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Air toxics What is the problem and how do we deal with it?
D. Kent Berry O&e of Air Quality Planning and Stundurds Environmental Protection Agency Research Triangle Park, N.C. 27711
A number of inhalable air pollutants have been found likely to cause human cancer. Section 112 of the Clean Air Act requires EPA to protect public health from exposure to these and other hazardous air pollutants. During the past several years, however, state officials, Congress, environmental advocates, and EPA managers have expressed concern about EPA's program for controlling hazardous air pollutants. In August 1983 the General Accounting Office released a report about the
delays in EPA's program for regulating hazardous air pollutants ( I ) . On the basis of that report, Rep. John Dingell (D-Mich.), chairman of the House Energy and Commerce Committee, held hearings to examine issues connected with the implementation of Section 112 of the Clean Air Act. During discussions that took place within EPA before the hearings, it became clear that the agency had p r l y defined the scope and causes of health problems that air toxics cause. Three fundamental questions were raised concerning the magnitude and nature of the health risks: Do air toxics present a significant health problem? If air toxics do pose a significant health problem, what pollutants and sources are responsible?
This article not subject lo U.S. copyright. Published 1986 American Chemical Society
Is there an important part of the national air toxics problem that Section 112 cannot address effectively? Late in 1983, EPA began a study of the problem of airborne carcinogens to stimulate policy discussions and to guide further studies. In its report, issued in 1985, the agency attempted to assess the magnitude and nature of the air toxics problem by developing quantitative estimates of the cancer risks posed by selected air pollutants and their sources (2). Even though quantitative estimates of risk are presented in the report, the study was not conducted to support specific regulatory decisions. Instead, its goal was to obtain a quick assessment of the air toxics problem in the United States; it should be regarded as a scoping study. Environ. Sci. Technot.. VoI. 20, NO. 7. 1986
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The risk estimates presented in this article should be regarded as only rough approximations of total incidence and individual risk and should be used in a relative sense only (that is, to judge the magnitude of the air toxics problem relative to other causes of cancer and to determine the most important compounds and source categories). &timates for individual compounds are highly uncertain and should be used with extreme caution. As more data be come available, these risk estimates undoubtedly will change. This discussion of the air toxics problem should be re garded as a preliinary pichlre that will certainly change as new data become available.
Only readily available data regarding compound potencies, emissions, and ambient levels were used, no new data were collected. The only health effect examined quantitatively was cancer; health data on teratogenicity and acute health effects related to short-term exposures were not considered. Normally, cancer incidence and other effects of exposure to air toxics are evaluated, to the extent the data permit, to make regulatory decisions on individual toxic air pollutants. They were not included in this study, however, because of the lack of readiiy available data to permit quantification on a nationwide Mi. Air toxics meetings The subject of toxic air pollution h a s become the major theme of the ac. tivities of the Air Pollution Control
Analytical methods Three major analyses were undertaken to estimate cancer incidence and individual lifetime risk; each included a separate set of compounds, although there was considerable overlap. The first study used ambient data for five metals, 10 volatile organic compounds, and benzo[a]pyrene @[alp) to assess these risks. ' b o other analyses used emission estimates and exposure models to assess the incidence of cancer and the maximum individual risk associated with the pollutants selected. In addition, a B[a]P surrogate a p proach was used to estimate cancer incidence associated with products of incomplete combustion (PICs). A dose-response coefficient relating lung cancer incidence and PICs was generated from epidemiological studies, and cancer incidence associated with PIC exposures was estimated by applying this coefficient to ambient B[a]P levels. F d y , quantitative risk assessments fromother EPA studies of asbestos, radionuclides, and all parts of the gasoline marketing cbain were incorporated into the study.
