Document Ne9250RJNJyNkrao21YEY829Q

./ i 4aufivfl orricco i. a / (Bl'inket License Ho. h_iC99) Keasuey & Mattisox Compaxy nliewtumit or AMitroi m **<* wcv imm <fi Amblsr.Pexmsyjlvakl* March 3, 1943. KKJ No. 2331 W. W. F. Shepherd, Fsq., Turner & Newell Ltd., Spotland, Rochdale. Dear Ur. Shepherd: Subject: Dr. Leroy TJ. Gardner's Asbestos Dust Emeriments. Further to this subject, I now have pleasure in handing you herewith photostat copy of Dr. Gardner's letter of February 24, 1943 to Ur. Fandiver Brown, and also copy of the "Outline of Proposed Monograph on Asbeatosis." , I have found this outline to be extremely interest ing. It brings out a number of important new develop ments, but we feel that reference to the question of cancer susceptibility should be omitted from the report since it is inconclusive. I would appreciate receiving any comments which you may have to taska concerning the enclosed outline, and also will forward you the final report as soon as received. :.V *s Kncl. First Follow Second Follow / The Saranac Laboratory FOR THE STUDY OF TUBERCULOSIS ' OF TNI SJWAtD (. TKUOSAU FOUNDATION Saaamac Laki, N.Y. February 24, 1943 Li.-.M bi?l J Hr. Vandiver Brovrn Johns-Kanville Corporation 22 East 40th Street New York, New York ' Dear Mr. Brown: .. * I have at last succeeded In analyzing nost of our 'VQtJS&Anous experimental data and assessing the results J I realize . this should have been completed before this, but the emergency has left me short-handed In the Laboratory and also necessitated my doing a good deal of extra traveling.. I hope that the sponsors of our study of asbestosls will be charitable and realize that the work has far exceeded Its original scope. We have done over 40 different experiments, many of then divided Into several parts, vhloh Involved exposure of animals for 1 to 3 years to various dusts. The business of preparing micro- scoplc sections and ohenlcally analyzing the tissues on more than 800 animals has been a Job in itself. Hy time for studying sections and analyzing data has been so limited that we are behind our sched ule. T have still not had tine to write a full report of this work which will of necessity be monographic. However, for the benefit of the contributors, I am submitting a table of contents and an an notated outline to Indicate conclusions and the line of argument that will be developed. The latter itself occupies 15 pages, but I hope they will find it sufficiently Interesting to read. I shall work on the final manuscript as I have opportunity. There are a- few experiments still In progress which should be completed by the time we are ready for them, *he work on methods.of dust determination, I oonsider important enough to In clude in the study. The question of cancer susceptibility now seems more significant than I had previously Imagined. I believe I can obtain support for repeating it from the cancer research group. As It will take two or three years to complete such a study, I believe It would better be omitted from the present report. If it should become possible to make this study, I hope that I any count on some of your members to supply me with enough pure, long fibre asbestos for the purpose. . Mr. Vandiver Brown 2- February 24, 1943 Naturally, I shall veloome any oritlolam that you or any of the other contributors would oare to offer. Should any of thea want to dlaouas details, I-would be pleased to meet with them. May I take this opportunity to thank all the aponaore through you for the support that ve have had. ` Sincerely yours, LUG: =SH Leroy U. Gardner, M. D. Direotor / OUTLINE OP PROPOSED MONOGRAPH ON ASBESTOSIS Saranac Laboratory Study under Grant from Asbestos Association PART I HUMAN AS3E3T0SI3 1 Human Pathology - a study of 2S autopsyoases, Illustrated 2 X-ray Patterns in Aabestosia, Illustrated 3 Ash and Mineral Values in Human Aabeatoals 4 Coopllcatlona of Aabeatoals * (a) Susceptibility to infection . 1 Tuberouloua . 11 Non-Tuberculoua ill Cancer of the lung ' . 