The World Health Organization (WHO) indicates that particulate matter (PM) air pollution is one of the main causes of mortality. Professionals argue that it causes approximately 800,000 premature deaths annually (Jahn et al.). Such critical statistics attracted the attention of numerous prominent researchers, motivating them to study the way air pollution affects health. As a result, past studies conducted since the beginning of the 21st century provided confirmatory evidence that air pollution causes acute and long-term health problems even regardless of differences in local atmospheres. In addition to that, it was proved that the presence of PM makes these impacts more critical (Jahn et al.). In particular, the attention is paid to:
- Mortality rate, especially in older adults and people with chronic illnesses.
- Health condition of older adults with preexisting cardiopulmonary diseases.
- Symptoms of acute and chronic pulmonary disease.
- Irritation of eye and respiratory system (Franchini et al.; Holgate et al.; Riedl).
Previous studies shared an important premise on the assumption that increased concentrations of PM and mortality are associated. What is more, they provided support for the connection of PM with the morbidity of those illnesses that affect the respiratory system, including bronchial asthma and bronchoconstriction, etc. (Koening et al.; Lawther et al.; Mazumbar et al.). Epidemiological studies conducted by Pearlman et al. and Ostro et al. revealed such association as well. The data they gathered suggested that high levels of PM lead to frequent incidences of acute respiratory diseases. In addition to that, Kagawa et al. and Hsu et al. argued that increased PM decreases pulmonary function.
The classification of air pollution is provided by the International Agency for Research on Cancer (IARC). According to it, those pollutants, comprising PM are classified as Group 1. They are carcinogenic to human beings and often include benzo[a]pyrene in addition to other polycyclic aromatic hydrocarbons (IARC). Diesel engine exhaust emissions that are often identified in cities also belong to this group. Gasoline engine exhaust emissions, on the other hand, refer to Group 2B and are treated as possibly carcinogenic (Pedersen et al.).
It was identified by Bateson and Schwartz that the most vulnerable to air pollution is children. Their lungs and immune system are just developing and cannot resist adverse influences decently. The same can be said about the immaturity of their physiological state (Pedersen et al.). These characteristics become critical because infant’s air intake is twice that of an adult; they also perform a higher intake of food and water (Pedersen et al.). The effects on school children are also critical, as asthma and air pollution prevent them from attending educational institutions. Bener et al. determined that kids from 6 to 12 years of age showed significant school absenteeism. Wilhelm et al. discussed the influence of Pb and Cs on mothers and their infants. The professional indicated that the sample from Germany had increased levels of Pb in blood that were connected with its levels in the air they breathe.
The evidence can be easily obtained when focusing on children but not adults because they tend to spend more time outdoors, be occupied in active behaviors, and get a larger minute volume of air per body weight. These peculiarities lead to the increased PM dose they obtain because of the air pollution and presuppose crucial influence on the developing lungs (U.S. EPA).
The connection between PM and respiratory issues in the selected population was investigated in the recent epidemiological studies as well. The evidence obtained due to them revealed that individuals less than 18 years had more adverse respiratory effects from PM exposure in comparison to adults (Host et al.; Lall et al.; Peel et al.; Slaughter et al.; Strickland et al.). A study conducted by Larrieu et al. also supported previously discussed results and indicated that asthmatic children miss classes more when being affected by increased PM.
Except for children, many scientists propound the view that the elderly is a susceptible population. They experience a decline in physiological processes, which affects their health condition (U.S. EPA). The studies reveal the reduced clearance of PM in the respiratory system of older adults (U.S. EPA). The reasons for vulnerability also include the higher risks of cardiovascular and respiratory diseases.
Since the 1980s, a vast number of research studies were conducted to examine short-term influences of air pollution on human’s health. In particular, attention was paid to mortality and hospital admissions. Some of them revealed changes in daily death counts connected with changes in PM. According to the US professionals, in the majority of cases, the results of the studies showed that daily mortality increased by 1% when PM increased by 10μg/m3 (Bell et al.; Fairley; Pope et al.; Schwartz et al.).
