Air pollution and health

The health effects of air pollution have been subject to intense study in recent years. Exposure to pollutants such as airborne particulate matter and ozone has been associated with increases in mortality and hospital admissions due to respiratory and cardiovascular disease. These effects have been found in short-term studies, which relate day-to-day variations in air pollution and health, and long-term studies, which have followed cohorts of exposed individuals over time. Effects have been seen at very low levels of exposure, and it is unclear whether a threshold concentration exists for particulate matter and ozone below which no effects on health are likely. In this review, we discuss the evidence for adverse effects on health of selected air pollutants.     

Air pollution and chronic airway diseases: what should people know and do?

The health effects of air pollution remain a public health concern worldwide. Exposure to air pollution has many substantial adverse effects on human health. Globally, seven million deaths were attributable to the joint effects of household and ambient air pollution. Subjects with chronic respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma are especially vulnerable to the detrimental effects of air pollutants. Air pollution can induce the acute exacerbation of COPD and onset of asthma, increase the respiratory morbidity and mortality. The health effects of air pollution depend on the components and sources of pollutants, which varied with countries, seasons, and times. Combustion of solid fuels is a major source of air pollutants in developing countries. To reduce the detrimental effects of air pollution, people especially those with COPD or asthma should be aware of the air quality and take extra measures such as reducing the time outdoor and wearing masks when necessary. For reducing the air pollutants indoor, people should use clean fuels and improve the stoves so as to burn fuel more efficiently and vent emissions to the outside. Air cleaners that can improve the air quality efficiently are recommended.     

What can individuals do to reduce personal health risks from air pollution?

In many areas of the world, concentrations of ambient air pollutants exceed levels associated with increased risk of acute and chronic health problems. While effective policies to reduce emissions at their sources are clearly preferable, some evidence supports the effectiveness of individual actions to reduce exposure and health risks. Personal exposure to ambient air pollution can be reduced on high air pollution days by staying indoors, reducing outdoor air infiltration to indoors, cleaning indoor air with air filters, and limiting physical exertion, especially outdoors and near air pollution sources. Limited evidence suggests that the use of respirators may be effective in some circumstances. Awareness of air pollution levels is facilitated by a growing number of public air quality alert systems. Avoiding exposure to air pollutants is especially important for susceptible individuals with chronic cardiovascular or pulmonary disease, children, and the elderly. Research on mechanisms underlying the adverse health effects of air pollution have suggested potential pharmaceutical or chemopreventive interventions, such as antioxidant or antithrombotic agents, but in the absence of data on health outcomes, no sound recommendations can be made for primary prevention. Health care providers and their patients should carefully consider individual circumstances related to outdoor and indoor air pollutant exposure levels and susceptibility to those air pollutants when deciding on a course of action to reduce personal exposure and health risks from ambient air pollutants. Careful consideration is especially warranted when interventions may have unintended negative consequences, such as when efforts to avoid exposure to air pollutants lead to reduced physical activity or when there is evidence that dietary supplements, such as antioxidants, have potential adverse health effects. These potential complications of partially effective personal interventions to reduce exposure or risk highlight the primary importance of reducing emissions of air pollutants at their sources.     

Air pollution and chronic obstructive pulmonary disease

Limited data suggest that outdoor air pollution (such as ambient air pollution or traffic-related air pollution) and indoor air pollution (such as second-hand smoking and biomass fuel combustion exposure) are associated with the development of chronic obstructive pulmonary disease (COPD), but there is insufficient evidence to prove a causal relationship at this stage. It also appears that outdoor air pollution is a significant environmental trigger for acute exacerbation of COPD, leading to increasing symptoms, emergency department visits, hospital admissions and even mortality. Improving ambient air pollution and decreasing indoor biomass combustion exposure by improving home ventilation are effective measures that may substantially improve the health of the general public.     

Air Pollution and Arrhythmias

Air pollution is commonly defined as the contamination of the air we breathe by any chemical, physical, or biological agent that is potentially threatening to human and ecosystem health. The common pollutants known to be disease-causing are particulate matter, ground-level ozone, sulphur dioxide, nitrogen dioxide, and carbon monoxide. Although the association between increasing concentrations of these pollutants and cardiovascular disease is now accepted, the association of air pollution and arrhythmias is less well established. In this review we provide an in-depth discussion of the association of acute and chronic air pollution exposure and arrhythmia incidence, morbidity, and mortality, and the purported pathophysiological mechanisms. Increases in concentrations of air pollutants have multiple proarrhythmic mechanisms including systemic inflammation (via increases in reactive oxygen species, tumour necrosis factor, and direct effects from translocated particulate matter), structural remodelling (via an increased risk of atherosclerosis and myocardial infarction or by affecting the cell-to-cell coupling and gap junction function), and mitochondrial and autonomic dysfunction. Furthermore, we describe the associations of air pollution and arrhythmias. There is a strong correlation of acute and chronic air pollutant exposure and the incidence of atrial fibrillation. Acute increases in air pollution increase the risk of emergency room visits and hospital admissions for atrial fibrillation and the risk of stroke and mortality in patients with atrial fibrillation. Similarly, there is a strong correlation of increases of air pollutants and the risk of ventricular arrhythmias, out-of-hospital cardiac arrest, and sudden cardiac death.     

