Particulate matter air pollution components and risk for lung cancer

Highlights

• Particulate matter air pollution is a human lung carcinogen.

• The particulate matter components being responsible have not been identified.

• This study indicates that various components are responsible.

• The sulfur and nickel containing particles might be particularly important.

Abstract

Background

Particulate matter (PM) air pollution is a human lung carcinogen; however, the components responsible have not been identified. We assessed the associations between PM components and lung cancer incidence.

Methods

We used data from 14 cohort studies in eight European countries. We geocoded baseline addresses and assessed air pollution with land-use regression models for eight elements (Cu, Fe, K, Ni, S, Si, V and Zn) in size fractions of PM_2.5 and PM₁₀. We used Cox regression models with adjustment for potential confounders for cohort-specific analyses and random effect models for meta-analysis.

Results

The 245,782 cohort members contributed 3,229,220 person–years at risk. During follow-up (mean, 13.1 years), 1878 incident cases of lung cancer were diagnosed. In the meta-analyses, elevated hazard ratios (HRs) for lung cancer were associated with all elements except V; none was statistically significant. In analyses restricted to participants who did not change residence during follow-up, statistically significant associations were found for PM_2.5 Cu (HR, 1.25; 95% CI, 1.01–1.53 per 5 ng/m³), PM₁₀ Zn (1.28; 1.02–1.59 per 20 ng/m³), PM₁₀ S (1.58; 1.03–2.44 per 200 ng/m³), PM₁₀ Ni (1.59; 1.12–2.26 per 2 ng/m³) and PM₁₀ K (1.17; 1.02–1.33 per 100 ng/m³). In two-pollutant models, associations between PM₁₀ and PM_2.5 and lung cancer were largely explained by PM_2.5 S.

Conclusions

This study indicates that the association between PM in air pollution and lung cancer can be attributed to various PM components and sources. PM containing S and Ni might be particularly important.

Introduction

We recently reported from the European Study of Cohorts for Air Pollution Effects (ESCAPE) that particulate matter (PM) in air pollution with diameters of < 10 μm (PM₁₀) and 2.5 μm (PM_2.5) is associated with a risk for the development of lung cancer (Raaschou-Nielsen et al., 2013). This result, among others, formed the basis for classification of outdoor air pollution and PM in outdoor air as carcinogenic to humans in a recent Monograph of the International Agency for Research on Cancer (Loomis et al., 2013). Most knowledge about associations between air pollution and risk for lung cancer is based on measures of exposure to PM as a whole (Hamra et al., 2014), sulfur oxide-related pollution (Dockery et al., 1993, Pope et al., 2002), oxides of nitrogen (Nafstad et al., 2003, Raaschou-Nielsen et al., 2011) or cruder indicators such as proximity to traffic (Beelen et al., 2008, Hystad et al., 2013). PM is a complex mixture of particles from different sources with different composition. Little is known about the associations between specific components of PM and risk for cancer, although this could be of major importance in choosing the most efficient strategies for reducing the exposure of populations to carcinogenic air pollution.

As the concentrations of specific components of PM in air are often correlated, it is difficult to single out the specific components responsible for observed associations with health effects. A specific issue in air pollution epidemiology is to assess whether associations for specific components are stronger than associations for particle mass (Mostofsky et al., 2012). Particle mass is used in air quality regulations. Associations with lung cancer have been indicated in studies of exposure to the PM components elemental Carbon (Garshick et al., 2012, Steenland et al., 1998) and polycyclic aromatic hydrocarbons (Yuan et al., 2014), but, to our knowledge, no work on associations between exposure to other elements of PM and risk for lung cancer in general populations has been published. PM elements in air can serve as indicators of air pollution from different sources, but their compounds may also be carcinogenic for the lung per se, as seen for nickel International Agency for Research on Cancer Monograph Working Group, I, 2012.

Within the European study of Transport-related Air Pollution and Health Impacts—Integrated Methodologies for Assessing Particulate Matter (TRANSPHORM; www.transphorm.eu/), we analyzed data from the 14 cohort of the ESCAPE (www.escapeproject.eu/) study on lung cancer where PM air pollution was measured to determine associations between elementary components of PM air pollution at the residence and risk for lung cancer. A secondary aim was to investigate whether any particular elementary component could explain the previously observed association between PM air pollution and lung cancer.