Document zzeGZG2OYVKp0M6JvrEy0jLE3

American Laboratory o Asbestos By Walter C. McCrone and Ian M. Stewart IN may 1968, Dr. IrvingJ. Selikoff of the Mount Sinai Hos pital in New York established his position as the Rachel Carson of the industrial hygiene world. A series of New Yorker articles at that time was based largely on Dr. Selikoffs experiences in the study of asbestosis, lung and stomach cancer, mesothelioma, and other causes of death related to ex posure to asbestos. His careful analyses of mortality of industrial workers in known asbestos fiber contaminated areas are convinc ing arguments that asbestos is one of the most deadly industrial hygiene hazards. The reputation of large indus trial concerns has not always been good when faced with evidence that their plant environments may be contributing to worker disabil ities, if not death. However, large ly through Dr. Selikoffs effort, Dr. McCrone is Scientific Adviser and Mr. Stewart is Manager, Electron Optics Group, McCrone Associates, Inc. followed up by the FDA, Depart ment of Labor, and other inter ested parties, most responsible companies are now doing their best to minimize, if not eliminate, asbestos as a health hazard. The microscopist has an im portant role in this program to control asbestos as a contaminant in the air we breathe, the fluids we drink, and the food we eat. He must be able to identify asbestos fibers and quantify their size and number. There are problems be cause there are other fibrous sub stances confusingly similar to as bestos, and there are several dif ferent types of asbestos (Table I), differing in optical properties and composition and possibly in the degree of their hazard to humans. Analytical methods must be sensitive enough for the identifica tion of single fibers. Of course, only a microscope and a trained microscopist can do this. There are methods, e.g., x-ray diffrac tion and DTA, that identify min ute percentages of asbestos in i' . Chrysotile fiber bundle. \ I 'O* Table 1 Composition Asbestos Serpentine Amphibolee CHRYSOTILE ACTINOLITE TREMOLITE ANTHOPHYLLITE 3MgO*2SiO]> 2CaO*4MgO* 2CaO*5MgO* 2H20 FeO*8SIOj*HjO 8SI0j*H70 7Mg0*8Si02* H20 Specific gravity Crystal system Refractive indices 2.36-2.5 monoclinic 1.49-1.57 3.03-3.5 monoclinic 1.62-1.68 2.S-3.2 monoclinic 1.60-1.65 2.85-3.5 orthorhombic 1.60-1.66 l BB 001581 AMOSITE v>GROetDOLlTE 5*5FeO* 1*5MgO 8SIOj*HjO 2.6-3.0 monoclinic 1.66-1.70 NajOFejOj* 3FeO*8SiOj HjO 3.0-3.45 monoclinic 1.69-1.71 AMERICAN LABORATORY : 13 ASBESTOS contmu&o t Table 2 Asbestos type Chrysotile Anthophylllte Amosite Crocidollte Dispersion staining colors for asbestos Refractive index liquid Dispersion staining color 1.560 1.610 1.670 1.700 Parallel light blue blue-green red magenta magenta Perpendicular magenta golden yellow golden yellow blue magenta small samples, but only the microscopist can hope to identify in dividual fibers. Fortunately, the crystallographic properties of the different types of asbestos are suf ficiently distinct to enable certain identification. If the fibers are thicker than about 0.5 /im, light microscopy suffices; smaller fibers require the electron microscope. Identification of the larger fi bers by light microscopy is based on refractive index measurement using a polarizing microscope. The easiest way to apply refrac tive index measurement to asbes tos fiber identification is by use of dispersion staining, an optical staining procedure. This is based on annular or central screening of the objective aperture in common with specific refractive index me dia, such as the Cargille liquids. Under these conditions each type of asbestos shows two character istic dispersion staining colors, one for the light vibration direc tion parallel, and another perpen dicular, to the fiber length (but only in one particular refractive f index liquid). Table 2 shows the colors obtained with several kinds of asbestos when mounted in ap* propriate Cargille refractive index liquids. Different colors or no colors are observed if other than the specified liquids are used for each particular asbestos sample. Finding small percentages of very fine asbestos fibers requires care ful application of the method. In particular, intense Kohler illumi nation with carefully centered substage and objective apertures is essential. A careful microscopist should, however, be able to detect 0.01% of >0.5 fimthick fibers by this technique. Light microscopy is ideal for rapid identification of asbestos in most powdered samples: dust, mortar, insulation or wallboard, mineral samples such