2S – Air pollution & health

Supporting article S: An extract from an announcement for a cyber seminar on the effects that air pollution has on health

Health Effects of Air Pollution*
Vinod Mishra
December 1-15, 2003

That air pollution causes ill health and death is well recognized. Air pollution is caused by both natural and man-made sources. Major man-made sources of ambient air pollution include industries, automobiles, and power generation. In indoor environments, tobacco smoke and combustion of solid fuels for cooking and heating are the most significant sources. In addition, construction material, furniture, carpeting, air conditioning, and home cleaning agents and insecticides can also be significant sources of chemical and biological pollutants indoors. For the purposes of this seminar, I propose that we limit the discussion to man-made sources of air pollution. I also propose that we exclude health effects of tobacco smoke from this discussion, given a large body of well researched literature on that subject. Of course, we should include both natural sources of air pollution and tobacco smoke in the discussion to the extent they confound or modify the health effects of man-made air pollution.

Fuel combustion is the primary source of a large number of health-damaging air pollutants, including fine and respirable particulate matter (PM2.5 and PM10), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs), ozone (O3), and atmospheric lead. Some of these pollutants are direct by-products of fuel combustion, but others (such as O3) are formed in the air through chemical reactions with other agents in the atmosphere.

Air pollution has both acute and chronic effects on human health. Health effects range anywhere from minor irritation of eyes and the upper respiratory system to chronic respiratory disease, heart disease, lung cancer, and death. Air pollution has been shown to cause acute respiratory infections in children and chronic bronchitis in adults. It has also been shown to worsen the condition of people with preexisting heart or lung disease. Among asthmatics, air pollution has been shown to aggravate the frequency and severity of attacks. Both short-term and long-term exposures have also been linked with premature mortality and reduced life expectancy.

Health impact of air pollution depends on the pollutant type, its concentration in the air, length of exposure, other pollutants in the air, and individual susceptibility. Different people are affected by air pollution in different ways. Poor people, undernourished people, very young and very old, and people with preexisting respiratory disease and other ill health, are more at risk. In cities, for instance, poor tend to live and work in most heavily polluted areas, and in rural areas poor are more likely to cook with dirtier fuels. In some countries, air quality standards tend to be more lax around industrial areas in cities, where many poor tend to live in squatter settlements. Poor also tend to be more malnourished, more likely to suffer from ill health and disease, and have less access to health care.

Air pollutants can also indirectly affect human health through acid rain, by polluting drinking water and entering the food chain, and through global warming and associated climate change and sea level rise.

As a result of several decades of tighter emission standards and closer monitoring, levels of certain types of air pollutants have declined in many developed countries. Although, even at much reduced levels, air pollution continues to threaten public health in these countries. On the other hand, the ambient air pollution levels are a growing problem in urban centers in many developing countries.

Several factors contribute to the worsening air pollution levels in developing-country cities, including rapid growth in urban population, increasing industrialization, and rising demands for energy and motor vehicles. Other factors, such as poor environmental regulation, less efficient technology of production, congested roads, and age and poor maintenance of vehicles, also add to the problem.

In many rural areas of developing countries air pollution exposures tend to be highest indoors where majority of households use unprocessed solid fuels (biomass and coal) for cooking and space heating. These fuels are typically burned indoors in simple household cookstoves, such as a pit, three pieces of brick, or a U-shaped construction made from mud, which burn these fuels inefficiently and are often not vented with flues or hoods to take the pollutants to the outside.

Under these conditions, high volumes of a number of health-damaging airborne pollutants are generated indoors, resulting in high exposures, especially among women who do the cooking and young children who stay indoors with mothers. The individual peak and mean exposures experienced in such settings are often much greater than the safe levels recommended by the World Health Organization.

Causal Mechanism
Causal biological mechanisms about health effects of air pollution are only partly understood. Air pollution exposure has been associated with compromised pulmonary immune defense mechanisms in both animals and humans. Tobacco smoking has also been shown to cause depressed immune system responses. Of the specific air pollutants, exposure to respirable particulate matter has been shown to induce a systemic inflammatory response involving stimulation of the bone marrow, which can contribute to cardiorespiratory morbidity. Other evidence indicates that exposure to polycyclic aromatic hydrocarbons —especially benzo[a]pyrene— can cause immune suppression and can increase the risk of infection and disease. Benzo[a]pyrene, a known carcinogen, also can increase the risk of lung and other types of cancers. Acute exposures to oxides of nitrogen and sulfur have been associated with increased bronchial reactivity and susceptibility to bacterial and viral infections.

Carbon monoxide combines with hemoglobin to form carboxyhemoglobin, which reduces the oxygencarrying capacity of the blood and can contribute to anemia and adverse pregnancy outcomes, including miscarriage, stillbirth, low birth weight, and early infant mortality. In cases where biological pathways of effect are not known, questions remain as to how to establish causality.

About the author:
Vinod Mishra, PhD, MPH
Chair, PERN Steering Committee and Fellow, Population and Health Studies, East-West Center, Honolulu, Hawaii.