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FILE NAME: Talc (TALC) DATE: 1973 May 8 DOC#: TALC103 DOCUMENT DESCRIPTION: Proceedings of the Symposium on Talc - US Dept of the Interior 8639 Bureau of Mines Information Circular/1974 Proceedings of the Symposium on Talc, Washington, D.C., May 8,1973 UNITED STATES DEPARTMENT OF THE INTERIOR Information Circular 8639 Proceedings of the Symposium on Talc, Washington, D.C., May 8,1973 Compiled by Aurel Goodwin Metal and Nonmetal Mine Health and Safety, Washington, D.C. UNITED STATES DEPARTMENT OF THE INTERIOR Rogers C. B. Morton, Secretary BUREAU OF MINES Thomas V. Falkie, Director This publication has been cataloged as follows: GoodwPirno,ceAeudrinegl,s coofmtph-e Symposium on Talc, Washington, D.C., May 8, 1973. [Washington] U.S. Bureau of Mines [1974] 102 p. illus., tables. (U.S. Bureau of Mines. Information circular 86I3n9c)ludes bibliography. 1. Talc--Cong. I. Symposium on Talc, Washington, D.C., 1973. II. U.S. Bureau of Mines. III. Title. (Series) TN23.U71 no. 8639 622.06173 U.S. Dept, of the Int. Library CONTENTS Page Abstract................................................................ 1 Introduction............................................................ 1 Opening Statement, by Donald P. Schlick................................. 2 Opening Remarks, by Arthur P. Nelson.................................... 3 Mortality Experience of New York Talc Miners and Millers, by Morris Kleinfeld................................................... 4 Characterization of Talc Dusts, by R. S. Lamar.......................... 12 Characterization and Occurrence of Talc, by H. T. Mulryan............... 16 Discussion of the Mineralogy of Industrial Talcs, by C. S. Thompson..... 22 Experimental Studies on Biological Effects of Tremolite Talc on Hamsters, by William E. Smith...................................... 43 The Biological Action of Talc and Other Silicate Minerals, by Gerrit W. H. Schepers.............................................. 49 Applicability of Asbestos Standard to Fibrous Talc, by William J. Nicholson.......... 77 Aspects of Mineralogy of Talc, by Arthur M. Langer...................... 82 Mineralogy, Identification, and Quantification of Airborne Talc Dust, by T. D. Oulton....................................................... 89 Medical Aspects of Talc, by Richard M. Spiegel.......................... 97 PROCEEDINGS OF T H E SYMPOSIUM ON T A L C , WASHINGTON, D .C., MAY 8, 1973 . compiled by Aurel Goodwin1 ABSTRACT A symposium on the health hazards of respirable dust in the mining and milling of talc was held on May 8, 1973, in Washington, D.C. The results of medical effects on both human and animal subjects were presented. Methods for identification and classification of talc minerals were also presented. Ana lytical techniques discussed included X-ray diffraction, scanning electron microscope observation, electron probe, and optical microscopy. INTRODUCTION The Secretary of the Interior has the responsibility under the Metal and Nonmetallic Mine Safety Act to develop standards for the purpose of the pro tection of life and the promotion of health and safety in metal and nonmetal mines. There are approximately 66 different mineral commodities produced by these mines. The multitude of minerals in the ore and host rock present a varied hazard to the health of employees of the mineral industries. It therefore becomes necessary to attempt to evaluate the unique health effects and levels of exposure which can be tolerated for the working lifetime of individuals exposed to these minerals without adverse effect on their health. It also becomes necessary to be able to identify and quantitatively measure the concentration of these minerals in respirable dusts. This symposium was held to receive data relevant to both the health effects and mineral identification of talc.- Talc is a term used for a product having certain physical properties. The mineral composition of talc varies depending on its source and on the uses for which it is intended. Presentations were given relating to the characterization of airborne dust from mining and milling of talc minerals and medical data from studies of talc workers, asbestos workers, and animal studies. 1 Chief, Division of Health, Metal and Nonmetal Mine Health and Safety (now Chief, Health Division, Mining Enforcement and Safety Administration (MESA), Washington, D.C.) 2 OPENING STATEMENT by Donald P. Schlick1 Ladies and gentlemen, I should like to welcome you to this symposium. My name is Donald P. Schlick and I am Deputy Director--Health and Safety. Until about 30 years ago, occupational chest disease meant primarily diseases related to breathing dust containing free silica. Now, however, we recognize that a number of other dusts also are involved in contributing to occupational diseases such as coal dust and the silicates--asbestos and talc. This symposium was called to obtain data relating to the characterization of "talc" dust and the adverse affects on persons occupationally exposed to talc dust during their working life. This data is intended to provide at least a partial basis for developing a standard adequate to protect those per sons employed in the mining and milling of talc minerals. As used commercially, the term "talc" refers primarily to physical prop erties rather than to a specific mineral. Thus, the American Conference of Governmental Industrial Hygienists in their Threshold Limit Values (TLV) refers to "talc" and to "talc (fibrous)." In the documentation of the TLV s they refer to talc (nonasbestiform) and talc (fibrous)--tremolite. Thus, fibrous talc is the talc with the associated amphibole-tremolite. The only reference in the documentation for nonasbestiform talc is dated 1935 and the most recent reference to fibrous talc is dated 1963. Current standards for exposure in mining and milling of talc are the Threshold Limit Values. Because of the difficulties in distinguishing fibrous and nonfibrous talc and because of much recent work on asbestos, particularly on the toxic effects of the different types of "asbestos," we have called this meeting. This meeting is called, however, to consider asbestos only as it relates to so-called fibrous talc. Our goal is to establish a standard which will assure that persons work ing in the mining and milling of "talc" will not suffer impaired health due to their employment. We hope that this symposium will result in providing up-todate information on which to base a standard. As stated in the announcement of the meeting, we shall, however, include written communications received before June 1, 1973, as part of this symposium. I should like to request that all speakers who do not have written statements provide a written copy of their presentation by that time. I thank you all for coming, and I will now turn the meeting over to Arthur P. Nelson, Acting Assistant Director, Metal and Nonmetal Mine Health and Safety. _______ ____ ______________ _______ __________________ _ 1Acting Deputy Administrator, Mining Enforcement and Safety Administration, Washington, D.C.; formerly Deputy Director, Health and Safety, Bureau of Mines. 3 OPENING REMARKS by Arthur P. Nelson1 This the first meeting we have had of this type for Metal and Nonmetal Mines. We are gathering data prior to developing new standards and presenting them to our Advisory Committee. As you know, our standards for air quality presently are the American Conference of Governmental Industrial Hygienists Threshold Limit Values. We have found inadequacies in these standards and will probably deviate from them more in the future as better data become available. The talc industry is composed of approximately 65 operations, employing about 1,200 workers. These operations are distributed throughout the United States; U.S. production in 1972 was about 1.1 million tons with 86 percent produced in five States: California, Montana, New York, Texas, and Vermont. A small amount of talc, about 30,000 tons, is imported annually, mainly from Canada, Italy, and France. The proceedings of this meeting will be used in part to arrive at stan dards for exposure of persons working in mining and milling of talc minerals. The Bureau of Mines and the U.S. Department of Health, Education, and Welfare are planning a joint survey of environmental conditions and health status of employees in the talc mining and milling industry. Data that will be presented here today should be of immense value and will contribute much that in the past has not been available to support the development of improved standards. I welcome you here today and I hope that you have a good and productive meeting. Thank you. 'Acting Assistant Administrator, Metal and Nonmetal Mine Health and Safety, Mining Enforcement and Safety Administration, Washington, D.C.; formerly Acting Assistant Director, Metal and Nonmetal Mine Health and Safety, Bureau of Mines. 4 MORTALITY EXPERIENCE OF NEW YORK TALC MINERS AND MILLERS by Morris Kleinfeld, M.D.1 My former colleagues in the Division of Industrial Hygiene of New York State and I have had the opportunity to conduct numerous studies of talc workers in New York State, including clinical, physiological, radiological, and environmental observations (5_).12 In addition, we have also studied the mortality experiences among workers in talc mining and milling. In most instances, we have had the invaluable opportunity to correlate the clinical with the environmental data. In general, we have found that sustained inhala tion of significant amounts of commercial talc dust over an extended period of time, or where there was a significant elapsed time from initial exposure, can produce a symptomatic form of pneumoconiosis. The commercial talc to which the talc workers were exposed contained not only the mineral talc, but also other silicates such as serpentine, tremolite, anthophyllite, and other ingredients, predominantly carbonates. Moreover, free silica was often pres ent in the dust in variable amounts, usually not averaging more than 3 percent. Specifically with regard to our mortality experiences among talc workers, we found in an earlier study of talc workers (miners and millers) who had 15 or more years of exposure to talc dust that the proportional mortality from carcinoma of the lung and pleura among these workers was four times that of the general population. However, the significant increase in incidence of malignancy appears in the older talc workers, namely, those in the 60- to 79-year age group, rather than in the 40- to 59-year age group (3). This observation in the talc workers was at variance with those found in a group of asbestos insulators who had the same duration of exposure covering a similar time period (2). The asbestos insulators showed an increased incidence of mortality from lung cancer in both age categories. The incidence of carcinoma of the gastrointestinal tract and peritoneum among talc workers was not sig nificantly different from that of the general population, whereas among the asbestos insulators the incidence of gastrointestinal malignancy was signifi cantly higher than that of the general population. We postulated that the earlier occurrence of malignancies among the asbestos insulators was due to two factors: The first was the relatively greater carcinogenicity of the chrysotile asbestos as compared to commercial talc; the second was the exposure o the insulators to greater quantities of chrysotile asbestos as compared to the talc workers who were exposed to lesser quantities of commercial talc dust which was admixed with appreciable amounts of tremolite and anthophyllite asbestos. Our observations favored the first factor. The earlier study C_) also showed an increased incidence of deaths due to talc pneumoconiosis and/or its complications. 1Formerly Director, Division of Industrial Hygiene, New York State. 2Underlined numbers in parentheses refer to items in the list of references at the end of each chapter. 5 A followup study was made to bring our mortality data among the talc workers up to date and to provide additional information not reported in the earlier study. The pertinent data is presented in the material that follows. All the talc workers employed in 1940 who had accumulated 15 or more years of exposure to commercial talc dust as well as those who achieved a min imum of 15 years of such exposure between 1940 and 1969 were included in the followup study. The group totaled 260 workers and it is believed that the overall number constituted the total work force in the worker population under study. The data were obtained from a number of sources. Plant records were examined and the work history of each individual was detailed to include job changes and specific years of employment. Death certificates were studied in all instances where they were available. The records of the physicians who had attended the workers privately were reviewed. Substantial medical infor mation on the majority of the workers was available in the files of the Divi sion of Industrial Hygiene and was used as an additional source of data. Hospital records, including autopsy reports and histological specimens, were examined wherever available. Autopsy or biopsy records were obtained in 38 of the 108 deaths. A comparison was made of the observed proportional mortality rates from the specific causes with the expected rates among similar population groups and was found satisfactory for a descriptive study of this nature. The pro portions of observed mortality attributed to cancer of the lung and pleura and of the gastrointestinal tract and peritoneum and cardiac diseases were com pared to the expected mortalities due to the above causes in the various age groups. The expected mortality for the total group represents the proportion of deaths among white men in the United States due to the specific causes in the year 1955. This particular year was chosen as standard because it was the median year of death among the 108 deaths. For each of the 5 -year periods, the median years, namely, 1942, 1947, 1952, 1957, and 1962 were selected. In the group of 260 talc workers studied, there were 108 deaths. There were a total of 25 deaths from malignancies. Of these 25 deaths, 13 were due to lung and pleural malignancies; 9 were due to gastrointestinal and perito neal malignancies and 3 were due to other malignancies. Thirty deaths resulted from cardiac disease, other than cor pulmonale, and 29 deaths were attributable to pneumoconiosis and its complications. Accidents and suicides accounted for 8 deaths and there were 16 deaths due to other causes (table 1). The average age at death of the 108 talc workers was 60.3 years, with a range of from 38 to 84 years. Environmental exposure data was available in 97 of the 108 death cases. The mean duration of exposure for this group was 24.1 years, with a range of 15 to 47 years. The dust exposure was predominantly to talc, tremolite, anthophyllite, carbonate dusts, and a small amount of free silica. Comparative dust counts at the talc mines and mills prior to 1945 and between 1946 and 1969 were obtained (table 2). 6 TABLE 1. - Causes of death in 108 talc workers from 1940 to 1969 Cause of death Malignancies........................... Lung and pleura........................... Gastrointestinal and peritoneal................ All other malignancies............................. Cardiac deaths (other than enr pulmonale)........... Pneumoconiosis and complications..................... Accidents or suicides......................... All other causes................................ Total...................................... No9.5 Percent 9** 1 <J J. 1J^ 19 n 9 8.3 3 2.8 30 27.8 29 26.9 8 7.4 16 14.8 108 100.0 TABLE 2. - Comparative dust and fiber counts at the various talc mining and milling operations Dust count1 Drilling... Mucking.... Crushing... Screening.. Milling.... Garnering Average 1Median Pre-1945 818 413 120 30 Pre-1948 180 69 69 61 92 75 Average Median 1946- 65 5 3 . 5 5 1948- 65 42 13 37 37 25 20 Average Median 1966 -69 19 19 9 9 1966 -69 28 20 - - 40 24 and separating 278 70 27 27 - - Pulverizing - 28 28 - - Bagging--- 151 129 27 23 Railroad 29 25 and truck loading... - - 73 63 Blow room3 . 1,227 1,196 - - 43 20 - - Open chutes3 ... 125 83 - - - - x Dust count in mppcf. 2Fiber counts in No. fibers/ml >5y, in length. 30peration discontinued after 1948. Dust count1 Average 1Median 1972 7 7 3 3 Fiber count8 3 2 35 15 62 - 7 7 25 13 9 27 - - ' 27 27 47 36 28 24 _ - - - - - With regard to the deaths due to malignancies, 12 of the 13 malignancies of the lung and pleura were carcinomas of the lung and 1 was a fibrosarcoma of the pleura. Of the nine malignancies of the gastrointestinal tract and perito neum; three were cancers of the stomach, two were cancers of the liver, one of of which was a primary hepatoma of the liver and the other a metastasis from a gastrointestinal malignancy; one was a cancer of the colon; two were cancers of the pancreas; and one was a pertoneal mesothelioma. The three malignancies involving other sites included one retroperitoneal reticulum cell sarcoma; one chronic lymphatic leukemia, and one Hodgkins' disease (table 3). The overall proportional mortality or carcinoma of the lung and the pleura was four times 7 t expecied. Consistent with our previous observation, a significant increase appeared to occur in the 60- to 79-year age group rather than in the 40- to 59-year ^ l t S 1 wfs S UP ble haVe already mentioned, this finding among talc workers w s at variance with what we had observed among asbestos insulators where the observed values in both the 40- to 59-year and 60- to 79-year age groups were sig- nificantiy different from the expected values. In the absence of Adequate smoking i^thp cannot assess the role played by smoking in accounting for the differences m the occurrence of malignancies. umerences TABLE 3. - Causes of death in 108 talc workers1 from 1940 to 1969 Cause of death Malignancies: Lung and pleura........... Stomach.............. Liver............... 1940-44 1 1945-49 o i 1950-54 1 Colon............... ,. 1 Pancreas.............. Peritoneum.............. Other malignancies........ Cardiac diseases.......... 2 H Pneumoconiosis and complications.............. 0 / Accidents and suicides...... 1 1 1 Others............... 3 1 Total.................. -1 - - .-----:--- . '11*" 7 17 8 Includes workers having had at least 15 or more years 1955-59 1960-64 1965-69 Tota 5 3 2 13 1 1 3 1 " - 2 " - - 1 1 1 2 1 1 - 1 3 6 8 7 30 8 9 4 29 2 2 1 8 1 5 6 16 25 28 23 108 of exposure to talc dust TABLE 4. - Deaths and proportional mortality from carcinomas of the respiratory tract,,, of the gastrointestinal tract, and from cardiac diseases among workers by age group from 1940 to 1969 Age group 40 40-59 60-79 80-84 Total Total deaths 3 47 54 4 108 Dea ths and prtiportional mor tality frorn respira- tory cane:ers No. Observed, Expected, percent percent 0 0 1.6 4 8.5 5.2 9 16.6 3.6 0 0 1.1 13 12.0 3.7 Deaths and proportional mortality from gastro intestinal cancers No. Observed, Expected, percent percent 0 0 2.5 3 6.4 5.7 4 7.4 7.2 1 25.0 5.3 8 7.4 6.5 Deaths and proportional mortality from cardiac diseases No. Observed, Expected, percent 1 33.3 21.1 11 24.4 44.2 17 31.5 1 25.0 30 2.8 47.8 47.1 45.8 When carcinoma of the lung and pleura was related to each of the six 5 -year periods, namely from 1940 to 1969, it is important to note that the observed propor tional mortality from carcinoma of the lung was approximately four times as much as the expected mortality during the period 1945-49 and dropped to approach the expected mortality from 1960 to 1964 and from 1965 to 1969 (table'5). The differ ences between the observed and expected mortality rates were significant in 1950-54 and insignificant in 1960-64 and in 1965-69. The improved mortality experience between 1960 and 1969 and to 1973 for lung and pleural cancers is particularly per tinent since environmental control have resulted in an appreciable reduction in the dust count in the mines and mills, although the fiber count still exceeds the pres ent threshold limit value for asbestos dust by approximately four to five times (table 2). This finding indicates that the present threshold limit value of 8 5 fibers/ml with a fiber length greater than 5 microns for fibrous talc including tremolite and anthophyllite, is basically adequate. TABLE 5. - Deaths and expected mortality from cancer of the lung. and pleura and of the gastrointestinal tract and peritoneum among talc workers from 1940 to 1969 Lung and pleura Gastrointestinal tract and peritoneum Proportional mortality, Proportional mortality, oercent P Deaths Dercent p 1940-44 1945-49 02 1950-54 1 1955-59 5 1960-64 3 1965-69 2 Total 13 Observed 0 11.7 12.5 20.0 10.7 8.7 Exoected 2.0 3.1 4.3 5.7 6.7 7.7 -1 S1 Ss 1 3 NS 1 NS 2 -9 Observed Expected 14.3 7.8 NS 5.8 12.5 12.0 17i .