Document 99znj13peZ8184yav9yyVqw3q

FRICTION MATERIALS STANDARDS INSTITUTE, INC. E-210 ROUTE 4, PARAMUS, N.O. #37652 August 30, 1972 Tot Asbestos Study Committee Subject: "Health Hazards of Asbestos", by J. C, Gilson Enclosed is an article "Health Hazards of Asbestos" by J. C, Gilson. Mr. I. H. Weaver, Chairman of the Committee, felt this was a good overview of the entire asbestos health situation as it now stands, and suggested that it be distributed to members of the Committee. EWD/erc Enclosure E. W. Drislane Executive Director CCs British Council AIA/NA (Swetonic) Committee Members FMSI-0128 FMSI 02812 'M EM'O from Ike desk oj I.H. WEAVER I thxnk the attached article gives a good overview of the entire asbestos/ health situation at it now stands. I suggest you distribute copies to the other members of the Asbestos Study Committee. Ike FMSl 02813 Health hazards of asbestos j. c GILSON* Inhaled fibres of asbestos can cause fibrosis of the lungs and 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 bo used in compo sites. Mure than -1000 years ago day pots in Finland wete strengthened by adding unthopltyllite fibres'. In classical times asbestos cloth was used to preserve (he ashes of the eminent. The oldest known piece of asbestos doth from the New World, dating from about 1740. is a small purse nude of trcinolite in the Sir Mans Slonne collection of mineral;, in the British Museum (Natural History). The modern asbestos industry is about IIX) years old. starting neatly simultaneously in Canada and the USSR, but it was not until 30 years later that the first medical repotts appeared in France and England, indicating that there might be a specific type of damage to the lungs following inhalation of the dust. By the late 1920s j: was cleat front surveys made in this country and in USA,-J 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 asbestosis. DISEASES CAUSED BY ASBESTOS DUST Research carried out in the 1930s, supported hv the greatly expanded investigations during the last 15 years into (be types of disease caused bv asbestos, now provides a touch clearer piettne of the specific hazards and how damage to health can be avoided in the future. Table 1 lists the diseases. Table 1 Dnrares cauif-ct by asbestos dust Astdi&iobis Cancer Astx;vta? Corns Fmrosis oi lungs Bronchial Iking) Mesothelioma Skin Asbestosis In aheslosis the dust causes scarring and thickening ol the tissues of the Itmg. 1 he two parts paiticularly affected are the Ii11osI ait passages (respiratory bronchioles) where they '.'ranch into the lermm.:l air sacs (the alveoli), and the Mirlace oi the lung (piem.i) The thickening of the tissues mdu'.'d by the aslu.siws dust altvcts the function th the 1 iib' iv. lime wav., fin.' volume when fully ir'I'i.Prd a1 'he "id >! a lull ir -; m p. less ih.m nonit.ii. I lie tioi.es * *. MIU l'!'tiiiiri..nnpsis l n({. M imlnu.'l; Mo-p-'.ik I'd,' , i rl.ii . i;\n) ( l ft i W.. I k become stiller than normal so that the compliance is reduced. The thickening in the alveolar walls, when the disease is extensive, also teduccs the gas transfer for oxygen, so that the blood leaving trie lung is no longer fully saturated with this 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 die frequency of breath ing 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 furthei dust exposure. The less the dust exposure, the longer interval before the onset of disease, lire less its severity; and the less chance of being affected. This-dose response relationsh.jp is used to fix the acceptable dust levels - threshold limit values - for those working w'ith 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. Asbestos cancers Some years after the recognition of asbestosis as an impor tant problem in the asbestos textile industry, articles began to appear in the medical journals4 suggesting an association between asbestosis and lung cancer. A survey in 1955 firmly established that those- who had v. oil.eu in tire asbestos textile industry before the improvements in dust control, introduced in the 1950s, had a 10-fold excess risk of developing lung cancer5. The survey, however, also indicated that the improvement in dust control introduced at a particular factory after 1953 had very materially reduced the risk. Later surveys at this factory have confirmed this15, The lung cancers seen in asbestos wmkers are similar to those caused by cigarette smoking. Recent research indi cates that there