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CS National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20, 1977. (Issued November 1978) GENERAL DISCUSSION OF MINERALOGICAL ASPECTS L. SWENT: Homestake Mining Company management is very aware of the implications that the Homestake mine study referred to by Mr. Ross will have for industry. We believe that we have a serious responsibility to see that a study is done and that it is a properly done study. The first study, done by NIOSH without consultation with Homestake Mining Company, was published in June 1976, and contained a number of serious defects of procedure, assumptions, and reasoning, which make its conclusions invalid. As a result, NIOSH and Homestake Mining Company have entered into a cooperative arrangement for a second study. The mortality analysis part of the study has been con- tracted to SRI International. NIOSH has begun the environmental sampling work in the mine, and SRI has started reviewing the Homestake personnel records for the mortality study. Anyone interested in reading a critique setting forth the defects which invalidated the conclusions of the first NIOSH study may obtain a copy by writing to: L. W. Swent, Vice President-Engineering, Homestake Mining Company, 650 California Street, San Francisco, California 94108. W. DIXON: I wanted to ask Malcolm Ross if he has studied fibers which are inter- mediate between talc and anthophyllite in their characteristics and composition? M. ROSS: Yes, that is the work of Veblen, Buseck, and Burnham; their papers on this will be coming out within the next few months (Science, Vol. 198, p. 359-365). These minerals are intermediate chemically and structurally between anthophyllite and talc. They have been found in two or three places; I'm sure we'll probably find more. DIXON: I'd like to make a general request that if anyone participating in this conference has comments to make on the toxicity of those types of materials mentioned above I would be glad to hear of any information that might be available. NOTE: No response was received to this request. (CCG). , R. LEE: I would like to make a comment on a couple of things. First is the outward morphology of amosite versus cleavage fragments; it's generally been written in the literature, which I've seen, that they're indistinguishable. This is, I think, the way a lot of people look at it. We've been doing some studies on amosite, penge amosite versus grunerites, and we find that indeed in the amoslte it's generally a (100) face when you get a single crystal diffraction pattern near 0,0 on your microscope. In the grunerites, they tend to lie about 28° away from this, which puts them on a (110) face, in other words a cleavage plane. The second comment is that our studies on the size distributions of airborne particles show that the aspect ratio of airborne serpentines and very fibrous amphiboles tend to be much, much larger than the size distribution of the corresponding cleavage fragments which were airborne. Something like a minimum of 30 to 1, or an average of 30 to 1 for the particles we observed in an electron microscope, versus about 7 or 8 to 1 for amphibole fragments. But the point I want to make is that we should not only be looking at the health effects, we should be making sure that we know whether we are looking at cleavage fragments or at amosite. ROSS: To add to this, Ann Wiley brought up one clue as to whether amosite or grunerite is really similar to the penge amosite from South Africa. Do the minerals have parallel extinction at the very highest optical magnification? Most of the garden variety cummingtonite-grunerite minerals have inclined extinction; even for the individual crystallites. The parallel extinction is caused by small lamellae randomly oriented about the fiber axis. Optically the specimen looks orthorhombic; optical observation is the Preceding page blank 65 2063104865

first technique to use in order to get an idea whether an amphibole may be similar to the known commercial asbestos. N. TATE: I wonder if you know of Judge Bowder's investigation among the miners in Quebec, where he's found very heavy incidence of disease which was not previously reported. Figures range-from 45 percent among workers, nonsmokers with low exposures, up to 70 percent lung changes in workers with heavy exposures. I also had the opportunity of talking to Prof. McDonald just before I left London. He has a new study which will be published shortly; he says he's found excess disease among the miners at Thetford, half of it the normal asbestos diseases and half of it shows that asbestos workers have lower resistance to all disease. These are two studies which I think should be taken into account. ROSS: Certainly, that's why I want to bring out the Canadian work. It should be taken into account; but you have to recall that these men have been exposed to heavy dust. Friends of mine who go there on geological field trips tell me that up until recently people would hose down the windows in the morning to see out of them, that's how thick the dust was up there. They have, in the past, gotten tremendous amounts of dust in their lungs. Now what the Canadian study is attempting to do is to divide the workers into what they consider low, intermediate, heavy, and very heavy exposure levels to see If they can see a difference in health risk. Now the reports I've seen indicate that below 200 mpcf- yr there's a very low health risk, but all I know is what I read in their papers. I want to point out that somewhere we have to find a tolerable health risk or we'll have to close down the surface of the earth. A. SUNDARAM: Dr. Ross, I'm wondering how you graded the various types of asbestos in relation to the toxicity or pathogenicity? There are at least four distinct types of pathogenicity arising from asbestos exposure: asbestosis, lung cancer, mesothelioma, and cancer of the gastrointestinal track; also it is claimed in other organs. When you graded it so easily: crocidolite, amosite, anthophyllite, and chrysotile, did you do the gradation yourself or are you quoting any paper? ROSS: I'm quoting Gilson. SUNDARAM: And is the gradation based on animal data or epidemological data? ROSS: I can give you the reference (Inserm Symposia Series 52, p. 107-116 (1976)); it's a summary paper by Gilson where he suggested this generalization. Perhaps you can find something wrong with it, but it was a generalization. I made an additional generali- zation that the chemical activity of these four minerals seemed to be similar in that crocidolite can undergo on the surface more chemical reactions than amosite, and amosite more than anthophyllite, and chrysotile being the least chemically reactive. I'm just pointing this out as a generalization, something to start from; maybe it might give some clues for the formation of cancer, I don't know. It may not be that it is the only factor, because the shape and the aerodynamics are apparently very important, and the lung clearance functions are very important, so there are many parameters that have to be taken into consideration. The chemical reactivity of the surface is one of them. I believe that the chemical reactivity of the surface is important. Consider a standard fiber lxlx5 pm in size. There will be 100 times more surface area if you divide a standard fibeir into 10,000 smaller fibers. So one big fiber might be a 100 times less effective, as far as the surface chemistry is concerned, than 10,000 small ones - yet they both would have the same weight in nanograms. SUNDARAN: So you mean to say that the gradation is based on chemical reactivity and not on any toxic parameter? ROSS: Well, I'm saying chemical reactivity may enter into the toxic parameters. What causes lung cancer? Does the fiber interreact with a chemical such as in tobacco smoke and then with the human tissue, and so forth? Does the fiber interreact directly with the human tissue chemically? I'm basically getting down to a chemical answer in the end. 66

B. WHITE: As you know we are in the process of putting together so called emergency regulations, relative to the Rockville Quarry. Now these regulations deal primarily with the containment of the crushed stone. You're inferring that you feel that this sort of approach is not indicated based on the Canadian work? ROSS: The Canadian work would suggest there is not a health danger with this level of asbestos dust. Now all the data are not in. What we would need is ambient air measurements in the Rockville area. Dr. Selikoff suggested, at the National Institutes of Health hearing on this a few weeks ago, 45 nanograms is the limit in ambient air. What level of ambient air do you want to have for chrysotile? I haven't seen an ambient air figure for the Washington, D.C. area. I don't know what it is. I'm really pointing out that we can shut down all the serpentinite quarries on the East Coast. If it's serpentinite it is going to have some chrysotiie in it. But then, where do we go from there? We also have tremolite; we can shut down other mines because of tremolite or because of fibrous hornblende and on and on and on. Now I think that I'm pointing out, from a mineralogical and geological point of view, that this is an immense problem. EPA is now getting set up to get crusher runs on mines and quarries all down the East Coast. It's going to run into millions of dollars. It's already running into millions in the Montgomery County area. Now I think that the health people have got to get together and decide what they're going to call asbestos, what dust levels are going to be considered dangerous, and what sort of mining operations they think they are going to have to shut down. You can shut down a mining operation very easily by putting so many requirements on it that the contractors say, "heck with it, I'll go to Frederick and get carbonate rock." I'm pointing out it's an immense problem, it's economic, it's political, it's health, and so forth. WHITE: I agree with you very much; our intent is certainly not to close down the mine, and I agree also that the health people must come to grips with the issue of the ambient air. Now obviously since there are no standards, our approach is purely on the mechanical side of this, which is trying to reduce the dust emission as much as possible and, quite frankly, I feel until there is more data on the amount that can be floating around in the air that this is a very sensible approach, a preventive approach actually of dealing with the problem. Even though there is nothing that one can hang the hat on from the health side, I personally think that to allow the crushed rock to be used indiscriminately is just simply not a good approach to preventive medicine. Thank you. R. DAVIS: We live in a complex world and you pointed out that contractors might use carbonate stone. A number of the state highway departments have shown that carbonate contributes to lower skid resistance. We are faced with the problem of how many people are going to die from cancer from the chrysotile type of material and how many are going to die from lowered skid resistance on the highways. These are very complex problems. ROSS: What makes it so frightening is if you pull a string and all of a sudden a lot more string comes out, you don't know