*8 NS NS 6.7 NS 3.6 6.3 NS 9.5 6,1 NS - - P = Probability. S = Significant. NS = Not significant. With regard to cancer of the gastrointestinal tract and peritoneum among the talc workers, we did not find any significant difference between the observed and expected values in the overall and specific age groups studied (table 4) and these findings are consistent with those reported by Kiviluoto and Meurman (1) among anthophyllite workers. These findings differ from those observed in asbestos insulators where a significant increase in the observed incidence of gastrointestinal malignancy was found in the overall and specific age groups studied (3). Our findings among asbestos insulators were similar to those reported by Selikoff, Hammond, and Churg (7,)* Of the 29 deaths due to pneumoconiosis and its complications, 20 were due to cor pulmonale, 5 to advanced tuberculosis, and 4 to bronchopneumonia. The lapsed time from the first commercial talc dust exposure to death in this group averaged 30.9 years with a range of 15 to 46 years. All 29 had their initial exposures prior to 1945 at which time more effective engineering con trols, including wet drilling in the talc mines, were introduced. The percent age of deaths due to pneumoconiosis and its complications has decreased by more than 50 percent in the last 5 -year period studied, namely, 1965-69, as compared to the preceding 5-year period, 1960-64 (table 3). The number o deaths probably reflects the greater exposures which occurred in the earlier years of employment. A longer interval must elapse, however, before the effect of controls on the incidence of pneumoconiosis can be appraised more definitively in the plant studied. It is noteworthy, however, that in another study of a different plant processing a similar mixture of talc, tremolite and anthophyllite, but wherein controls were installed at the inception of opera tions in 1948, only 1 out of 39 workers had a chest roentgenogram consistent with pneumoconiosis. The mean exposure of the 39 workers was 16.2 years with a range of from 11 to 22 years. The worker whose chest roentgenogram was 9 oonhStr i w Jth Pneumoconiosis was a 75-year old man who had a nonproductive cough, a Grade 1 dyspnea and who worked as a janitor for 11 years. The w incidence of pneumoconiosis was found despite the presence of relatively hieh ereater T t V ^ 13 Plant count eKc" S ybyl S ,, f 6 .preSent f M h old limit value of 5 fibers/ml with a length rf-Jlw 5 " lcrons- In terms of time-weighted averages, Murphy and^sso- tiSes per cubif fo * * ) * * * % * workers exposed lesf than 6? million par^ cubic foot (mppcf) years to chrysotile and amosite in ship con-P 1 ations (41 S ! ! ! J the plant havinS controls since the star? of oper- T f * 1 v fUnd hat an aPPrecl-able number of workers exceed the P 60 mppcf-years but did not show any evidence of pneumoconiosis as determined ^pian"tehavingrsco^ntrole^SsSrffriobmra0tgheenaisCtar*t"aofcSo^petraitSio-nsa^sTugKgesitttfhSatectormempoalriatbele3^^d fcq \ 3S ? &rdi&c deaths> excluding cor pulmonale, 22 had coronary artery disease, 5 had hypertensive heart disease, and 3 had rheumatic heart disease 7 Rather surprising was the observation that the observed proportional mortality from cardiac disease was lower than the expected mortality in all 5-year 7 periods except the first, namely, 1940-1944 (table 6). i? s L m s r L ^ b i e to ?innain remaininS data that the overall observed propor tional mortality from cardiac disease among talc workers was lower than the c a n l t v expected mortality. The decreased mortality from cardiac diseale workers cannot be attributed to a predisposition to lung a^on? Sic a ly results m the death of these workers at earlier ages before theySmight be expected to succumb to cardiac disease. As demonstrated, the decreased proportional mortality from cardiac disease was present in both the 4 0 ! ?o 59-year as well as the 60- to 79-year age groups (table 4). If malignancy of the iung was a factor, one would have expected a difference in incidence c a T d t Z di??LeWL age ST PS- Th8 trUe eXplanation or the W r incidence of cardiac disease is open to conjecture. The rural environment in which the lc workers lived, as well as the possibility that they smoked less may " t ^ i :r a t i ^ mrtality due to cardiac disease as compared to the TABLE 6. - Deaths and expected mortality from cardiac disease among talc workers from 1940 to 1969 1940-44 1945-49 1950-54 1955-59 1960-64 1965-69 Total Deaths 3 6 0 6 8 7 30 Proportional mortality, percent Observed Expected 42.8 37.4 35.3 41.0 0 46.0 24.0 46.5 28.6 46.6 30.4 45.5 - 10 I trust that the information I have submitted this morning will P ^ i d e the Bureau of Mines with essential data relating to the occupational hazards of exposure to talc, fibrous talc, and tremolite dust in order to evaluate the adequacy of the existing threshold limit value for pure talc and talc mixed with tremolite and anthophyllite. 11 References K" ; R -' " ? L ; Meurman' Results of Asbestos Exposure in Finland. ^ umoco^ osls ed- by H. A. Shapiro. Proc. of the Internet. ; : i " r?97o?uth Arlca> 1969' pp- 18(M86: ^ K1rin,mld^ a `k MeTSTSi.te> and * Kooyraan. Mortality Experience in a W 6 7 ? w . 177-180. " * * * ArChiVeS f Enviroranental Health, v. 15, 3. Kieinfeid, "S " M., J. Messite, 0. Kooyman, and in?" " ' ^*"""1 M. Zaki. Mortality Amone Talc Archl',as o Km 4. J M^eSSiie ' and M> Laner * A Study of Workers Exposed to Asbestiform Minerals in Commercial Talc Manufacture. Environmental Res., v. 6, No. 2, June 1973, p. 132. 5. K1^in5e!d/ Messite' J - Shapiro, and R. Swencicki. Effect of Talc Dust mhalation on Lung Function. AMA Archives of Environmental Health, v. 10, 1965, pp. 431-437. 6. Murphy, R. L. M . , Jr., B. G. Ferris, W. A Burgess, and others. Effects of Low Concentrations of Asbestos. New England J. of Medicine, v. 285, 1971, pp. 1271-1278. 7. Selikoff, I. J., E. C. Hammond, and J. Churg. , : .. , ' -- - -- `6 ' Mortality Experiences of Asbestos Insulation Workers, 1943-1968. Ch. in Pneumoconiosis, ed by H. A. Shapiro. Proc. of the Internat. Conf., Johannesburg, South fnca, 1969, pp. 180-186; Oxford University Press, Cape Town, 1970. 12 CHARACTERISTICS OF TALC DUSTS1 by R. S. Lamar*123 The Nature of Commercial Talcs It is important to make a clear distinction between commercial talc and talc mineral. Pure talc mineral is a hydrous magnesium silicate having the composition Mg6 (Si802o)(0H)4 .3 Limited isomorphous substitutions can occur within this structure.4 Crystal form is generally monoclinic. Individu particles of pure, finely milled talc appear platy or micaceous under the microscope. Commercial talcs may or may not be pure talc mineral. These products are commonly mixtures of talc mineral with other related minerals that were involved in the paragenesis of the talc mineral. These associated minerals are in many cases calcite, dolomite, quartz, serpentine, magnetite, magnesite, chlorite, tremolite, anthophyllite, and in some cases chrysotile.56 These may occur in various amounts and proportions in commercial talcs from different sources or mines. Not all of these associated minerals occur in all commercial talcs. Some products are entirely free from asbestiform minerals, and this distinction is also important. The so-called "fibrous talcs" appear fibrous because of the presence of asbestiform minerals. Pure talc mineral rarely appears fibrous in crystal habit and is much more commonly platy, lamillar, or micaceous. Specifically, we disagree with the definition of talc (fibrous)-- tremolite as it appears in "Documentation of the Threshold Limit Values for Substances in Workroom Air, published by the American Conference of Governmental Industrial Hygienists, 3d edition, 1971, p. 243. It is our opinion that this documentation for talc "fibrous" should be rewritten to eliminate any reference to fibrous talc but should refer to the fact that the talc ores can contain fibrous contaminants which are asbestiform minerals. This is important in view of the fact that 1John Wiley & Sons, Inc. Encyclopedia of Chemical Technology. Talc! V. 19, 2d ed., 1969, p. 608. 2Research Manager, Celite Division. Johns-Manville Corporation. 3Deer, W. A., R. A. Howie, and J. Zussman. Rock-Forming Minerals. Sheet Silicates. Longmans, Green and Co., Ltd., London, 1962, V. 3, p. 1/1. 4Page 124 of work cited in footnote 3. 5Pages 126-129 of work cited in footnote 3. , 6Page, Ben M. Talc Deposits of Steatite Grade, Inyo County, California. Div. of'Mines, State of California, Special Rept. 8, August 1951. Wright, Lauren A. Geology of the Silver Lake Talc Deposits, San Bernardino, California. Div. of Mines, State of California, Special Rept. 38, July 1954. 13 .definition of the American Conference of Governmental Industrial stall* HiTM s S e t f a d eH e : u r i c t " dat0ry St<ffldard " 4" 0 ,6 Metal - ^ than 5-micron maximum particle size Tho oa determines the particle lire retired.' c * iner, to less " the pr0<luCt ^ " " all, Characterization of Talc Dusts .al nTalC may be characterized according to mineral composition, chemi- d escr* ed Sse p a te " ShaPe> P a m c U S lze' Eaoh f *U t*> Characterization of Mineral Composition method!^ b6 dne aCCrdinS t0 3 Variefcy of conmnly used and accepted Petrographic Examination A highly skilled petrographer, working with a petrographic microscope can, in many cases, determine various mineral species bySmeasuring such opti- cS. beiow S Mi Tr t " f iefiaCtd0n' f tinCtln ^ birefringence^ aL Particle size of a mineral dust is reduced to much renlhle n^ HeSe m ?aaurements become increasingly difficult and less reliable. Most commercial talcs contain a high proportion of particles smaller than 5 microns and other methods are therefore more reliable1 Electron Probe dor hhvl Ti! w ! ! iC Ln ?rS Ciple underlyin8 the dlffraction is that each identification of materials by X-ray crystalline substance has its own characteristic atomic structure which diffracts X-rays or electrons in a par ticular pattern. The recognition of the pattern establishes uniquely ^ d i f fracting substance. Newly developed electron probes, operating through an electron microscope, make possible the identification of individual particles as small as 1 micron by this method. The equipment is very costly and not readily adopted to routine measurements. 7 8 X-Ray Diffraction OT.a1 i iS P*01^ 1? the most Powerful and useful tool available for the min eral characterization of talc dusts.9 Using equipment and techniques commonly 7Industrial Minerals. Talc: Micronized Grades Lead the Way. January 1971 8 p ` 9* 'Erindiey G. W. Experimental Methods. Ch. 1 in The X-Ray Identification and Crystal Structures of Clay Minerals, ed. by G. Brown. 1961, pp. 35-36. Page 1 of work cited in footnote 8. 14 employed in the talc industry, it is possible to identify as little as 1 per cent of tremolite in otherwise pure talc mineral. There is evidence that dif ferent tremolites respond differently and may show different lower limits of detectability depending on crystal size and perfection. Differential Thermal Analysis (DTA) This procedure is useful but not as definitive as X-ray diffraction. Talc, chlorite, serpentine, and the carbonate minerals show characteristic D.T.A. curves but many of the peaks overlap and are not clearly defined in mineral mixtures. Tremolite shows a relatively weak D.T.A. reaction because of its low content of chemically combined water.101*3 While D.T.A. is a useful tool for qualitative analysis, it is of limited value for quantitative deter minations. Particle size, sample composition, and experimental and instru mental variables are complicating factors. Characterization bv Chemical Composition Complete chemical analyses are useful in identifying talc dusts but are by no means definitive. Quantitative analyses by conventional wet methods or by X-ray fluorescent methods only help but do not yield the type of positive mineral identification obtainable by X-ray diffraction. Particle Shape Partial morphology, shape, and structure are powerful tools for identifi cation of mineral dusts. Measurements made with an ordinary light-microscope can be misleading. For example, a talc platelet observed on edge, or on an angle, may appear to be a fiber. Scanning electron micrographs are far more reliable and revealing because of greater possible magnification and depth of field. When observed in this manner, some talc platelets appear to roll up into a tubular shape not unlike kaolin-halloysite or serpentine-chrysotile. However, in the case of talc, this tubular structure is far more rare and is seldom complete. Particle Size Particle size may be determined by direct microscopic measurement using a filar micrometer eyepiece or by measurement of particles in an electron micro graph.11 Television scanning techniques and equipment are also available. Other procedures involve settling rate determinations in water or other liquids. The Andreasen pipette is commonly used for this purpose. 10Mackenzie, Robert C. (ed.). The Differential Thermal Investigation of Clays. Mineral. Soc., Clay Minerals Group, London, 1957. 11 Allen, Terence. Particle Size Measurement. Chapman and Hall Ltd., London, 1968, pp. 45-61. l30rr, Clyde, Jr., and J. M. DallaValle. Fine Particle Measurement. The Macmillan Company, New York, 1959, pp. 43-78. 15 Conclusions _ We have attempted to show in the above presentation that the characteri zation of talc dusts is not simple. No one procedure or method is completely definitive. We believe that mineral composition can best be determined by X-ray diffraction. Particle morphology is best defined by means of scanning electron micrographs and particle size determined by sedimentation involving the Andreasen pipette. 16 CHARACTERIZATION AND OCCURRENCE OF TALC by H. T. Mulryan1 My name is H. T. Mulryan. I am president of Cyprus Mines Corporation's United Sierra Division. The division is the world's largest producer of talc in terms of product value. It operates talc mines in the States of Montana, Nevada, California, and Texas and talc processing units in the States of Montana, California, and Nebraska, Belgium, and through an affiliate, Mexico. The division employs about 180 persons at its talc production units. Approximately half of them work in our Montana mines and mills, the remainder are scatterd among the other eight talc locations. The Montana product approaches the purity of pure talc mineral and its habit is platy or granular, depending on the material source and fineness of grind. Figures 1 and 2 illustrate the nature of the particles by transmission and scanning electron microscope, respectively. On the other hand, mixtures of minerals from other sources may contain little or no talc mineral and still be correctly known commercially as "talc." Figures 3 and 4 show the particle shapes of "talcs" from the Gouverneur district of New York State. The needles or fibers are mainly tremolite with anthophyllite also commonly present. This type of commercial talc is not confined to New York State, being extensively mined and processed in California. Table 1 compares the mineral content of talc from New York, California, and Montana. The Silver Lake, Calif., tremolitic talc is similar to a typical New York State talc except for the missing anthophyllite and quartz impurities. TABLE 1.` - Comparison of mineral content of talc from New York, California, and Montana, in percent ' Talc type New York............ Silver Lake, Calif... Panamint, Calif..... Yellowstone* Mont.... Beaverhead, Mont.... Talc 62 54 82 99 98 Carbonate " - 3 12 1 1 Tremolite 30 43 " - - Anthophyllite 5 - Quartz 3 Trace <0.5 - Other " 2 Mont. 4 Mica. 1 Chlorite 1President, Cyprus Mines Corporation's United Sierra Division. 17 L- , i. .i 5 micrometers FIGUR E 1. Nature of particles by transmission and scanning electron microscope (X 6,000). F IG U R E 2. - Nature of particles by transmission and scanning electron microscope (X 4,400) 19 5 micrometers FIGUR E 3. * Particle shapes of " ta lc s " from the Gouverneur District of New York State (X 6,000). 5 micrometers F IG U R E 4. Particle shapes of " ta lcs" from the Gouverneur D istrict of New York State (X 880). 21 . - cottier California talc, the Panamint, contains calcite and mica as prin cipal impurities with no asbestos minerals present. The two Montana talcs, Yellowstone and Beaverhead, are high purity and also free of asbestos minerals. It has been the policy of the Cyprus Mines Corporation to X-ray the production workers at all of our operations annually. This policy has been in effect for 5 years and these examinations have not turned up any lung or pleural cancer among our talc tory disease of any kind. workers, nor have they revealed chronic res*pira Seven of the employees were first exposed to talc dust 25 to 44 years ago All the long service group were California workers who had been exposed to tremolitic talcs as well as tremolite-free materials. _ When the threshold limit values for tremolitic talcs were first made pub lic, we became concerned about the possibility that our people had been inad vertently exposed to a health hazard and we took two steps. First, the division ceased production of all talcs containing detectable amounts of tremolite and established an X-ray diffraction facility at our California mines to assure control. Second, the seven long-service employees together with four retirees and ex-employees were subjected to exhaustive physical examinations with emphasis on the respiratory system, chest, and abdomen. This group's first exposure to talc dust ranged from 25 to 49 years ago. There are no records to tell us what conditions were like in the talc mines and mills of the 1920's and 1930's but neither were mining nor milling techniques designed with dust control as a * major objective. The oldtime worker was, therefore, exposed to vastly greater amounts of dust than his modern counterpart. Nevertheless, these exhaustive examinations failed to detect any sign of cancer among any of the long-service group. One of the retirees did reveal signs of possible pneumoconiosis. Cyprus Mines Corporation's interest in this proceeding is one of concern for the welfare of its workers and for the truth. Although the medical data presented are admittedly limited, they contain no indication that talcs of either the pure Montana type or less pure California varieties are carcinogenic. We should emphasize that Cyprus' talc operations are in compliance with threshold limit values both as relates to dust from nonasbestiform talc and fiber count. We realized that any dust in excessive amounts cannot be a posi tive health factor and are making every effort to minimize employee exposure. 22 DISCUSSION OF THE MINERALOGY OF INDUSTRIAL TALCS by C. S. Thompson, Ph. D.1 Discussion The purpose of this presentation is to discuss the mineralogy, crystal lography, and morphology of the major constituents of industrial talcs. It is also to present information regarding the nomenclature used to describe these materials with the hope of clarifying the terminology, which is so important in the formulation and understanding of regulations. Industrial talcs vary greatly in mineralogic composition from relatively pure mineral talc, MgsSi802 o (0H)4 , to mixtures containing mineral talc and numerous other minerals, principally: serpentine, Mg3Si305 (0H)4 (antigorite and/or chrysotile); dolomite, CaMg(C03)3 ; tremolite, CagMg5Si8022(OH,F)s ; anthophyllite, (MgFe)7Si8022(OH,F)2 ; and chlorite, (Mg,Al,Fe)l2(Si,Al)802o(OH)16. Due to the recent definition of the term "asbestos" in the Federal Register of June 7, 1972, which incorrectly included all forms of anthophyllite, tremolite, and actinolite as "asbestos minerals, many domestic, industrial talc producers have found themselves legislated into being "asbestos" producers as well. It is the purpose of the following dis cussion to correct this error. The term "asbestos" (see appendix) is a nonscientific commercial term normally restricted in use to the long, threadlike fibrous varieties of sev eral hydrated silicate minerals, whose fibers can be separated mechanically and pressed, spun, or woven into articles of all types that are resistant to heat and chemical action. Although present usage is generally limited to the commercially available silicate minerals, chrysotile, crocidolite, ampsite , anthophyllite asbestos, tremolite asbestos, and actinolite asbestos, other minerals regardless of chemical composition, which possess similar qualities of great elongation, flexibility, high-tensile strength, heat and chemical resistance, spinability, etc., could properly be classified as asbestos. The asbestos minerals mentioned above all have nonasbestos counterparts of the same chemical composition and crystal structure which are far more abundant and widespread than the asbestiform variety. These (see table 1) occur as common rock-forming mineral constituents of many igneous and metamorphic rocks. The crystallization of these normally nonfibrous minerals in fibrous form is a rare occurrence in nature dependent upon unusual combinations of physical and chemical conditions during the metamorphism of preexisting nonasbestiform minerals. As shown in table 1, the asbestiform varieties of the serpentine and amphibole minerals groups have, in part, been given individual names which, in themselves, imply their fibrous nature. In the case of the 1Manager of Ceramics, Paper, and Specialties, Research and Development, R. T. Vanderbilt Company, Inc. 23 three amphiboles, anthophvllite, tremolite. and aetinolite, which occur so rarely as the asbestiform variety (all three account for an estimated 1 per cent of the total asbestos production), no special name was given to the asbestiform variety, and therefore, a qualifying morphological term such as anthophvllite asbestos, tremolite asbestos, and actinolite asbestos must be used when referring to that particular crystal form. I am convinced that it was this lack of a special name in the mineralogical and other literature which caused, incorrectly, the inclusion of all forms of anthophyllite, trem olite, and actinolite in the Asbestos Dust Standard (29 CFR 1910.93a) instead of only the asbestiform varieties, as was undoubtedly intended by the formulators of the regulation. It is obvious from the studious omission of the nonfibrous varieties of the other asbestos minerals, that is, antigorite, riebeckite, and cummingtonite from the asbestos standard, that if special names had existed for the asbestiform varieties of the remaining amphiboles, they would have been included as well, and anthophyllite, tremolite, and actinolite would also have been omitted. TABLE 1. - "Asbestos" minerals as listed in Federal Register Asbestiform variety Serpentine group: Chrysotile.... Amphibole group: Crocidolite.................... Anthophyllite asbestos......... Tremolite asbestos............. Actinolite asbestos............ Chemical composition Mg3 (Sis0B)(0H)4 .......... Nonasbestiform variety Antigorite, lizardite. NagFe3Fe2 (Sig0g2 ) (UH)2 .... (Mg ,Fe)7 (SioOop) (0H)2 .... (Mg,Fe)7 (Si022)(0H,F)8 ... Ca2Mg5 (Si8 )s2 ) (0H,F)s .... Cag(Mg,Fe)s (Si802S) (0H,F)s Riebeckite. Cummingtonite. Anthophvllite. Tremolite. Actinolite. NOTE: Underlined mineral designations are those listed in the Federal Register. The term "fiber" connotes a greatly elongated particle with threadlike qualities such as high-tensile strength, flexibility, spinability, etc. (see appendix). Asbestos fiber, in particular, refers to a particular crystalliza tion of common nonfibrous rock-forming minerals, resulting in long fiber bundles, which continue to break down during crushing or processing into fibrils of smaller and smaller diameter until near molecular diameters are reached, while still maintaining relatively great elongation. The use of an aspect ratio (length to width) of 3 to 1 as the lower limit of a fiber (as defined in the Federal Register, NIOSH, and so forth), most certainly refers to fragments or pieces of much longer, previously recognizable asbestos fibers, since it is obvious that any other nonasbestos, nonfibrous minerals, such as feldspars, pyroxenes, amphiboles, calcite, gypsum, etc., could not be consid ered to have become fibrous on the basis that, during processing, they are reduced to particles or fragments which exceed an aspect ratio of 3 to 1. Many such minerals normally occur in elongated prismatic or acicular crystals, which.have a tendency to elongate as they are subjected to attritioning but have little tensile strength, tend to be quite brittle, and are therefore not fibrous. 