Plain English Guide-Clean Air Act

Reducing Toxic Air Pollutants

Toxic air pollutants, or air toxics, are known to cause or are suspected of causing cancer, birth defects, reproduction problems, and other serious illnesses. Exposure to certain levels of some toxic air pollutants can cause difficulty in breathing, nausea or other illnesses. Exposure to certain toxic pollutants can even cause death.

Persistent Bioaccumulative Toxics (PBTs)

PBTs such as mercury and DDT last for a long time in the environment with little change in their structure or toxic effects. This means that a persistent toxic chemical transported in the wind can be just as toxic 10,000 miles away as it was at the smokestack from which it was released. Some PBTs, such as polychlorinated biphenyls (PCBs), have been found in remote parts of the Arctic, far away from the industrial sources that produce them.

Some of the PBTs that move through the air are deposited into water bodies and are concentrate up through the food chain, harming fish-eating animals and people. Small fish may consume plants that live in water contaminated by PBTs, which are absorbed into plant tissues. Big fish eat smaller fish and as the PBTs pass up the food chain, their levels go up. So a large fish consumed by people may have a much higher concentration of PBTs in its tissues than the simple plant first absorbing the PBTs. PBTs can concentrate in big fish to levels thousands of times the levels found in the contaminated water.

Over 2000 U.S. water bodies are covered by fish consumption advisories, warning people not to eat the fish because of contamination with chemicals, usually PBTs. Those compounds have been linked to illnesses such as cancer, birth defects, and nervous system disorders.

The 1990 Clean Air Act gave EPA the authority to reduce PBT levels by requiring pollution sources to install control devices or change production methods.

Some toxic air pollutants are of concern because they degrade slowly or not at all, as in the case of metals such as mercury or lead. These persistent air toxics can remain in the environment for a long time and can be transported great distances. Toxic air pollutants, like mercury or polychlorinated biphenyls, deposited onto soil or into lakes and streams persist and bioaccumulate in the environment. They can affect living systems and food chains, and eventually affect people when they eat contaminated food. This can be particularly important for American Indians or other communities where cultural practices or subsistence life styles are prevalent.

The majority of air toxics come from manmade sources, such as factory smokestack emissions and motor vehicle exhaust.

Gasoline also contains air toxics. When you put fuel in your car, gases escape and form a vapor. You can smell these vapors when you refuel your vehicle.

When cars and trucks burn gasoline, toxic air pollutants are emitted from the tailpipe. Those air toxics are combustion products-chemicals that are produced when gasoline is burned. EPA is working with industries to develop cleaner-burning fuels and more efficient engines, and is taking steps to make sure that pollution control devices installed in motor vehicles work properly. EPA has issued requirements that are leading to cleaner-burning diesel engines, reducing releases of particle pollution and air toxics.

Air toxics are also released from industrial sources, such as chemical factories, refineries, and incinerators, and even from small industrial and commercial sources, such as dry cleaners and printing shops. Under the 1990 Clean Air Act, EPA has regulated both large and small sources of air toxics, but has mainly focused efforts on larger sources.

Before the 1990 Clean Air Act Amendments, EPA regulated air toxics one chemical at a time. This approach did not work well. Between 1970 and 1990, EPA established regulations for only seven pollutants. The 1990 Clean Air Act Amendments took a completely different approach to reducing toxic air pollutants. The Amendments required EPA to identify categories of industrial sources for 187 listed toxic air pollutants and to take steps to reduce pollution by requiring sources to install controls or change production processes. It makes good sense to regulate by categories of industries rather than one pollutant at a time, since many individual sources release more than one toxic chemical. Developing controls and process changes for industrial source categories can result in major reductions in releases of multiple pollutants at one time.

EPA has published regulations covering a wide range of industrial categories, including chemical plants, incinerators, dry cleaners, and manufacturers of wood furniture. Harmful air toxics from large industrial sources, such as chemical plants, petroleum refineries, and paper mills, have been reduced by nearly 70 percent. These regulations mostly apply to large, so-called "major" sources and also to some smaller sources known as "area" sources. In most cases, EPA does not prescribe a specific control technology, but sets a performance level based on a technology or other practices already used by the better-controlled and lower emitting sources in an industry. EPA works to develop regulations that give companies as much flexibility as possible in deciding how they reduce their toxic air emissions-as long as the companies meet the levels required in the regulations.

The 1990 Clean Air Act requires EPA to first set regulations using a technology-based or performance-based approach to reduce toxic emissions from industrial sources. After EPA sets the technology-based regulations, the Act requires EPA to evaluate any remaining ("residual") risks, and decide whether it is necessary to control the source further. That assessment of remaining risk was initiated in the year 2000 for some of the industries covered by the technology-based standards.

Chemical Emergencies

The 1984 chemical disaster that resulted in thousands of deaths in Bhopal, India, inspired sections of the 1990 Clean Air Act that require factories and other businesses to develop plans to prevent accidental releases of highly toxic chemicals.

The 1990 Act also established the Chemical Safety Board, an independent agency that investigates and reports on accidental releases of toxic chemicals from industrial facilities. The Board operates much like the National Transportation Safety Board, the agency that investigates airplane and train crashes. The Chemical Safety Board assembles the information necessary to determine how and why an accident involving toxic chemicals happened. The goal is to apply understanding of accidents to prevent other accidents involving toxic chemicals.

Air Toxics and Risk

The Clean Air Act requires a number of studies to help EPA better characterize risks to human health and the environment from air toxics. Those studies provide information for rulemaking and support national and local efforts to address risks through pollution prevention and other voluntary programs. Among these risk reduction initiatives are:

  • The Integrated Urban Air Toxics Strategy includes local and community-based initiatives to reduce local toxic air emissions. The primary goal of the strategy is to reduce public health risks from both indoor and outdoor sources of toxic air pollutants. More information can be found at
  • The Great Waters Program incorporates activities to investigate and reduce the deposition of toxic air pollutants to the "Great Waters," which include the Chesapeake Bay, Lake Champlain, the Great Lakes, National Estuary Program areas, and National Estuarine Research Reserves. To learn more, visit
  • Initiatives targeting emission reductions of persistent bioaccumulative toxics (PBTs) like mercury, DDT (a pesticide banned in the United States), and dioxins.


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