as talc, etc. When the presence of asbestos in a liquid medium, such as a water supply, soft drink, beer, or pa renteral solution is suspected, one must assume most of the fibers, if not all, will be too fine to ob serve by light microscopy. One turns, then, to the transmission electron microscope (Figure 1). The transmission electron micro scope (TEM) is superior to the scanning electron microscope for two reasons. Smaller fibers can be observed and identified by TEM, and selected area electron diffraction (SAED) is more de pendable for identification of as bestos than the elemental analysis capability of the SEM. Figure 1 Model 200KV transmission electron microscope. EXTENDING MAN'S VISION IN THE SEAS The seas are our new frontier. From an underwater Nikonos Scientists are exploring the camera to the compact Model vast resources of the oceans, H microscope, we are produc not only for links to our origins, ing instruments used by our but for new sources of food. scientist/conservationists to Many scientists believe that insure the continuation of the our beleagured planet cannot species, man. forever support the popula Producing the finest instru tion explosion. ments available for science The warning voices of these men are at last being heard. and industry is a constant challenge. Mankind is slowly awakening Wherever essential research to the frightening realization is being conducted: on land, that even our seas cannot beneath the seas, or in space-- withstand the absorption of we are meeting that challenge. man's waste without dire Extending your vision is our consequences. main concern. Nikon is in the forefront of undersea research technology. The finest optics in the world. Nikon Instrument Division, Ehrenreieh Photo-Optical Industries. (Nikon 623 Stewart Ave., Garden City, N.Y. Tel. (516) 248-5200. In Canada, Anglophoto Ltd., Ontario. Nikon SSV1Z Stereo Zoom Microscope Total magnification ran#e, 4X to 120X. Provides S time zoom ranjje without change in focus. Excep tional wide range of accessories. Reader Card = 107 Nikon EpMliuminetor Fitsanv standard Nikon microscope Designed tor observation ot opauue specimens Provides ^ollimated on-axis illumination with held and aperture control. Dark held reflected light wsiems available Reader Caru* 10 1 BB 0015813 J Nikon Kt Compact Versatile Ijhorjiorv microscope with built-in transformer, continuously variable light intensity control, and inha.se volt* meter. Features brilliant Koehler tvpe illumination and full ranee oi Nikon accessories Reader C'jrd = 10 AMERICAN LABORATORY : IS ASBESTOS continued # * Figure 2 Chrysotile fibers filtered from a water supply, 3Q,OOOX. Figure 3 Selected area electron diffraction pattern tor a single chrysotile fiber. A sample of water of known volume is filtered through the fin est membrane filter. A section of filter approximately 2-3 mm* is then placed particle side down on a previously carbon-coated elec tron microscope grid, and the membrane filter is dissolved using acetone in a Soxhlet extractor. The sample grids are examined in our laboratory with a JEM 200 electron microscope, using an ac celerating voltage of 150 kv at a magnification of 17,000X on the M3 range of the instrument. This magnification is chosen to focus the intermediate lens aperture in line with the specimen plane; thus, a SAED pattern of the fiber is ob tained with no other adjustments to the microscope. In this way it is possible to spot check the dif fraction pattern of individual fi bers rapidly (Figures 2 and 3). The total number of asbestos fibers is related to a definite area of the filter, and hence a definite volume of sample, by counting fi bers over a known number of TEM grid squares (having known areas). The length and width of each asbestos fiber is recorded. Interpolation from the screen scribed at half-centimeter intervals allows an accuracy of measure ment on the screen of approxi mately +0.05 cm, or about +34 nm. Measurements of the indi vidual fibers are read into a tape recorder; this permits the operator to devote full attention to the screen, precludes duplicate count ing of single fibers, prevents miss ing fibers, and maintains the op erator's dark accommodation. The recorded data are trans cribed onto punch-tape and com puter processed to give listings of the length, width, and aspect ratio of the fibers, together with a com puted mass of each fiber calcu lated on the basis of density D and dimensions L and W (D X Lx W*). Density values for the different asbestos types are given in Table 1. Also presented in the computer