Document ZBD32JvMNZJV9Qv0MzdzzMDJ8

The "Asbesto*" Minerals: Definitions, Description, Modes of Formation, Physical and Chemical Properties, and Health Risk to the Mining Community Malcolm Ross tJ.S. Geological Survey National Center, 959 Reston, VA 22092 To be published in: Workshop on Asbestos: Definitions and Measurement Methods. National Bureau of Standards Special Publication (1977). ASARCO ALV 0002746 Abstract The mineralogical description of "asbestos" given here is based on a very special feature common to all forms of commercial "asbestos" -- the property that permits the minerals to separate into long tubes or fibrils only a few tens of nanometers thick. This separation can be accomplished by very light grinding or agitation; the common nonfibrous amphiboles do not separate into such fibrils even after intense grinding. The ease of such fibril separation may be caused by the special nature of the crystal structures of the commercial "asbestos" minerals. Repeated twinning on (100) in amosite and crocidolite, the curling of layers of chrysotile to form tubes, and the presence of triple, quadruple, and rv-tuple chains ("Wadsley" defects) in amosite, crocidolite"/ anthophyllite, and tremolite are the structural features that probably promote the formation of thin fibrils. Stability diagrams in the system MgO-SiOj-H^O indicate possible geochemical processes by which commerical "asbestos" can form. The relative health risk posed by exposure to the "asbestos" minerals may be related to the fibril composition, crystal structure, size, shape, and total surface area. The relative chemical reactivity of the fibril surface is predicted to be chrysotile < anthophyllite < amosite < crocidolite on the basis of the types of oxidation-reduction and exchange reactions that may occur. According to epidemiological studies relative health risk appears to be anthophyllite < chrysotile < amosite < crocidolite. "Asbestos" health risks in the mining and milling industry and environs-is reviewed. Health studies done in the chrysotile mining district of Quebec, Canada, have presented good evidence that realistic "asbestos" dust standards can be set that not only protect the worker and resident of the mining areas from undue health risk but also allow the industry to operate economically. ASARCO ALV 0002747 Key Words Asbestos, amphibole, chrysotile, talcbole, tremolite, actinolite, anthophyllite, amosite, cummingtonite, hornblende, amphibolite, serpentinite, grunerite, crocidolite, mesothelioma, lung cancer, health risk, Wadsley defects, asbestos stability, ambient air, dust levels, surface chemistry, chrysotile mining, chrysotile emissions, Thetford Mines, Quebec, Canada, Orals, U.S.S.R., Homestake Mines, S.D., Hunting Hill Quarry, Rockville, Md. ASARCO ALV 0002748 Introduction It is generally a rather straightforward, though often time-consuming mineralogical task to describe the physical and chemical properties of amphiboles and serpentines, including those varieties referred to as "asbestos". Exceptions are minerals such as fibrous tremolite and fibrous talc that to date do not have adequate mineralogical descriptions. Defining minerals that constitute an "asbestos" health hazard is an entirely different and a much more complex problem, for it involves many factors not included within the science of mineralogy. This commentary is concerned with the various definitions of "asbestos" as they relate to: (1) the medical profession, which must determine which types of mineral particles constitute an "asbestos" health hazard; (2) the legal and regulatory professions, which must enact and enforce the laws relating to "asbestos" use, (3) the mineralogical profession, which must describe the chemical, structural, and physical properties of such minerals, and (4) the mining auarrying industries, which may be affected by these A* definitions. ' What is "Asbestos"? Three definitions of "asbestos" found in the Glossary of Geology [9, p. 41] are quoted as follows: "asbestos (a) 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, are heat resistant and chemically inert, and possess a high electric insulation, and therefore are suitable for uses {as in yarn, cloth, paper, paint, brake linings, tiles, insulation, cement, fillers, and filters) where incombustible, nonconducting, or chemically resistant material is required. (b) A mineral of the asbestos group, principally chrysotile (best adapted for spinning) and certain fibrous varieties of amchibole (esp. tremolite, actinolite, and crocidolite). (c) A term strictly applied to the fibrous variety of actinolite." ASARCO ALV 0002749 The term "asbestos," from a geoscientist's point of view, applies only to the minerals chrysotile (one of the serpentine polymorphs), "amosite" (a _' variety of grunerite), "crocidolite" (a variety of riebeckite), anthophyllite, tremolite, and actinolite when they are present in sufficient quantity to be commercially valuable for their special physical and chemical properties, which include fibrous habit, insulation qualities, low electrical conductivity, fire resistance, end suitability for weaving. Many other minerals sometimes possess habits described variously as acicular, asbestiform, elongate, fibrous, bladed, lamellar, filiform, prismatic, or columnar; for example, minerals of the zeolite group having acicular habit, fibrous calcite and quartz, acicular wollastonite, prismatic pyroxenes, elongate crystallites of attapulgite, and filiform sepiolite. Since these minerals are not exploited for the - _ commercially valuable properties listed above, they are not called "asbestos" by geoscientists. . At present, the most widely used definition of "asbestos" by various groups concerned with environmental health problems, including the U. S. Environmental Protection Agency (EPA) and the U. S. Mining Enforcement and Safety Administration (MESA), is from the notice of proposed rulemaking for "Occupational Exposure to Asbestos" published in the Federal Register (Oct. 9, 1975, . p. 47652, 47660) by the U. S. Occupational Safety and Health Administration (OSHA). In this notice, the naturally occurring minerals chrysotile, amosite, crocidolite, tremolite, anthophyllite, and actinolite are classified as "asbestos" if the individual crystallites or crystal fragments have the following dimensions: length - greater than 5'micrometers, maximum diameter - less than 5 micrometers, and a length to diameter ratio of 3 or greater. Any product containing any of these minerals in this size range are also defined as "asbestos," The crushing and milling of any rock usually produces some mineral particles that are within the size range specified in the OSHA rules. Thus, these regulations present a formidable problem to those analvsino for "asho^tnc" ASARCO ALV 0002750 minerals in the multitude of materials and products in which they may be found in some amount, for not only must the size and shape of the "asbestos" . particles be determined, but also an exact mineral identification must be made. A wide variety of amphiboles is found in many types of common rocks; many of these amphiboles might be considerd "asbestos" depending upon the professional training of the person involved in their study and the methods used in mineral, characterization. Campbell et al. [3] have carefully described the differences between the relatively rare fibrous varieties of the amphiboles and the common nonfibrous forms. ' If the definition of "asbestos" from the point of view of a health hazard does include the common nonfibrous forms of amphibole, particularly' the. horn blende and cummingtonite varieties, then we must recognize that "asbestps" is present in significant amounts in many types of igneous and metamorphic rocks covering perhaps 30 to 40 percent of the United States. Rocks within the serpentinite belts; rocks within the metamorphic belts higher in grade than the greenschist facies, including amphibolites and many gneissic rocks; and amphibole-bearing igneous rocks such as diabase, basalt, trap rock, and granite would be considered "asbestos" bearing. Many iron formations and \ copper deposits would be "asbestos" bearing, including deposits in the largest open-pit mine in the world at Bingham, Utah. "Asbestos" regulations would thus pertain to many of our cointry's mining operations, including much of the construction industry and its quarrying operations for concrete aggregate, dimension stone, road metal, railroad ballast, riprap, and the like. The "asbestos" regulations would also pertain to the ceramic, paint, and cement industries and to many other areas of endeavor where silicate minerals are used. We do not know whether health investigators will consider other minerals that commonly possess a fibrous or acicular habit to be health hazards; minerals such as wollastonite, the fibrous forms of calcite and quartz, acicular minerals of the zeolite mineral group, the pyroxenes, the sepiolite ASARCO ALV 0002751 minerals including attapulgite, and the calcium silicates found in Portland cement. Certainly if the common amphiboles such as hornblende, tremolite, actinolite, gedrite, and cummingtonite with their typical prismatic cleavage are considered health hazards, the common pyroxenes having similar habits should also be considered health hazards. A Mineralogical Description of Commercial "Asbestos'' The commercial deposits of "asbestos" contain one of the following minerals: chrysotile, Mg3Si205(OH)4; amosite, (Fe2+,Mg)7Sig022(OH)2 (a variety of grunerite); crocidolite, Na2(Fe2+,Mg)3Fe2+Sig022(OH)2 (a variety of riebeckite); "fibrous" anthophyllite, (Mg,Fe)7SiQ022(OH)2? and "fibrous" tremolite and actinolite, Ca (Mg,Fe) Si 0 (OH) . Tremolite and actinolite -' 2 5 8 22 are now, as they were in the past, of little economic importance; -_ anthophyllite is of little economic importance now. About 95 percent of the commercial asbestos now used in the United States is chrysotile,- of which about 90 percent is imported from Canada. Ho commercial amosite or crocidolite has ever been mined in the United States. In addition to being compositionally different, the five amphibole forms of commercial "asbestos" have completely different crystal structures from that of chrysotile. The structure of chrysotile consists of double layers, each consisting of a layer of linked SiO_ tetrahedra that is coordinated to a 4. ` second layer of linked MgO^COH)^ octahedra through the sharing of oxygen atoms; the composite double layer rolls up, like a window shade, to form long hollow tubes. The diameters of the individual tubes are on the order of 25 nm; the length-to-diameter ratio can vary from 5 or 10 to well over 10,000. The structures of the anrohibole minerals, on the other hauid, are composed of strips or ribbons of linked polyhedra, which join together to form the three- dimmensional crystal. The individual strips are composed of three elements--two 5 ASARCO ALV 0002752 double chains of linked (Si,Al)o tetrahedra that form a "sandwich" with a *" 4 strip of linked HgOg, FeO^, or AlOg octahedra. The structural relationship of the upper double tetrahedral chain to the octahedral part of the strip is shown in figure 1. The three-dimensional arrangements of these strips or "I-beams" [26] in orthoamphibole (anthophyllite) and in clinoamphibole (tremolite, amosite, actinolite, and crocidolite) are shown in figure 2. One feature is common to the six "asbestos" minerals: their ready separation into long fibrils or tubes only a few tens of nanometers in diameter. This separation can be accomplished by very light grinding or by agitation in water by means of an ultrasonic separator. The common . nonfibrous amphiboles do not separate into such fibrils even after intense grinding; instead, they break up along cleavage plcuies into rather short ~ stubby prisms--th. ough the length-to-diameter ratio may still be greater than 3:1. > What causes the special type of fibril separation found in commercial forms of "asbestos" but generally not in the nonfibrous amphiboles? Three observations are pertinent: (1) Chrysotile, which forms individual hollow tubes, can separate into fibrils as thin as the diameter of the individual tube. The chemical bonding between tubes is very weak and perhaps is due only to van der Waals forces; thus, the tubes are easily separated from one another. (2) Amosite and crocidolite "asbestos" from South Africa is repeatedly twinned on (100) as has been observed in electron microscope studies [4, 15, 25, 34]. This "polysynthetic" twinning,.which produces repeated planar faults parallel to (100), is extremely rare in the nonfibrous calcium-rich amphiboles (temolite, hornblende) and uncommon in nonfibrous amphiboles of the curcming- tonite-grunerite series [30, 31, 32]. 6 ASARCO ALV 0002753 (3) Amosite, crocidolite, fibrous anthophyllite, and fibrous tremolite have been shown bo possess chain defects, also called "Wadsley" defects [8, 15, 36, 37, 38]. These defects are caused by the formation of expanded "I-beams" that are composed of triple, quadruple ...etc. chains of linked (Si,Al)0 4 tetrahedra rather than the double chains found in all amphibole crystal struc tures. If these "I-beams" are expanded indefinitely, the resulting strip becomes identical with the single talc layer of composition Mg^Si^O^(0H)4; recall that the composition of anthophyllite is Mg_Si 0,,(0H) . These expanded 7 8 22 2 ".I-beams" units can intermix with the regular amphibole "I-beams" to form a variety of minerals that I refer to as "talcboles" in allusion to their hybrid character--between talc and amphibole. Veblen [38] has described the detailed structures of four of these "talcboles" obtained from specimens originally described as "fibrous anthophyllite." In these crystal structures, "I-beams" of one or two types form an ordered three-dimensional structure. Veblen [38] showed evidence, as did Hutchison et al. [15], that disordered arrangements of these structural units also occur. Hutchison et al. [15] reported the presence of expanded "I--beams" structures in fibrous tremolite, and Franco et al. [6] reported the apparent presence of triple-chain lamellae, seen as planar faults on (010}, in crocidolite from Western Australia. Formation of "Asbestos" How do chrysotile and the "talcboles" form? Modes of origin can be inferred from the stability relationships among talc, anthophyllite, enstatite, forsterite, -entigorite, and chrysotile given by Hemley et al. [13]. Their mineral stability fields at 1 .kbaJ^O, in terms of crystallization temperature and molality of aqueous silica, are given in figure 3. This _ ' -fof figure shows a mnfter of relationships pertinent to the problem ofA"asbestiform" minerals. As the "temperature decreases, forsterite (Mg-rich olivine) can react 7 ASARCO ALV 0002754. to form antigorite or chrysotile depending on the silica concentration in the aqueous solutions to which the olivine-bearing rock is exposed. One chemical reaction that may lead to the formation of brucite-bearing serpentinite is: 2Mg SiO + 3H O -* Mg Si O (OH) + Mg (OH) 24 2 3 25 4 2 fosterite chrysotile brucite This reaction may explain the origin of the very long brucite needles, referred to as "nemalite," that are found in various serpentinites. Thirty-centimeter- long needles of this mineral were collected by C. E. Brown (U.S. Geol. Survey) from a Quebec serpentinite locality and were examined by single-crystal X-ray methods (Malcolm Ross, unpub. data). The brucite needles show hexagonal. symmetry, a_ = 0.315 nm, c_ = 0.474 nm, and the long direction of the needles are parallel to the brucite a-direction. The rather marked line broadening that appears in the X-ray pattern suggests that the brucite needles are composed of many small crystallites oriented so that their a^axes are parallel to the fiber direction. The brucite needles are intergrown with chrysotile, for chrysotile X-ray reflections are superimposed on the diffraction pattern of brucite, and extremely long chrysotile fibrils remain when the brucite needles are dissolved by dilute ENO^. At higher concentrations of aqueous silica forsterite may alter to talc by the reaction: 3Mg_SiO + 5 (H SiO.) -* 2Mg,,Si 0 (OH) + 8H 0 24 4 4 aq. 3 4 10 2 2 At silica concentrations near the quartz saturation curve, anthophyllite can alter directly to talc by the reaction: 3Mg7Si 0,,(0H)_ + 4(H.SiOj - 7Mg Si 0 (OH) + 4H O 8 2 2 4 aq. 3 4 10 2 2 This reaction may be of importance for the formation of fibrous anthophyllite and talc. As the tenperature decreases and the H20, Mg2+ , and silica 8 ASARCO ALV 0002755 activities remain within geologically reasonable limits one probable reaction sequence is: enstatite anthophyllite - talc. If the alteration of a chain silicate to talc proceeds by an intragranular reaction, "talcbole7type" phases may form as intermediates between anthophyllite and talc during low-tenperature alteration. Figure 4 shows the stability fields of forsterite, enstatite, anthophyllite, and talc in terms of temperature and molality of aqueous silica [13]. A stability (or metastability) field for the "talcboles" (labeled "asbestos") is superimposed on this diagram, overlapping the fields of talc and anthophyllite. The fibrous nature of the "talcboles" cm be explained if the alteration process of a. chain silicate (anthophyllite) to a sheet silicate (talc) proceeds by reforming the double chains at the unit-cell level. In figure 4, the phase boundary between enstatite (a pyroxene having the formula Mg^i^Og) and anthophyllite suggests the possibility of having mixed single chain (pyroxene) and double chain (amphibole) structures. . The fibrous nature of commercial amosite and crocidolite appears to be related to the crystal growth mechanism; perhaps the crystallites nucleate at many centers and grow as individual fibers only a few tens of nanometers thick (see Franco et al. [8, figures 1, 2]). The presence of (100) twinning and "Wadsley" defects may be the result of rapid growth and, in addition, may hinder growth in a direction perpendicular to the fiber axis. Properties of "Asbestos" that may be Related to Health Risk Health studies suggest that of -the four economically important forms of "asbestos," crocidolite has been responsible for the greatest health risk, followed by amosite, then chrysotile, and lastly anthophyllite [11]. If we 9 ASARCO ALV 0002756 assume that the_ health hazard caused by the commercial "asbestos" minerals is due to some combination of their chemcial, structural, and physical properties, we can make some predictions about their relative biological activity. All commercial "asbestos" minerals separate into very thin fibrils; possible reasons for this have been discussed previously. The thickness, length, and flexibility of the fibrils apparently is important in determining to how the fibrils lodge in human tissue and how readily they are cleared from the lung areas. The straight fibrils of small diameter, particularly those of crocidolite, can more readily move to the periphery of the lung, where they are in a position to penetrate the pleura and thus produce mesotheliomas .