Long-term exposure to tiny particles of soot or dust found in traffic fumes and industrial emissions may be more deadly than previously thought even at levels below current European Union (EU) air-quality limits according to an analysis of two decades of data on more than 360 000 residents of large cities in 13 European countries.
The study, published in The Lancet, estimates that for every increase of 5 microgrammes per cubic metre (5 µg/m3) in annual exposure to fine-particle air pollution (PM2.5), the risk of dying (from natural causes) rises by 7%.
"A difference of 5 µg/m3 can be found between a location at a busy urban road and at a location not influenced by traffic", explains one of the study participants Dr Mark Nieuwenhuijsen, a researcher at the Centre for Research in Environmental Epidemiology (CREAL), an ISGlobal alliance research centre. The study leader, Dr Rob Beelen from Utrecht University in the Netherlands, adds "Our findings support health impact assessments of fine particles in Europe which were previously based almost entirely on North American studies".
The researchers analyzed data on 367 251 people included in 22 ongoing cohort studies within the European Study of Cohorts for Air Pollution Effects (ESCAPE). Annual average air pollution concentrations of nitrogen oxides and particulate matter were linked to home addresses using land-regression models to estimate exposures. Traffic density on the nearest road and total traffic load on all major roads within 100 metres of the residence were also recorded.
Overall, 29 076 participants died from natural causes during the average 13.9 years of follow up. The results showed that prolonged exposure to PM2.5 posed a significant threat to health even when levels were well below current European Union limit values.
The association between prolonged exposure to PM2.5 and premature death remained significant even after taking into account a wide range of confounding factors, such as smoking status, socioeconomic status, physical activity, education level, and body-mass index.
The researchers also noted a gender effect in that PM2.5 was associated with excess mortality in men but not in women.
According to Beelen, "Our findings suggest that significant adverse health effects occur even at PM2.5 concentrations well below the EU annual average air-quality limit value of 25 µg/m3. The WHO air-quality guideline is 10 µg/m3 and our findings support the idea that significant health benefits can be achieved by moving towards this target."
In their comments on the study published in the Lancet researchers from the University of Edinburgh said, "Despite major improvements in air quality in the past 50 years, the data from Beelen and colleagues' report draw attention to the continuing effects of air pollution on health. These data, along with the findings from other large cohort studies, suggest that further public and environmental health policy interventions are necessary and have the potential to reduce morbidity and mortality across Europe. Movement towards more stringent guidelines, as recommended by WHO, should be an urgent priority".