Document NGJ2o2vNO1g17MQjR843p07gD

FILE NAME: Union Carbide (UC) DATE: 1974 Jan DOC#: UC048 DOCUMENT DESCRIPTION: Health Hazards of Asbestos - A Review of Recent Trends . V i : `.s- The Journal of the Society of i-m . i'n fr :Vki."*r1 5. -x * . A ; V . . .-. ........ , ... y , y , ..i. . 24 v 7^ . ' r ' Number 1 ' - / * . ; : * ? - s -, v * . -V . "* . ~'.^..q..i.... *" - ` January 1974 P~r.........*.-,\ .1!.:yJcJrr-w\:t..; , .1 M`l in.. ! ' '- ...'w -t&JAVXV. ._ Contents rsN'CsI.Rsx-''. .T^^i.^l^fta^raijjr-?*' -- . . -.-.%y]y - .. . Editorial Have we an Interest in Mental Health ? ' ,-r . , v v^VVX, . ^ 4 't .. *' '*- '*" *?`"t^iX 'X -*^.-'y^v. .~[T4<>C._>. - v;,i%';C*;Vm-n'^^W- *;' % . Health Hazards, o f Asbestos- H. C. Lewinsohn "./.H ard Metal Disease and Tool Room Grinding A. O. Bech :\ 11 - n e f . . . -.. . , , . : .._;. -' . jy Principles of Design of Occupational Health Records C. G. Pearson and D. Radwanski . - 17 . f 'A Code o f Practice for Lead' R. I. 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V'.'vrv .. - .v*.*.'...:.-.:: , ' .. . - ,. ^"'- ^ . .* .,; . . ' - ^'^\>C;.Vv'.. ' '  ": .* ' ?,i Anr ne a^ ^xos _3 ilth Hazards of Asbestos: A Review of Recent Trends .1LT0N C. LEWINSOHK , : - C h V ^ O fc 'r . Summqfy ^ ^ - A " 1' /j . .r.; f h" -1? ? Mem" iid Dr J. C Gilson nphasized. the main areas where- further research was needed into the health hazards of hw ip, s;n~. 19^ many of his recommendations have been carried out This vmw attempts to examine recent tr e n d s T 2 e ~ id ? S asbestos and its effects on health by comparing them with the points made by Gilson and t h e ^ K > S T d^ i V %. ! > * -. nffermd 1965)- Jh relationsGhirp0-Uopf 0t1h1e AphsbycssctaotschCemaniccaelr 0f me?* * means <* S S S S S S J ^ S 1 ^ * tto o u g h o t "meats " *" '* ' ' * ' '*" .The Sub-Committee on Asbestosis of the above Commission met in September, 1970 (Sardinia 1970). An International Symposium on thi biological effects of asbestos was held in Dresdes (Hammond and Selikoff, 1972) in 1968 and tt subject of asbestos was discussed*in depth at tfc International Conference on Pneumoconiosis Johannesburg in 1969 (Shapiro, 1970). 1 ' Iton Ocetobher, 1972 a Meeting of a Working Grotu! * *Re*vie"w *the BRiionIlnoi^rvil E f t d i o,,f Aa s. 1b__e__s_to___s___w_1` held in Lyon (WHO, IARC, 1972). Intfaisartide" nrn<rr*ec ------ --------------------- - . . .. A* -- rent state or attairstobe presente, amq| cro.c U( smaamti prep, varii cent MP Redl ,1 Unit-' man - fron1 T lj impr sevei Physics and Chemistry of Asbestos Fibres . X S d . n0nS ? * " fu,ure co*`-o f the hazard are Gilson (1966) pointed out that four main types q fibre are of commercial interest. Speil and T.;n. e: Introduction - .---.wZ.-t- : - J "s revie^ of cent trends"ur the- study of'thc - o f J. C- Gilson's Wyers M e m o S j ^ , ^ r T weber (1968) have reviewed the role of asbestc minerals in modem technology.. Asbestos is , generic term for a variety of hydrated <ijrati minerals which have one common attribute, namelv tni* ahlllfo/ tr \ Ua r a . . A_I i ___ .1 . 3 tJ* ?b,hty} ! * " P * TM ^ from the parent rock -- .w..,, uuuit. xuc term asoesios applies toe account o f th e conference oo^the " Biological Ashes*05 'held.in New Y orkia October ,1964, was published (Whipple, 1965). . Gilson minerals which fit the above description aaini asbestiform minerals ' is perhaps a better descri tive term. , .. . -, . . . . ^ .,.r 1 There ^re two main classes of asbestifo minerals, dependent upon their basic crys = : 5S2s Z S S g .S S ? ^ ^ .s s s s s s a s - r > - 2- ei H F 3 B a ^ F ^ A s a a s a , 'S S S iM sk - h? * - * 2^S,,2i S ^ S S K T r a s E ? y sL srs i.s S S is de v. h V y~ health hazards of asbestos >o4 Working Group recommended that bronchioles at bifurcations and that this may ..jard reference samples of respirable size of explain why fibrosis tends to be associated first amosite, chrysotile, tremolite, anthophyllite and with respiratory bronchioles and with long fibres. crocidolite be prepared from as pure parent Rats exposed to dust clouds of chrysotile and material as possible. Timbrell (1972a) reported that amphibole UICC samples at equal concentration samples of chrysotile and crocidolite had been retain six times more amphibole than chrysotile prepared in Johannesburg., from donations by after six months. Timbrell suggests that this may various asbestos producers. The two distributing be partly due to the characteristic ` rectilinear' centres for the ` UICC samples Johannesburg shape of amphibole fibres compared to the ` curly ' PRU (Pneumoconiosis Research Unit), and the morphology of chrysotile