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i Z5 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 ANALYTICAL METHODS M. ROSS: I first would like to congratulate the U. S. Steel group. That was a beauti- ful presentation. I think that they have shown a method to use electron diffraction in a quantitative way, which is very important. Also, I like to mention that my own colleague at the U. S. Geological Survey, Gordon L. Nord, is also working in this area from a slightly different point of view, developing a method of indexing electron diffraction patterns. His and U. S. Steel's methods, I think, will have a great use in making electron diffraction really useful and quantitative and much simpler than it has been in the past. Next, I would like to address myself to the..... R. LEE: Malcolm, may I interrupt? We'd like to acknowledge the fact that without Gordon Nord there's an awful lot of twin patterns around my lab that wouldn't have been indexed. ROSS: Gordon Nord will have a paper on the subject of indexing electron diffraction patterns coming out in a volume concerned with identification of microparticles based on a conference held earlier this year in Denver ("State-of-the-Art" of the analytical transmission electron microscope, in Proc. S~~o on Elec. Microscoy and X_Ray lications to Environmental and Occu atio'nal HeaTth Ana sis Ann r/~bor Sci.-6ub1., in press 8). he nf- ezt ting-f li e to ring up now s more of an observation. I'd like to quote a paragraph from my paper for this conference. "The crushing and milling of any rock will usually produce mineral particles that are within the size range specified in the OSHA rules. Thus, these regulations present a formidable problem to those analyzing for 'asbestos' 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." Now as far as Dr. Anderson's presentation of an amphibole analysis in water samples, with his method you will find asbestos in every mine and mill effluent in the country, unless you make strict rules of identification and characterization of asbestos. To go back to my discussion the first day when I showed the maps of the U. S., you will be affecting every hard rock mining and quarrying operation in the United States unless you can get an identification and a definition of asbestos that does not include every amphibole, pyroxene, zeolite, and gosh knows what else that's in the crust of the earth. C. RUUD: Listening to what Malcolm Ross says I can't help but agree, but I think if you read the Federal regulations with respect to water, you will find the word asbestos and then several mineral names following. Until it can be demonstrated that a chain silicate is distinguishable from an asbestos chain silicate on a single fiber basis in the microscope, then Chuck Anderson and the rest of us are stuck with the situation that Malcolm points out, that is to say that the whole world is dangerous. LEE: Clay, I think our point here is that if you look at the electron diffraction pattern from amosite particles, at least 70 percent lie on a 100 face. If they lie on a 100 face, they have to have a b* component, which is the 18 A d-spacing, perpendicular to that face; therefore, it has to be very close to the normal to the electron beam. Hence, within a couple of degrees - we were using apout five on this study - of the 00 tilt in your microscope, you should find a strong 9 A row through the center of your diffraction pattern. We would say, on the basis of these data, that particular pattern is, as far as we are concerned, close to being diagnostic. Now you also have diffraction patterns from cleavage fragments which tend to lie between 110 and 010, and those patterns can give you the standard kind of pattern that people are using for identification of amphiboles and cleavage fragments in lake water. RUUD: Rich, you and I have discussed this and I think you have an excellent point and we both agree that it has to be demonstrated. If we can do that, and if our micro- scopists are able to recognize what you are saying at a glance in the microscope, I think Preceding page blank 413 2063105203

i t wi l 1 be an i mportant step. I' d 1 i ke to make one more comment wi th respect to what Jim Kramer mentioned this morning. Jim was asking Chuck Anderson why he did not outline the method for recognition of an SAED pattern. Well, first of all it takes a highly experienced technician to do good transmission electron microscopy. On top of that it takes a much better technician to do SAED. To train that man to recognize patterns is probably one of the easiest things. S. COHEN: My question is directed to Dr. Cossette. You mentioned recommending a secondary sampling method using a mini-impinger. I was wondering if you could expand on that and, if any studies have been done, comparing that to the membrane filter. M. COSSETTE: Yes, some studies have been done. We found better reproducibility, but not that much better. We think it should be used if somebody wants to get correlation data to compare against the epidemiological data that we have. The large epidemiological studies are all based on midget impinger and you cannot translate midget impinger counts to fiber counts, not directly, not right across the board. I. STEWART: I had a comment which is really diametrically opposed to Clay Ruud's comment. It's my feeling really that everything that we've seen an these requires