is likely to be a synergistic effect of cigarette smoking and exposure to asbestos dust, The precise quantitative inter-relationship between asbestos, cig.netio, and other factors is not fully established, but present evidence indicates that those who smoke cigarettes am! are exposed to asbestos dust have a risk of developing mug .ancer at lean fifty times gieatcr than non-smokers \>h ' Vc not exposed to asbestos dust. to the last / 5 years (here has been much new inferntatn'n aboui I Ho I,ok between exposure to asbestos at ill .nothci previously very rare type of cancer aflecting lire wr .v~,rrt rov? $7 FMSI 02814 surface of the lung and the gut1'. Reports of these rneso thdiomas as they are called have increased steeply over the last 10 years. There is general agreement in most industti.ilized countries that there has been a real increase of t..is form of cancer''. In about SOVo 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 raiely less than DO 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 occulted 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 he other co-factors present as well as asbestos1. The only other specific injury caused is the formation of asbestos corns on the fingers when the fibtes lodge in the skin. The removal of the fibre usually cures the corn and no cancers of the skin telalable to asbestos have been reported. PRACTICAL IMPLICATIONS OF THE BIOLOGICAL EFFECTS OF ASBESTOS Inhalation of the fibre For all practical purposes the risk from asbestos is limited to inhalation of the fibres. Thus control of the an borne dust levels and their monitoring by insliumeuts, which will measure that part of the dust which can gain access to the deeper pails of the lung, is an essential step in the safe use of all types of asbestos. Although asbestos fibtes can be ingested in minute amounts in beverages which have been filtered through asbestos, or water supplies", there is no firm evidence that such tiny traces have any iii-el!ects. Feeding massive doses of asbestos to animals has so far failed to produce any mesotheliomas oi other cancers. Size and shape of fibres Recent research has helped to clarify the probable influ ence of fibre length and diameter in producing asbestosts and the bronchial cancels. The fibrosis is thought to be caused principally by the fibres between about 5 and 100 pm in length. Fibres much largci than this it the euviti'i-.mcii! settiV out quickly and arc not inhaled. Further si/e separation occurs in the air passages, the important sine paratuctet being fibre diameter since n is this dimen sion lulhei than fibre length that governs the falling speed of the lihres. Thus libies greater in diameter than about 2 pm (these also tend to be the longest) mostly fall or impacl m the uppei respiratory tract and are carried away with the sputum In the narrow airways any long fibres remaining are deposited by interception and fibres longer than about 100 pm seldom leach the finest bronchioles This means that for the control of asbestosts. and probably hionclual canccts. the dose of fibtes between about 5 pm and I Oil pm in length and up to about 2 pm in diametci o the tiavfioii of the dust winch has to he measured. Ft 'he mesotheliomas the evidence about the bio logically important size is much less complete IMng, inionnafi.-n fioin many sources, such us die aerodynamic KInn mui o| fine fibre... the size and shape of libies winch lie lel.nned jn .be lungs of animals and man Inllowuig exposinc to dilfviem types u| asbestos, ami the epi demiological studies of the incidence of these tumours in man for different types of fibre, it seems probable that the important fibres are likely to be those winch arc straight, small in dtatr.eicr (up to about I pin) and perhaps !0pm in length. It is not vei known whether the ultra-fine fibres only visible under the electron microscope arc biologically Important. Such fibres arc present in large numbers in the lungs of those who have been exposed to asbestos, but then combined mass is extremely small. It is too early yet 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 extiemely 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 in dusts of all types of fibre less than 0-5 pm dia meter a"d several micrometres in longih. Types of asbestos and occupations within the industry The last 10 years have shown the importance to health of the type of asbestos inhaled and the occupation of the wmkers within the