"I am speaking for myself, but it is my strong opinion that the risk assessment is not now in a form complete enough for wise decision making." And although EPA may be "thoroughly sick" of this multiyear project, Harrison recommended EPA make changes and submit the assessment for another peer review. However, Harrison also noted weaknesses in the general area of assessing risk of accidents. The problem, he said, is in multiplying a very large number representing serious consequences by a very small number that is the probability of them happening. The result, he said, is "a falsely numerical operation" in which a number is found that may be reassuring but is associated with huge uncertainties. In the ecological area, EPA's analysis was a "screening" document, intended to identify potential ecological risks from the plant, rather than a detailed ecological risk assessment. The draft found that WTI's metals and formaldehyde emissions may have an impact on the environment, said Glenn Suter, with the Environmental Sciences Division, Oak Ridge National Laboratory, but the assessment did not say what should be done to address these risks. Suter said his group's primary recommendation was that EPA clearly state whether a detailed ecological risk assessment for the emissions identified should be conducted or whether the goals of the screening document should be changed. Other areas of concern, he said, were that the risk assessment did not consider the ecological impact of background pollution, including emissions other than air that come from the plant, and the impact of accidents on the ecosystem. Both Suter and Harrison backed the need for the risk assessment and urged EPA to develop a system to speed up the process. Several reviewers, Harrison among them, also noted heightened concern about risk because of the facility's location. "This is a very poor site," Harrison added, but he noted the panel's role was to the review the risk assessment document, not the site. —JEFF JOHNSON
NEWS TECHNOLOGY Study finds no correlation between chlorine incineration and dioxin formation Chlorine levels in waste fuels do not directly influence the amount of dioxin generated during incineration, concludes a new study prepared by the American Society of Mechanical Engineers (ASME). The results challenge the position of some environmental groups that in order to cut dioxin emissions, it is necessary to remove heavily chlorinated materials, such as polyvinyl chloride and plastics, from incinerator waste streams. In announcing the study, ASME bluntly stated, "The findings refute claims by public interest groups that there is a direct relationship between chlorine and dioxin." However, critics of the engineering society's 1900page report charge that it controlled for only one variable, chlorine, and looked only for dioxin exiting the stack, ignoring dioxin in fly ash that is captured in pollution control equipment. Dioxin was defined as all chlorinated dibenzo-p-dioxins and dibenzofuran isomers. Nearly all dioxin created during waste incineration is formed immediately after flue gases exit the combustion chamber and cool below 400 °C. In a properly operating incinerator, dioxin is thought to be formed and collected within the pollution control equipment where it attaches to fly ash and other combustion byproducts and is trapped. The ash is then transported to landfills (ES&T, Jan. 1995, 33A). The report does not question the accepted mechanism of how dioxin is formed through burning chlorinated materials, said H. Gregor Rigo, a mechanical engineer and president of Rigo & Rigo Associates, Inc., one of three consulting firms that prepared the study. Although chlorine may be necessary to form dioxin, Rigo said, the study shows that the relationship is not direct, and that even small amounts of chlorine— from table salt, meat scraps, or paper—are sufficient to form dioxin during incineration.
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The study simultaneously characterized dioxin in stack gas emissions with chlorine in waste at 107 combustion units at 90 facilities. It examined emissions from incinerators of municipal, medical, and hazardous waste; biomass combustors; boilers; industrial furnaces; and cement kilns. Seventy-two facilities (80%) showed no statistically significant relationship between chlorine input and dioxin levels in the gas stream. The remainder were divided among those showing more dioxin with more chlorine in wastes and those showing the opposite. Several committees within ASME sought the study and directed the contractors in conducting it, according to a society official who noted there is "a lot of industry interest in the relationship between dioxin and chlorine." An ASME panel peer reviewed the results of the study, which was funded by the Vinyl Institute, the Chlorine Chemistry Council, and Environment Canada. The report notes that "any effect chlorine has on dioxin concentrations in commercial-scale systems is masked by the effect of air pollution control systems temperature, ash chemistry, combustion conditions, measurement imprecision, and localized flow stratification." The report, however, did not control for any of these other variables, and critics say this is a fundamental weakness. "This is a joke. They designed the study to prove exactly what they intended," said Barry Commoner, director of the Center for Biology of Natural Systems, Queens College, City University of New York. Commoner charged that by using data from different incinerators with dissimilar designs and operating characteristics as well as different pollution control devices and fuels, the researchers had no control over any variable but chlorine. Conse-
Dioxin in flue gas versus chlorine in feed by facility
Dioxin measured in picomoles per dry standard cubic meter/ 7% 0 2 .