The effect of pollutional haze on pulmonary function

Detrimental health effects of atmospheric exposure to ambient particulate matter (PM) have been investigated in numerous studies. Exposure to pollutional haze, the carrier of air pollutants such as PM and nitrogen dioxide (NO₂) has been linked to lung and cardiovascular disease, resulting increases in both hospital admissions and mortality. This review focuses on the constituents of pollutional haze and its effects on pulmonary function. The article presents the available information and seeks to correlate pollutional haze and pulmonary function.     

Outdoor air pollution and emergency room visits at a hospital in Delhi

Several reports from large metropolitan cities have indicated significant association between acute morbidity and mortality from cardio-respiratory disorders and daily levels of major pollutants in the ambient air. Despite the wide-spread public concern about the adverse health effects of air pollution, there is substantial uncertainty regarding the effects of these pollutants at a concentration typical of Delhi, which is one of the ten most polluted cities in the world and the most polluted city in India. This study was undertaken to correlate the daily levels of various pollutants with the number of patients visiting the All India Institute of Medical Sciences (AIIMS, New Delhi) casualty for aggravation of certain defined cardiorespiratory disorders. Daily counts of patients visiting the emergency room of the AIIMS for acute asthma, acute exacerbation of chronic obstructive airway disease (COAD) and acute coronary event was obtained in prospective manner from January 1997 to December 1998. Daily mean levels of ambient CO, NOx and SO2 were monitored along with temperature and humidity. Data was analysed using one day time lag for events of interest. Time series analysis was undertaken using Poisson regression and population averaged general estimation equation, correcting for auto-correlation, days of the weak and season. The ambient levels of pollutants exceeded the national air quality standards on most of the days, over the two year period. Further, emergency room visits for asthma, COAD and acute coronary events increased by 21.30%, 24.90% and 24.30% respectively on account of higher than acceptable levels of pollutants. It is concluded that there is considerable burden of cardiorespiratory diseases in Delhi due to high levels of ambient air pollution.     

Interventions to reduce individual exposure of elderly individuals and children to haze: a review

Given rapid economic developments and urbanization over the last few decades, China has experienced frequent haze episodes, which have adverse effects on public health. Children and elderly individuals are more susceptible than the general population to air pollution. In this study, we introduce interventions to reduce the exposure of elderly individuals and children to air pollution during hazy weather. These interventions include avoiding outdoor activities, wearing a dust mask, reducing burning biomass fuels, reducing frying and smoking at home, using an air filtration unit and taking supplemental antioxidants. However, the actual benefits of these measures remain unproven and are unlikely to be adequate. Sustained clean air policies remain the most important and efficient solution to reduce air pollution-related health effects.     

Outdoor air pollution and respiratory health in Asia

With the rapid economic development occurring in the last decade in many countries of Asia, the level of air pollution has increased from both industrial and motor vehicle emissions. Compared with Europe and North America, the potential health effects of this increasing air pollution in Asia remain largely unmeasured. Recent data published by the Health Effects Institute from some major cities in India and China reveal that a 10 µg/m³ increase in PM₁₀ was associated with an increase in mortality of 0.6% in daily all‐natural cause mortality, with higher risks being found at extremes of high temperatures and in the lowest economically advantaged population. Other Asian studies have confirmed the link between hospital admissions for the worsening of COPD and the increase in asthma prevalence to levels of outdoor air pollutants. Although potential health effects appear to be similar to already‐published Western data, it is important that further studies be carried out in Asia that will inform the public and the authorities of the necessity to curb levels of outdoor air pollutants to acceptable levels.     

Urban air pollution and chronic obstructive pulmonary disease: a review.

