HAZARDOUS AIR POLLUTMS Report on Two Recent Conferences BY STANTON MILLER ith 189 hazardous chemicals listed under the Clean Air Act Amendments of 1990 (CAAA), the quintessential question is whether any chemical will be present in sufficient amounts to require its regulation. Chemical emissions are of concern to electric utilities and incinerator operations because reports on such emissions are due to Congress under CAAA requirements. Technical meetings are being held to evaluate emissions. One such meeting, held on the Massachusetts Institute of Technology campus in Cambridge, MA, in June, was the Toxic Combustion By-Products Congress. It attracted scientists from industry, government, and academia to discuss technical issues relating to combustion, associated pollution controls, and its impact on health. International congresses on toxic combustion by-products started four years ago at the University of California at Berkeley, the next congress will be held there in 1995. In Washington, DC. in July, the El Research Institute (EPRI) Conference on Managing Hazardous Air Pollutants attracted a similar mix of attendees to address trace emissions from pawer plants, to assess the transport of hazardous emissions in the environment, and to evaluate potential ecological or human impacts. EPRI's first conference on the subject was held 18 months earlier. Such meetings provide information and hope for a consensus on four key reports on hazardous air pollutants (HAPS).The first report, an EPRI synthesis report on power plant emissions and risks,will be completed in earIy 1994.The second report is the EPA mercury study, which addresses total mercury emissions fmm all sources, health and environmental effects, and means of control. The thiid report is the EPA electric utility emissions report, due to Congress in November 1995,which will also contain updated mercury information. Finally, the Great Waters study (which includes the Great Lakes region) of HAPS is due to Congress in November 1993.This study will also include data on mercury emissions, risk, and available controls. Biennial updates are due thereafter.
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M c i s articles are reports of meetings of unusual significance, international or national devel ments of environmental importance, signific public policy developments, and related items.
The EPRI conference Title I11 of the CAAA mandated that EPA evaluate emissions and health risks associated with the 189 HAPs from electric utility steamgenerating stations. Consequently, researchers are addressing trace emissions of heavy metals, halides, a n d organic c o m p o u n d s from power plants; the transport of emissions into the environment; and the potential ecological and health impacts of these emissions. If these emissions pose any significant health risk, EPA would recommend the issuance of regulations to reduce impacts. At the EPRI conference Winston Chow and Leonard Levin said their organization’s primary concern is to understand and evaluate strategies for managing potential risks caused by HAPS. They said that a key component of their program is the Power Plant Integrated Systems: Chemical Emissions Study (PISCES). PISCES researchers are assessing the source and pathways of chemicals in the process streams within power plants. Initiated in 1988, PISCES measures chemical inputs to plants (fuels and additives), their transformations during the combustion and control process, and their partitioning into chemical outputs. To date, Chow and Levin continued, field tests have been conducted at more than 20 plants covering a variety of fuels, including bituminous and subbituminous coals, oils, and natural gas as well as conventional control devices such as electrostatic precipitators, wet and dry scrubbers, and fabric filters. EPRI scientists also study the transport and dispersion of trace substances that have been emitted from power plant stacks. Initially, EPRI has focused on characterizing emissions, ambient concentrations, and depositions, and on developing equations that estimate chemical transformations among the substances. EPRI plans ultimately to incorporate these results into plume models that will lead to better predictions of fate and transport of trace substances-critical for estimating health and environmental exposure to these substances. Of the 189 HAPs, mercury causes the most concern because of uncertainties about its sources and chemistry, and known high mercury levels in some fish stock around the United States. According to Chow and Levin, initial research has focused on developing a complete understanding of the environmental fate of mercury emissions. EPRI’s