5 Disability, causes and comparison with silicosis Diagnosis . . (a) History of adequate exposure (b) X-ray film pattern (o) Physical examination ' (d) Aabeatoals bodies in sputum, their significance (2) PART II Experimental Aebeatoslq 1 Methods > (a) Inhalation exposure to plant dusts. ' (b) Injection Into lungs through trachea of pure minerals. (c) Injection of pure minerals Into other organs. 2 Species Susceptibility Man, guinea pigs, rabbits, oats, white mice and rats, dogs. - 3 Peculiar Characteristics of Asbes.tosls ' (a) Unusual locallralon of chrysotlle fibre in lungs. (b) Rate of resultant tissue reaction more rapid than to quart z. (c) Reaction to chrysotlle not progressive after exposure ceases; again the reverse of the situation In silicosis. (d) Aabestoals Bodies 1 Composition and methods of formation. 11 Occurence In different species. . Ill Formation does not parallel development of fibrosis lv Gradual disappearance after exposure ceases. 4 Comparative Effects of Different Asbestlform minerals. ' (a) Canadian Chrysotlle. (b) Arliona Chrysotlle, low Iron. (c) Crocldollte - 1 Bolivian specimen, stiff and elastic. 11 South African, soft and flexible. (d) Anthophyllite (e) Aooslte. . (f) Tremollte. . . . 5 Effects of Control Minerals . . (a) Grannular Serpentine, sane chemical composition as .. chrysotlle. . . (b) Glass Wool, a synthetic silicate fibre. (o) Bruolte, a fibrous magnesium hydroxide almost free of silica . , 6 Chemical Composition of Asbestlform minerals In Relation to Irritation. (a) Nothing In composition correlated with relative lrritatl capacity. * (b) Preliminary acid treatment . * 1 Hydrochloric acid 11 Carbonlo acid (o) Effects of Aluminum 7 Physloal Properties in Halation to Irritation (a) Length of fibre (b) Effect of Crushing (o) Heat treatment ' 8 Nature and Significance of Aabestosls Body (a) Formation (b) Protective effect preventing further Irritation (o) Ultimate solubility In tissue 9 Theories of Action of Aabestlform Minerals (a) Chemical - reasons for considering Invalid (b) Mechanical - experimental demonstration of. * 10 Complications - (a) Infection, tuberculosis and other varieties (b) Cancer of lung - experimental data suggestive but not proven _ . 11 Disability 12 Essential Features of Hazardous Exposure (a) Nature of dust - fibrous component and size factors (b) Atmospheric Concentrations - probably lower than for . . quartz . 1 Inadequacy of standard lmplnger sampling method ' which does not collect the dangerous fibres 11 Electrostatic pr eel pit atat* sampling preferable but . method must be modified (c)'Duration of Exposure 13 Heoomnendatlone for a New Standard of Safe Atmospheric Con . centratlons of Asbestos Dust (a) The Quasl-officlal standard-of 4 to 5 million particles per cu. ft. (b) Work upon better method of sampling . (c) Necessity for comparison of results with X-ray findings In employees 14 Prevention (a) Chemical means not practical 1 Acldoala neoeaaary to dlasolve fibre In lungs worse ' than Aabeatoala : ' 11 Alunlnun Therapy Inapplicable 111 Chief reliance atill upon duat prevention with special enphaala upon the flbroua oomponenta 1 X- ASBESTOSIS - AU"CTED OUTLINE INDICATING RESULTS . -- - *-------------------------------------------------------------------------PART I - HUMAN A3BEST03I3 1 Human Pathology and X-ray Patterna - Description Baaed upon 23 human autopsies 2 Ash and Mineral Values in Human Lungs. 3 Complication of Aabestoaia (a) Susceptibility to Infeotlon 1 Tuberoulous- High incidence in English experience not duplicated in surveys of American Plants. a Available autopsy statistics deceiving because of sel ection of .material. 11 Non-Tuberouloua- The same reason probably applies should be checked. by analysis of ab - senteeiem among asbestos workers* 111 Cancer of Lung Ditto, but there are now on record 10 ' , cases of. lung cancer In asbestos workers. Compared to the total number of autopsies on asbestosis, this Incidence.is excessive. No such frequency has been discovered In silicosis ,^r other forms of pneumoconio sis except^ the Schneeberg miners of radio active ores. The evidence la `suggestive but not conclusive that asbestosis may - precipitate`the development of cancer in ausoeptlble Individuals. 