[11]. That curly fibrils, especially those of chrysotile, are more readily,arrested in the upper respiratory tract, is given as a reason for the low incidence of mesotheliomas in chrystotile miners and millers [11, 19, 23]. Assessment of the role of fibril size in relation to lung cancer is less clear [11]; however. Gross [12] cited evidence that-"asbestos" fibers less than 5 ^im long cause negligible pathogenicity, both of the lung and pleura. The problem of fibril size in relation to cancer incidence is of some importance, for the average ambient airborne "asbestos" fiber is shorter than the average fiber in the whole rock. Brulotte [2] reported that the average concentration of airborne dust particles in the chrysotile mining district of Thetford Mines, Quebec, was 80,500 ng/m3 during active mining and 39,600 ng/m3 during a 5-month period when the mines were closed. If we assume that the rock contains 4 weight percent chrysotile, these measurements suggest a minimum chrysotile dust concentration in the. ambient air of 3220 and 1534 ng/m3.i/ The total surface area of the inhaled fibrils and the chemical reactivity of this surface may have an important influence in the production of cancer. 10 ASARCO ALV 0002757 1/ Conversion of_these figures (nanograms chrysotile per cubic meter of air) to numbers of "fibers" per cubic centimeter of air (the value usually given in health studies) is estimated by using the following relations: (1) density of chrysotile ^=2.53g/cm =2.5 x 109ng/cm3 (2) volume of 1 ng chrysotile = 4xl0-10cm3 = 400 pm3 (3) volume of chrysotile fibers in pm3/cm3 = ^bOO^ (4) if a fiber having dimensions 1 um x 1 pm x 5 pm (5pra3) is designated as a "standard fiber," then 1 ng chrysotile = 80 "standard fibers" (5)number of chrysotile "standard fibers"/cm3 = .(u9/m )_ 12,500 - 11 ASARCO ALV 0002758 Researchers have not yet determined whether this surface plays a direct part in the formation-of cancerous tissue, or whether a carcinogenic chemical adheres to the mineral surface and the chemical itself later reacts with the tissue or in some way catalyzes the carcinogenic process. The high incidence of lung cancer in men who worked in the "asbestos" trades (textiles, brake lining frabrication, insulating) and who also smoked (33] indicates that carcinogenic chemicals in the tobacco smoke may somehow interact with the "asbestos" fibrils. If many of the fibrils are not easily cleared from the lung, they may adsorb these chemicals and hold them indefinitely. Injection of "asbestos" fibrils directly into the pleura of animals causes a high _ incidence of mesothelioma [40]. These experiments suggest a direct. -- relationship between the active fibril surface and production of pleural " cancer. However, other dissimilar substances injected into animals also cause tumors; for example, nonfibrous hematite (Fe O ), sanidine (KAlSi O ), 23 3 8 and corundum (Al^O^)' ^27]. As a generalization, the relative chemical reactivity of the exposed fibril surfaces of the four important forms of commercial "asbestos" in aqueous solutions is: . chrysotile < anthophyllite < amosite < crocidolite. Chrysotile, the least reactive of the four, is composed of rolled-up layers that possess no broken chemical bonds except where the edges of the layers are exposed at the ends of the tubes. The three amphiboles, on the other hand, have broken chemical bonds on all surfaces of the fibrils. Anthophyllite can alter to various other silicates in aqueous solutions, as has been explained above. Similar alteration mechanisms might also exist for crocidolite and amosite, although to my knowledge, these have not been . 12 ASARCO ALV 0002759 docmented. However, studies of the geochemistry of silicates indicate that A *" the exposed surfaces of these two amphiboles present some interesting possibilities for chemical change. Amosite (and also crocidolite) can under go oxidation-reduction reactions of the type, , . Fe7*Si8022<0al2Fel*I'ersi802202 * 2 Ernst and Wai [6] have demonstrated that this reaction takes place in iron bearing sodic amphiboles at 705C. The complete reversibility of such a reaction in the chemically similar silicate mineral biotite, has been demonstrated by Wones [42] and by Takeda and Ross [35]. In the experiments of Wones, auto-oxidation was accomplished in a neutral atmosphere (flowing argon) at 500 to 700C. Reduction was accomplished by passing hydrogen'gas over the crystals. Analogous reactions can take place at much lower * temperatures.but also at much lower rates. Cation exchange reactions take place in the amphiboles known as richterites [14]; exchange is accomplished within the A-site of the amphibole structure at 775-850C by the reaction (Na)CaNaMg5Sia022(0H,F)2 + K+^UOCaNaMg^igO^ (0H,F) 2 + Na+. Crocidolite having a partially filled A-site such as that from Bolivia [41] can also undergo exchange reactions with postassium being replaced by sodium b and possibly oxonium and ammonium ions. Crocidolite with a partially or A completely vacant A-site may undergo exchange reactions coupled with oxidation-reduction, e.g. Na2Fe|+Fe23+Si8022(0H)2 + R+ + e * (R+)Na2Fe42+Fe3+Sig022(OH)2 where R+ = K+, Na+, H 0+, or NH*, and = a vacant site. 34 . ` 13 ASARCO ALV 0002760 Whether such reactions can take place within animal tissue is not known, Jr - but the charge and reactive surfaces of crocidolite and amosite fibrils appear A ~~ ' to offer excellent sites or templates for the initiation of complex chemical changes. a. The surface cure available for adsorption is, of course, directly related to fibril thickness or diameter. The specific surface of chrysotile, as measured both by nitrogen adsorption and permeability, is about twice that of amosite and crocidolite [28]. Because chrysotile forms hollow tubes, this larger area for adsorption in chrysotile is predictable if the average fiber thickness is similar for all three minerals. The strain-free layer of chrysotile has a radius of curvature of abput 8.8 nm [5]; thus, the minimum diameter of the tube' should not be much less than 17 nm. The most frequently measured tube diameter is about 26 nm. Bates and Comer [1] found in a study of chrysotile from Arizona and Quebec, a range of diameters from 11.4 to 85 nm; the average diameter was 25 nm. The fiber size ranges in the other forms of commercial "asbestos" have not come to my attention, although some crocidolite fibers from Western Australia [8] appear to be on the order of 50 nm wide. "Asbestos" Health Risks in the Mining and Milling Industry and Environs Although a significant health risk for those who work in the "asbestos" trades, particularly for those who smoke, has been well documented, such a risk is not clearly documented for those in the "asbestos" mining and milling industry and for those who reside in areas of such activity. The most detailed study of an "asbestos" mining community is that of the chrysotile mining areas of Quebec, Canada; the studies were started in 1966 and continue 14 ASARCO ALV 0002761 to the present [20, 21, 22, 23]. Similar studies of chrysotile miners on a smaller scale have been undertaken by Kogan et al. [16] in the Urals, U.S.S.R., and by Vigliani [39] in Italy. According to McDonald [17, 18] these other studies came to the same conclusions on health risk as the Quebec studies, the latter of which have led the way in making some assessment of the health risk relative to the amount of dust to which the workers were exposed. Health-risk studies of workers in the "asbestos" trades, for the most part, have not given reliable dust-exposure figures, or even the relative amounts and types of "asbestos" inhaled. Chrysotile has been mined in the Thetford Mines, Black Lake, and'Asbestos localities of Quebec for nearly a century, beginning in 1886. Production has increased steadily since then, reaching 907,000 metric tons in 1956 and 1,500,000 metric tons in 1976. A tremendous amount of ambient dust has been generated over the years both by mining activities and by the winds blowing over the huge tailings piles. Even in 1974, when dust-emission controls had much improved over those of the earlier years (72 million particles per ft3 in 1950 to 4 million particles per ft3 in i975 [20]) as a result of wet drilling, watering of haul roads, etc., emissions of particles from chrysotile mining and milling operations in the Province of Quebec amounted to 140,000 metric ~ tons, of which about 4 percent (5600 metric tons) was "asbestos" dust [2], The ambient dust levels for this region have already been discussed. Is there a high incidence of cancer of the lung and pleura among the 35,000 residents of the Thetford Mines area of Quebec, 10 percent of whom are employed in the chrysotile industry? According to McDonald et al. [17, 18, 19, 20, 21, 22, 23], the cancer incidence for the male employees in the Quebec chrysotile industry is similar to the male cancer incidence in the whole of Canada. In table 1 is given the proportional mortality from lung 15 ASARCO ALV 0002762 cancer and mesothelioma for the Quebec and North Italian chrysotile miners and millers and also for the entire populations of various countries in the year 1970., In the period 1936-1973 seven cases of mesothelioma have been reported in the Quebec mining and milling industry [19, table 12]. The world-wide incidence of mesothelioma in those who worked in the chrysotile mining and milling industry for the period 1958 to 1976 is 11 cases [19, table 4]. The Canadian studies do show an increased incidence (2.1 to' 3.6 times) of lung cancer for those workers exposed to the highest concentrations of dust -- 400 to 800+ mpcf-yrj/ However, these studies show that little health risk is experienced by workers breathing less than 200 mpcf-yr for a working life of 50 years. An unusually high number of deaths caused by lung cancer in Homestake gold miners during the period 1960 to 1973 has been reported by Gillam et _al. [10]. The cohort consisted of 440 individuals who in 1960 had worked 5 years or more underground. Gillam et al. attributed the high incidence of lung cancer to inhalation of cummingtonite amphibole. They did not specify whether the hornblende amphibole, also present in the rock being mined, also contributed to health risk. In rebuttal to this work, McDonald et al. [24] reported on a health analysis of a cohort of 1321 Homestake miners whose working period was from as far back as 1937 to the end of 1973; each of the miners had more than 21 years mining service. Deaths resulting from malignant neoplasm were very close to those expected (93 observed, 90.5 expected); this includes the subcategories of malignant neoplasm -- respiratory, gastro-intestinal, and "other" cancers. The excess death found in the Homestake miners was due in fact to.silicosis, silico-tuberculosis, and heart disease. McDonald et al. [24] stated, "The pattern of mortality of men with long employment in this 16 ASARCO ALV 0002763 " This unit expresses (in millions) the average number of particles (includ ing approximately 4% chrysotile) contained in each cubic foot of air inhaled during a worker's career in the mines or mills times the number of years the worker was employed. If the dust is assumed to contain 4% chrysotile, then working for 50 years at a dust level of 16 mpcf (800 mpcf-yr) is roughly equivalent to inhaling 23 chrysotile particles for every cm^ of air taken into the lungs during the employment lifetime. A figure of 200 mpcf-yr is roughly equivalent to 6 particles of chrysotile/cm^. Conversion from dust particle measurements to chrysotile fibers per cm^ is difficult because * chrysotile abundance varies from place to place. * 17 ASARCO ALV 0002764 industry indicates a serious pneumoconiotic hazard characteristic of hard rock miners but not of cancer." Fears [7] has made an epidemiological study of cancer risk, including respiratory cancer, in 97 U. S. counties in 22 States known to be mining chrysotile or amphibole "asbestos." He found no excess of cancer mortality compared with cancer mortality rates in 194 demographically matched counties in which such minerals are not known to be mined; cancer mortality in both groups of counties was significantly below the national average. At present, people are concerned about the possible health hazards associated with the quarrying of serpentine rock at Hunting Hill quarry near Rockville, MD, and its. use as a surface material for roads, playgrouncls,_and parks. The rocks being quarried here are very similar geologically to -those of the chrysotile mining localities of Quebec, except that they contain much less chrysotile -- about 0.5 weight percent. Rohl et al. [29] from Mount Sinai Hospital reported chrysotile fiber abundances of 500 to 4700 ng/m3 of air sampled adjacent to roads and a parking lot paved with loose crushed stone from the Hunting Hill quarry. The highest figures were measured during "moderate" motor vehicle use. The Mt. Sinai figures are equivalent to 0.2 to 1.9 ym3 of chrysotile per cm3 of air or 0.04 to 0.4 "standard fibers" per cm3 of air. Air samples taken near the perimeter of the Hunting Hill quarry gave chrysotile mass concentrations of from 0.02 to 64 ng/m3 or 2 x 10~6 to 5 x 10"3 "standard fibers" per cm3 of air (U. S. Bureau of Mines, State of Maryland, and McCrone Assoc.,unpublished data). The present U. S. Government limits for "asbestos" content of air are 2 fibers/cm3 (OSHA) and 5 fibers/cm3 (MESA) where a fiber is defined as longer than 5 ym, less than 5 ym wide, and having a length-to-width ratio of 3:1 or greater. '' 18 . ASARCO ALV 0002765 The publicity about the possible health risk because of dust emission from the Hunting" Hill quarry and its rock products had caused the quarry to lose about 30 percent of its business by July 1, 1977. Montgomery County, MD, expected to pay about $2.3 million in its initial effort to seal the roads so as to reduce dust emissions and to remove loose stone from the parks (The Council Report, Montgomery County, vol. 6, no. 22, July 1, 1977). Apparently, other mining and quarrying operations along the "serpentine belt" of the eastern U. S. from Maine to Alabama also will be considered . health risks to the general public [29]. Rohl et al. [29] suggested that exploitation of crushed amphibolite rock also raises the possibility of ~ contamination of the air by "asbestos"-like minerals. - Discussion The cancer incidence among those employed in the chrysotile mining and milling industry does not appear to be excessive when compared to national populations (table 1). However, the incidence of cancer among those employed in the "asbestos" trades is very high (table 1); incidence of lung cancer being 3 to 4 times that of the average population, incidence of mesothelsoma being 130 to 220 times that of the average population . The "asbestos" trades generally utilized a variety of "asbestos" minerals including amosite and/or crocidolite, sometimes mixed into a paste for lagging. If we consider that 80 to 90 percent of all the commercial "asbestos" ever mined was chrysotile and that there is a low incidence of cancer in the chrysotile mining industry, we are led to conclude that either amosite and crocidolite are very hazardous or that there is an additional factor relating to health risk in the "asbestos" trades which has not yet been discovered. Previously, I have discussed some reasons why these two minerals may be more chemically reactive than chrysotile. 