"Toxic" drywall, formaldehyde emissions, mold, asbestos, lead-based paint, radon, PCBs in caulk, and many other indoor pollution problems have concerned scientists, federal policy makers, and regulators during the last 30 years. Some problems have been resolved, others remain of concern, and new indoor pollution problems continually emerge, often unexpectedly. Because people spend a high percentage of their time indoors, and concentrations of pollutants often are higher in indoor air than outdoors, the human health risks indoors generally can be greater relative to risks from exposure to pollutants in the ambient (i.e., outdoor) air. In 1987, indoor air quality was identified by EPA scientists as one of the greatest sources of environmental risk to human health. EPA's Science Advisory Board, an independent body of experts, reviewed and endorsed this comparative risk ranking and in 1990 called upon the agency to give a higher priority to funding such high-risk environmental problems. In 1997, the Presidential and Congressional Commission on Risk Assessment and Risk Management again considered the relative risks presented by various environmental problems and concluded that indoor pollution could pose a substantial public health risk. In 2011, a report by the Institute of Medicine warned that many indoor air quality problems might get worse if adaptations to climate change are made without better information and programs aimed at pollution prevention. For example, methods to make homes better insulated and more energy efficient may result in less circulation with outdoor air, potentially increasing indoor concentrations of pollutants unless effective filtration or treatment technologies can be incorporated. This report describes common indoor pollutants, discusses federal statutes that have been used to address indoor pollution, and analyzes key issues surrounding some general policy options for federal policy makers. The focus is on indoor chemical contaminants, rather than on temperature, humidity, or pollution from animals, fungal or bacterial organisms, or plant pests. Indoor pollutants are chemicals that are potentially harmful to people and may be found in the habitable portions of buildings, including homes, schools, offices, factories, and other public gathering places. Indoor pollutants are many and varied. Many exposures may be through indoor ai r . Some substances, like lead or ozone, are also ambient (outdoor) air pollutants. Others, like formaldehyde or asbestos, may be found either indoors or out, but are most often of concern when found at unhealthful concentrations indoors. Indoor pollutants may be natural (for example, carbon monoxide or radon) or synthetic (such as polychlorinated biphenyls [PCBs]), may originate indoors or outdoors, and may be deliberately produced, naturally occurring, or inadvertent byproducts of human activities. People may be exposed to indoor contaminants in the air, tap water, or dust by inhalation, skin contact, or mouth. Some examples of common indoor pollutants are discussed below. Some indoor pollution originates indoors as a result of fuel combustion for home heating or cooking. Fuel type, combustion efficiency, and ventilation affect the nature and extent of pollutant emissions and accumulations. Pollutants produced by combustion include smoke and carbon monoxide. Smoke contains a number of potentially harmful gases and small particles which may aggravate asthma and other health conditions. In developing countries, indoor smoke is a major concern. According to the World Health Organization (WHO), "[i]ndoor air pollution generated largely by inefficient and poorly ventilated stoves burning biomass fuels such as wood, crop waste and dung, or coal—is responsible for the deaths of an estimated 2 million people annually." Indoor combustion also is a concern in the United States, especially in homes without adequate furnaces where people may rely upon unvented space heaters or other devices to keep warm. Indoor combustion also is particularly common in the United States during emergencies when electricity or vented equipment may become unavailable, prompting residents to run generators indoors or to heat or cook with unvented portable devices such as barbeque grills. Accumulation of carbon monoxide, which is a colorless and odorless gas, is responsible for numerous deaths annually in the United States. Smoking that produces environmental tobacco smoke is another source of indoor air pollution. The respiratory tracts of young children are especially vulnerable to infections as a result of exposure to secondhand smoke. Radon is a naturally occurring, extremely toxic, colorless gas that is formed naturally from rocks and soil as a result of radioactive decay of radium. Radon emissions vary widely, but high levels of radon contamination occur in every state. Radon gas can enter homes through porous basement walls or dissolved in drinking water from which it may escape into the air, for example, during showering. Indoors, radon gas may accumulate and pose a long-term risk for lung cancer. There is no known safe level of radon in indoor air. EPA and the Surgeon General recommend fixing a home when the radon level is 4 picocuries per liter of air or greater. EPA recommends that every home be tested for radon levels. According to EPA, exposure