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Fact Sheet
INITIAL RESULTS OF STUDY ON NATIONAL ESTIMATES OF 1990 AIR TOXICS
Under the Clean Air Act of 1990, EPA has issued standards that will reduce air toxics emissions by over one million tons per year -- almost 10 times greater reductions than were achieved in the previous 20 years. These standards affect about 50 categories of major industries, such as chemical plants, oil refineries, aerospace manufacturers, and steel mills. Air toxics, also known as hazardous air pollutants, include pollutants that are known or suspected to cause cancer and/or other serious health effects, such as birth defects or reproductive effects.
While we are taking actions to reduce air toxics, we are also working to develop better estimates of total air toxics concentrations. As part of this effort, EPA staff have developed initial estimates of 1990 air toxics concentrations for every area, at the census tract level, in the continental United States. The study has for the first time estimated outdoor concentrations of toxic air pollutants across the entire country for all sources (e.g. cars, large stationary sources and smaller sources).
Two peer-reviewed scientific journals have published articles documenting the initial results of the study. Three EPA scientists, in collaboration with scientists outside the agency, co-authored the two articles:"Public Health Implications of 1990 Air Toxics Concentrations Across the United States", published in the May, 1998, vol. 106, issue of the Environmental Health Perspectives journal, and "Application of Health Information to Hazardous Air Pollutants Modeled in EPA's Cumulative Exposure Project" published in Vol.14, No.3,1998 issue of the journal of Toxicology and Industrial Health. Additional Cummulative Exposure Project data and information is available at the Office of Policy.
The study and subsequent follow-up work in this area will help prioritize the Agency’s efforts to reduce emissions of air toxics that may be impacting public health. Specifically, these efforts to characterize the scope and nature of air toxics concentrations across the country will help EPA focus efforts on air toxics that represent the highest potential health risks, and will help EPA identify what areas of the country are most impacted by these pollutants.
BACKGROUND
In 1990, Congress amended the Clean Air Act and added provisions to provide EPA with authority to reduce emissions of 189 hazardous air pollutants (also known as air toxics).
Although air quality monitoring for some air toxics is currently being undertaken, the data from these monitors are limited in nature (only measures concentrations for a subset of air toxics) and scope (does not measure concentrations in all locations). In addition, there is incomplete information on the full range of health effects associated with air toxics. Consequently, relatively little is known about the range of health effects, and the scope and level of concentrations of air toxics in the atmosphere.
In 1994, EPA’s Office of Policy, Planning and Evaluation began the Cumulative Exposure Project which consists of three national analyses of multiple toxic contaminants in air, food and drinking water. The air component of the project uses information on the emissions of pollutants from a variety of source types in conjunction with computer models, to predict concentrations of 148 air toxics throughout the country (a subset of the 188 toxic air pollutants listed in the 1990 Clean Air Act).
The Environmental Health Perspectives article presents the initial results of the analysis of concentration estimates for 148 air toxics in over 60,000 census tracts for the year 1990. Census tracts are geographic areas that vary in size but contain approximately 4,000 - 5,000 people. The entire United States (except Alaska and Hawaii) is represented by these 60,000 census tracts.
The study assesses the potential for adverse public health effects from ambient concentrations of air toxics by comparing health benchmarks to estimated air toxics concentrations. A health benchmark is a concentration of the pollutant below which there is likely to be no public health concern.
To estimate potential cancer concerns, the authors used a health benchmark of 1 in a million excess risk of cancer. A risk level of 1 in a million implies that one person, out of one million equally exposed people, would contract cancer if exposed continuously (24 hours per day) to the specific concentration over 70 years ( an assumed lifetime). This would be in addition to those cancer cases that would normally occur in an unexposed population of one million people.
For non-cancer hazard, the authors used a health benchmark based on the inhalation reference concentration (i.e., the concentration below which there is little probability of adverse effects for noncancer endpoints). A complete list and description of the health benchmarks is contained in the Toxicology and Industrial Health journal article.
HOW DID THE STUDY ESTIMATE CONCENTRATIONS OF AIR TOXICS ?
The study predicts 1990 pollutant concentrations by combining estimates of pollutant emissions from a variety of sources (cars, factories, waste combustors, dry cleaners, etc.) with a computer model that simulates the behavior of pollutants after being emitted.
The computer model considers factors such as wind speed and direction, breakdown of pollutants, and removal of pollutants in rainfall, to estimate the concentrations of pollutants in outdoor air resulting from the estimated emissions.
The authors of the study compared the modeled air toxics concentrations to the limited available monitoring data. This comparison showed that the study's modeled concentrations of air toxics have a general tendency to underestimate concentrations (underestimates were found about three times as frequently as overestimates).
The study's modeling methodology was peer-reviewed by the EPA's Science Advisory Board in 1996. This board is a body of outside scientific and technical experts who review technical work developed by EPA.