24 The accompanying sets of photographs and photomicrographs will illustrate the marked morphological difference between the asbestiform and nonasbestiform varieties of the "asbestos" minerals under discussion. We must apologize for the lack of pictures of the asbestiform varieties of tremolite and actinolite. Several specimens so labeled have been examined, but all had been mistakenly identified. A study of these pictures (figs. 1 through 11) will indicate the differences just mentioned as well as the great similarity of the physical forms and grinding characteristics of the nonasbestiform amphibole varieties, riebeckite, cummingtonite, anthophyllite, tremolite, and actinolite. A com parison of these photographs with those of the talc products (figs. 12 through 17) clearly shows that the amphibole minerals, occurring in domestic indus trial talcs, are present as the nonasbestiform variety. It is hoped that this presentation has accomplished the following: 1. Illustrated the differences between asbestiform and nonasbestiform varieties of the same mineral. 2. Helped clarify the nomenclature used in reference to asbestos. 3. Indicated the importance of correct terminology in the formulation of regulations. 4. Presented evidence which shows that the amphibole minerals associated with domestic industrial talc are present as the nonasbestiform variety and are therefore not asbestos. 25 26 FIGURE 2. - ABn, tcigloosreituep;noCn,apsbheostotimfoircmrogvraarpiehty(2. .7A5,/Simpe/Dciimv.e)n. ; CROCIDOLITE 28 FIGURE 4. - Riebeckite nonasbestiformvariety. A, Specimen, B, closeup; C, photom icrograph (2.75 F m /D iv .). FIGURE 5. - Amosite asbestiform variety. A, Specimen; B, closeup; C, photomicrograph (2.75 ^m/Div.). FIGURE 6. - Cummingtonite asbestiform variety. A, Specimen, B, closeup; C, photomicrograph (2.75 pm/Div.). FIGURE 7. - ASpntehcoimpheny;11Bit,e calsobseeustpo;s Ca,sbpehsottiofomrimcrovgarraiepthy(.2.7A5, fitn/Div.). 32 FIGURE 8. - Anthophyllite nonasbestiform variety. 4 Specimen; B, closeup; C, photomicrograph (2.75 ^m/Div.). FIGURE 9. - Tremolite asbestos asbestiform variety. A, Speci men; Bjcloseup; C, photomicrograph (2.75 ^m/Div.). 34 FIGURE 10. - Tremo!ite nonasbestiform variety. A , Specimen; B , closeup; C , photomicrograph (2.75 /m/Div.). FIG U RE 11. - Actinolite nonasbestiform variety. A , Specimen; B, closeup; C, photomicrograph (2.75 ^m/Div.). 36 FIG UR E 12. - New York tales, Nytal 99 (~50 percent tremolite), 5.5 /m/ Div. 37 38 Appendix Bibliography of Asbestos Terms Source 1: Berger, Hans (translated by Ralph E. Osper). Asbestos Funda mentals --Origins, Properties, Mining, Processing, Utilization. Chemical Publishing Company, Inc., New York, 1963. In the mineralogical sense the term asbestos is extended in part also to other fibrous minerals, without reference to composi tion, structural constitution, properties, and technical-industrial significance. Two main groups are differentiated with respect to origin, mode of formation, mineralogical relationships, structure, composition, and properties of the asbestoses: namely, the serpen tine asbestoses (chrysotiles) and the amphibole asbestoses. The^ fibrous crystalline variants of the minerals have in part been given individual names to which, in the interest of a precise terminology, the word asbestos must not be appended. For example, the fibrous form of serpentine is called chrysotile, serpentine-asbestos, or fibrous serpentine-but not chrysotile asbestos. The accepted names of the five asbestoses used commercially are given as follows: Grout) Serpentine asbestos Amphibole asbestos. Designation of mineral Gruenerite........... Designation of asbestos Chrysotile. Crocidolite, blue asbestos Amosite. n- ..... Anthophyllite........ Anthophyllite asbestos.1 Do............ . Tremolite............ Tremolite asbestos.1 1These varieties have no special designation. Source 2: HM Factory Inspectorate, United Kingdom. Asbestos Health Precau tions in Industry Department of Employment. Health and Safety at Work, No. 44 1971. Asbestos is the common name given to a number of inorganic, fibrous, silicate minerals that possess a crystalline structure. Chrysotile, the most abundant of the fibrous silicates and the one most extensively used in industry, belongs to the serpentine group of rock-forming minerals and is mined mainly in Canada, Russia, and Rhodesia. The other forms of asbestos belong to the amphibole group. They are crocidolite, commonly known as 'blue asbestos which is^ found in South Africa; Western Australia and Bolivia; amosite which occurs only in South Africa; anthophyllite, the fibrous form of which is found in Finland and Africa; and the fibrous forms of tremolite (available in Italy) and actinolite, which has been found xn South Africa. 'Asbestos' means any of the following minerals, that is to say, crocidolite, amosite, chrysotile, fibrous anthophyllite and any mix ture containing any of the said minerals. 39 Source 3: Ladoo, Raymond Bardeen. Non-Metallic Minerais. McGraw-Hill New York, 1st ed., 1923. ' , Asbestos, 'amphibole' asbestos, 'hornblende' asbestos, and Italian' asbestos are various terms given to the monoclinic amphi boles, tremolite CagMgg(Si8022)(OH,F)s and actinolite, Ca(Mg,Fe)s (Si03 )4 , when they occur in fine silky fibers. Source 4: Dana, Edward Salisbury. A Textbook of Mineralogy. Extended Treatise on Crystallography and Physical Mineralogy. Sons, Inc., New York, 1947. With an John Wilev & y A ctin o lite. Calcium-magnesium-iron amphibole....In cry sta ls, either short- or long-bladed, as in tremolite; columnar or fibrous- granular massive--- The fibrous and radiated kinds are often called asbestiform actinolite and radiated actinolite.....ASBESTOS. Asbestos. Tremolite, actinolite, and other varieties of amphibole, excepting those containing much alumina, pass into fibrous varieties, the fibers of which are sometimes very long, fine, flexible, and ' easily separable by the fingers, and look like flax. These kinds are called asbestos (from the Greek for incombustible).... CROCIDOLITE. . Blue Asbestos--Probably to be considered as a fibrous variety of riebeckite. Fibrous, asbestos-like; fibers long bur deli cate and easily separable. Source 5: Hurbut, Cornelious S., Jr. Dana's Manual of Mineralogy. John Wiley & Sons, Inc., New York, 18th ed., 1971. # Serpentine occurs in two distinct forms: (1) a platy variety, antigorite, which conforms in its properties to those of the phyllosilicates, and (2) a fibrous variety, chrysotile. ...The variety chrysotile is the chief source of asbestos. The uses of asbestos depend upon its fibrous, flexible nature, which allows it to be made into felt and woven into cloth and other fabrics, and upon its incom bustibility and slow conductivity of heat. Asbestos products, there fore, are used for fireproofing and as an insulation material against heat and electricity. Massive serpentine, which is translu cent and of a light to dark green color, is often used as an orna mental stone and may be valuable as building material. Source 6: Gary, Margaret, R. McAfee, Jr., and C. L. Wolf, Glossary of Geology. American Geological Institute, Washington, D.C., 1972. Amosite: A commercial term for an iron-rich, asbestiform vari ety of amphibole occurring in long fibers. It may consist of an orthorhombic amphibole (anthophyllite and gedrite) or of a mono clinic amphibole (commingtonite or grunerite). Asbestos: A commercial term applied to a group of highly fibrous silicate minerals that readily separate into long, thin, strong fibers of sufficient flexibility to be woven,...certain fibrous varieties of amphibole... 40 Crocidolite: A lavender-blue, indigo-blue, or leak-green asbestiform variety of riebeckite, occurring in silky fibers and in massive and earthy forms. Syn: Blue asbestos: Krokidolite. Source 7: Deer, W. A., R. A. Howie, and J. Zussman. V. 2, Longman Group Ltd., London, 1963. Rock Forming Minerals. Riebeckite also occurs as an extremely fibrous mineral, when it is known as blue asbestos or crocidolite. The best known occur rences of blue asbestos are in South Africa where it occurs in bedded ironstones, the seams of crocidolite conforming to the bed ding of the ironstones. The composition of the crocidolite is remarkably similar to that of the ironstone and the crystallization of the amphibole, initially in the form of massive riebeckite, occurred with little or no addition of material under conditions of moderate temperature and pressure consequent on the burial of the ironstones to moderate depth..... Both Peacock (1928) and Hall (1930) favor the hypothesis that NagO was originally uniformly distributed throughout the ironstone and subsequently concentrated in certain bands. The later transformation of the massive riebeckite to the fibrous crocidolite may result from the instability of the riebeck ite during a period when the ironstones were subjected to shearing stress....... The members of the cummingtonite-grunerite series are typically found in both regionally and contact metamorphosed rocks. The more magnesian members are found also in some igneous rocks, including those of hybrid origin. The. asbestiform varieties amosite and montasite are of economic importance...... The characteristic habit of the members of the cummingtonite-grunerite series is acicu lar or fibrous. The asbestiform variety, amosite, when fresh is ash-grey in color; the mineral, however, is frequently coated with iron oxides, when the color is brown to yellow. The fibers of the montasite variety are less harsh than amosite and are often soft and silky in texture...... The habits of the anthophyllite minerals vary from fibrous and asbestiform to bladed and prismatic. The fibers of anthophyllite asbestos generally do not have any great tensile strength and are of less economic importance than the amosite and crocidolite fibers....... Mass-fiber anthophyllite asbestos occurs as a replacement mineral in ultrabasic rocks at Kamiah, Idaho (Anderson, 1931)....... Laudermilk and Woodford (1930) have described an asbestiform anthophyllite in veins in serpentinite at Coffe Greek, Carvill, California. Source 8: Deer, W. A., R. A. Howie, and J. Zussman. Rock Forming Minerals. V. 3, Longmans, Green and Company, Ltd., London, 1962. The principal minerals of the serpentine group all have the approximate composition H4Mg3 Si209 , and comparatively little substi tution of other irons is found to occur in natural specimens.^ The most well known serpentine mineral, chrysotile, often occurs in veins of silky fibers and is the most important source of commercial asbestos. 41 Source 9: Read, H. H. Rutley's Elements of Mineralogy. pany, London, 25th ed., 1953. Thomas Murby* & Com Mineralogically, asbestos includes the fibrous forms of amphibole; the fibers are generally very long, fine, flexible, and easily separated by the fingers; the color.... The term asbestos in the strictest sense is confined to the fibrous forms of actinolite but the asbestos of commerce includes fibrous varieties of a number of silicates.... SL h " S l pp.H' EleCtrn Micrsraphs o AsbestloTM >" > 1 .. Tremolite does not break down into fibers that approach a uni form rectangular cross section, as crocidolite does. Two samples (figures 9 and 10) indicate that the fibers break into fragments. Some of the fragments are quite thin, while others are rather thick. The fragments are composed of thin sheets. Some of the small sheets (figure 9) are so thin that they are almost translucent to the elec tron beam. Dark streaks are again noticeable in the thin sheets of tremolite, as they are slightly wrinkled for Bragg reflections. The thin sheets are probably less than 100 A. in thickness. Actinolite is generally considered the basic amphibole asbestos member. The fibers of actinolite are quite poor; and, because it rarely has commercial value, it is not very well known. The sample examined was splintery and very brittle. It was not expected that the mineral would break down into fibers for electron microscopic study, but we felt it worth the effort to try, since it is the basic member of the amphibole group. Figure 11 reveals that it did not break into single fibers. Low magnification was used, as the mate rial broke into large, opaque pieces. Source 11: Gaze, Richard. The Physical and Molecular Structure of Asbestos. Ann. New York Academy of Science, article 1, v. 132, 1965, pp. 23-30. The name asbestos 1 is used to describe any mineral that breaks down into fibers when it is crushed or processed. Source 12: Kingery, W. D. Introduction to Ceramics. John Wiley & Sons Inc., New York, 1963. ' Asbestos: 'Asbestos' is the name given to a group of hydrous magnesium silicate minerals which have a fibrous texture. The crys tal structure of these minerals is characterized by the presence of long chains of silicate tetrahedra which can be readily cleaved in directions parallel to the silicate chains but not in directions that cut the chains, with the result that these minerals can be shredded into fibers... 42 Source 13: McGraw-Hill Book Company, Inc. Mineral Raw Materials, by the F o r e i g n Minerals Division, U.S. Bureau of Mines, 1937, p. Asbestos is not a distinct material but a commercial term used to express the fibrous nature of several minerals. Source 14: Colliers Publishing Co. Colliers Encyclopedia, 1972. Asbestos, any of several varieties of fibrous minerals whose fibers may be spun or felted to make fabrics, panels, or coatings that are resistant to heat and chemical action. Asbestos is also valued for its electrical insulating properties. Source 15: Encyclopedia Americana--International Edition, 1969. Asbestos, general name for a group of silicate minerals that occur as fibers or fibrous masses and that can be woven into heat resistant materials. The fibers are separated mechanically and pressed, spun, or woven, often with cotton, wire, rubber, orcement, to produce fireproof articles of all types: clothing, curtains, electric cable insulation, brake linings and clutch facings, insulat ing boards, sheets, shingles and talcs. Asbestos is a fibrous mineral substance...In its natural state, asbestos is found encased in rocks. Its fibrous quality makes it a remarkable mineral. Asbestos is as dense as the rock in which l is encased, but it is a mass of tiny fibers that become as fluffy and light as thistledown when separated mechanically from rock. Souircs 16. Encyclopedia Bititannica, 1971* Fibre--A fibre may be defined as a unit of matter of hair-like dimensions whose length is at least 200 times greater than its width 43 experimental studies on biological effects OF TREMOLITE TALC ON HAMSTERS by William E. Smith, M.D.1 My name is William E. Smith. I am director of Health Research Institute at Fairleigh Dickinson University, Madison, N.J. I am a doctor of medicine. Over the past 25 years, I have studied more than 200 chemical materials for carcinogenicity in animals and have reported results of these tests in scien tific journals. In the past 8 years my associates and I exposed animalt to various mineral dusts, maintained them over their natural life spans, and studied them for pathologic changes by gross and microscopic examination of their tissues and organs. The principal purpose of these latter studies has been to develop infor mation on possible fibrogenic and/or carcinogenic properties of various prepa rations of mineral dusts. The principal support for this work was provided by Research Grant EC 00226 from the Bureau of Occupational Safety and Health, U.S. Public Health Service. Thus far, we have published five papers (listed in the bibliography section of this paper) describing some of our findings in animals exposed to various preparations of asbestos. Today, I would like to offer a brief summary of our experiments with, asbestos and describe as yet unpublished data from studies we have made with a sample of talc containing a large amount of tremolite. From our work, we identified the Golden Syrian hamster as a species that was capable of developing pulmonary fibrosis resembling asbestosis seen in man. Those experiments were done by repeated intratracheal injections of chrysotile or amosite asbestos. The method used for those experiments, weekly intratracheal injections, is technically tedious and time consuming. We found that we could compare the relative fibrogenicity and carcinogencity of mineral dusts more conveniently by depositing the dusts by a single injection into the pleural space of hamsters. After single intrapleural injection of preparations of the chrysotile, amosite, anthophyllite, or crocidolite types of asbestos, we found that ham sters developed extensive pleural adhesions. These adhesions were composed mainly of round cells and multinucleated giant cells in the first few months after injection. Within 5 months, these adhesions became densely fibrotic. Adhesions induced by the chrysotile, amosite, anthophyllite, or crocidolite types of asbestos tended to extend over large areas of the surfaces of the lungs. 1Director, Health Research Institute, Fairleigh Dickinson University, Madison, N.J. 44 In contrast, we saw very little reaction when we gave hamsters intra pleural injections of a sample of tremolite talc, which I shall identify by our sample number, FD-14. After intrapleural injection of this tremolite talc, the particles were gathered into small depots on the lung surface. These depots contained round cells and multinucleated giant cells, but there was very little formation of fibrous tissue. The experiments thus show that ^ fibrogenic activity of tremolite talc is very much less than the fibrogenic action of the four principal types of asbestos. Also, in hamsters that had been given intrapleural injections of the four principal types of asbestos, we found intrathoracic tumors that we designate as mesotheliomas (table 1). TABLE 1. - Number of mesotheliomas in groups of 50 hamsters Dose, ms 25 10 1 Chrvsotile 9 4 0 Amosite - 3 0 Anthophvllite 3 - Crocidolite - 10 2 From the data in table 1, it can be seen that the yield of mesotheliomas, in groups of 50 hamsters per sample, was related to dose. In response to a large dose (25 mg) of chrysotile, nine hamsters developed mesotheliomas. In response to a smaller dose (10 mg) of chrysotile, four hamsters developed meso theliomas. In response to a still smaller dose (1 mg), there were no mesothe liomas. This experiment provides evidence to show that the carcinogenic action of chrysotile is related to dose, hence should be controllable by appropriate industrial hygiene measures to control dose. At the 10 mg dose level, amosite and anthophyllite gave about the same yield of mesotheliomas as did chrysotile, but crocidolite induced more than double the number of mesotheliomas gotten with the other types of asbestos. Also, crocidolite induced mesotheliomas in two hamsters treated with the lowest dose level (1 mg) whereas no mesotheliomas occurred in animals treated with that dose of chrysotile or amosite. Table 2 shows results of tests for carcinogencity of six preparations of chrysotile in groups of 50 hamsters each. Each of these preparations was tested at our highest dose level (25 mg per injection). The table gives data on the mean fiber length and mean fiber diameter of these samples. It can be seen that 8 to 10 mesotheliomas were induced by three of these samples: harsh chrysotile, soft chrysotile, and the same sample of soft chrysotile heattreated to achieve some of the properties of harsh chrysotile. These three samples that proved carcinogenic had mean fiber length of 5.3 to 6.9 microm eters and mean fiber diameter of 0.2 to 0.8 micrometer. These three active preparations of. chrysotile were subjected to further milling to reduce the majority of particles to submicroscopic dimensions. The 45 table shows that this reduction in particle size eliminated the carcinogenic .effect of these samples. It also greatly reduced their fibrogenic action. TABLE 2. - Tests for carcinogenicity of six preparations of chrysotile in groups of 50 hamsters each Chrysotile preparation Soft......... Soft (heated) . Harsh........ Mean fiber length OM, EM, micrometers micrometers 32.5 6.9 - - 38.9 5.3 Mean fiber diameter OM, EM, micrometers micrometers 2.2 0.18 - 2.9 .2 Soft......... _ .9 _ .03 Soft (heated). - - - - Harsh........ - .4 - .07 OM Optical microscope. EM Electron microscope. No. of mesotheliomas 8 10 9 0 0 . 0 Now, we have tested a sample of tremolite talc for carcinogenicity in hamsters. Electron diffraction studies of this sample showed it to contain 50 percent fibrous tremolite and 35 percent talc (table 3). A majority of the talc particles were platy, but some were rolled or fibrous. TABLE 3. - FD-14 (tremolite talc): Composition Selected area electron diffraction: Fibrous tremolite................... Antigorite.......................... Talc1 ............................... Chlorite.... ........................ 10f this about 75 percent is platy and 25 percent is rolled or fibrous. Percent 50 10 35 5 In this sample, the fibrous particles had an average length of 5.7 microm eters and an average diameter of 1.6 micrometers (table 4). They are there fore in a size range that might be carcinogenic in our experiments with chrysotile. However, this sample of tremolite talc induced no mesotheliomas after intrapleural injection into hamsters. TABLE 4. - FD-14 (tremolite talc): Size measurement1 (Phase microscopy lOx ocular, lOOx objective) Length, micrometers Range Average Fibrous particles...... 2.5-16.5 5.7 Platv particles........ - - '-Ratio fibrous to platy particles: 3 to 1. Diameter, Range 1- 5 1-10 micrometers Average 1.6 2.0 46 Table 5 gives detailed data on these tests which were conducted at our highe-fio.. level (25 mg). In via o the long latent period before develop, ment of tumors, if we wish to compare relative carcinogenicity of diffe "ITSpz iieTsto th a validity of the comparisons depends later periods of the tests. In on the number of animals survxvtable 5, the number of survivors in^each group at each time period is shown as the denominator. The cumul iv number of animals bearing mesotheliomas is shown as the numerator. TAm.F. 5 . - Yields of mesotheliomas in hamsters after intrapleural tn^fiction at 25-mg dose level1 3 Sample Soft chrysotile...... Harsh chrysotile.... . 151 days 0/44 1/41 340 davs 0/33 4/26 372 days 1/30 4/21 450 davs 1/20 7/16 500 davs 4/11 7/13 550 days 4/9 7/9 600 days 7/3 8/5 650 days 8/1 9/2 700 days ) (3 ) Heat-treated soft chrysotile......... Tremolite talc...... . 0/37 1/35 1/32 1/27 4/17 5/15 8/4 10/1 (3 ) 0/52 0/35 0/34 0/29 0/27 0/23 0/20 0/15 0/7 1Numerator : Cumulative number or namsters w n u 2 Denominator: Number of hamsters surviving on stated day^ 3 Survivors at 650 days in chrysotile groups were killed on that day. Pleural adhesions, but no tumors, were found in them. We started with about 50 hamsters in each group. The first tumor was found at 151 days in an animal that had been treated with harsh chrysotile. Now let us look at the situation as it was 500 days after start of tests. At that time, 4 mesotheliomas had occurred in the group treated with soft chrysotile and only 11 animals survived. In the group treated with harsh chrysotile, 7 mesotheliomas had occurred and 13 hamsters were still living. In the group given heat-treated soft chrysotile, there were 4 mesothe liomas and 17 survivors. By comparison, no mesotheliomas had occurred in the group treated with tremolite talc, and there were 27 survivors. The group on tremolite talc thus had many more animals at risk in the late stages of the tests, yet no mesotheliomas developed m them. died In or the three groups on preparations of ch^ys ^ 1 311 were killed to close out those groups by 650 days. ^ At th^ that t i m f > ^ h l f final yield of mesotheliomas in those groups was 8, 9, and 10, respec y By comparison, the group on tremolite talc had by 650 days, and there were still 15 animals living and at risk m at that time. that group 47 Eight of these survivors died of various causes between 650 and 700 days. No mesotheliomas were found in them. The remaining seven survivors on tremolite talc were killed for examina tion at 700 days. No mesotheliomas were found in them. Throughout the tests, animals treated with the preparations of chrysotile in table 5 were found to have thick fibrous pleural adhesions extending over large areas of the lung surfaces, whereas animals treated with tremolite talc never showed more than small depots of the mineral particles with relatively little tissue reaction. In summary, our experiments show profound differences between the bio logic effects of tremolite talc, in respect to both fibrogenicity and carcino genicity, as compared with the biologic effects of the four principal types of asbestos: chrysotile, amosite, anthophyllite, and crocidolite. 48 Bibliography 1. Hiller, L., W. E. Smith, and S. W. Berliner. Tests for Effect of Asbestos on Benzo(a)pyrene Carcinogenesis in the Respiratory Tract. Annals of the New York Academy of Sei., v. 132, article 1, 1965, pp. 489-500. 2 Smith W. E. Asbestos in Relation to Tumors of the Respiratory Tract. Ch, ' in Lung Tumors in Animals, ed. by L. Severi. University Perugia, Italy, 1966, pp. 565-570. 3. Smith, W. E., D. D. Hubert, and M. Badollet. Biologic Differences in Response to Long and Short Asbestos Fibers. Am. Industrial Hygiene Assoc. J., v. 33, February 1972, p. A162. 4. Smith, W. E., L. Miller, and J. Churg. An Experimental Model for Study of Cocarcinogenesis in the Respiratory Tract. AEC Symp. ser. 21, 1970, pp. 299-316. 5. Smith, W. E., L. Miller, R. E. Elssser, and D. D. Hubert. Tests for Carcinogenicity of Asbestos. Annals of the New York Academy of Sei., v. 132, article 1, 1965, pp. 456-488. 49 THE BIOLOGICAL ACTION OF TALC AND OTHER SILICATE MINERALS by Gerrit W. H. Schepers, M.D., D.Sc.1 Introduction The recent revelation that prolonged human inhalation of certain fibrous minerals (for example, crocidolite) may be associated with-excess prevalence of malignant neoplasia of the lung, and even of other organs such as the stomach or colon, has focussed attention on the biological potentials of all the fibrous minerals. For reasons not quite clear to this author, talc has somehow and probably quite unjustifiably become embroiled in the issue of the carcinogenicity of asbestiform minerals. Talc, though a silicate, is by no means a fibrous mineral. It is quite important, however, to thoroughly review biological reactiv ity to talcs because their industrial uses are so diversified. Direct human exposure is considerable, involving all elements of humanity, practically from cradle to grave. There also is a contradiction between the stringent rules for dust suppression in mining or milling of talc and the almost total lack of controls over talc when released for private use. The crucial issue is whether all silicate minerals are equally pathogenic. To resolve this question it is necessary to review what is on record concern ing the biological action of talc and compare this with what is known about the adverse properties of other silicates and especially the asbestiform minerals. The biological potentials of a variety of natural and synthetic silicates have been personally researched over the past 3 decades. These studies have included investigation of human subjects, experimental animals, and a review of the literature. Human studies include observations on crocidolite and amosite miners and millers in Africa, chrysotile, tremolite, and talc miners, millers, and industrial workers in the United States and Canada, and textile workers in fiberglass and synthetic fiber industries. The number of human subjects studied exceeds 10,000. These studies are evaluated against a back ground of familiarity through personal clinical experience and research of the pathogenic action of a variety of other natural and synthetic siliceous, non siliceous, and chemical and synthetic substances. The clinical subjects exceed 100,000 and necropsies have been performed on over 10,000 deceased industrial workers. (7 ) Animal studies have recently been reviewed in a Primates and Rodents These included researches publication on Tumors of on the biological proper ties of 407 industrially important materials through experimental exposures of 7,906 animals. 1Chief, Medical Service of Veterals Administration, Lebanon, Pa. 50 The published literature is vast and ever increasing. In excess of 4,000 papers have been reviewed. If these do not include all that has been written on this subject of pneumoconiosis, any omissions would be unintentional. For practical purposes all references cannot be cited nor will it be reasonable in a paper of the intended scope of this presentation to recapitu late all that is known about the biological actions of talc and fibrous envi ronmental agents. It will be feasible only to summarize pertinent highlights. Fibrous and Nonfibrous Dusts There appears to be considerable difficulty in differentiating between respiratory inhalants which may be called "fibrous" as compared with "nonfi brous" substances. There is no problem when we consider substances such as crocidolite, amosite, chrysotile, anthophyllite, fiberglass, rockwool, or natural or synthetic textiles (wool, cotton, nylon, rayon, dacron, orlon, etc.). These materials are predominantly composed of elongated delicate com ponent elements which are indisputably "fibers." There appears to be no absolute definition of what constitutes a fiber-neither with mineralogists nor with textile experts. Review of discordant terminologies almost leads one to the conclusion that a fiber is a fiber when it is obviously so. Physicochemically speaking, however, a fibrous mineral would be a substance with a propensity for cleavage in two planes of space. Some mineral fibers can, however, also form when aluminosiloxane sheets are "rolled" to form tubules. Sporadic and possible spurious attempts have been made to classify miner als such as talc or tremolite as fibrous dusts. This is apparently on the basis of three properties: 1. There is the fact that talc and tremolite are mineralogically classi fiable as silicates, as are most fibrous minerals such as the asbestos series. 2. Some samples of talc and tremolite contain a minority of oblong par ticles which are considerably longer than they are thick. These elongated particles are only very rarely true "fibers" in the conventional sense and are more properly designated spicules, rods, or needles. 3. It is a fact that some talc or tremolite deposits occur geologically in close juxtaposition to chrysotile or other ore bodies so that some contami nation of talc with serpentine, dolomite, magnetite, pyrophyllites, and clays may occur. The logic in designating any nonfibrous silicate as fibrous, for the latter two reasons, somehow evades this author. If this principle were applied to other substances, there would be no sensible way to classify miner als or environmental contaminants. For example, hematitite or magnesite ores are often "contaminated" with siliceous materials, both fibrous and crystal line. Coal often contains mica, clays, asbestos, silica, etc. Do these admixtures justify classifying hematite as anything other than hematite; 51 * 16+ * * * 4x Si++++ \ , i ! I* lx K + 10- 4x0-- 2x 0H' * 16 + * * * 4x Si ++++ SILOXANE SILOXANE I I o O0 o o o 12- > / 1 / i / 6x 0 ii , 1->:iII! .o o o 10- 4x0-- 2x OH' n o o 12+ 6x M g ++ Ooo oo O 12- magnetite as anything but magnetite; coal as anything except coal; and so forth? Perhaps the solu tion lies in subclassi fying the silicate materials (table 1) as those which belong to an asbestiform group arid those that are not primarily asbestiform in nature. This may make mineralogical sense and may agree with some of the bio logical propensities of these materials. Such a classification may also be extended to embrace minerals and textiles, whether natural or synthetic. PiriiDCi ^rv 6x0 M O U R E I. - Diagram of the alumina*siloxane templates of silicates. To resolve these issues it is necessary to take a closer look formed^ShiPt f silicate minerals. These substances^errall1031 f l TM o/f sI ti1Ho l Se 0f,,certain hiShly characteristic coordinative properoxygen* 'and aluminum atoms. When the earth's crust was formed, these atoms sought one another to form the "substrate" for varieties of sxixcates: T^ s substrate is the alumina-siloxane moiety formed in all whethreand i5 ' ^ ?ndivfdual silicates differ from one another according to " certain other elements such as iron, magnesium, manganese, sodium, and calcium become interposed in the "micropores" of the siloxane ShySdraatted. TahLis liss af ShighVly c"o"mplSica"tedd thaeltmhoaungnherviinrtu"ahllclhy fthulelsey decoded sci ence. Indeed, because of the advanced state of the science of silicate chem- muShin-a 7 ia 1industrially possible to synthesize a number of these multibillion-year-old natural silicate minerals-though not yet at suffi ciently low cost to be competitive with mineral silicates. For our present olatrrnni^ i?rtinent to summarize that, based on the alumina-siloxane tem plate concept, there is a precise physicochemical explanation why silicate sheeM- ai \ Pr Sent- S nature as microPrus crystalline substances, or as A -ar'J ^ " iathlike, oblongate, acicular, or fibrous miner- prei^ted in S f " ' 111" tM n the ba8ls thls 1* 52 TABLE 1. - Fibrous respirable aerosols Natural Silicate: Asbestiform Crocidolite Amosite Anthophyllite Chrysotile I Synthetic MINERAL Silicate: Fiberglass Rockwool Nonsilicate: Potassium titanite Nonasbestiform Talc Tremolite Nonsilicate: Brucite Cotton Wool Hair Silk TEXTILE Nylon Dacron Orion Rayon TABLE 2. - Silicate minerals Microporous crystalline Laminar: Analcite Chabazite Heulandite Fibrous: Natrolite Sheetlike Aluminous: MontmorilIonites Montmorillonite Nontronite Hectorite Saponite Mic aceous Biotite Illite Muscovite Phlogopite Vermiculite Pyrophyllite Kaolinites Kaolin Actinolite Tubular or hollow Hydrated: Chrysotile Endellite Anhydrous: Hallovsite Ribbonlike Attapulgite Sepiolite Paligorskite Oblone particulate Tremolite Acicular Sericite Antigorite Sillimanite Fibrous Actinolite Anthophyllite Amosite Crocidolite N onaluminous: Talc It is to be noted that talc is here classified as a sheetlike silicate which is in a group quite separate from other laminar silicates or from tremolite which is often also called talc. Because talc (Mg3Si4010(OH)g) lacks the aluminum atoms which have such a strongly bonding effect between the siloxane 53 polymeric layers, the talc silicate readily splits primarily and predominantly along one plane of space to form fine lamina. However, cleavage along the two other planes of space occurs secondarily. This provides for the fine divisi bility of talc. The nonadherence of the flat particle surfaces to one another furnished the "greasy" or "slippery" property of talc. Scanning electron microscopy has well demonstrated this flaky character of the talc particle (fig. 2). Tremolite also is often classified as talc, perhaps because it also lacks the aluminum atom. Since two calcium atoms substitute for aluminum, tremolite belongs mineralogically with the amphiboles (which all have achieved compar able substitutions). It has the empirical formula: CagMgsSi8022(0H)2 . From the point of view of its siloxane structure, tremolite differs from talc in that it cleaves almost equally readily in two planes of space whereas cleavage in the third plane is a secondary feature. For this reason the classical tremolite particle is cuboidal to oblongate instead of platelike (fig. 3). A minority of tremolite "crystals" cleave less well in the third dimension than they do in the other two. These particles then manifest as stiff rods or needles. For this reason the appropriate location of tremolite in table 3 lies between the sheetlike silicates and the acicular silicates (sericite, antigorite, and sillimanite). The latter habitually cleave in such a manner that their natural format is a short needle or rod. The amphibole minerals, as mentioned above, have substituted other ele ments for aluminum. Thus in actinolyte and anthophyllite both magnesium and FIGURE 2. - Electron microphotogram of talc showing its laminar character (X 7,500). FIGUR E 3. - Microphotograph of typical oblong tremolite crystals, (Magnification unknown.) 54 iron are present (MgFe)7Si80sa(OH)a . In crocidolite there are both sodium and bivalent and trivalent iron (NagFeg Fea3 SieOsS (0H)S ) . Amosite is a mixture of actinolite and anthophyllite. Aluminum is absent from all of these. Their cleavage in relation to the siloxane substrate is predominantly and equally in two parallel planes. For this reason, they occur in nature as elongated fibers, which will bend rather than break in the third spatial plane. Conse quently, these fibers have high tensile strength and flexibility which is why they are so industrially important. TABLE 3. - Pathogenicity of silicates Rating 0 1 2 3 4 5 6 7 8 9 Minerals Montmorillonite, kaolinite, talc, tremolite. Talc + antigorite, magnesite, dolomite, and spinell. Tremolite with many rods or needles. Sericite, antigorite, sellimanite, mica. Chrysotile.. Actinolite. Anthophy11ite. Amosite. Crocidolite. Asbestos + silica or other minerals. Chrysotile is unique among the nonaluminum-containing silicates. Its empirical formula is MgsSi40lo(0H)a . It is classifiable as a tubular or hol low silicate. Its siloxane template, however, is basically a sheet which becomes rolled upon itself to form a tube. For this reason chrysotile is classifiable with endellite which is rolled in the opposite direction. When dehydrated to form halloysite the prior endellite tube splits lengthwise to assume a ribbonlike or lathlike form. It then resembles the silicates, attapulgite, sapiolite, and paligorskite. What does all this have to do with the biological properties of talc? Probably a great deal. These physicochemical characteristics of the various silicates are the bases for their particulate size, their ease of entry into the respiratory system, their penetration into cellular and intercellular tissue elements, their retention in or elimination from tissues, their solu bilization, their chelation or interaction with other elements within the bio logical system, and their acceptance or rejection by living matter. These biological counterparts may now be examined. Differential Biological Properties of Silicate Minerals There are marked differences between the capacities of the individual classes of silicate minerals to provoke responses in human and animal tissues There also are major misconceptions as to what these substances can do when inhaled by man or other mammals. Two of the most extreme of these are _ (1) that all siliceous minerals are equally pathogenic and (2) that there is even the least semblance between the effects of the asbestiform and the non- asbestiform silicates. 55 To express these differences in a practical manner one may accord a per centile value of pathogenicity to each substance. Since it is not really pos sible to discriminate biological responses with complete precision, a scale of zero to 10 may suffice. My appraisal of the differential pathogenicity of the silicate minerals is recorded in table 3. Since there are in the medical literature disease categories such as talc lung or talc pneumonconiosis, many explanations are needed to clarify why talc and tremolite (as pure substances) have been given a zero rating and why chrysotile asbestos is classified at the lower end of the pathogenic spectrum whereas crocidolite and amosite asbestos are at the opposite end. Since it is extremely difficult to disprove a Jack and the. Bean Stalk myth, multiple facets of the problem need be explored. It is necessary to examine more closely the origins and the erroneous premise that all silicate minerals.are equally injurious. The loose use of the terms asbestos or asbestosis and the facile identification of other amphiboles with "asbestos" may be a factor. How did this come about? Part of the problem originates in the manner in which physicians make diagnoses of conditions such as "asbestosis" or the techniques used in drama tizing a description of newly identified disease entity. Often the diagnosis is not based on precise and painstaking verification of the pertinent issues. Not uncommly, loose association and coincidence are the guiding criteria. Careful work histories are not always taken, so that a lung lesion found in an employee of a certain industry may become identified with the final occupation, whereas it might have had its origin in nocuous dust exposures encountered in a prior unrelated decade. Far too often the isolated rare exotic example is the sole basis for the generic concept of a "new" pneumoconiosis. The excep tion becomes the rule. Even unrelated disease, such as tuberculosis or mycosis or sarcoidosis have been misidentified as new pneumoconioses, merely because they occurred in an employee of the suspected occupation. This prob lem has been discussed more fully elsewhere (2-3, 8). Pneumoconiosis usually is identified during life through radiography. The radiologist who expertly examines "shadows" of lesions must rely on the pathologist who has studied necropsy specimens. The latter often is quite uncritical of the source of his material and not uncommonly quite poorly informed in the field of pneumoconiology. In the entire United States with its thousands of excellent pathologists, there are probably not more than a half a dozen true connoisseurs of this eclectic branch of forensic medicine. This may be true also in other countries. To make a reliable identification, the pathologist must not only have had years of experience in decoding this type of man-made disease, but must also have access to appropriate microscopy, chemistry, and petrographic equipment and skills. It also is quite unusual to encounter "pure" cases of a particular disease. Industrial workers, especially in America, tend to be quite mobile. They shift from one trade to another and potentially receive multiple expo sures so that the pneumoconiosis which ultimately emerges often is a mani festation of a prior dust or chemical exposure or a composite of many 56 successive exposures to diverse agents, some of which may not even be sepa rately pathogenic, but which may produce disease through the principle of potentiation. The phenomenon of individual susceptibility often also is over looked and disease, which develops in an unusual isolated case among many unaffected employees, is seized upon as a "typical" example of how dangerous the suspected silicate may be. Sometimes insufficient heed is paid to the question of dosage. Almost any substance is harmful in overwhelming amounts. Even substances which are biological necessities can be harmful in excessive concentration. We all need oxygen but cannot survive perpetually in an all oxygen environment without adverse results. Our bodies need water, but our tissues can "drown" therein. So it is with "inert" minerals. If a worker is grossly, recklessly, and long exposed to almost any dust, the pulmonary defenses will be overcome and harm will result. This point is well illus trated in experiments for instance with fiberglass utilizing the intratracheal versus the inhalation techniques. If a quantity of glass fibers is injected into the lungs of animals, gross pulmonary lesions swiftly follow (fig. 4). When, however, the same glass particles are inhaled in smaller daily dosage for periods of up to 2 years, no disease is induced even though the total amount of glass inhaled may greatly exceed the amount introduced as a single "slug" (fig. 5). FIGUR E 4. - Pulmonary lesion induced within 4 months in a guinea pig by intratracheal injestion of 1 mg of glass fibers in successive doses (X 40). FIGUR E 5. - Lack of pulmonary response to glass fibers inhaled daily by guinea, pig for 18 months in an aerosol concentration of 1 mg per cubic foot of air (X 40). 