There is consistency in the findings that relate the acute increases in urban air pollution (mainly the particulate matter) and the short-term health effects (i.e. mortality and hospital admissions) on patients suffering from chronic obstructive pulmonary disease (COPD). Beyond the acute effects, a relevant public health and scientific question is to what extent chronic exposure to air pollution is related with lung function impairment and development of COPD. The few cross-sectional studies showed an increase of self-reported diagnosis of chronic bronchitis and emphysema, breathlessness and mucus hypersecretion and lower levels of lung function in the more polluted areas. The two cohort studies in children have found a retardation of pulmonary function growth, and the only cohort in adults a faster decline of lung function. Given the intrinsic limitations of cross-sectional studies to separate the timing between exposure and effects, and the weaknesses of the cohorts (ie. few areas, short follow-up, only one retest, lack of individual weighting of air pollution measure) there is a need for new prospective studies. These should be performed in a large number of geographical areas and with a long follow-up to asses the impact of long-term air pollution on lung function growth and decline, and on incidence, duration, severity and survival of chronic obstructive pulmonary disease.     

Outdoor air pollution: particulate matter health effects

Numerous investigations studying multiple populations across a variety of environmental settings have demonstrated a strong association between ambient air particulate matter and cardiopulmonary morbidity and mortality. In most studies, the effect size of ambient air particulate pollution on health outcomes is small. However, the exposed population worldwide is very large. Accordingly, particulate air pollution appears to be an important public health hazard that makes an important contribution to the total burden of disease and death in populations across the world. Much of the evidence linking ambient air particulates with adverse health effects is derived from population-based, observational research with potential unidentified confounding exposures, precluding definitive assessments about causation and providing limited mechanistic insights. A growing body of research suggests particulate-associated adverse health effects result from the induction of proinflammatory responses in the lower respiratory tract. Ambient air particulates may increase lung cancer risk.     

Outdoor air pollution: ozone health effects

Ozone is a respiratory irritant associated with a spectrum of adverse health events. Ground-level ozone has been shown to cause decreases in lung function and has been associated with other important respiratory health effects. Some reports suggest short-term increases in ozone lead to increased cardiopulmonary mortality. Other studies have found no association between exposure and measured health effects. Outdoor air pollution consists of multiple copollutant exposures complicating definitive assessments about ambient air ozone exposure-effect relations.     

Outdoor air pollution: nitrogen dioxide, sulfur dioxide, and carbon monoxide health effects

Nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide are important ambient air pollutants. High-intensity, confined space exposure to NO2 has caused catastrophic injury to humans, including death. Ambient NO2 exposure may increase the risk of respiratory tract infections through the pollutant's interaction with the immune system. Sulfur dioxide (SO2) contributes to respiratory symptoms in both healthy patients and those with underlying pulmonary disease. Controlled human exposure studies have demonstrated that experimental SO2 exposure causes changes in airway physiology, including increased airways resistance. Both acute and chronic exposure to carbon monoxide are associated with increased risk for adverse cardiopulmonary events, including death. However, studies have not demonstrated a clear dose-dependent health risk response to increasing amounts of these pollutants except at high concentrations. In addition, a number of studies examining the effects of ambient level exposure to NO2, SO2, and CO have failed to find associations with adverse health outcomes.     

Impact of Particulate Air Pollution on Cardiovascular Health

Purpose of Review

Air pollution is established as an independent risk factor for cardiovascular diseases (CVDs). Ambient particulate matter (PM), a principal component of air pollutant, has been considered as a main culprit of the adverse effects of air pollution on human health.

Recent Findings

Extensive epidemiological and toxicological studies have demonstrated particulate air pollution is positively associated with the development of CVDs. Short-term PM exposure can trigger acute cardiovascular events while long-term exposure over years augments cardiovascular risk to an even greater extent and can reduce life expectancy by a few years. Inhalation of PM affects heart rate variability, blood pressure, vascular tone, blood coagulability, and the progression of atherosclerosis. The potential molecular mechanisms of PM-caused CVDs include direct toxicity to the cardiovascular system or indirect injury by inducing systemic inflammation and oxidative stress in circulation.

Summary

This review mainly focuses on the acute and chronic effects of ambient PM exposure on the development of cardiovascular diseases and the possible mechanisms for PM-induced increases in cardiovascular morbidity and mortality. Additionally, we summarized some appropriate interventions to attenuate PM air pollution-induced cardiovascular adverse effects, which may promote great benefits to public health.

     

Air pollution: The "heart" of the problem

Air pollution exposure is associated with an increased risk of acute and chronic cardiovascular mortality. Recent observations have implicated fine particulate matter (PM_2.5) as one of the most important pollutants. Inhalation of PM_2.5 causes acute pulmonary inflammation and oxidative stress. The subsequent generation of a systemic inflammatory response could link air pollution exposure with the development of cardiovascular disease. Human experiments have demonstrated pro-arrhythmic alterations in cardiac autonomic tone, increased blood pressure, higher serum C-reactive protein levels, and alterations in blood rheology favoring coagulation following controlled pollution exposures or in relation to elevated ambient PM_2.5 levels. Recent studies have also uncovered several harmful impacts on the systemic vasculature, including the triggering of acute vasoconstriction and the enhanced development of atherosclerosis. Many questions, however, remain unanswered and future studies will be required to clarify the relevant biologic mechanisms and to identify the specific constituents responsible for mediating the adverse health impacts.     