The scientists from European countries combined their works to extend the population to more than 40 million people from 29 countries at the end of the 20th century. The Air Pollution and Health: A European Approach project was maintained on the basis of two series of studies (Katsouyanni et al.). Professionals were not focused on the causes of daily mortality but concluded that, regardless of the main exposure, it increased by more than 0.5% along with the 10μg/m3 increase in PM10. Such outcomes were supported by the evidence obtained in Asia, Australia, and New Zealand (Barnett et al.; Omori et al.). Samoli et al. examined previously conducted studies one more time and found out that the increase in daily mortality observed regardless of its causes in such locations as Canadian, Europe, and the USA is associated with acute increases in PM. In addition to that, adverse influences are revealed not only in the framework of critical illnesses and death. In many cases, mortality increased within those populations that included people with one or more risk factors (Samoli et al.). Samet et al. conducted a research study to discuss short-term effects of air pollution in the USA. They focused on the 20 largest metropolitan territories areas of the country. The results showed that mortality increased along with PM10, which supported previous findings. The association between high PM concentrations and hospital admissions among the elderly was investigated in 10 US cities. It was found out that persons over 65 years tended to spend more time in hospitals due to the air pollution. Admissions because of chronic obstructive pulmonary disease increased by 1.5% and cardiovascular disease by approximately 1% (Atkinson et al.; Hsu et al.; Zanobetti et al.). According to the research studies conducted by Host et al., Larrieu et al., and Pope et alThe incidence of hospital admissions because of cardiovascular disease among the elderly increased due to the effects of PM10–2.5, which aligned with more recent works. However, Metzger et al. did not obtain any evidence of an association between cardiovascular issues and hospital admissions when they compared this population to people of younger ages. Thus, it is impossible to claim that scientists provided consistent evidence of PM influence on the respiratory system of older adults and increased hospital admissions (Fung et al.).
In a similar framework, no proofs were obtained to state that PM increases morbidity when concentrating on the epidemiological literature. Only the information gathered from the human exposure and toxicological studies supported the proposed premise and allowed to claim that PM increases cardiovascular issues. For example, decreased heart rate variability was observed in the elderly who were affected by PM regardless of their previous condition, such as the presence or absence of chronic obstructive pulmonary disease (Devlin et al.; Gong et al.; Suh and Zanobetti).
A lot of research reviews provided proof of association between air pollution and short-term health effects. In the majority of cases, they were focused on the vehicular exhaust pollution that is rather common in large cities all over the world (Dominici et al.; Larrieu et al.; Maitre et al.; Nawrot et al.; Pope et al.). It was revealed that DNA damage and malignant neoplasms could be caused by traffic-related air contamination because of the vast amount of genotoxic/mutagenic chemical substances.
The mutagenic potential of airborne PM was widely discussed in the 21st century. Professionals maintained various short-term that revealed the evidence that proved the presence of this element in the air. In the majority of cases, scientists addressed the genotoxicity of extractable organic compounds and mixtures. In addition to that, they paid attention to the water-soluble substances and volatile organic compounds (Buschini et al.; de Kok et al.; Knaapen et al.).
A scientist from China, Schoket, examined the influence of polycyclic aromatic hydrocarbons (PAHs) and variations in DNA. The professional focused on two cities from Poland and Czech Republic because they were widely known as the territories with the major sources of PAHs. As it turned out, the effects of coal-based industry and domestic heating led to alterations in white blood cell DNA adducts. In addition to that, DNA damage was observed in different proportions depending on people’s location (rural and urban) and season. A similar biomarker study in other locations was conducted by Schoket. The sample included bus drivers, traffic police officers, and citizens. Focusing on the differences between people from rural and urban territories, the professional identified alternations in DNA damage. It was found out that vehicular emissions pollute the air with PM so that both human beings and plants are influenced geno toxicologically. In this way, even PAHs that are inert and do not provide any critical impacts themselves, they start affecting nucleophilic centers of DNA because of metabolic activation (Schoket).