4 Disability Clinical experience suggests that truly disabling aabestoaia la manifested by leas striking X-ray changes than a corresponding degree of ailloosia. Such disability in asbestosis is due to disease within the lungs and not to secondary heart disease. As in silicosis , associated pulmonary infection increases the amount severity of the dust fibrosis with resultant accentuation of disability. There is urgent need for a careful physiological study of pulmonary function in asbestosis of varying severity. Undoubtedly, there are many diagnosable oases with no significant disability. . ' 5 Diagnosis depends upon three faotors. (a) History of adequate exposure, usually 6 to S years, some times longer, at work where both the concentration and character of the "asbestos1* duet are hazardous. / - 'A'rrfc : ' ^> . "F ***.* V " ' ' - ** . . .- `*4%. ` ^ ..... . 4. . ` ';>. *' i? * ` * * (b) Evidence of disease'.in a characteristic X-ray pattern. ** p */ *. (c) A physical jxaninatlon which, reveals certain characteristics signs and cay reveal evidences of disability if present., r--. (4) Asbestosis bodies in the sputum are confirmatory when the;;. previous. factors are* all positive. However, the bodies ' . , nay be absent / particularly 1:. the absenae of bronchitis .V/ infection. ' Asbestoslibodies unsupported by other evidence do not make X. a diagnosis. Occasional ones have been found in about 15 autopsy speolnens of persons with no known exposure and no ' fibrosis, probably pfvnon-ocoupational origin. . . . ....... **#*** - -f. .. V--ni>.- * PART IJ Experimental Aebestosla ... ..... '... I . Methods r # V* -f'-v ' . ^r . (a) Inhalation Exposures to Plant Dus .-.Specific fibrosis. lungs, but no changes elsewhere. $ ..... ' 4"*-^>*"1 v ' * * ^\\V * (b) Injections of- Suspensions of Pure Minerals into Traohea:4.^`r' ' Similar results. . . ; ; . . . (c) Iniectlon of Suspensloha of Pure'Mineral into other organs - . Fibres dissolved; no asbestosis bodies; tissue reaction'.con fined to phygooytosia and encapsulation. Compare' tb asbestos G&rma of human,subjects -.. ' II Species Susceptibility *': >-****' * ' :U '** .* Unlike free silica,Vaabeatoa\does not"produoe its speolflo effects in i ' * " ' ' * ------- -- the Species Flbro Kan 4+ " - 4+ $-* Gat* * >'*'V--: Guinea Pig 2+ Rabbit "ra, 3+' - - > 4. ; r >-.- Vhit e ` Mouae '0 - ---ad 'Scht . ' i;--- '* jfl V" : White Rat 0 >" " .- .* S.*-* - _ -Tl*" -V" > -~ vpiry .asall. atypical aabfifltQa bodlf,)"'- Dogu~.-r -. 0 =`$8* III Peculiar Characteristics of Asbestosis - / (a) Localization of granular  1' Fibres like" ohrysotlle having a oertain degree of flexibility ^ and elasticity aorunulate within the finest air tubes; granular K dust is oarried further on and la widely soattered through the 1 terminal air spaces. _ (b) Rate of tissue reaction to asbeetos Is much more rapid than to ah active dust like quartz. Evidences of formation appear ` as soon as sufflolent concentration of fibres has localized 'In specific areas; with quartz, there la a latent period of . months. ^ (c) Reaction to asbestos does not progress on cessation of expos ure. Young scar tissue that may have formed, contracts and becomes more dense but the area of Involvement decreases in size. In sllloosla, the .young nodules become larger after exposure ceases. (d) Asbestosia Bodies are a specific conoommlt&nt of this form of pneumoconiosis. They are due to a deposit of protein and iron upon the surface of inhaled fibres. In guinea pigs they form after about 60 days of oontaot with the tissue. They are abund ant In man and guinea pigs, (See paragraph 2 above) but much ' . larger in the former probably because the larger sized air tubes admit larger fibres. In cats,- rabbits and mice, there Is an atypical coating of a few of the fibres after muoh longer resi dence In the lungs; In rats and dogs no bodies could be dia covered. From paragraph 2 it is apparent that their occurence does not parallel development of fibrosis. In lung injection experiment*, the bodies have jsa '.eveloped unfair After fibrosis if. iS'wuaU adrr.nced. The number of bodies seems to decrease ' several years after exposure oeases. Comparative Effeots of Different Asbeatosls Minerals * - - (a) Canadian ^hrvaotlle - highly irritating. - (b) Arizona ^hrvsotlle (low in iron) equally irritating and pro ' duces Just.