Sourcesand risks
course on air toxics were c during the meeting. APCA also will convene a sym sium on toxic air pollutants as par its 1987 annual meeting. In additi the association olans a series oneday workshops in various locat the United States
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Point sources (major industrial sources) and area sources (smaller sources that may be spread widely across a given area,such as solvent use and motor vehicle emissions) appear to contribute significantly to the amount of toxic substances in the air. Large point sources are associated with many high individual riskq area sources a p pear to be responsible for the majority of aggregate cancer incidence (the estimated number of cancer cases per year in the exposed population that are caused by a particular compound or by several compounds). Although there is considerable uncertainty associated with risk estimates for some substances, available data indicate that numerous pollutants may be important contributors to aggregate
cancer incidence from air toxics. These include metals, especially chromium and arsenic; asbestos; PICs; formaldehyde, benzene; ethylene oxide; gasoline vapors; and chlorinated organic compounds, such as chloroform, carbon tetrachloride, perchloroethylene, and trichlorcethylene. Sources that contribute to individual risk and aggregate incidence from air toxics include motor vehicle emissions and emissions from coal and oil burning, woodstoves, metallurgical industries, chemical production and manufacturing, gasoline marketing, solvent use, and waste oil disposal. Combustion and incineration are probably the greatest sources of risk. Large city-to-city and neighborhoodtc-neighborhood variations in pollutant levels and sources were found in those. cities for which sufficient data were
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available for analysis. The current air toxics data base, however, cannot characterize most local air toxics problems acmately. Three analyses quantified estimated cancer risks ascribable to 1 5 4 5 toxic air pollutants (the number of pollutants examined varied with the different analyses). The estimates resulting from these analyses indicate a summed risk for the pollutants examined ranging from 1300 to 1700 cases annually nationwide. This fmding is quite surprising when one considers the different approaches used and the large uncertainties in each analysis. By way of perspective, estimated nationwide cancer cases and cancer deaths for 1983 were 850,000 and 440,000,respectively. These risk estimates, nevertheless, are highly uncertain, and convergence of the various analyses on a seemingly narrow range is somewhat coincidental, given that estimates for individual compounds varied widely among the different analyses performed. A maximum lifetime individual risk
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of at least (one chance in 10,000) in the vicinity of major point sources was estimated for 21 pollutants, about half of those studied. Maximum lifetime individual risk is defined as the probability of contracting cancer following continuous exposure to the maximum measured or modeled concentration during a 70-year lifetime. A maximum lifetime individual risk of at least IO-' ( I in 1000) was estimated for 13 pollutants. In urban areas, additive lifetime individual risks attributable to simultaneous exposure to I O to 15 pollutants ranged from IO' to IO4. These risks, which were calculated from monitoring data, do not appear related to specific point sources. Instead, they represent a portion of the total risk associated with the complex pollutant mixtures typical of urban ambient air.
Some low-production organic chemicals appeared to contribute little to aggregate incidence. Twenty-one of these were estimated to account for a total of less than 1.O cancer cases annually nationwide. This conclusion may arise, in part, from the lack of data concerning the emissions and toxicity of these lower volume chemicals. Other sources of air toxics, such as publicly owned treatment works and treatment, storage, es, may pose importan1 risks in some locations. For instance, preliminary findings suggest that publicly owned treatment works that receive industrial discharges emit volatile organic compounds in excess of 100 tons each year. EPA's programs for attaining the National Ambient Air Quality Standards for particulate matter and ozone appear to have done more to reduce air toxics levels than have regulatory actions aimed at specific toxic compounds. An analysis of 16 pollutants, which used both monitoring and emission data to evaluate progress made in abating air
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toxics between 1970 and 1980, was completed as part of the study on the air toxics problem in the United States (2). The estimated cancer incidence rate for these air pollutants in 1980 was less than half that for 1970 there were 3600 cases in 1970 and 1600 cases a decade later. This seems reasonable in light of the comprehensiveness and effectiveness of the criteria pollutant control program, which indirectly reduces emissions of toxic pollutants. Even after regulations are implemented under Section 112 of the Clean Air Act for benzene and arsenic, these pollutants will still apparently make significant contributions to aggregate incidence. This suggests that the base for the air toxics regulatory programs should be broadened to include emissions from small area sources, such as combustion, motor vehicles, and solvent use
