Abstract
There is large epidemiological evidence on the short-term health effects of O3 and NO2. These gaseous pollutants induce oxidative stress through their oxidative potential. Therefore, the evaluation of their combined oxidative capacity (Ox) has been proposed rather than studying the effect of either gas individually. To study the short-term effects of daily concentrations of O3, NO2, and Ox on mortality in Rome, in 2002–2015, daily deaths from the city mortality registry were analyzed along with O3 and NO2 levels observed in Rome and with estimated Ox and Owt (Ox, weighted by the redox potential of O3 and NO2). A Poisson regression model was used considering trends, and meteorological and population changes. The effects on mortality were estimated at lag 0–1 and 0–5 for 10 μg/m3. O3 and NO2 were associated with mortality, with the highest effects at lag 0–5, 0.81% (0.45–1.17) and 2.72% (2.07–3.37), respectively. Ox had an intermediate effect between the two gases. After adjusting for PM10, Owt had a stronger effect (1.72%; 1.14–2.30) than either gas, 0.86% (0.50–1.22) for O3 and 1.61% (1.15–2.06) for NO2. Both Ox and Owt were associated with cerebrovascular, respiratory and, to a lesser extent, cardiac mortality more than either gas. These results suggest that the use of Ox (or Owt) can provide a better assessment of the combined role of O3 and NO2 on mortality and can avoid the uncertainty of the threshold level for ozone. The brain and lungs seem to be the main targets of O3 and NO2.
Highlights
The potential to cause a redox reaction refers to the capacity of environmental factors to oxidize target molecules generating reactive oxygen species (ROS) (Ayres et al 2008; Künzli et al 2006; Møller et al 2014)
The daily distribution of O3, NO2, and oxidative capacity (Ox) levels (Supplementary Fig. 1) shows Ox levels higher than both gases, with NO2 making the larger proportion of Ox at lower Ox and O3 making inversely the larger proportion of Ox at higher Ox, suggesting that Ox levels might be most influenced by O3 in hot seasons
Combined Ox has an effect comprised between that of the two gases, while weighted oxidative capacity has a stronger effect on mortality than either of the two gases when 1-h levels are considered, which remains significant after adjusting for PM10 or PM2.5
Summary
The potential to cause a redox reaction refers to the capacity of environmental factors to oxidize target molecules generating reactive oxygen species (ROS) (Ayres et al 2008; Künzli et al 2006; Møller et al 2014). Oxidative stress could be considered as beneficial at low doses and harmful at moderate to high doses (Schieber and Chandel 2014). Gaseous pollutants, such as gaseous ions, organic components, and secondary radicals, induce oxidative stress through their oxidative potential, but few studies (Delfino et al 2013; Pavlovic et al 2015; Steenhof et al 2014; Weichenthal et al 2016; Williams et al 2014) have dealt with this topic due to objective difficulties in estimating oxidative potential from atmospheric gases. The difficulty regarding gases consists essentially in the measurement given that redox active semi-volatile compounds such
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