Long-term exposure to air pollution appears to still be linked to higher mortality despite the existence of air quality standards that restrict levels of pollution, suggests a study published online in The BMJ today.
Previous studies have found an association between long term exposure to outdoor air pollution such as those in the form of fine particles in the air (known as particulate matter or PM2.5) and nitrogen dioxide (NO2) and illness or mortality.
While air pollution concentrations have fallen substantially in Europe since the 1990s, it is unclear whether there still is a link between pollution and ill health or death at pollution levels under permitted levels.
Therefore, researchers set out to determine if there was an association between low levels of air pollution concentrations and natural and cause-specific deaths.
Low-level air pollution was defined as concentrations below current limits set by the European Union, US Environmental Protection Agency and the World Health Organization (WHO).
The researchers analysed data on eight groups of people within six European countries. Their study recruited participants in the 1990s or 2000s. Of the 325 367 participants who were followed up over an almost 20-year period, around 14.5% (47 131 people) died during the study period.
An increase of 5 µg/m3 (a concentration measure of particulate matter) in particulate matter (PM2.5) was associated with a 13% increase in natural deaths while the corresponding figure for a 10 µg/m3 increase in nitrogen dioxide was 8.6%. Associations with PM2.5 and NO2 were largely independent of each other.
Moreover, even at low to very low concentrations, associations with PM2.5, NO2, and black carbon remained significant. For people exposed to pollution levels below the US standard of 12 µg/m3, an increase of 5 µg/m3 in PM2.5 was associated with a 29.6% increase in natural deaths. People exposed to NO2at less than half the current EU standard of 40 µg/m3, a 10 µg/m3 increase in NO2 was associated with a 9.9% increase in natural deaths.
The study also has some limitations, the researchers said, such as the fact that it focused on exposure in 2010 which was towards the end of the follow-up period for most participants and, given falling air pollution, this measure might not exactly reflect the concentrations experienced during follow-up.
However, this was a large study from multiple European groups of people with detailed information provided. As such, the authors concluded: “Our study contributes to the evidence that outdoor air pollution is associated with mortality even at levels below the current European and North American standards and WHO guideline values.
“These findings are therefore an important contribution to the debate about revision of air quality limits, guidelines and standards, and future assessments by the Global Burden of Disease [study].”
Source: The BMJ
