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Toxic Air Pollutants


Note: EPA no longer updates this information, but it may be useful as a reference or resource.

Please see www.epa.gov/airtrends for the latest information on Air Quality Trends.


Nature and Sources:
Toxic air pollutants are those pollutants known or suspected to cause cancer or other serious health effects, such as birth defects or reproductive effects. Examples of toxic air pollutants include dioxins, benzene, arsenic, beryllium, mercury, and vinyl chloride. The Clean Air Act currently lists 188* toxic air pollutants to be regulated by EPA. They are emitted from all types of sources, including motor vehicles and stationary sources, such as manufacturing plants. ( * Captrolactam was recently removed from the list of toxic air pollutants, which originally numbered 189.)

Control of toxic air pollutants differs in focus from control of the six principal pollutants for which EPA has established national air quality standards (discussed earlier). For the six principal pollutants, a variety of control strategies are used in geographic areas where national air quality standards have been violated. In contrast, for toxic air pollutants, EPA has focused on identifying all major industrial sources that emit these pollutants and developing national technology-based performance standards to significantly reduce their emissions. The objective is to ensure that major sources of toxic air pollution are well controlled regardless of geographic location.

EPA's toxic air pollutant program and the NAAQS program complement each other. Many toxic air pollutants are emitted in the form of particulates or as VOC. Control programs to meet the NAAQS for ozone and PM-10 also reduce toxic air pollutant emissions. Likewise, emission requirements under the toxic air pollutants program can significantly help achieve the NAAQS for ozone and PM-10. For example, EPA's final toxic air pollutant regulation for organic chemical manufacturing is expected to reduce VOC emissions (which form ground-level ozone or smog) by an amount equivalent to removing millions of cars from the road.

The toxic air pollutant program is especially important in reducing emissions at or near industrial locations and in controlling pollutants that are toxic even when emitted in small amounts. Companies handling toxic chemicals are required by EPA to develop plans to prevent accidental releases and to contain any releases in the event they should occur.

Health and Environmental Effects:
At sufficient concentrations and exposure durations, human health effects from toxic air pollutants can include cancer, poisoning, and rapid onset of sickness, such as nausea or difficulty in breathing. Other less measurable effects include immunological, neurological, reproductive, developmental, and respiratory effects. Toxic air pollutants may also be deposited onto soil or into lakes and streams, thereby affecting ecological systems and eventually human health through consumption of contaminated food (mainly freshwater fish).

Trends In Toxic Air Pollutants:
EPA will soon begin using the National Toxics Inventory (NTI) to track nationwide emissions trends for toxic air pollutants listed in the Clean Air Act. NTI contains information on toxic emissions in 1990 of approximately 8.8 billion pounds. As illustrated in the chart below, NTI includes emissions from large industrial or "point" sources, smaller stationary sources called "area" sources, and mobile sources. NTI builds on emissions data from EPA's Toxic Release Inventory, which reflects about half the total emissions from large industrial point sources and about 14 percent of national total emissions.

Area, point, and mobile sources emit roughly equal proportions

to the total amount of toxic air pollutants


According to National Toxics Inventory data, area sources account for 31 percent of U.S. toxic emissions, mobile sources account for 39 percent, and point sources account for 30 percent.

Selected VOC Concentration Changes
From PAMS Sites (Summer 1994-1995)

These substances have high ozone forming potential and/or they are toxic
Pollutant Number of Sites Median % Change
2,2,4-Trimethylpentane 17 -23
Acetaldehyde 6 -14
Benzene 19 -38
Ethylbenzene 17 -23
Formaldehyde 6 +4
M/P-Xylene 14 -21
N-hexane 17 -8
O-xylene 17 -18
Styrene 17 -17
Toluene 17 -23

As of October 1996, EPA has issued air toxics standards for 47 source categories, such as chemical plants, oil refineries, aerospace manufacturers, and steel mills, as well as area sources like dry cleaners, commercial sterilizers, secondary lead smelters, and chromium electroplating. When these standards are fully implemented, toxic emissions from stationary sources should be reduced by approximately 35 percent. Toxic emissions from point sources have already declined, a trend that is expected to continue as the result of emissions standards. By the year 2005, EPA projects that the toxic air pollutant program will reduce toxic emissions by 75 percent. Because controls for toxic air pollutants also reduce VOC and PM-10 emissions, over the next 10 years, the program should realize reductions in VOC and PM-10 emissions of more than 4 billion pounds per year.

Preliminary analysis of specific VOC measured in urban locations classified as "serious," "severe," or "extreme" ozone nonattainment (PAMS network - see Ozone section) indicate that ambient concentration levels of certain toxic VOC appear to be declining. For example, as illustrated in the above table, benzene levels showed a significant decline between 1994 and 1995 (approximately 38 percent), possibly as a result of the use of reformulated gasoline in those areas. It should be noted that PAMS measurements have only been taken for 3 years and that continued efforts in the PAMS program are expected to provide more confidence in evaluating the long-term trends of benzene and other toxic VOC.

This document is provided for historical purposes only. The most recent version can be found at AIRTrends


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