57 refu* analysis of the minralogie composition of the lungs and the work histories of deceased industrial workers with various grades of silicateinduced disease has shown that "pure" examples of specific silicatoses are extremely rare. It is almost axiomatic that if any advanced grades of disease are found among workers m silicate industries, the causative agents are mul tiple and likely to have potentiated each other's adverse propensities. For this reason the worst examples of severe pulmonary fibrosis or other lesions generally fall in category 9 as shown in table 3. A typical example of such a severe mixed silicatosis is illustrated in figure 6. are found among workers in silicate industries, the causative agents are mul tiple and likely to have potentiated each other's adverse propensities. For this reason the worst examples of severe pulmonary fibrosis or other lesions generally fall in category 9 as shown in table 3. A typical example of such a severe mixed silicatosis is illustrated in figure 6. Pure crocidolite or amosite pneumoconioses are rarely found in America today. They used to be common in England 30 or more years ago and of course are specifically associated with South Africa. The severe disease (category 8 or 7) which these intensely and relentlessly fibrogenic silicates cause (figs. 7 and 8) has strongly influenced the image of "asbestosis." For decades crocidolite pneumoconiosis was asbestosis. The problem is that when the word asbestosis" is today used in relation to other fibrous silicates such as chrysotile, the horrible image of crocidolite pneumoconiosis is con jured up. Indeed, it is extremely difficult to find examples of pure chrysotile asbestosis. Most workers with advanced pulmonary disease who are said to have chrysotile asbestosis usually have had prior or secondary exposure to other silicates, silica, and other minerals or chemicals. The few rare cases of pure chrysotile asbestosis are not characterized by gross pathology such as is found with amosite or crocidolite asbestosis (fig. 9). Chrysotile pathogenicity is, therefore, given a value of 4 on the scale of 0 through 9. The only human examples of tremolite or talc pneumoconiosis which have been placed on record were caused by tremolite which contained a high propor tion of needles or rods or talc which was significantly adulterated with other \SUCh aS 5remolite (CasMSs (H)2 SieS2 ) dolomite (CaMg(C03 )8 ), spinell (MgAlg04 ), magnesite (MgC03 ), magnetite (FesOs ), antigorite (Mg(0H)RSi40! _), chromite (FeCr204 ), etc. The amount of disease seen in these cases even after prolonged exposure is minimal (fig. 10). Pathogenicity ratings of 2 and 1 have been accorded these aberrant variants of tremolite and talc. Pure talc, Mg3Si4Ol0(0H)8 , appears to be biologically inert. It is true that the mineral can be found in the lungs after significant prolonged expo sure, but it is simply here as a stored material. Histologically this is a thesaurosis only without any thesaurismosis (for example, cytogenic, cytotoxic or fibrogenic reaction to the talc particles). ' For this reason talc is accorded a zero pathogenicity rating along with the clays and kaolin. Tremolite also belongs here when it occurs as oblong crystals with a minority of rods or needles. 58 FIGURE 6. - Dense pulmonary carnification in a human subject occupational ly exposed to successive aerosols containing quartz, fluxcalcineddiatomite, crocidolite, amo site, and chrysotile (X 1). FIGUR E 7. - Dense interstitial fibrosis caused in human lung by exposure to crocidolite dust (X 1). FIGURE 8. - Subpleural and interstitial pul monary fibrosis caused in man through exposure to crocidolite and amosite (X 1). 59 FIG U R E 9. - Limited reaction of the human lung to the inhalation of chrysotile dust for 22 years as a miner and mill worker (X 1). FIGUR E 10. Histological Gradation Limited human path ology characterizing exposure to impure tremolite dust for 18 years (X 1). The differential biological potentialities of the silicates are also recognizable onhistological review of "pure" examples of human exposure. Starting with talc the examples of tissue reaction shown in figures 11 to i3 clearly demonstrate the inert nature of this mineral. The close crowding of the myriads of talc particles, which are brilliantly revealed by polarized iight microscopy, is typical. The individual represented in the X-ray had worked in an automobile tire manufacturing factory for 2 decades and during all of this time he was regularly and heavily exposed to talc dust. He then left this industry to take employment for 11 years in a nondusty trade. He never developed symptoms during life. He died following an automobile acci dent. The talc lesions were discovered on routine review of the tissues and the work history as described was reconstructed retrospectively. The lack of tissue reaction, particularly the lack of fibrogenesis, correlates well with the symptomless state during life. There is no damage to the bronchial or vascular elements and alveolar space, pleura, and regional lymph nodes remained unaffected despite the abundant presence of talc particles around or in these lung components. The number of talc particles per unit square area of lung tissue at standard magnification is inversely proportional to the tissue reactivity to silicates. The excessive dysratio of particles to cellu lar or interstitial tissue is about as great as one may ever observe and serves as an index of biological inertness of talc. By subsequent petro graphic and X-ray diffraction techniques the talc retained in the lung tissue 60 FIGUR E 11. - Microphotograph of talc par ticles in the alveolar wall of the human lung, rendered visible by polarization of transmitted light grade 0 thesaurosis (X 1,000). FIGUR E 12. - Microphotograph of talc par ticles in the human bronchial lymph node, visualized by polarization mi croscopy., grade 0 thesaurosis (X 1,000). FIGURE 13. - Transmitted light micropho tograph of the alveolar wall in a man who had been occupationally exposed to talc dust for 20 years, grade 2 thesaurosis (X 100). of this case was shown to be an approximately 70 percent talc and 30 percent tremolite mixture* This case, therefore, further demonstrated the inertness of tremolite and proves that tremolite does not potentiate any latent patho genicity which talc may have or vice versa. The next example shows that tissue reaction in a talc worker who had been exposed for a protracted period to talc which contained a variety of impuri ties including tremolite rods, clays, and silica. The worker remained essen tially sympton free during approximately 24 years of exposure to this dust. His death was due to a myocardial infarction about 7 years after retirement. Three features are evident by contrast with the first case (fig. 14). First there is patchy or minimal interstitial fibrosis of alveolar walls. Second, collars of dust-filled cells may be observed in the lymph channels around small blood vessels and bronchiles. Third, occasional ferruginous bodies can be seen in the areas of fibrosis (fig. 15). There is minimal distortion of the air spaces and some focal pleural sclerosis. This grade of tissue pathol ogy is, therefore, no longer a thesaurosis or mere storage response, such as was seen in the case of pure talc exposure. We are now dealing with an example of early thesaurismosis or true tissue reaction to stored dust but without physiologically discernable adverse effect. This class of response typifies mineral or grade 1 reaction to the silicate dust. The stage 2 pneumoconiotic reaction is characterized by a quantitatively greater prevalence of the abnormalities seen with stage 1. There are about twice as many fibrotic plaques in the alveolar walls (fig. 16). There is FIGURE 14. - Focal lesions in human lung of an employee who had been exposed to dust containing talc, tremolite, clay, and silica . Grade 1 silicatosis (X 100). FIGURE 15. * Ferruginous bodies revealed by Perl's stain in case 15 (X 1,000). 62 FIGURE 16. - Grade 2 silicatosis in a human lung after prolonged occupational exposure to tremolite containing a high proportion of rods or nee dles (X 100). FIGURE 17. - Typical focal les ion caused by prolonged inhalation of chrysotile fibers, grade4 silicatosis (X 100). FIGUR E 18. - Chrysotile body as visualized by transmitted light. Note the splintered clublike ends of the body (X 400). FIGURE 19. - Chrysotile body showing the ferroproteinaceous matter in the capsule around the chrys otile fiber, Perl's stain (X 400). 63 minimal alveoloar space arid bronchilar distortion. The patient had, however, displayed no symptoms during life despite his known prolonged exposure to tremolite which contained about 20 percent rods and needles. Chrysotile dust inhalation, when unaccompanied by other exposures, causes slightly more reaction than that just described. This is grade 4 biological reactivity. There now is more involvement of alveolar walls and characteris tic spiderlike or octopuslike lesions are found (fig. 17). The chrysotile fibers are quite characteristic and may be found as chrysotile bodies (fig. 18) which also stain vividly blue and in typical dumbbell fashion with Perl's stain (fig. 19). Under oil immersion X 1,000 magnification bare chrysotile fibers of great delicacy may also be visualized (fig. 20).- There is fairly diffuse pleural thickening and slight perivascular, and peribronchiolar fibrosis is discernable throughout. Slight airspace distortion is evident even though there was no macroscopically or physiologically detectable emphy sema. This man had worked as a chrysotile miller for approximately 23 years and had never been exposed to any other dust, having formerly been a farmer in Quebec Province. Detailed physiological analyses were inconclusive for func tional deficits. No diffusion defect was revealed. The reason for this is readily evident when the relationship of the alveolar fibrosis to the alveolar fibrosis to the alveolar capillaries is analyzed (fig. 21). Since the capil laries remain intact on the alveolar surfaces, no physiological impairment has resulted except for minimal stiffening of the lungs with sequential minimally increased breathing effort. Gas exchange has remained unaffected. Such cases of pure chrysotile exposure are extremely rare. More usually the disease is the culmination of dust exposures which occurred during a mixed career of mining and participation on other dusty occupations. Depending on the variety in the mixture of dusts and the intensity and duration of exposure, FIGURE 20. - Bare chrysotile fibrils imbed ded in fibrous tissue within an alveolar wall of a chrysotile miller, Masson tri chrome stain (X 1,200). 64 FIGUR E 21. - Alveolar wall of chrysotile mil ler showing integrity of capillar ies despite underlying fibrosis, Masson stain (X 1,200). FIGURE 22. - Interstitial lesion representa tive of grade 6 silicatosis. Prolonged occupational exposure to anthophyllite dust (X 10). FIGUR E 23. - Interstitial pulmonary lesion produced by prolonged expo s u re to c r o c id o lit e . Grade 8 silicatosis (X 10). FIGURE 24. - Interstitial reaction to mixed silica and chrysotile dust ex posure. Grade 9 silicatosis (X 10). 65 all gradations of tissue reaction from 5 through 9 may be found (figs. 22-24). Strongest potentiation is between silica (quartz) and chrysotile, as happens in the transit pipe industry. The lung tissue becomes diffusely and densely carnified^leaving very little viable and functional lung. This happens rela tively swiftly and the tragedy is that the fibrogenic process goes on relent lessly long after exposure to dust has ceased. This silica destroys what chrysotile avoids and vice versa. The lesions produced by amosite or crocidolite acting alone are very severe (grades 7 and 8). Characteristically the fibrous amosite or crocido lite fibers seek out perivenous, perilobular, and pleural lymph and tissues (fig. 25). Dense sclerosis results in a weblike manner, thus producing severe pulmonary restrictive damage. There is so much fibrous tissue that the causa tive crocidolite fibers are relatively scarce and difficult to detect, espe cially since these fibers are less ferrophilic than the less harmful chryso tile fibers (fig. 26). Proliferation of pleural mesothelium is a classical sequel to crocidolite exposure which leads to neoplasis (mesothelioma) in a high proportion of cases (fig. 27). Experimental Evidence The differential pathogenicity of silicates has been experimentally ( 9 ) , probed by this author and several others. Some results researches have been published but much additional of personal data remain to be reported. One of the principle experiments was to explore the comparative effects of fibrous and nonfibrous types of silicates and to evaluate the pathogenicity of long versus short fibers and ball-milled fiberless silicates. The intra tracheal, intravenous, intracardiac, intracerebral, intraocular subcutaneous and inhalation routes were utilized by this author. Others have experimented additionally with the intrapleural and intraperitoneal routes. Rats, guinea pigs, rabbits, and monkeys were the principal experimental subjects of this author. Others have also conducted experiments on mice, cats, dogs, and hamsters. Talc has consistently stood out in all experiments as an inert material. It could be injected into diverse tissues in relatively large quantities with out evoking the least reaction. When introduced into the bloodstream, talc was still found cirulating freely after 18 months. In this respect talc dif fers radically from silica (as quartz) which vanished from the bloodstream within hours after intravenous or intracardiac introduction. The experiment with talc was limited to a study of the nonfibrous form of the silicate. No fibrous talc was obtainable and by the aformentioned physico chemical definition probably does not exist. Tremolite could be studied in both its particulate and rod or needle form. As a particulate variant (even when there were up to 5 percent rods) tremolite proved wholly inert. As the proportion of rods was increased, about 20 percent of focal lesions were demonstrable in the experimental aminals. Intratracheal 66 FIG UR E 25. - Proliferation of perivenous tissues in person occupa tionally exposed to amosite dust (X 100). FIG UR E 26. - Typical crocidolite fiber in pulmonary lesion (X 400). FIGURE 27. - Pleural mesothelioma which developed after prolonged exposure to crocidolite (X 100). 67 injection induced significant pulmonary pathology. By inhalation, however, the tremolite proved relatively innocuous, even though some fibers were trapped in alveolar phagocytes and converted to "tremolite" bodies (fig. 28). Although these bodies resemble those of asbestos, the tremolite bodies do not have the ominous significance of the asbestos bodies. When the effects of short tremolite rods (less than 5 microns) were compared with long rods (20 to 50 micrometers) an interesting result was obtained. The short needles proved inert. The long tremolite rods induced tissue reaction. This emphasized the fact that it is not the chemical composition which is the basis for biological reactivity to the silicate but only the elongated shape of particles which furnishes a pathogenic stimulus. Comparable results were obtained with anthophyllite and chrysotile. Long fibers (20 to 50 micrometers) consistently induced pulmonary lesions in all experiments. These varied in severity according to dose or duration. When fibers were milled to less than 5 micron length neither of these silicates produced significant pathological responses in experimental animals. This reaffirmed the principle that it is the length of the anthophyllite or chryso tile fiber particles and not their chemical composition which serves as the pathogenic stimulus. This author has not had comprehensive personal experience with the effects of amosite or crocidolite on experimental animals. The few experi ments personally performed and review of the sparse literature on this subject confirms, however, that these two silicates are significantly more pathogenic to diverse animal species than is either anthophyllite or chrysotile. This reaffirms the high pathogenicity classification offered in table 3. FIGUR E 28. - Tremolite body located with in alveolar space of guinea pig fol lowing prolonged daily inhalation exposure at concentration of 1 mg per cubic foot of air (X 400). 68 A further principle was brought out in parallel experiments with fiber glass. Inhalation by guinea pigs of long and short fibers did not result in interstitial fibrosis. These glass fibers were 5 microns or more in caliber. An experiment performed with fibers less than one-twentieth of this diameter (average 0.2 micron) resulted in significant pulmonary fibrogenesis. This result suggests that the biological activity of glass in particular and per haps other fibrous silicates may be a product of either the particle length or particle diameter. It is not known at this stage if this principle would truly apply to all fibrous silicates. Nor is it known whether length and fine ness of fiber caliber can potentiate each other in producing tissue responses. The latter experiment still needs to be performed. There is, however, some human evidence that this may be the case. The electron microscope has in recent years been applied to the study of pneumoconiotic lesions. Through this instrumental modality it has been possible to demonstrate large numbers of extremely fine asbestos fibers within pulmonary fibrotic lesions which appeared almost devoid of "asbestos bodies" as visualized by conventional optical microscopy. Electron microscopy has also revealed that there are many delicate fibers among conventional-sized fibers normally discernable in ^ asbestos dusts as viewed by maximum magnification optical microscopy. Similar fine submicron fibrils have not been observed in specimens of talc or tremolite. The presence of these ultramicroscopio components in asbestos minerals, therefore, constitutes a further explanation for the great differences between the biological actions of the talcs and asbestiform silicates. ' Carcinogenicity The controversy over the carcinogenicity of some asbestos minerals and the applicability of this to the talcs now requires closer examination. The propensity of crocidolite and amosite to evoke neoplastic responses in man has been a well-documented phenomenon for more than half a century, requiring almost no further elaboration except the following comments: (1) There is today less lung cancer in crocidolite workers than formerly because of improved dust control; (2) pleural mesotheliomatosis has recently emerged as an important neoplastic sequel to crocidolite exposure; (3) there is an enhanced prevalence of cancer of nonpulmonary tissues in employees ot crocidolite industries; (4) cigarette smoking and urban air pollution have m recent years surfaced as a complicating issue, so that there may now be some doubt whether all crocidolite-associated neoplasia is exclusively due to the crocidolite; (5) inhalation experiments with crocidolite have not been con vincing in demonstrating neoplasiogenesis; (6) implantation studies, espec i a u f p i "ural .pace deposition of U r g e quantities of crocidolite have show, a positive correlation between oncogenesis and crocidolite dosage, (7) latter observation is mitigated by the experimental demonstration that ordi narily noncarcinogenic substances, such as quartz dust, canalso produce pleural mesotheliomatosis, so that the pleural response is m a sense nonspecific. Amosite probably also is carcinogenic though perhaps not as decisively as is crocidolite. There also is some question whether the crocidolite or site are in themselves carcinogenic or whether other chemicals, with which 69 these fibers are impregnated or mineralogically associated are the oncogenic agents. Benzpyrenes and cancer-producing metal salts (arsenic, nickel, beryllium) have been demonstrated in crocidolite and amosite ores. Nothing comparable has been demonstrated for talc or tremolite. Because the latter has been classified as an amphibole mineral, it has naturally come under suspicion as a theoretical carcinogen. Theory and fact, however, have never matched up in either human experience or animal experimentation. For decades workmen have been engaged in talc and tremolite mining or milling or have been exposed to talc products in secondary industries employing talc and tremolite as slippage agents or fillers or for insulating purposes, etc. Excess prevalence of lung cancer, which could not equally reasonably have been accounted for in terms of exposure to cigarette smoke, urban pollution or to prior, concurrent, or sequential exposure to true asbestos, has been convinc ingly recorded. One of the earlier epidemiological surveys of tremolite miners in New York State did hint at an enhanced incidence of lung cancer among relatively young, 45- to 55-year-old, employees of selected mines. This was a disturbing observation. However, subsequent surveys of the same miners have shown a dis tinctly lower incidence of neoplasia even though the miners now were an aver age of 1 decade older with commensurately longer tremolite exposure and, of course, with longer periods of cigarette smoking. Two explanations may clar ify this change. The first is that the average level of dustiness in the tremolite miners had been appreciably reduced during the past 2 decades. Prior to the institution of vigorous dust control, it was not uncommon to find mine and mill workers smothered in clouds of tremolite dust-- particle counts probably having been 100 to 1,000 times greater than has recently been per mitted. The second feature uncovered by detailed analyses of the work histo ries of the tremolite industry employees of the prior era (that is before 1955) showed that with rare exceptions all these employees had spent a large part of their working lives in industries other than talc mining. Many had been exposed to asbestos or to rock and metal ore dusts. Analysis of the lung tissue of a representative number of these employees confirmed the presence of quartz, asbestos, metals, and other substances. This clearly created doubt whether the earlier epidemiological findings have true validity with respect to tremolite. The alleged carcinogenicity of chrysotile, which is mined in the vicinity of one of the major tremolite deposits in North America, has been an addi tional confusing factor. Persons who are not thoroughly familiar with the rather major mineralogical and biological differences between tremolite and chrysotile may have been confused by the geological close association of these ore bodies and the erroneous assumption that both tremolite and chrysotile are asbestos minerals. The latter issue has already been discussed and it has been established that, although tremolite may be an amphibolelike substance such as anthophyllite, amosite, or crocidolite, there are no premises for assuming that tremolite is likely to behave biologically as do the other three amphiboles. 