print-out is the num ber of fibers per liter of water, the size distribution of the fibers based on length and width, and the distribution of fibers by aspect ratio. The program automatically assigns the longest dimension to the fiber length and excludes all fibers with an aspect ratio below three. This procedure, designed by Ian Stewart of our laboratory, has been applied with excellent suc cess to a number of water samples containing large numbers of amphiboles per liter but very low weight percentages. Most of these samples show no asbestos fibers by light microscopy. It is there fore important to specify the method of analysis when stating analytical results. The same sam ple of talc could be analyzed by different methods with very dif ferent results, e.g.: 1- X-ray diffraction shows no chrysotile or amphiboles. 2. A phase-contrast method (similar to the NIOSH procedure to determine the number of fibers per milliliter of air) shows 1500 fibers greater than 5Mm/m3 of sample. 3. The scanning electron mi croscope with energy dispersive x-ray analyzer shows about 104 `-AN LABORATORY : 17 ASBESTOS continued * fibers/liter suspected of being am- phibole asbestos. 4. Dispersion staining shows 150 anthophyllite fibers/gram of sample. 5. Transmission electron mi croscopy shows 5 X 10* anthophyllite fibers/liter of sample. The AEI Scientific Apparatus, Ltd. EMMA-4 (Figure 4) only recently installed in our labora tory will undoubtedly be the ideal instrument for the detection and identification of very fine asbestos fibers. A combination transmis sion electron microscope and electron microprobe analyzer (EMA), it enables the microscopist to see the smallest fiber and to identify it by diffraction pattern and elemental analysis. Although a given sample mounted on a TEM grid can be examined successively by TEM and EMA, the advantage of being able to examine many particles in a sam ple with assurance of one-to-one correspondence of particle size, shape, diffraction pattern, and elemental analysis is obvious. We have already applied this instru ment to some asbestos samples with excellent results, and expect it will be the instrument of choice for such samples in our labora tory. The monitoring of asbestos as a contaminant in our environment is an excellent example of one important problem solved by microscopy. The importance of choosing the proper analytical tool and having a well-trained op erator is also emphasized by this application to asbestos detection and identification. Figure 4 EMMA-4, a combined transmission electron microscope and electron microprobe analyzer. rmjtnr-i pi'.i: rnuttii'-. -.prei* innfrrr.V .lu'n m/Jh( -'irii: (.irfuit', '-.tf* pp*M TUM'.I.iT nv tnilfxrrs Motnri/i'd UniSInii1 'on`-,,r:;cttnn '..inn l.tt ?0 .ihi.rjt' in 7 cf/nfT H ,ud)l) St''U". t fi 4l)0!) !v,ri*"-. -J ' t 11 h" U`n'th', *c -JH" {n^mfM'nrv d.it.i hmI pn es in '7 upon n'Ui/F-'.f UNISUOE POWER Unt^itiU' f'oA'uf ,i tori/ed v^tTh ,il slidt? ,is*- 1'nnstn.jited On '.t^Dlo platform*, tor fui.usmf STANDS v*'111 ,il positioning of p;o!jos tr.msdni n v t;ir ets rtf 411V fIN* ff1114*d provicfrs to? mi r'1 ; opr .ift.u nm>nt m f.i pur,i*`-s I fj.trM1 ,inri inn f(j. U`. (np Py f,vO -Sf pir n tiidton Of toot \Aitc ti i r t r :jl f npint'Pr mi; d ft f mi! pf ii rs m Cl.it Hop A 17 upon jrciui/st ' * Velmex. /NC. P.O. BOX 38 E BLOOMFIELD, NY 14443 Telephone 315/657-6151 Circle Reader Service Card No. 69 18 : APRIL 1974 JonM'MtftvHI* !i3iENVIRONMENTAL FACTS/Asbestos Asbestos A Family of Minerals SUMMARY: This paper sets forth some of the reasons why the term "asbestos" should not be used loosely in discussing medical questions. There is no single mineral known as asbestos. "Asbestos" is a name given to a family of minerals. It includes two major groups, containing a total of six varieties of asbestos. Each of these six differs from the others, physically, chemically and in biological effect. Any study of the effects of asbestos is complicated by this diversity. Studies of both people and animals show differing types of reaction to the various types of asbestos. Animal studies of excessive exposure made with three of the major commercial types of asbestos indicate that commonly-used chrysotile is least likely to produce a reaction. Because different varieties of asbestos produce different reactions, scientists are working on better methods for identifying the types of asbestos involved in their studies on human health. Other complications arise because trace amounts of mineral impurities are often found in sam ples of raw asbestos ore and