Susan Mayor, 22 June 2009
Long term exposure to air pollutants is associated with increased mortality, warns a major UK report published this week, which has also defined the most useful measure of air pollution in developing strategies to reduce adverse effects on health.
The new report follows up a 2001 review that looked at the long term effects of exposure to air pollutants on health, itself based on two major US studies. That review said that a causal relationship with mortality was “more likely than not” and that the studies’ findings were applicable in the UK.
Research in the field has progressed rapidly since its earlier review, so the Committee on the Medical Effects of Air Pollutants—an expert committee that advises the UK government—decided it needed to review the latest evidence, including a European cohort study.
“We are left with little doubt that long-term exposure to air pollutants has an effect on mortality and thus decreases life expectancy,” the committee warns in its report, and it explains that the new evidence has strengthened the association, particularly with particulates.
After reviewing a first draft of the report Michael Krzyzanowski, regional adviser on air quality to the World Health Organization and health head of the European Centre for Environment and Health, Bonn, said, “The estimates of burden of disease, based on the conclusions from this evidence, indicate very significant public health impacts and have important policy implications.”
The committee recommends PM2.5 (the mass per cubic metre of particles passing through the inlet of a size selective sampler with a transmission efficiency of 50% at an aerodynamic diameter of 2.5 micrometres) as the best measure of particulate air pollution for quantitative assessment of the effects of policy interventions. Particles less than 2.5 micrometres in diameter are small enough to be deposited in the alveoli, particularly in high risk groups such as children and sick people.
The committee found that the relative risk of mortality from all causes rose by 6% with a 10 microgram per cubic metre increase in PM2.5. With the same increase in particulate matter, the risk of cardiopulmonary mortality rose by 9% and of lung cancer mortality by 8%.
Evidence for the possible effects of long term exposure to the common air pollutant gases—sulphur dioxide, nitrogen dioxide, and ozone—was less clear than that for particulate air pollution.
“In none of these cases [gases] have we been persuaded that the evidence base is yet sufficiently strong to warrant quantification,” the committee reported. “The problem is one of inadequate evidence rather than evidence for there being no effects. Better evidence might well lead us to change our views in this area.”
The committee is now working on a further report looking at the effects of exposure to air pollutants on morbidity.