Agency for Toxic Substances and Disease Registry 
Case Studies in Environmental Medicine (CSEM) 

Taking an Exposure History
What Are the Possible Sources of Indoor Air Pollution?

Learning Objectives

Upon completion of this section, you will be able to

• identify the possible sources of toxicants from indoor air pollution.

Introduction

Studies from the U.S. and Europe show that persons in industrialized nations spend more than 90 percent of their time indoors. The concentrations of many pollutants indoors exceed those outdoors. The clinician should consider the following possible sources of indoor air pollution, when eliciting information on exposures

• asbestos
• biologic agents
• building materials
• radon
• tobacco smoke
• wood stoves/gas range/other heating devices

Environmental Tobacco Smoke

Environmental tobacco smoke (ETS) is now considered an unacceptable and entirely preventable public health hazard. A recent article provides an overview of the composition of ETS and the major diseases and disorders strongly linked to ETS, emphasizing the effects of ETS on pulmonary function, asthma, and lung cancer (Dhala, Pinsker et al. 2006).

The EPA study found that ETS is a mixture of irritating gases and carcinogenic tar particles and is one of the most widespread and harmful air pollutants. Forty-three of the more than 4,700 chemical compounds contained in cigarette smoke are known carcinogens (US Environmental Protection Agency and US Consumer Product Safety Commission 1995).

Wood Stoves, Gas Ranges, Other Heating Devices

Aside from environmental tobacco smoke, the major combustion pollutants that may be present at harmful levels in the home or workplace stem chiefly from malfunctioning heating devices, or inappropriate, inefficient use of such devices. Incidents are largely seasonal.

Among possible sources of contaminants: gas ranges that are malfunctioning or used as heat sources; improperly vented fireplaces, furnaces, wood or coal stoves, gas water heaters and gas clothes dryers; and unvented or otherwise improperly used kerosene or gas space heaters.

Gas ranges, which may produce nitrogen oxide, a respiratory irritant, are used for cooking in more than half of the homes in the United States. Proper ventilation and routine inspection and maintenance of the equipment is necessary in residences where wood or gas stoves are used (US Environmental Protection Agency and US Consumer Product Safety Commission 1995).

When not properly maintained and vented, wood stoves emit noxious gases including carbon monoxide, oxides of nitrogen, particulates, and hydrocarbons. Studies have shown that children living in homes heated with wood stoves have a significant increase in respiratory symptoms compared with children living in homes without wood stoves (US Environmental Protection Agency and US Consumer Product Safety Commission 1995).

Building Materials

Building materials, home improvement products, and textiles used in the home can pose health risks. For example, formaldehyde volatilizes from particle board, insulation materials, carpet adhesives, and other household products. This is a particular problem in the confined spaces of mobile homes. Formaldehyde exposure can cause rhinitis, nausea, dry skin or dermatitis, and upper respiratory and eye irritation. It has also been reported to precipitate bronchospasm in persons who have asthma (US Environmental Protection Agency and US Consumer Product Safety Commission 1995).

Asbestos

Asbestos was widely used from 1950 to the early 1970s in areas requiring soundproofing, thermal proofing, or durability (e.g., floor and ceiling coverings, heating and water pipe insulation). Intact, undisturbed asbestos-containing materials generally do not pose a health risk. These materials may become hazardous and pose increased risk if they are damaged, are disturbed in some manner, or deteriorate over time and thus release asbestos fibers into building air. Exposure to these fibers has been associated with lung cancer, asbestosis, and mesothelioma.

The occurrence of disease is influenced by the type of asbestos mineral inhaled, the concentration and dimension of the fibers, and the duration of the exposure.

Smoking cigarettes in addition to being exposed to asbestos increases the risk of cancer by an order of magnitude above smoking alone or asbestos exposure alone.

Children may be at greater risk than adults because children have a longer life expectancy than adults, higher activity rates, higher breathing rates, increased amounts of time spent near the floor where fibers accumulate, and a greater likelihood of contact (through curiosity or mischief).

Further information on the health hazards of asbestos exposure is available in the Case Studies in Environmental Medicine: Asbestos Toxicit.

Radon

Radon, a colorless, odorless gas, is a decay product of uranium and is found in significant concentrations in some areas. Radon itself does no harm, but its progeny attach to airborne particulates such as cigarette smoke and can be inhaled. During subsequent decay, the progeny emit high-energy alpha particles that may injure adjacent bronchial cells, thereby causing lung cancer. Five to 10 percent of single-family homes in the U.S. have been estimated to exceed the EPA radon recommended guideline of four picocuries per liter of air. EPA estimates that approximately 14,000 lung cancer deaths per year are attributable to radon (US Environmental Protection Agency and US Consumer Product Safety Commission 1995).

For further information about radon exposure and its health effects, see Case Studies in Environmental Medicine: Radon Toxicity.

Biologic Agents

Biological air pollutants are found to some degree in every home, school, and workplace. Sources include outdoor air and human occupants who shed viruses and bacteria, animal occupants (insects and other arthropods, mammals) that shed allergens, and indoor surfaces and water reservoirs where fungi and bacteria can grow, such as humidifiers.

A number of factors allow biological agents to grow and be released into the air. Especially important is high relative humidity, which encourages house dust mite populations to increase and allows fungal growth on damp surfaces. Mite and fungus contamination can be caused by flooding, continually damp carpet (which may occur when carpet is installed on poorly ventilated concrete floors), inadequate exhaust of bathrooms, or kitchen-generated moisture. Appliances such as humidifiers, dehumidifiers, air conditioners, and drip pans under cooling coils (as in refrigerators), support the growth of bacteria and fungi.

Biological agents in indoor air are known to cause three types of human disease: infections, where pathogens invade human tissues; hypersensitivity diseases, where specific activation of the immune system causes disease; and toxicosis, where biologically produced chemical toxins cause direct toxic effects. In addition, exposure to conditions conducive to biological contamination (e.g., dampness, water damage) has been related to nonspecific upper and lower respiratory symptoms. Evidence is available that shows that some episodes of the group of nonspecific symptoms known as "sick building syndrome" may be related to microbial contamination in buildings.

Key Points

• It is important to not overlook the potential exposure sources of indoor air pollution.

Progress Check