How large a risk to health is air pollution in the European Region, and is there evidence indicating effective measures to reduce it?

Summary of a HEN network member’s report

The issue

Exposure to ambient air pollution has been linked to a number of health outcomes: from modest transient changes in the respiratory tract and impaired pulmonary function; to restricted activity, reduced performance, emergency room visits and hospital admissions; and finally to mortality. Increasing evidence for the adverse effects of air pollution covers not only the respiratory system, but also covers the cardiovascular system. This evidence stems from studies on both acute and chronic exposure.

People are exposed to a mixture of pollutants, emitted by a variety of sources. To a large extent, these sources are related to everyday human activity in a number of sectors, such as transport, energy production, industry and agriculture. Some of the pollutants are created in the atmosphere from precursor pollutants, and some travel over long distances, cross national borders and create health risks far from the source of the emissions. The main health concerns are associated with particulate matter (PM) – that is, solid particles and droplets suspended in the air. The size, composition and origin of PM vary, and it can be emitted directly or can be created from precursor gases in the atmosphere. Another common air pollutant of concern to health is tropospheric ozone, which is created from nitrogen oxides and other gases in the presence of ultraviolet radiation – emitted mostly from processes that involve combustion.

Findings

Reviewing the adverse effects on health of ambient air pollution is a challenging task. It involves the assessment of a remarkably large body of evidence, which includes hundreds of recently published scientific papers that address such aspects as exposure, and toxicological and epidemiological findings on adverse health effects.

Risks to health

A recent analysis, conducted to support the development of a European strategy on clean air, concluded that long-term exposure to PM in air claims an average of 8.6 months from the life of every European. Every year, more than 280 000 premature deaths are attributed to long-term exposure to PM in the 25 countries of the European Union (EU). Less severe, but even more numerous, are the cases of chronic bronchitis, days of restricted activity, unscheduled admissions to hospitals due to respiratory and cardiac symptoms, and episodes of respiratory diseases in children and adults. Considering that pollution levels in many non-EU countries are higher than in the EU, the harmful, significant impacts of air pollution on health are an important public health issue in all European Region.

Evidence indicates that PM increases the number of deaths from cardiovascular and respiratory diseases. Even a short-term rise in PM concentration increases the risk of emergency hospital admissions for cardiovascular and respiratory causes. Inhaled, particles with a diameter smaller than 10 µm (designated PM10) may reach the upper part of the airways and lungs. Fine particles, with a diameter smaller than 2.5 µm (designated PM2.5), are more dangerous, as they penetrate more deeply into the lungs and may reach the alveoli. The risk of mortality is increased by about 6% with increase of long-term exposure by PM2.5 by 10 µg/m3. Studies, however, have been unable to identify a threshold concentration below which PM in ambient air has no effect on health.

Evidence also indicates that every year, in the 25 EU countries, exposure to ozone causes more than 21 000 deaths, 14 000 hospital admissions for respiratory causes and hundreds of thousands of episodes of respiratory symptoms that require the use of medication. Moreover, recent studies have strengthened the evidence for the short-term effects of ozone on mortality and morbidity, which are independent of the effects of PM. A WHO meta-analysis indicates that daily mortality increases by about 0.3% with a 10-µg/m3 increase in daily 8-hour mean ozone concentration.

Effective measures to reduce air pollution

In the past, after the introduction of clean air legislation, reductions in PM concentrations in ambient air were associated with positive impacts on public health. More recently, a limited number of studies reported such positive impacts. Toxicological findings also suggest that qualitative changes in PM composition may lead to reductions in PM-induced adverse effects on health.

There are very few opportunities, per se, to evaluate reduced exposure to ozone. One study of intrastate migrants showed a beneficial effect on lung function in children who moved to areas with lower PM and ozone concentrations. Also, a decrease in ozone concentration during the 1996 Olympics was associated with a reduction in asthma admissions to hospitals. The interpretation of these findings, however, is unclear.

Policy considerations

Although reduced exposure to PM and ozone are key to improving health, it will not eliminate all significant adverse health effects of such exposure. This means it is important to reduce PM pollution to concentrations lower than those specified in current legislation. To accomplish this task, already existing cost-effective methods should be used.

Type of evidence

The review assessed information from different research disciplines, including observational epidemiology, controlled human exposure to pollutants, animal toxicology and in vitro mechanistic studies. Each of these approaches has its strengths and weaknesses, and the integration of these sources of information led to the conclusions presented herein.

The views expressed in this summary are based on a publication of a HEN Network member agency and do not necessarily represent the decisions or stated policy of WHO/Europe.