-as many asbeatosls. bodies as the Canadian product --VltH over 11 times as much iron. . (c) Crocldollte - The South African blue asbestos is known to cause asbestosis. Only a limited supply of this material In pure form was available, most of It was used-earlier in the work in non-productive experiments. For the later critical injection teste into the lungs, a Bolivian variety was substituted be cause of its high purity. Its fibres were much atralghter, stiffer and more elastic than the cottony South African variety. Perhaps because of these peculiarities, it has not given reactions comparable to ohrysotlle. It produced asbeatosls bodies but did not localize in the terninal air tubes nor cause any fibrosis. Tests now being repeated with a typical South African crocidolite with physical characteristics simulating chrysotile. , - fc.lc (3) j f -4?-, 'ft- -- ;u . . (d) Anthoohylllte -- stiff, straight fibres - atypical asbestosls bodies forna slowly but no localization or fibrosis in lungs. (e) Anosite - Ditto. (f) Aophlbole - Ditto. . \* . . y,- ' . ... ! *' - . *; ' (ff) Trenollte - Ditto but very few asbestosls bodies - Observation being continued,. v.va'. .'v..'.*.. ' . .'' f Control Mineral (a) Granular Serpentine of sane chemioal composition as ohryeot^le Is inert causing no fibrosis in lungs or other organa. Ct\^:' attracts iron from the lungs but of course, no "bodies* develop.* (b) Glass Wool(a synthetic silicate) flbree are not lnhalable from air-borne suspensions, apparently because of their stiffness (the diameter is not responsible as some used were less than .l"? ; 1 micron thick) On injection into the lungs, they do not ' ; localize in the air .tubes but are widely scattered. They cause no fibrosis. After 3 or 4 months in oontaot with lung fluid, v a few glass fibres take up iron but remain smooth. They.never show the swollen ends and lateral projections of the true ' asbestosls bodies. (c) Bruclte of interest beoauae it is a fibrous mineral praotlcally free of silica (o.9%). Crystallographically the arrangement of itaMe and OH groups in each unit oell la similar to that in chrysotlle. The sample used also contained about ld iron, pro bably from contaminating magnetite. The fibres are stiff and needle like. Obaervdlons not yet completed but after 2 months in the lungs, typlpal asbestosls bodies develop but there is as yet no fibrosis. Ahe fibre are aaattered .through the lung instead of being, localized Inside the terminal air tubes and tissue react Ion"..occurs around, instead of within the tubes. I Chenicel Composition in Relation to Irritation (a) Nothing in the following chemical compositions can be. cor related with variations in capacity to provoke tissue reaction. (See Table Next.Page) f. _ i. r. t > ' Ve 'i.#.' - T4..' ' ' * * /= Chrys- Croold- Antho-:r^.i5-Ai9iitaf^AapMft^Xroo^J.5a rvPrBalt&,r&.- \ o 0, 0 37.43* _2.35* 0 54.99*. 16.27* 4.29< V *?.*'-* '46.23* '"* -x> : - 53I04*r" '56.20* "0.90*<*^ 0.51* ^ 4'06* v' :'3.o*v *7.21* -6.78* ** 0 7? 33.83* - ' ' r*-.i. 0 - - '9.36**'^^ 0.36* 1.02* .0 0.05* 0.79* 10 38.77* 12.25* 4.0 0.29 _ 6.92 .0 0.08 . 0.57 is 4105 4.30 0.02 ' >105 14.92 g.sg________ 0.23* - 0.44* 29.54* 0.52 0.13 --0.62 1.09* 2.01* 6.29* 0;33 0.10 0.66 1.51 1^69* 0.56* `. 0.46*'-^ 12.22* ` 4.45* ' 0.40* ' ` t 23.29* 20 .*52*' '53.99*'"--: i ' .v .* 0.40 * 6.78 0.91 ' ' - 0.12 0.32 . . ' V' 1- .' * ! ' 0.99 '0.16 ' ' ,****.-tt* ' , - 0.34__ 0.53 - 3.39*' '*v' 2.78 26.66 : (b) Acid treatnent .of ohryaotlle fibre* v.> ; . . irti'... - ' * -"T*'* *v'- *-** * *J*A-v'i* *,* 1 One hour in dilute or oonoentrated HCL doee not alter ap-*- pearance of fibre but after auoh treatnent it rapidly die- aolves and diaappears on injecting into living tissues; 11 Treatnent with COg bubbled through water or lung Juice auapenalona of ohryaotlle flbree oauaea partial aolutlon , . with liberation of ailioa and magnesia. . ` (c) Colloidal allumina does not neutralize the*effeeta of asbestoa as it doea quartz. On injecting ohryaotlle suspended In , . .. aluninun hydrate aolutlon, fibrosis and asbestos bodies dev elop at the usual rate, it remains to demonstrate whether the fibres*become ooated with a layer of aluminum monohydrate aa . ` has been proved In the case of quartz, if they have, the ooati. does not affect their oapaolty to irritate tissue. v # VII Physical Properties in Relation to Irritation of Lung Tissue . ^ ; . . ' I; , , (a) Length of Fibre ;* `If}*; Short ohryaotlle fibres under 3 niorona are practically inert. 