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Perspectives in Disease Prevention and Health Promotion Toxic Air Pollutants and Noncancer Health Risks -- United States

Previous evaluations of the health risks associated with chemical pollutants of ambient air have focused on the potential for carcinogenic effects (1). However, other potential health effects that may result from exposure to these pollutants include nonmalignant respiratory disease, hematopoietic abnormalities, neurotoxicity, renal toxicity, developmental toxicity, and reproductive toxicity. To address these concerns, the U.S. Environmental Protection Agency (EPA) conducted a national study to assess the noncancer risks of toxic air pollutants (EPA, unpublished data). This report summarizes the findings of this assessment. United States

During 1987 and 1988, air monitoring data were used to examine exposure to individual and multiple pollutants. During 1987, ambient monitored data were obtained on 319 volatile organic compounds from 123,000 samples collected during 1980-1987 in 310 U.S. cities and, during 1988, on six trace metals monitored primarily during 1980-1988 across the country at more than 1500 sites. Average annual concentrations were estimated, or modeled, for 40 pollutants emitted from more than 3500 individual facility sites (e.g., factories and businesses). Information on potential health effects and estimated exposures were available for 143 (43%) of 334 pollutants.

For the 143 pollutants, the maximum and median concentrations monitored during a 24-hour period or the average modeled annual concentrations, as applicable, were compared to the lowest-observed-adverse-effect-level (LOAEL) and to the health reference level.*

For 54 (38%) of the 143 pollutants, air concentrations exceeded the health reference level at one or more sites; several pollutants exceeded the health reference level at more than 25% of the sites studied.** An estimated 50 million persons lived within 6 miles (10 km) of monitored sites or within 1 miles (2 km) of modeled facilities where the concentrations of one or more chemicals exceeded the health reference level. For the LOAEL, the comparable population estimate was 19 million persons. Typically, several pollutants were present simultaneously in ambient air. In evaluating the potential impact of exposure to chemical pollutant mixtures, this study concluded that combined exposures may pose risks for the respiratory, neurologic, and reproductive systems and a risk for adverse developmental effects. Reported by: B Hassett-Sipple, Office of Air Quality Planning and Standards, I Cote, PhD, J Vandenberg, PhD, Health Effects Research Laboratory, US Environmental Protection Agency, Research Triangle Park, North Carolina. Air Pollution and Respiratory Health Activity, Div of Environmental Hazards and Health Effects, Center for Environmental Health and Injury Control, CDC.

Editorial Note

Editorial Note:

In 1988, the U.S. manufacturing sector emitted an estimated 2.4 billion lbs of toxic pollutants into the atmosphere (3). Although the data base available for assessing noncancer health risks is limited, the findings in this report underscore the need to focus attention on the noncancer health risks of toxic air pollution.

The 1970 Clean Air Act required the EPA to publish a list of hazardous air pollutants and develop a national emission standard for each.*** Under those provisions, only eight chemicals have been listed as hazardous air pollutants--in part because of the difficulties in determining risks to the public's health and developing appropriate standards. These difficulties, coupled with regulatory procedures, have prompted major changes in the strategies for controlling hazardous air pollutant emissions (4), as reflected in the Clean Air Act Amendments of 1990.**** Under these provisions, the EPA has listed 189 substances as hazardous air pollutants. Initially, the EPA will develop and implement technology-based emission standards; the EPA will then evaluate the remaining emissions and associated residual risks. If warranted, the EPA will develop risk-based emission standards.

The 1990 provisions require that the EPA perform risk assessments throughout the 1990s. In addition, the act provides a basis for state and local agencies to perform risk assessments. For example, states are required to conduct public hearings on air-quality permit applications and emission-control decisions. At such hearings, the public may request information on the health risks posed by emissions from facilities requesting permits. Therefore, state and local health departments and air quality management agencies also have an important role in implementing the 1990 amendments. The final report of the studies cited will be available from the Pollutant Assessment Branch, Emissions Standards Division, Office of Air Quality Planning and Standards, EPA, Research Triangle Park, NC 27711; telephone (919) 541-5346.


  1. Environmental Protection Agency. Cancer risk from outdoor exposure to air toxics. Washington, DC: US Environmental Protection Agency, 1990; publication no. EPA-450/1-90-004A.

  2. Environmental Protection Agency. Reference dose (RfD): description and use in health risk assessments. Appendix A. Integrated Risk Information System documentation. Vol 1. Washington, DC: US Environmental Protection Agency, 1987; publication no. EPA-600/8-86/032a.

  3. Environmental Protection Agency. Toxics in the community: 1988 national and local perspectives. Washington, DC: US Environmental Protection Agency, 1990; publication no. EPA-560/4-90-017.

  4. Quarles J, Lewis WH Jr. The new Clean Air Act: a guide to the clean air programs as amended in 1990. Washington, DC: Morgan, Lewis, and Bockius, 1990:32-3. *LOAEL=the lowest dose or exposure level at which an adverse effect has been observed. Health reference level=the adjusted LOAEL divided by appropriate uncertainty factors (2) (i.e., to account for intra- and interspecies variations and differences between no effect and LOAEL). **Chemicals for which more than 25% of sites had modeled or monitored levels that exceeded the associated health reference level in the United States: acetaldehyde, acrolein, arsenic, benzene, beryllium, carbon disulfide, carbon tetrachloride, chloroform, ethylene oxide, formaldehyde, hydrogen sulfide, methyl ethyl ketone, methyl isocyanate, methyl methacrylate, nitrobenzene, perchloroethylene, phenol, phthalic anhydride, styrene, tetramethyl lead, toluene diisocyanate, and vinyl chloride. ***Public Law no. 91-604, Section 4(a) (42 U.S.C. Section 7412). ****Public Law no. 101-549, Section 301 (42 U.S.C. Section 7412).

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