fibres, allowing the Medical Research Council PU (Pneumoconiosis amphiboles to penetrate to deeper parts of the Unit), Penarth, have recorded 250 recipients and lung more efficiently than chrysotile fibres. He has many more researchers have obtained supplies demonstrated this by means of studies using lung from colleagues. = casts. A reasonable theory has thus been proposed The UICC samples have been analysed for their to explain the reason for the development of important physical an d ' chemical properties in mesotheliomas. It is based upon the ability of several countries (Timbrell, 1970). The samples certain types of fibre to penetrate deeper into the have been checked for homogeneity, contamination lungs than others and to reach the pleural cavity and oil content. The chemical composition of the by direct penetration. Timbrell points out that in reference samples has been compared with that of rats exposed to dust clouds of UICC samples at commercial fibre of the same type and has been equal concentrations and killed immediately after found to be unchanged- The samples have been a ` short exposure ', small numbers of crocidolite prepared in such a manner that the fibre length fibres have been detected near the visceral pleura, distributions will extend up to 200 pm., being fewer amosite fibres have been found in this comparable with asbestos fibre lengths detected region, still fewer anthophyllite fibres and chrysotile in lungs. Longer fibres are undesirable bause fibres have very seldom been found near the pleura. they impede the use of the sample for injection Work is currently in progress using radioactive experiments. A special dispenser has been tracer studies to attempt to confirm this observa developed to generate dust clouds for inhalation tion. It is possible that short, straight, chrysotile experiments (Timbrell et al., 1968). - : . fibres may behave aerodynamically like amphibole Gilson (1966) has stressed the importance of fibres. - fibre length and aerodynamic equivalent diameter The significance of Timbrell's theory regarding in determining the respirability of airborne dust. the role of interception and penetration in the Timbrell (1972a) has reviewed the importance of ultimate deposition of asbestos fibres, either in the physical properties of asbestos in the aetiology respiratory bronchioles or near the pleural surface, of asbestos diseases. He states that the ability of is that it offers a reasonable explanation for the long fibres (up to 200 pm.) to reach the alveolar difference in incidence of pleural mesothelioma regions, if they are thin enough not to be deposited in crocidolite exposed populations as opposed to earlier by sedimentation and impaction, explains chrysotile exposed populations. The difference satisfactorily the numerous long fibres found in between the incidence of mesotheliomas in the lung sections. He points out that *the epidemio* north-west Cape and the Transvaal (where logical, pathological and experimental evidence tumours are very rare), may be related to the fact presents a series of paradoxes which are useful in that differences in particle size in the crocidolite testing ideas' concerning the aetiology '. /The from these regions affect their aerodynamic marked difference in physical properties- between behaviour and deposition in the lung. It has been the asbestos minerals from the north-western shown that Transvaal fibres, both crocidolite and Cape Province and the Transvaal may. be a clue amosite, are on average three times the diameter to the difference in the incidence of mesotheliomas and three times the length of north-western Cape in these two mining regions. .. -- . ' crocidolite fibres. Hence a sample of north Timbrell (1972b) suggests that long fibres western Cape asbestos will produce twenty-seven are preferentially deposited in the . respiratory times the number of fibres as the same mass, of '? 1 \ I - i i t t > / i r '1 s; -s 11 '. JB - 2 . ,e ... r . it . ic < " ' - )V e ' ... K t a . e -y * i rndHUm .c in e . *. . ' = -iocstos. Transvaal asbestos liberates 1 are removed relatively rapidly from the respiratory i -uptrable fibres, fibres have a higher settling tract by ciliary action. This method is being usedi .ate and hence shorter time available for inhalation in an attempt to discover the mode of deposition and they have* less efficient penetration to the of fibres in different areas of lung. Langer et al deeper parts of the lung than north-western Cape (1970), using electron microprobe analysis, have asbestos^ The latter characteristic may explain studied the inorganic composition of asbestos the difference in