Document dYpzR4ZV7YmqmBoEKj62bZZqB

WRG 001910 6. D. CAMUYLC THOMPSON, M.O, EXECUTIVE OFFICER ANO SECRETARY Helena, Montana July 71 191 K. E. Dykoski City of Minneapolis Division of Public Health Public Health Center 250 South Fourth Street Minneapolis, Minnesota Dear Kenneth: Thank you for your letter of June 28, 1961 concerning the "effect" business. Perhaps this vill help me to remember which one to use correctly. Relative to the veimiculite question, several samples collected at the source of all veimiculite mined in the Western United States indicate a free-sillca content of less than two percent. Although the dust concentrations might be extremely high, the frep-fill-irR content, as noted, is quite low. In a letter received from Mr. Paul F. Woolrlch of the U.S. Public Health Service a few years back, he described veimiculite asy | an essentially hydrous magnesium mica which was usually an alteration I * product of local phlogopite or biotite micas. Attempts to assign a definite minerological formula for veimiculite has been unsuccessful because of its highly variable composition. However, analysis of typical veimiculite from Libby, Montana is as follows: "SiQ2 4l# caO 1* Phlogopite mica is: H2KMg3Al (SiO^)^ Biotite mica is: (H, K)2 (Ml, Fe)2 Al^ (SiOlj.)^ A -type of pneumoconiosis has been found to occur among workers whose only exposure was to mica dust. Dressen, et al, in an examination of 57 men exposed to dust generated by grinding hand-sorted mica (which X-ray examination of 456 men, with more than half their industrial ex posure in the mica field, and an additional, group of 79 workers so employed. wtr K. E. Dykoski 250 Sooth Fourth Street Minneapolis July 7, 1961 Page 2 revealed dust pathology of 9.4 percent and 11.4 percent, respectively-- double that in a comparable group with no mica exposure." As we discussed, it might be productive to look into the asbestosis angle, since a portion of the mined ore contains from five to twenty percent short fibre asbestos. There is an attempt made in the milling process to remove the asbestos which I believe is essentially successful; however, there is no doubt that some of the material is not excluded and would show up in the final product. At an expanding plant where the vermiculite is heat treated to produce the product zonolite, a maximum free-silica content of four percent was noted in the rafter dust. A few years back, we sent in some sputum samples to the U.8. Public Health Service for examination for asbestoais bodies which are typical in workers having asbestosis and all were negative; however, the samples may not have been satisfactorily collected and no further work was done in this area. Only three men submitted samples and it would be unlikely that three out of ninety or so ip. the plant might have been afflicted with this disease. I tope this information will be of some value to you. I would be interested in 1 pnm-tng the results of your study in this field. Sincerely yours. BFW/dl Benjamin F. Wake Industrial Hygiene Engineer Division of Disease Control