Sources of uncertainty Many assumptions and extrapolations are necessary to transform measured or modeled levels of air pollutants into exposure estimates. Whether such assumptions introduce a high or low bias into the results is difficult to assess. It is clear, however, that the use of such assumptions injects a high degree of uncertainty into the analyses. Several factors may have caused the risk of cancer related to air toxics to be understated. For instance, ambient urban air contains dozens, perhaps hundreds, of substances. Risk estimates for most of these pollutants could not be calculated because of certain data limitations imposed. Indoor concentrations of certain pollutants, such as radon, tobacco smoke, formaldehyde, and some volatile organic compounds, are commonly several times higher than outdoor concentrations of the same pollutants. The estimated cancer incidence associated with indoor exposure to passive smoking (500-5000 cases annually), with exposure to radon (loOo-20,000cases annually), and with exposure to five organic compounds (1600 cases annually) indicates that indoor sources contribute significantly to risks posed by toxic air pollutants. Although the risks attributable to compounds formed in the atmosphere could not be quantified in the analyses that used exposure models, there are indications that these risks may be significant. For example, formaldehyde is formed in the atmosphere by the breakdown of other organic compounds, and certain compounds, such as toluene, may be converted into toxic substances through photochemical reactions. Some factors mav have caused the cancer risks associaied with air toxics
to be overestimated. EPA unit risk values (estimates of carcinogenic potency) are generally regarded as plausible, up per-bound estimates. That is, the unit risks are not likely to be higher but could be considerably lower. In many cases, unit risk values are preliminary. The weight of evidence of carcinogenicity for the compounds examined varies greatly, from limited to substantial. Moreover, the extent of evaluation and health effects assessments performed varies considerably from one compound to another. For this study, it was assumed that all compounds included in the report are human carcinogens. The risk assessments are based on the assumption that people living in an area are exposed to the estimated ambient levels around the clock for 70 years. This assumption severely compromises estimates of maximum lifetime individual risk. Few plants operate for 70 years, most people change residences several times during their lives, and most leave their neighborhoods during the day. The degree to which outdoor emissions of many pollutants, such as trace metals and ozone precursors, penetrate indoors is largely unknown. If emissions of a pollutant from outdoor sources do not penetrate indoors and if there are no indoor sources of that pollutant, the risks will be overstated.
Stratw for routine releases The study described above was completed and a draft was released for public and peer review late in 1984 (the final report was published in 1985). Simultaneously, on the basis of the preliminary findings of the analyses, EPA began a series of activities designed to examine the need for a new national strategy for air toxics. Activities include discussions of the results of the study and of possible new national strategies with all interested groups, including industry, public interest organi-
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II of the Clean Air Act to set stand- tions in which the health effects are not
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zations, state and local governments, and legislative stafSs. EPA’s stmtegy, which deals with routine and sudden accidental releases, was announced in June 1985 (3). The strategy for routine releases covers three main areas: national regulation, expansion and enhancement of state programs, and evaluation and control of urban “hot spots” cawed by multiple sou~cesand pollutants. National regulation. EPA has completed its commitment to Congress to consider 20-25 chemicals for regulation under Section 112 of the Clean Air Act. The agency will continue to use the l i n g and development of emission standards under W o n 112 to regulate individual toxic chemicals for which there are source categories causing significant aggregate risk. Between May 1984 and January 1986, EPA issued decisions on 22 potential air toxics. Nine of these have been Notices of Intent to List under Section 112, one (coke oven emissions) was listed under Section 112, and one (methylene chloride) will be regulated under Section 112 or other federal authority (4, 5). The pollutants covered by Notices of Intent to List are carbon tetrachloride, cadmium, chromium, chloroform, ethylene oxide, ethylene dichloride, butadiene, perchloroethylene, and trichloroethylene (6-14). Emission standards for these pollutants are now being developed. EPA also will regulate entire emission streams under Section 112 when a complex combination of toxic chemicals is k i n g emitted. The agency used this approach in listing coke oven emissions. Other regulatory mechanism also are being employed. They include: the use of Section 111 (New Source Performance Standards) to control classes of area sources, such as wood stoves and synthetic organic chemical plants; the use of various provisions of Title 650
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ards for motor vehicles and fuels to reduce the significant risks resulting from theii use; reduction of evaporative losses from sewage treatment plants, which can be a serious source of toxic emissions, through continued implementation of pretreatment programs for water pollution sources that discharge into municipal sewers; control of toxic air pollutants from hazardous waste treahnent, storage, and disposal facilities by setting strict standards and by restricting wastes from land disposal under the authority of the Resource Conservation and Recovery Act; and control of other volatile chemicals under the authority of the Toxic Substances Control Act (TSCA). With respect to Title II, special emphasis will be placed on the emission of toxic particulates from diesel-powered vehicles and on evaporative hydrocarbon losses. The program to reduce such losses will significantly reduce exposure to benzene and other hazardous substances. In short, section 112 will be used in the usual way, but at an accelerated pace, for those situations to which it is applicable. At the same time, Section 112 will be applied in less traditional ways to address sources of multiple pollutants. Other provisions of the Clean Ai Act and virtually all of EPA’s other statutory powers will be used to reduce the risk associated with exposure to air toxics.