70 Is chrysotile a carcinogen? This is a very perplexing question. A crescendo of popular opinion has sought to incriminate chrysotile. This author remains unconvinced. The main premise for carcinogenicity stems from epidemiological observation of employees of the insulation and shipbuilding industries. In both these industries there has been in the past considerable exposure of pipe laggers to asbestos dust. Only in recent decades, however, have these insulation bats been composed predominantly of chrysotile.^ In former years crocidolite and amosite were important components. Studies of lung tissues of deceased laggers have verified the presence of amphibole as well of serpentine asbestos. Which then was the carcinogen? It is a known fact also that in recent years fiberglass has to an increasing extent begun to substitute for asbestos in this industry. The increasing demonstration of lung cancer in insulation workers coincides with the latter event. Which agent then is the carcinogen? It is further known that insulation workers have during decades become heavily exposed to methylethyl ketone-type solvents in the synthetic glues presently used to bond the bats of asbestos or fiber glass to the pipes or ducts which are being insulated. Formerly the glues did not contain such highly volatile solvents. Indeed, one of the occupational diseases of significance in this industry now is polyneuropathy due to the inhaled solvent vapors. These solvents come in direct contact with respira tory epithelial surfaces, whose lipid surface membranes and organelles are highly vulnerable since they are readily solubilized into methylethyl ketones or similar solvents. Which then is the true carcinogenic substance? Finally, it should be pointed out that the role of cigarette smoking has not been satisfactorily discounted in the referenced epidemiological studies of lung cancer among insulation workers. In some groups reported an excess prevalence of lung cancer was not demonstrable when cigarette smoking was taken into consideration. Epidemiological surveys of chrysotile workers in ^ Quebec showed no excess of lung cancer. A review of pleural mesothiliomatosis in Canada also failed to focus attention on Quebec or any other center where chrysotile industries are concentrated. There also is conflicting experimental evidence about chrysotile. In one personally conducted study the theoretical carcinogenicity of chrysotile asbestos was probed by an inhalation study in which tumor induction in rats exposed to beryllium sulfate (a potent carcinogen) was compared with tumor rates in rats similarly exposed to chrysotile dust and to chrysotile foil g 1_). beryllium sulfate and also to chrysotile dust BeS04 . The results were striking (2, In exposure preceding exposure to the beryllium group the mean incidence of lung cancers was 15.4 percent. In rats exposed to both chryso tile and BeS04 , the malignant tumors totaled only 8.5 Percnt- No tumors developed in t s which were exposed only to chrysotile and there were o n undosed controls observed for 24 months. This clearly shows that so f" J rom chrysotile acting as a carcinogen or as a cocarcinogen with a known potent carcinogen, the chrysotile behaved like an anticarcinogen with respect to the beryllium. Mention may also be made of an experiment conducted with Mtoral versus synthetic chrysotile deposited into the pleural space. The U t t ciated with some tumor production. The synthetic chrysotile had the contr y 71 effect (1). The difference between the two is that natural chrysotile some times is contaminated with metallic salts absorbed by the serpentine fiber surfaces or perhaps trapped within the chrysotile tubules. Some of these metals include known carcinogens such as nickel, chromium, and arsenic. Since these metals are not universally present in equal degree in all samples of chrysotile, caution must be used in stigmatizing this mineral unnecessarily as a carcinogen. It should also be stressed that the intrapleural experiment is highly artificial so that cancer production by this technique may be expected with true carcinogens as well as with substances which are not ordinarily car cinogenic for man (for example silica). The demonstration, therefore, that synthetic chrysotile, natural tremolite, and talc are incapable of evoking pleural mesotheliosis may be highly significant testimony that these sub stances may not possess latent carcinogenic properties for man. Sequelae and Complications Carcinogenesis has been separately discussed since it is not established whether it is an independent property of carcinogenic minerals or a sequel or complication of the pneumoconiotic pathology induced by these silicates. It is necessary to review several principle sequelae and complications of exposure to dusts. The first is tuberculosis. The close association between pulmonary tuberculosis and silica inhalation has been convincingly established through epidemiological studies and experimental inquiry and the pathogenic principles f(5o)r. tuberculogenesis by Do the silicates siliceous minerals has probably been fully clarified also promote the development of pulmonary tuberculosis? There is no real epidemiological evidence for this and no laboratory proof. The relatively closed communities in South Africa where crocidolite and amo site are mined and processed and the comparably closed community in Quebec where chrysotile is produced constitute excellent epidemiological models. No significant excess of tuberculosis has been demonstrated for these occupa tional groups whose life careers could be followed to a satisfactory degree. A large number of these miners and mill workers were personally studied by this author and a number of necropsy specimens were likewise examined. By contrast with silica workers, tuberculosis was consistently conspicuous by its absence or infrequency. Since the pathogenic asbestiform silicates proved nontuberculogenic, it is no surprise that tuberculosis has not been associated with talc and tremo lite mining. Of 300 mine and mill workers who have been followed over the past 25 years not a single individual developed tuberculosis. This is an amazing record, which speaks for itself since tuberculosis is by no means a conquered disease, especially among industrial workers. Heart Disease There are no indications that arteriosclerotic heart disease is any more prevalent in asbestos workers than in the general population. The incidence indeed appears to be lower. This may be due to the excess prevalence of cor 72 FIG U R E 29. - Partly destroyed blood ves sel in lung of asbestos work er (X 10). FIGUR E 30. - Perivascular fibrosis show ing stenosis of pulmonary blood vessels. Silica and asbestos t v irv\ FIGUR E 31. - Asbestos bodies in wall of blood vessel as demonstrated by Perl's stain. Mixed amosite and chrysotile exposure (X 10). 73 pulmonale. The latter constitutes a significant problem and has a direct explanation m the perivenous pulmonary fibrosis and elastosis and the conse quent destruction of the vascular system (figs. 29 to 31). in tremolite workers some cor pulmonale does occur. This is usually traceable to prior, concurrent, or subsequent exposure to asbestos dust. Review of the life histories of 300 tremolite employees shows an incidence of 8.3 percent of the fatal cardiac disease. This is not significantly different from the occurrence of arteriosclerotic heart disease among age-matched con- I h l l troi groups that never were exposed to tremolite. Less is know about pure ^ dUS^rial *"*- Jhe lack of epidemiological data at least established that thus far no problem has surfaced. Emphysema, Bronchitis, and Bronchiectasis So many industrial agents cause emphysema and/or bronchitis (4) that an inquiry about this matter seems pertinent. There are no indications that either emphysema or bronchitis are selec tively more prevalent among asbestos workers than with the general public The underlying pathology induced by asbestos is not of such a nature as to foster either of these conditions. There is no primary bronchopathy and con sequently no alveolar distension induced by obstruction. Nor is there alveo lar mural destruction. The very nature of asbestosis protects the lungs against this, since the fibrous and elastic tissue in the alveolar walls strengthens rather than weakens these structures (fig. 23). At a later stage there may be some compensatory emphysema as areas of the lung collapse. This is, however, limited and regional only. Bronchiectasia is another matter. It is quite a common sequel of pro gressive interstitial pulmonary fibrosis in asbestosis. The bronchi and bronchioles are distended by the contraction of fibrous tissue in the pulmo nary parenchyma between them. This form of lung pathology may be seen as a late sequel of crocidolite, amosite, or chrysotile asbestosis. Unlike bron chiectasis in nonoccupational groups, the asbestotic form of the disease is initially nonsymptomatic because there is little or no associated infection. However, the latter may occur later. None of this is seen with pure talc workers. There has been no excess prevalence of either emphysema, bronchitis, or bronchiectasis unless there has been prior or concurrent or subsequent asbestos exposure. Precise epidemio logical data are available for tremolite workers. Thus, of 264 employees fol lowed since 1948 only four developed emphysema. This reflects an incidence of approximately 1.51 percent. This is far below the incidence of emphysema in the general population. Bronchitis without emphysema was observed in seven individuals. No bronchiectasis was found among these workers. This clearly shows that talc and tremolite not only behave differently from chrysotile, amosite, or crocidolite but may even be associated with a lower incidence of these disorders which now are among the most prevalent and disabling illnesses in North America. Whether talc or tremolite protect the lungs against 74 ''zsrxzzr" - ? ^ " iL w answered affirmatively on the basis or tne and can be Conclusion W ^ d Pt t ^ " l"ariy" S deM " i i i l Cp r o ^ S X l c f H i t T i i l l e t . of asphalt rubber and roofing materials,^as ceramics, paints, insecticides, P P . arting'compounds. A small proportion wire and cable coverings, or as foundryJ ^ o c L s S industries. Through of talc enters into the toiletry an subiects come into contact with ttahllcSea"ndd1treSmdoliiutae Stfoorreeavverayi rem^pidujyai Contributing & to tphraoldrucptrioodnu.ctioInt, isAmdeirf- ica produces and uses "^ J ^ ^ ^ i o n ficult to imagine how modern civilizati ful and relatively inexpensive minerals. pan be sustained without these usev _ .. hhovofm-P that talc and tremolite are so biologi- It seems fortunate, therefore, ithat t t0 eliminate all tally inert. There is environmental hazards. No one q w" h the humanitarian ideology . materials have been haphaz- inspiring such enthusiasms. Too trnny h a t a ^ H t " Cld bC better to control ardly released into the human environment an security. Not only does ,11 industrial ^ s t a n c e s "7 this seem logical, but it seems re ill unnecessarily increase the cos up the orks somewhere along the lane. t0 counsel against restraints which f everyone or which may gum and artlc. r.p laes itself as ularly the t L s e Pdefenses can he OTerahelmed"through long exposure to " ^ " `^ " ^ " 'Thirfac^should be ST.S for dust control in the talc industry. Summary 1. The physicochemical relationships of Although there are superficia resem an empirical formulas of olite, there are significant 2. Mineral silicates may he best c l a s s i f ^ i n terms ofjheir capa^ity^ to be formed as sheets, tubules, r " a1' icai c jassifications of serpentines instead of using the conventional mineralogrcal classitrca or amphiboles or of asbestiform minerals. , . rpiativelv inert substances and 3. Talc and tremolite are bl r,athoeenicity of amosite and crocido- S S ^Chrysotlle^ccupies^an^intermediate position, but its biological pro penalties are closer to those of talc and tremolite. 75 4. Experimental and epidemiological studies provide closely confirmatory data with respect to the points just mentioned. It is extremely difficult to identify large numbers of employees who have been exposed exclusively to one or another mineral. Many pulmonary lesions in silicate-industry employees are composites of multiple-dust and chemical exposures and many of the nocuous agents derive from sources other than the silicate industry in question. 5. Lung cancer has been definitely associated epidemiologically with exposure to crocidolite. There is no evidence that talc or tremolite possess the biological propensity to induce neoplastic lesions. There also is some doubt as to the role of chrysotile in carcinogenesis. Even though some stud ies suggest that chrysotile may foster the development of lung cancer under certain circumstances, other studies flatly contradict this evidence so that the issue still seems unresolved. 6. The sequelae and complications of exposure to asbestos include bron chiectasis and cor pulmonale. Obstructive bronchopathy and emphysema do not normally occur as a consequence of exposure to asbestos. Talc and tremolite exposure are devoid of any of these pathological responses. 76 References 1. Gross, P. Fibrous Dust Seminar Industrial Hygiene Foundation of America. ' Medical Bull., No. 16, 1970. ,, , 2- 601. ~ TT u Rinlncriral Effects of Asbestos. Annals of the New m , 1 3 2 . 2 , 385, 7 , * * . . Chronic Berylliosis. Archiv fr Gewerbepath und Gewerbehyg, v. 19, 3. 1962. . Industrial Bronchitis and Asthma. Ind. Medicine and Surgery, 4. v. 24, 1955, p. 52. Silicosis and Tuberculosis. Ind. Medicine and Surgery, v. 33, 5. 1964, p. 381. 6< _____ . Thesaurosis Versus Sarcoidosis. JAMA, v. 181, 1962, p. 635. 7. . Tumors of Primates and Rodents. Ind. Medicine and Surgery, v. 40, ' 1971, p. 48. 8- L TwThTM,, .; 2j,?T- Km S ; Durkan , * * 1 The Effects of - Inhaled .Talc .Mining p. 182. 9. . An Experimental Study of the Effects of Talc Dust on Animal Tissue. AMA Archives Industrial Health, v. 12, 1955, p. 77 applicability of asbestos standard to fibrous talc by William J. Nicholson, Ph.D.1 I would like to speak about the application of the current asbestos stan dard to fibrous talcs, to tremolite, and to the variety of fibrous minerals that are found in several of the talc deposits, especially those talc deposits that have widespread industrial use in the United States. Specifically, I would like to demonstrate here that health data indicate that all fibrous min eral material should be considered equally for the purpose of standard setting, that the current asbestos standard is limited in its provisions and represents a bare minimum standard for all fibrous minerals, and, finally, that control measures exist that would reduce dust concentrations in mines and mills below those required by the current asbestos standard. Let me briefly go into some of the background of the asbestos standard and the data that led to the specification of a current standard of five fibers per milliliter of air and a later standard in 1976 of two fibers. The standard specifically includes the six asbestiform minerals--amosite, crocidolite, chrysotile, tremolite, anthophyllite, and actinolite--and it is appli cable to all industries covered by the Department of Labor in the United States. The equality of consideration of the various minerals has a back ground in several studies. For example, crocidolite and its severe problems have been documented in work that has come out of South Africa and Great Britain in studies by Dr. Wagner and Dr. Newhouse. In the United States, data have been developed by Dr. Selikoff of the Mount Sinai School of Medicine on the mortality experience of factory workers exposed only to amosite. Here, one finds that roughly half of those individuals who died, died either of cancer or asbestosis. More extensive data have developed among the insulation workers. These workers have been exposed predominantly to chrysotile, also to a little amo site during World War II and since World War II, especially in shipyards. Of that group of workers, one in five who died, died of lung cancer, nearly one in 10 of mesothelioma, one in 10 of gastrointestinal cancer, three times the expected amount, and almost 10 percent died of other forms of cancer. Another 7 percent of the deaths are from asbestosis--scarring of the lungs. All told 53 percent of the deaths of a group of New York and New Jersey insulation workers are from one of these two sources--asbestosis or cancer. Nearly 40 percent of their total deaths can be related to their occupational exposure to asbestos. We can also consider a major asbestos manufacturing facility, one which uses extensive amounts of chrysotile. In fact, 95 percent of the manufactured products (asbestos used in manufacturing) in the United States utilize 1Mount Sinai School of Medicine of the City University of New York. 78 chrysotile asbestos. Again the same statistics are obtained, with excep tion, and that is in the textile department. Here, the percentage of deaths die to cancer were relatively low, about 20 percent. This came about because the deaths due to pneumoconiosis in the textile department resulting from the extremely high dust concentrations exceeded 40 percent. So we have the grim data that pneumoconiosis can, in one sense, protect against cancer. ese persons die before they reach the time of onset of lung cancer or any of t other cancers. In fact, the period of time from onset of exposure to death _ due to either mesothelioma or lung cancer among asbestos insulation workers xs about 35 years. Very few deaths occur prior to 30 years, virtually none prior To ll years since onset of exposure. The cancers we are speaking about, those associated with occupational exposure to asbestos, are a long time in coming. If any cause gives rise to death prior to that, then the cancers will not be seen. If we look now at the very limited data available on the mortality of talc miners and millers, we see that asbestos exposure results m similar causes of death. In the early data of Kleinfeld, for example, we have infor mation on 91 workers and the causes of their death, which were as follows. 2o!9 percent, malignancies; 27.5 percent, cardiac deaths (other than cor oulmonale); 30.7 percent, pneumoconiosis; and the remaining 20.9 percent, oiher caus^. Approximately half the deaths attributed to malignancy were due to cancers of the lung and pleura. While we have only limited data on what happens to humans exposed to talc mine dust containing the wide variety of minerals Dr. Langer has described for you the mortality data we do have indicates that the mining and use of such minerals compares should be treated with the mining and milling extreme of talc caution. with the In fact, as mining and m f an aside, ll8 c iTMf ~ o dian chrysotile as reported by McDonald, one would postulate that talc is a materia/that is far more dangerous than chrysotile. However, I do not think that this is necessarily an appropriate assumption to make. From the data we have I do think it can be said at this time that there is no reason for saying that any one of the asbestos varieties or a fibrous talc is more carcinogenic or less carcinogenic or more fibrogenic or less fibrogemc than another. Some animal data have been referred to previously in this symposium. Virtually all such data must be considered with caution. They can be usedto indicate^potential problems and, indeed, problems have been suggested by n mal experiments. For instance, recent data from the National Cancer Institute (NCI) indicate that all durable fibrous material, re.spec v ely f heir chemical composition, when implanted on the pleura TlwinZ cinogenwith equal intensity. For example, fibrous glass, fibrous alumi o S d f and the various forms of asbestos in these NCI experiments induced mesothelioma at approximately the same frequency. Similar experiments in Germany in which fibrous glass, several varieties of asbestos, and flbr were iniected into the peritoneum of animals also produced mesothe- U o m l rougMy of^qualintensity. I think in this case nemolite was the most carcinogenic.7 Thus, two separate experiments with animals indicate that wideVariety of fibrous materials are equally potentially dangerous. 