to radon in homes accounts for about 20,000 lung cancer deaths annually. Asbestos is a fibrous mineral that is found in certain natural rock formations. It was mined and widely used in the manufacture of fire-retardant materials, including automotive brake linings; roof, ceiling, and floor tiles; and insulation for furnaces, air ducts, and pipes. As the asbestos materials in buildings have deteriorated over time, and when they have been removed for remodeling or otherwise disturbed, asbestos fibers have been released to indoor air. When inhaled, such asbestos fibers have caused lung cancer and other lung diseases. Lead hazards are found in many homes and other buildings where lead-based paint has been applied and is deteriorating, lead solder or plumbing contaminates drinking water, or contaminated soil is tracked indoors. Childhood exposure to lead hazards can lead to brain and nervous system damage, behavior and learning problems, slowed growth, hearing problems, and headaches, according to EPA. Although exposure most commonly is to the lead in dust that gets onto hands and then enters a body through the mouth, indoor air inhalation of lead also can occur, for example, as a result of home renovation, or when contaminated outdoor air enters buildings. Sometimes synthetic chemicals accumulate to noxious levels in indoor air or dust as a result of uncontrolled emissions from building materials, paints, or furnishings, or evaporation following the use of cleaning supplies. Other synthetic chemicals may be inadvertently released (e.g., an ozone-producing machine may be used to "freshen" air). Still other indoor pollution originates outdoors but intrudes into homes, for example as contaminated air infiltrates through porous basement walls or is brought into the home through heating or air conditioning systems, or as contaminated drinking water. Outdoor contamination which migrates into the indoor air through groundwater and soil beneath homes and buildings often is referred to as "vapor intrusion." Prominent examples of industrial pollutants that have been found indoors include formaldehyde, which is emitted to air from some composite wood products; PCBs released from deteriorating caulk, paints, coatings, or plastics; and contamination from dry cleaning solvents, such as trichloroethylene (TCE) or perchloroethylene (PERC), which have migrated indoors through vapor intrusion at many sites. There also has been increasing attention to the potential risks of indoor exposure to perchlorate contamination through vapor intrusion or groundwater sources used for drinking water supplies. Perchlorate is a substance commonly used in solid propellants in military munitions and commercial fireworks. Pesticides released within buildings or around the foundation of buildings also may be indoor contaminants. Termiticides, insecticides, flea foggers, and roach or rodent control products are particularly common sources of toxic chemicals indoors. Even years after use, some of these products may persist where sunlight and rain cannot reach them. For example, scientists found relatively high levels of DDT in indoor dust samples taken in Cape Cod recently. No federal agency has broad statutory authority concerning pollution indoors. On the other hand, numerous federal agencies (at least 23 in spring 2012) have some authority to conduct research or to control particular indoor pollutants, sources of pollution, or environmental quality in particular structures. For example, the EPA has some authority under the Toxic Substances Control Act (TSCA) to address asbestos in schools; building standards, testing, and research related to radon; and lead-based paint hazards in housing. Key agencies and authorizing statutes are briefly described below. For more information about the authorities and activities of federal agencies with respect to indoor air quality, see EPA's 1989 Report to Congress on Indoor Air Quality, Volume 2, chapter 8. For additional background information about the research conducted by federal agencies, see the 1999 report by the U.S. General Accounting Office (GAO, now the Government Accountability Office), Indoor Pollution: Status of Federal Research Activities , GAO-RCED-99-254. A more recent summary of federal research and development and outreach activities related to indoor environments is available in Report of the Surgeon General's Workshop on Healthy Indoor Environment, January 12-13, 2005. Information is also available on agency websites. For direct links to some agencies' indoor environmental quality programs, visit http://www.epa.gov/iaq/ciaq/members.html . The origin of the Environmental Protection Agency (EPA) is rooted in a reorganization of the executive branch under the Nixon Administration. In Reorganization Plan No. 3 of 1970, President Nixon proposed the establishment of EPA to integrate the administration of numerous federal pollution control laws that had been carried out by several federal agencies. This plan was part of a broader effort to reorganize an array of environmental responsibilities of many federal agencies. The Nixon Administration created EPA through this reorganization with congressional approval under procedures established in the Reorganization Act of 1949, as amended. This reorganization provided the administrative framework for the creation of EPA.