Document eLk4O9gynZK8JjVMGqb6bZ5G

J C. GILSON* A 1 Inhaled fibres of asbestos can cause fibrosis of the lungs arid two kinds of cancer. Protection of asbestos workers calls for monitoring and controlling their, working environment and linking these records with records of their health historical Asbestos was the first inorganic, fibre to be used in compo sites. More than -4000 years ago clay pots in Finland were, strengthened by adding anthophyllite fibres'.'. In classical times asbestos cloth, was used to, preserve .the ashes of the eminent. The oldest known piece of asbestos cloth front the New World, dating front about 1740. is a small purse made of tremolite in the Sir Hans Sloane collection of minerals in the British Museum (Natural History). The modern asbestos industry is about . 100 years old,: starting nearly; simultaneously: in Canada and the USSR, but it was not until 30 years later that the first medical reports appeared in France and England, indicating that there might be a specific type pfdamage to the lungs following inhalation of the dust. By the late 1920s it was clear from surveys made in this country and in USA1,3 that a high proportion of older workers in the asbestos textile industries were, becoming severely disabled by. a specific - type of chest disease due to the dust. 'This was named asbcstosis. v- .... . DISEASES CA USED B YASBESTOS DUST become stiffer than normal so that the compliance is reduced: .The thickening in the alveolar walls, when the disease is extensive, also reduces the gas transfer for oxygen, so that the blood leaving the lung is np longer fully . saturated with tliis gas. The transfer of carbon dioxide from the blood to the air in the lungs is not, however, appre ciably affected. The reduced oxygen transfer is partly compensated for by an increase in the frequency of breathring so that, the subject notices breathlessness on slight exertion. These alterations of lung function are used to assist in diagnosis of asbestosis and measure the severity of the damage. Asbestosis takes a number of years to develop, even 'under very dusty conditions, but once established it is a progressive disease not materially affected by avoiding further dust. exposure; The less the dust exposure, the longer interval before the onset of disease, the less its severity;1 and the less .chance of being affected. This-Jose, response- relationship is used to fix the acceptable dust' levels -- threshold limit values - for those working with . asbestos. The article by Holmes in this issue describes how these standards are applied in practice. Prevention by avoiding exposures to a dangerous quantity of dust is an essential step towards the safe use of Asbestos. Research carried out in the I930si supported by the greatly expanded investigations during the. last 15 years into the types of disease caused by asbestos,' now. provides a much . clearer picture of the specific hazards and how damage" to health can be avoided in the future: '. Table 1 lists the diseases. ' - -'--'r-i-V: Asbestos cancers ~ ;A;- : 'Some years after the recognition of asbestosis as an impor tant problem in the asbestos textile industry, articles began , to appear in the medical journals* suggesting an association between 'a$j>estosis and lung cancer. A survey in 1955 ,fimily.Vestablished; that, those- who. had worked in.'tlie Table 1 Diseases caused bv asbestosdust^-'- asbestos textile industry before theVimprovemeats in dust Asbestosis 7 fibriasisof Jungs " PojiitroCintrbdueed in"the 1930s, had a 10-fold'excess risk . of developing . lung cancer*.. The survey, however, also Cancer ' . ' 'V 'Bronchial tiling) * ` `ij.i- Mesothelioma ^indicated that the improvement in dust control introduced at a particular factory after 1933 had very materially Asbestos Corns' : Skin :.' : reduced .the risk; .Later survey's at this factory have cohfirrnqji this6. 'The fung cancers seen in asbestos workers arc similar to Asbestosis ...i - In asbestosis'the dust, causes scarring and .thickening of tfie ' - those"caused by cigarette smoking.. Recent research indi- cates that there is likely to be a synergistic effect of tissues of. the Inna.;. The, two parts particularly-affected aie '1 -cigarette smoking and`exposure: tri asbestos ilnst7 The the finest air Passages7 (respiratory bronchioles! where they j ' precise quantitative inter-relationship between asbestos, branch into the terminal air;sacs .