20 to 50 micron fibres cause typical fibrosis. ; The effects of longer ones could not be tested for technical - - reasons. A*. (b) Crushing completely destroys the fibrous structure of 1 ohryaotlle. With loss of structure, all, capacity to Irritate disappears. , . . -v \ Till <"The physical change altera typical localization-within lunge, no fibroses develops,-reaction-limited topfayagooytoela^-- Ho Asbestosia bodies formed. r:s .,V ,,.......... Nature & fllgnlfloanra ai Aabaatoala Boaiea'*.- ,. r ...' .....'[l.nr';.: . (a) Bodies; probably result from depoaitionTof lron\and organic matter on a slowly, dissolving-fibre .of ^asbestos'U;-:The source . of the iron is more likely tojbe the lung -tissue than'the . .. mineral Itself as ths :coating ia^'Juat ?as: heavy 'on -fibrous . . minerals of lo^. iron -contenV-aa-'upon, those'high.in iron. /;' v ' (b) .The effect of asbestosia' body^ornation* is assumed to be pro-^f- tectlve although it has not*beea~poesibleWto; isolate a large 'C : enough quantity of. these structures; in';unaltered'-form for . purposes of test. The smooth Grounded-ends/, presented-by the bodies would not be mechanically lrrlta'Clng,''',;'/='^<-^--,^ ^-/If. .t x. - ' (c) If they were capable of caueing irritation, <the fibrosis in the lunge should progress after exposure.ceases.which it does not. . . N, . (d) The gradual disappearance of bodies (and^flbrea) long after * exposure'joints, to ultimate solubility in" tissue fluida. , . (e) ^he bodies are probably a fortuitous oonoonnitant rather than a cause of fibrosis. Theories of Irritant Action of Aabestlfora Minerals . (a) Cheulcal These experiments do not confirm the theory that asbestosia is merely a form of silicosis resulting from free silica liberated in the solution of a silioate molecule. If this were true asbestos,llke auartzshould cause flbrosia In . any organ of any species for the experiments have shown that injected asbestos dissolves In these looatlons. However, It does not. c.^use such reaction in any location but the lungs of * ,, . species. . . . (b) Mechanical Irritation ' We ore proposing the theory of mechanical irritation which is : manifested only in the lungs because this organ is the only one ! whose normal physiological functions involve a high degree of mobility. Experiments designed to prove the necessity for motion ! In this tissue have failed for technical reasons. . ' : For this theory to be applicable,it ia necessary that the fibres be concentrated in the fhye terminal air tubes. It has be$n. ahown that only ohrysotlle of the aebeatiform minerals thus , faunas the proper physical characteristics.to insure such .j i ; localization. It is also essential that-the fibre shall persist long enough before it dissolves In the.lungs of species like mice, ratsdogs. It apparently dissolved so rapidly that it " ' exerts no irritation. Similarly rapid solution may explain : In part, the lack of flbrosia in organa other than the lungs. r \. _ ` . . The fibres must be long enough so that they oannot be completely 1 surrounded by phagocytic oells which would prevent contact of these round, broken ends with the delicate cells supporting the air tubes. Observation has demonstrated that these conditions are realized in guinea pigs treated with long fibre chrysotile and fibrosis results. With the other asbestlforn ninerals that have been tested, some or all of the prerequisite were lacking and no fibrosis developed. (c) If the irritation were chemical, fine serpentine which has the sane* ohemical composition as chrysotile should have also caused fibrosis. The crushed chrysotile shouai have been more active than Intact fibres, because of the greater surface areas ex posed to body fluids. On the assumption that