Long-term exposure to elemental components of fine particulate matter and natural and cause-specific mortality in a Danish nationwide administrative cohort

Abstract

BACKGROUND AND AIM: Fine particulate matter (PM₂.₅) is an established risk factor for premature death, but it remains unclear which components and sources are most responsible. We investigated the associations between long-term exposure to PM₂.₅ components and mortality from all-natural causes, cardiovascular disease (CVD), respiratory diseases (RD), lung cancer, diabetes, chronic kidney disease (CKD), dementia, and psychiatric disorders in a Danish nationwide administrative cohort. METHODS: We followed all Danish residents aged ≥30 at January 1, 2000 (3,081,244) until December 31, 2017. Residential annual mean exposure PM₂.₅ components levels (copper, iron, zinc, sulfur, nickel, vanadium, silicon, and potassium) were estimated by Europe-wide land-use regression models at a 100×100m scale, developed within the "Effects of Low-Level Air Pollution: A Study in Europe” project, with two modeling approaches: supervised linear regression (SLR) and random forest (RF). We used Cox proportional hazard models to evaluate the associations between each component and mortality, adjusting for demographic, socioeconomic factors, and PM₂.₅ mass. RESULTS: The cohort accumulated 46,992,890 person-years, and 803,373 died from natural causes. For natural mortality, we observed significant positive associations [hazard ratios (HRs); 95% confidence intervals per interquartile range increase] with SLR-silicon (1.04; 1.03-1.05) and SLR-potassium (1.03; 1.02-1.04) and with RF- iron (1.02; 1.01-1.02), RF-zinc (1.02; 1.01-1.03), RF-nickel (1.01; 1.00-1.02), RF-vanadium (1.02; 1.01-103), RF-silicon (1.01; 1.00-1.02), and RF-potassium (1.06; 1.05-1.07). Potassium and silicon were most strongly associated with all causes of death except CKD and diabetes, respectively, with the highest HRs observed for psychiatric disorders. Furthermore, iron was associated with RD, lung cancer, CKD, and psychiatric disorders, zinc with RD, CKD, and lung cancer, and nickel and vanadium with lung cancer. CONCLUSIONS: We present novel findings that different PM₂.₅ components were relevant to different causes of death. Potassium and silicon seemed most consistently associated with mortality in Denmark. KEYWORDS: Long-term exposure, PM₂.₅ components, mortality