whether you've increased health risk or decreased it. You've decreased it in one area and perhaps increased it in the other. One possibility is that people would be so scared of asbestos, they won't use it for anything. Asbestos has saved many lives when used for fireproofing. We could carry on with fiberglass which has a lot of similarities to asbestos, or we can get rid of fiberglass, and we can insulate with organic chemicals, like some that form carbon monoxide and HCN when they burn. The total picture is a big one and I think that we all should try to get a feeling for the entire situation, and consider some of the problems that could arise. E. COX: I'd like to ask M. Ross or Dr. Zoltai if you could tell us when the first commercial mining of asbestos took place, what type it was, and where it was? T. ZOLTAI: About a couple of thousand years ago; on a cowserciai scale the major mines started in the late 19th century. COX: About 1880-1890? ZOLTAI: Yes. COX: And where were they, sir? 67 N ~ ~ a v

ZOLTAI: In Canada. COX: In Canada, and what were they? ZOLTAI: Chrysotile.7 K. HEINRICH: I'd like to ask Malcolm Ross if you have information of the size distribution of chrysotile in Thetford and if it is similar to that in Montgomery County? ROSS: Tom Bates did a size study of chrysotile from the Thetford area, Canada, and also on the beautiful chrysotile from Arizona. I have the figures in my paper but I think in the Canadian chrysotile he had a minimum o 110 R outside diameter and a maximum of several hundred with an average of about 250 ~. I think the Arizona chrysotile had a generally larger diameter. You meant length, I'm sorry, I was thinking of width. I don't know that, I don't have that figure. Some of the Canadian chrysotile was in beautifully long fibers. This material set the chrysotile industry off, because in 1886 they found these exceptionally good types of asbestos. I imagine some of it was very long fiber material, but of course much of it would be short fiber also as the Rockville chrysotile is. J. ZUSSMAN: I have two comments and one question. One is the point about when some commercial use of asbestos started. I believe there is some record of something industrial in Italy with products like asbestos paper. There is also mention of the manufacture of asbestos socks and gloves at a place in Russia. These were both before the start of large scale mining at Thetford. Another comment is in connection with Or. Ross's remarks about the reactivity of various forms of asbestos, in which he put chrysotile low down on that scale. In one sense perhaps chrysotile is high up in the scale of reactivity in that it is less resistant to acid, and quite dilute acids can attack and start to dissolve away chrysotile. It has a rather exposed layer of magnesium hydroxide and this is obviously going to be quite reactive to dilute acids. I am not sure whether its reactivity in this sense makes chrysotile less or more physiologically harmful. I'd like to ask one question of Dr. Ross about the synthesis. I was very interested to hear of his colleague Or. Hemley's work on stability fields of the serpentine and amphibole minerals, and I would like to ask whether or not the chrysotile or amphibole formed was asbestiform or not. Quite a lot of work has been done on the stability fields of amphiboles and serpentines in general, but rather little pinpointing when long thin chrysotile fibers form and when other serpentines like lizardite and antigorite form; also when asbestiform and when non-asbestiform amphiboles form. I wonder if the products of those experiments were identified as asbestiform or not. ROSS: Yes, Dr. Hemley's work, I think, was really one of the outstanding contribu- tions we've had in this area of geochemistry this year. These experiments were very difficult; they are run at relatively low temperatures, so his run times were many weeks duration. Concerning the stabilities of the individual polymorphs of serpentine, he attempted to define an antigorite and chrysotile field. He did some electron microscopy, I believe, and found platy-serpentine, which he called antigorite. I asked Julian Hemley - "if you injected some chrysotile into the human blood stream or into the lung, what would you expect to happen?" He thought about the various parameters in the human body that might affect that system and he said, "I don't think anything would happen." Nevertheless, chrysotile is very soluble in dilute acids, and Dr. Langer will agree ingested chrysotile in the stomach should decompose quite readily. Hemley did not think that the pH range of the human body, other than the stomach, would contribute to any appreciable dissolution of the chrysotile. 0. MENIS: He suggested it would last and last. Being a chemist, I would like to ask the mineralogist why they have neglected would like materials, the to and OH group, the hydroxylation process. I wonder if Prof. Zussman and others comment an the role of the OH, the potential of local pH values of these the ease of the hydroxylation which is known from thermal data where you N have a great difference between the various amphiboles and chrysotile. .~i 68