Some scientists also performed a range of epidemiological studies to find out if the association between PM and cardiovascular issues can be affected by diabetes. Initially, the focus was made on short-term PM10 exposure. In their works, Chen et al., as well as Zanobetti and Schwartz, provided evidence to support the discussed premise. They revealed that individuals who suffer from diabetes are at increased risk of cardiac diseases (>75%) triggered by PM than those who do not have such diagnosis. However, other professionals did not come to the same conclusions. A range of multicity and single city research studies that were also focused on the influences of PM exposure and diabetes did not show any data to prove the existence of an association between them (Pope et al.; Wellenius et al.; Zanobetti and Schwartz). In addition to that, other epidemiological studies revealed that people who were diagnosed with diabetes could potentially be at a higher risk of mortality due to PM (Goldberg et al.; Zeka et al.).
Epidemiological research studies conducted by Bates and Samet et al. gathered the data that indicated evident associations between long-term exposure to PM and different adverse health outcomes. For instance, professionals reported some cases of reduced lung function, bronchitis, lung cancer, and severe cardiovascular issues. Braun-Fahrlander et al. and Zemp et al. discussed air pollution with PM in children and adults. They also gathered enough data to argue its association with respiratory health effects.
Other scientists, including Donaldson et al., focused on the way long-term exposure to PM affects the cardiovascular system. There was overwhelming evidence for the notion that vehicular exhausts influence heart rate and blood characteristics, lead to cardiac arrhythmia, thrombosis, coronary artery disease, and even strokes (Baccarelli et al.; Baccarelli et al.; Brook et al.; Calabrò et al.; Seaton et al; Delfino et al.). What is more, Ghio et al. revealed an increased risk of inflammatory lung injury, elevated blood plasma viscosity, endothelial dysfunction and myocardial infarction.
Hamoda stated that PM affects people’s health mainly because it consists of such pollutants as PAHs and volatile organic compounds (VOCs). These elements, VOCs in particular, are dangerous to public health and should be of its concern. They were often discussed along with waste treatment and disposal facilities.
Thus, on the basis of the previously discussed information, it can be stated that the literature shows consensus on the connection between air pollution, respiratory, and cardiovascular problems. However, a lot of researchers also indicated an increased incidence of cancer, which was partially discussed at the beginning of the paper (Lester and Seskin; Lin et al.; Saldiva et al.). First of all, it is evident that professionals indicated the relation between PM2.5 and PM10 exposure and increased risk of lung cancer. A lot of large epidemiological cohort studies were conducted to discuss this issue and obtain enough information in order to develop a plan for improvement. In the majority of cases, scientists focused on the population of the USA and Europe. In addition to that, they were highly interested in other risk factors that lead to this type of cancer, such as active and passive smoking and occupational exposures, etc. (Dockery et al.; Gallus et al.; Vineis et al.; Dockery et al.).
Even though a lot of different professionals conducted research studies related to PM and its effects on human health, the most important evidence was obtained from the article prepared by Pope et al. The authors revealed confirmatory data on the association between PM2.5 with lung cancer and cardiopulmonary mortality. Even though this research is not actually up to date and was maintained at the beginning of the 1980s, the insights it provided are highly valued by contemporary professionals. The sample included 1.2 million adult participants who completed a questionnaire on the individual risk factors. Mainly, their answers dealt with physical characteristics, habits (such as smoking), diet peculiarities, and occupational exposure, etc. In order to conduct this study, professionals discovered the risk factor data for 500,000 individuals from the US metropolitan territories. They aligned it with air pollution data and causes of death. They estimated the average PM concentration by site and area and obtained an opportunity to associate it with increased mortality. As a result, it was revealed that 10μg/m3 increase in PM leads to 4-8% increase in cardiopulmonary risk and lung cancer mortality. However, the information obtained from coarse particles and TSP did not provide enough evidence to prove connections with mortality (Pope et al.). However, a review of epidemiological evidence that was recently maintained supports the existence of a relationship between PM and mortality. The available data suggests that negative influence on health condition depends on concentrations of PM and the length of exposure. In this way, it was stated that long-term exposures lead to the most serious effects (Pope et al.).
