Temporal trends of PM and its impact on mortality in Lombardy, Italy.

Introduction: Exposure to particulate matter with diameter ≤10 μm (PM) entails well documented adverse effects on human health. In the last decade, concentration of PM in Lombardy (10 million inhabitants), Italy, has been gradually decreasing. We evaluated how the mortality burden due to PM varied in that same period.

Methods: We focused on 13 areas of the Region in 2003-2014: 11 cities with more than 50,000 inhabitants, 1 smaller alpine town and 1 agricultural province. For each area, we collected PM annual average concentrations and natural mortality data, and we used the posterior area-specific effects from a previous Bayesian meta-analysis to estimate the short-term impact of PM on mortality, in terms of deaths attributable (AD) to annual average exposures exceeding the WHO threshold of 20 μg/m.

Results: PM annual average values showed a non-homogenous decreasing trend in the investigated time period in most of the areas. Overall, the population-weighted exposure levels decreased, except for a peak in 2011, but never met the WHO threshold. In 2003-2006, PM levels were responsible, on average, for 343.0 annual AD from natural causes that decreased to 253.5 in 2007-2010 and to 208.3 in 2011-2014. Overall we estimated that PM was responsible for about 1% of all natural deaths (min-max range: 0.86%-1.42%); the impact was heterogeneous among areas.

Conclusions: By collecting routinely available data for the most populated areas in Lombardy, we returned a picture of air pollution and health trends in the last decade. Notwithstanding the observed reduction in PM between 2003 and 2014 and the resulting decline in the number of AD, the impact is still relevant. Hence, appropriate policies for emission reduction could have a further beneficial effect on population health. Studies based on routine data and local effect estimates are recommended to properly inform the policy-making process.