Toxic Air Pollutants are substances regulated by the EPA that have been proven to cause cancer, severe health problems, or incur environmental damage through exposure. The Clean Air Act Extension of 1970 directed the EPA to develop and enforce regulations concerning these substances.

The EPA only regulates environmental exposure. Workplace exposure is regulated by the Occupational Safety and Health Administration and the Mining Safety and Health Administration.

The act has since been amended and expanded by newer versions of the Clean Air Act with the most recent update being a 2005 revision. The Act is expected to go through another round of changes following a recent Supreme Court decision that ruled the EPA has the responsibility and authority to regulate greenhouse gas emissions from automobiles.

Exposure to toxic air pollutants does not have to solely occur through the air, people can be exposed through contaminated drinking water or eating organisms with high concentrations of a pollutant.

Under the law, the EPA has the ability to regulate the levels of those contaminants and can enforce violations. States can choose whether or not they want to individually enforce the law or whether the EPA does it for them on a federal level. The law also allows for citizen suits against private entities for violations.

The government regulates use and releases through rules set on large industrial complexes (major sources), smaller industrial/commercial businesses (area sources), and fuels used to power combustible engines (mobile sources). An acceptable exposure level is determined after the agency agrees on the greatest possible reduction in the release of a specific substance. The post-reduction level then becomes the acceptable standard for that substance.

For example if the release of a toxic substance can be cut by a maximum of 90%, then the remaining amount is deemed the acceptable level.

The EPA maintains a list of 188 substances that have been defined as toxic air pollutants.

Some of the substances on the list include:

• Arsenic
• Asbestos
• Benzene
• Chlorine
• Formaldehyde
• Hexane
• Lead
• Mercury
• Methanol
• Xylene

A brief summary of some of the chemicals on this list:

Asbestos – Commonly found in homes and buildings built before the 1980s it was often used for insulation or fire proofing. When damaged it releases microscopic fibers that when inhaled can become trapped in the lungs. Over time exposure can cause serious health conditions including mesothelioma, asbestosis, and lung cancer.

Benzene – Once a common chemical solvent and additive in gasoline, it has slowly been phased out of use. The chemical has recently been found in some soft drinks which scientists speculate may be a possible byproduct of the mixing of various ingredients. Exposure over time can cause chronic immune system problems and damage to bone marrow which often leads to anemia.

Lead – A common industrial chemical it is a dangerous neurotoxin that accumulates in tissue and bone over time. Lead is most harmful to children as it can damage nerve connections and lead to very serious health problems. The most common occurence is lead acetate a common ingredient in sweeteners and cosmetics throughout history. It was used as a paint additive until paints containing lead were removed from U.S. markets in 1978. Organic compounds that bind to lead are known as alkyl-leads and are classified aschemicals by the EPA.

Mercury – Once commonly used in medicine it has since become a problem with large accumulations in the environment. Mercury often enters bodies of water through soil or runoff and can create health problems as it is absorbed in the tissues of many organisms. The effects of mercury poisoning include damage to the nervous system and kidneys. Methly mercury and dimethly mercury are the most common and dangerous industrial forms. As a vapor mercury is readily inhaled into the lungs and is extremely potent. The EPA classifies it as a Persistent Bioaccumulative and Toxic chemical.