someone with the knowledge of diffraction. If you're looking for somebody to drive your microscope, this should be a first requirement, a knowledge of the mineralogy of these materials and a knowledge of their diffraction patterns. You can teach any monkey to push the right buttons. I've done it over the phone. This is no respect really to the biologist. I'd like to make this comment, that this is in the health effects field; that a lot of people in the health effects field are biologists. They're damned good electron microscopists; they have never had to do any diffraction in the past; they have never been exposed to diffraction theory, and they are going to have a problem because they have to learn first of all the technique of getting the pattern and then what it all means. Now Rick has mentioned the fact that he had problems with some of the twin materials. There is probably more diffraction done in his field, in metallurgy, particularly in high voltage electron metallography, than there is in any of the other material sciences, and I think this highlights the problem that you need someone who is highly skilled in the interpretation of the diffraction patterns (first requirement); secondly, the knowledge of the variations that you get in mineral structures, the variations you can get in the natural mineral within a single crystal, and then you can say I have a man who is worth training on the electron microscope. R. FISHER: Perhaps the solution to this - we recognize the difficulties - would be to establish a central facility with a big computer, with an automatic digitizing device, and where people send in their diffraction plates and these are processed in a routine way. The people processing would have no idea what the sample is, they wouldn't have any leanings, whether they want, or do not want, to find amphiboles, and the cost of doing this could be I think reduced considerably over every individual becoming an expert diffractionist, and then measuring them by hand and calculating by hand unless he has a computer and the computer library of data available. This is one possibility of an interim solution I think to set up one facility; the plates are mailed in and they are analyzed and identified on a more routine basis. K. CHOPRA: I think there will be another problem with respect to giving you the camera constant and operator's judgment on how he got the camera constant, and if you don't have that right you might as well not do an analysis on it. LEE: I'd like to respond to Dr. Chopra. Let's say you have two minerals that you're interested in identifying and you want to reject any other mineral. In that case I can take the angle between the rows and the ratio of the d-spacings; they are the only two things which are independent of the camera constant and pretty much independent of the operator - from those I think you have a very high certainty of a correct identification or a rejection. There will be cases when you can't accept the identification because there is not enough information available. J. ZUSSMAN: I'd like to join the others in complementing Dr. Fisher and his group on his very fine presentation of what has obviously been a very careful, painstaking piece of work. After making that comment, I'd like to say that the kind of approach to analytical 414

es techniques used for a given problem depends very much upon that problem. If there is a completely open new situation where very little or nothing is known about the sample, then I'm quite sure that the approach which Dr. Fisher and his group have explained is the only safe one to adopt, because it's the only way of being sure of your identifications of not only what you think is likely to be there but what you may not expect to be there. But it is obviously a lengthy procedure. I agree fully with what others have said. Ian Stewart talked about the need to have really well-trained people to execute these techniques, and to understand diffraction above all because you need to understand diffraction to interpret not only diffraction patterns but to interpret the electron micrograph as well. They aren't just pretty pictures and shadowgraphs; there's more to it than that. Diffraction comes into it. Not everybody can employ highly trained crystallographers to do lengthy procedures for long periods of time and it isn't always necessary. There may come a stage in a situation where you do know quite a lot of the background of the problem and you don't have to worry too much about unexpected things coming up. In this case you can take shortcuts once you get to know the kind of field you are in. But one should always bear in mind, and there will be enough critics to keep an eye on you I'm sure, that you may have overlooked something unexpected. For example, the question of using in addi- tion to electron microscopy, energy-dispersive, analytical methods has been mentioned, and I think this is a very useful technique to adopt. It can give you clues as to what mineral might or might not be present. If an ambiguity exists in an electron diffraction pattern which doesn't allow you to resolve this, or if you don't have an electron diffraction pattern, the energy-dispersive analysis can narrow down the possibilities. It is done much more rapidly, and less expertise is required perhaps than for the interpretation of electron diffraction patterns. So I do think that perhaps the