indoor air pollution

Rising energy costs during the past 30 years have led to increased insulation and decreased ventilation of homes, which elevates the level of indoor air pollutants. The health hazards of environmental tobacco smoke have already been discussed.

Other sources of indoor air pollutants are gas cooking stoves and furnaces, wood stoves, construction materials, furniture, radon, allergens associated with pets, dust mites, and fungal spores and bacteria.

Carbon Monoxide

This odorless, colorless gas is a byproduct of combustion produced from burning gasoline, oil, coal, wood, and natural gas. It is also a major pollutant in tobacco smoke, and its untoward effects were discussed earlier along with cigarette smoking. Here we should note that carbon monoxide levels in ambient air should not exceed 9 ppm; however, indoor levels of 2 to 4 ppm have been measured in homes during the winter.

Such carbon monoxide pollution of indoor air can reduce exercise capacity and aggravate myocardial ischemia. Higher levels can cause poisoning manifested as headaches, dizziness, loss of motor control, and coma. Approximately 900 accidental deaths due to asphyxia are caused by indoor carbon monoxide pollution each year in the United States.

Nitrogen Dioxide

Gas stoves and kerosene space heaters can raise indoor levels of nitrogen dioxide to 20 to 40 ppm in homes; this is several orders of magnitude higher than outdoor air levels. Children are more susceptible to the untoward effects of nitrogen dioxide. It impairs lung defenses and is hence associated with increased respiratory infections.

Wood Smoke

This is a complex mixture of nitrogen oxides, particulates, and polycyclic aromatic hydrocarbons. High concentrations of wood smoke in poorly ventilated homes can increase the incidence of respiratory infections in children.

Formaldehyde

This highly soluble, volatile chemical has been used in the manufacture of many consumer products, including textiles, pressed wood, furniture, and urea formaldehyde foam insulation. Although indoor levels are usually less than 1 ppm, it can cause acute irritation of the eyes and upper respiratory tract and exacerbation of asthma.

Formaldehyde is frequently emitted with acrolein and acetaldehyde, which may have additive or synergistic irritant effects. Additional volatile organic compounds that may be present at low levels in indoor air include benzene, tetrachloroethylene, polycyclic aromatic hydrocarbons, and chloroform.

The potential for toxicity or carcinogenicity at these exposure levels is low, although occupational exposure to these volatile compounds can be hazardous. Formaldehyde at high doses (6 to 14 ppm) has produced nasal tumors in rats.

Radon

Radon, a radioactive gas, is a decay product of uranium widely distributed in the soil. Radon gas emanating from the earth is prevalent in homes. Indoor levels of radon average around 1.5 pCi/L; approximately 4% of homes have an annual average level greater than 4 pCi/L. Radon gas is inhaled into the lungs; its decay products emit alpha radiation, which has been associated with lung cancer in miners. According to some estimates, the low levels found in indoor air account for 10,000 lung cancers per year in the United States.

Asbestos Fibers

Homes and public buildings built before the 1970s in the United States contain asbestos insulation, pipe covers, ceiling tiles, and flooring. If these materials are nonfriable and undisturbed, low levels of fibers can be measured in indoor air. Maintenance and abatement workers who repair or remove asbestos-containing materials are at risk for lung cancer and mesothelioma if they do not use respirators.

Manufactured Mineral Fibers

Fiberglass has been widely used as an asbestos substitute for home insulation. Low levels of these fibers can be measured in indoor air. Maintenance and construction workers can develop skin and lung irritation when using these materials.

Bioaerosols

Aerosolization of bacteria responsible for Legionella pneumonia has been associated with contaminated heating and cooling systems in public buildings (Chapter 8). More common hazards in indoor air are allergens associated with pets, dust mites, cockroaches, fungi, and molds. These allergens cause allergic rhinitis and exacerbate asthma.

The etiology of the so-called sick building syndrome, or multiple chemical sensitivity syndrome, is less clear. In some cases, high levels of one or more of these indoor air pollutants may be responsible. In most cases, poor ventilation is at fault.

See also

 air pollution

• outdoor air pollution
• industrial exposures