(the anH rh. '-.cigarettes,'and other factors is -not fully established, but surface oiltjit- lnag cpleiir-iiiTlievihickening of .the tissues* - present evidence indicates, that those who smoke cigarettes induced by'the ashesips'dust- affects the functipiv d^ the- and, arc exposed to asbestos dust have a risk of developing {'. lung canjsi^at least fifty times greater than non-smolcei s l ing m thiee ways,..' The volume when fu)ty-inflated at the end o: a full in-puau.m is jess iliarv normal. The tissues'- V- tt It'ohie not exposed to ashestos dust. . In the last 15 years there has been much new informa- * IJmvli.r. MRC t l.'tndougli !lo>pi*af, Ten-. J^idn^abdut; tlip: Jink ..between exposure to asbestos and jUIi, Gbi . iij-.in c j <i 1XW, f K,'s.'*. . -; - another previously very tare type of cancer affecting the " -V-** v- COMPOSITES Marcb-1972 Si HWBUI0004625 "sdtface of the lung, and the gut8: Reports of these mesb-' ' ti.gliunias as they are called have increased steeply over, jthe last 10 years. There is general agreement in most . industrialized countries that there has been a real increase of L.is form of cancer'. In about 80% of cases there is a history of exposure to asbestos dust at some time in the past. A feature of these' tumours is the long interval between first exposures to asbestos dust and the detection of the cancer. It is rarely less than 20 years and may be up to 50 or more years.-. In some instances the exposure to the dust.has been short, only a few months, but the highest incidence of tumours lias occurred in those most heavily exposed to asbestos dust.. Cigarette smoking seems to play no part in these tumours, but some research workers think there may be other co-factors present as well as asbcsios10. The only other specific injury caused is the formation of asbestos corns on the fingers when the fibres lodge in the skin. The removal of the fibre usually cures the corn and no cancers of the skin relatable to asbestos have been reported. demioi^gical studies of the incidence of these tumours in man fijr -different types of fibre, it seems probable that the important fibres are likely to be those wind) are straight, small in diameter (up iio about J jam) and pernaps lO/am ' in length. ICiS not Veflthown whether tne ultra-line fibres only visible under the electron microscope are biologically important. .Such fibres are present in large numbers in the lungs or those who have been exposed to asbestos, but their combined mass is extremely small. It is too cailyyct to use this information to establish with confidence' a separate dust standard to prevent the development of these mesotheliomas. This is a field of intensive research at the present. '* Some of the new evidence suggests that the size and shape of the fibre are more important than its chemical - composition, provided it is relatively insoluble. It may be that extremely fine fibres of many different materials can penetrate cells without immediately killing them, but once inside can damage? the mechanisms of cell divisions. An . implication of this view is that care should be taken to avoid exposure to dusts of all types of fibre less than 0-5 pin dia meter knd several micrometres in length. i PRACTICAL IMPLICATIONS OF THE . BIOLOGICAL EFFECTS OF ASBESTOS ...' Inhalation of the fibre r- v. . / -A. . > , Types of asbestos and occupations within the industry.- The last 10 years have shown the importance to health of For all practical purposes the risk from asbestos is limited ./ the type of asbestos inhaled and the occupation of the to inhalation of the fibres. Thus control .of the airborne workers within tlie industry. Earlier medical reports did not dust levels and their monitoring by instruments, which will differentiate between one type of asbestos and another, and measure that part of the dust which can gain access to the - . most of the surveys were concerned with asbestos textile deeper parts of the lung, is an essential step in the safe use . workers. A full assessment of the risks would ideally be of all types of asbestos. Although asbestos fibres can ,bc based on studies of workers only exposed to each type of ingested in minute amounts in beverages which have been ,, fibre and in all .the operations within the industry in which filtered through asbestos, or water supplies", there is no . this fibre was used. In practice the information is ffiech-cS> firm evidence that such tiny traces have any ill-effects. . less'complete than this. Exposures to one type of fibre Feeding massive doses of asbestos to animals has so far " have usually occurred only in the mining and fibre separat- failed to produce any mesotheliomas or-other cancers; iiig: This work usually takes place iri countries where the . S\-, V . , . - ` - medicaf records are scanty and the labour turnover is rapid. Size and shapp ftf fihrps ;> ,. '. A notable exception is in the chrysotile mines in Quebec .'.A;A; '* where) a very comprehensive survey has just been com- Recent research has helped to clarify the probable influ- - pleted?2-14. In the manufacturing countries several types ence of fibre length and diameter in producing asbestos^ r of fibre are often mixed together or have been processed and the hi-.