19 ASARCO ALV 0002766 Definitive epidemiological studies of the amosite mining regions of South Africa and_the crocidolite mining regions of South Africa, Bolivia, and Australia appear to be lacking; such studies are needed in order to understand the high cancer incidence in certain trades utilizing these minerals. It is important to point out that the "asbestos" minerals should be considered separately when analysing their effects on the worker's health. Reasoning by analogy is dangerous; high cancer incidence associated with one form of "asbestos" in a particular occupation does not necessarily mean that there will be the same incidence when utilizing another form of "asbestos" in that or another occupation. Unfortunately, this type of reasoning, has led many to assume that any anphibole in any__ environment will cause high cancer mortality. ~- The operational problems in defining and characterizing fine mineral particles ctnd the unknown health effects on humans by minerals not generally regarded as "asbestos" appears to be causing more and more investigators to accept rather broad definitions for "asbestos." The present analytical tech niques used by the EPA and OSHA do not distinguish between amphibole cleavage fragments and the minerals geoscientists generally consider to be true "asbestos." In fact, if electron diffraction is not used expertly, many pyroxenes might be called "asbestos." For example, bronzite, a common orthopyroxene having the composition (Mg,Fe) Si 0,., is very similar chemically to anphiboles of the cummingtonite-grunerlte series, (Mg,Fe) Si 0,_(OH) . Also, orthopyroxene gives an electron diffraction pattern similar to that of cummingtonite -- both patterns possess 0.52 nm spacings between the diffaction row lines in the ho reciprocal lattice net. A full interpretation of the patterns is necessary for positive identification. Similarly, calcic pyroxenes might be confused with anphiboles of the temolite-actinolite series 20 ASARCO ALV 0002767 or with hornblende. Cummingtonite (and possibly hornblende) is considered an "asbestos" health hazard by health investigators from the National Institute of Occupational Safety and Health (NIOSH), as reported by Gillam et al. [10]. The Mt. Sinai group [29] suggested that crushed amphibole-bearing rocks (amphibolite) used as road-surfacing material may result in wide-spread "asbestos" contamination of community air. Along with the general use of broader definitions of "asbestos" is a trend toward setting lower and lower limits on the acceptable amount of "asbestos" permitted in the environment (at present the OSHA standard is 2 fibers/cm^; the MESA standard is 5 fibers/cm^, but it will soon be changed to the OSHA value). ' A more stringent "asbestos" health standard is presently being proposed by the National Institute for Occupational Safety and Health (Reexamination and Update of Information on the Health Effects of Occupational Exposure to Asbestos, December 1976; document prepared by NIOSH for transmittal to OSHA, as requested by the Assistant Secretary of Labor). This document states (p. 92-93): "Evaluation of all available human data provides no evidence for a threshold or for a safe level of asbestos exposure." ' "In view of the above, the standard should be set at the lowest level detectable by available analytical techniques--------." "Since phase contrast microscopy is the only generally available and practical analytical technique at the present time, this level is defined as 100,000 fibers >5 pm in length/m^ (0.1 fibers/cc)---------." A definition of "asbestos" to include many amphiboles, chrysotile', and possibly other minerals that appear fibrous or acicular in the electron microscope coupled with a fiber-concentration standard of 0.1 fibers/cm^ should serve to shut down a large number of our hard rock mines and quarries. ASARCO ALV 0002768 Also, nothing has yet been said about the effect of such standards on con struction workers_building highways, tunnels, bridges, or dams on amphibole- bearing rock, nor of the agricultural workers who are exposed to fiber- containing dust while working the croplands. If the present concept of low or "zero threshold" health risk and broad use of "asbestos" defintions continue, much of the crust of the earth could be considered a health hazard. A way of minimizing the effect on the mining industry of the present and proposed "asbestos" standards, yet still maintaining a good level of health safety^is presented by the Canadian studies of the Quebec chrysotile workers. Here J.. C. McDonald and his colleagues G. W. Gibbs, A. D. McDonald, M. R. Becklake, J. Siemiatycki, C. E. Rossiter, F. D. K. Liddell, ~- 0. A. El Attar, A. Harper, and many others [17, 18, 19, 20, 21, 22, 23] have undertaken not only to delineate areas of health risk in the Quebec environment but also to assess the exposure limits of rock dust where the incidence of cancer and other diseases is at an acceptably low level. No occupation can be considered to have a zero health risk. It would seem that similar studies in this field would be of value in the United States. 22 ASARCO ALV 0002769 tMARTINEZ A: L/''' Srf i-C *.' /O j-71 The "Asbestos" Minerals: Definitions, Description, Modes of Formation, Physical and Chemical Properties, and Health Risk to the Mining Community Malcolm Ross U.S. Geological Survey National Center, 959 Reston, VA 22092 To be published in: Workshop on Asbestos: Definitions and Measurement Methods, National Bureau of Standards Special Publication (1977). ASARCO ALV 0002770 Abstract The mineralogical description of "asbestos" given here is based on a very special feature common to all forms of commercial "asbestos" -- the property that permits the minerals to separate into long tubes or fibrils only a few tens of nanometers thick. This separation can be accomplished by very light grinding or agitation; the common nonfibrous amphiboles do not separate into such fibrils even after intense grinding. The ease of such fibril separation may be caused by the special nature of the crystal structures of the commercial "asbestos" minerals. Repeated twinning on (100) in amosite and crocidolite, the curling of layers of chrysotile to form tubes, and the presence of triple, quadruple, and n-tuple chains ("Wadsley" defects) in amosite, crocidolite, anthophyllite, and tremolite are the structural features that probably promote the formation of thin fibrils. Stability diagrams in the system MgO-SiC^-HjO indicate possible geochemical processes by which commerical "asbestos" can form. The relative health risk posed by exposure to the "asbestos" minerals may be related to the fibril composition, crystal structure, size, shape, and total surface area. The relative chemical reactivity of the fibril surface is predicted to be chrysotile < anthophyllite < amosite < crocidolite on the basis of the types of oxidation-reduction and exchange reactions that may occur. According to epidemiological studies relative health risk appears to be anthophyllite < chrysotile < amosite < crocidolite. "Asbestos" health risks in the mining and milling industry and environs is reviewed. Health studies done in the chrysotile mining district of Quebec, Canada, have presented good evidence that realistic "asbestos" dust standards can be set that not only protect the worker and resident of the mining areas from undue health risk but also allow the industry to operate economically. ASARCO ALV 0002771 Key Words Asbestos, amphibole, chrysotile, talcbole, tremolite, actinolite, anthophyllite, amosite, cummingtonite, hornblende, amphibolite, serpentinite, grunerite, crocidolite, mesothelioma, lung cancer,'health risk, Nadsley defects, asbestos stability, ambient air, dust levels, surface chemistry, chrysotile mining, chrysotile emissions, Thetford Hines, Quebec, Canada, Urals, U.S.S.R., Homestake Mines, S.D., Hunting Hill Quarry, Rockville, Md. ASARCO ALV 0002772 Introduction It is generally a rather straightforward, though often time-consuming mineralogical task to describe the physical and chemical properties of an\phiboles and serpentines, including those varieties referred to as "asbestos". Exceptions are minerals such as fibrous tremolite and fibrous talc that to date do not have adequate mineralogical descriptions. Defining minerals that constitute an "asbestos" health hazard is an entirely different and a much more complex problem, for it involves many factors not included within the science of mineralogy. This commentary is concerned with the various definitions of "asbestos" as they relate to: (1) the medical profession, which must determine which types of mineral particles constitute an "asbestos" health hazard; (2) the legal and regulatory professions, which must enact and enforce the laws relating to "asbestos" use, (3) the mineralogical profession, which must describe the chemical, structural, and physical properties of such minerals, and (4) the mining quarrying industries, which may be affected by these A definitions. What is "Asbestos"? Three definitions of "asbestos" found in the Glossary of Geology [9, p. 41] are quoted as follows: "asbestos (a) 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, are heat resistant and chemically inert, and possess a high electric insulation, and therefore are suitable for uses (as in yarn, cloth, paper, paint, brake linings, tiles, ' insulation, cement, fillers, and filters) where incombustible, nonconducting, or chemically resistant material is required, (b) A mineral of the asbestos group, principally chrysotile (best adapted for spinning) and certain fibrous varieties of amphibole (esp. tremolite, actinolite, and crocidolite). (c) A term strictly applied to the fibrous variety of actinolite." ASARCO ALV 0002773 The term "asbestos," from a geoscientist's point of view, applies only to the minerals chrysotile (one of the serpentine polymorphs), "amosite" (a variety of grunerite), "crocidolite" (a variety of riebeckite), anthophyllite, tremolite, and actinolite when they are present in sufficient quantity to be commercially valuable for their special physical and chemical properties, which include fibrous habit, insulation qualities, low electrical conductivity, fire resistance, and suitability for weaving. Many other minerals sometimes possess habits described variously as acicular, asbestiform, elongate, fibrous, bladed, lamellar, filiform, prismatic, or columnar; for example, minerals of the zeolite group having acicular habit, fibrous calcite and quartz, acicular wollastonite, prismatic pyroxenes, elongate crystallites of attapulgite, and filiform sepiolite. Since these minerals are not exploited for the commercially valuable properties listed above, they are not called "asbestos" by geoscientists. . At present, the most widely used definition of "asbestos" by various groups concerned with environmental health problems, including the U. S. ' Environmental Protection Agency (EPA) and the U. S. Mining Enforcement and Safety Administration (MESA), is from the notice of proposed rulemaking for "Occupational Exposure to Asbestos" published in the Federal Register (Oct. 9, 197 p. 47652, 47660) by the U. S. Occupational Safety and Health Administration (OSHA) In this notice, the naturally occurring minerals chrysotile, amosite, crocidolite, tremolite, anthophyllite, and actinolite are classified as "asbestos" if the individual crystallites or crystal fragments have the following dimensions: length - greater than 5 micrometers, maximum diameter - less than 5 micrometers, and a length to diameter ratio of 3 or greater. Any product containing any of these minerals in this size range are also defined as "asbestos." The crushing and milling of any rock usually produces some mineral particles that are within the size range specified in the OSHA rules. Thus, these regulations present a formidable problem to those analysing for "asbestos" 4A fftlInwe) ASARCO ALV 0002774 minerals in the multitude of materials and products in which they may be found in some amount, for not only must the size and shape of the "asbestos" particles be determined, but also an exact mineral identification must be made. A wide variety of amphiboles is found in many types of common rocks; many of these amphiboles might be considerd "asbestos" depending upon the professional training of the person involved in their study and the methods used in mineral characterization. Campbell et al. [3] have carefully described the differences between the relatively rare fibrous varieties of the amphiboles and the common nonfibrous forms. If the definition of "asbestos" from the point of view of a health hazard does include the common nonfibrous forms of amphibole, particularly the horn blende and cummingtonite varieties, then we must recognize that "asbestos" is present in significant amounts in many types of igneous and metamorphic rocks covering perhaps 30 to 40 percent of the United States. Rocks within the serpentinite belts; rocks within the metamorphic belts higher in grade than the greenschist facies, including amphibolites and many gneissic rocks; and amphibole-bearing igneous rocks such as diabase, basalt, trap rock, and granite would be considered "asbestos" bearing. Many iron formations and copper deposits would be "asbestos" bearing, including deposits in the largest open-pit mine in the world at Bingham, Utah. "Asbestos" regulations would thus pertain to many of our country's mining operations, including much of the construction industry and its quarrying operations for concrete aggregate, dimension stone, road metal, railroad ballast, riprap, and the like. The "asbestos" regulations would also pertain to the ceramic, paint, and cement industries and to many other areas of endeavor where silicate minerals are used. We do not know whether health investigators will consider other minerals that commonly possess a fibrous or acicular habit to be health hazards; minerals such as wollastonite, the fibrous forms of calcite and quartz, acicular minerals of the zeolite mineral grovp, the pyroxenes, the sepiolite ASARCO ALV 0002775 minerals including attapulgite, and the calcium silicates found in Portland cement. Certainly if the common amphiboles such as hornblende, tremolite, actinolite, gedrite, and cummingtonite with their typical prismatic cleavage are considered health hazards, the common pyroxenes having similar habits should also be considered health hazards. A Mineralogical Description of Commercial "Asbestos" The commercial deposits of "asbestos" contain one of the following minerals: chrysotile, MgjS^Os(OH)4; amosite, (Fe2+,Mg)ySig022(OH)j (a variety of grunerite); crocidolite, Na2(Fe^5+ ,Mg)3Fe23+Sig022(0H)2 (a variety of riebeckite); "fibrous" anthophyllite, (Mg,Fe)ySi^C^(OH)and "fibrous" tremolite and actinolite, Ca (Mg,Fe) Si 0 (OH) . Tremolite and actinolite .2 5 8 ** * are now, as they were in the past, of little economic importance; anthophyllite is of little economic importance now. About 95 percent of the commercial asbestos now used in the United States is chrysotile, of which about 90 percent is imported from Canada. Ho commercial amosite or crocidolite has ever been mined in the United States. In addition to being compositionally different, the five amphibole forms of commercial "asbestos" have completely different crystal structures from that of chrysotile. The structure of chrysotile consists of double layers, each consisting of a layer of linked SiO^ tetrahedra that is coordinated to a second layer of linked MgO^OH)^ octahedra through the sharing of oxygen atoms; the composite double layer rolls up, like a window shade, to form long hollow tubes. The diameters of the individual tubes are on the order of 25 nm; the length-to-diameter ratio can vary from 5 or 10 to well over 10,000. The structures of the amphibole minerals, on the other hand, are composed of strips or ribbons of linked polyhedra, which join together to form the three- dimmensional crystal. The individual strips are composed of three elements--two 5 ASARCO ALV 0002776 double chains of linked (Si,Al)0 tetrahedra that form a "sandwich" with a 4 strip of linked MgO , FeO , or A10, octahedra. The structural relationship 66 o of the upper double tetrahedral chain to the octahedral part of the strip is shown in figure 1. The three-dimensional arrangements of these strips or "I-beams" {26] in orthoamphibole (anthophyllite) and in clinoamphibole (tremolite, amosite, actinolite, and crocidolite) are shown in figure 2. One feature is common to the six "asbestos" minerals: their ready separation into long fibrils or tubes only a few tens of nanometers in diameter. This separation can be accomplished by very light grinding or by agitation in water by means of an ultrasonic separator. The common nonfibrous amphiboles do not separate into such fibrils even after intense grinding; instead, they break up along cleavage planes into rather short stubby prisms--through the length-to-diameter ratio may still be greater than 3:1. What causes the special type of fibril separation found in commercial forms of "asbestos" but generally not in the nonfibrous anphiboles? Three observations are pertinent: (1) Chrysotile, which forms individual hollow tubes, can separate into fibrils as thin as the diameter of the individual tube. The chemical bonding between tubes is very weak and perhaps is due only to van der Waals forces; thus, the tubes are easily separated from one another. (2) Amosite and crocidolite "asbestos" from South Africa is repeatedly twinned on (100) as has been observed in electron microscope studies [4, 15, 25, 34]. This "polysynthetic" twinning, which produces repeated planar faults parallel to (100), is extremely rare in the nonfibrous calcium-rich amphiboles (temolite, hornblende) and uncommon in nonfibrous amphiboles of the cumming- tonite-grunerite series [30, 31, 32]. 