incidence of mesothelioma in the bodies and one of their conclusions is that bi< two regions. . .. ; ' t < logical interactions may tend to affect chrysoti At the Lyon Conference, the Physics and much more than amosite or crocidolite. Asbestos Chemistry Panel of the Advisory Committee on bodies obtained from the ashed lung tissue of Asbestos Cancers, in the report which it makes to asbestos worker, known to have been expo: the Director of the IARC, suggests a number of to amosite until ten years before his death, we: future studies-. on the preparation o f asbestos analysed and compared with asbestos bodies from; samples.. from different geographical -areas- to ashed lung tissue of an asbestos worker who attempt to determine the influence of fihr size employed in the Canadian chrysotile fields. and shape on carcinogenicity (WHO, 1973). Their data indicate that amosite has remain* Information is required to help t o identify the chemically unaltered in at least ten years of bi* biologically important fraction-and-to help logical residence, whereas chrysotile bundles hav* with the interpretation of epidemiological and tended to split into sub-microscopic fibrils pathological studies. Dust counting methods in chrysotile fibres break down into units not occupational and environmental studies require to resolved by the probe and they lose magnesium! be standardized and data collected overan extended readily. Morgan and Cralley (1972) have recently^ period will be valuable in correlating the health documented the inorganic mineral content of$ hazard with epidemiological evidence^ -- - ^ . *. .............. - Experimental Pathology and Pathology asbestos and the solubility of the principal typesi Chrysotile loses magnesium from the crystal lattice: in vivo at a finite rate and the effect of this on thd Gilson (1966) has discussed the importance of the cytotoxicity and carcinogenicity of chrysotile re-: I' renewed interest in experimental asbestosis. The quires further investigation. The solubility of thei problems enumerated by him in the-Wyers Mem constituents of chrysotile asbestos, as demon- i / orial Lecture may be summarized briefly as follows: strated by radioactive tracer techniques, associated! k-\ 1. Why is inhaled chrysotile so- much morewith the leaching of magnesium, confirm that rapidly eliminated than the otherthseednstsT asbestos fibre type is chemically unstable i: . 2. What is the role o f particle length in- the biological environments (Morgan and Holmes. development of fibrosis and to what extent is this 1970). The marked physical changes which taki independent of, o r dependent upon* mass, surface place in vivo, when chrysotile fibres, composed oi area and the number of fibres inhaled? bundles of fibrils, tend to break open and dispei _ -- 3. What is the role of phagocytosis in the clear into ultimate fibrils, may account for its clearance; ance mechanism? '- - i h <" ' - - ' from the lungs. Such effects have not been ob 4. How is the asbestos body involved in the. served in in vivo studies with amphibole asbesto pathogenesis of fibrosis? >- types, e.g. amosite (Langer et al., 1970). --~ L& Not all these questions can be answered as yet, The experimental work briefly reported on thud but some plausible theories have emerged to far, in conjunction with the work on the effect oi explain some of them. Most of the constituents of shape on particle penetration and retention i asbestos can be made radioactive by neutron animal lungs, indicates that, apart from phag irradiation in -a nuclear reactor. Morgan and cytosis, chrysotile fibres are cleared from lun Holmes (1970) have applied radiometric techniques because: - ' in their investigation of the composition of asbestos 1. Interception of long, thin, curly fibres occur^ ' and its behaviour in biological systems. In studying in bronchioles with ciliated epithelium, and these| lung clearance they have found that their technique. fibres are then partially cleared by the cilial action. may be used satisfactorily in inhalation experi - 2. Chrysotile is chemically unstable and its ments. Comparatively large amounts of asbestos 'constituents dissolve in body fluids, and n 3.; cnab be The fibre' has i' sider; effect It of a Mac! Rezz (197C effect absei ampl of as cells five i are r cytos comp out < some and event (5-25 some can * enteri pksn disruj asbes mesoi cytic, chrys well. Thi shifte (1972 in le carcii applit panic for c bcliev to be to thi mas * impla oxide -V '-P-T-. !.. <*4. HEALTH HAZARDS OF ASBESTOS 5 , were jfroms was jields Rained B bio" < hav siui ir'enti; <4t ol >types B] ^tticefl jo thi ,e rejf the istnonuiated