-ihrliial canrero, The. fihrntjt; ic thnH^ht 'in ly . , 'sir that `mployrfr have been exposed to caused principally by. the fibres between ahnnt 5 and -c<>wrt of fihTM hi unknown quantities.. Past records 100 jinilin lengfiia Fibres- Witch', larger -than this. in:the w V of dustinessare rarely'available for relating to the incidence . environment settle outquickly and are nofThlialed. Further. 7 of the diseases.- Thus the current assessment of thc-relative size separation, occurs in the air passages, the-important ... risks in the past from different types of fibre and occupa- size parameter being fibre diameter sinceit'is- thisdimen- : ' .' tions is based On information which is far from complete.. sion rather than Tibr'e length that governs the falling-Speed Use can be made pf experiments in animals.'especially rats-, . bl the fibres: ' Thus fibres utealer .in diameter 1l*'*n M1*1111 because most of the diseases seen in man can be produced 2 fmi (these also lend to be I the longest ! mostly fall or... -.. in these animals. New information is rapidly accumulating impact in the upneiJtespiraioiy tract and are carried awav. ' - which may gave a clearer indication of the way in which ilthJbfeipwuuH.. In the. narrow, airways any long fibres . different-types of asbestos produce their biological effects, remaining are deposited by interception and fibres longer ' There is general agreement thait asbestosis and bronchial than about 100 pm seldom reach the, finest bronchioles \ cancers can be caused by all types of commercially used tins means that for the control of asbestoiis. and probably asbestos(aiiiosite,anthophyllitc. chrysotile. and crocidolitej bronchial caiicers. the' dose' of fibres between about Sum ?- - if the dust is inhaled in sufficient quantities, but it now and 100 pm in length and up to about 2 am in diameter is --seems likely.tjiat the risk from chrysotile may be less than tF~e fyicflon of the dust which has to be measured. ; ...' ; with the other types of fibre. There is also evidence that For the mesotheliomas tlie evidence about the bio- . . . ' the 'risk is ..lowest iri mining and increases along the fibre logically important '.size is much'' Icssi.! complete.;.' I-sing > separating and manufacturing processes.: This is thought to 1 infotmaiion fiom many' sources, such as the aerodynamic ' - be dip- to the higher proportion of airborne dust consisting heh.-iv i.-tir of fine fibres, the; size and shape of fibres which.-r:. ;of ieipirable fibres able to penetrate into the deepest part are retained in' the lungs of jmmiy>..ati5l'ti)ah;.ifj)i.owuig.r;: ^>ftlie (ling: ; ilri practice, this'means that (lie 'deader the exposure to dtfierent' :types fof ;asbestosi.''aiidthe epir\j?A ' 'fibre aftil. the nnire cohipletely it is sepaiated into-individual 58 COMPOS!TESMarch 1972 ''''' - `V V' ' -' """"" ' ^ HWBUI0004626 >v n n nr -- -fibres and small bundles, the greater the iisk.' There isalso ' .surcmenls of exposure; the medical records of those 1'iiod evidence of a dose response relationship for asbestosis ,, exposed. Computers now make it easy to store this infor pnd bronchial cancers and thus, il the dust levels are kept mation, but we still need the foresight and administi.:iion within life new standards. the risks ot asbestosis and bron to see that it is achieved. If it is not done we may still in chial cancers in the fuluie should be very small, 20 years or so be in no better position to answer important Tfie^jisk:of developing mesotheliomas has a different questions which are at present unanswerable because of the relation to fibre type. It is probably highest with crocidulite paucity of past records. and lowest with chrysolite.; No cases clearly related to anthophyllite alone have been reported,, despite careful search. The risk with aniosite probably lies between " CONCLUSION crocidolite and chrysolite. The evidence for a dose response relationship is less clear in the case of mesotheliomas and hence the threshold limit value is more difficult to assess. In the Asbestos Regulations 19<i9,s the standard tor ciocidoljte is set at one-lentil of that for other types ofasbestos. The recent increase in the number of cases of asbestosis a nr other diseases related to past exposure to asbestos is th\ .. result of relatively heavy exposures to the dust, particularly in parts of the asbestos industry not covered by .the 193 Ij Asbestos Regulations. Much new information about the biological effects oil asbestos has been acquired recently.. The new Asbestos^ Regulations 1969 based on this information, if correctly COMPARISON OF OCCUPATIONAL RISKS ' applied, should greatly reduce the risks in the future. What is the