This study sought to determine the relationship between short-term exposure to air pollutants and hospital admissions and cardiovascular and respiratory mortality in Shahrekord, Iran.
We found a direct and significant statistical relationship between O3 in lag4 with total mortality (RR = 1.616 (95% CI: 1.092–2.390)) which is associated with a 61% increase in total mortality risk. A study by Jerrett M. in the United States found no significant association between ozone and cardiac mortality and total deaths. However, after modification of PM2.5, a slightly positive correlation was observed between ozone and mortality due to heart disease (Jerrett et al., 2009).
A study by Dockery et al. in the United Kingdom and Pope et al. in the United States reported no association between ozone and death from heart disease (Dockery et al., 1993; Pope et al., 2002).
In a study by Lipsett et al. in California, the association between ozone and death from ischemic heart disease (IHD) patients was hardly significant (hazard ratio (HR) = 1.06, 95% CI: 0.99–1.06). However, when the analysis was limited to summer, a significant positive correlation was found between ozone and IHD-related death. No association was observed between ozone and cardiac deaths (HR = 1.09, 95% CI: 1.01–1.19) (Lipsett et al., 2011).
Studies in the Netherlands, Finland and Germany on the effects of air pollution on blood pressure have found a significant negative correlation for ozone in multicenter studies (Ibald-Mulli et al., 2004).
The results of this study showed a statistically significant and direct relationship between exposure to PM10 and total deaths in lag1 (RR = 1.105 (95% CI: 1.016–1.202)), which was associated with a 10% increased risk of total death. There was also a statistically significant and direct relationship between PM10 exposure and respiratory mortality in lag4 (RR = 1.894 (95% CI: 1.281–2.799)), and lag1 (RR = 1.533 (95% CI: 1.019–2.308)), which was associated with 89% and 53% increases in risk, respectively.
A study in Ahvaz showed that the toxicity and risk of PM10 for the lung is more severe on dusty days than on other days due to more inhalation of pollutants (Naimabadi et al. 2016).
The EPA has shown that PM10 is exposed to oxidative stress and increased inflammatory markers in individuals (US Environmental Protection Agency. 40 CFR Part 50. National Ambient Air Quality Standards for particulate matter. Final rule. Fed Regist 2006;71:61144-233).
Analysis of the results of several studies has suggested that PM10 is effective in admitting respiratory patients to the hospital. For example, a 2001 study by Atkinson et al. in eight European cities found that for every 10 micrograms of PM10 increase, the risk of respiratory disease increases to 0.9 percent (Atkinson et al., 2001).
The results of this study showed a statistically significant and direct relationship between exposure to PM2.5 and cardiovascular admissions in lag5 (RR = 1.146 (95% CI: 1.042–1.261)), respiratory mortality in lag4 (RR = 1.842 (95% CI: 1.076–3.154)) and respiratory admissions in lag3 (RR = 1.138 (95% CI: 1.003–1.292)).
A study by Kloog et al. (2014) on three million CVD admissions in the United States estimated that for every 10 micrograms per cubic meter of PM2.5, the delay increased from 0–1 PM2.5, 1.04 (0.56٪ ، 1.51٪) 0.7٪ (0.44٪, 0.96٪) were observed in rural and urban areas, respectively (Kloog et al., 2014).
A study by Qing Tian et al. in Shanghai, China, found that for every 10 micrograms per cubic meter of PM2.5, there would be a 1.26 percent increase in cardiovascular disease (CVD) mortality (1.26%) (95 % CI: 0.40%, 2.12%) which is higher compared to other studies (between 0.63% and 0.80%) (Achilleos et al., 2017; Lu et al., 2015).
A multicenter meta-analysis study in Shanghai, China, East Asia suggested that for every 10 micrograms per cubic meter of PM2.5 increased by 0.96%, 0.96% (95% CI: 0.46%, 1.46%), there was an increase in mortality from heart disease, which is relatively similar to this study (Lee et al., 2015).
A study by Xu et al. showed that increasing every 10 micrograms per cubic meter of PM2.5 concentration is positively associated with a 0.56% increase in CHD uptake in lag0–1 (95% CI: 0.16–0.95%), and an increase of 0.81% (HRD) to 1.57% lag0–1 (95% CI: 0.05 - and 1.21% increase in (HF) (95% CI: 0.27–2.15%) (Xu et al., 2016).
A significant relationship was found between daily mortality with an increase in PM2.5 and PM10 in one day and a cumulative delay of 6 days in Taiyuan, which is consistent with previous studies (Liang et al., 2018).
Several studies have shown a positive statistical association between CVD-related mortality and infection with PM2.5 (Ma et al., 2017; Su et al., 2016).
A recent study on 248 cities in China found that a 10 µg/m3 increase in PM2.5 was significantly associated with a 0.26% increase in hospital admission for transient ischemic attack (TIA) (Gu et al., 2020).
A statistically significant relationship was found between NO2 exposure and death from loss of respiration in lag1 (RR = 1.236 (95% CI: 1.017–1.502)), with a 23% increased risk as well as cardiovascular mortality in lag0 (RR = 1.057 (95% CI: 1.008–1.109)), with a 5% increase in risk.
Multivariate regulated analysis used in a study on relationship between air pollution and mortality in French showed that relative risk of deaths from heart disease is 1.27 NO2 micrograms per cubic meter (95% CI: 1.04– 1.56), which is statistically significant (Filleul et al., 2005).
Dadbakhsh et al. in Shiraz found that NO and NOX had a significant and direct relationship with total deaths from heart disease and female deaths in the same month and the following month (Dadbakhsh et al., 2016).
The strengths of this study were: Firstly, all data related to diseases and mortality were collected from government and trusted organizations in Chaharmahal and Bakhtiari Province (Shahrekord), making it a relatively large sample size. Secondly, a 7-year period and the large amount of data allowed us to examine interactions with a high level of validity and reliability. Thirdly, inclusion of three air pollution monitoring sites provided us the basis for better demonstration of the effects of air pollution compared to other studies.
Another strength of our study is taking advantage of approaches and methodology used in studies conducted in Europe, examining the potential role of dust as a mediator of the relationship between exposure to particles and mortality.
Our research has some limitations. Similar to other studies, the effects and interplay between air pollutants and health (mortality and hospital admission) requires further research. The effect might vary for each region.
4.1. Conclusion Air pollution is significantly associated with hospital admissions and mortality in Shahrekord, Iran. Effective interventions and environmental policies need to be implemented and adopted to mitigate air pollution and minimize exposure to pollutants.