1. Introduction
Dust storms are natural phenomena, most of which originate in desert or semi-desert drylands, in which dust particles are transported away from the main source, sometimes over thousands of kilometers [
1]. The northern region of the Arabian region is characterized by complex dust storm trajectories where they pass through the western desert of Syria and Iraq toward the Mesopotamian flood plain reaching the northeastern region of the peninsula into Kuwait at a dust fallout rate of 61.4 tons per km
2 per year, where fallen dust compromises 37% of sand particles [
2,
3]. A particular feature of blown dust is its extreme particulate matter intensity that increases the ambient air dust concentrations for several days. Dust particles include both PM
10 and PM
2.5 particle sizes which have an aerodynamic diameter smaller than 10 and 2.5 μm, respectively. A large number of desert dust contains particles with concentrations exceeding the guidelines established by the World Health Organization (WHO) for human health protection (20 μg/m
3 annual average; 50 μg/m
3 a daily average) [
4]. Atmospheric concentrations in individual dust events have recorded PM
10 levels of 1000 μg/m
3, with extreme values exceeding 10,000 μg/m
3 during the notorious Red Dawn event in Australia in September 2009 [
1]. Daily PM
10 levels over 200 μg/m
3 were suggested for small to medium scale dust events, while a higher cut-off point of 400 μg/m
3 was used to define severe dust events [
5,
6]. Other studies have used much lower PM
10 levels to identify dust storm days [
7,
8,
9,
10].
Because most air quality monitoring stations record data based on the PM
10 measurements as opposed to other particulate matter size, the majority of epidemiological studies use PM
10 level as exposure indicator. The World Health Organization air quality guidelines have provided a basis for characterizing human health effects of major air pollutants including PM
10 [
4]. The assessment of personal exposure to air pollution is a critical component of epidemiological studies in the evaluation of health effects from airborne particulate matter (PM). The recognized air pollution effects over public health include increased risk of hospital admissions and mortality by respiratory or cardiovascular diseases. An aggregate risk index is a useful tool to identify the additive effects of short-term exposure of the main air pollutants, including PM
10 and PM
2.5 [
11]. Although fine particles below PM
2.5 comprise the greatest health concern, since they are more likely to penetrate deep into the alveoli sacs of the lungs, the PM
10 course particles represent the predominant part of dust in dust storms and cover most of the respiratory health issues, as large particles become trapped in the nasal passages, nose hair follicles and upper respiratory tract [
12]; in contrast, fine particles decline due to high wind speed and long travel distances of dust storms [
13,
14].
Dust storm events have been strongly associated with mortality and morbidity rates with a broad range of health effects, but predominantly to the respiratory and cardiovascular systems. Several studies from various countries have examined the effects of dust storms and particulate matter on morbidity and mortality rates, and hospital admissions for various ill-health effects. During Saharan dust days, a daily increase of 10 μg/m
3 of PM
10 increased daily mortality by 8.4% in Barcelona (Spain) [
15]. A 10 μg/m
3 change in daily PM
10 was associated with an approximately 1% increase in cardiovascular and respiratory mortality in the Coachella Valley, California [
16]. Dust storms in Taiwan had a 7.66% increase in the risk for respiratory diseases [
17], congestive heart failure [
8] and daily pneumonia hospital admissions [
9]. Asian dust storms had a 4.1% increase in the rate of deaths from cardiovascular and respiratory causes in Seoul, South Korea [
18] and a significant increase in respiratory hospitalizations in China [
19,
20]. Dust blown from the Sahara to the Eastern Mediterranean resulted in an increase in all-cause hospital admissions including respiratory and cardiovascular diseases in Nicosia, Cyprus [
7]. An Australian dust storm which lasted for only one day resulted in a 39% increase in hospital emergency admissions [
21]. Increased asthma emergency admissions were associated with Saharan dust in the Caribbean island of Trinidad [
22] and with Asian dust in Toyama, Japan [
23].
Little information is available on the assessment of health impact about dust storms and PM
10 concentration levels in the Middle Eastern despite the facts that the region experiences frequent dust storms [
24] and is considered a major source of global dust [
1,
3,
25]. Many studies from Iran have demonstrated a positive association between dust particles and total mortality including cardiovascular and respiratory mortalities [
26,
27,
28,
29,
30,
31,
32,
33,
34] and hospital admissions for cardiovascular and respiratory diseases [
35,
36]. Only three studies were conducted in Kuwait to determine the health impact of dust storms on morbidity and mortality rates. A study conducted by Thalib and Al-Taiar [
24] concluded that dust storms had a significant impact on asthma and respiratory hospital admissions. Al-Rifaia et al. [
37] and Al-Taiar and Thalib [
5] showed that dust storms had little impact on short-term respiratory, cardiovascular or all-cause mortality.