this LC Limes,] take Iptf ofe ^(perse t a-anc ta ot i0estos & . cDtthus Cvpt o h i it iesa8c b^ni -tt fit* bmhese o<doni A-, ^ - 3. it is physically altered in biological residence in an elegant experiment in vitro, have shown that I enabling clearance by (1), (2), or phagocytosis to the lengths of glass fibres which will induce growth , be more readily achieved. - ` of fibroblasts in culture correlate with the lengths * The role of particle length in the development of of asbestos and other mineral fibres which will j fibrosis and the other biological effects of asbestos induce mesothelioma in the rat. has not been resolved^ This factor must be con Particles smaller than 20 pm. in length do not sidered in conjunction with the fibre type and the induce growth in vitro or mesothelioma in vivo. ' effects of asbestos on macrophages and other cells. The experiments of Rajan et al. (1972) and Mar It is now generally accepted that certain types oudas. et al. (1973) demonstrate the value to be i of asbestos can interact with cell membranes. derived from the study of organ culture and-cell MacNab and Harrington (1967), Secchi and culture systems in investigating the effect of various Rezzonico (1968) and Schnitzer and Pundsack fibres, chemicals and carcinogens in a relatively ' (1970) have demonstrated the marked haemolytic short period. - ~ effects of chrysotile and have confirmed the The significance o f labile cations attached to absence of marked haemolytic properties in the the silicon-oxygen lattice, metallic contaminants, amphiboles. Allison (1972) has studied the effects and adsorbed organic compounds (of geological of asbestos particles on macrophages, mesothelial origin or from contamination during commercial cells and fibroblasts. He has found that, irrespec handling) is being investigated. Harrington (1962) tive of the asbestos type, short fibres (< 5 pm) has demonstrated the presence of oils in asbestos are readily and completely taken up by phago samples, one of which is 3,4-benzpyrene. Harring cytosis whereas long fibres (>25 pm) are never ton (1965) has also described the possible completely taken up. Part of the long fibre remains contamination of asbestos fibres by jute oils. out of the phagocyte. Two or more cells can Gibbs (1970) has shown that fibre stored in sometimes be seen attached to a single long fibre polyethylene bags may become contaminated with and there is a suggestion that cell fusion may ` oils '. Wagner et al. (1970) have shown that the eventually occur. Particles o f intermediate size presence or absence of the oils found by Hamngton (5-25 pm) are sometimes completely ingested and does not appear to alter the incidence of meso sometimes not. Allison has shown that chrysotile theliomas produced by intrapleural inoculation in can exert an early cytotoxic effect soon after rats. Reeves et al. (1971), reviewing progress in entering the cell because of interaction with the experimental asbestos carcinogenesis, point out plasma membrane or a late effect as a result of that the major metallic components present in disruption of the lysosomal membrane. When asbestos are aluminium, magnesium and iron. asbestos particles are added to organ cultures of Trace levels of chromium, nickel and cobalt are mesothelium, these cells prove to be highly phago regularly found. While iron itself is not regarded cytic, showing delayed cytotoxicity to high doses of as carcinogenic, experimental tumours have been chrysotile. They tolerate small doses of crocidolite produced by iron-dextran complexes, where the bonding of iron to the polymer may have been well. . " . :' The emphasis in experimental pathology has similar to that in asbestos (Richmond, 1959 quoted shifted from asbestosis to carcinogenesis. Stanton by Reeveset al., 1971). The trace levels of chromium (1972) has shown that fibres about 20-200 pm and nickel in asbestos may play a role as environ in length or 0*5-5 pm in diameter are more mental carcinogens. Dixon et al. (1970) reported carcinogenic than larger or smaller fibres. This that Fe3+ and Cr*+ both of which can be found in applies to both asbestos fibres and to glass fibre chrysotile asbestos, inhibit the action of benzpyrene particles (the latter having been specially prepared hydroxylase, a detoxifying enzyme that protects for experimental purposes only), and Stanton . the organism from the effects of benzpyrene: believes that carcinogenicity of such particles seems The interesting possibilities which this observation to be related to their shape and size rather than opens up with regard to asbestos carcinogenesis and to their physico-chemical properties. Mesothelio the rote of tobacco smoke have not yet been mas can be produced experimentally by pleural investigated in any depth. ' implants of asbestos, glass fibre and aluminium Since Gilson posed the questions regarding the oxide fibres of similar size. Maroudas et al. (1973) role of asbestos bodies in the pathogenesis of .r\ c; and are being ;.ography b u ' emerged b n th is .