6 ASARCO ALV 0002777 (3) Amosite, crocidolite, fibrous anthophyllite, and fibrous tremolite have been shown to possess chain defects, also called "Wadsley" defects [8, 15, 36, 37, 38]. These defects are caused by the formation of expanded "I-beams" that are composed of triple, quadruple ...etc. chains of linked (Si,Al)0 4 tetrahedra rather than the double chains found in all amphibole crystal struc tures. If these "I-beams" are expanded indefinitely, the resulting strip becomes identical with the single talc layer of conposition Mg^Si^O^tOH) recall that the conposition of anthophyllite is Mg^Si 0^ (OH) These expanded "I-beams" units can intermix with the regular anphibole "I-beams" to form a variety of minerals that I refer to as "talcboles" in allusion to their hybrid character--between talc and anphibole. Veblen [38] has described the detailed structures of four of these "talcboles" obtained from specimens originally described as "fibrous anthophyllite." In these crystal structures, "I-beams" of one or two types form an ordered three-dimensional structure. Veblen [38] showed evidence, as did Hutchison et al. [15], that disordered arrangements of these structural units also occur. Hutchison et al. [15] reported the presence of expanded "I-beams" structures in fibrous tremolite, and Franco et al. [8] reported the apparent presence of triple-chain lamellae, seen as planar faults on (010), in crocidolite from Western Australia. Formation of "Asbestos" How do chrysotile and the "talcboles" form? Modes of origin can be inferred from the stability relationships among talc, anthophyllite, enstatite, forsterite, antigorite, and chrysotile given by Hemley et al. [13], "* . Their mineral stability fields at 1 kbaJ^0* terms of crystallization temperature and molality of aqueous silica, are given in figure 3. This O-f- ' -fWwtlM figure shows a number of relationships pertinent to the problem of^"asbestiform" minerals. As the tesperature decreases, forsterite (Mg-rich olivine) can react 7 ASARCO ALV 0002778 to form antigorite or chrysotile depending on the silica concentration in the aqueous solutions to which the olivine-bearing rock is exposed. One chemical - reaction that may lead to the formation of brucite-bearing serpentinite is: 2Mg2Si04 + 3H20 - Mg3Si205(0H)4 + Mg(OH>2 fosterite chrysotile brucite This reaction may explain the origin of the very long brucite needles, referred to as "nemalite," that are found in various serpentinites. Thirty-centimeterlong needles of this mineral were collected by C. E. Brown (U.S. Geol. Survey) from a Quebec serpentinite locality and were examined by single-crystal X-ray methods (Malcolm Ross, unpub. data). The brucite needles show hexagonal symmetry, & = 0.315 nm, = 0.474 nm, and the long direction of the needles are parallel to the brucite ^-direction. The rather marked line broadening that appears in the X-ray pattern suggests that the brucite needles are composed of many small crystallites oriented so that their ia-axes are parallel to the fiber direction. The brucite needles are intergrown with chrysotile, for chrysotile X-ray reflections are superimposed on the diffraction pattern of brucite, and extremely long chrysotile fibrils remain when the brucite needles are dissolved by dilute HNO 3 At higher concentrations of aqueous silica forsterite may alter to talc by the reaction: 3Mg_SiO. + 5 (H SiO ) 24 4 4 aq. 2Mg,Si O (OH) + 8H 0 3 4 10 2 2 At silica concentrations near the quartz saturation curve, anthophyllite can alter directly to talc by the reaction: 3Mg,Si 022(OH) + 4^,810,) - 7Mg,Si 0 (OH) ,, + 4H 0 ' 8 2 2 4 aq. 3 4 10 2 2 This reaction may be of importance for the formation of fibrous anthophyllite and talc. As the temperature decreases and the H20, Mg2+ , and silica 8 ASARCO ALV 0002779 activities remain within geologically reasonable limits one probable reaction sequence is: enstatite - anthophyllite talc. " If the alteration of a chain silicate to talc proceeds by an intragranular reaction, "talcbole7type" phases may form as intermediates between anthophyllite and talc during low-temperature alteration. Figure 4 shows the stability fields of forsterite, enstatite, anthophyllite, and talc in terms of temperature and molality of aqueous silica [13}. A stability (or metastability) field for the "talcboles" (labeled "asbestos'') is superimposed on this diagram, overlapping the fields of talc and anthophyllite. The fibrous nature of the "talcboles" can be explained if the alteration process of a chain silicate (anthophyllite) to a sheet silicate (talc) proceeds by reforming the double chains at the unit-cell level. In figure 4, the phase boundary between enstatite (a pyroxene having the formula Mg^Si^Og) and anthophyllite suggests the possibility of having mixed single chain (pyroxene) and double chain (amphibole) structures. The fibrous nature of commercial amosite and crocidolite appears to be related to the crystal growth mechanism; perhaps the crystallites nucleate at many centers and grow as individual fibers only a few tens of nanometers thick (see Franco et al. [8, figures 1, 2]). The presence of (100) twinning and "Wadsley" defects may be the result of rapid growth and, in addition, may hinder growth in a direction perpendicular to the fiber axis. Properties of "Asbestos" that may be Related to Health Risk Health studies suggest that of the four economically important forms of "asbestos," crocidolite has been responsible for the greatest health risk, followed by amosite, then chrysotile, and lastly anthophyllite [11]. If we 9 ASARCO ALV 0002780 assume that the health hazard caused by the commercial "asbestos" minerals is due to some combination of their chemcial, structural, and physical properties, we can make some predictions about their relative biological activity. All commercial "asbestos" minerals separate into very thin fibrils; possible reasons for this have been discussed previously. The thickness, length, and flexibility of the fibrils apparently is important in determining to how the fibrils lodge in human tissue and how readily they are cleared from the lung areas. The straight fibrils of small diameter, particularly those of crocidolite, can more readily move to the periphery of the lung, where they are in a position to penetrate the pleura and thus produce mesotheliomas [11]. That curly fibrils, especially those of chrysotile, are more readily arrested in the upper respiratory tract, is given as a reason for the low incidenct of mesotheliomas in chrystotile miners and millers [11, 19, 23]. Assessment of the role of fibril size in relation to lung cancer is less clear [11]; however. Gross [12] cited evidenct that "asbestos" fibers less than 5 urn long cause negligible pathogenicity, both of the lung and pleura. The problem of fibril size in relation to cancer incidence is of some importance, for the average ambient airborne "asbestos" fiber is shorter them the average fiber in the whole rock. Brulotte [2] reported that the average concentration of airborne dust particles in the chrysotile mining district of Thetford Mines, Quebec, was 80,500 ng/m^ during active mining and 39,600 ng/m3 during a 5-month period when the mines were closed. If we assume that the rock contains 4 weight percent chrysotile, these measurements suggest a minimum chrysotile dust concentration in the ambient air of 3220 and 1584 ng/m3.--^ The total surface area of the inhaled fibrils and the chemical reactivity of this surface may have an important influence in the production of cancer. 10 ASARCO ALV 0002781 1/ Conversion of these figures (nanograms chrysotile per cubic meter of air) to numbers of "fibers" per cubic centimeter of air (the value usually given in health studies) is estimated by using the following relations: 3 o3 (1) density of chrysotile =2.5g/cm =2.5 x 10 ng/cm (2) volume of 1 ng chrysotile = 4xl0"3'cm3 = 400 um3 (3) volume of chrysotile fibers in pm3/cm3 = (4) if a fiber having dimensions 1 pm x 1 pm x 5 ym (5ym3) is designated as a "standard fiber," then 1 ng chrysotile = 80 "standard fibers" (5) number of chrysotile "standard fibers"/cm3 = (n<?/m ) , 12,500 11 ASARCO ALV 0002782 Researchers have not yet determined whether this surface plays a direct part in the formation of cancerous tissue, or whether a carcinogenic chemical V adheres to the mineral surface and the chemical itself later reacts with the tissue or in some way catalyzes the carcinogenic process. The high incidence of lung cancer in men who worked in the "asbestos" trades (textiles, brake lining frabrication, insulating) and who also smoked [33] indicates that carcinogenic chemicals in the tobacco smoke may somehow interact with the "asbestos" fibrils. If many of the fibrils are not easily cleared from the lung, they may adsorb these chemicals and hold them indefinitely. Injection of "asbestos" fibrils directly into the pleura of animals causes a high incidence of mesothelioma [40]. These experiments suggest a direct relationship between the active fibril surface and production of pleural cancer. However, other dissimilar substances injected into animals also cause tumors; for example, nonfibrous hematite (Fe O ), sanidine (KAlSi O.), 23 3 8 and corundum (Al^O^)' As a generalization, the relative chemical reactivity of the exposed fibril surfaces of the four important forms of commercial "asbestos" in aqueous solutions is: chrysotile < anthophyllite < amosite < crocidolite. Chrysotile, the least reactive of the four, is composed of rolled-up layers that possess no broken chemical bonds except where the edges of the layers are exposed at the ends of the tubes. The three amphiboles, on the other hand, have broken chemical bonds on all surfaces of the fibrils. Anthophyllite can alter to various other silicates in aqueous solutions, as has been explained above. Similar alteration mechanisms might also exist for crocidolite and amosite, although to my knowledge, these have not been 12 ASARCO ALV 0002783 docmented. However, studies of the geochemistry of silicates indicate that A the exposed surfaces of these two amphiboles present some interesting possibilities for chemical change. Amosite (and also crocidolite) can under go oxidation-reduction reactions of the type, Fe7+Si822(0H)2^Fe5+Fe2+Si82202 + H2 Ernst and Wai [6] have demonstrated that this reaction takes place in iron bearing sodic amphiboles at 705C. The complete reversibility of such a reaction in the chemically similar silicate mineral biotite, has been demonstrated by Wones [42] and by Takeda and Ross [35]. In the experiments of Wones, auto-oxidation was accomplished in a neutral atmosphere (flowing argon) at 500 to 700C. Reduction was accomplished by passing hydrogen gas over the crystals. Analogous reactions can take place at much lower temperatures but also at much lower rates. Cation exchange reactions take place in the amphiboles known as richterites [14]; exchange is accomplished within the A-site of the amphibole structure at 775-8506C by the reaction (Na)CaNaMg5Sie022(0H,F)2 + K^OOCaNaMg^i^j (OH,F>2 + Na+. Crocidolite having a partially filled A-site such as that from Bolivia [41] can also undergo exchange reactions with postassium being replaced by sodium and possibly oxonium and ammonium ions. Crocidolite with a partially or A completely vacant A-site may undergo exchange reactions coupled with oxidation-reduction, e.g. ONajFel+Fej^SigOjj (OH) 2 + R+ + e" (R+)Na2Fe42+Fe3+Sig022 (OH) 2 where R+ * K+, Na+, H,,0+, or NH*, and * a vacant site. i 4 - 13 ASARCO ALV 0002784 Whether such reactions can take place within animal tissue is not known, d but the charge^ and reactive surfaces of crocidolite and amosite fibrils appear to offer excellent sites or templates for the initiation of complex chemical changes. A The surface are^ available for adsorption is, of course, directly related to fibril thickness or diameter. The specific surface of chrysotile, as measured both by nitrogen adsorption and permeability, is about twice that of amosite and crocidolite [28]. Because chrysotile forms hollow tubes, this larger area for adsorption in chrysotile is predictable if the average fiber thickness is similar for all three minerals. The strain-free layer of chrysotile has a radius of curvature of about 8.8 nm [5]; thus, the minimum diameter of the tube should not be much less than 17 nm. The most frequently measured tube diameter is about 26 nm. Bates and Comer [1] found in a study of chrysotile from Arizona and Quebec, a range of diameters from 11.4 to 85 nm; the average diameter was 25 nm. The fiber size ranges in the other forms of commercial "asbestos" have not come to my attention, although some crocidolite fibers from Western Australia [8] appear to be on the order of 50 nm vide. "Asbestos" Health Risks in the Mining and Milling Industry and Environs Although a significant health risk for those who work in the "asbestos" trades, particularly for those who smoke, has been well documented, such a risk is not clearly documented for those in the "asbestos" mining and milling industry and for those who reside in areas of such activity. The most detailed study of an "asbestos" mining community is that of the chrysotile mining areas of Quebec, Canada; the studies were started in 1966 and continue 14 ASARCO ALV 0002785 to the present [20, 21, 22, 23]. Similar studies of chrysotile miners on a smaller scale have been undertaken by Kogan et al. [16] in the Urals, UiS.S.R., and by Vigliani [39] in Italy. According to McDonald [17, 18] these other studies came to the same conclusions on health risk as the Quebec studies, the latter of which have led the way in making some assessment of the health risk relative to the amount of dust to which the workers were exposed. Health-risk studies of workers in the "asbestos" trades, for the most part, have not given reliable dust-exposure figures, or even the relative amounts and types of "asbestos" inhaled. Chrysotile has been mined in the Thetford Mines, Black Lake, and Asbestos localities of Quebec for nearly a century, beginning in 1886. Production has increased steadily since then, reaching 907,000 metric tons in 1956 and 1,500,000 metric tons in 1976. A tremendous amount of ambient dust has been generated over the years both by mining activities and by the winds blowing over the huge tailings piles. Even in 1974, when dust-emission controls had much improved over those of the earlier years (72 million particles per ft3 in 1950 to 4 million particles per ft3 in 1975 [20]) as a result of wet drilling, watering of haul roads, etc., emissions of particles from chrysotile mining eind milling operations in the Province of Quebec amounted to 140,000 metric tons, of which about 4 percent (5600 metric tons) was "asbestos" dust [2]. The ambient dust levels for this region have already been discussed. Is there a high incidence of cancer of the lung and pleura among the 35,000 residents of the Thetford Mines area of Quebec, 10 percent of whom are employed in the chrysotile industry? According to McDonald et al. [17, 18, 19, 20, 21, 22, 23], the cancer incidence for the male employees in the Quebec chrysotile industry is similar to the male cancer incidence in the whole of Canada. In table 1 is given the proportional mortality from lung 15 ASARCO ALV 0002786 cancer and mesothelioma for the Quebec and North Italian chrysotile miners and millers and also for the entire populations of various countries in the year 1970. In the period 1936-1973 seven cases of mesothelioma have been reported in the ' Quebec mining and milling industry [19, table 12]. The world-wide incidence of mesothelioma in those who worked in the chrysotile mining and milling industry for the period 1958 to 1976 is 11 cases [19, table 4]. The Canadian studies do show an increased incidence (2.1 to 3.6 times) of lung cancer for those workers exposed to the highest concentrations of dust -- 400 to 800+ mpcf-yr--^ However, these studies show that little health risk is experienced by workers breathing less than 200 mpcf-yr for a working life of 50 years. An unusually high number of deaths caused by lung cancer in Homestake gold miners during the period 1960 to 1973 has been reported by Gillam et al. [10]. The cohort consisted of 440 individuals who in 1960 had worked 5 years or more underground. Gillam et al. attributed the high incidence of lung cancer to inhalation of cummingtonite amphibole. They did not specify whether the hornblende amphibole, also present in the rock being mined, also contributed to health risk. In rebuttal to this work, McDonald et al. [24] reported on a health analysis of a cohort of 1321 Homestake miners whose working period was from as far back as 1937 to the end of 1973; each of the miners had more than 21 years mining service. Deaths resulting from malignant neoplasm were very close to those expected (93 observed, 90.5 expected); this includes the subcategories of malignant neoplasm ~ respiratory, gastro-intestinal, and "other" cancers. The excess death found in the Homestake miners was due in fact to silicosis, silico-tuberculosis, and heart disease. McDonald et al. [24] stated, "The pattern of mortality of men with long employment in this 16 ASARCO ALV 0002787 2/ ' - - This unit expresses (in millions) the average number of particles (includ ing approximately 4% chrysotile) contained in each cubic foot of air inhaled during a worker's career in the mines or mills times the number of years the worker was employed. If the dust is assumed to contain 4% chrysotile, then working for 50 years at a dust level of 16 mpcf (800 mpcf-yr) is roughly equivalent to inhaling 23 chrysotile particles for every cm3 of air taken into the lungs during the employment lifetime. A figure of 200 mpcf-yr is roughly equivalent to 6 particles of chrysotile/cm3. Conversion from dust particle measurements to chrysotile fibers per cm3 is difficult because chrysotile abundance varies from place to place. G. W. Gibbs (in McDonald and Becklake [20]) suggested an average conversion factor of 5.27 (mpcf -* fibers/cm3); use of this factor indicates that working at dust levels of 800 mpcf-yr and 200 mpdf-yr is equivalent to inhaling 84 and 21 chrysotile fibers per cm3 of air, respectively. 