The primary objective of this study was to assess the environmental burden of outdoor air, specifically dust storms and PM10 airborne concentration on the health impacts in Kuwait regarding morbidity and mortality rates.
2. Experiments
A prospective time-series study of daily PM10 concentrations and daily morbidity and mortality through hospital admissions were evaluated in a single district in Kuwait, Ali Sabah Al-Salem (ASA) during 2012. The effect of changes in daily levels of PM10 hospitalization for respiratory, non-respiratory, cardiovascular and all-cause diseases was investigated using parametric (Pearson) and non-parametric (Spearman) correlations. Daily attendance rates of air pollution-related group of diseases in ASA primary health care center were evaluated. Daily attendance rates were adjusted to correspond to hospital visits per week. Data collection also included daily PM10 concentration levels, PM10 respiratory-related morbidity rates and mortality rates. Daily PM10 concentrations were adjusted to represent weekly rates. The data of both PM10 and air pollution-related diseases allowed for the investigation of the pattern of association between air pollution and morbidity by correlating visits to public health centers for air pollution-related diseases and the daily measurements of PM10 pollutant level during 2012. Dust storms, rising dust, and suspended dust were collected from Kuwait international airport station for the last 53 years (1962–2015). PM10 pollutant levels were obtained from the Kuwait Environment Public Authority (KEPA) for the year 2012.
2.1. Study Area Description and Justification
Ali Sabah Al-Salem (ASA) is a suburban area of 7.65 km2, located south of Kuwait and it lies at the terminal of the urbanization areas. The estimated population during 2012 was 48,685 residents, of which 32,341 were Kuwaiti nationals. Although the area was recently built and inhabited, its occupants complained of air pollutants. Air pollution in this area may be due to its proximity (within 4 km) to industrial facilities which were established before the build-up of this community. ASA was considered as the research study index district on the basis that its population was demanding for studying the health impact of air pollution resulting from industries, and the fact that the district is located upwind from natural environmental events, such as sand and dust storms. ASA contains fixed meteorological stations that continuously monitor the level of air quality. Multiple air pollutants were studied during the whole project. The air pollutants were grouped into three categories: gaseous pollutants (SO2, NO2, H2S, O3, CO, CO2), organic pollutant compounds (CH4, NH3, NCH4), and PM10. PM10 and dust storm events were investigated to determine their potential impact on morbidity and mortality rates.
2.2. Health Classification
The International Statistical Classification System of Diseases and Related Health Problems from the World Health Organization ICD-10 was used for health classifications in the study [
38]. ICD-10 was endorsed in May 1990 by the Forty-third World Health Assembly. It is cited in more than 20,000 scientific articles and used by more than 100 countries around the world. ICD is the foundation for the identification of health trends and statistics globally, and the international standard for reporting diseases and health conditions [
38]. The list of a group of diseases related to air pollution was used to determine the selected diagnosis. Each group of diseases was classified under a heading following the ICD. A person may have one disease or more per year and coded as a case for each one. Thus, the number of cases and the attributed estimate rates may exceed the total population in some incidents. Respiratory diseases were identified by the ICD-10 codes J00-J99 and contain acute upper respiratory infection (J00-J06), influenza and pneumonia (J09-J18), other acute lower respiratory infection such as acute bronchitis (J20-J22), other diseases of upper respiratory tract such as chronic rhinitis (J30-J39), chronic lower respiratory diseases such as emphysema (J40-J47), bronchial asthma (J45-J46), and lung diseases due to external agents (J60-J70).
2.3. Quality Control
Certain quality control measures were incorporated throughout the study period. Health records of Kuwaiti citizens residing in ASA and meteorological records of the same district were investigated prospectively during the same period. Primary health care morbidity and mortality data were obtained from the information technology electronic database of the Ministry of Health of Kuwait. A case with multiple admissions for different morbidities was counted as multiple cases. Records of cases registered in Kuwait health information electronic file as suffering or dying from a pre-selected list of air pollution-related releases were selected. A special format was used to record daily average of continuous measurements for the ten air pollutants mentioned above. A record of any case present in the selected health establishment but residing in another area was excluded from data analysis. Digital raw data about particulate air pollution was obtained from the database of Kuwait Environment Public Authority (KEPA) fixed station located in the selected district. Only 11 days (<3%) had missing values from KEPA meteorological station (n = 354 days recorded out of 365 days/year).
2.4. Statistical Analysis
Descriptive statistics, parametric and non-parametric correlations were used in the study. Descriptive statistics were utilized to determine frequency distributions, measures of central tendencies (mean, medians) and measures of variability from data related to dust, PM10 and hospital visits for respiratory diseases. Pearson product-moment correlation, a parametric statistical test was used to determine the degree of association between PM10 concentration and morbidity health rates. Spearman’s rho rank correlation was utilized to investigate the monotonic association between dust storms, rising dust and suspended dust.