ohrysotile, like quartz, becomes coated with a very thin layer of aluminas on treatment with colloidal aluminum hydroxide, capacity .to cause fibrosis should be destroyed if the sotion were chemical but such i$ not the case. . (d) ``he heavy coating resulting from asoestosls body formation ap parently does stop tissue reaction but here the effects are probably mechanical for reasons cited. (e) Heat sufficient to alter chemioal structure d estroys power . to irritate but it also alters essential physioal characteristic that affect localization of the fibres in the lung's. X Complications (a) auscentlbllltv to Infection . ' . ch/i h 1 tuberculous - Asbestos behaves like most other mineral/, in this respect and not like auartz which specifically Increases native susceptibility to the tubercle bacillus. This in fection may spread for a time but then heals. The resultant fibrosis accentuates that caused by the mineral fibre. ii Non-Tuberoulous - of no greater frequency than in animals Inhaling dusts of other kinds. Occasional epidemics of ' pneumonia occur in our dust rooms, but these are due to methods of housing rather than to dust; they also occur in unexposed anloals. ill'*'- Cancer of Lungs *. No experiments were,, designed to elucidate this point but certain evidence suggests that asbestosls may actually favor development of tumors in susceptible species. 1 In guinea plgSi rabbits/ rats, oats and dogs lung tumors are rare. 2 When these species were subjected to 2 to 3 years in- * halation of asbestos dust, the incidence of lung tumor vaa not increased. ' . r 3 Sone strains of whits nice do develop tumors without . apparent oause. } - 4 **uch a strain of white aloe waa unintentionally used la three inhalation experiments with asbestos. ' 5 Of 11 aloe inhaling long fibre asbestos for 15 to 24 months 3 developed malignant tumors in their lungs and 6 of them . had tumors in other organs. The Incidence rate 81. B* is _ excessive. 6 Of 22 aloe inhaling short fibre asbestos for not longer than 12 nontha only 3 developed lung tumors. Hate 12.6% 7 As controls, we have only the experience with aloe in other dust experiments. - For short periods. there were 51 mice exposed to 4 other kinds of dust for 10 to 12 months. Incidence of lung tumor 1.9*. For long periods. there were 143 mice exposed to 4 different kinds of dust, including pure quartz, 23 to 31 months. For all this group of aloe the average incidence of lung tumor waa 13.q: the highest rate (25*7 was in a subgroup exposed to flint dust. Thus the incidence of lung canoer in the long fibre asbestos mioe was over 16 times the average for nice inhaling other dusts for comparable periods and over 3 times the naxlaum for any other*group. Mice exposed to the practically inert short fibre asbestos showed fewer lung tumors although 7 times more than those in short exposures to other dusts. .' *hese observations are suggestive but not conclusive evidence of a cancer stimulating aotlon by asbestos dust. T&ey are open to several criticisms. The strain of mice was not the same in the asbestos experiment as lq many of the others cited; apparently the former were unusually susceptible. Not enough animals survived in the dust for longer thgn the 15 months apparently necessary to produce many 'tumors. Ahere were no unexposed controls of the same strain and age and no dlmllar controls exposed to other dusts. It is hoped that this experiment can be repeated under properly controlled conditions to determine whether asbestos actually favors cencer.pf the lung. XI Disability . Cannot be determined in animals, ^'he accidental deaths were from the sane causes met with in all our dust inhalation experi ments. /. / XII Essential Factors o (a) Mature of Pus 1 *he hazrda Increases with the proportion of-Intact fibres in the dust. Granular material and oruahed fibre are inert diluents. v - . * *> > f. 11 ^he long fibres must be thin enough (1-3 Microns) and short \ enough Tunder 50.Microns?) to be inhaled. 