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American Journal of Industrial Medicine 15:487 (1989) LETTER TO THE EDITOR Mesothelioma in Railroad Workers Key words: mesothelioma, amphiboles, railroad workers The paper by Mancuso [1988] on 14 mesothelioma deaths in a cohort of 181 railroad machinists first employed 1920-1929 includes several statements one might wish to challenge. We will confine our comments to two points that appear important. 1. The interval between year of hire and year of death in the 14 cases ranged from 33 to 64 years (median 45 years). This is unusually long for mesothelioma and suggests that the relevant exposure began at a later date. Even from 1940, when amphiboles were widely used in the USA. the intervals would have ranged from 17 to 45 years (median 31 years), which is typical for this disease. 2. We have seen documentary evidence that both crocidolitc and amosite were being imported to the USA for manufacture of thermal insulation products from 1924 or earlier. In the decade 1930-1940, the United States was in fact importing annually about the same amount of crocidolite as the U.K. Amphiboles were particularly needed for thermal insulation in locomotives, turbines, chemical factories, and paper mills because of their acid resistance. On both these counts, we believe that Mancuso was not justified in attributing ` ^ mesothelioma in his cohort to chrysotile rather than to amphiboles, whenjllniasLa fother evidence to date would suggest the contrary* McDonald and McDonald, 1987. Because most of the deaths occurred since 1970, if doubt remains, it should be possible to obtain at least some lung tissue samples for clcctron-microscopic analysis. Corbett McDonald, MD, frcp Alison McDonald, MD, ffcm Department of Clinical Epidemiology, The Cardiothoracic Institute London, SW3 6HP, UK REFERENCES Mancuso TF (1988): Relative risk of mesothelioma among railroad machinists exposed to chrysotile. Am J tnd Med 13:636-657. McDonald AD, McDonald, JC (1987): Epidemiology of malignant mesothelioma. In Antman K, Aisner J (eds): "Asbestos-Related Malignancy." London: Grune and Stratton Inc., pp 31-55. Address reprint requests to Dr. J.C. McDonald, The Cardiothoracic Institute, Dept, of Clinical Epide miology, Eulham Road. London SW3 6HP, UK. Accepted for publication August 20, 1988. 1989 Alan R. IJss, Inc. 490 Mancuso the pleura because chrysotile has demonstrated a marked preference for the pleura and very little in the lung tissue even though high chrysotile exposure had occurred. Basically, there was chrysotile in the pleura and amphibole in the lung. Similarly, any analysis of mesothelial tumor tissue itself would be misleading, because the tumor by its growth would physically markedly reduce any amount of the chrysotile for identification analysis if it had been present previously. Dr. Thomas Mancuso Graduate School of Public Health, University of Pittsburgh, Pittsburgh PA 15232 REFERENCES LeBouffant L (1980): Physics and chemistry of asbestos dust. Wagner JC (ed): Biological Effects of Mineral Fibres." IARC Sci Pub., Lyon, 30:15-33. Mancuso TF (1988): Relative risk of mesothelioma among railroad machinists exposed to chrysotile. Am J Ind Med 13:639-657. Mancuso TF (1989): Response to Ohlson. Am J Ind Med 15:353-356. Sebastien P, Janson X, Bonnaud G (1979): Translocation of asbestos fibers through respiratory tract and gastrointestinal tract according to fiber type and size. Dust and Disease Pathotox. Publ. Park Forest South, IL pp 65-77. Sebastien P, Janson X, Gaudichet A, Hirsch A, Bignon J (1980): Asbestos retention in human respiratory tissues: Comparative measurements in lung parenchyma and in the parietal pleura. In Wagner JC (ed): "Biological Effects of Mineral Fibres." IARC Sci Pub, Lyon, 30:237-246.