strengthening state air toxics programs. In addition to conducting an expanded federal regulatory program, EPA also is working to strengthen state programs. The principal reason is to ensure that states can play the same vigorous role in evaluating problems and developing and enforcing requirements for controlling toxic air pollutants that they now play in abating conventional air pollutants. Congress intended states to play a central role in the national effort to control conventional pollutants under the 1970 amendments to the Clean Air Act. This has led to a substantial reduction in emissions of air toxics. Efforts are under way to impart to state and local air pollution agencies the technical and financial ability to continue their efforts to control air toxics. EPA’s goal is to initiate an effective air toxics control program in every state and major local air pollution control agency by the end of 1986. State and local programs complement the federal regulatory effort for certain pollutants. EPA’s assessment of the risks posed by certain pollutants and source categories has uncovered situa-
widespread enough to warrant setting a federal standard but in which local risks of concern are observed at a limited number of industrial plants. In these cases, EPA provides technical and financial assistance to state and local agencies for extensive directed data collection and evaluation of such risks. EPA is implementing this approach in a 1Cstate pilot study of emissions of acrylonitrile (Is). Geographic approaches to evahmtion and control of toxic pollutants. EPA will expand its current studies of local toxics problem and will work more closely with state and local governments on the identification and control of problem l i e d to multipollutant, multisource interactions in urban areas. The agency will provide grant assistance and technical support to state and local agencies to encourage them to evaluate and control “urban soup” air toxics problems. A d d e n t a l releases There is an informal but workable division of activity between the public and private sectors for preventing and mponding to accidental releases of toxic air pollutants. Much of the ability to prevent accidents has developed because of corporate self-interest. In addition, although some federal controls tend to promote accident prevention, the role of government emphasizes technical information sharing, guidance, and emergency preparedness and RSponSe. Among the most important federal regulations for emergency preparedness is the reportable quantities provision of the Comprehensive Environmental Response, Compensation, and Liability Act (Superhd). This set of rules requires a release of specified amounts of substances listed under the authority of S u p e r h d to be reported
by the responsible party and aims at promoting the safe handling of chemicals. It also provides EPA and state agencies with information in the event of a release, either to initiate emergency response or to identify requirements for further emergency preparedness. Other important regulations under TSCA require record-keeping and reporting of certain hazards that might result from an accident. Statutes administered by the Occupational Safety and Health Administration and the Department of Transportation are directly related to accident prevention; like those of the Coast Guard, they provide important regulations for emergency preparedness and response. Nevertheless, state and local authorities are almost always the first to respond in the event of a spill or release. There also are national and regional response teams. The National Response Team (NRT), which is managed by EPA, and of which the Coast Guard is a member, consists of representatives of every federal agency with the authority to respond to hazardous substance emergencies or to conduct emergency preparedness programs. The regional teams include members from the same federal agencies that make up the NRT and representatives from state and local governments. A preparedness committee has been established by EPA, and a national assessment of state and local emergency preparedness is under way. The response teams operate under the Superfund National Contingency Plan, which was designed during the 1960s for responding to oil spill emergencies. The plan was thoroughly revised after Superfund was passed in 1980, and then was incorporated into Superfund. It has undergone further revision in the areas of coordination, planning, and response. Upgrading preparedness The chemical industry is in the process of evaluating and upgrading its safety systems. Although EPA considers this activity appropriate, agency officials believe that EPA also must upgrade current government systems for emergency preparedness and response. EPA is taking steps to strengthen state and local authorities’ abilities to respond to emergencies. By expanding its regional staff and by establishing a staff in Washington to focus on these efforts, the agency will be able to offer a number of services to state and local governments in the areas of contingency planning, technical assistance, training, and response. Moreover, EPA is taking steps to coordinate and improve national policy and planning for emergency preparedness and response through the NRT, as