Don Porcella is studying virtually all aspects of mercury cycling, including emissions, chemical transformations, deposition, concentration in water and soil, uptake by plants and animals, and human exposure and health. One result has been the development of a sophisticated mercury cycling model that simulates mercury dynamics i n lakes and estimates mercury methylation and demethylation, sedimentation, outflow into groundwater, and bioaccumulation in fish. These efforts enhance our understanding of the potential ecological consequences of mercury emissions. Assessing the risks posed by utility trace emissions raises complex issues and involves the quantification of significant uncertainty. Under the Comprehensive Risk Evalua t i o n (CORE) project, EPRI i s pulling together information from ongoing research to provide the most accurate picture possible of the likely impacts of trace substance emissions. The CORE project has estimated the risk from each power plant i n the United States with greater than 25 MW capacity. EPRI is developing another model, called Total Risk of Utility Emissions (TRUE). TRUE links existing models for multimedia risk evaluation, allowing assessment of risk caused by air emissions, water pollutants, and solid plant discharges, analogous to EPRI’s multimedia PISCES work for power plants. TRUE assesses human exposure via inhalation, food ingestion, skin contact, and other routes. This allows assessment of overall exposure and ensures a more accurate depiction of the total risks associated with power plants. According to Chow and Levin, arsenic and mercury are examples of our relative level of understanding regarding different substances and their impacts. Arsenic is a relatively well-understood substance. PISCES tests appear to provide reliable measurements of arsenic in fuel and in the outlet stream. However, the toxicity of arsenic has not been established for low-level exposures; consequently the likely impacts of trace emissions of arsenic cannot be determined with reasonable certainty. Mercury represents the other extreme for which neither the emissions from human activity nor mercury vapor released from natural sources such as volcanoes, ocean water, forest fires, and mineral deposits are well understood. Consequently, the risks caused solely by
electric utility mercury emissions are extremely uncertain. Our knowledge of other trace pollutant emissions lies somewhere between that of these two substances. The conclusion of the EPRI overview paper is that even for substances that are extensively studied, like arsenic, determining potential risks caused by their emission from power plants remains a challenge. Despite efforts to prevent mercury contamination of the environment by localized industrial discharges, significant levels of mercury continue to be found even in remote areas because of long-range atmospheric transport, according to the paper by Philip Galin of the New York Department of Environmental Conservation and colleagues elsewhere. To clarify the relevant sources, transport, and fate of atmospheric mercury, a large-scale monitoring program has been operating since July 1992 at five locations across upstate New York. Vaporphase mercury is automatically collected from the air during four 24-h periods each week on low-mercury charcoal sorbants. The sorbants are sent to MIT, where they are analyzed for mercury by instrumental neutron activation. The sorbant and collection systems were designed, built, and tested at MIT, and the neutron irradiation is performed at room temperature using an MIT research reactor. Results for the five sites during December 1992 show values between 0.6 and 3.6 ng/m3. The small range is consistent with the vapor-phase mercury being a regional or global pollutant. These data contrast with data from other scientists obtained for the same period for particulate mercury, which exists in concentrations of tens of picograms per cubic meter. The relationship between these two phases of atmospheric mercury needs to be studied further. In a paper entitled “Transformations of Mercury i n the Atmosphere,’’ Jacek Wrobel and colleagues at ENSR Consulting and Engineering (Alameda, CA) reviewed the research literature on the theoretical study of the atmospheric chemistry of mercury. As a way to control mercury, EPRI’s Chow mentioned injecting activated carbon in the emission control system that would collect mercury, partially as mercury metal and partially as Hg+’. EPRI’s end-of-year report should be available in the spring; an update of emissions will be available in the summer of 1994.
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Coal cleaning is an option to reduce the level of trace metals from coal prior to combustion or gasification, according to a paper by Steven A. Benson (University of North Dakota) and colleagues. Conventional coal-cleaning technologies have been found to reduce the level of many trace metals in the coal. The level of removal from the coal is related to mode of occurrence in the coal, the method of cleaning, and the cleaning plant operation.