79 A technical reason also indicates that all fibrous mineral material should be treated equally in a standard. It is impossible for an individual technician, counting fibers in an industrial air sample, to distinguish whether it is a fibrous talc, an asbestos mineral, or any other mineral fiber. All one can determine, using a phase contrast microscope, is the presence of a fiber, determined by its length and width. Without the very sophisticated instrumentation that you have already heard about, it is inappropriate to require that a dust counter, either in the Bureau of Mines or in industry, dis tinguish between fibrous minerals. Currently, in a mixed exposure with asbestos, no such discrimination is made by the U.S. Department of Labor in assessing exposure. The data we have just discussed, the evidence Dr. Danger has presented of asbestos in talc deposits, the finding of severe health problems in one group of talc mines and mills, the similarity in toxicity of all fibrous minerals in animals, and the inability of a technician to distinguish one fiber from another using a phase contrast microscope, all these indicators show that the standard for asbestos should be applied to all fibrous minerals in talc mines and mills. When one suggests that the asbestos standard be equally applicable to the fibrous minerals associated with talc, let us briefly consider the background that led to that standard to get an appreciation of its adequacy here. Infor mation on dust levels associated with disease is limited. Six studies have documented asbestos dust levels in insulation work. All of them give average exposures ranging from 10 to 15 fibers per milliliter of air, but none were done 20 to 30 years ago directly on the groups of workers whose mortality has been documented. In a recent group of workers that were examined by Dr. Selikoff much lower exposure levels were associated with radiographic evi dence of asbestosis. These were workmen who sand the taping compound, the spackly that is applied to the joints of wallboard. In the past they did this no more.than 20 percent of their time and now, even less. Dust counts here showed average exposures on the order of five fibers per milliliter or less when sanding. These data give no comfort with a standard of five fibers per milliliter. When one speaks of dust count in terms of fibers per milliliter of air, it should be recognized that one is looking only at the tip of an iceberg. The standard specifies that only fibers longer than five microns be counted, because these fibers are readily seen in an optical microscope. In the elec tron microscope, myriads of shorter fibers can be seen. This would not be a problem if the fraction counted were the same in all exposures. Unfortunately, it is not. In chrysotile exposures we have seen the fraction counted to be 1 in 250, or 1 in 50, or even 1 in 20. When other asbestos minerals were counted, such as amosite, the fraction could be as great as 1 in 3. So, what we have is a standard that specifies determining an asbestos exposure with what is really a rubber yardstick. We are looking at tips of icebergs, but the icebergs, unfortunately, have variable densities. What we have, really, is only a very qualitative estimate of exposure in any occupational circum stances where fibers are determined by this standard. One should exercise extreme caution in certifying that a work place is safe to a workman who may 80 have to spend 8 hours per day, 5 days per week, 50 weeks per year in such an environment. Moreover, in considering this standard, little weight was given to a safety factor that would be possibility for a threshold appropriate for cancer. No for asbestos-induced cancer data and exist onTMthe cation that the five fibers per milliliter currently specified as ^ defined as it is, provides adequate protection against cancer for U.S. workmen using asbestos and other fibers. Finally, the data on the incidence of asbestosis which went into the cur rent standard and which received great weight are now in doubt. The data were concerned with the prevalence of asbestosis in men who worked only after the application of dust control measures from 1931 to 1933 in a British asbestos factory. The men were examined in 1966. All were stxll at work and only 13 individuals in the study group had more than 30 years of exposure. That same group now has been reexamined 5 years later and the data have been pub lished. There is considerably more evidence of asbestosxs among the worker than was first published, perhaps 10 times as much. Thus, we see that the asbestos standard that I suggest be applied bere' as it has been in the past, to the fibrous forms of talc and tremolite is a standard that is really a very inadequate one. It represents an absolute m m inum standard. We do not have the luxury of relaxing it whatsoever. Moreover, the full scope of that standard should be applied to the fibrous minerals con sidered here! Mandatory monitoring and surveillance, the JPplicationofengx peering controls, the use of personnel protection equipment, the availability of change rooms for workmen, and periodic medical examinations are import n parts of that standard. Along with such protection for the workmen it is necessarythatlabeling provisions similar to those in the asbestos standard apply to the fibrous talc and the fibrous minerals that may be present in talc. Much of.thes^ ^ a^ al are later used in industry. The rubber industry is one extensive user that has already been mentioned. Similarly, concern for exposure extends into the consumer area For instance, last summer the Board of Education of New York City found that they had in their stockrooms modeling material that `' " ^ i t h 50 percent asbestos. This was used by children who mixed the P ^ * r ^ th y o d e l s water to form a paste that could be used for shaping various and art t o l d works. The Board of Education went to the supplier and him.that th material was unsafe and they did not want to use it. He said, We 11 c h u g our formulation." The formulation that came back substituted fibrous t 1 from the Gouverneur deposit in New York for the asbestos Xhe f e r i a l dis plaved on the slides by Dr. Langer was the material that was substituted for S s t o d e u S S e r i a l 7 Again, the City of Be York did because of the concern for health. Caution labels as applied in the curren asbestos standard are eertainly applicable to all such fibrous mineral mate rial that can be disseminated into the air. The concern for surveillance and maintaining a safe environment in the mines extends into the community and here the currently proposed standard of 81 the Environmental Protection Agencv , concerned with the monitoring of m U s sione does not consider mines ,,,d ,,,i u ; nn " Spe'ial burden n U x . TM standard for asbestos emls- from such sources will be controlled by thim? t U"Ptln that TMlssi.ons measures 1,, the work place. I only h o L t h ^ f f f " PPtoptiate control justified. y nope this confidence of the EPA is I L Control is feasible t where average fiber levels, dl t e m i n e d ^ v Department of Health, ranged from tio to fi^e pure asbestos ore, levels were achieved t ^ dard I am suggesting be applied to ore bod* of fibrous material. dies I m l U in California f ^ f ^ and the State P6r milliliter- With ln comPliance with the stan- containing only a small fraction . In suramary, I would strongly urge that- t-v,Q , m the past be continued. The e L ^ n g applied to fibrous talc and the v 2 Is tI^ d ! ^ d T r T Which W3S fHowed asbestos should be Equal application of the standard all Preaant in the talc, health and technical reasons, ^ e standard t 2 iS diCtated ^ tively weak one and no relaxation of it should 2 3Ppl^ d 1S} in fact> a rela- application of such a standard is app^opria^ h considered. Finally, the exist that will allow it to be met PFropriate because engineering controls 82 ASPECTS OF MINERALOGY OF TALC by Arthur M. Langer*1 My name is Arthur M. Langer. I am an Associate Professor of Mineralogy at the Mount Sinai School of Medicine. For the last 8 years I have been pro fessionally associated with the Environmental Sciences Laboratory in that institution. I serve as Head of the Physical Sciences Section. My research has concentrated in the environmental and occupational health areas. My fiel of specialization is mineralogy, and I concern myself with the identification of biologically important mineral particles in the environment, identification, and characterization of mineral particles in human tissues, and in various types of consumer products. I have written many papers in these areas, and they are available upon request. I am going to apologize because I was not present at the symposium this morning. I think that some of my statement might be a review of what has pre viously been covered. However, some of these points are important and worth stressing again. I would like to emphasize, first, the complex nature of the term "talc." Talc is a mineral species. However, the word talc, as often used in industry, refers to a property rather than a true mineral entity. Finely ground-up ^ _ material with a resultant high surface area is often called talc. The simi larity ends here between the mineral talc and "talc" as used in the industrial experience. The same word, therefore, means different things to different people. One must define mineralogically the "talc" in question. Talc geologi cally forms, generally, from an altered ultramafic rock, one which is composed mainly of magnesium silicates. Anthophyllite and serpentine asbestos ^ (chrysotile) may form during this process as well. Talc may also originate through the metamorphism of a carbonate rock with the introduction of sill In this latter rock type the introduction of silica would produce calcium m gnesium silicates which may include the asbestos mineral tremolite. There are 10 States in the continental United States that are major producers of talc. In each of these States there is generally a different geologic material respon s i b L for the talc production. The nature of these deposits may be extremely complex. For example, at the Gouverneur, New York, talc deposit, several o thePasbestos fibe/types occur with the talc. The senior author of a paper on that deposit is here in the audience, Dr. Malcolm Ross of the U.S. Geological Survey. He and his colleagues published their findings in the American Mineralogist." I would recommend this paper to anyone wishing to learn about the complexities of the talc deposits. Talc deposits are complex and almost always include asbestos as a natural contaminant.______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1Associate Professor--Mineralogy, Mount Sinai School of Medicine of the City University of New York. 83 Vi 1th experiences of some r^,=`~"r ,, r c r '.rr, s f Br. Weinfeld ^ ^ " t o t -- miners and 1 ^ e X u e h * r t " S c S - they m i l representative of ma y there are fine talcs t be intergrown with TsT S ob S M l . ^ U " ;BeS eS tfe%utfight, ^ StCedP CorSthe o r e ^ c a u s e e ; , s r ^ r i a c ^ a n y intK8rain boun; r ' ^ ^ r e four r ^ ^ anthophyllite, ocidol^e, into consideration becau ^ nt-her fiber types do- in Z^^SSSi do not commonly occur y forefflentioned e York S common tremolite. S" talc deposit there calcium magnesium ROecies of tremolite s s . "^ - ds : r" i a in the biological env1" "" asbestos, serpentine mine S addition to the amphiboly a MbettoB fibers ocean: in amounts. ocQur naturally and chrysotile. r t i l f / a P O S i t s . these are anthophyll , lea! Me prefer to 1 rtcrirally characterize talc from asbestos. How does one ^ineralogicajT ^ to differentiate t a l ^ electron micro r^tX ed information ^ nc^ ^ strument). We are able ^ separate fibrou* ^ ar electron probe-typei them. W e can ^ u t i n ^ ^ more curvilinear eralsa from>asbestos. S talc ay be characterised, i u t met desoribe s e 'E5SiS>l!rrTl S i * ls ,,hat the fibrous 84 FIG UR E 1. - Transmission electron micrograph of a typical fibrous talc sample ram the Gouverneur deposit, New York State. Fibers constitute a significant p ro p Hon of the sample. The fiber population is made up of talc fibers, tremolite, and anthophyllite. Arrow in center of photograph indicates a 2- by 10-microm eter fiber of tremolite. (Magnification unknown.) one of the major mineral phases within the sample (table 1). Major < ents in all cases were also anthophyllite and tremolite. other" * lvtical techniques supported this observation as well. With high-resolutio transmission electron^microscopy, one sees that talc plate, may contain many different mineral entities with a single grain. Intergrowth, of talc with asbestos minerals are common (fig. 2). What the biol.ogical consequences iire incumbent upon the inhalation of large quantities of such y be retained on a cellular level for a very long time period, is presen ly unknown. We do know, from our experience with microchemical analysis of 85 asbestos fibers, that particles are chemically degraded while residing in vivo. They also have an extremely long period of residence in the biological systems, talc particles themselves may be intergrowths of many mineral phases, some of which may be asbestos. TABLE 1. - Minerals identified in the New York State fibrous talc deposit by X-rav diffraction* 3 3 Sample TALC TREM ANTH SERP CHLOR Sample talc TREM ANTH SERP CHLOR 1 .......... MAJ MAJ MAJ MAJ TR 9......... MAJ MAJ MAJ MAJ TR 2 .......... MIN MAJ MAJ MIN TR 3 .......... MAJ MAJ MAJ MAJ TR 10......... MAJ MAJ MAJ MAJ TR 11......... MAJ MAJ MAJ MAJ TR 4 .......... MAJ MAJ MAJ MAJ TR 12......... MAJ MAJ MAJ MIN TR 5 .......... MAJ MAJ MAJ MAJ NIL 13......... MAJ MAJ MAJ MAJ TR 6.......... MAJ MAJ MAJ MAJ TR 14......... MAJ MAJ MAJ MAJ NIL 7.......... MAJ MAJ MAJ MAJ NIL 15......... MIN MAJ MIN MAJ NIL 8 .......... MAJ MAJ MAJ MAJ TR 16......... MAJ MAJ MIN MAJ TR MAJ Major phase. MIN Minor phase (only most intense reflections are visible). TR Trace (major peaks discernible but just above background). NIL No peaks observed. 1Prominent mineral phases: TALC = the mineral talc; TREM = tremolite; ANTH = anthophyllite; SERP = serpentine minerals; CHLOR = chlorite. s0ther phases observed: Mg-rich calcite; phlogopite (?); pyrophyllite; pyroxene, various diopside. 3The number of peaks observed in the scans 3 to 70 2 0 (theta) averaged about 60 with intensities 5 times greater than background. All visible reflections numbered about 90. Many of the overlapping peaks were counted as single reflections. The above phases account for more than 85 percent of each sample analyzed. I will now discuss some of our experience in human case material. This illustration is an electron micrograph of a tissue obtained from a workman who worked in a rubber factory for 30 years (fig. 3). He worked with talc; the talcs used in this factory were fibrous talc. Those particles that you see are both amphibole and chrysotile asbestos fibers. It is possible to examine tissues of workmen exposed to talc dust and determine, with a high degree of certainty, what the mineral particles are which were retained in the lung tis sues . Examination of lung tissues of individuals who have worked with talc shows, invariably, that inhalation of talc dust means inhalation of asbestos as well.1 1 think that the major points stressed indicate that there are talcs, and there are talcs. Some mineral deposits are extremely complex and the mineral ogy reflects this. The methods recommended for proper characterization of talc would be polarized light microscopy, X-ray diffraction (using step scan ning mode), transmission electron microscopy with selected area electron dif fraction, and microchemical analysis. Asbestos minerals may be distinguished from talc in this manner. 86 FIG UR E 2. - Transmission electron micrograph of a talc " composite grain" from the Gouverneur deposit (arrow). The amphibole asbestos fiber to the right of the grain is about 0.2 micrometer thick. The amphibole fibers intergrown in the talc host are only several hundred angstroms in thickness. (Magni fication unknown.) FIG UR E 3. - Transmission electron micrograph of a carbon extracted lung tissue specimen fromaworkman exposed to talc dust in a rubber factory. This individual died of talcosis and lung cancer as primary causes. Autopsy revealed the presence of a primary cancer of the sigmoid colon. Most fibers shown in this photo graph are chrysotile. Talc plates arealso visible. (Magnification unknown.) 87 We would feel, and I think I am speaking for the rest of my group, that it would be prudent at this time for the Bureau of Mines not to change the present restrictions on fibrous talc. We feel that talc is a mixture of many different components, including asbestos, and that talc deposits themselves are extremely complex and zoned, so that any one mine cannot be counted upon to yield the same kind of dust by the month or even by the day. Thank you. This is the end of my formal presentation. I would like to add some pertinent remarks: I do not know whether this was discussed this morning, but I would like to comment on a group of men studied by Kleinfeld and colleagues (3.), who were exposed to talc dust at the mines and mills of Gouverneur, New York. None of the cohort of 39 men had X-ray evidence of pneumoconiosis. However, 25 percent showed clinical signs of shortness of breath, dyspnea, and cough, which could be correlated with early stages of pneumoconiosis. We have reported these observations in that paper. These men, exposed only some 16 years on the average, were apparently exposed to extremely high concentrations of talc dust so that on a comparative scale we would consider that talc contaminated with asbestos would be somewhat less fibrogenic than comparable dust exposures to pure asbestos. But there are several nuances here of which everyone should be aware. It takes an extremely long time for the clinical symptoms of disease related to asbestos exposure to manifest themselves. Generally, it takes 20 to 30 years from onset of expo sure to asbestos dust to bring about either lung scarring (asbestosis) or the various malignancies associated with the exposure. Therefore, in our report, we were very cautious. We indicated that the time period of observation of this small group of men was too short to really make any dramatic statement that tremolite talc, anthophyllite talc, or talc itself is a biologically less harmful material than pure asbestos. We feel that this group of men has to be followed for a much longer time period, and that malignancies, if they do occur, certainly would not appear for another 10 years at least. 88 Bibliography 1. Hobbs, A. A. A Type of Pneumoconiosis. Am. J. Roentgenology, v. 58, 1950, p. 488. 2. Kleinfeld, M . , J. Messite, 0. Kooyman, and M. H. Zaki. Mortality Among Talc Miners and Millers in New York State. AMA Archives of Environ mental Health, v. 14, 1967, p. 663. 3. Kleinfeld, M . , J. Messite, and A. A. Langer. A Study of Workers Exposed to Asbestiform Minerals in Commercial Talc Manufacture. Environmental Res., v. 6, June 1973. 4. Porro, F. W . , J. R. Patton, and A. A. Hobbs. Pneumoconiosis in the Talc Industry. Am. J. Roentgenology, v. 58, 1942, p. 488. 5. Ross, M . , W. L. Smith, and W. Ashton. Triclinic Talc and Associated Amphiboles From Gouverneur Mining District, New York. Am. Mineral., v. 53, 1968, p. 751. 89 MINERALOGY, IDENTIFICATION, AND QUANTIFICATION OF AIRBORNE TALC DUST by T. D. Oulton1 Introduction Johnston, v t . , 1 , together r t E h * f , 0,8 p U t y varlety unsaid p e r s S S I S m j j f ! f l "f1* tionai L a r i Which we intend to make tary - * - he te" e TM t and m h , w % r" j: "d that as left S 'f 10 "*- " d aPProPrtate. The points * ~ - discussed^by S j T ^ h l J J Pfred to that ot the asbestos minerals sl* S S went> in o j o;inio" qT t e ^ L i " r eSf : L " d T " ' " * " ** " the composition and crystalloRranhv of J h f complete exposition of m t 7 ogy l ^ a n r o f ! o i a ^ d o c TM e n t aa ^ rd e T CiStadeSCrlptlVe temlnol- IdentlflJtlons such as" " J e d thfr, "i" " ?escript1'TM -i-eralogical istration (OSHA), 29 CFR 1910 qqa h ccuPa tonal Safety and Health Admin- "amosite" L given equll w L L t L 't h \ trivial or trad* name such as for some of the other amphiboles w ? systematically correct nomenclature tion of the term "f i L ? L L e d in L , , t0 the Strained ^terpreta- little doubt about what is acSufllv m e L dcument. Although there can be 1S actually meant in the context, the term "fiber" in 90 general English usage certainly implies a whole set of functional properties quite distinct and different_from the so-called "fibrous" character assigned to at least some of the amphiboles. 4 We regard the blanket identification arbitrarily as "asbestos" or as "asbestiform" or any; particulate matter with a projected area length to di eter ratio of 3 t T l when observed at X 450 magnification by phase contrast microscopy as a completely unacceptable technical oversimplification, and we hnlri that the burden of proof that such an observed particulate can indeed be r a t e d oJUpr" en to be "asbestos" or an asbestos-related particulate lies wholly with the observer. 5 In furtherance of the preceding remarks, we fully support the conten- t - z & z z i = ttp f 8SlOTel I T techniquest^combined ith energy-dispersive electronanalysis 1. every M . : as powerful and in some cases even less ambiguous than is " . mi th selected area electron diffraction. The race is, microscopy these available techniques serve to complement and supple- these complexly interrelated minerals. We obiect to the very transparent attempt of the Mt. Sinai group ing^the^discussio^and evidence presented by Drs Kleinfeld, Shepers^and Smith, as well as the vital pe^snnel.rf^dhretiSCnecessarily an identifi- reviewed by Lamar, Mylryan, and Bacon)e ^ n be labeled as "tremolitosis." able pathological response to tremoli , merely restated the old The Mt. Sinai group had no new evidence to offer and merely rest ,, expect a paraprofessional field inspectionn highly complex diagnostic instrumentation beenmentioned above. On tlsfactlon and incredibility astoeiated^with phase contrast microscopic method 91 = and rofotrod to tho appropriate ^,1211^11X~ ^^1^-- ASTM an^oversimplistic S HuLZ^ T'''*1TM' BUt " ''lsh " > ^ . 1 ^ and milling industry could easil^result^atory document for the talc mining that an important American industrial T S6Vere economic dislocations to a p o i n t e r K i - W bo reduced The technical discussion which makpQ nr -p i i - . mainly on etandard I. II. III. IV. V. VI. Classification of the Silicate Minerals Based on Grouping of Si04 Tetrahedra C lass Nesosilicates.... Sorosilicates.... Cyclosilicates___ Inosilicates.... Phyllosilicates... Tectosilicates.... Grouping of Si04 tetrahedra Singles....... Groups (sisters).... Rings........ Chains...... Sheets...... Frameworks..... Linkages of Si04 tef.Tahiar-r 0 1 2 2 3 4 Oxygen atoms Der 4 ai 16 14 12 12 10 8 2Winchell, A. N. Elements of Optical Mineralogy. ] a erals - John Wiley & Sons, New York, 1951. Pavarennykh, A. S. Crystal Chemical Classificatioj Press, New York, 1972. 