australia's national air quality standards and regulatory mechanisms is currently underway, with the federal government calling for public consultation in the revision of the National Environmental Protection Measure (Ambient Air Quality) for particulates. Engagement in this consultation process requires that the risks be communicated in a way that the public can understand.

A large published cohort study can be of assistance.2 The mortality impacts of both particulate air pollution less than 2.5 µm in diameter (PM2.5) and of cigarette smoking for a large American cohort were followed up for 16 years. The relative risk of all-cause mortality associated with smoking 22 cigarettes a day was 2.58, while the relative risk associated with each 10 µg/m3 of PM2.5 exposure was 1.04 (95% CI, 1.01–1.08), making smoking 24 times as risky to survival (relative risks combine exponentially; 1.04 raised to the power of 24 = 2.58). Assuming that the effects are linear, breathing air including 10 µg/m3 PM2.5 is equivalent in mortality terms to smoking 22/24 of a cigarette each day. The Australian ambient air quality standard for PM2.5 exposure is set at an annual average of 8 µg/m3, which in this metric would be equivalent to 0.73 cigarettes a day. This calculation is based on mortality alone, and says nothing about the amount of particulate matter in cigarette smoke. In 2013, the New South Wales Environmental Protection Authority monitor at Beresfield, near the coal corridor to Newcastle, recorded annual average PM2.5 exposure of 8.3 µg/m3, so every adult and child in that district is exposed to this risk.

Debate continues as to whether there is a safe PM2.5 level, below which there is no health effect. Using the smoking analogy again, we cannot point to a cohort study showing health damage from smoking one cigarette a day, but no one would suggest that this level of smoking is safe.

There are many opportunities to improve air quality in Australia, such as restricting the mining and transport of coal in close proximity to residential areas, phasing out wood-burning heaters, shifting the electricity supply away from coal, and enforcing Australian emissions standards on ships in port. These improvements will not eventuate unless the public demands them, and better risk communication allows public participation in this technically complex area.