^ ey (1972) bas reviewed the formation ,,oestos bodies and using the electron micro.,)pe has studied the composition and character ssuuechn boouduiiews e6axit*racvvt*ed- f--rom.....h--um-an lun~gs.. The Cjcstos bodies studied have come from the lungs ipersons exposed to the four types-of commercial bestos fibre. He. has found that bodies rarely L on fibres, less than 10 pm in length, and "actically always on straight fibres. They occur p, frequently on chrysotile fibres than the other Ppn . ^ nvestigated to ascertain whethei me recognize those-who are developing. oorr wwiillll ddeevveelloopp,, wtumrnou>t_s._tTumer-Warwickn('n1d9Ae7r1j\ states that preliminary analysis of her study un er-j taken to identify and define sme of the immuno logical host responses in persons exposed t asbestos, supports the suggestion that anbnucled antibody (ANA) acts as an accelerator of fibrosis anuoouy , ^ ^ ^ - - 'separate agent, once it has been initiated by a sepa 6 ^ British Occui its Hygiene ; Dust in June.' and based oi exposure dur textile factory high prevale: however,'is t where it has dust exposur and X-ray c fo tte . Results from all the lung specimens _ BOHS Comi :iow that bodies always coexist m the material 9 f . heaith h o ard s of asbestos h; Committee c ;si h c r with uncoated S br and tbat u n ^ T t a clarifying carrea Standard in j ires are far more numerous than coated fflres. ,,carding the physical and chemical change be m i; h e n am p h ib o le fibre is p re s e t t h e r e j i s w y ^ oroS t i e s o ^ a s b ito s and attempting to plaa Standard be ' Terence in the ratio of coated to oerspective with regard to the pathological designed to re to 1 percent* % in those tissues containing - m ShaniSis S o lv e d in the aetiology of asbestosis to dust. By ;nuncoated to coated fibres^very ^mparison. Ashcroft and Hepplesto. (1975) S n c ^ a n o m a and mesothelioma. - -- - lu g encaged in the practice o f occu earliest dem< p y attempted to a s s e s s a s b e j o s c o n ^ t ^ ^ O T paS n a i medicine ?s perhaps more conscious ol asbestos. TI :aag tissue showmg various degrees and forms o f p enidemiologist, in its widest sense affected to tl jis,rosis. In mild and moderate asbestosis-di^feda his " p the ,,legation of this importam depends upo I ogressive increase in concentration of asbestos and may wonder a t t ^ c g Qf ^ paper. years per cm5 tion o f2 fibn fu>res, both coated and uncoated, no ~ T h is^as been done deliberately, as the epidemi- :Verity of fibrosis,whereas in severe asbestosis asbestos-induced lesions will be all the less than a 1 ierrelarionexistsbetweenthefibreconomO^^d. o l after examining the aetiological demonstrablt n1e form or the extent of the considerations outUned in the preceding^sections. Tphatehosilzoegircaanli "r It is obvious that progress has oractical lessons to be learned from the lungs, is ex ^iswering some of ^ q u e s tio n s he>secUbut further study is required. TteAdwsoiy SdeSiological studies thus far published relate! p " ^ g of the industrial environment, the* fibres per a lonunittee on Asbestos Cancers m tt o n q io m, Qf exp0sed individuals and the rol4 determined is^the Director of the I n t e m a t i o n a L A ^ ^ S T n S in monitoring and controlling tb method. In hepsearch on Cancer have o K o m m e n d ^ t^ v ra k . J products on the general environment count '.bres T r , . cand `t done on methods for ^Eoidem idom cal evidence since 1964 has accurnu hebes and structural features o f a s b e j o s i a i ^ e P ^ many countrics and illustrate betwx*r ' the >lek that the pathological assessment ofifae seventy teo P occupations in which asbesto: exposure, wl ^ a sb e sto sis be standardized. It was occur? The presence of asbesto Sub-Commil 4 cinoma in persons ^cupationafly ^ P e d filters used for tb asbestos exp was produc Tould be compared with lung caranoma m -^ ^ of beverages, beers, wines, etc., an* classification posed individuals.. The purpose o f tin* ite oresence in drugs given parenteraUy, has be puld be to examine the incidences of tmooms i P . - et ai., i% 3; Cunninghai pneumoconi of asbestos [1vsaurciohutsusmiteosuor f s origin , and in to the cor lu re ng lat a e n t d the hese cyto with ogy the pontefract 1971 ` Rickards and Badami, 1971 ^ d P o n tefr^ , 1971 w ex 1972b national Lai :snce or absence of asbestosis.' S m o k in g ta to .v , classificatiot iuld be noted in this study to assess the influence Rickards, 19 increased- with regard to tb may well b m tt*AhhiWee hhaabbiitt oonn mt.hee. mincaiudce*nu.cwe o_f _t--u_m--fkoau;fr varieties a -m-Ki,anf difgferent var.ie.t.ies of<fib-r-e---a-n-da i:s no lionnnguep detection ai of asbestos i VO uumug v----- ' - A tew small groups of factory workers exposed t one type of fibre only have now been identifie allowed wid pleural pla* A'/r' . T. : ->. ; :. v - v.i.u-r -- 'W S : V 'h ea l t h HAZARDS OF ASBESTOS 7 4 *r- l* cr sis t1 fc . )as mt ;W yce (3ll ;:*-.is, V ' >:i:- ol ( se, t -nl ; er. f ii- fc I cal'! r. is* I He ; Jit Tie r* he it: |s-uJ - U os f.:ih y ' ll i ,m 'r mi :: l & tl - K 5ft calcification are more often caused by asbe^os nd are being studied (Selikoff et al., 1972a). p ie inhalation than was previously recognized. The British Occupational Hygiene Society published use of this classification has shown the importance its Hygiene Standards for Chrysotile Asbestos of separating rounded and irregular opacities, Dust in June, 1968. The data used were scanty, pleural thickening and pleural calcification. and based on factory experience o f continuous Rounded small opacities are more prevalent where exposure during working hours at an asbestos exposures have been to other mineral dusts as well textile factory situated in a conurbation with a as to asbestos, in particular silica. They relate high prevalence of chronic . bronchitis. This, more closely to estimates of past dust exposure however, is the only population studied thus far intensity. Irregular opacities have not yet been where it has been possible, because of reasonable related to the mass of asbestos or other dusts in dust exposure records, to relate clinical findings the lung, and may well be an index of tissue res and X-ray changes to dust counts. When the ponse rather than the amount of dust present. BOHS Committee on Hygiene Standards Sub In view of the development of this radiological Committee on chrysotile asbestos reviewed the classification and its apparent effectiveness m Standard in 1973, it was recommended that no demonstrating early changes due to asbestos change be made at the present time but that the exposure, the next review of the Standard which is Standard be kept under review. The Standard is undertaken may have to be based on such changes designed to reduce the risk of contracting asbestos to 1 per cent of those who have a lifetime's exposure rather than basal rales. . The evidence for a dose-response relationship to dust. By asbestosis the Committee meant the for asbestosis appears to have been confirmed in earliest demonstrable effects on the lung due to the textile section of the asbestos industry by the asbestos. The probability that the risk, of being decreasing incidence of the disease following the affected to this extent will be less than l per a n t introduction of the Asbestos Industry Regulations depends upon a cumulative exposure o f 100 fibre (1931), which took effect in 1933 (Smither and years per cm*. I f a man works in a dust concentra Lewinsohn, 1972). In other industries, not covered tion of 2 fibres per cm* for 50 years, he should have bv the Regulations, the incidence of asbestosis less than a 1 per cent risk of developing the earliest appeared to increase, and case-finding exercises m ,' demonstrable effects on the lung due to asbestos. naval dockyards (Harries, 1968) and elsewhere The size range of fibres to be counted, based upon added to the number. The Asbestos Regulations pathological observation of fibres retained m the 1969 were made and took effect m May 1970. lungs, is expressed in terms of the number of These Regulations were designed to apply to ail fibres per cm3 greater than 5 pm m length, as manufacture or uses of asbestos where dangerous determined with the standard membrane filter concentrations of dust are found. The sta"Jirds method. In industrial practice it is customary to to be applied in the interpretation of these Regula . count fibres in the 5-100 pm range. ; tions are to be found in Technical Data Note 13, The standard is derived from the correlation published by HM Factory Inspectorate in the between the development of basal riles and dus Department of Employment (1969). K W TM exposure, while X-rays were not considered by the theapparent difference in biological effects between Sub-Committee to reflect the earliest effects of chrysotile and crocidolite, the Regulations specify, asbestos exposure on the lungs. Since the standar