Effects of exposure to chemical components of fine particulate matter on mortality in Tokyo: A case-crossover study

Fine particulate matter (PM_2.5) is composed of a variety of chemical components, and the dependency of the health effects of total PM_2.5 on specific components is still under discussion. We hypothesised that specific PM_2.5 components are responsible for the health effects, and investigated the association between PM_2.5 components and mortality in 23 Tokyo wards. We obtained mortality data from the Ministry of Health, Labour and Welfare for the period from April 2013 to March 2017. At a monitoring site within the study area, we collected daily samples of PM_2.5 on a filter, and determined the daily mean concentrations of total carbon (organic carbon and elemental carbon) and ions such as nitrate and sulphate. A case-crossover design was employed, and a conditional logistic regression model was used to estimate the strength of the association. Over the study period, we identified 280,460 total non-accidental deaths, and the average daily mean concentration of total PM_2.5 was 16.0 (standard deviation = 8.9) μg/m³. We observed a positive association of total PM_2.5 with total, cardiovascular, and respiratory mortality. After adjustment for total PM_2.5 and its components associated with mortality in the single-component models, the percentage increase per interquartile range (2.3 μg/m³) increase in the average total carbon concentration of the case- and previous-day was 2.1% (95% confidence interval = 1.0 to 3.1%) for total mortality. Carbon elements were associated with respiratory but not cardiovascular mortality. Our results suggest that specific components of PM_2.5 account for its adverse health effects.