4. Discussion
The health impact of dust storms and PM
10 concentrations have been thoroughly studied in North America, Europe, and East Asia and to a lesser extent in Iran; however, only three studies have explored the association between dust particulates and health morbidity or mortality in Kuwait, of which two of the studies were done by the same authors [
5,
24]. Moreover, all regional Iranian studies [
26,
27,
28,
29,
30,
31,
32,
33,
34,
35,
36] have used the AirQ 2.3.3 software to model the health impact of short-term exposure to PM
10; this software was developed by the WHO to model European morbidity and mortality rates and may overestimate the relative risk and increase prediction error if used by non-European countries because of the obvious higher dust storm events and elevated levels of PM
10 concentrations, especially in the Arabian region. This study used actual cases of morbidity and mortality and concluded that dust particulates were strongly correlated with acute lower/upper respiratory disorders and asthma. This study also revealed that dust storms, suspended dust, rising dust and PM
10 followed a similar pattern throughout the studied period with high peaks during summer months, specifically in June, and lower during winter months; this finding confirms the robust link between dust storm events and ambient air PM
10 levels and is in agreement with other studies in similar arid conditions [
6,
29,
43,
44]. Increased PM
10 concentrations during the summer can be associated with the Middle Eastern dust storms from the arid lands of Iraq, Jordan, and Saudi Arabia which are the particular sources of dust events coming to Kuwait from the Northwest [
2,
29,
45].
Two interesting studies by Thalib and Al-Taiar [
5,
24] used the generalized additive model (GAM) to analyze hospital admission and mortality data about dust storms after adjusting for covariates. This statistical model estimates the relative risk on admission and mortality counts, which typically follow a Poisson distribution, after adjusting for potential cofounders like temperature, relative humidity, weekday or weekend, and seasons as adjustment variables using various smoothing parameters. In this study, we presented correlation variables (
r) derived from bivariate plots. Estimated effects from the time-series (GAM) model were not shown; however, proportionate and cause-specific mortality rates were derived using simple mathematical calculations. Statistical modeling processes of ecological time series studies are complex, and GAM models using R software (version 2.14.2) were shown to produce problematic standard errors [
5]; others researchers recommend the use of S-plus software [
46] which was not available during the current research study.
This study concluded that dust particulates were strongly correlated with acute lower/upper respiratory disorders and asthma. Thalib and Al-Taiar [
24] showed that Kuwaiti children with asthma are particularly vulnerable to dust storm events. Other studies showed that respiratory admissions to hospitals were attributable to PM
10 concentrations above 20 μg/m
3 [
47]. An estimated effect of 3% decline in daily forced expiratory volume (FEV1) change was observed for every 10 μg/m
3 increase in ambient PM
10 level [
48]. Other studies showed a strong association between dust events and asthma admissions in Japan [
23], Trinidad [
22], Taiwan [
49], South Korea [
50,
51] and southern Europe [
52].
This study identified that cause-specific respiratory and cardiovascular mortality rates for all pollutants including PM
10 ranked third after congenital anomalies and perinatal diseases. Studies of 29 European cities [
53] showed an increase in daily mortality with an increase in PM
10 concentrations. The impact of particulate matter on daily mortality has been shown by similar studies [
54,
55]; other studies demonstrated that short-term impacts of PM
10 on mortality were exceeded even at concentrations complying with the European air ambient monitoring regulation [
56].
Some limitations of this study are the unknown composition of the chemical and biological dust particles; future research should provide analysis of total dust and PM10 compositions and study the link between the individual components and the health impact. Another limitation of this study is that it did not consider intra-individual susceptibility to health disorders, particularly the impact of dust storms on asthma patients; further epidemiological studies are needed.
5. Conclusions
The impact of dust storms on human health has drawn great interest of research from various regions, especially in the western and east Asian countries; very little research was conducted to study the association of Arabian Peninsula dust storms or PM
10 levels and associated health impact. The evidence on airborne particulates and its impact on morbidity and mortality are consistent in showing adverse health effects in both developed and developing countries. Dust storm events and PM
10 concentration levels may vary across different regions in Kuwait, but only to a limited degree because of the very small geographic area (17,000 km
2) and similar climatic conditions across the country. It is assumed that dust concentration variation may not be very significantly different across multiple cities and individuals are most likely to be exposed to the same level of exposure. All the population is affected, but susceptibility to the pollution may vary with health or age. Findings of this study suggest that there are strong associations between dust storms and PM
10 and morbidity rates of asthma and acute upper and lower tract infections. The risk for various outcomes has been shown to increase with exposure, and there is little evidence to suggest a threshold below which no adverse health effects would be anticipated [
3]. However, it may be worthwhile to further investigate the health impact of dust storm events across Kuwait, and such further evaluation can improve our understanding of the health impact of dust storms and PM
10 pollutants.