certain stringent conditions relating to the iwe of was produced an internationally recommended the latter and impose a tighter standard m TDN 13 classification of the radiographic appearances of It is the hazard of malignant disease which stimu pneumoconiosis, suitable for use in the surveillance lates the continued interest m the biological effects of asbestos workers has been developed. (Inter of ib e s to s .. Merewether (1949) first demonstrated ) national Labour Office, 1972). The early use of this a clear-cut association between asbestosis a n d 8 classification indicates that the chest radiograph carcinoma. Over 50 per cent of asbestosis sufferers may well be the most important means for the die as a result of lung cancer and in populations detection and monitoring of the biological effects where asbestosis still occurs of asbestos in the lungs. Systematic studies have of excess deaths (Buchanan, 1965). ^ " been allowed wider recognition of the fact that bilateral shown that where the level of exposure is reduced pleural plaques, pleural thickening and pleural mm (' 'll r, e it: U. u r * / a` _ i ' ' .rri ' Kx .vr.'\;.>-V;...,'i. v . 8 OCCUPATIONAL MEDICINE ' ` 1 . and there is a lowered incidence of asbestosis, the cancer risk is also considerably reduced but not completely eliminated (Knox et al., 1968). The incidence of lung cancers in cigarette smokers exposed to asbestos indicates that smoking may be an important, if not essential, co-factor in this situation (Hammond and Selikoff, 1972).--:... , ' Malignant mesothelioma of the pleura or peri toneum is perhaps the most important condition requiring detailed epidemiological study. In The Harold.. Dom Memorial Lecture (1970) Richard Doll quotes Dom as follower. - . The absence of reliable statistical data concerning variations in.the incidence of cancer partially exphnnsthe existence of conflicting and inconclusive theories abaci-the etiology of human cancer, since most of these.theories,are derived from the analysis of clinical data which >3 to satisfy the require ments of statistical-adequacy. .. _ . .. , , The information regarding the incidence of malig nant mesothelioma is incomplete; the dust concen trations required to produce d: are-not known and the diagnostic criteria, have not been finalized. It is now known that the-fibrertypemay be import ant in^the aetiology of this tnmour but thus far only anthophyllite ap p ears'to be innocent. A proportion oF mesotheliomas-s- apparently not related to past exposure to asbestos. In order to determine the exposure r is k - ir is necessary to estimate the dust concentrations and to identify the fibre types to which occupational-groups have been or are exposed. Similar dara are. required to quantify th e risk to the general population said to be minimally exposed-- The- emergence of a possible publie~health r i s t i f d i j e to the- finding of asbestos bodies in random, autopsy series, the neighbourhood and domestic exposure cases described and the recent interest in asbestos in the urban environment.. As has been commented on in the earlier pages o f this review,, on epidemio logical evidence, crocidolite from- the north-west Cape Province of South Africa (and from mines no longer operational in Western Australia) seems to be the most likely fibre to produce mesothelioma. Crocidolite from the Transvaal seems less likely to do so, the risk is also less with amosite and apparently less with chrysotile as well. : This difference may be explained.by Timbrell's theories already referred to. . Before concluding this section I should like to summarize the main conclusions to be drawn from epidemiological studies to date r - . ; . ... * 1. Asbestosis appears to be dose-response relate and is caused by all fibre types. 2. Lung cancer is responsible for the exces deaths in populations where asbestosis occurs ancfl may be associated with more than 50 per cent oil asbestosis cases. _ . . _ 3. Lung cancer incidence decreases with thi decline in incidence of asbestosis but has thus not been entirely eliminated. , : 4. Cigarette smoking and significant asbestos! exposure have a multiplicative effect in the don of lung cancer. - . *. . . ` 5. Mesothelioma appears to occur more ofteii in association with crocidolite from the north-west Cape whereas Transvaal crocidolite is far lesi dangerous. Only anthophyllite is innocent o: causing this malignant tumour thus far. - . . j 6. Before denying a public health risk froni exposure to asbestos in the urban environment! in food and in fluids and beverages, detailed epidemiological and pathological investigation^ are required. On the evidence