most powerful, the ultimate technique is the combination of all - electron micrographs, energy-dispersive analysis, and electron diffraction pattern analysis in full. A good approximation can be gotten perhaps in certain circumstances using the x-ray spectrometric analyses to guide you. That's one general point that I wanted to make. Another point: Dr. Anderson has expressed his worry about not being able to distinguish between what is asbestos and what is not asbestos. We've heard again with great interest the promising signs which seem to show us that it may be possible, even when you have started out with a true asbestos on the one hand, or you have started out with a clearly non-asbestos material on the other, and you grind the hell out of both of them, to recognize one from the other. I think there are promising signs that you can. But, faced with the situation that you're not convinced by this, there's a way out: you just don't commit yourself. Why call something asbestos if you don't know or, in some circumstances, when you know darned well that it started out as being non-asbestos and yet it's listed at the head of table "Content of Asbestos Particles." Why not use a nomencla- ture in a more sensible way, depending upon the amount of information you have about the specimen? If all you know is that it's crystalline and you say it's a fiber, define the fiber how you like, as long as you tell us, 3 to 1, 5 to 1, but specify what it is you have in mind. Say it's a crystalline fiber and that's all you know, perhaps. At the next stage of knowledge you might say it's a mineral fiber or an inorganic fiber. At the next stage you might say you know it's an amphibole fiber but you don't know which amphibole. That's O.K., say amphibole fiber. You might then have identified it as tremolite: say it's a tremolite fiber. If you know that it's asbestos because it has come from an asbestos deposit, say tremolite asbestos, but if you don't, say tremolite fiber, numbers of fibers, numbers of amphibole fibers, not numbers of asbestos fibers. Those are my general comments. I'd still like to make two very small points. On technique, I agree with the experience of my colleague in Manchester, Dr. Champness. Our work has been done with the carbon coating method; and we agree that there doesn't seem to be any great percentage loss in carbon coating. Secondly, I wondered if anyone else has this experience: she tells me also that she uses dimethyl sulfoxide as a solvent for getting rid of the Nuclepore filter. I haven't heard it mentioned here at all. There's been chloroform and acetone, but Dr. Champness swears by dimethyl sulfoxide as being a solvent which dissolves the plastic more slowly and therefore causes less disruption to the carbon film. Also, it's a more pleasant material to work with. It isn't as volatile and so it has less unpleasant fumes and there are other factors which she thinks favor the use of that solvent. 415 2063105205

0.1 K. HEINRICH: Would you agree that probably x-ray spectrometry would be more useful in that area if one could determine, for instance, the magnesium-silica ratio with better accuracy than one can presently? ZUSSMAN: You mean using energy-dispersive methods? HEINRICH: Yes. ZUSSMAN: Certainly. The greater accuracy you can get the more satisfactory it will be. But I think with proper use of the energy-dispersive method, and with intelligent application of it to the right kinds of specimens, specimens of the right thickness, that is, you dan get very good accuracy which enables you to distinguish nearly all of these various magnesium silicates, but not all. There may be an occasional overlap, but 90 percent of them can be done within the present state of the art for accuracy, I believe. HEINRICH: Thank you, Prof. Zussman. Would you have any comments as to Prof. Zussman's points? CHOPRA: I think he's brought up very good points. I think this combination of two which is using EDS/SAED in morphology combination and just calling them fibers is the way to go at it. A. SUNOARAM: I have to congratulate Dr. Fi'sher for his braveness in suggesting 10 to 1 ratio and 2 micrometer length. If we accept your definition of asbestos, we having the regulatory responsibility are faced with at least two major problems. Number one, if you insist on a 10 to 1 ratio and have the length as 2 micrometers, that means we've got to have the diameter of the fiber as .2 micrometer. Then immediately the use of optical microscopy for monitoring purposes is ruled out. If we take your method of detecting fibers of only 2 micrometers in diameter (should be, length? [90]), 1 just would like to know how feasible it is for a routine monitoring basis. Also, as a standard reference method, I'd like you to find out on that; that's number one. Number two, we have another responsibility now to show that fibers below 2 micrometer are not hazardous, so we are faced with that problem as well. Number three, I would like you to comment on the use of the in vivo studies as well as in vitro studies and the use of those to prove that 2 micrameter Tength is a safe length of choice. FISHER: Well, working backwards, I can try to comment on the proper testing. What I had in mind is to say, let's divide these particles into domains that can be clearly identified and there's no question that 10 to I does that. There's very little overlap between the fragments