17 ASARCO ALV 0002788 industry indicates a serious pneumoconiotic hazard characteristic of hard rock miners but not of cancer." ; Fears [7] has made an epidemiological study of cancer risk, including respiratory cancer, in 97 U. S. counties in 22 States known to be mining chrysotile or amphibole "asbestos." He found no excess of cancer mortality compared with cancer mortality rates in 194 demographically matched counties in which such minerals are not known to be mined; cancer mortality in both groups of counties was significantly below the national average. At present, people jure concerned about the possible health hazards associated with the quarrying of serpentine rock at Hunting Hill quarry near Rockville, MD, and its use as a surface material for roads, playgrounds, and parks. The rocks being quarried here are very similar geologically to those of the chrysotile mining localities of Quebec, except that they contain much less chrysotile -- about 0.5 weight percent. Rohl et al. [29] from Mount Sinai Hospital reported chrysotile fiber abundances of 500 to 4700 ng/m3 of air sampled adjacent to roads and a parking lot paved with loose crushed stone from the Hunting Hill quarry. The highest figures were measured during "moderate" motor vehicle use. The Mt. Sinai figures are equivalent to 0.2 to 1.9 pm3 of chrysotile per cm3 of air or 0.04 to 0.4 "standard fibers" per cm3 of air. Air samples taken near the perimeter of the Hunting Hill quarry gave chrysotile mass concentrations of from 0.02 to 64 ng/m3 or 2 x 10" to 5 x 10"3 "standard fibers" per cm3 of air (U. S. Bureau of Mines, State of Maryland, and McCrone Assoc.,unpublished data). The present U. S. Government limits for "asbestos" content of air are 2 fibers/cm3 (OSHA) and 5 fibers/cm3 (MESA) where a fiber is defined as longer than 5 pm, less than 5 pm wide, and having a length-to-width ratio of 3:1 or greater. 18 ASARCO ALV 0002789 The publicity about the possible health risk because of dust emission from the Hunting Hill quarry and its rock products had caused the quarry to lose about 30 percent of its business by July 1, 1977. Montgomery County, MD, expected to pay about $2.3 million in its initial effort to seal the roads so as to reduce dust emissions and to remove loose stone from the parks (The Council Report, Montgomery County, vol. 6, no. 22, July 1, 1977). Apparently, other mining and quarrying operations along the "serpentine belt" of the eastern U. S. from Maine to Alabama also will be considered health risks to the general public [29]. Rohl et al. [29] suggested that exploitation of crushed amphibolite rock also raises the possibility of contamination of the air by "asbestos"-like minerals. Discussion The cancer incidence among those employed in the chrysotile mining and milling industry does not appear to be excessive when compared to national populations (table 1). However, the incidence of cancer among those employed in the "asbestos" trades is very high (table 1); incidence of lung cancer being 3 to 4 times that of the average population, incidence of mesothelsoma being 130 to 220 times that of the average population . The "asbestos" trades generally utilized a variety of "asbestos" minerals including amosite and/or crocidolite, sometimes mixed into a paste for lagging. If we consider that 80 to 90 percent of all the commercial "asbestos" ever mined was chrysotile and that there is a low incidence of cancer in the chrysotile mining industry. We are led to conclude that either amosite and crocidolite are very hazardous or that there is an additional factor relating to health risk in the "asbestos" trades which has not yet been discovered. Previously, I have discussed some reasons why these two minerals may be more chemically reactive than chrysotile. 19 ASARCO ALV 0002790 Definitive epidemiological studies of the amosite mining regions of South Africa and the crocidolite mining regions of South Africa, Bolivia, , and Australia appear to be lacking; such studies are needed in order to understand the high cancer incidence in certain trades utilizing these minerals. It is important to point out that the "asbestos" minerals should be considered separately when analysing their effects on the worker's health. Reasoning by analogy is dangerous; high cancer incidence associated with one form of "asbestos" in a particular occupation does not necessarily mean that there will be the same incidence when utilizing another form of "asbestos" in that or another occupation. Unfortunatley, this type of reasoning has led many to assume that any auphibole in any environment will cause high cancer mortality. The operational problems in defining and characterizing fine mineral particles and the unknown health effects on humans by minerals not generally regarded as "asbestos" appears to be causing more and more investigators to accept rather broad definitions for "asbestos." The present analytical tech niques used by the EPA and OSHA do not distinguish between amphibole cleavage fragments and the minerals geoscientists generally consider to be true "asbestos." In fact, if electron diffraction is not used e^qgertly, many pyroxenes might be called "asbestos." For example, bronzite, a common orthopyroxene having the composition (Mg,Fe) Si 0_., is very similar chemically o 8 24 to amphiboles of the cummingtonite-grunerite series, (Mg,Fe) Si O (OH) . . 7 8 ** 2 Also, orthopyroxene gives an electron diffraction pattern similar to that of cummingtonite -- both patterns possess 0.52 nm spacings between the . diffaction row lines in the hot reciprocal lattice net. A full interpretation of the patterns is necessary for positive identification. Similarly, calcic pyroxenes might be confused with amphiboles of the temolite-actinolite series 20 ASARCO ALV 0002791 or with hornblende. Cummingtonite (and possibly hornblende) is considered an "asbestos" health hazard by health investigators from the National Institute of Occupational Safety and Health (NIOSH), as reported by Giilam et al. [10]. The Mt. Sinai group [29] suggested that crushed amphibole-bearing rocks (amphibolite) used as road-surfacing material may result in wide-spread "asbestos" contamination of community air. Along with the general use of broader definitions of "asbestos" is a trend toward setting lower and lower limits on the acceptable amount of "asbestos" permitted in the environment (at present the OSHA standard is 2 fibers/cm3; the MESA standard is 5 fibers/cm3, but it will soon be changed to the OSHA value). A more stringent "asbestos" health standard is presently being proposed by the National Institute for Occupational Safety and Health (Reexamination and Update of Information on the Health Effects of Occupational Exposure to Asbestos, December 1976; document prepared by NIOSH for transmittal to OSHA, as requested by the Assistant Secretary of Labor). This document states (p. 92-93): "Evaluation of all available human data provides no evidence for a threshold or for a safe level of asbestos exposure." "In view of the above, the standard should be set at the lowest level detectable by available analytical techniques---- "Since phase contrast microscopy is the only generally available and practical analytical technique at the present time, this level is defined as 100,000 fibers >5 urn in length/m3 (0.1 fibers/cc)--------." A definition of "asbestos" to include many amphiboles, chrysotile', and possibly other minerals that appear fibrous or aciculax in the electron microscope coupled with a fiber-concentration standard of 0.1 fibers/cm3 should serve to shut down a large number of our hard rock mines and quarries. 21 ASARCO ALV 0002792 Also, nothing has yet been said about the effect of such standards on con struction workers building highways, tunnels, bridges, or dams on amphibolebearing rock, nor of the agricultural workers who are exposed.to fibercontaining dust while working the croplands. If the present concept of low or "zero threshold" health risk and broad use of "asbestos" defintions continue, much of the crust of the earth could be considered a health hazard. A way of minimizing the effect on the mining industry of the present and proposed "asbestos" standards, yet still maintaining a good level of health safety is presented by the Canadian studies of the Quebec chrysotile workers. Here J. C. McDonald and his colleagues G. W. Gibbs, A. D. McDonald, M. R. Becklake, J. Siemiatycki, C. E. Rossiter, F. D. K. Liddell, O. A. El Attar, A. Harper, and many others [17, 18, 19, 20, 21, 22, 23] have undertaken not only to delineate areas of health risk in the Quebec environment but also to assess the exposure limits of rock dust where the incidence of cancer and other diseases is at an acceptably low level. Mo occupation can be considered to have a zero health risk. It would seem that similar studies in this field would be of value in the United States. 22 ASARCO ALV 0002793 References [1] Bates, T.F.jand Comer, J.J., Further observations on the morphology of chrysotile and halloysite, Clays Clay Min., 6, 237-247 (1959). [2] Brulotte, Raynald, Study of atmospheric pollution in the Thetford Mines area, cradle of Quebec's asbestos industry, Atmospheric Pollution, M.M. Benarie, ed., Elsevier Sci. Pub., Amsterdam, 447-458 (1976). [3] Campbell, W.J., Blake, R.L., Brown, L.L., Cather, E.E., and Sjoberg, J.J., Selected silicate minerals and their asbestiform varieties: mineralogical definitions and identification-characterization, U`S' (Jv/t&A'S * f f>/es*A-/*n 87&/j S"6fp- (i177) [4] Champness, P.E., Cliff, G., and Lorimer, G.H., The identification of asbestos, J. Microscopy, 108, 231-249 (1976). [5] Deer, W.A., Howie, R.A., and Zussman, Jack, Rock-forming Minerals, vol. 3_, Sheet Silicates, Longmans, Green, and Co. Ltd., London (1962). [6] Ernst, H.G.^and Wai, G.M., MSssbauer, infrared, X-ray, and optical study of cation ordering and dehydrogenation in natural and heat- treated sodic amphiboles, Am. Mineral., 55, 1226-1258 (1970). [7] Fears, T.R., Cancer mortality and asbestos deposits. Am. J. Epidemio logy, 104, 523-526 (1976). [8] Franco, M.A., Hutchison, J.L.,Jefferson, D.A., and Thomas, J.M., Structural imperfection and morphology of crocidolite (blue asbestos), Nature, 266, 520-521 (1977). 19] Gary, Margaret, McAfee, R, Jr., and Wolf, C.L., Glossary of Geology. Am. Geological Inst., Washington, D.C. (1972). ' [10] Gillam, J.D., Dement, J.M., Lemen, R.A., Wagoner, J.K., Archer, V.E., and Blejer, H.P., Mortality patterns among hard rock gold miners * exposed to an asbestiform mineral. Annals. N.V. Acad. Sci., 271, 336 344 (1976). 23 ASARCO ALV 0002794  [11] Gilson, J.C., Asbestos cancers as an example of the problem of compara tive risks, Insenn Symposia Series, 52, XARC Scientific Publications No. 13, Environmental pollution and carcinogenic risks, 107-116 (1976). [12] Gross, Paul, Is short-fibered asbestos dust a biological hazard?. Arch. Environ. Health, 29, 115-117 (1974). [13] Hemley, J.J., Montoya, J.W., Shaw, D.R., and Luce, R.W., Mineral equilibria in the Mg0-Si02-H20 system:II Talc-antigorite-forsterite- anthophyllite-enstatite stability relations and some geologic impli cations in the system, Am. J. Sci., 277, 353-383 (1977). [14] Huebner, J.S.,and Papike, J.J., Synthesis and crystal chemistry of t sodium-potassium richerite, (Na,K)NaCaMgcSio0_.(0H,F) : A model for A Do 2 amphiboles, Am. Mineral., 55, 1973-1992 (1970). [15] Hutchison, J.L., Irusteta, M.C.,and Whittaker, E.J.W., High-resolution electron microscopy and diffraction studies of fibrous airphiboles, Acta Cryst., A31, 794-801 (1975). [16] Kogan, F.M., Guselnikova, N.A., and Gulevskaya, M.R., The cancer mortality rate among workers in the asbestos industry of the Urals, Gig. Sanit. 37, 29-32 (1972). [17] McDonald, J.C., Cancer in chrysotile mines and mills. Biological effects of Asbestos, Lyon, International Agency of Res. on Cancer, 189-194 (1973a). [18] McDonald, J.C., Asbestosis in chrysotile mines and mills. Biological . effects of Asbestos, Lyon, International Agency of Res. on Cancer, 155-159 (1973b). . [19] McDonald, J.C.^and McDonald, A.D., Epidemiology of mesothelioma from estimated incidence, presented at XVII Intn. Congr. on Occup. Health, Brighton, Sept. 16, 1975 (in press). ' ASARCO ALV 0002795 [20] McDonald, J.C.,and Becklake, M.R., Asbestos-related disease in Canada, Hefte z. Unfallheilkunde, 126, 2. Deutsch-Osterreichisch-Schweizerische, Unfalltagung in Berlin 1975, Springer-Verlag, Berlin, 521-535 (1976). [21] McDonald, A.D., Harper, A., El Attar, O.A., and McDonald, J.C., Epidemiology of primary malignant mesothelial tumors in Canada, Cancer, 26, 914-919 (1970). [22] McDonald, J.C., McDonald, A.D., Gibbs, G.W., Siemiatycki, J., and Rossiter, C.E., Mortality in the chrysotile asbestos mines and mills of Quebdc, Arch. Environ. Health, 22, 677-686 (1971). [23] McDonald, J.C., Becklake, M.R., Gibbs, G.H., McDonald, A.D., and Rossiter, C.E., The health of chrysotile asbestos mine and mill workers of Quebec, Arch. Environ. Health, 28, 61-68 (1974). [24] McDonald, J.C., Gibbs, G.W., Liddell, F.D.K., and McDonald, A.D., Mortality after long exposure to cumjngtonite-grunerite (abstr.). Am. Rev. Resp. Disease, Supp., 115, no. 4, 230 (1977). [25] Nord,[ Jr. ^ "State-of-the-Art" of the analytical transmission electron microscope, in Proc. Symposium on Electron Microscopy and X-ray applications to environmental and occupational heath analyses, Ann Arbor Scl. Publ., in press (1978). [26] Papike, J.J.,and Ross, Malcolm, Gedrites: Crystal Structures and intracrystalline cation distributions. Am. Mineral. 55, 1945-1972 (1970) [27] Pott, F., and Friedrichs, K.H., Tumoren der Ratten Mach I.P. Xnjektion faser formiger Staube, Maturw., 59, 318 (1972). [28] Rendall, R.E.G., The data sheets on the chemical and physical properties of the D.X.C.C. standard reference samples, in Pneumoconiosis, H.A. Sha'piro, ed. , Oxford U. Press, (1970). .~ [29] Rohl, A.N., Danger, A.M., and Selikoff, I.J., Environmental asbestos pollution related to use of quarried serpentine rock. Science, 196, ASARCO ALV 0002796 1319-1322 (1977). [30] Ross, Malcolm, Papike, J.J., and Weiblen, P.W., Exsolution In clinit , amphiboles. Science, 159, 1099-1102 (1968 ). [31] Ross, Malcolm, Smith, W.L., and Ashton, W.H., Triclinic talc and associated amphiboles from the Gouvemeur Mining District, Hew York, Am. Mineral., 53, 751-769 (1968 ). [32] Ross, Malcolm, Papike, 3.3., and Shaw, K.W., Exsolution textures in amphiboles as indicators of subsolidus thermal histories, in Mineral. Soc. Am. special paper no. 2, 3.3. Papike, ed., pp. 275-299 (1969). [33] Selikoff, I.J., Hammond, E.C., and Churg, Jacob, Asbestos exposure, smoking, and neoplasia, J. Am. Med. Assoc., 204, 106-112 (1968). [34] Seshan, K., and Henk, H.-R., Identification of faults in asbestos minerals and application to pollution studies, in Proc. Electron Microscope Soc. Am., 34th annual meeting, G.W. Bailey, ed., 616-617 (Claitor's Pub. Div., Baton Rouge, 1976). [35] Takeda, Hiroshi, and Ross, Malcolm, Mica polytypism: Dissimilarities in the crystal structures of coexisting lM and 2M^ biotite. Am. Mineral. 60, 1030-1040 (1975). [36] Veblen, D.R.,and Burham, C.W., Triple-chain biopyriboles: Newly discovered intermediate products of the retrograde anthophyllite-talc transformation, Chester, Vt. (abstr.), Trans. Am. Geophys. Union, 56, 1076 (1975). [37] Veblen, D.R.,and Burnham, C.W., Biopyriboles from Chester, Vermont: The first mixed-chain silicates (abstr.), Geol. Soc. Am. Abstracts with Programs , 1153 (1976). [38] Veblen, D.R., Trlple-and mixed-chain biopyriboles from Chester, Vermont, Ph.D. thesis, Harvard University, Cambridge, Mass. (1976). 26 ASARCO ALV 0002797 [39] Vigliani, E.C., Asbestos exposure and its results in Italy, in Proc. International Conf. on Pneumoconiosis, Johannesburg, Oxford 0. Press, 192-196 (1970). - [40] Wagner, J.C., Berry, G., and Trimbrell, V., Mesotheliomata in rats after inoculation with asbestos and other materials, Brit. J. Cancer, . 28, 173-185 (1973). [41] Whittaker, E.J.W., The structure of Bolivian crocidolite, Acta Cryst., 2, 312-317 (1949). [42] Wones, D.R., Physical properties of synthetic biotites on the join phlogopite annite, Am. Mineral. 