available to date; and in view of the negligible quantities of asbestos, detected in the urban air, in foods and in fluids and, beverages, the Advisory Committee on| Asbestos Cancers of the IARC believes that therri is no risk to the general public. . . ., Conclusions . . .. ,-- 'ij The study of the biological effects of asbestos! cannot be conducted unless a multi-disciplinarjf approach is adopted. The practical application of? this approach is to be found in the medical surveil4 lance programme design, the environmental monitoring programme and the detailed scrutiny o: morbidity data, mortality records and dust coun figures in the asbestos industry. - .. The future need is for the development, of objective methods for the early detection an surveillance of the effects caused by asbest The following are listed by the Advisory Com mittee: . . .. 1. Immunological techniques for screening foi fibrosis and neoplasia. . .... . ,: - . . 2. Functional tests of changes in the periphe: airways. ~ .- - - . - ; 3. Detection of pleural thickening. 4. Assessment of the specificity of small irregul; opacities in the chest radiograph as defined i: ILO U/C Classification, 1971. . - . - . 5- Tests of the usefulness of different techniqu >& m M ini HEALTH HAZARDS OF ASBESTOS 9 ,nest radiography, including the use of 100 nun. / ' ' / 6. Development of statistical procedures for /analysis and presentation of serial observations. A shcroft, T . an d H eppleston, A . G . (1973) The optical and electron microscopic determ ination of pulmonary asbestos fibre concentration and its relation to hum an pathological reaction. Journal o f Clinical Pathology 26,224-234. British Occupational Hygiene Society Committee on Hygiene The diagnostic criteria for asbestosis have not Standards (1968) Annals o f Occupational Hygiene I I , 47. been greatly altered since the days of Merewether Buchanan, W. D. (1965) Annals o f the New York Academy .W (1930) except for the addition of lung function o fSciences 132, A rt. 1,507-518. Ft Cunningham , H . M. and Pontefract, R . (1971) Asbestos / a j tests as confirmatory evidence of pulmonary fibres in beverages and drinking water. Nature 232,332. fibrosis. Correlation between the dust content D epartm ent of Employment (1969) Factories: The Asbestos of .the factory environment* the dust content in Regulations 1969. Statutory Instrum ents 1969, N o. 69Q_ e the lungs, radiographic appearances, - physical London, HMSO. 1 n signs and physiological changes is urgently re D eDpuarsttmCeonntcoenftEramtiopnlofyomr eUnste(1w9i6th9)thSetaAnsdbaersdtos sfoRregAuslbaetisotonss 0 lie quired. The reason for the apparent differences 1969. HM Factory Inspectorate--Technical D ata Note 13. 1 between miners and millers of asbestos and asbestos Deutsches Z entralinstitut fur Arbeitsm edizin--Berlin Gesell r textile workers might be forthcoming from such schaft fur Arbeitshygiene und Arbeitsschutz in der DDR r detailed studies. u - - (1968) Internationale Konferenx iiber die Biologischen * The Department o f Employment has com Wirkungen des Asbestes, 22-25 A pril 1968, Dresden. ; D ixon, J. R. et al. (1970) The role o f trace metals in chemical A menced a prospective epidemiological survey of carcinogenesis: asbestos cancers. Cancer Research 30, 1 asbestos workers which should assist in clarifying 1068-1074. the relationship between fibre type, dust concen D oll, R . (1971) Cancer and ageing: the epidemiological 3 tration, radiological changes and physical signs. evidence. In : Year Book o f Oncology, Volume V. New Y ork, Y ear Book Medical Publishers, pp. 1-27. ' l The data will be analysed after taking into account Gibbs, G . W. (1970) Asbestos fibre contam ination by storage \ individual smoking habits, age, sex and dust in polythene bags. In : Shapiro, H. A. (ed.), Pneumo t `ids! exposure besides asbestos in order to determine coniosis: Proceedings o f the International Conference, r their combined effects. ` ' Johannesburg, 1969. Cape Town, Oxford University Press, pp. 165-167. c The value o f all this research, to the industrial Gilson, J. C. (1966) Wyers M emorial Lecture 1965--H ealth medical officer is that it enables medical surveillance hazards of asbestos: recent studies on its biological effects. t programmes designed to monitor specific infor Transactions o f the Society o f Occupational Medicine 16, i mation to be developed, and thereby gives purpose 62-74. c and direction to his efforts on behalf o f the exposed G iPlsroonc,eJe.dCin.g(s197o3f) AthsebesRtoosycaalncSeor:cpieatsyt aondf fuMtuerdeichinazeard66s., i worker. 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