WHAT DO THE RESULTS OF THE STUDY SHOW?
The number of air toxics exceeding concentrations of potential public health concern for 1990 ranged from eight to 28 per census tract, with a median of 13.
Of the 77 air toxics for which the authors were able to identify cancer benchmarks, fifty-six were estimated to have ambient concentrations greater than the 1 in a million cancer risk in at least one census tract based on the modeled 1990 data.
Thirteen air toxics had estimated concentrations greater than a 1 in 10,000 cancer risk in at least one census tract.
Overall, ten percent of census tracts across the United States, covering about 20 million people, had at least one toxic air pollutant with an estimated concentration greater than a 1 in 10,000 cancer risk level.
Estimated background concentrations for eight pollutants are greater than the 1 in a million cancer risk level. Background concentrations are estimates of the concentrations that would exist even if emissions from man-made sources in the U.S. were immediately eliminated. Background concentrations represent pollution levels that result from emissions from natural sources (e.g. plants, oceans), historic man-made emissions that persist in the environment, and transport of pollutants from other countries. Emissions in 1990 add to the background levels in the model’s estimates of 1990 concentrations.
Twenty-two air toxics had estimated ambient concentrations that exceeded a concentration of potential public health concern for noncancer effects.
Even though there are a number of limitations and uncertainties associated with the study, the results are important because they provide a comprehensive picture of the 1990 air toxics problem nationwide and support efforts to further reduce air toxics emissions in the U.S.
WHAT ARE THE LIMITATIONS ASSOCIATED WITH THIS STUDY?
The study estimates air toxics concentration for 1990 and emissions of air toxics have changed since then. Since 1990, EPA has issued standards that will reduce air toxics emissions by over one million tons per year. These standards affect about 50 categories of major industries, such as chemical plants, oil refineries, aerospace manufacturers, and steel mills.
The EPA’s National Air Pollutant Emissions Trends report estimates that emissions for total volatile organic compounds (VOCs), many of which are air toxics, declined 3% from 1990 to 1995. Emissions from onroad mobile sources declined about 11%, while emissions from chemical manufacturing and nonroad mobile sources increased slightly.
In addition, ongoing programs to address air toxics at the state and local levels have achieved reductions in air toxics since 1990 which are not reflected in the analysis. For example, since 1990, monitoring data from California have shown a decline in concentrations for two important pollutants, benzene and 1,3-butadiene. Benzene has declined between 55 - 78% and 1,3-butadiene has declined 10 - 50%. Declines may be less in other areas, since California has been very active in reducing their air toxics concentrations. For example, monitoring data from New York have shown modest changes in benzene concentrations between 1990 and 1993.
Also, modeled pollutant concentrations are affected by uncertainties in emissions estimates and modeling techniques. Models can only approximate actual conditions.
WHAT ACTION IS EPA TAKING TO REDUCE AIR TOXICS?
EPA is developing emissions standards, or regulations, for over 170 categories of industrial sources of air toxics emissions. EPA already has issued many technology or performance-based standards (known as maximum achievable control technology or "MACT" standards) and expects to issue the remainder by November 15, 2000. As the standards are phased in, EPA expects emissions of air toxics to decrease significantly.
For example:
The Synthetic Organic Chemical Manufacturing Industry rule (also know as the "Hazardous Organics NESHAP" or the "HON"): expected to reduce air toxics emitted by this industry by approximately 90 percent (510,000 tons) from 1994 levels.
The Municipal Waste Combustors rule: expected to reduce dioxin emissions from these sources by 99 percent from 1990 levels, and mercury emissions by 90 percent, when implemented fully by December 2000. These sources account for over 61 percent of the total dioxin emissions and almost 19 percent of the national man-made emissions of mercury.
Hospital/Medical Infectious Waste Incinerators rule: when implemented fully by September 2002, is expected to reduce dioxin emissions from these sources by 94 percent and mercury emissions by 95 percent. These sources account for 11 percent of the total dioxin emissions and 10 percent of the national man-made emissions of mercury.
EPA estimates that the air toxics standards that will be implemented by the year 2000 should reduce emissions of air toxics by approximately one million tons. EPA also estimates that by 2010, emissions of four toxic air pollutants (benzene, 1,3-butadiene, formaldehyde and acetaldehyde) from mobile sources will be reduced by an average of 60 percent.
Under the air toxics regulatory program, EPA’s goal by the year 2010 is to significantly reduce the risks to Americans of cancer and other serious adverse health effects by reducing air toxics emissions by 75% from 1993 levels. While EPA has made significant strides toward achieving this goal, considerable work remains.
The Office of Air and Radiation’s home page on the Internet contains a wide range of information on the air toxics program, as well as many other air pollution programs and issues. The Office of Air and Radiation’s home page address is: http://www.epa.gov/oar/.