refined fiber. TYPES OF ASBESTOS Any attempt to assess the effect of asbestos on health is complicated by the fact that asbestos is not a single chemical or physical entity. "Asbes tos" is a generic name given to a group of hydrated silicate minerals that have one common attribute -- namely, the ability to be separated into relatively soft, silky fibers. The known varieties of these minerals can be divided into two main classes on the basis of their crystalline structures: serpentine asbestos and amphibole asbestos. The lone member of the serpentine class is chrysotile asbestos, which is by far the most common of the asbestos minerals. About 95 per cent of the asbestos used in this country is chrysotile, principally from mines in Canada. There are five recognized varieties of amphibole asbestos: crocidolite, amosite, anthophyllite, tremolite and actinolite. Of these, crocidolite and amosite have the greatest commercial sig nificance, although the use of anthophyllite is increasing. Each of the six types of asbestos differs from the others, chemically and physically. To add to the complexity, chrysotile asbestos from one Canadian mine, for example, will differ in chemical impurities and physical properties from the chrysotile taken from another Canadian mine. CHARACTERISTICS OF THE FOUR MAJOR TYPES Each of the four types of asbestos that are most important commercially -- chrysotile, crocidolite, amosite and anthophyllite--exhibits distinguishing characteristics. --------- ------------------- Chrysotile | BB 0015821 J " ---- Bv far the leading producers are Canada and the Soviet Union. Smaller deposits are found in South Africa, Rhodesia, China, the United States and Italy. Chrysotile is a white serpentine asbestos and occurs in areas where serpentine rock was cracked by earth movement thousands of years ago and subjected to intense pressure and the flow of volcanic waters. This action transformed some of the granular serpentine 1 Jotw-Manviik DS1 ENVIRONMENTAL FACTS/Asbestos into fibrous chrysotile. Chemically, chrysotile is hydrous magnesium silicate with a magnesium hydroxide surface. It has a positive electrical charge. It can be attacked by acids. It is a flexible fiber and does not pulverize readily. Commercial chrysotile contains small and varying amounts of iron and calcium compounds, depending upon its origin. Crocidolite The bulk of the world's supply comes from South Africa; there are also small deposits in Australia, but they are no longer mined com mercially. Crocidolite is an amphibole asbestos occurring in iron-rich sedimentary rock. Chemi cally, it is a ferrous sodium silicate with a silica surface. It has a negative electrical charge. It is acid-resistant. It is characterized by a deep blue color. Crocidolite is less flexible than chrysotile. Amosite The Transvaal district of South Africa is the only place in the world where amosite is mined commercially. It is a member of the amphibole asbestos family, occurs in the same type of rock as does crocidolite, has the same negative electrical charge, but is brown in color. Chemically, amosite is a ferrous mag nesium silicate with a silica surface. It is acid-resistant, but less so than crocidolite. It is brittle and pulverizes easily. Anthophyllite The least used of the commercial fibers, it comes primarily from Finland but small amounts are mined in the United States. It is an amphibole asbestos, has a negative electrical charge, and is white in color. Chemically, anthophyllite is a magnesium silicate with a silica surface. It is acid resistant like the other amphiboles. It is brittle and pulverizes easily. Because of the basic chemical and physical differences among chrysotile, crocidolite, amosite and anthophyllite, it would be expected that over-exposure to the four varieties would show varying biological effects. And scientific observa tion confirms this expectation. There seems to be broad agreement that chrysotile, the type of asbestos most widely used in the United States is least likely of the three most commercially significant fibers (chrysotile, crocidolite, amosite,1 to produce asbestosis, a non-malignant luny disease brought on after inhalation of excessive concentrations of asbestos dust over a period of many years. ANIMAL EXPERIMENTS SHOW DIFFERENT EFFECTS Dr. j. C. Wagner experimented with three types of asbestos (chrysotile, crocidolite and amosite) on various laboratory animals, and found that - crocidolite produced the most severe asbestosis, and amosite was more than five times as.likelv to produce a reaction as chrysotile. He