required by the National Contingency Plan. The NRT is increasing its training of state and local authorities and is adding staff to increase its ability to provide technical assistance to state and local governments in planning, preparedness, and response. In addition, EPA is taking action to reinforce existing programs and undertake new activities. The agency already has revised or will revise operating guidelines, and it will increase resources and provide expanded staff training to enforce reportable-quantity requirements and record-keeping and reporting rules mandated by TSCA. These actions will provide the data necessary to ensure prompt response in case of emergency and will result in a higher level of comprehensive reporting on spills and releases on which to base contingency planning. When reports indicate a pattern of mishandling of chemicals, EPA will join with other federal agencies and state governments to inspect facilities or to determine whether situations exist in which chemical practices may be unsafe. The administration has requested that provisions for additional civil enforcement be incorporated into the Superfund legislation to provide increased opportunities for enforcement actions that may result from reportable-quantity violations. EPA has issued an Acutely Toxic Chemicals List (ATCL) (16). This list includes chemicals that are most likely to cause serious harm to those exposed during an accidental release. The agency has issued profiles of each chemical on the list, providing information on health effects, physical and chemical properties, fire and explosion hazards, reactivity, use, and steps to take in case of an accidental release. This information has been released in interim form; the period for public comment has expired, and a final set of profiles is expected to be issued in the late summer of 1986. The list will be used in several ways. First, it has been sent to state and local governments, together with guidance for inspections, audit programs, and increased preparedness and response efforts that are to be undertaken at the local level (16). Second, EPA will use the list to target federal emergency response and preparedness activities. Efforts to increase technical assistance to states and communities in the areas of contingency planning, training, and response will focus on sites at which chemicals listed on the ATCL are handled, stored, processed, formulated, or manufactured. Use of the list also will facilitate sitespecific contingency planning by local authorities who will receive technical
assistance and guidance from the federal government. Finally, the chemicals identified on the ATCL will be the focus of community right-to-know programs. Without such a focus, communities will not be equipped to set priorities. Without federal guidance, communities may have either so little information that effective action will be difficult or so much that the ability of the community to plan for and respond to emergencies will be impaired. The list should help communities determine the best ways to address their air toxics problems. A framework for action As it is presently understood, the air toxics problem in the United States is complex and widespread. It calls for EPA, state and local authorities, and industry to develop comprehensive solutions to this problem. EPA’s air toxics strategy establishes the framework for action that agency officials believe will reduce risks to the public from exposure to air toxics.
References (I)“Delays in EPA‘s Regulation of Hazardous
Air Pollutants.” GAOIRCED-83-199: Gcnera1 Accounting Office: Washington. D.C.. lo*, l,y,.
(2) Haemisegger, E. et al. “The Air Toxics Problem in the United States: An Analysis of Cancer Risks to Public Health for Selected Pollutants,” EPA ~ ~ ~ I I - x ~ EPA: ooI Washington, D.C., 1985. (3) “A Strategy to Reduce Risks to Public Health from Air Tories.” EPA: Washington. D.C., 1985. (4) Fed. Re@. 1984,49. 36560. (5) Fed. ReKifr. 1985,50, 42037. (6) Fed. Rqisr. 1985, 50, 32621 (7) Fed. Rqirr. 1985,50. 42000. ( 8 ) Fed. Rqisl. 1985, 50. 24317. (9) Fed. Repirr. 1985, 50, 39629. (IO) Fed. Regis!. 1985.50, 40286. ( 1 1 ) Fed. Repist. 1985.50, 41994. (12) Fed. Regisl. 1985,50,41446. (13) Fed. Rryirr. 1985,50, 52880. (14) Fed. Rryi.sl. 1985,50,52422. (15) Fed. Repist. 1985.50, 24319. (16) “Chemical Emergency Preparedness Program Interim Guidance.” EPA: Washington, D.C.. 1985.
D. Kent Berry is assisranr d!recror of rhe Srroregies ond Air Srmdmds Division in the O g c e of Air Quoliry Planning and Srandards ar EPA (Resmrch Triangle Park, N. C.). He was previously rhe direcror of rhnf o g c e k policy analysis slag: He has been involved in rhe developmenr and review of srare implemenrarion plans. BerT hos an M.S. in environmenral engineering from the University of Norrh Carolina. Environ. Sci. Technol.. VoI. 20. NO. 7, 1986
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