industry. Father medical reports did not differentiate between one type of asbestos and another, and most of the surveys were concerned with asbestos textile woikers. A full assessment of the risks would ideally be based on studies of workers only exposed to each type of fibre and in all the operations within the industry m which this fibre was used, fit practice the information is much less complete than this. Kxposures to one type of fibre have usually occurred only in the mining am) fibre separat ing. This work usually takes place in countries where the medical records are scanty and the labour turnover is rapid. A notable exception is in the chrysotilc mines in Quebec where a very comprehensive survey has just beer, coinpletedn-14. In the manufacturing countries several types of fibre are often mixed together or have been processed concurrently so that employees have been exposed tc several types of fibre in unknown quantities. Past records of dusting* s are rarefy available foi tciaimg to the incidence of the diseases. Thus the current assessment of the lelativi risks in the past from different types of fibre and occupa tions is based on information which is far from complete. Use can be made of experiments in animals, especially rats, because most of the diseases seen in man can be pioduced in these animals. New information is rapidly accumulating which may give a dearer indication of the way in which different types of asbestos produce their biological effects. T here is general agreement that ashestosis and bronchia! cancers can he caused by all types of commercially used asbestosfamositc. anthophyllite. chrysotile, and crocidolite) if the dust is inhaled in sufficient quantities, but it now seems likely that the risk from chrysotilc may be less than With the olhei types of fibre. Them is also evidence that the ii.k is lowest in mining and mcteascs along the fibre sepat.ttmg and inannfarlni mg processes. This is thought to he diw to the liigiict p'upoitnui of an home dust consisting oi ie.pit.tble libies able to penetrate into the deepest pari .'I ti.e lung. In pi.iitice this means that the cleaner the fihie and the ntoie completely it issepauted into individual r\ ffvuv f r f ft -. i. ti'm FMSI 02815 .fi!>;s ;in<l small bundles, the grrilcr lire risk. There Is also goo;' evidence "f a dose response relationship lor asbestosis and bioiichi.il cancers and thus, if the dust levels are kept within the new standards, the risks of asbestosis and bron chial cancers in the fuluie should he very small. The risk of developing mesothelioma! Iras a different relation to fibre type. It IS probably highest With trOCitl'llilC and lowest with chrysolite. No rases clearly related to antitopliyllite alone have been reported, despite careful search. The risk with amosite probably lies between crocidolitc and ebrysolile. The evidence for a dose response relationship is less clear in the case of mesotheliomas and lienee the threshold limit value is more difficult to assess. In the Asbestos Regulations l%915 the standard for ciocidolite is set at one-tenth of that for other types of asbestos. COMPARISON OF OCCUPATIONAL RISKS What is the magnitude of the risk of developing ill-health from asbedos':' No simile index provides a satisfactory measure of injuty to health. Thus the excess risk of death before a specified ape may be a useful index for those diseases causing sudden or uipid death, but it is an inappropriate index for diseases cauong a long period of disability but little shortening of iil'c. I he cancers associated with asbestos exposure fall into the first group and asbestosis the second group. In different occu pational groups comparisons of mortality are easier to make than those of illness. Hut even for mortality the compari sons are not straightforward. For example, the more the selection is limited to a definable group with a high past exposure, the worse the risk will appear. Allowance lias also to be made for tlie effects of age, length of exposure, and how long the occupational group Iras been followed. When such allowances are made the excess mortality from `all causes' in groups of workers heavily exposed to the more damaging types of asbestos dusts in the past is closely comparable to that of coalminers who have developed the severer form of coalworkers' pneumoconiosis or that of deep-sea fishermen who have the highest rales of acci dental deaths of any occupation. However, the