48, 1300-1321 (1963). 27 ASARCO ALV 0002798 TABLE 1. Proportional mortality from lung cancer and mesothelioma for selected male populations. Group General populations ./ Canada (1970) OSA (1970) Finland (1970) Italy (1970) England - Hales (1970) Chrysotile mining-milling --^ Cohort No. men All causes 82,052 988,620 22,332 252,795 278,617 Quebec (1936-73) N. Italy (1932-70) 10951 1098 Anthophyllite mininq-millinq / Finland (1936-67) "Asbestos" trades --^ 900 3938 270 216 insulators Asbestos factory 26505 10781 2137 1422 Deaths % lung cancer 1* tmesothelioma 5.3 5.1 7.1 4.7 8.9 0.03 0.03 0.04 0.06 5.7 0.18 2.2 0 9.7 0 19.6 15.0 6.7 3.1 a/ Entire male population over 24 years of age [19, table 13] b/ [19, table 12; 20, p. 525] / [19, table 12] d/ Composite figures [19, table 12] 28 ASARCO ALV 0002799 FIGURES Figure 1. Structural relationship between the upper double chain of linked (Si,ADO4, tetrahedra and the octahedra part of the amphibole strip or "I-beam." The circles represent Mg,Fe, or A1 atoms in octahedral coordination; at the apices of the polyhedra are oxygen atoms. Tetrahedral Si and A1 atoms are not shown. The "I-beams" extend infinitely in a direction parallel to the c-axis (the fiber axis). The width of the "I-beam" in the b-direction is three octahedra. Figure is modified from Papike and Ross [26]. - Figure 2. Arrangement of the amphibole strips or "I-beams" in (A) orthoamphibole (space group Pmma) and (B) clinoamphibole (space group C2/m). The "I-beams" are viewed end-on (parallel to the fiber c-axis). The central portion of the "I-beam" is conposed of (Mg,Fe,Al)0o. octahedra; the upper and lower portions are composed of double chains of (Si,AlO ) tetrahedra. The "I-beams" 4 are stacked in two ways: (1) +++... (clinoasphibole), and (2) + - + - .... (orthoamphibole). Figure modified from Papike and Ross [26]. Figure 3. Mineral stability relations in the system MgO-SiO^-I^O as a function of log of molality of aqueous silica and temperature, at 1 ki lobar.H^O pressure. Figure modified from Hemley et al. [13] Figure 4. Adaptation of the enstatite-anthophyllite-talc-forsterite stability relationships at 1 kbar H^O to show a possible stability or metastability field of "talcbole asbestos" (stippled). Figure modified from Hemley et al. [13]. Anth. " anthophyllite. 29 ASARCO ALV 0002800 figure 1 I 30 ASARCO ALV 0002801 Figure 2 CUNOAMPHIBOLE CZ/m Figure 2 31 ASARCO ALV 0002802 Figure 3 20!SUU on- 32 ASARCO ALV 0002803 (1 kbar H00 ) I F ig u re 4 ASARCO ALV 0 0 0 2 8 0 4 l&/ji>/7 7 - The "Asbestos" Minerals: Definitions, Description, ModLen/of Formation, . * Physical and Chemical Properties, and Health Risk, to the Mining Community Malcolm Ross D.S. Geological Survey National Center, 959 Reston, VA 22092 To be published in: Workshop on Asbestos: Definltiomand Measurement Methods. National Bureau of Standards Special Publication (1977). ASARCO ALV 0002805 abstract The mineralogical description of "asbestos" given here is based on a very special feature common to all forms of commercial "asbestos" -- the property that permits the minerals to separate into long tubes or fibrils only a few tens of nanometers thick. This separation can be accomplished by very light grinding or agitation; the common ncnfibrous amphiboles do not separate into such fibrils even after intense grinding. The ease of such fibril separation may be caused by the special nature of the crystal structures of the commercial "asbestos" minerals. Repeated twinning on (100) in amosite and crocidolite, the curling of layers of chrysotile to form tubes, and the presence of triple, quadruple, and rv-tuple chains ("Wadsley" defects) in amosite, crocidolite, anthophyllite, and tremolite are the structural features that probably promote the formation of thin fibrils. Stability diagrams in the system MgO-SiOj-H^O indicate possible geochemical processes by which commerical "asbestos" can form. The relative health risk posed by exposure to the "asbestos" minerals may be related to the fibril composition, crystal structure, size, shape, and total surface area. The relative chemical reactivity of the fibril surface is predicted to be chrysotile < anthophyllite < amosite < crocidolite on the basis of the types of oxidation-reduction and exchange reactions that may occur. According to epidemiological studies relative health risk appears to be anthophyllite < chrysotile < amosite < crocidolite. "Asbestos" health risks in the mining and milling industry and environs d.s reviewed. Health studies done in the chrysotile mining district of Quebec, Canada, have presented good evidence that realistic "asbestos" dust standards can be set that not only protect the worker and resident of the mining areas from undue health risk but also allow the industry to operate economically. ASARCO ALV 0002806 Kev Words Asbestos, amphibole, chrysotile, talcbole, tremolite, actinolite, anthophyllite, amosite, cumningtonita, hornblende, amphibolite, serpentinite, grunerite, crocidolite, mesothelioma, lung cancer, health risk, Wadsley defects, asbestos stability, ambient air, dust levels, surface chemistry, chrysotile mining, chrysotile emissions, Thetford Mines, Quebec, Canada, Orals, U.S.S.R., Komestake Mines, S.D., Hunting Hill Quarry, Rockville, Md. ASARCO ALV 0002807 Introduction It is generally a rather straightforward, though often time-consuming mineralogical task to describe the physical and chemical properties of amp'niboles and serpentines, including those varieties referred to as "asbestos". Exceptions are minerals such as fibrous tremolite and fibrous talc that to date do not have adequate mineralogical descriptions. Defining minerals that constitute an "asbestos" health hazard is an entirely different and a much more complex problem, for it involves many factors not included within the science of mineralogy. This commentary is concerned with the various definitions of "asbestos" as they relate to: (1) the medical profession, which must determine which types of mineral particles constitute an "asbestos" health hazard; (2) the legal and regulatory professions, which must enact and enforce the laws relating to "asbestos" use, (3) the mineralogical profession, which must describe the chemical, structural, and physical properties of such minerals, and (4) the mining auarrying industries, which may be affected by these A~ definitions. ' What is "Asbestos"? . Three definitions of "asbestos" found in the Glossary of Geology [9, p. 41] are quoted as follows: "asbestos (a) 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, are heat resistant and # chemically inert, and possess a high electric insulation, and therefore are suitable for uses (as in yarn, cloth, paper, paint, brake linings, tiles, insulation, cement, fillers, and filters) where incombustible, nonconducting, or chemically resistant material is required. (b) A mineral of the asbestos group, principally chrysotile (best adapted for spinning) and certain fibrous varieties of amphibole (esp. tremolite, actinolite, and crocidolite). (c) A term strictly applied to the fibrous variety of actinolite. ASARCO ALV 0002808 The term "asbestos," from a geoscientist's point of view, applies only to the minerals chrysotile (one of the serpentine polymorphs), "amosite" (a f variety of grunerite), "crocidolite" (a variety of riebeckite), anthophyllite, tremolite, and actinolite when they are present in sufficient quantity to be commercially valuable for their special physical and chemical properties, which include fibrous habit, insulation qualities, low electrical conductivity, fire resistance, and suitability for weaving. Many other minerals sometimes possess habits described variously as acicular, asbestiform, elongate, fibrous, bladed, lamellar, filiform, prismatic, or columnar; for example, minerals of the zeolite group having acicular habit, fibrous calcite and quartz, acicular wollastonite, prismatic pyroxenes, elongate crystallites of attapulgite, and filiform sepiolite. Since these minerals are not exploited for the commercially valuable properties listed above, they are not called "asbestos" by geoscientists. ` At present, the most widely used definition of "asbestos" by various .. <: '' groups concerned with environmental health problems, including the 0. S. Environmental Protection Agency (EPA) and the U. S. Mining Enforcement and Safety Administration (MESA), is from the notice of proposed rulemaking for "Occupational Exposure to Asbestos" published in the Federal Register (Oct. 9, 197: p. 47652, 47660) by the U. S. Occupational Safety and Health Administration (OSHA). In this notice, the naturally occurring minerals chrysotile, amosite, crocidolite, tremolite, anthophyllite, and actinolite are classified as "asbestos" if the individual crystallites or crystal fragments have the following dimensions: length - greater than 5' micrometers, maximum diameter - less than 5 micrometers, and a length to diameter ratio of 3 or greater. Any product containing any of . these minerals in this size range are also defined as "asbestos." The crushing and milling of any rock usually produces some mineral particles that are within the size range specified in the OSHA rules. Thus, these regulations present a formidable problem to those analysing for "asbestos" ' `4a (4b follows) ASARCO ALV 0002809 minerals in the multitude of materials and products in which they may be found in some amount, for not only must the size and shape of the "asbestos" , particles be determined, but also an exact mineral identification must be made. A wide variety of amphiboles is found in many types of common rocks; many of these amphiboles might be considerd "asbestos" depending upon the professional training of the person involved in their study and the methods used in mineral, characterization. Campbell et al. [3] have carefully described the differences between the relatively rare fibrous varieties of the amphiboles and the common nonfibrous forms. If the definition of "asbestos" from the point of view of a health hazard does include the common nonfibrous forms of amphibole, particularly the horn blende and cummingtonite varieties, then we must recognize that "asbestos" is present in significant amounts in many types of igneous and metamorphic rocks covering perhaps 30 to ,40 percent of the United States. Rocks within the serpentinite belts; rocks within the metamorphic belts higher in grade than the greenschist facies, including amphibolites and many gneissic rocks; and amphibole-bearing igneous rocks such as diabase, basalt, trap rock, and granite would be considered "asbestos" bearing. Many iron formations and \ copper deposits would be "asbestos" bearing, including deposits in the largest open-pit mine in the world at Bingham, Utah. "Asbestos" regulations would pertain to many of our country's mining operations, including much of the thus y construction industry and its quarrying operations for concrete aggregate, dimension stone, road metal, railroad ballast, riprap, and the like. The "asbestos" regulations would also pertain to the ceramic, paint, and cement industries and to many other areas of endeavor where silicate minerals are used. We do not know whether health investigators will consider other minerals that commonly possess a fibrous or acicular habit to be health hazards; minerals such as wollastonite, the fibrous forms of calcite and quartz, acicular minerals of the zeolite mineral group, the pyroxenes, the sepiolite. / / ASARCO ALV 0002810 minerals including attapulgite, and the calcium silicates found in Portland cement. Certainly if the common amphiboles such as hornblende, tremolite, actinolite, gedrite, and cummingtonite with their typical prismatic cleavage are considered health hazards, the common pyroxenes having similar habits should also be considered health hazards. A Mineralocical Description of Commercial "Asbestos" The commercial deposits of "asbestos" contain one of the following minerals: chrysotile, MgjSijOs(OH)4; amosite, (Fe2+,Hg)^Si8022(OH)2 (a variety of grunerite); crocidolite, Na2(Fe2+,Mg)3Fe|+Sig022(OH)2 (a variety of riebeckite); "fibrous" anthophyllite, (Mg,Fe)7Sig022(OH)and "fibrous" tremolite and actinolite, Ca^ (Mg,Fe) tjSigO^ (OH) 2> Tremolite and actinolite are now, as they were in the past, of little economic importance; anthophyllite is of little economic importance now. About 95 percent of the commercial asbestos now used in the United States is chrysotile/ of which about 90 percent is imported from Canada. Ho commercial amosite or crocidolite has ever been mined in the United States. In addition to being compositionally different, the five amphibole forms of commercial "asbestos" have completely different crystal structures from that of chrysotile. The structure of chrysotile consists of double layers, each consisting of a layer of linked SiO^ tetrahedra that is coordinated to a second layer of linked Mg02(OH)4 octahedra through the sharing of oxygen atoms; the composite double layer rolls up, like a window shade, to form long hollow tubes. The diameters of the individual tubes sure on the order of 25 nm; the length-to-diameter ratio can vary from 5 or 10 to well over 10,000. _ The structures of the amphibole minerals, on the other hand, are composed of strips or ribbons of linked polyhedra, which join together to form the three dimmensional crystal. The individual strips are composed of three elements--tw 5 ASARCO ALV 0002811 double chains of linked (Si,ADO tetrahedra that form a "sandwich" with a 4 strip of linked MgO_, FeO , or AlO. octahedra. The structural relationship 66 o . of the upper double tetrahedral chain to the octahedral part of the strip is shown in figure 1. The three-dimensional arrangements of these strips or "I-beams" [26} in orthoamphibole (anthophyHite) and in clinoamphibole (tremolite, amosite, actinolite, and crocidolite) are shown in figure 2. One feature is common to the six "asbestos" minerals: their ready separation into long fibrils or tubes only a few tens of nanometers in diameter. This separation can be accomplished by very light grinding or by agitation in water by means of an ultrasonic separator. The common nonfibrous amphiboles do not separate into such fibrils even after intense grinding; instead, they break up along cleavage planes into rather short stubby prisms--th ough the length-to-diameter ratio may still be greater than 3:1. ' What causes the special type of fibril separation found in commercial forms of "asbestos" but generally not in the nonfibrous amphiboles? Three observations are pertinent: (1) Chrysotile, which forms individual hollow tubes, can separate into fibrils as thin as the diameter of the individual tube. The chemical bonding between tubes is very weak and perhaps is due only to van der Waals forces; thus, the tubes are easily separated from one another. (2) Amosite and crocidolite "asbestos" from South Africa is repeatedly twinned on (100) as has been observed in electron microscope studies [4, 15, 25, 34]. This "polysynthetic" twinning, which produces repeated planar faults parallel to (100), is extremely rare in the nonfibrous calcium-rich anphiboles (temolite, hornblende) and uncommon in nonfibrous amphiboles of the cumming- tonite-grunerite series [30, 31, 32], ASARCO ALV 0002812 (3) Amosite, crocidolite, fibrous anthophyllite, and fibrous tremolite have been shown to possess chain defects, also called "Wadsley" defects [8, 15, 36, 37, 38]. These defects are caused by the formation of expanded "I-beams" that are composed of triple, quadruple ...etc. chains of linked (Si,Al)0 ** 4 tetrahedra rather than the double chains found in all amphibole crystal struc tures. If these "I-beams" are expanded indefinitely, the resulting strip becomes identical with the single talc layer of composition Mg,Si (3 (OH) ,; 6 8 20 4 recall that the cocposition of anthophyllite is Mg^Si^O^COHJ^. T*iese expanded "I-beams" units can intermix with the regular amphibole "I-beams" to form a variety of minerals that I refer to as "talcboles" in allusion to their hybrid character--between talc and amphibole. Veblen [38] has described the detailed structures of four of these "talcboles" obtained from specimens originally described as "fibrous anthophyllite." In these crystal structures, "I-beams" of one or two types form an ordered three-dimensional structure. Veblen [38] showed evidence, as did Hutchison et al. [15], that disordered arrangements of these structural units also occur. Hutchison et al. [15] reported the presence of expanded "I-beams" structures in fibrous tremolite, and Franco et al. [8] reported the apparent presence of triple-chain lamellae, seen as planar faults on (010), in crocidolite from Western Australia. Formation of "Asbestos" How do chrysotile and the "talcboles" form? Modes of origin can be inferred from the stability relationships among talc, anthophyllite, enstatite, forsterite, antigorite, and chrysotile given by Hemley et al. [13]. Their mineral stability fields at 1 20, in terms of crystallization temperature and molality of aqueous silica, are given in figure 3. * This rtw** of figure shows a number of relationships pertinent to the problem of^"asbestiform" minerals. As the temperature decreases, forsterite (Mg-rich olivine) can react 7 ASARCO ALV 0002813 to form antigorite or chrysotile depending on the silica concentration in the aqueous solutions to which the olivine-bearing rock is exposed. One chemical reaction that may lead to the formation of brucite-bearing serpentinite is: 2Mg SiO, + 3H O f Mg Si 0 (OH) + Mg(OH) 24 2 3204 2 fosterite chrysotile brucite This reaction may explain the origin of the very long brucite needles, referred to as "nemalite," that are found in various serpentinites. Thirty-centimeter- long needles of this mineral were collected by C. E. Brown (U.S. Geol. Survey) from a Quebec serpentinite locality and were examined by single-crystal X-ray methods (Malcolm Ross, unpub. data). The brucite needles show hexagonal symmetry, a = 0.315 nm, c_ = 0.474 nm, and the long direction of the needles ( are parallel to the brucite a-direction. The rather marked line broadening that appears in the X-ray pattern suggests that the brucite needles are composed of many small crystallites oriented so that their a^axes are parallel to the fiber direction. The brucite needles are intergrown with chrysotile, for chrysotile X-ray reflections are superimposed on the diffraction pattern of brucite, and extremely long chrysotile fibrils remain when the brucite needles are dissolved by dilute HNO^. At higher concentrations of aqueous silica forsterite may alter to talc by the reaction: 3Mg,,SiO. + 5 (H SiO.) '2 4 4 4 aq. 2Mg,Si 0 (OH) + 8H O 3 4 10 2 2 At silica concentrations near the quartz saturation curve, anthophyllite can alter directly to talc by the reaction: 3M*7Si822(OH)2 + 42Sl4,q. " '"Wio't0H) 2 + 4H2 ' This reaction may be of importance for the formation of fibrous anthophyllite and talc. As the temperature decreases and the S^Q, 2+ Mg , and silica 8 ASARCO ALV 0002814 activities xeaain within geologically reasonable limits one probable reaction sequence is: . enstatite anthophyllite talc. If the alteration of a chain silicate to talc proceeds by an intragranular reaction, "talcboleytype" phases may form as intermediates between anthophyllite and talc during low-temperature alteration. Figure 4 shows the stability fields of forsterite, enstatite, anthophyllite, and talc in terms of taqperature and molality of aqueous silica [13]. A stability (or metastability) field for the "talcboles" (labeled "asbestos") is superimposed on this diagram, overlapping the fields of talc and anthophyllite. The fibrous nature of -the "talcboles" can be explained if the alteration process of a . chain silicate (anthophyllite) to a sheet silicate (talc) proceeds by reforming the double chains at the unit-cell level. In figure 4, the phase boundary between enstatite (a pyroxene having the formula Mg^i^Og) and anthophyllite suggests the possibility of having mixed single chain (pyroxene) and double chain (ampbibole) structures. . . 'The ffihanons nature of commercial amosite and crocidolite appears to be ' related to the crystal growth mechanism; perhaps the crystallites nucleate at many centers and grow as individual fibers only a few tens of nanometers thick (see Franco et al. [8, figures 1, 2]). The presence of (100) twinning and "Wadsley" defects may be the result of rapid growth and, in addition,, may hinder growth in a direction perpendicular to the fiber axis. # Properties of "Asbestos" that may be Related to Health Risk Health studies suggest that of the four economically important forms of "asbestos," -crocidolite has been responsible for the greatest health risk, followed fay emosite, then chrysotile, and lastly anthophyllite [11]. If we ASARCO ALV 0002815 assume that the health hazard caused by the commercial "asbestos" minerals is due to some combination of their chencial, structural, and physical properties, we can make some predictions about their relative biological activity. All commercial "asbestos" minerals separate into very thin fibrils; possible reasons for this have been discussed previously. The thickness, length, and flexibility of the fibrils apparently is important in determining to how the fibrils lodge in human tissue and how readily they are cleared from the lung areas. The straight fibrils of small diameter, particularly those of crocidolite, can more readily move to the periphery of the lung, where they are in a position to penetrate the pleura and thus produce mesotheliomas {11]. That curly fibrils, especially those of chrysotile, are more readily arrested in the upper respiratory tract, is given as a reason for the low incidenct of mesotheliomas in chrystotile miners and millers [11, 19, 23]. Assessment of the role of fibril size in relation to lung cancer is less clear [11]; however, . Gross [12] cited evidenctf that-"asbestos" fibers less than 5 ^im long cause negligible pathogenicity, both of the lung and pleura. The problem of fibril size in relation to cancer incidence is of some ' importance, for the average ambient airborne "asbestos" fiber is shorter than the average fiber in the whole rock. Brulotte [2] reported that the average concentration of airborne dust particles in the chrysotile mining district of Thetford Mines, Quebec, was 80,500 ng/m^ during active mining and 39,600 ng/m3 during a 5-month period when the mines were closed. If we assume that the rock contains 4 weight percent chrysotile, these measurements suggest a minimum chrysotile dust concentration in the ambient air of 3220 and 1534 ng/n3.--^ The total surface area of the inhaled fibrils and the chemical reactivity of this surface may have an important influence in the production of cancer. 10 ASARCO ALV 0002816 Conversion of these figures (nanograms chrysotile per cubic meter of air) to numbers of "fibers" per cubic centimeter of air (the value usually given in health studies) is estimated by using the following relations: ** 3 93 (1) density of chrysotile =2.5g/cm =2.5 x 10 ng/cm (2) volume of 1 ng chrysotile = 4xl0_3-0cm3 = 400 ym3 (3) volume of chrysotile fibers in ym3/cm3 = ^oOQ^* (4) if a fiber having dimensions lymxlymxSym (5ym3) is designated as a "standard fiber," then 1 ng chrysotile = 80 "standard fibers" (5) number of chrysotile "standard fibers"/cm3 = (n<?/m 12,500 11 ASARCO ALV 0002817 Researchers have not yet determined whether this surface plays a direct part in the formation of cancerous tissue, or whether a carcinogenic chemical adheres to the mineral surface and the chemical itself later reacts with the tissue or in some way catalyzes the carcinogenic process. The high incidence of lung cancer in men who worked in the "asbestos" trades (textiles, brake lining frabrication, insulating) and who also smoked [33] indicates that carcinogenic chemicals in the tobacco smoke may somehow interact with the "asbestos" fibrils. If many of the fibrils are not easily cleared from the lung, they may adsorb these chemicals and hold them indefinitely. Injection of "asbestos" fibrils directly into the pleura of animals causes a high incidence of mesothelioma [40]. These experiments suggest a direct relationship between the active fibril surface and production of pleural cancer. However, other dissimilar substances injected into animals also cause tumors; for example, nonfibrous hematite (Fe O ), sanidine (KAlSi O ), 23 3 8 and corundum (Al^O^) * [273. As a generalization, the relative chemical reactivity of the exposed fibril surfaces of the four important forms of commercial "asbestos" in aqueous solutions is: chrysotile < anthophyllite < amosite < crocidolite. Chrysotile, the least reactive of the four, is composed of rolled-up layers that possess no broken chemical bonds except where the edges of the layers are exposed at the ends of the tubes. The three amphiboles, on the other hand, have broken chemical bonds on all surfaces of the fibrils. Anthophyllite can alter to various other silicates in aqueous solutions, as has been explained above. Similar alteration mechanisms might also exist for crocidolite and amosite, although to my knowledge, these have not been ASARCO ALV 0002818 docmented. However, studies of the geochemistry of silicates indicate that the exposed surfaces of these two amphiboles present some interesting possibilities for chemical change. Amosite (and also crocidolite) can under go oxidation-reduction reactions of the type, ^YSLa22m2^TeVF4*SiB0222 * H2 , Ernst and Wai [6] have demonstrated that this reaction takes place in iron bearing sodic amphiboles at 705C. The complete reversibility of such a reaction in the chemically similar silicate mineral biotite, has been demonstrated by Wones (42] and by Takeda and Ross [35]. In the experiments of Wones, auto-oxidation was accomplished in a neutral atmosphere (flowing argon) at 500 to 700C. Reduction was accomplished by passing hydrogen gas over the crystals. Analogous reactions can take place at much lower temperatures, but also at much lower rates. Cation exchange reactions take place in the amphiboles known as richterites [14]; exchange is accomplished within the A-site of the amphibole structure at 775-850C by the reaction (Ha)CaNaMg5Sia022(0H,F)2 + K+-5(K)CaNaMg5Sig022 (0H,F) 2 + Na+. Crocidolite having a partially filled A-site such as that from Bolivia [41] can also undergo exchange reactions with postassium being replaced by sodium V and possibly oxonium and ammonium ions. Crocidolite with a partially or A completely vacant A-site may undergo exchange reactions coupled with oxidation-reduction, e.g. Ha2Fe|+Fe23+Si8022(OH)2 + R+ + e" ^(R+)Na2Fe42+Fe3+Sig022 (OH)2 where R+ K+, Na+, H 0+, or NH*, and O = a vacant site. J4 ' 13 ASARCO ALV 0002819 Whether such reactions can take place within animal tissue is not known, <L ' but the charge and reactive surfaces of crocidolite and amosite fibrils appear A to offer excellent sites or templates for the initiation of complex chemical changes. CL The surface are available for adsorption is, of course, directly related to fibril thickness or diameter. The specific surface of chrysotile, as measured both by nitrogen adsorption and permeability, is about twice that of amosite and crocidolite [28]. Because chrysotile forms hollow tubes, this larger area for adsorption in chrysotile is predictable if the average fiber thickness is similar for all three minerals. The strain-free layer of chrysotile has a radius of curvature of about 8.8 nm [5]; thus, the minimum diameter of the tube should not be much less than 17 nm. The most frequently measured tube diameter is about 26 nm. Bates and Comer [1] found in a study of chrysotile from Arizona and Quebec, a range of diameters from 11.4 to 85 nm; the average diameter was 25 nm. The fiber size ranges in the other forms of commercial "asbestos" have not come to my attention, although some crocidolite fibers from Western Australia [8] appear to be on the order of 50 nm wide. "Asbestos" Health Risks in the Mining and Milling Industry and Environs Although a significant health risk for those who work in the "asbestos" trades, particularly for those who smoke, has been well documented, such a risk is not clearly documented for those in the "asbestos" mining and milling industry and for those who reside in areas of such activity. The most detailed study of an "asbestos" mining community is that of the chrysotile mining areas of Quebec, Canada; the studies were started in 1966 and continue 14 ASARCO ALV 0002820 to the present [20, 21, 22, 23]. Similar studies of chrysotile miners on a smaller scale have been undertaken by Kogan et al. [16] in the Urals, U.S.S.R., f. and by Vigliani [39] in Italy. According to McDonald [17, 18] these other studies came to the same conclusions on health risk as the Quebec studies, the latter of which have led the way in making some assessment of the health risk relative to the amount of dust to which the workers were exposed. Health-risk studies of workers in the "asbestos" trades, for the most part, have not given reliable dust-exposure figures, or even the relative amounts and types of "asbestos" inhaled. Chrysotile has been mined in the Thetford Mines, Black Lake, and'Asbestos localities of Quebec for nearly a century, beginning in 1886. Production has increased steadily since then, reaching 907,000 metric tons in 1956 and 1,500,000 metric tons in 1976. A tremendous amount of ambient dust has been generated over the years both by mining activities and by the winds blowing over the ^ huge tailings piles. Even in 1974, when dust-emission controls had much improved over those of the earlier years (72 million particles per ft in 1950 to 4 million particles per ft3 in 1975 [20]) as a result of wet drilling, watering of haul roads, etc., emissions of particles from chrysotile mining and milling operations in the Province of Quebec amounted to 140,000 metric tons, of which about 4 percent (5600 metric tons) was "asbestos" dust [2]. The ambient dust levels for this region have already been discussed. Is there a high incidence of cancer of the lung and pleura among the 35,000 residents of the Thetford Mines area of Quebec, 10 percent of whom # are employed in the chrysotile industry? According to McDonald et al. [17, 18, 19, 20, 21, 22, 23], the cancer incidence for the male employees in the Quebec chrysotile industry is similar to the male cancer incidence in the whole of Canada. In table 1 is given the proportional mortality from lung 15 ASARCO ALV 0002821 cancer and mesothelioma for the Quebec and North Italian chrysotile miners and millers and also for the entire populations of various countries in the year 1970. In the period 1936-1973 seven cases of mesothelioma have been reported in the Quebec mining and milling industry [19, table 12]. The world-wide incidence of mesothelioma in those who worked in the chrysotile mining and milling industry for the period 1958 to 1976 is 11 cases [19, table 4]. The Canadian studies do show an increased incidence (2.1 to 3.6 times) of lung cancer for those workers exposed to the highest concentrations of dust -- 400 to 800+ mpcf-yr!/ However, these studies show that little health risk is experienced by workers breathing less than 200 mocf-yr for a working life of 50 years. An unusually high number of deaths caused by lung cancer in Homestake gold miners during the period 1960 to 1973 has been reported by Gillam et al. [10]. The cohort consisted of 440 individuals who in 1960 had worked 5 years or more underground. Gillam et al. attributed the high incidence of lung cancer to inhalation of cummingtonite amphibole. They did not specify whether the hornblende amphibole, also present in the rock being mined, also contributed to health risk. In rebuttal to this work, McDonald et al. [24] reported on a health analysis of a cohort of 1321 Homestake miners whose working period was from as far back as 1937 to the end of 1973; each of the miners had more than 21 years mining service. Deaths resulting from malignant neoplasm were very close to those expected (93 observed, 90.5 expected); this includes the subcategories of malignant neoplasm -- respiratory, gastro-intestinal, and "other" cancers. The excess death found in the Homestake miners was due in fact to.silicosis, silico-tubereulosis, and heart disease. McDonald et al. [24] stated, "The pattern of mortality of men with long employment in this 16 ASARCO ALV 0002822 -- This unit expresses (in millions) the average number of particles (includ ing approximately 4% chrysotile) contained in each cubic foot of air inhaled during a worker's career in the mines or mills times the number of years the worker was employed. If the dust is assumed to contain 4% chrysotile, then working for 50 years at a dust level of 16 mpcf (800 mpcf-yr) is roughly equivalent to inhaling 23 chrysotile particles for every cm3 of air taken into the lungs during the employment lifetime. A figure of 200 mpcf-yr is roughly equivalent to 6 particles of chrysotile/cm3. Conversion from dust particle measurements to chrysotile fibers per cm3 is difficult because chrysotile abundance varies from place to place. 