Respiratory health effects of diesel particulate matter

Particulate matter (PM) emissions involve a complex mixture of solid and liquid particles suspended in a gas, where it is noted that PM emissions from diesel engines are a major contributor to the ambient air pollution problem. While epidemiological studies have shown a link between increased ambient PM emissions and respiratory morbidity and mortality, studies of this design are not able to identify the PM constituents responsible for driving adverse respiratory health effects. This review explores in detail the physico-chemical properties of diesel PM (DPM) and identifies the constituents of this pollution source that are responsible for the development of respiratory disease. In particular, this review shows that the DPM surface area and adsorbed organic compounds play a significant role in manifesting chemical and cellular processes that if sustained can lead to the development of adverse respiratory health effects. The mechanisms of injury involved included inflammation, innate and acquired immunity, and oxidative stress. Understanding the mechanisms of lung injury from DPM will enhance efforts to protect at-risk individuals from the harmful respiratory effects of air pollutants.     

Chronic effects of air pollution on respiratory health in Southern California children: findings from the Southern California Children’s Health Study

Outdoor air pollution is one of the leading contributors to adverse respiratory health outcomes in urban areas around the world. Children are highly sensitive to the adverse effects of air pollution due to their rapidly growing lungs, incomplete immune and metabolic functions, patterns of ventilation and high levels of outdoor activity. The Children’s Health Study (CHS) is a continuing series of longitudinal studies that first began in 1993 and has focused on demonstrating the chronic impacts of air pollution on respiratory illnesses from early childhood through adolescence. A large body of evidence from the CHS has documented that exposures to both regional ambient air and traffic-related pollutants are associated with increased asthma prevalence, new-onset asthma, risk of bronchitis and wheezing, deficits of lung function growth, and airway inflammation. These associations may be modulated by key genes involved in oxidative-nitrosative stress pathways via gene-environment interactions. Despite successful efforts to reduce pollution over the past 40 years, air pollution at the current levels still brings many challenges to public health. To further ameliorate adverse health effects attributable to air pollution, many more toxic pollutants may require regulation and control of motor vehicle emissions and other combustion sources may need to be strengthened. Individual interventions based on personal susceptibility may be needed to protect children’s health while control measures are being implemented.     

Ultrafine particles in urban air and respiratory health among adult asthmatics.

Airborne particles are associated with adverse health effects and contribute to excess mortality in epidemiological studies. A recent hypothesis proposes that the high numbers of ultrafine (<0.1 microm diameter) particles in ambient air might provoke alveolar inflammation and subsequently cause exacerbations in pre-existing cardiopulmonary diseases. To test the hypothesis adult asthmatics were followed with daily peak expiratory flow (PEF) measurements and symptom and medication diaries for six months, while simultaneously monitoring particulate pollution in ambient air. The associations between daily health endpoints of 57 asthmatics and indicators of air pollution were examined by multivariate regression models. Daily mean number concentration of particles, but not particle mass (PM10 (particle mass <10 microm), PM2.5-10, PM2.5, PM1), was negatively associated with daily PEF deviations. The strongest effects were seen for particles in the ultrafine range. However, the effect of ultrafine particles could not definitely be separated from other traffic generated pollutants, namely nitric oxide, nitrogen dioxide and carbon monoxide. No associations were observed with respiratory symptoms or medication use. Particle mass measurements can be strongly influenced by mechanically produced, soil-derived particles, which may not be associated with adverse health effects. Therefore, air quality monitoring should include particle number concentrations, which mainly reflect ultrafine particles.     

Air pollution and cardiovascular disease in the Multi-Ethnic Study of Atherosclerosis

Research to date demonstrates a relationship between exposure to ambient air pollutants and cardiovascular disease (CVD). Many studies have shown associations between short-term exposures to elevated levels of air pollutants and CVD events, and several cohort studies suggest effects of long-term exposure on cardiovascular mortality, coronary heart disease events, and stroke. The biologic mechanisms underlying this long-term exposure relationship are not entirely clear but are hypothesized to include systemic inflammation, autonomic nervous system imbalance, changes in vascular compliance, altered cardiac structure, and development of atherosclerosis. The Multi-Ethnic Study of Atherosclerosis provides an especially well-characterized population in which to investigate the relationship between air pollution and CVD and to explore these biologic pathways. This article reviews findings reported to date within this cohort and summarizes the aims and anticipated contributions of a major ancillary study, the Multi-Ethnic Study of Atherosclerosis and Air Pollution.