excess mortality from `all causes' in those occupational groups is less than that of male smokers of twenty cigarettes and inoic a day compered with non-smokers. Hus is the position for deaths from `all causes'. Inn deaths fiom specdic causes, such as mesnlbelu'inia-,. asbestosis. oi lung cancels relative to that of tbs' genei.tl public, are of course proportionately much mote increased. Ibis is because mesotheliomas and asbestosis arc extremely 1,11c in those who have not worked with asbestos. C ontusion sometimes occurs between the proportion of individuals exposed who develop a disease and the excess risk o! a particular disease in exposed individuals compared with the general public. The first may be relatively small and the second extremely high. THE FUTURE As in in.my n, ciipa!ioivjI diseases proof o! the cftie.rey of new pivw'i'ne iiummoos. including lhe validity ol the cm tent tl.icdiohl limit values, can only conic 1'iom linking iriloiniatioii ol tlucc types the mar.utaelurinp process and tin- types u! fibre and other materials used llu* men r-ureinenls of exposure; tne medical lecoids of those exposed. Computers now make it easy to store this infor mation, but we still need the foiesigltl and administration to see that it is achieved. If it is not dune wc may still in TO years or so be in no better position to answer important questions which ate at present unanswer able because of tire paucity ttl pasi records. CONCLUSION The recent increase in the number of cases of asbestosis and other diseases related to past exposure to asbestos is the result of relatively heavy exposures to the dust, particularly in pans ol the asbestos industry not covered by the 1931 Asbestos Regulations. Much new information about the biological effects of asbestos has been acquired recently. The new Asbestos Regulations 1069 based on this information, if correctly applied, should greatly reduce the risks in the future. The selection of which types of asoestos to use in new process:,. should lake into account their biological effects if the risk of dust exposure is likely to occur during manu facture or in the use of the products. When working with extremely l ine fibres of any material which may become airborne, caution is needed. An exami nation ot the possible biological effects is required if the product is to be widely used and risks of damage to health arc to be avoided in the future. Proof of the efficacy of present preventive measures depends on much belter record keeping than has been tile case in the past. REFERENCES 1 Noro l.co. American Industrial Hygiene Association Journal. Vo! 5V.p 195 {19hft) 2 Mi'tmiether Ik K. A. ar.d Price C. W., Report on the effects of asbestos dust on the lungs and dust suppression in the Asbestos Industry'. London, HMSO (1930) 3 Drccssen W. Dallavallc J. M., Kdwards T. L. Miller J. W., Sayers R. R., `A study of asbestosis in the asbestos textile industry*. US Treasury Department, Public Health Service. Public Health Bulletin No 24 \ (August 193K> 4 Merewether l\ K. A. Annual Report. Inspector of factories, london, HMSO (194?) $ Doll Richard. Rrin.sh lour ~! of trufustriji MiJuoie, V\4 !j. r St f f ( Knox J, I-., holmes S.. Doll R., and HiK i. 1)., Hritisit Journal of f>u/nw iat .)/(i o! .\5, ft S'lS (J90SJ 7 Sclikotf I. J.. J'titnu:! oj the Anurtran MeJicaf Association. I'ot SO I. KN i IVnS) K Watnoj J. ('., Gilson J. Herty Cl.. ar.d Timbrell V\, tfritish V.'.hcn/ ituiletm VolSl.p 71 (IV71) 9 (-'.is m J. O'., `Asbestos health h.vurdv'. in Shapiro, H. A. (cdtton, 'Pr.eumoconi.'kiv', Pioceedinp;. ol the hiicmaius'.it ( onfr/civo, Johunnosbtitp, ?4 April -J Ma> 1%`C p 173. (.tpc Tokti etc.. Oxford Univcrsit) Pics* (1970) 10 Webster I., `Asbestos exposure in South Africa', ibid, p 20 11 CunninjJtani H. M. and Pontefract R., Nature. I 'ol JJS. p J32 UW) 12 Hoc Make Margaret It., l?ournier-Massey (jisclc. McDonald /. (,'.. Sicmiaiycki J., and Rossitcr C\ I'., Hulie tin dc Physio- Puihoto):ic flesptrctoire. Vol b. p (>J7 (fV70) I 3 McDonald J. Corbett, McDonald Absent I)., Ctbbs Graham W., , Siemutj < ki Jack, ami Rossitcr l Italics Archives of /tiiTii.tiMtiiiii/ Health. Vol J.?. p b 77 (1*771f I \ .hnloiu tidies. iihif. (I Vi.. Mjoklcnj P. T.. McDonald J. C\, It,-ki.tkc M.uimh ! 1' . \nitrtiiiv AYwoe of Respiratory' /Vtoft ( of iitt. p s 7.S Is Si.t(ti*t'iy Ifi'-tfurtci'fy 19ft 9 N f9l, lactoricv, The Arbestos It'/ul.'.ii.ii.k \ .indon. HMSO ll'A*9i FMSI 02816