Association between air pollution, socioeconomic inequalities and cause specific mortality in a large administrative cohort in a contaminated site of central Italy

Introduction

The association between air pollution and mortality has been extensively explored in epidemiological literature in recent decades. Individual factors such as socioeconomic status (SES) and gender have been identified as significant contributors to population vulnerability to the health effects. This study aims to assess how individual (SES), environmental (air pollution) factors and their influence the risk of cause-specific mortality in an administrative cohort of residents of the River Sacco Valley (RSV), a contaminated site of central Italy.

Materials and methods

Individual exposure to pollutants (PM₁₀, PM_2.5, NO₂, SO₂, C₆H₆, O₃) at residential addresses was evaluated using dispersion models (FARM) with a 1 km² resolution from the Environmental Protection Agency of Lazio Region (ARPA Lazio). SES was determined by a 5-level area index at the census block level (high to low). Health data, coded with ICD-9 and ICD-10, included non-accidental (0–799 and (A00-R99)), cardiovascular (390–459 and (I00-I99)), respiratory (460–519 and (J00-J99)), and malignancy (140–250 and (C00-C97)) causes of mortality. Residents in the RSV and adjacent area (∼100 municipalities) were enrolled from January 1, 2008, to December 31, 2018. We used Cox proportional hazard models, adjusted for gender, SES, and air pollution to estimate the associations between exposure and outcomes. We also evaluated the interaction between air pollution and SES on the study outcomes. Finally, we estimated the health impact of air pollution by SES category.

Results

We enrolled 665,160 subjects (median age: 41 years) at the baseline. High SES constituted 8% while low SES 13% of the study population. We observed 59,767 non-accidental deaths during the study period. SES-related estimates show a clear pattern for each outcome, with HR for low SES up to 1.165 (1.097, 1.238) for non-accidental and 1.184 (1.087, 1.290) for cancer mortality. Air pollutants exhibited positive associations with cancer and respiratory mortality only, with estimates up to 1.05 (1.02, 1.07) and 1.06 (1.03, 1.09) for PM_2.5 and C₆H₆. Air pollution-SES interaction estimates were higher in the low SES category, with HRs up to 1.14 (1.07, 1.21) and 1.19 (1.10, 1.29) for non-accidental and cancer mortality with C₆H₆ exposure. Attributable fraction of causes-specific deaths were higher in lowest SES categories compared to highest ones.

Conclusions

Socioeconomic deprivation indicates individual frailty, and air pollution is a major environmental risk factor. However, the association of long-term exposure vary across the population. Higher effects were detected in socioeconomical deprivated subjects. A major public health concerns has to be faced about that.