Interaction between oxidant pollutants and ambient temperature on cardio-cerebrovascular mortality risks in Guangzhou, China

Background  The increasing threats of air pollution and extreme weather have been widely recognized in recent years in China, but their individual and joint effects on cardio-cerebrovascular mortality are unclear.

Objective  This study aims to investigate the individual effects of and potential interactions between oxidant pollutants and ambient temperature on cardio-cerebrovascular mortality risks.

Methods  We collected daily data on death counts of cardio-cerebrovascular diseases, concentrations of ambient air pollutants, and meteorological parameters in Guangzhou, Chinabetween 1 January 2006 and 31 December 2016. A generalized additive model with a Poisson distribution was conducted to assess the associations of oxidant pollutants and ambient temperature with cardio-cerebrovascular mortality risks. Bivariate response surface models and stratified analyses were further adopted to qualitatively and quantitatively examine the potential interactions between oxidant pollutants and ambient temperature on cardio-cerebrovascular mortality risks.

Results  During the study period, the daily averages were 60.3 μg·m⁻³ for ozone (O₃), 50.9 μg·m⁻³ for combined atmospheric oxidant capacity (O_x), 32.5 μg·m⁻³ for nitrogen dioxide (NO₂), and 22.3℃ for ambient temperature. The average daily death counts of coronary and stroke diseases were 20 and 15, respectively. Per 10 μg·m⁻³ increment in O₃, O_x, and NO₂ were associated with increased coronary mortality risks (excess risk, ER) of 1.26% (95%CI: 0.79%-1.74%), 1.61% (95%CI: 0.99%-2.23%), and 1.33% (95%CI: 0.59%-2.07%), and with increased stroke mortality risks of 1.56% (95%CI: 1.04%-2.09%), 2.30% (95%CI: 1.60%-3.01%), and 2.93% (95%CI: 2.07%-3.79%) over cumulative lags of 2-5 days, respectively. The exposure-response relationships between ambient temperature and coronary and stroke mortality risks exhibited an inverse "J" shape, with the minimum mortality at temperatures of 25.7℃ for coronary disease and 27.3℃ for stroke. Our results further showed potentially synergic effects of higher temperatures and higher levels of O₃ and O_x exposures on coronary mortality risks, and the relative ER due to interactions was 0.103 (95%CI: 0.028-0.178) for O₃ and 0.079 (95%CI: 0.004-0.154) for O_x. We didn't find evidence of an interaction between oxidant pollutants and low temperature.

Conclusion  Short-term exposures to oxidant pollutants are associated with increased cardio-cerebrovascular mortality risks, and the interactive effects of high temperature and oxidant pollutants are synergistic in relation to cardio-cerebrovascular mortality risks.