Carcinogenic risks of particulate matter during Middle Eastern dust events and normal days
Introduction
Air pollution is known as the leading environmental health risk factor, causing more than seven million deaths annually (WHO, 2014). Among the criteria air pollutants, particulate matter (PM) produces the most significant risks. PM is categorized based on the aerodynamic diameter and emission sources (Wang et al., 2006). Particles originating from different sources may have different toxicities (Rich et al., 2019; Croft et al., 2020; Hopke et al., 2020). Recently, several epidemiological studies have suggested that the effects of dust particles on mortality and hospitalization differ from those of urban PM. Most of these studies have reported that the risk of dust PM is greater than anthropogenic PM (Mallone et al., 2011; Stafoggia et al., 2016). The mechanism and magnitude of this difference have been an important subject for recent studies.
Strong associations between exposure to PM and lung cancer has been observed (Straif et al., 2013). This effect stems its chemical constituents such as carbonaceous compounds and heavy metals present in the particles. Heavy metals such as arsenic (As), cadmium (Cd), chromium (Cr), nickel (Ni), and lead (Pb) have been designated as human carcinogens (As, Cd, and Cr) or probable human carcinogens (Ni and Pb) (USEPA, 2017). These species are emitted by various sources including industries (metal industries, cement manufacture, chrome plating, etc.), vehicles, and natural sources (Ashrafi et al., 2018). Therefore, lifetime inhalation of these elements can increase the risk of cancer in a population exposed to polluted air.
Ahvaz is a city in southern Iran that is one of the most polluted cities in the world owing to the presence of multiple emission sources (Hopke et al., 2017). First, this city is affected by the severe dust storms called Middle Eastern dust storms (MED) during most of the year MED produce elevated PM concentrations with aerodynamic diameter <10 μm (PM10), <2.5 μm (PM2.5), and <1 μm (PM1) with concentrations up to ~5000, 900, and 500 μg/m3, respectively. Second, the presence of large oil extraction and petrochemical industries and other industries release a wide range of pollutants to the atmosphere. Ahvaz has a population about 1.5 million and is affected by traffic-related air pollution. Source apportionment studies of the PM in Ahvaz have shown that the likely sources of particles include crustal dust, road dust, motor vehicles, marine aerosol, secondary aerosol, metallurgical plants, petrochemical plants, fossil fuel combustion, and vegetative burning (Sowlat et al. 2012, 2013; Ashrafi et al., 2018).
The air quality and toxicity of airborne PM of Ahvaz has been extensively studied (Goudarzi et al., 2019; Naimabadi et al., 2016). However, no evidence has been reported about the carcinogenic risks of exposure to chemical species present in airborne PM. Such studies can demonstrate the excess cancer risk induced by exposure to carcinogen compounds and elements (Kermani et al., 2018; Park et al., 2008). The work presented here is clearly relevant throughout the Middle East and into India and Nepal where dust can be transported under Western Disturbances (e.g., Tiwari et al., 2015) that occur in winter and bring air masses from the Middle East that include dust loads. These storms aerosolizing and transported dust in this region is on international interest from a health perspective. Since the concentrations and chemical composition of PM on dusty and normal days are different, it can be hypothesized that the carcinogenic effects from these two types of atmospheric pollution will be also different. A health risk assessment study investigating the cancer risks of both dust and normal days with their actual frequencies in a year can reflect the real excess carcinogenic risks imposed to the population. In addition, since the concentrations of PM and heavy metals can vary significantly in different years or areas, conducting a Monte Carlo simulation which estimate the distribution of risks based on the distribution of concentrations would provide a more realistic estimation. This has been neglected in most of the similar studies. Therefore, the aim of this study was to estimate and compare the carcinogenic risks due to exposure to PM-bound heavy metals during dusty and normal days in Ahvaz, Iran.
Section snippets
Study design and sampling
This study was conducted in Ahvaz, located in an arid area of southwestern Iran. Eight major sources of air pollution in this city may include: dust storms (41.5%), road dust (5.5%), motor vehicles (11.5%), marine aerosol (8.0%), secondary aerosol (9.5%), metallurgical plants (6.0%), petrochemical industries and fossil fuel combustion (13.0%), and vegetative burning (5.0%) (Sowlat et al., 2013). Dust storms in this area mainly originate from other countries such as Saudi Arabia, Kuwait and
Results
The concentrations of 5 p.m.-bound heavy metals (arsenic, cadmium, chromium, nickel, and lead) were measured during both dust and non-dust days. The data were fitted to normal and lognormal distributions as shown in Figs. S1–S6 in supplemental material. In each case, the null hypothesis of a lognormal distribution could not be excluded based on Kolmogorov-Smirnov tests. Table 1 presents the geometric mean and geometric standard deviation of PM10 and five heavy metals. Geometric mean vales of PM
Discussion
In the present study, PM10 was sampled for one year, and the concentrations of PM-bound heavy metals including As, Cd, Cr, Ni, and Pb were determined. The total carcinogenic risks of heavy metals were substantial on both dusty and normal days. In addition, season of year positively affected the carcinogenic risk. A recent epidemiological study in Ahvaz showed that daily mortality had a higher association with PM10 on extreme dust days than on moderate dust days (Shahsavani et al., 2020).
Conclusions
In this article, the carcinogenic risks attributed to the PM10-bound heavy metals observed during dust and non-dust days were estimated. The summed carcinogenic risks in both dust and non-dust days exceeded than the US EPA's limit. Our study indicated that occurrence of dust events can increase the carcinogenic risks via inhalation. Although dust events are short-term, acute episodes, their high frequency and intensity in some affected areas such as Ahvaz with about 100 dust days per year can
CRediT authorship contribution statement
Meghdad Pirsaheb: Formal analysis, Writing - original draft. Kiomars Sharafi: Formal analysis, Writing - original draft. Philip K. Hopke: Formal analysis, Writing - original draft. Mostafa Hadei: Formal analysis, Writing - original draft. Abbas Shahsavani: Formal analysis, Writing - original draft.
Declaration of competing interest
The authors declare no conflicts of interest.
Acknowledgements
The authors wish to thank Kermanshah University of Medical Sciences and Tehran University of Medical Sciences for their full support.
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2021, Science of the Total EnvironmentCitation Excerpt :In addition, the short- and long-term exposures to air pollution are allied with health effects in the vascular system and the respiratory system. The most important components of air pollutants are particulate matter (PM) that are linked to hospital visits due to cardiovascular and respiratory diseases (Khamutian et al., 2015; Mirzaei et al., 2015; Pirsaheb et al., 2020; Sharafi et al., 2015). It has calculated that for a 10 μg/m3/day increase in the concentration of PM2.5, the rate of respiratory diseases is increased by 2.07%, and the hospital attending rate is increased by 8% (Zanobetti et al., 2009).
Peer review under responsibility of Turkish National Committee for Air Pollution Research and Control.