Short-term effect of fine particulate matter on daily mortality: Effect modification by prolonged continuous exposure to high concentration

Abstract

BACKGROUND AND AIM: Although the evidence for short-term mortality effect is very high, the epidemiological study for the effect of prolonged continuous exposure to high concentration is rare. The aim of this study is to investigate how the size of the mortality effect of PM₂.₅ would be modified when high concentration period persist. METHODS: We used daily mortality counts (non-traumatic all-cause, respiratory, and cardiovascular), simulated daily PM₂.₅ concentrations, measured daily mean temperature and relative humidity data in seven metropolitan cities (Seoul, Busan, Daegu, Incheon, Gwangju, Daejeon, and Ulsan) during 2006 to 2019. Generalized additive models (GAMs) with quasi-Poisson distribution in the seven cities and Random effect meta-analyses for pooling the city-specific effects were used to examine the short-term effects of PM₂.₅ on mortality. To investigate effect modification by prolonged continuous exposure to high concentration(referent level: 35 μg/m³), we applied categorical consecutive day variables to the GAMs as effect modification terms with PM₂.₅ concentration variables. RESULTS:The daily percent changes per 10 μg/m³ of daily PM₂.₅ concentration for all-cause, respiratory, and cardiovascular mortality were 0.31% (95%CI: 0.16 – 0.46, lag 0 model), 0.61% (95%CI: -0.02 – 1.24, lag 0-2 model), 0.37% (95%CI: 0.08 – 0.66, lag 0 model), respectively. In the effect modification model for all-cause mortality applied lag 0-1 PM₂.₅ exposure, the daily percent changes per 10 μg/m³ for first, second and third, and fourth day or more of consecutive days were 1.30% (95%CI: 0.05 – 2.57), 0.18% (95%CI: -0.70 – 1.06), and 1.19% (95%CI: 0.31 – 2.08). This pattern was similar in the models for cardiovascular than respiratory mortality. CONCLUSIONS:We found a greater effect on daily mortality of daily PM₂.₅ exposure when the high concentration day began and the days lasted for more than fourth days with high concentration. KEYWORDS: Air pollution, Short-term exposure, Environmental epidemiology, Mortality