magnitude of the risk of developing ill-health from asbestos? No single index provides a satisfactory measure of injury to health. Thus the excess ride of death before a specified age may be a useful index for those diseases causing sudden or rapid death, but it is an inappropriate index for diseases causing . a long period of disability but little shortening of life. The cancers associated with asbestos exposure fall into the first group and asbestosis the second group. In different oocu- ... pational groups comparisons of mortality are easier to make than those of illness. Rut even for mortality the compari sons are not straightforward. For example, the more.the The selection of which types of asbestos to use in new processes should take into account their biological effects if the risk of dust exposure is likely 10 occur during manu facture or in the use of the products. . When working with extremely fine fibres of any material which may become airborne, caution is needed. An exami- , nation of the possible biological effects is required if the ' product is to be widely used and risks of damage to health are to be avoided in the future. Proof of the efficacy of present preventive measures depends on much better record keeping than has been the case in the past. ' selection is limited to a definable group with a high past exposure, the worse the risk Will appear. Allowance has also tp be made for the effects of age, length of exposure, ; REFERENCES . and how long the occupational group has been followed. : When such- allowances are made the excess mortality from 'all , causes*in groups ofworkcrsheavilycxposcd to ` 1 - Noro Leo, American Industrial Hygiene Association Journal, >, .' Vol 29.p l95 (l9bSj / 2 Mcrcncthcr E..R. A. and Price C. W., `Report on the effects the more damaging types of asbestos dusts in the past is, of asbestos dust on the lungs and dust suppression in tire closelycomparable to tliat ofcoalminers Who have developed the severer form of coalworkefs' pneumoconiosis or that of deep-sea fishermen who have the highest rates of acci- 7 .r - Asbestos Industry'. London, IIMSO (1930) 3 . Drcessen W. C.t Dailavalle J. M..Edwards T. I.. Miller J. W., V-` : Sayers R. R., `A study of asbestosis in the asbestos textile industry', US Treasury Department. Public Health Service. dental deaths of any occupation. However, the cptcess ~. . Public Health Bulletin No 241 (August 19381 mortality from `all causes* in these occupational groups is ; - Mcrewcther E. R. A. Annual Report, Inspector of l-actorics. Journal of Industrial Medicine, Vot 12, ............... S,, Doll R., and Hill I. D., BritishJountal deaths from specific causes, such as mesotheliomas. tisbcs- i"--* ~\.'ofIndustrial Medicine. Vot 25. p 293 (19t>S> tosis. or lung cancers relative to that of llic gencral piiblic. ` ;7 Selikoff 1. J.. Journal of the American Medical Association. arc of course proportionately much more increased. [ This' V is because mesotheliomas anil asbestosis are extremely rare Vot 204. p .104'{/ 90S) Wagner J. Gilson J. C,, Berry G.-. and Timbroil V., British .. MedicalBulletin. Vot 27.p71 (1971) in those Who have not worked with asbestos. Confusion /.Gilson J. I-'.,. `Asbestos health hazards', in Shapiro. H. A. sometimes occurs between .the. proportion of individuals ^ (editor), `Pneumoconiosis'. Proceedings of the International exposed who develop, a disease and the excess risk V>t'a particular disease in exposed individuals compared witli the general public. The first may be relatively small arid the second extremely high.. Conference, Johannesburg, 24 April-2 May 1969, p 173. Cape Town etc., Oxford University Press (1970) .10 5. Webster I., .'Asbestos exposure in South Africa*, ibid, p 120 11 - Cunningham H.M. and Pontefract R., Nature, Vol 232. P 332 bv?7ij t ; 12 .. Becfclake Margaret R., Foufnier-Massey Giscle. McDonald J. . . C.. Siemiatycki J,, and Rossitcr C. E., Bulletin dePhysio- :rPathologic Respiratoire. Vol 6, p 637 (I97l)j THE FUTURE 13 McDonald J. Corbett, McDonald Alison D., Gibbs Graham W., ` :,||feijiiat)`cki Jack, and Rossitcr Charles E.. Archivet As in many ivcupat.ion.al diseases proof of the.efficacy'of ' ^ilirironincnlalHealth. Vol 22. p 677(1971/ new pievemiye nteaSutes. including die valid jib of the,,,. Jo*loin Giilcs, GihbvG. W., Maeklem P. T.. McDonald J, C., current ihicdiold 'limit values, can only come ticrtll linking * 3 Ihyklake Margaret/..{ft.. Ainernan Rcricw of Respiratory. ; Diseases. Vol 104.p 523 119 71) information of three types thee m...a...n..uriac tu1 riiig proce->s fe ^IS- (statutory instruiiieiits I9f>9 No 690,1l-actories. The Asbestos and the types of fibre and other Iliateriiils use dt:p.t=j!t-c: ptba^y #i` Re^uJ umru 1969:-,,i on.Ion. IIMSO <19969) f. ... S- ,, HWBUI0004627