produced by grinding and the fibers produced by the fibril growth habit that occurs in what is well known as asbestos. When you take 5 to 1, now you kind of get into that middle ground again. When you get down to 3 to 1, why it's just hopeless to run any tests and decide that there's any distinction in the biological activity above and below 3 to 1. You couldn't prepare the samples. There's already a problem with some small fraction of long fibers occurring in the so-called short-fiber specimens and this completely, I think, affects the results. Now your point about at the limit of the 10 to 1 and the smallest fibers getting down to pushing the analytical techniques, that is a good one, that would indicate that some of those would be lost from the analysis. F. CHUNG: We routinely use x-ray diffraction, x-ray emission and microscopy for material characterization including asbestos. We actually analyzed many hundreds of asbestos samples either on membrane filters or as bulk powder. Based on our experience, I would like to make some comments: (1) Identification: The term "asbestos fiber" combines two different features: the work "asbestos1r indicates chemical composition and crystal structure; the word "fiber" indicates morphology, i. e., external shape and size. The OSHA phase-contrast microscopical method is adequate to count the number of fibers, but not the ASBESTOS fibers. As to the methodology of identification of asbestos (chemical composition and crystal structure) we have to make a distinction between a single fiber and components in a mixture. For components identification, x-ray diffraction is about the only choice; for single fiber identification, combined results of electron diffraction, and x-ray emission 416

C. 5 (Mg/Si, Mg/Si/Fe, Mg/Si/Ca ratios) are most convincing. Dispersion staining and polarizing microscopy can give only supplementary information. (2) Bulk Materials: For asbestos analysis we have to differentiate between membrane filter sample and bulk sample. The OSHA phase-contrast microscopical method cannot be used to obtain a fiber count for bulk samples. A reasonable indicator of asbestos content in bulk samples would be its weight percent, be it amosite, tremolite, or others. X-ray diffraction analysis can provide this weight percent with a precision of about ±10 percent relative. (3) Monitoring Methods: An official monitoring method ought to be practical and not too expensive. An optical microscope costs $1,000~52,000. An x-ray diffraction unit costs 520,000tiS30,000. An electron microscope costs $100,0004200,000. In order to be "practical and not too expensive," I believe the current phase-contrast microscopical method is good enough for fiber counting and the x-ray diffraction method is adequate for identification and/or quantification. Note that if no fiber is observed under a microscope, identification by x-ray diffraction is not necessary. When the combined results of microscopy and x-ray diffraction are doubtful or challenged, then electron diffraction, x-ray emission, dispersion staining, and polarizing microscopy can be called upon for further confirmation. (4) Definition of Fiber: An important feature of a fiber under a microscope is a pair of sides parallel lengthwise. This feature combined with a high aspect ratio, say 20 to 1, would exclude all the "cleavage fragments" which are non-fibrous and should not be regulated. FISHER: I think on this identification question the problem has now been defined and recognized and I'm sure methods, reasonably satisfactory methods, will be developed in the near future. Also, on the counting, there are automatic image analysis facilities becoming available on microscopes. So I think the main point is to recognize that the problem is difficult, and the approaches that must be followed to get an absolutely positive identification; there are approaches that will give you a fairly high degree of reliability and I think that the next step now is to really document what these are. RUUD: I'd like to cast my vote with Dr. Zussman that I think it's high time that we come up with a nomenclature that is clear with respect to what we are trying to describe. Perhaps, Kurt Heinrich and the NBS will have that task. With respect to sending off electron diffraction patterns to a central source: we have been working in our laboratory with metallic substrates for transmission electron microscopee samples and have settled upon a fine-grain alloy that gives us some very sharp Debye rings that could well be used to determine the camera constant. T. ODGEN: I've got a question for Dr. Cossette. Did I understand you to say that you would prefer to use size-selective sampling and then to determine the mass of asbestos? This is the same as giving weight to the larger fibers in the respirable range, isn't it? Have you any medical evidence for this, epidemiological evidence, or is it that you just feel it would be a more accurate thing to determine? COSSETTE: You're right in your assumption that we would like to classify fibers before we collect them on the filter, eliminate the oversized ones and the undersized ones. We've examined the literature on short fibers and we find generally two situations. In some cases there has been no biological activity, or little activity. In other cases they have shown some biological activity, but in those cases the short fiber invariably contained a significant percentage of long fiber; and this, in our view, faults the results. J. SAUNDERS: I just have a comment to reply to Dr. Zussman's comment. Asbestos isn't the only thing in the world that has teeth. If I were going to play with dimethyl sulfoxide I'd be very careful to look up and see what it does. It seems to me a number of years ago there was some research done on how it caused other materials to penetrate the skin. So, before I work with DMSO, or other solvents for that matter, I'd be careful. 417 2063105207