:IO CS ZUSSMAN: I look to my colleagues because I really don't know much about it, and I don't know that very much is known about the comparative effects of the hydroxyl in these different minerals. Certainly in the amphiboles, and crocidolite in particular, some work has been done on oxidation-reduction phenomena, because there you have not only the hydroxyl but you have the ferric ion and the combination of the two is conducive to chemical reac- tions going on. I don't know of any work which has examined the effect of OH in the grunerites or very much in serpentine except with regard to decomposition. If you heat them, then they break down at different temperatures, and you mentioned the question of differential thermal analysis giving different results. I think one has to be very cautious about this because it's notoriously easy for a variety of results to be obtained in the decomposition temperatures by DTA methods, which may or may not be significant. In the amphiboles, hydroxyl is there, and so is fluorine (I hadn't mentioned that because there was a limit to the complication that one could go into in the time available for my paper), but it's quite possible that the ratio of hydroxyl to fluorine, the presence of fluorine or the presence of chlorine could be relevant. These are all minor variables and there has not been much systematic study of how many of these variables are relevant to the comparison of asbestos and non-asbestos amphiboles or serpentines, and their effects. Malcolm Ross may have some comments on this. ROSS: If you pass hot, inert gas over grunerite crystals, hydrogen will be removed and you'll get two atoms of trivalent iron. This is quite reversible, at least in other similar phases. Ernst and Wai have done this experiment with sodic amphiboles. Repeated experiments on biotite by Wones shows complete reversibility of this oxidation-reduction reaction. In amosite as well as crocidolite, the iron may be oxidized by removal of hydrogen. This can go very readily at higher temperatures. It is unknown whether this can go on in the human lung, but it is a possible chemical reaction. Also another reaction is ion exchange in crocidolite. You can oxidize or reduce the iron, and exchange oxonium, ammonium, potassium, or sodium in the vacant site. Thus there are some very interesting possibilities for chemical change on the surface of these crystals. J. KRAMER: I might make a comment. I think back to the original question on chemical reactivity. One of the ideas of looking at surface reactions in the amphiboles originally was that these crystallites forming the asbestos form of the amphibole may be hooked together with 0H0 bonds, and we thought we might see some differences here. Our type of measurements which I quickly alluded to, are crude. They're gross and are in no way domain measurements. We didn't find any differences. The other thing is of course that chrysotile versus the amphiboles has a much different zero point of charge, quite a bit different double layer in terms of surface reactions. One might want to compare these two groups in order to look at reactions involving the hydroxyl groups. But I think maybe Dr. Zoltai may like to comment upon some of his surface charge measurements because I think these are much more specific to the individual fiber. I'd like to hear your comments. ZOLTAI: Actually we haven't done any sophisticated work to be able to answer a question of that level. All I can say is that what we were trying to do was to detect surface charges at the level of single fibers rather than in bulk quantities of fibers. By using distilled water containing positive or negative labelling sols in suspension, we tried to detect the surface charges of amosite from South Africa and non-asbestiform cummingtonite. In other words, there was only one experiment, and in that case the asbesti- form material appeared to have much higher negative surface charge. However, the two specimens came from two different localities, besides being only one test that could not be considered very meaningful. Actually, the reason we did that was to see whether the technique is applicable to asbestos. It would be very nice to have a technique where you can get an indication of the surface charge at the scale of single fibers. KRAMER: Did you notice any domains pertinent to your technique? ZOLTAI: Occasionally, yes. UNKNOWN: I'd like to ask Dr. Zussman a question. Have you any way of estimating what fraction of the total amphibole structure might be defective, what are the length dimensions of the defects, and how much of a chemical variation would you expect to be associated with the defects that you outlined? 69 2063104869

ZUSSMAN: The little work that has been done on this shows the frequency of defects in the limited number of samples that have been looked at and, in some of the ones I can remember, the defect occurred about one every 50 cells, so it was a small proportion in that particular sample. Other samples may show a much higher density of defects, but I think just not enough samples have been looked at in that respect. As to the importance of defects, they coulb be very important in terms of crystal growth, and in terms of mechanical properties. Perfect crystals without defects have very different tensile strengths and other mechanical properties compared with crystals from the same substance but with defects, and it's conceivable that chemical reactivity may be concentrated at the sites of defects. It's an area which is not being looked into to my knowledge; perhaps somebody else can say otherwise. Added after meetin : My answer above about the density of defects was related to Wadsley defects. I omitted to say that the other kind of defect (stacking and twinning) have been reported as very abundant in crocidolite, amosite and tremolite asbestos. Only the Wadsley type of defect would have a direct effect on chemical composition, but it would be rather small if there are relatively few of them. SUMMARY: Dr. Mason, the session chairman, indicated that he felt the General Discussion provided a very adequate summary of the mineralogical aspects. 70