quently, Commoner said, they cannot determine the impact of a single variable when the many individual variables that influence the creation of dioxin were left uncontrolled. He also questioned the value for the study's methods of measuring the small fraction of dioxin in the stack, when most is in the ash. " [Environmental critics] are not saying that there is a direct correlation between chlorine and dioxin in the gas," Commoner said. "But we are saying that if no chlorine goes into the fuel, no dioxin will come out." Valerie Thomas, a staff researcher with the Princeton University Center for Energy and Environmental Studies, is the coauthor with Thomas Spiro of a 1995 study that showed the opposite result of ASME's study {Toxicol. Environ. Chem. 1995, 50, 1-37). Thomas and Spiro looked at diverse combustion sources and fuels—gasoline, wood, municipal and hospital waste, and others—with wide ranges of chlorine content and determined the average dioxin level emitted by overall source categories. As the ASME researchers did, Thomas and Spiro measured dioxin in stack gas, not captured fly ash, but they found a strong correlation between chlorine content of fuel and dioxin generation. Incinerators of municipal and hospital wastes emitted the most dioxin, the study found, especially when the facilities did not have adequate pollution control equipment. On the other hand, no correlation was found between
chlorine and dioxin in stack gas for hazardous waste incinerators with state-of-the-art pollution control equipment, which emitted very low levels of dioxin even though chlorine made up 20% or more of the fuel. "But that is not surprising," she said. "They have the best pollution control equipment we know how to make. There are really good ways of controlling dioxin emissions besides limiting chlorine, but that doesn't mean that chlorine doesn't have a lot to do with dioxin formation." Rigo is convinced, however, that chlorine is not the driver in dioxin formation, but he acknowledged that the ASME study does not reveal what is. "Spending a lot of money trying to divert chlorine is not going to accomplish anything and in some instances may make things worse," he added. "Once in ash, it doesn't leach off." A more pragmatic ap-
proach, he said, is to rely on pollution control equipment, which is EPAs goal through its combustion strategy. Commoner said, however, "The moment you have dioxin, you've got to do something with it. When you incinerate, you increase the world's supply of dioxin, and knowing what we do about dioxin, it makes no sense to create more of it." James Kilgroe, an EPA project officer and expert on the dynamics of incineration who reviewed the ASME study, agrees with Rigo. He noted that EPA's control strategy for municipal waste incinerators relies on good combustion practices coupled with a combination of spray dryers, fabric filters or electrostatic precipitators, and carbon injection to cut dioxin in stack gas. Kilgroe is also conducting incinerator research at EPA's laboratories in Research Triangle Park, N.C., using a bench-scale combustor. EPA is not looking into the chlorine question, he said, but is in the early phase of several related studies, among them one to determine if burning coal along with refuse-derived fuel (nuggets of shredded municipal waste) will suppress dioxin formation because of coal's sulfur content. An ASME official said that a follow-up study looking at inexpensive ways to control incinerator emissions will include data on the dioxin content of ash captured by pollution control equipment. The official noted that most incinerator operators are reluctant to submit their ash for examination. —JEFF JOHNSON
EPA, DOE move to pilot-scale tests of contaminated N.Y./N.J. sediments This month, the Department of Energy, EPA, and a consortium of universities will move a step closer to a technology capable of cleaning up some of the world's most contaminated dredged sediments. In March, finalists from among seven technology developers that have completed benchscale tests will be selected to progress to the pilot-scale level in the federally funded technology assessment program.
Along with showing that pollutants can be cleaned from the sediments, the technology vendors must demonstrate that the work can be done for less than $100 per ton, a cutoff level selected by EPA and DOE. The program's goal is by year's end to find technologies that can decontaminate millions of tons of sediments that must be dredged to keep New York/New Jersey Harbor open. The contamination
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