Kunzli et al. prepared a research study focused on traffic-related air pollution. The attention was paid to a 10 μg/m3 increase in PM just like in previous studies, but the location was changed to Austria, France, and Switzerland. The findings suggested that more than 5% of all deaths were caused by air pollution. In fact, it was about 40,000 cases per year, which proved the issue to be extremely critical. In addition to that, a half of these deaths was attributed to traffic-associated pollution. Professionals mentioned that more than 25,000 adults and 290,000 children were diagnosed with bronchitis, about 500,000 had asthma attacks and more than 15 million cases of restricted activities. Similar results were also obtained by Efrim et al., Laden et al., Ostro et al., and Pope et al., which proved their validity at least for the US population.
In the Netherlands, air pollution caused by traffic lead to adverse health outcomes as well. In fact, mortality by increased by more than 70% (Hoek et al.). A study conducted by Toren et al. in Sweden revealed that those individuals who experience occupational PM exposure had more than 12% increase in mortality caused by cardiovascular issues. Laden et al. reached the same conclusions and indicated that reduces PM concentration can decrease the rate of mortality associated with cardiovascular and lung cancer.
Sex-stratified analyses can be observed only in a few recent epidemiological studies. The results they reveal differ from those obtained from dosimetric studies. The lack of consistency still allows us to see the exposure-result relations between PM2.5 exposure and mortality. Franklin et al. and Ostro et al. found evidence of slightly increased risk for women for non-accidental and cardiovascular mortality. Naess et al. also emphasized connections with lung cancer mortality. Males, on the other hand, turned out to be at increased risk for respiratory-related mortality (Franklin et al.; Naess et al.).
Several recently conducted epidemiological studies discussed the relationship between PM influenced on people’s health and their demographic characteristics, especially race and ethnicity. Unfortunately, the obtained information was not enough to develop a generalized claim because results varied across locations. Ostro et al. provided evidence to prove that mortality rate for European Americans and Hispanics increases due to the PM influences in California. However, such outcomes are not consistent with African Americans. In addition to that, Hispanics were identified as the most vulnerable population, specifically in the framework of cardiovascular mortality, when being compared with European Americans (Ostro et al.). Another study conducted by Malig and Ostro also revealed these tendencies. Still, Hispanics were claimed to be more vulnerable to cardiovascular mortality but not non-accidental one.
In the 21st century, many scientists discussed ambient airborne PM as a critical environmental pollutant. They associated it with various cardiopulmonary diseases and lung cancer (Valavanidis et al.). With the course of time, the influence of reactive oxygen species (ROS) and oxidative stress was discussed in the same framework. Knaapen et al. and Risom et al. proved them to be a part of the toxicological mechanism that caused lung cancer. It was revealed that ROS could be generated more actively due to constituents of PM that affect metabolism and inflammation, etc. Thus, it can be claimed that PM can damage DNA (Kasai; Moller et al.). PM bring about the oxidative stress that turns out to be connected with the generation of ROS. Soluble compounds affect the activation of inflammatory cells that produce ROS (Risom et al.). On these grounds, Dagher et al., Haddad, Hetland et al., and Shukla et al. argued that the generation of ROS and the secretion of inflammatory cytokines could be connected. Professionals revealed that they induced cell death by apoptosis.
According to recent experimental studies, redox active PM components causes the generation of ROS. Affected areas include lungs, blood, and vascular tissues. This process is followed by oxidative stress. Thus, there is a possibility of increased airway and systemic inflammation and cardiovascular issues (Ayres et al.; Utell et al.). In this way, the natural antioxidant capacity falls behind the production of ROS. The exposure to pro-oxidant air pollutants is often seen as a previous exploration. All in all, oxidative stress is likely to be the main trigger of the negative respiratory and cardiovascular outcomes caused by air pollution. It affects immune modulation and leads to both inflammation and thrombogenic activity.