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When we think of air pollution, we usually don’t associate it with air inside our buildings, but indoor air pollution actually causes more deaths each year than does outdoor air pollution. Most of these deaths occur in the developing world. The amount of time one spends indoors depends on culture, climate, and economic situation. The quality of indoor air is highly variable and when polluting activities take place indoors, exposure to pollutants in a confined space can be a significant health risk.

Learning Objectives

After reading this module you should be able to

Although it generally receives less attention than outdoor air pollution, indoor air pollution is a hazard all over the world. The reasons for indoor air pollution and its characteristics differ between the developing world and the developed world.

Developing Countries

In Chapter 13 we saw that around the world, more than 3 billion people use wood, animal manure, or coal indoors for heat and cooking. Biomass and coal are usually burned in open-pit fires that lack the proper mix of fuel and air to allow complete combustion. Usually, there is no exhaust system and little or no ventilation available in the home, which makes indoor air pollution from carbon monoxide and particulates a particular hazard in developing countries (FIGURE 50.1). Exposure to indoor air pollution from cooking and heating increases the risk of acute respiratory infections, pneumonia, bronchitis, and even cancer. The World Health Organization estimates that indoor air pollution is responsible for approximately 4 million deaths annually worldwide, and that more than 50 percent of those deaths occur among children less than 5 years of age. Ninety percent of deaths attributable to indoor air pollution are in developing countries.

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Developed Countries

There are a number of factors that have caused the quality of air in homes in developed countries to take on greater importance in recent decades. First of all, people in much of the developed world have begun to spend more and more time indoors. Although improved insulation and tightly sealed building envelopes reduce energy consumption, these tightly sealed buildings also keep existing air in contact with the inhabitants of homes, schools, and offices for greater amounts of time. Finally, an increasing number of materials in the home and office are made from plastics and other petroleum-based materials that can give off chemical vapors. As FIGURE 50.2 shows, all of these factors combine to allow many possible sources of indoor air pollution to impact occupants.

Because a house is a closed system with an abundance of manufactured materials, there is ample opportunity for indoor air pollutants to accumulate and for the occupants of that house to come into contact with harmful substances. Indoor air pollutants are for the most part different from outdoor pollutants, although, as we will see, carbon monoxide is one pollutant that causes problems both indoors and outdoors.

Carbon Monoxide

We have already described carbon monoxide as an outdoor air pollutant, but it can be even more dangerous as an indoor air pollutant. It occurs as a result of malfunctioning exhaust systems on household heaters, most typically natural gas heaters. When the exhaust system malfunctions, exhaust air escapes into the living space of the house. Because natural gas burns relatively cleanly with little odor, a malfunctioning natural gas burner allows the colorless, odorless carbon monoxide to build up in a house without the occupants noticing, particularly if they are asleep. In the body, carbon monoxide binds with hemoglobin more efficiently than oxygen, thereby interfering with oxygen transport in the blood. Extended exposure to high concentrations of carbon monoxide in air can lead to oxygen deprivation in the brain and, ultimately, death.

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Asbestos

Asbestos is a long, thin, fibrous silicate mineral with insulating properties. For many years it was used as an insulator on steam and hot water pipes and in shingles for the siding of buildings. The greatest health risks from asbestos have been respiratory diseases such as asbestosis and lung cancer found at very high rates among those who have mined asbestos. In manufactured form, asbestos is relatively stable and not dangerous until it is disturbed. When insulating materials become old or are damaged or disrupted, however, the fine fibers can become airborne and can enter the respiratory tract. In the United States, asbestos is no longer used as an insulating material, but it can still be found in older buildings, including schools. Removal of asbestos insulation must be done under tightly controlled conditions so that the fibers, typically less than 10 microns in diameter, cannot enter the air inside the building. Some studies have shown that when asbestos removal is complete, the concentration of asbestos in the air of the remediated building can be greater in the year after removal than during the year before removal. For this reason, it is absolutely necessary that asbestos removal be carefully done by qualified asbestos abatement personnel.

Radon

Radon-222, a radioactive gas that occurs naturally from the decay of uranium, exists in granitic and some other rocks and soils in many parts of the world. The map in FIGURE 50.3 shows areas for potential radon exposure in the United States. Humans can receive significant exposure to radon if it seeps into a home through cracks in the foundation, or from underlying rock, soil, or groundwater. Radon-222 decays within 4 days to a radioactive daughter product, Polonium-210. Either the radon or the polonium can attach to dust and other particles in the air and then be inhaled by the inhabitants of the home.

The EPA, the federal agency most responsible for identifying, measuring, and addressing environmental risks, estimates that about 21,000 people die each year from radon-induced lung cancer. This is 15 percent of yearly lung cancer deaths, and makes radon the second leading cause of lung cancer, after smoking. The EPA suggests that people test their homes for airborne radon. If radon levels are determined to be high, it is important to increase ventilation in the home. Other relatively inexpensive actions, such as sealing cracks in the basement, can be beneficial if radon is coming from underlying soil and bedrock.

VOCs in Home Products

Many volatile organic compounds are used in building materials, furniture, and other home products such as glues and paints. One of the most toxic of these compounds is formaldehyde, which is used widely to manufacture a variety of building products such as particle board and carpeting glue. Formaldehyde is common in new homes and new products made from pressed wood, such as cabinets. The pungent smell that you may have noticed in a new home or one with new carpeting comes from formaldehyde, which is volatile and emits gases over time. A high enough concentration in a confined space can cause a burning sensation in the eyes and throat, and breathing difficulties and asthma in some people. There is evidence that people develop a sensitivity to formaldehyde over time; though they may not be very sensitive at first, with continued exposure they can experience irritation from ever-smaller exposures. Formaldehyde has been shown to cause cancer in laboratory animals and has recently been suspected of being a human carcinogen.

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Many other consumer products such as detergents, dry-cleaning fluids, deodorizers, and solvents may contain VOCs and can be harmful if inhaled. Plastics, fabrics, construction materials, and carpets may also release VOCs over time.

Sick Building Syndrome

In newer buildings in developed countries in the temperate zone, more and more attention is given to insulation and prevention of air leaks in order to reduce the amount of heating or cooling necessary for a comfortable existence. This reduces energy use but may have the unintended side effect of allowing the buildup of toxic compounds and pollutants in an airtight space. In fact, such a phenomenon has been observed often enough in new or renovated buildings to be given a name: sick building syndrome, which describes a buildup of toxic pollutants in airtight spaces such as in newer buildings. Because new buildings contain many products made with synthetic materials and glues that may not have fully dried out, a significant amount of off-gassing occurs, which usually means that the indoor levels of VOCs, hydrocarbons, and other potentially toxic materials are quite high. Sick building syndrome has been observed particularly in office buildings, where large numbers of workers have reported a variety of maladies such as headaches, nausea, throat or eye irritations, and fatigue.

The EPA has identified four specific reasons for sick building syndrome: inadequate or faulty ventilation; chemical contamination from indoor sources such as glues, carpeting, furniture, cleaning agents, and copy machines; chemical contamination in the building from outdoor sources such as vehicle exhaust transferred through building air intakes; and biological contamination from inside or outside, such as molds and pollen.