'V': 111 Very short fibre* (under 3 Microns) are practically inert, (b) Atno8oheric Concentration Still under study. Apparently this factor Is lower than In the case of dusts ooopoaed of granular minerals but methods of estimation are misleading. . .: ' . . - . - 2* . y * I The average standard Public health Service lnplnger count in the long fibre asbestos dust room'was .40 million particles per cu. ft. of air. *hia`concentration;oaused fibrosis visible to the naked eye in 20 to 24 ninths. For comparison the average lnplnger counts in an experiment with pure ouartz was 120 million particles per cu. ft.*and fibrosis developed at about the same rate. r . *., t*. *-'* . . . .. II However, ioplnger oounts are deceptive because by this - method of sampling very few fibres, wt^ch are the significant elements in the dust are collected.\ . ; ! ill Sampling with an electrostatic precipitator is a much more , efficient means of collecting fibres from air-borne aua- " . pensions. Samples from our long fibre asbestos room showed that the dust in the air contained 32.5^ of fibres few of which had been oolleoted or counted in the lnplnger sample. ?he latter sampled largely the inert granular partl- oles. N* . . ' ..' /" . * lv As ordinarily employed precipitator samples are weighed and the results expressed in mg. per cubic foot of air. There la no means of converting such values into numbers of . ^particles particularly when these vary in size, shape and '"specific gravity. . . . . ***** -* *. * v Simultaneous sampling with precipitator and standard lm- plnger yielded the respective values of 0.65 mg and 60 mil lion particles per oubio foot of air. vi theoretically the best index of hazard would be either the number or weight of fibrous elements in the dust. i,,_ u taft X+* V.X .. v; t -y *.. ' *. > rr -10- I _ I.' . A '<*.; (c) Duration. of Exposure A. 1 Fibrosis visible to Increases In extent the naked eye In subsequent after 12 nontha 13vnonths. exposure * , , **. li .. . . The span of Ufa of our noet susceptible laboratory animal,/* the guinea pig has prevented continuing bxpoaure longer than three years. In this period only-the comparatively early . stage* of asbeatosia have.been-produced.: With the know- " ledge that we have gained, it- is probable that more extensive disease could have been produced with a purer long fibre chryaotile. The long livedspecies,.like cats, dogs are un fortunately not susceptible-: . v. iii 'For these reasons X-ray changes have been nlninal and we were not able to fulfill one of the objectives of this pro- j ' gram. ... > .. , . ^XIH Recommendation for> New 3yndArd of 3afe'Atmospheric Concentration ' of.Asbestos uat. A " ~ i- `. ti- While there is no official standard, the'teennttsa'tive one of * 4 or 5 million particles per cubic foot .'of air is frequently P:--;';. J quoted. . . -r: * * `IT* : I (b) This is probably unreliable because it ;ia: based upon sampling, with a standard inpinger which we havershown does not collect . amsfof the fibres that are the source ofja^'zard. (c) We now think that a standard should be based upon sanples collected with an electrcstatio precipitator if it is feasible i; to determine readily the relative proportion of-fibres in such material. 'J Vv.. -* - ` .. ' ' (d) Work la still in progress upon-the lattejP'poipt. ' . -. Y'. .. - V ' (e) To be of *value the* new standard vould<haye'.*to-1be correlated v XIV The experiments have failed .toT`develop .anytjaractical .chemical means of neutralizing the action.-of fibrous-'asbestos..-. . ' f :fr- ry'-ui- .'P .A (a) To alter the hunanflung ao' that it vouldTdiaaolvevasbestos fibres rapidly like a rat would necesa 11ate> (*vola'&\t) creating an acidosis which would by/worse *than the effects of xne riDroeie.. . -^.^^-.14 ./, 9. 4! : \ >^ . * . j-~-M2ys.f*r *. r :,* x" -- \ . ;> \+' S- "r 4f; J v>.? r: ` : ' . . : ' - *. ' f *?*? ( . : v. i r* fibrous 'ri . -.' . (;o-f.:-`ffetww noiaFses it W,'rt2.SF'2^% *r-e^"$-*?tJl-eo:i-r n1'ioal''ihter8tVto treaties?--. V4--r *<*' halation V* J2&^-?^oaV:*raa aabeatoaiB-.by sal\jminua-'ttv^^:. &3.. ,>;A-^V*r^J'ststamStnioletnrSaloGvfhPoAoonrmunZaii5%thi**}*W*'*rAalurea.i-nduuen' <apigiVii^r^hyeqel^ooacXe- Vn6iw\ifrrattXs&;^- ?f *0, wT, ^ 11 .d ..itn^n. ^nfm^nf dust IntThS :V'*/X*tVffc**'--8.* yV . 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