0. BEAMAN: I'd like to ask Dr. Fisher: is your computer program available and can it be used on anything other than your instrumentation? LEE: In answer to your second question, as part of this ASTM round robin, I've recently analyzed some diffraction patterns from several labs. There are some labs who properly record the diffraction pattern. I have no problem indexing and interpreting their diffraction patterns, taken on either 100 kV microscopes or 80 kV. I found that other labs weren't as careful with their patterns, and I had difficulty with the measure- ments. So the answer is: yes, our methods can be used if you get a zone axis. If you get a very incomplete pattern, our methods are unusable. However, our preliminary data, and we want to emphasize it's preliminary data, suggest that the characteristic amphibole pattern that is recognized by people with experience is that of the amphibole cleavage fragment and thus they wouldn't recognize the typical pattern from a single crystal amosite, asbestos particle. FISHER: You really asked about the availability of the program and I see no difficulty with that, making copies available. D. GIOIELLO: Question to Dr. Cossette. What TWA is the committee recommending for the two industrial groups that you split up, what excursion or fifteen minute exposure limit, and what is your medical justification for it? COSSETTE: This is not completely settled and that is why I didn't mention any specific figures. The numbers that we are considering presently for the mines and mills are the same as the MESA regulation, which is five fibers, and for manufacturing and end use industries are the same as the OSHA regulation, which is two fibers, but this is not yet resolved. The justification for it is a review of the literature where we considered all the significant information published, particularly epidemiological data. We were not as strongly concerned with animal experimentation, but with the health effects on humans. T. PANG: I would like to ask Dr. Fisher to comment on the identification of chrysotile fibers. LEE: In the quantitative identification of chrysotile fibers, I have very limited experience. We have been working primarily on the identification of amphiboles. I have not obtained chrysotile patterns which I have indexed. I use a reference pattern which looks a lot like that which anyone else would use, as the pattern is diagnostic of rotational symmetry. I think a problem occurs only if you don't have some indication of the chemistry or no SAD pattern, for then you could be talking about a very acicular clay mineral or anything else. HEINRICH: Would anybody else want to comment on the identification? ZUSSMAN: The least one can say about chrysotile is that if you are looking at the electron diffraction pattern, now I'm talking about chrysotile asbestos, then the diffrac- tion pattern is simpler to interpret because you don't have a rotation problem. A single fiber has already produced a rotation effect, because it is cylindrical, and no matter how much you turn it about the fiber axis it won't affect the pattern. So you are up against less of a problem than in the amphiboles, of the kind we have heard about. I would have thought that on the whole, if it is true chrysotile asbestos you are interested in, well, rather than with other forms of serpentine (some of which ma,y have greater or less similarities), the problem is very easy because the morphology is also relatively easy to see, the length-to-width ratios are usually extremely high, the diameters are extremely low, and you can often see the central void channel in a number of the fibrils you look at. Other forms of fibrous serpentine, though not asbestiform, not silky, not things which would have on the macro scale the properties of silky asbestos, let's say, give diffraction patterns somewhat similar, similar enough I think to put you on the right track, but not identical to asbestos. 418

You can index quite a number of the reflexions, quite a number of the spots, but some of the spots are not spots, they are streaks. You can do some sort of approximation to indexing those, but it is not as easy, but again there are fewer of them, and there are not many spots and streaks to index because the structure is rather randomized and not very we'11 crystallized. ROSS: I would like to make a comment again, concerning health aspects of asbestos. Perhaps we are now beginning to understand which shapes and sizes of certain minerals cause ill health, but it comes down to what actually causes cancer. What are the chemical properties of silicate minerals which relate to cancer development? High health risk is known only for four commercial forms of asbestos. I don't know of any health studies that relate to other types of minerals that may or may not be asbestos, but have never actually been commercial. So I'd like to