CORRESPONDENCE Visualizing Chemistry Chlorine incineration
101
investigations to fascinate and educate your students
Visualizing Chemistry: Investigations for Teachers Focusing on a variety of topics and concepts — including energy changes, solubility, kinetics, acids and bases, electrochemistry, and oxidation-reduction — these investigations enable the teacher to illustrate the chemical principles being taught in the classroom. Presented in an easy-to-read format, the investigations can be skimmed for lists of materials and safety information. Historical information about the investigations is provided where relevant. Also includes references, structure drawings, and equations where appropriate. A great starting point for science projects! Julie B. Ealy and James L. Ealy, Jr. 448 pages (1995) Paperbound ISBN 0-8412-2919-8 $29.95 ORDER FROM American Chemical Society 1 155 Sixteenth Street, NW Washington, DC 20036 Or CALL TOLL FREE
1-800-227-5558 (in Washington, DC 872-4363) and use your credit card! FAX: 2 0 2 - 8 7 2 - 6 0 6 7 . ACS Publications Catalog now available on internet: gopher acsinfo.acs.org or URL http://pubs.acs.org
Dear Editor: I was most disappointed by the depth and tone of your news story on the American Society of Mechanical Engineers' study on the relationship between chlorine and dioxin formation in waste combuster stacks (March 199,, p. 112A), for which I was the principal investigator. The study was directed by a respected, professional society that incorporated extensive peer review comments frorn more than 20 independent North American and European experts before being reviewed a second time by the steering prior to publication. Remarks by critic Barry Commoner that the report was "a joke" and "they designed the study to prove exactly what they intended" are unconscionable as well as a libelous ascription of motives and an assertion of scientific misconduct The story quotes Commoner as saying that none of the masking factors from the report, which were reiterated in the story, were considered in the analysis. This assertion is not correct. While no new experiments were done, these critical variables were incorporated into the statistical and engineering methods employed. Data taken along the flue gas path— exiting the furnace and boiler, at points within the air pollution control system and in the stack—were used whenever available. When data from single units taken under f*OTTlparable operating conditions are studied the effect of changes in a single variable can be observed Also facility design and operating characteristics and site differences were specifically considered in the aggregated multiple plant data meta analyses Commoner's statement that without chlorine there can be no dioxin is a truism since dioxin is a chlorinated organic chemical. The relevant question, however, is whether there is already so much chlorine in incinerator feed stocks that even Herculean efforts are unlikely to produce appreciable change.
2 3 2 A • VOL. 30, NO. 6, 1996 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
Stoichiometrically, nanograms of chlorine are needed to make nanograms of dioxin. Theoretical chemistry makes it clear that going from a ten-million-fold to a million-fold chlorine excess does not materially alter the kinetics or end point of the catalytic, solid-phase reactions thought to produce dioxins in incinerators. Our evaluation of all the available data supports this explanation. Commoner states that the report does not consider the relationship between chlorine and dioxin in the ash. He is correct. As stated in the report, data availability focused the ASME study on dioxins entrained in the flue gases. Given the apparent validity of the theoretical construct just described, I expect that solid residue dioxin concentrations are also independent of chlorine concentration. However, this conclusion cannot be tested with the available data. The article also quotes Valerie Thomas who says our conclusions are at variance with hers. However, a bibliographic comparison reveals that Thomas and Shapiro {Toxicoll Environ. Chem. 1995, 50, 1-37) used a small subset of the 1900 data points analyzed in the ASME report. The problem may be as simple as an unfortunate data bias. I stand firmly behind our conclusions. Once again, I encourage others to use the database published in the report to check our work and to reach new insights. H. GREGOR RIGO Rigo & Rigo Associates, Inc. Berea, Ohio 44017-2534
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