reported 1 in 1963: "With chrysotile dust it was possible to produce severe lesions in the lungs of guinea pigs, slight fibrosis in monkeys, while no significant effect was observed in two rabbits. Amosite dust causes marked asbestosis in all three kinds of animals. Lesions occur more rapidly in guinea pigs exposed to this dust than in those exposed to chrysotile. There is an indication that the disease is progressive in monkeys and rabbits. Similar pathology to that which occurred in a monkey exposed to chrysotile for 22 months was observed in a monkey ex posed to amosite for four months. The impure crocidolite dust caused severe disease in guinea pigs, and the rate of respiratory infection among animals exposed to this dust was more marked than with the other types. It is possible that this may be due to the high quartz content of the dust. "Finally, asbestos bodies could be demon strated in the lungs of animals exposed to all three types of asbestos dust. These were scanty in the animals exposed to chrysotile and usually segmented. Only occasional fibers were observed. In contrast to this, the asbestos bodies in the animals that were dusted with amosite were plentiful, and segmentation was rare: fibers were extremely nujrnerous and far outnumbered the bodies." ---------- ---------- 1 BB 0015822 I Johns`Mr)v)U IZ\ENVIRONMENTAL FACTS/Asbestos Following further investigation, Dr. Wagner ottered an explanation2 for this observation at a medical symposium in 1965: "A method of producing asbestos dust clouds has been devised and an' animal inhalation experiment carried out to test it... The elimina tion rate of Rhodesian chrysotile has been found to be three times greater than that of the amosite and crocidolite, which suggests an explanation for the previously observed reduced fibrogenicity of this dust. The reason for the difference in the elimination rate remains to be determined." COMMERCIAL ASBESTOS CONTAINS OTHER MATERIALS Asbestos ore and refined asbestos fiber contain mineral impurities, trace elements, and trace quantities of organics, which vary from type to type and from mine to mine. In addition, the ore may pick up additional trace organic impurities when in transit. These trace materials are also the subject of medical study to see if they mav have a role in any of the health effects observed in animals. Trace impurities of nickel, chromium and manga nese, for example, were found bv Cralley, et al.3 in samples of chrysotile used in the asbestos tex tile industry. Other impurities in commercial asbestos fiber include iron, aluminum, calcium, sodium and potassium. WORLD ASBESTOS BANK Much scientific research has focused on studving the varying biological effects of different tvpes of asbestos and on developing techniques for identi fying asbestos fibers of unknown origin. In 1967, a "World Asbestos Bank" was established in lohannesburg, South Africa, under the direction of the British Medical Research Council. The purpose of the "bank" is to provide standardized samples of asbestos from regions all over the world to be supplied to medical researchers for chemical, physical and biological investigation and for com parison purposes in clinical studies. CHARACTERISTICS OF MAJOR COMMERCIAL TYPES OF ASBESTOS NAME CLASS COLOR CHEMICAL COMPOSITION SURFACE COMPOSITION ELECTRICAL CHARGE REACTION TO ACID TEXTURE Chrysotile Serpentine White Hydrous Magnesium Silicate Magnesium Hydroxide Positive Susceptible Flexible Crocidolite Amphibole Blue Ferrous Sodium Silicate Silica Negative Resistant Medium Flexibility Amosite Amphibole Brown Ferrous Magnesium Silicate Silica Negative Resistant Brittle Anthophyllite Amphibole White Magnesium Silicate Silica Negative Resistant Brittle ] BB 0015823 J 1 REFERENCES ' Wagner, J. C., "Asbestosis in Experimental Animals," BRITISH IOURNAL OF INDUSTRIAL MEDICINE. 20:1, 1963. 2 Wagner, |. C. and Skidmore, J. W., "Asbestos Dust Deposi tion and Retention in Rats," ANNALS OF THE NEW YORK ACADEMY OF SCIENCES, December 31, 1965. 3 Crallev, L.Keenan, R. G. and Lynch, J. R., "Exposure to Metals in the Manufacture of Asbestos Textile Products," AMERICAN INDUSTRIAL HYGIENE ASSOCIATION IOURNAL, September/October, 1967. General Reference: Speit, S. and Leineweber, J. P., "Asbestos Minerals in Modern Technology," INTERNATIONAL CONFERENCE OF BIOLOGICAL EFFECTS OF ASBESTOS; Dresden, East Ger many; April, 1968. For further information on this subiect please contact: Environmental Affairs Department, lohns-Manville Greenwood Plaza Denver. CO 80217 EA-4P-376 } BB 0015824 | Primed "it-