Meetings Ceramics symposium The Division of Industrial & Engineering Chemistry's 12th State-of-the-Art Symposium, entitled "Ceramics in the Service of Man," will he presented June 7-9, at Carnegie Institution, Washington, D.C. Fifteen technical societies are cosponsoring the event. Featured speakers on the program are Dr. W. D. Kingery, Massachusetts Institute of Technology; Dr. Rustum R. Roy, Pennsylvania State University; Dr. Andrew Breidenbach, assistant administrator for water and hazardous materials, EPA; Richard J. Anderson, associate director of the energy program, Battelle Memorial Institute; Dr. Chalmer G. Kirkbride, science adviser, ERDA; and Dr. A. E. Paladino, Office of Technology Assessment. General chairman of the symposium is Dr. Robert S. Shane, a consultant to the National Materials Advisory Board, NAS, and president, Shane Associates. Concentrating on the innovative use of modern ceramic materials in solving present societal problems, the symposium will explore applications in such fields as bioceramics, construction, pollution and emission control, and nuclear waste management. Structural application problems and reliability will be examined. A second major emphasis will be on innovative uses of ceramics in energy production: fossil energy, electric generation and storage, and advanced systems. Reports of developments in nuclear converter reactors, high-performance batteries, coal utilization systems, flywheel energy storage, controlled thermonuclear devices, laser fusion, turbines, and solar materials will be presented. On-site registration will begin at 8:30 AM, Monday, June 7. Fees are $50 for members of cosponsoring organizations, $60 for nonmembers, $15 for one day only. Copies of the proceedings will be provided to all full registrants. For further information, contact Barbara R. Hodsdon, Meetings & Expositions Department, ACS, 1155—16th St., N.W., Washington, D.C. 20036, phone (202) 872-4399.
Letters Continued from page 3 Even assuming the Harkin study to be valid and the concentration of airborne selenium in a xerography room to be 6 X 10~ 8 grams/cu m, what is the significance of these numbers? The current OSHA limit for airborne selenium is 2 X 10~ 4 grams/cu m based on a 40-hour week [Fed. Reg., 39 (125), 23542, June 27, 1974, Washington, D.C] and this is 3333 times greater than the highest selenium concentration reported by Harkin. Since it is now well documented [Frost, D. V., Lish, P. M., Ann. Rev. Pharmacol., 15, 259 (1975)] that selenium is a nutritionally essential
trace element and is readily absorbed through the respiratory tract [Dutkiewicz, T., Balcerska, J., Dutkiewicz, B., Bromatol. Chem. Toksykol., 4 (2), 185 (1971); CA, 76, 10843k (1972)] it may be worthwhile to relate Harkin's highest reported level to nutritional intake. If we assume a human minute volume of 8.2 liters (volume of air breathed by an average person during one minute) [Hartado, A., in "Handbook of Physiology," Ed., Dill, D. B., Waverly Press, Sect. IV, 1964, page 8 5 5 ] , Harkin's highest reported airborne selenium concentration (6 X 1 0 - 8 grams/cu m) and total respiratory deposition (highly unlikely), we can calculate ingestion of 2.4 X 1 0 - 7 grams of selenium during an eighthour work day. This value is 27 times less than the amount of selenium (6.4 X 1 0 - 6 grams) in a single 23-gram slice of white bread and 64 times less than the amount of selenium (1.5 X 10~ 5 grams) from the same size slice of whole wheat bread [calculations based on data from Scott, M. L , in "Organic selenium compounds; their chemistry and biology," Eds., Klayman, D. L , Gunther, W. H. H., Wiley-lnterscience, New York, 1973, page 6 5 2 ] . In the past, we have measured selenium emissions from Xerox machines and have found them to be several orders of magnitude below the OSHA limit and below the usable limit of our analytical methodology. However, since the question has been raised, we have initiated a renewed effort externally in order to assure that we have the most accurate data possible. R. A. Parent, Ph.D. Staff Specialist in Biochemistry, Product Safety, Xerox Corp.
Mitochondrial membrane SIR: Blondin and Green's article (C&EN, Nov. 10, 1975, page 26) and the letters which followed (E. Racker, Letters, March 22, page 5, and the reply of G. A. Blondin and D. E. Green, on the same page) are incisive presentations of two entirely different points of view. Since the mitochondrial membrane potential plays an important role in their considerations [Racker refers to Skulachev's review, Curr. Top. Bioenerg., 4, 127 (1971) and Blondin and Green to our experiments: Tupper, J. T., Tedeschi, H., Proc. Nat. Acad. Sci., 63, 370, 713; Science, 166, 1539 (1969); and Maloff, B. L , Scordilis, S. P., Tedeschi, K, Biophys. J., 16, 18a (1976)], we feel the need for further discussion. Our comments will be restricted to the membrane potential of mitochondria. However, the presumed presence of a metabolically induced membrane potential is central to the Mitchell hypothesis as now formulated, since at low ionic strength the electrochemical gradient (i.e., the so-called protonmotive force) is presumably expressed almost entirely by the electrical potential across the mitochondrial membrane [Mitchell, P., Moyle, J., Eur. J. Biochem., 7, 471 (1969)]. At present, there is no evidence for a metabolically induced electric potential across the mitochondrial membrane. Generally, the estimate of membrane potential from the distribution of ions is not based on sound theoretical principles. Some data actually contradict the postulate of an electrogenic process directly dependent on metabolism. Other data are at best inconclusive. The absence of a membrane potential directly dependent on metabolism is shown by a variety of experiments. For example, in the experiments of Mitchell and Moyle (1969) the proton efflux
corresponds quantitatively to the K + influx in the presence of valinomycin and after introducing an O2 pulse to activate metabolism in an anaerobic suspension of mitochondria. It follows that the anionic charges (X~) inside the mitochondria previously neutralized by H + will now be neutralized by (K + ). At steady state inside the mitochondria, {)C) ^ (K + ). Hence, if the mitochondrial permeability to K + is high (because of the presence of valinomycin) as postulated by Mitchell, the distribution of ions in the absence of an electrogenic pump should be governed by the classical Gibbs-Donnan distribution. Therefore ()C) + (A~)i = (K+)/ and (K+ ),/(/