2, Description of Minof Minerals. Plenum 92 Inosilicates (IV) The amphiboles in the subgroup of inosilicates (IV) are common rock forming minerals which make up a substantial fraction of the earth s crust; any of the amphiboles may be but are not necessarily fibrous in morphology, and in fact, the commercially useful fibrous amphiboles are relatively rare. Following the notation suggested by Pavarennykh, the amphibole group can be represented by the formula: 1 RgKg[Si^OljJg(OH)g , where RgR5 combined are basic cations supplying a total of 14 plus charges, and " indicates that the silica double chain structure is linear and can extend infinitely in only one direction. Another common system of nomenclature groups all of the amphiboles, except anthophyllite (cummingtonite), under the generic name "hornblende," which is further divided into the common hornblendes, the oxyhornblends (which may be partially or totally dehydroxylated), and the soda-hornblendes in which sodium plays a prominent role in the basic cation RgR.5 (+14 charge) complement. In some of these varieties there may also be some ionic proxying for Si in the [Si4 0lx] double chain silica tetrahedral (amphibole characteristic) portion of the structures. According to Pavarennykh's systematic classification: Anthophyllite subgroup, orthorhombic monoclinic, Z - 4, 2 (not all members included): Name Anthophyllite...... Cummingtonite...... Amosite (magnesian grunerite). Chemical formula Mg7 [Si40u ]2 (0H)g" x (Mg.Fe^CsUOiJaiOH),," (MgFe)[Si4 Ol l ] 2 (0H)a Space group D16 - Pnma h Cgh " C2 /m Cgh - C2/m a 18.56 9.56 9.56 b 18.08 18.45 18.45 c 5.28 5.34 5.34 Tremolite subgroup, monoclinic, Z - 2 (not all members included): Name Chemical formula Space group Tremolite...... (CagMg5 )[Si40xl]2 (0H)a~ C|i, - C2/m c | h Actinolite..... Na(CasMGs)[Si40xx] 2 (OH) .,00 C|h - C2/m Ferroactinolite. (CagFes)[Si4 0xx ]s (0H)S" - C2 /m a 9.64 9.89 9.87 b 18.05 18.14 18.34 c 5.27 5.27 5.30 B 10442' 10548' 10430' NOTE.--Actinole is partially "dehydroxylated" approaching oxyhornblende com position with Na+ furnishing the 15th + charge required for negative lattice charge compensation. 93 The structural analogy between tremolite and actinolite can he nflri,ane fancucion or JNa tor IT m the hydroxyl glnroutphi-ngp,retcheudsl:n*1s t s b u U t lm " Glaucophane (a soda i --I.ii vuwuiwui i.uuuuia apace sroun Nas (Mg,Fe)3 (Al,Fe)a [Si40x ]a (0H)S= C|h - C2/m hornblende) . a 9.74 9.90 b 18.02 18.14 c 5.34 5.32 10410' 10330' Z TM NTE.--Glaucophane has perfect Mg-Fea+ isomorphism and somewhat less complete 1 -Fe isomorphism, so that under this classification the name "glaucophane" riebeckite ge^ rali^ed meaninB while the old species glaucophane and -- beckite become the subspecies magnesio-alumoglaucophane and ferro-ferri- glaucophane. The fibrous form of the latter is commonly caled S o c i d o M t e which thus has the ideal crystallographic formula: ----------- ' (NagFe+++2 )[Si^Oj x] 3 (0 H)2" . *_.._**: may als aoted at this Pint ^ a t the mineral name amosite cannot- bo hy applied found m any standard mmeralogical reference or classification and that the nomen- on E V n ^ecofn^zed mineralogists. Amosite is, in fact, a trade name based on the acronym for Asbestos Mines of South Africa and is to the production of I! ! 8 6 m n e S in WllCh the majr mineral constituent approaches the ideal structure of magnesian grunerite, that is, OfcFe*)* which in turn is the ferrous end-member of the cummmgtonite subspecies of anthophyllite. a1n1 ht! the thlS P!n! prescribed n Y (fibrous) Pssible to amphiboles; compare the crystallographic structure of representing the "amphibole part" of the Z l f Z ST b ! l TM ! T V ! hat 18 ^Si4 ll]3 (0 H)2 " as ' V it is evident that all of these species V SpaCe ?rUP' haVS substantially identical lattice parameters, and differ only in the composition of the charge-balancing (14+) divalent cations, thus: Anthophvllite Amosite Tremolite Actinolite "Ferroactinolite " Crocidolite (Mg? ) R (MgF e6 ) R 1 (CagMgg) R (C3gMgg) R, where R is [Si^Oj ]8 (ONa)(OH) (CagFe5 ) R (NagFe++3Fe+++2 ) R There seems to be at hand substantial evidence that the biological activity of Z Z Z these structures may vary over a relatively wide range of intensity; if so, the thlS ^ m?St reasonably be ought in the cation complex compositions with already some suggestions that those species highest in iron are relatively more car cinogenic than those from which iron is absent. Phyllosilicates The phyllosilicates are the sheet or layer structures in which the silica tetrahedra are arrayed (extended) infinitely in two directions (that is, planar). The group relevant to this discussion is the kao1inite-antigorite group. These are 94 1 to 1 layer lattice silicates consisting of parallel sheets of silica tetra hedra and basic cations in octahedral coordination. Quoting Pavarennykh: The minerals assigned here are structurally identical but represent polytypes and products of isomorphism. The kaolinite subgroup min erals have 2 / 3 of the positions in the octahedral layer filled (the di-octahedral subgroup) whereas all positions are filled in the antigorite subgroup (the trioctahedral subgroup). Both may have a tubular chrysotile structure, which is more common in the antigorite subgroup. Again following the Pavarennykh classification, the aluminian (diocta hedral) and the magnesian (trioctahedral) structural analogues can be represented: 1. Kaolinite subgroup, triclinic monoclinic (not all members included): Name Chemical formula id Al4 [Si4 0lo ](0H)8co Metahalloysite... Al4 [Si4 0 i0 ](0 H) 8 00 h0*.H 1 Space group Cb - Cm a b 5.14 8.93 5.15 8.9 c 7.37 7.9-7.5 B 10430' 105 2. Antigorite subgroup, monoclinic serpentines: Name Chrysotile......... Chemical formula Mg[Si4 01q ](OH)8" Mg6 [Si4 0lo](0H)8" Mgs[Si4 0lo](0H)S Space group Cm C2 C2/m a 5.30 5.31 5.34 b 9.20 9.20 9.25 c 7.46 7.31 14.65 B 9124' 90 9316' Of these minerals, both metahalloysite and chrysotile are tubular while kaolinite, antigorite, and lizardite are planar or "platy." A possible expla nation acceptable to many mineralogists was suggested by Bates by which the tubulation was due to the slight dimensional misfit between the tetrahedral and octahedral layers due to the different ionic sizes and bond lengths of the dioctahedral (Al+++)s and the trioctahedral (Mg+ + ) 3 layers. Such misfits set up a strained lattice structure which can be relieved by a rolling of the structure into a tubule with the Si04 lattice layer on the outside, as in metahalloysite but with the magnesian octahedral lattice layer on the outside as in chrysotile. Many of the special properties of these minerals can be accounted for on such a basis. No such strain relief is permitted to the planar or platy varieties (kaolinite, antigorite, or lizardite) so that the tetrahedral (Si0 4) sheet structure fit must be adjusted by distortions in bond angles and bond length. The point to be emphasized here is that chrysotile is a tubular (fibrous) 4 Bates, T. F. Morphology of Layer Lattice Silicates. L a b s . , v. 42, 1951, pp. 83-92. Dennison Univ., J. Sci. 95 h T t " ! !*"*?T aI" f ifyer 1fjFiCe ^Ph>'llosilicate) structure totally unrelated to that of Zu 3-layer lattice a t r ^ t T S J S S S " iUkl* * ^ 3. Pyrophyllite subgroup, raonoclinic: Pyrophyllite. Talc. Al2 [Si40lo](0H)3" Mgs rSi40lQ](0H) ^Ih - C2/c Cf - Cc; Z=4 a_ 5.15 5.27 18.95 18.85 9955 1 10000' U 1 ?or (00n11ithgt r PfStrUCt"r - ls that t" nets S1* tetrahedra paral : - k l (Ms) ricll with r e ^ e e f i o ^ h e " g b e C " se the - - i TM - ated, with highly perfect cleavage on (001). 1*? la spatially syTM,et- V y 011 ra a r j i 'j . - r c . - i T r - s , x `:TM demonstrated by structural or chemical analysis as i y , for enable selected rT"HrdT ^ analysis?trn dlfractln or ^ *1'd area energy dispersive electron f \ ? . 6 concentration of any of these prescribed (asbestos or asbesti- orra) ^nerals when they are admixed with any other material. Any and all of the amphiboles as well as the serpentine (antigorite subgroup) minerals c L x4ay d iffiL S m oipholoJS? 1 7 admif d With b th the Plafcy and f ib rous v a r ie tie s , and 6 SimP Y C3nn0t d iscrim in ate between the two , F^ allyi Y.Lu0111 like to make an additional comment relative to the efinition of fiber. We have searched the encyclopedic and lexiconographic as^sed by 0 S M bears any etymological relation to the Sord sed by OSHA. One essential characteristic of a "fiber" is that it can be T t *m T 1 WVen int a Cl0th> a characteristic of only a few of the varieties of asbestos included in the OSHA list. ASTM does have a con sensus definition (see AS1M D 2946-71) wherein a fiber is defied ^ o i i TM Fiber--any material in a form such that it has a minimum length to average maximum traverse dimension of 10 to 1 , and a maximum trans verse dimension of 0.255 mm. 96 We wish to thank the Bureau of Mines for organizing the Talc Symposium and we also wish to thank the organizers for the opportunity to make these supplementary remarks for the record- 97 medical aspects of talc by Richard M. Spiegel, M.D.1 rneuniocona-osis The literature contains cerned with the incidence of several studies over the past 3 talc pneumoconiosis (3-4, 6, 9, - ) or 4 decades con 11-12 16 21 2 7 reDortsSif1 With pathoSenesis 02-20), in addition to numero^'cMe"" PS eva}uations O , 1, 8, 14, 17-18). The bulk of the workers ated have been involved in mining and milling although various usage areas have also been examined. usage nnrf P ?V k -, h*fc ca* I " " 7 statement that nearly all of author findings talcLexPsare produce a clinical picture virtually would sup indistin guishable from asbestosis; but at a lower rata than with comparable asbestos exposure. The pulmonary function alterations (decreased vital capacity and diffusion capacity), the often thin and "chronically ill" appearance o / the sujects, the .ferruginous " bodies found on lung sections, the pleural plaques nd calcifications, and the roentgenographic picture of interstitial fibrosis predominantly m the lower lung fields, with diffuse, "reticular," irregular small opacities are all findings in common with talcosis and asbestosis. TM Importantly, they are special in each person, quite different from those usuS\li"si!* Ma?y cases with silicosislike signs ar reported, but and u n d o u b i ^ r Y " f S exPsed to talc with high free-silica content and undoubtedly represent silicotalcosis. . i brings up the major problem in establishing the toxic potential of talc--defining what we mean by "talc." The term is used in industry to refer to certain physicai properties rather than chemical composition. "Commercial talc with which all of the studies are concerned, can contain a great vari ety of related and unrelated constituents in an even greater variety of pro portions, mixed with "pure talc," a hydrous magnesium silicate, often to the point where pure talc" is a minor component (_2, 20, 24). The still unre solved question is how much damage, if any, is caused in the lungs by true talc and how much by the contaminants? The major suspects, because of their well-established pathogenicity, are tree silica and the asbestiform materials such as tremolite, anthophyllite and serpentine. The role of the former, however, can easily be separated,'as previously mentioned, by different clinical manifestations and simple environ mental assaying. The role of the latter substances, on the other hand, includ ing also hydrous magnesium silicates, is very hard to determine. True talc is to a great extent formed in nature by hydrothermal alteration of asbestiform 1Medical Investigations Branch, Division of Field Studies and Clinical Inves tigations, National Institute for Occupational Safety and Health, Cincin nati, Ohio. n 98 deposits and, therefore, the mined material is not only usually a mixture 0 the two but can also vary in percentage markedly, even in samples taken in relative close proximity. This compounds the problem because dl^ era^iation even in the laboratory is extremely difficult and entails generally electron microscopy. Because asbestos fibers generally form a part of "talc" exposure and the resultant talcosis is fairly identical with asbestosis some a^ r* that talc pneumoconiosis is actually being caused by the tremolite or other asbestos contaminants and that true talc plays no role. S^Ppor^ f e^ one study (19), which suggests that talc and tremolite produce different responses ^ m i m a l tissue, the former cytotoxic and the latter fxbrogenic and cytotoxic. However, intuitively it would seem likely that talc particles as seen in t h e s e fibrous talc, with similar structure and chemistry to asbestos particle should produce similar diseases. Also, as differentiation of P^icles is often unfeasible and fibrous talc is invariably contaminated with asbestos, there is no practical reason at this time to prove their relative toxicities. The present American Conference of Governmental Industrial Hygienists stan dard! reflecting this view, is set for fibrous talc at 5 *n length (the same as asbestos) without reference to type of fiber and is in a combined standard for "talc (fibrous) - tremolite." The differentiation implied just described between fibrous (or "tremolitic") talc and nonfibrous (granular or nonasbestiform) talc creates another source of disagreement. The distinction is based on the geologic com position of the mined deposit rather than on any filtering process, with two types lying at opposite ends of a continuum, rather than being separate entitles! In L y ocSpational "talc" exposure, both fibrous talc and granular talc standards must be met; that is, if the fiber content is lower than the fibrous TLV, the exposure can be considered strictly granular and must then meet the present American Conference of Governmental Industrial Hygienists granular L i e limit of 20 mppef. This standard la apparently based for some reason on Dreessen's study (3) of Georgia talc miners and millers, which included a group of workers exposed to levels of approximately 17 mpp , of whom had evidence of pneumoconiosis. However, not only was the talc involved 10 percent tremolite (certainly not granular) but no attempt was made to establish duration of exposure. Hogue and Mallette s study (4), sponsore by the Firestone Tire and Rubber Company, might be better suited for P pose. They examined 20 company employees with exposures of 10 to 36 years (only 4 employees less than 20 years) and levels at the time of the study ranging from 15 to 35 mppef, with allegedly higher levels m the past, and they found no evidence of pneumoconiosis. The talc used was reportedly pure talc" containing "no free silica, tremolite, chrysolite, chrysotile or actinolite," although no evidence was presented to support this s^temen . Opposing this would be some studies of Kleinfeld and Messite (2, which concluded that while the fibrous type was more pathogenic, both talcs c m pro duce pulmonary fibrosis. Their identification of the granular talc is not substantial, however. One study involved workers in two milling plants, one allegedly using fibrous, the other granular talc, but no evidence is offere 99 e ^ " e ihio r k 1sai l i i 1Catll>;;K ^ ^ ^ th e y comPared two m in in S Weiss6 ( 2 ^ ^ m e n t i o n s *** "" V " f tre^lita (fibrous) talc." v i l e use. n W e U docuraenfced Probably in some measure becausf of its Carcinogenesis but fStun-ii? b!n nly one mortality study in the literature on talc workers has has fn ! followe! ly 1 was a g StUdy- a group of fibrous talc miTnheersNewanYdomrikllSetrastesDinecpeart1m9e4n0t a nodf Labor ha ' Kleiifeld'Ver 1 articles concerning their health status, among which was Klemfeld's mortality study (12) 0f workers who had at least 15 vlars o H a l r " -1965 / pSoT52Si:* S S aihleVed L15 S S .*S L ^ L a S o T lST 9 `d STSL that- ?!Ch that seen drawn frnm attenJlon is iven in asbestos workers ,,r-h a worxers ((2j., to an1al9 y'*zingtj-.this rate and contrasting 12) . The only generalization that it with wlI-n can be nevertheless high risk of lung and pleural malignancy seen In exposure to the asbasti TM * v Summary uents^of thaet a ^ \ Path0l!?iC sequela of talc exposure depends on the constit- SSSr-SuTTsSi.E? - " - as; aListlider" iiit developing silicotic fexs1Lf?^TM* iWrit,,ht'"theine"s:' r irv a 1S'em^ayf deveip> * witnout asbestiform contaminants, can produce talcosis. Fibrous talc exposure has shown to yield a significantly h-fo-h exposure. ^W hether^ur^talc^shcarcinogenichhas^not^eEEEdreE s s 1 100 Annotated Bibliography NOTE.--Chronologically, references 21 and 22 report the initial morbidity study in 1940 of 221 fibrous talc workers. Thirty percent of those with over 10 years of exposure demonstrated advanced fibrous. Refer ences 6 and 16 present results of a followup study in the mid-50 s. New cases appeared less severe, attributed to improved mining tech niques. In reference 16 a comparison was made between the original group and miners in another area where talc was less fibrous and com parably less disease was seen. 1. Alivisatos, G. P., and others. Talcosis of Unusual Rapid Development. British J. of Industrial Medicine, v. 12, 1955, pp. 43-49. Eight case reports from Greece of "talcosis" after very short, but very heavy exposure. From description, silicosis probably played a role. 2. Bleier, A. P., and R. Arlon. Talc: A Possible Occupational and Environ mental Carcinogen. J. of Occupational Medicine, v. 15, February 1973, pp. 92-97. ' . Good recent summary of talc toxicity compared to asbestos experience. Only new information concerns consumer exposure in food. 3. Dreesen, W., and J. M. Dalla Valle. The Effects of Exposure to Dust in Two Georgia Talc Mills and Mines. Public Health Repts., v. 50, February 1935, pp. 131-141. One of the first, well-documented surveys of talc workers showing high incidence of pneumoconiosis (half of the heavily exposed subjects). 4. Hoeue W. L., and F. S. Mallette. A Study of Workers Exposed to Talc and Other Dusting Compounds in the Rubber Industry. J. of Industrial . Hygiene and Toxicology, v. 31, November 1949, p. 359. Industry study of 20 workers with long exposure to allegedly pure talc yielded no pneumoconiosis. 5. Hunt, A. C. Massive Pulmonary Fibrosis From the Inhalation of Talc. ThArax v. 11. 1956, pp. 287-294. Case report and discussion. Attributes massive pulmonary fibrosis to talc alone, disregarding silica because of lung ash findings. .6 Kleinfeld, M . , J. Messite, and others. Talc Pneumoconiosis. AMA Archives nf Ind Health, v. 12, July 1955, pp. 66-72. and References 6-13, 16, and 21-22 are all from the New York State Depart ment of Labor are concerned with longitudinal study of talc miners and millers. 7. . Problem Areas in Pneumoconiosis. AMA Archives of Environmental Health, v. 5, November I960, p. 498. the a . See a U o reference 6.  101 Pneumoconiosis. AMA Archives of Environmental Health, v. 7 July 1963, pp. 101-115. ' Post-mortem reports on six subjects with talcosis. Findings compared to asbestosis and silicosis. See also reference 6. -- Lung function in Talc Workers. AMA Archives of Environmental Health, v. 9, November 1964, pp. 559-566. A comparative morbidity study of workers exposed to fibrous and granu lar talc dusts using a different from that above population, all millers in two separate facilities. Those allegedly exposed to only granular talc had significantly less signs and symptoms of disease. See also reference 6. 10. -- _ . Pulmonary Ventilation Function and Talcosis of the Lung. Diseases of the Chest. AMA Archives of Environmental Health v 42 November 1964, p. 592. 1 Intensive pulmonary function evaluation of 20 men with clinical and radiologic diagnosis of talcosis. See also reference 6. 11. --- Effect of Talc Dust Inhalation on Lung Function. AMA Archives of Environmental Health, v. 10, March 1965, pp. 431-437. Study population from 9 as a whole compared with a group of matched controls in morbidity study showing significant differences. See reference 6. 12. -- . Mortality Among Talc Miners and Millers in New York State. AMA Archives of Environmental Health, v. 14, May 1967, pp. 663-667. Mortality study of original population. See reference 6. 13. -- . Mortality Experience in a Group'of Asbestos Workers. AMA Archives of Environmental Health, v. 15, August 1967, pp. 177-180. Similarly designed mortality study of asbestos workers, apparently set u.p primarily to compara with study 12. Sea reference 6. 14. McLaughlin, A. I G., and others. Talc Pneumoconiosis. British J. of Ind. Medicine, v. 6, 1949, pp. 184-194. Discussion and literature review of case report. 15. ____ Dust Diseases in Great Britain. AMA Archives of Ind. Health, v. 12, 1955, p. 83. General discussion. 16. Messite, J., M. Kleinfeld, and others. Pulmonary Talcosis, Clinical and Environmental Study. AMA Archives of Ind. Health, v. 20 1959 pp. 408-413. ' ' See reference 6. 17. Moskowitz, R. Talc Pneumoconiosis; A Treated Case. Chest, v. 58, July ' 1970, pp. 37-41. Recent case report of talcosis from chronic aerosol inhalation. Early changes on open biopsy shown to be granulomatous, responded well to steroid treatment, leaving small amount of more typical fibrosis. 102 18. Schepers, G. W. H . , and M. E. Durkan. The Effects of Inhaled Talc Mining on the Human Lung. AMA Archives of Ind. Health, v. 12, May 1955, pp. 182-197. . Histologic and mineralogie analysis of lung tissue from autopsies on men with talcosis. , An Experimental Study of the Effects of Talc Dust on Animal Tissue. AMA Archives of Ind. Health, v. 12, 1955, pp. 317-328. Animal experiment with intravenous and intratracheal injection of and its contaminants in a variety of species. talc 20'. Schulz, R. D., and C. R. Williams. Commercial Talc, Animal and Mineral ' Studies. J. of Ind. Hygiene and Toxicology, v. 24, April 1942, PP- 75-79. . . ,, Animal studies using mixed "talcs" injected intrapentonally. 21. Siegal, W . , and others. Talc Mining Including Roentgenological Findings in Talc Workers. Am. J. of Roentgenological Radiation Therapy, v. 49, January 1943, pp. 11-29. See reference 6. 22. . Study of Talc Miners and Millers. Industrial Bull., New York State Dept, of Labor, Div. of Ind. Hygiene, v. 22, No. 11, November 1943. See reference 6. 23. Van Ordstrant, H. D. Talc Pneumoconiosis, An Editorial. Chest, v. 58, July 1970, p. 2. .. - . Good recent review of the state of the art except for omission of evi dence of carcinogenicity. 24. Weiss, B., and E. A. Boettner. Commercial Talc and Talcosis. AMA Archives of Environmental Health, v. 14, February 1967, pp. 304-308 Analysis of various talc deposits in this country and a literature review on talcosis. *U.S. GOVERNMENT PRINTING OFFICE: 1974- 705- 925/704 IN T.-BU .O F M INES,PGH.,P A. H 3 I3