repeat that we need epidemiological studies in areas other than true asbestos mining, milling, and in the asbestos trades. The Homestake Mine is one. If the miners there can be proven not to have health problems due to amphibole, then there is a very high probability we can quit worrying about the grunerites, cumming- tonites, and hornblende and our common rocks. We should also look at the hard rock iron ore miners who are also exposed to these same minerals. I am not impressed with rat and animal studies. A great many solid state materials have been injected into the pleura of animals. Fiberglass may or may not cause disease. I saw one study where actinolite did not cause disease, one study where tremolite did, and so forth. I think it's got to boil down to the health of the people involved in the operations other than strict commercial asbestos mining. If we can find that there is not a health hazard in general mining communities, we can quit worrying about a great deal of country rock and concentrate on true asbestos. I think the mineralogists have shown that there are some very interesting mineralogical properties in what we consider true asbestos that may have something to do with cancer. R. THOMPSON: Everybody has danced around the issue, but nobody has addressed it. If you are going to set up a method for monitoring, and ultimately that is what you are coming to, you are going to have to have some kind of objective, and your objective is going to determine what method you use. I would contend for the objective I was given; I've got a method that works for chrysotile in ambient air samples. It would not be applicable to anything else, nor do I think that some of the mineralogical work we have done in depth would be possible or necessary on air samples when you are dealing with one part of asbestos in ten to the fourth of the total particulate matter. Then we are going to have everybody talking about a method as though you are going to have one to do every- thing with, and that is complete balderdash, so we are going to have lots of methods to determine lots of things and ultimately it's going to go back to health effects as has been mentioned. And maybe when the threshold response that was brought up yesterday is answered the main method we've got may prove to be of practical value there, who knows. QUESTION: Would you comment on the role, if any, of the optical microscope? THOMPSON: I say, for ambient air samples, optical microscopy is an impractical tool. I proposed in 1970 to do a fence to background study of the distribution of chrysotile by fiber length, to get a fiber length distribution. I believe you will find that if you do this you will be able to establish (up to a point) a ratio between the asbestos by the mass method and the optical count, and that might prove to be a survey tool. If your asbestos count is high enough, x-ray diffraction is very elegant and sophisticated, for survey work it depends on your loading again. Part of our primary concern is particulate matter in ambient air where asbestos is approximately one out of 104, again, one out of ten thousand parts by mass. There you are stuck, you have no choice; your flexibility has been removed. But, if you tell me the context then I think we, or anybody, is going to come up with a set of survey techniques that would be applicable. The ultimate objective of course is cost effectiveness, which I didn't go into this morning and should have, because I think I've got a winner on that basis. U. WALIA: I would like to commend the U. S. Steel researchers on employing interpre- tation of electron diffraction patterns for distinguishing fibrous and non-fibrous mineral particles. My optical microscopic observations of known fibrous and non-fibrous amphibole (mineralogical criteria) minerals seem to support that, that the fibrous particle (asbestos forming) tend to sit on 100 plane, and their counterpart non-fibrous particles 419 2063105209

C,s sit on 110 plane. This can be easily distinguished by measuring extinction angles. Of course, this is not the case with orthorhombic anthophyllite. I think this methodology should be looked into more, so it can be applied even on optical microscopic determinations. IEE: Thank you. I think that the only thing we are trying to suggest is that there is not a mystical transition between a massive cleavage fragment that is visible in the optical microscope and a cleavage fragment, at least at a range we are able to work, in the transmission microscope. That was one of them. H. RHODES: I am speaking for the Asbestos Information Association, which is a group of about 40 companies who produce and use asbestos. The question of the validity of the optical method has been touched on here only briefly and the conference seems to have focused on whether it is SEM or TEM that should be used. We in the industry, and I think the government would agree to this, have generated a lot of useful knowledge and field experience with the membrane filter method. We feel that with chrysotile asbestos and the volume of monitoring that is mandated by regulations, the method has a great deal of utility. It has shortcomings, but as long as you recognize these there are very many situations where this method is quite effective and we would hate to see a move to even scanning electron microscopy mandated as a primary compliance monitoring procedure. 420