Document RpND3RZvdrB55DZVXYJ4KQv1V

FILE NAME: Marley (MAR) DATE: 0000 DOC#: MAR025 DOCUM ENT DESCRIPTION: Published Article from American Laboratory Asbestos i VO' By Walter C. McCrone and Ian M. Stewart IN m a y 1968, Dr. Irving J. Selikofi 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. Selikofi's 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. SelikofTs effort, Dr. McCrone is Scientific Adviser and Mr. Stewart is Manager, Electron Optics Group, McCrone Associates, Inc. followed up by the FDA, Depart X ment of Labor, and other inter ested parties, most responsible \ V companies are now doing then- best to minimize, if not eliminate, \ asbestos as a health hazard. The microscopist has an im A t portant role in this program to control asbestos as a contaminant < ,r in the air we breathe, the fluids A. ' . . X we drink, and the food we eat. He must be able to identify asbestos fibers and quantify their size and V* . * V, V ~ !; number. There are problems be cause there are other fibrous sub jjk stances confusingly similar to as bestos, and there are several dif \ .. ferent types of asbestos {Table 1), A ., . differing in optical properties and composition and possibly in the * ' XX l! \ \\ degree of their hazard to humans. Analytical methods must be sensitive enough for the identifica \ tion of single fibers. Of course, / / \V only a microscope and a trained microscopist can do this. There are methods, e.g., x-ray diffrac tion and DTA, that identify min i/ / i 5 t . 5 ute percentages of asbestos in Chrysotile fiber bundle. Table 1 Composition Serpentine CHRYSOTILE 3M g 0-2 S i02* 2H20 ACTINOLITE 2C a04M g0 F e 0 8 S i0 2*H20 Asbestos Amphiboles TREMOLITE 2Ca05MgO* 8 S i02*H20 ANTHOPHYLLITE 7MgO*8SiC>2* h 2o Specific gravity Crystal system Refractive indices 2.36-2.5 monoclinic 1.49-1.57 3.03-3.5 monoclinic 1.62-1.68 2.9-3.2 monoclinic 1.60-1.65 2.85-3.5 orthorhombic 1.60-1.66 AMOSITE 5-5FeO* 1-5MgO 8S i02*H20 2.6-3.0 monoclinic 1.66-1.70 CROCIDOLITE Na20' Fe203* 3Fe0*8Si02 h 2o 3.0-3.45 monoclinic 1.69-1.71 MARDEP0Q0437 AM ERICAN LAB O R ATO R Y : 13 i ASBESTOS continued Table 2 Asbestos type Chrysotile Anthophyllite Amosite Crocidolite Dispersion staining colors for asbestos Refractive index liquid Dispersion staining color Parallel Perpendicular 1.560 1.610 1.670 1.700 light blue blue-green red magenta magenta 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 /xm, 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 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 fj.mthick 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. Scientists are exploring the vast resources of the oceans, not only for links to our origins, b u t for new sources of food. Many scientists believe that our beleagured planet cannot forever support the popula tion explosion. The warning voices of these men are at last being heard. Mankind is slowly awakening to the frightening realization that even our seas cannot withstand the absorption of man's w aste without dire consequences. Nikon is in the forefront of undersea research technology. 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SCIENTIFIC OPTICAL PRODUCTS DIVISION. 38804 BAUSCH STREET, ROCHESTER, N. Y. 14602 ASBESTOS continued Figure 2 Chrysotile fibers filtered from a water supply, 30,00QX. Figure 3 Selected area electron diffraction pattern lor 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 mm2 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 llers 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 + 3 4 am. 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 L X W2). 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 am phiboles 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 5/un/m3 of sample. 3- The scanning electron mi croscope with energy dispersive x-ray analyzer shcflpRgferoiff A K /lP Q If'A M I A R D D A T n D V 17 ASBESTOS continued 56 Manual models, 12 models motorized UniSlides Apply manual or motor driven precision UniSlides as complete translation units in your instrument or machine to linearly advance tool, work piece, optics, transducer or prod uct. UniSlides are compact, non-magnetic, noncorrosive, moderately priced. UNISUDE ASSEMBLIES Basic Dovetail Units. Lead Screw Models. Mi crometer Screw Models. Rapid Advance with Lock and Fine Screw Motion. Adapter Plates for Combining. UniSlides into 2 and 3 Coordi nate Traversing mechanisms. English or Metric Scales, Orive Screws and Verniers. Turntables. UNISUDE CONSTRUCTION: 2024-T4 Aluminum Dovetail Base, Aluminum sliding element with laminated Nylatron GS bearings, Precision machined and lapped dove tail ways. Cross section: A 1500 Series-1 Vh'' x W . A 2500 Series-2Va" X TV', A 4000 Series - 4 " x 1". Length; Manual units to 30". Engi neering data and prices in Catalog G-73 upon fibers/Iiter 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' anthophyllitfe fibers/Iiter 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 (EM A ), 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. VELM EX ,nc. P.O.BOX 38 E. BLOOMFIELD. NY 14443 Telephone 315/657-6151 C irc le R ead er S ervice C ard No. 69