The MIT Congress Both hazardous and solid waste are incinerated. According to EPA, five million tons of hazardous waste are burned annually in the United States. The emission of toxic metals and toxic metal compounds is of great concern to the public and to combustion scientists. The biggest challenge facing incineration is public acceptance. An incinerator is any enclosed device that uses controlled flame combustion to oxidize waste; it is more closely associated with destruction rather than treatment. Several examples of devices used for incineration include rotary kilns, liquid injection incinerators, cement kilns, and high-temperature boilers. In the 1980s cement kilns were considered the best place to burn liquid hazardous wastes. Alternative methods include molten salt pyrolysis, calcination, and wet air oxidation. For PCBs specifically, alternative disposal methods include solvent extraction, dechlorination, and biodegradation. However, there has been concern about emissions from incinerators. Of special interest are the emissions of toxic metallic particles such as lead, tin, mercury, cadmium, and chromium. These metals are typically in the submicrometer range, making it difficult to be captured in particulate control devices. Jerry C. Martin, director of corporate environmental affairs for the Dow Chemical Company, said at the meeting that incineration is in big trouble. Laypeople are skeptical about incineration because they are often excluded and feel outraged, he said. In 1991, 10 billion lb of SARA (Superfund) wastes were generated nationally; the same year, 10 billion lb were treated by industry using incineration and other techniques. According to the Chemical Manufacturers Association independent survey of toxic chemicals released by chemical manufacturing facilities (ESbT, Aug. 1993, p. 14653, 54% of the
waste was recycled into other products and processes; 31% was treated, including incinerated; 8% was converted to energy sources; and 7% was released to air, water, and land. He called attention to Dow’s WRAP (Waste Reduction Always Pays) program and called for the formation of a nationwide WRAP program. Communication is always a problem. Martin said that the companies need to share their knowledge about incineration emissions with their neighbors, and “open ourselves up to wider public involvement” and community groups in order to initiate projects that reduce waste. “When asked in a recent opinion poll the major causes of today’s environmental problems, the public pointed to industry,” Martin said. “They don’t trust the industrial sector, and they think government should impose and enforce more stringent regulations.” He added, “At Dow, each manufacturing operation must also pay for its own incineration costs, which impacts the businesses’ profitability. The less waste they generate and need to incinerate, the more profit will result. But we haven’t done an adequate job educating the public that this is our objective. . . Still, the negative public perceptions toward incineration and the distrust of how industry is managing it persist.” He summed up, “Up to now, industry has done a relatively poor job of risk communications. But there is light at the end of the tunnel. Martin also said, “At Dow, we have been pleasantly surprised with the success we’ve had discussing issues with community groups, environmental groups, and others. Some people might say we were crazy to sit down and talk to folks like Greenpeace, but it’s important to show that we have nothing to hide and that we believe in what we say. If we want the public to be more receptive to us, then we need to be more receptive to their concerns and needs. When citizens share in discussion and the decisionmaking process, they give more thoughtful attention to the issues. I’m not convinced that industry really has enough of a waste reduction mentality yet, but we are making progress. Industry must start viewing waste generation as an opportunity for improvement and competitive advantage.” On May 18, EPA Administrator Carol Browner announced an 18month freeze on the expansion of hazardous waste incineration capacity. When the Clinton-Gore ad-
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ministration had just come into office it was against the then-new hazardous waste incinerator in East Liverpool, Ohio, which has subsequently started operation after a judicial decision. The Coalition for Responsible Waste Incineration (CRWI), an association of companies, associations, and academics, founded i n 1987, has voiced a counter view. CRWI Executive Director Ian Moar said, “our member companies are disappointed that EPA took this action without the benefit of consultation with business, but accepts the opportunity to again demonstrate the safety and need of hazardous waste incineration.” He added, “as only 0.7% of all reported hazardous wastes are t r e a t e d by i n c i n e r a t i o n , more agency attention should be focused on the methods used to treat the other 99.3% of hazardous wastes.” Trace metal emissions from electric utilities as well as from municipal solid waste incineration pose a potential health and environmental problem. The metals of concern to the electric utility industry are Be, Cr, Hg, As, and Ni; the industry is also concerned with radionuclides in emissions. Polynuclear aromatic hydrocarbons (PAHs) form one of the most important classes of organic compounds as far as combustion is concerned. Preliminary health risk ass e s s m e n t s from EPRI’s CORE project have determined that electric utilities emit extremely low levels of PAHs. The concentrations found indicate that health risks are insignificant. In other cases involving hazardous waste incinerators, an organic compound does not always pass directly through the flame zone. When and if this happens, the toxicological data indicate that these products of incomplete combustion might be more toxic than the parent compound. It is also important to know the species formed in the combustion zone. For example, the toxicity of heavy metals is known to be a function of their oxidation state, so the speciation of each metal emission becomes important. Scientists are beginning to experiment with trace emissions from combustion sources, but concentrations need to be measured and evaluated before decisions can be made to regulate such emissions.
Stanton S. Miller is executive editor ofES&T.