17 ASARCO ALV 0002823 industry indicates a serious pneumoconiotic hazard characteristic of hard rock miners But not of cancer." Fears [7] has made an epidemiological study of cancer risk, including respiratory cancer, in 97 U. S. counties in 22 States known to be mining chrysotile or amphibole "asbestos." He found no excess of cancer mortality compared with cancer mortality rates in 194 demographically matched counties in which such minerals are not known to be mined; cancer mortality in both groups of counties was significantly below the national average. At present, people are concerned about the possible health hazards associated with the quarrying of serpentine rock at Hunting Hill quarry near Rockville, MD, and its use as a surface material for roads, playgrounds, and parks. The rocks being quarried here are very similar geologically to those of the chrysotile mining localities of Quebec, except that they contain much less chrysotile -- about 0.5 weight percent. Rohl et al. [29] from Mount Sinai Hospital reported chrysotile fiber abundances of 500 to 4700 ng/m3 of air sampled adjacent to roads and a parking lot paved with loose crushed stone from the Hunting Hill quarry. The highest figures were measured during "moderate" motor vehicle use. The Mt. Sinai figures are equivalent to 0.2 to 1.9 pm3 of chrysotile per cm3 of air or 0.04 to 0.4 "standard fibers" per cm3 of air. Air samples taken near the perimeter of the Hunting Hill quarry gave chrysotile mass concentrations of from 0.02 to 64 ng/m3 or 2 x 10"6 to 5 x 10~3 "standard fibers" per cm3 of air (U. S. Bureau of Mines, State of Maryland, and McCrone Assoc.,unpublished data). The present O. S. Government limits for "asbestos" content of air are 2 fibers/cm3 (OSHA) and 5 fibers/cm3 (MESA) where a fiber is defined as longer than 5 pm, less than 5 pm wide, and having a length-to-width ratio of 3:1 or greater. ' 18 ASARCO ALV 0002824 The publicity about the possible health risk because of dust emission from the Hunting Hill quarry and its rock products had caused the quarry to lose about 30 percent of its business by July 1, 1977. Montgomery County, MD, expected to pay about $2.3 million in its initial effort to seal the ' roads so as to reduce dust emissions and to remove loose stone from the parks (The Council Report, Montgomery County, vol. 6, no. 22, July 1, 1977). Apparently, other mining and quarrying operations along the "serpentine belt" of the eastern U. S. from Maine to Alabama also will be considered health risks to the general public [29]. Rohl et al. [29] suggested that exploitation of crushed amphibolite rock also raises the possibility of contamination of the air by "asbestos"-like minerals. Discussion The cancer'incidence among those employed in the chrysotile mining and milling industry does not appear to be excessive when compared to national populations (table 1). However, the incidence of cancer among those employed in the "asbestos" trades is very high (table 1); incidence of lung cancer being 3 to 4 times that of the average population, incidence of mesothelsoma being 130 to 220 times that of the average population . The "asbestos" trades generally utilized a variety of "asbestos" minerals including amosite and/or crocidolite, sometimes mixed into a paste for lagging. If we consider that 80 to 90 percent of all the commercial "asbestos" ever mined was chrysotile and that there is a low incidence of cancer in the chrysotile mining industry, we are led to conclude that either amosite and crocidolite are very hazardous or that there is an additional factor relating to health risk in the "asbestos" trades which has not yet~been discovered. Previously, I have discussed some reasons why these two minerals may be more chemically reactive than chrysotile. I.9 ASARCO ALV 0002825 Definitive epidemiological studies of the amosite mining regions of South Africa -and the crocidolite mining regions of South Africa, Bolivia, and Australia appear to be lacking; such studies are needed in order to understand the high cancer incidence in certain trades utilizing these minerals. It is important to point out that the "asbestos" minerals should be considered separately when analysing their effects on the worker's health.' Reasoning by analogy is dangerous; high cancer incidence associated with one form of "asbestos" in a particular occupation does not necessarily mean that there will be the same incidence when utilizing another form of "asbestos" in that or another occupation. Unfortunatk^y, t/ * this type of reasoning has led many to assume that any amphibole in any environment will cause high cancer mortality. The operational problems in defining and characterizing fine mineral particles and the unknown health effects on humans by minerals not generally regarded as "asbestos" appears to be causing more and more investigators to accept rather broad definitions for "asbestos." The present analytical tech niques used by the ERA and OSHA do not distinguish between amphibole cleavage fragments and the minerals geoscientists generally consider to be true "asbestos." In fact, if electron diffraction is not used expertly, many pyroxenes might be called "asbestos." For example, bronzite, a common orthopyroxene having the composition (Mg,Fe)gSi8024, is very similar chemically to amphiboles of the cummingtonite-grunerlte series, (Mg,Fe) Si 0__(OH) . /8 2 Also, orthopyroxene gives an electron diffraction pattern similar to that of cummingtonite -- both patterns possess 0.52 nm spacings between the- diffaction row lines in the hot reciprocal lattice net. A full interpretation of the patterns is necessary for positive identification. Similarly, calcic pyroxenes might be confused with amphiboles of the temolite-actinolite series 20 ASARCO ALV 0002826 or with hornblende. Cummingtonite (and possibly hornblende) is considered an "asbestos" health hazard by health investigators from the National Institute of Occupational Safety and Health (NIOSH), as reported by Gillam et al. [10]. The Mt. Sinai group [29] suggested that crushed amphibole-bearing rocks (amphibolite) used as road-surfacing material may result in wide-spread "asbestos" contamination of community air. Along with the general use of broader definitions of "asbestos" is a trend toward setting lower and lower limits on the acceptable amount of "asbestos" permitted in the environment (at present the OSHA standard is 2 fibers/cm3; the MESA standard is 5 fibers/cm3, but it will soon be changed to the OSHA value). . A more stringent "asbestos" health standard is presently being proposed by the National Institute for Occupational Safety and Health (Reexam~i nation and Update of Information on the Health Effects of Occupational Exposure to Asbestos, December 1976; document prepared by NIOSH for transmittal to OSHA, as requested by the Assistant Secretary of Labor). This document states (p. 92-93): "Evaluation of all available human data provides no evidence for a threshold or for a safe level of asbestos exposure." "In view of the above, the standard should be set at the lowest level detectable by available analytical techniques---------." "Since phase contrast microscopy is the only generally available and practical analytical technique at the present time, this level is defined as 100,000 fibers >5 um in length/m3 (0.1 fibers/cc)----." A definition of "asbestos" to include many amphiboles, chrysotile', and possibly other minerals that appear fibrous or acicular in the electron microscope coupled with a fiber-concentration standard of 0.1 fibers/cm3 should serve to shut down a large number of our hard rock mines and quarries. 21 ASARCO ALV 0002827 Also, nothing has yet been said about the effect of such standards on con struction workers building highways, tunnels, bridges, or dams on amphibolebearing rock, nor of the agricultural workers who are exposed to fibercontaining dust while working the croplands. If the present concept of low or "zero threshold" health risk and broad use of "asbestos" defintions continue, much of the crust of the earth could be considered a health hazard. A way of minimizing the effect on the mining industry of the present and proposed "asbestos" standards, yet still maintaining a good level of health safety;is presented by the Canadian studies of the Quebec chrysotile workers. Here J. C. McDonald and his colleagues G. W. Gibbs,. A. D. McDonald, M. R. Becklake, J. Siemiatycki, C. E. Rossiter, F. D. K. Liddell, 0. A. 21 Attar, A. Harper, and many others [17, 18, 19, 20, 21, 22, 23] have undertaken not only to delineate areas of health risk in the Quebec environment but also to assess the exposure limits of rock dust where the incidence of cancer and other diseases is at an acceptably low level. No occupation can be considered to have a zero health risk. It would seem that similar studies in this field would be of value in the United States. - 22 ASARCO ALV 0002828 References [1] Bates, T.F.jand Comer, J.J., Further observations on the morphology of chrysotile and halloysite. Clays Clay Min., 6^, 237-247 (1959). [2] Brulotte, Raynald, Study of atmospheric pollution in the Thetford Mines area, cradle of Quebec's asbestos industry. Atmospheric Pollution, M.M. Benarie, ed., Elsevier Sci. Pub., Amsterdam, 447-458 (1976). [3] Campbell, W;J., Blake, R.L., Brown, L.L., Cather, E.E., and Sjoberg, J.J., Selected silicate minerals and their asbestiform varieties: mineralogical definitions and identification-characterization, U-- ou/teA'J 0 Ci# C.L>/<a-/Z 87^/j S&fp- (1177^ [4] Champness, P.E., Cliff, G., and Lorimer, G.W., The identification of asbestos, J. Microscopy, 108, 231-249 (1976). [5] Deer, W.A., Howie, R.A., and Zussman, Jack, Rock-forming Minerals, vol. 3, Sheet Silicates, Longmans, Green, and Co. Ltd., London (1962). [6] Ernst, W.G.; and Wai, G.M., Mossbauer, infrared. X-ray, and optical study of cation ordering and dehydrogenation in natural and heattreated sodic amphiboles, Am. Mineral., 55, 1226-1258 (1970). [7] Fears, T.R., Cancer mortality and asbestos deposits. Am. J. Epidemio logy, 104, 523-526 (1976). . [8] Franco, M.A., Hutchison, J.L.,Jefferson, D.A., and Thomas, J.M., Structural imperfection and morphology of crocidolite (blue asbestos), Nature, 266, 520-521 (1977). 19] Gary, Margaret, McAfee, R> Jr., and Wolf, C.L., Glossary of Geology . Am. Geological Inst., Washington, D.C. (1972). [10] Gillam, J.D., Dement, J.M., Lemen, R.A., Wagoner, J.K., Archer, V.E., and Blejer, H.P., Mortality patterns among hard rock gold miners exposed to an asbestiform mineral. Annals. N.Y. Acad. Sci., 271, 336 344 (1976). 23 ASARCO ALV 0002829 [11] Gilson, J.C., Asbestos cancers as an example of the problem of compara tive risks, Inserm Symposia Series, 52, IARC Scientific Publications No. 13, Environmental pollution and carcinogenic risks, 107-116 (1976). [12] Gross, Paul, Is short-fibered asbestos dust a biological hazard?. Arch. Environ. Health, 29, 115-117 (1974). [13] Hemley, J.J., Montoya, J.W., Shaw, D.R., and Luce, R.W., Mineral equilibria in the MgO-SiO2-H20 system:II Talc-antigorite-forsterite- anthophyllite-enstatite stability relations and some geologic impli cations in the system, Am. J. Sci., 277, 353-383 (1977). [14] Huebner, J.S.,and Papike, J.J., Synthesis and crystal chemistry of t sodium-potassium richerite, A (Na,K)NaCaMgcSi 0. (OH,F) : DO 44 4 A model for amphiboles. Am. Mineral., 55, 1973-1992 (1970). [15] Hutchison, J.L., Irusteta, M.C.,and Whittaker, E.J.W., High-resolution electron microscopy and diffraction studies of fibrous amphiboles, Acta Cryst., A31, 794-801 (1975). [16] Kogan, F.M., Guselnikova, N.A., and Gulevskaya, M.R., The cancer mortality rate among workers in the asbestos industry of the Urals, Gig. Sanit. 37, 29-32 (1972). [17] McDonald, J.C., Cancer in chrysotile mines and mills. Biological effects of Asbestos, Lyon, International Agency of Res. on Cancer, 189-194 (1973a). [18] McDonald, J.C., Asbestosis in chrysotile mines and mills. Biological effects of Asbestos, Lyon, International Agency of Res. on Cancer, . 155-159 (1973b). . [19] McDonald, J.C.^and McDonald, A.D., Epidemiology of mesothelioma from estimated incidence, rf&d- , ^ C/777). ASARCO ALV 0002830 [20] McDonald, J.C.,and Becklake, M.R., Asbestos-related disease in Canada, Hefte z. Unfallheilkunde, 126, 2. Deutsch-Osterreichisch-Schweizerische, Unfalltagung in Berlin 1975, Springer-Verlag, Berlin, 521-535 (1976). [21] McDonald, A.D., Harper, A., El Attar, O.A., and McDonald, J.C., Epidemiology of primary malignant mesothelial tumors in Canada, Cancer, 26, 914-919 (1970). ' [22] McDonald, J.C., McDonald, A.D., Gibbs, G.W., Siemiatycki, J., and Rossiter, C.E., Mortality in the chrysotile asbestos mines and mills of Quebec, Arch. Environ Health, 22, 677-686 (1971). [23] McDonald, J.C., Becklake, M.R., Gibbs, G.W., McDonald, A.D., and Rossiter, C.E., The health of chrysotile asbestos mine and mill workers of Quebec, Arch. Environ. Health, 28, 61-68 (1974). [24] McDonald, J.C., Gibbs, G.W., Liddell, F.D.K., and McDonald, A.D., ' `Y* Mortality after long exposure to cumingtonite-grunerite (abstr.), Am. Rev. Resp. Disease, Suoo., 115, no. 4, 230 (1977). [25] Nord,^Jr.^JG.L. "State-of-the-Art" of the analytical transmission electron microscope, in Proc. Symposium on Electron Microscopy and X-ray applications to environmental and occupational heath analyses, Ann Arbor Sci. Publ., in press (1978). [26] Papike, J.J.,and Ross, Malcolm, Gedrites: Crystal Structures and intracrystalline cation distributions. Am. Mineral. 55, 1945-1972 (1970). [27] Pott, F., and Friedrichs, K.H., Tumoren der Ratten Nach I.P. Injektion . faser formiger Staube, Naturw., 59, 318 (1972). [28] Rendall, R.E.G., The data sheets on the chemical and physical properties of the D.I.C.C. standard reference samples, in Pneumoconiosis, H.A. [29] 1Sha piro. ed. , Oxford U. Press, (1970). Rohl, A.N., Langer, A.M., and Selikoff, X.J., Environmental asbestos pollution related to use of quarried serpentine rock. Science, 196, ASARCO ALV 0002831 1319-1322 (1977). [30] Ross, {Jalcolm, Papike, J.J., and Weiblen, P.W., Exsolution in clin- amphiboles, Science, 159, 1099-1102 (196S ). [31] Ross, Malcolm, Smith, W.L., and Ashton, W.H., Triclinic talc and associated amphiboles from the Gouvemeur Mining District, New York, Am. Mineral., 53, 751-769 (1963 ). [32] Ross, Malcolm, Papike, J.J., and Shaw, K.W., Exsolution textures in amphiboles as indicators of subsolidus thermal histories, in Mineral. Soc. Am. special paper no. 2, J.J. Papike, ed., pp. 275-299 (1969). [33] Selikoff, I.J., Hammond, E.C., and Churg, Jacob, Asbestos exposure, smoking, and neoplasia, J. Am. Med. Assoc., 204, 106-112 (1968). [34] Seshan, K., and Wenk, H.-R., Identification of faults in asbestos minerals and application to pollution studies, in Proc. Electron Microscope Soc. Am., 34th annual meeting, G.W. Bailey, ed., 616-617 (Claitor's Pub. Div., Baton Rouge, 1976). [35] Takeda, Hiroshijand Ross, Malcolm, Mica polytypism: Dissimilarities in the crystal structures of coexisting lM and 2Mj. biotite, Am. Mineral., 60, 1030-1040 (1975). . [36] Veblen, D.R.,and Burham, C.W., Triple-chain biopyriboles: Newly discovered intermediate products of the retrograde anthophyllite-talc transformation, Chester, Vt. (abstr.), Trans. Am. Geophys. Dnion, 56., 1076 (1975). ' [37] Veblen, D.R., and Burnham, C.W., Biopyriboles from Chester, Vermont: ' The first mixed-chain silicates (abstr.), Geol. Soc. Am. Abstracts with Programs , 1153 (1976). [38] Veblen, D.R., Triple-and mixed-chain biopyriboles from Chester, Vermont, Ph.D. thesis. Harvard University, Cambridge, Mass. (1976). . 26 ASARCO ALV 0002832 [39] Vigliani, E.C., Asbestos exposure and its results in Italy, in Proc. International Conf. on Pneumoconiosis, Johannesburg, Oxford U. Press, 192-196 (1970). [40] Wagner, J.C., Berry, G., and Trinbrell, V., Mesotheliomata in rats after inoculation with asbestos and other materials, Brit. J. Cancer, 28, 173-185 (1973). [41] Whittaker, E.J.W., The structure of Bolivian crocidolite, Acta Crvst. 2, 312-317 (1949). [42] Wones, D.R., Physical properties of synthetic biotites on the join phlogopite annite. Am. Mineral. 48, 1300-1321 (1963). 27 ASARCO ALV 0002833 TABLE 1. Proportional mortality from lung cancer and mesothelioma for selected male populations. Grouo General populations $/ Canada (1970) USA (1970) Finland (1970). Italy (1970) England - Wales (1970) Chrvsotile mining-milling --^ Cohort No. men All causes 82,052 988,620 22,332 252,795 278,617 Quebec (1936-73) N. Italy (1932-70) 10951 1098 AnthoDhvllite mining-milling S/ Finland (1936-67) "Asbestos" trades --^ too 3938 270 216 Insulators Asbestos factory 26505 10781 2137 1422 Deaths % lung cancer te %mesotheliom 5.3 5.1 7.1 4.7 8.9 0.03 0.03 0.04 0.06 . 5.7 2.2 0.18 0 9.7 0 19.6 15.0 6.7 3.1 a/ Entire male population over 24 years of age [19, table 13] b/ [19, table 12; 20, p. 525] c/ [19, table 12] d/ Composite figures [19, table 12] # 28 ASARCO ALV 0002834 FIGURES Figure 1. Structural relationship between the upper double chain of linked (Si,Al)0^ tetrahedra and the octahedra part of the amphibole strip or "I-beam." The circles represent Mg,Fe, or Al atoms in octahedral coordination; at the apices of the poly- hedra are oxygen atoms. Tetrahedral Si and A1 atoms'are not shown. The "I-beams" extend infinitely in a direction parallel to the c_-axis (the fiber axis). The width of the "I-beam" in the b-direction is three octahedra. Figure is modified from Papike and Ross [26]. Figure 2. Arrangement of the amphibole strips or "I-beams" in (A) orthoamphibole (space group Puma) and (B) clinoamphibole (space group C2/m). The "I-beams" are viewed end-on (parallel to the fiber -axis). The central portion of the "I-beam" is composed of (Mg,Fe,Al)0 octahedra; the upper and lower portions are o composed of double chains of (Si,AlO ) tetrahedra. The "I-beams" 4 are stacked in two ways: (1) +++... (clinoamphibole), and (2) + - + - .... (orthoamphibole). Figure modified from Papike and Ross [26]. Figure 3. .Mineral stability relations in the system MgO-SiC^-H^O as a . function of log of molality of aqueous silica and temperature, at 1 ki lobar pressure. Figure modified from Hemley et al. [13] Figure 4. Adaptation of the enstatite-anthophyllite-talc-forsterite stability relationships at 1 kbar H^O to show a possible stability or metastability field of "talcbole asbestos" (stippled). Figure modified from Hemley et al. [13]. Anth. = anthophyllite. ' 29 ASARCO ALV 0002835 Figure 1 30 ASARCO ALV 0002836 Figure 2 1-------------------r-b CLINOAMPH1BOLE CZ/m Figure 2 . 31 C ASARCO ALV 0002837 (1 kbar l-UD) CM 00 "T sO!S^J 901- lO 32 ASARCO ALV 0002838 640 T ,,C - * - 6 8 0 720 Figure 4 sO!SW 901- 33 ASARCO ALV 0002839 600