Document 0q1BEDZVb40B4YONzVw1zng7R

.. ------------- ---- ----- ---- --- ---------------------------19Sl(July); 1(1): 2 pages. JULY, 1981 ISSUE 111 VOLUME Ill This first in a series of "advisories" is designed to keep water utilities and public health officiais current on information regarding usage of asbestoscement pipe. Each Advisory issue will fa.ctuall.y summarize data. contained i~ scientific papers, government studies. media. reports, a.nd technical a.nd educational source material. GOVERNMENT ANIIVIAL FEEDING STUDIES SHOW NO CARCINOGENIC EFFECT OF INGESTED ASBESTOS Preliminary results of government-sponsored studies on the effect of ingested asbestos on laboratory animals show no carcinogenic or cocarcinogenic effect. . The studies are being conducted by. the National Institute of Environmental Health I Sciences (NIEHS) under the direction of the Public Health Service's National Toxicology i! Jrogram. The Environmental Protection Agency (EPA) has contributed a portion of ~ ~ ~he funding. Sa lfi ~~ ~ ;l f?f The aim of the NIEHS/EPA studies asbestos fibers which are ingested, or is to assess the biological (carcinogenic) effects taken into the body through the digestive tract,_.- . g ~ a::as in drinking water. I! iI ~!') ~ The studies call for asbestos to be fed continuously in the diet over the entire lifespan ~ m of the animal, which is defined as the age at which the animal begins eating solid food until its death. A total of 1,860 male and female hamsters were fed asbestos, and an equal number of hamsters were fed a. control diet with no asbestos over their lifetime of 18-23 months. Two types of asbestos fibers (chrysotile and amosite) commonly used in the manufacture of asbestos-cement products were administered. The dose of asbestos (1% of total diet by weight) fed to the hamsters was millions of times greater than levels which occur in drinking water consumed by the public in a lifetime, in areas where asbestos occurs naturally in the drinking water. NIEHS reports, ''There was no indication of major differences in the mortality rate between the hamsters receiving the asbestos diet or the control diet." Preliminary analysis of the hamster data. indicates that no carcinogenic or cocarcinogenic effect was observed. 1600 Wilson Boulevordp Suite 1008'6 Anington. Va 22209 b.. (703) 841-1_556 FMSI 05514 .. The analysis included thorough gross pathological evaluation at time of autopsy, as well as microscopic e-:xamination of some thirty tissues from test animals. In addition, preliminary results of rat studies in which a total of 5,158 rats were fed asbestos and control diets were also reported. The lifetime exposure phase of the study concluded, " ... longevity was not affected by exposure to the various types of fibers." These findings are consistent with a number of other studies of animals fed asbestos in food or drinking water. In 1980, the Health Research Institute at Fairleigh-Dickinson University reported no malignant tumors related to treatment in hamsters. maintained on drinking water containing 13 billion asbestos fibers per liter. References: 1. NIEHS, Biological Effects of Ingested Asbestos Status Report January 22, 1981, National Toxicology Program, Public Health Service. a. NIEHS, Biological Effects of Ingested Asbestos Status Report February 15, 1980, National Toxicology Program, Public Health Service. 3. Moore, J.A., NIEHS Oral Asbestos Studies, National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD July 18-20, 1977. FMSI 05515 BRITISH MEDICAL JOURNAL, 1981 (August 15); 283: 457-458. ~":'riOEH " Cod5e5208 ing is mai\c, and it lui:; the :11.1ded ad\-:mt:lgc that agent:. may be: inje\:tc:J. If bk\.'\ling continues skilled JUdlgrJJifnt is nc:edc:L.I, and joint c.:oNultation is essenti:ll; a be struck bc:twc:c:n c:arly incc:nc:ncion anu illnesses and accidents is c:li::JctcJ for the benefits provided by most producti..-e indu:;try. Society and iL~ elc\.'teU rc:presc:nta- tives need to be informed of the: risks in ordo:r that work em be made as safe as possible, COlllli:itent with the need to continue IX' increase produc:tiolil; but the ultimlltc: responsibility in a c~&:moe:raDe society for occupational morbidity and morality 10 32 36 82 restS with e"'er'/ individwal. Two problems that ca:mplify the: c:omple:city of theic i:isw:s arc bronchitis in the c:oal industry and lung c:anc::cr in the abestos industry. Chronic: bronchitis is one of the most C011UD0D disabling discasa in Britain and, thoush at.QrCility &am it has beeD falling, it still ranks high as a cause of dc:ath. Ia reJation to dpreae smoking is w~ lmowu,~ but it is also rdatcd strikiqly to the: Registrar Gcnc:ruls sociDl groupings (which are baed on occupation), to dust exposure in industry, md to area of residence,4 implying some influence of g=eral aaDOSphcric: poUution (at least in the past), overauwding, aud other.soc:ial fac:con. Cigarette smoking, with itS cffeas oa bach smokers and those who surround them, is also strongly reWed to soc:ial class.' In clinic:al. practice patientS di<Sablc:d by dlmnic: broachitis who bave. never been smukers are e:arc:mely mn:.. Talk of occupational bmnchitis, as though occupation were the sole cause of the potemially disabling or fatal disease illm iDdividaa1, is misfading Claims that exposure to dust cfaa DOC c:DIIUibaD= to tbc disase are, howner, equally false, siace there is good evidcm:e in the c:oal industry of relations between masured. dust esposure and symptoms, impairment of lung function, and monality from c:bronic: bronchitis.T . To disentangle the reJatift df'cas of dust and ciprettcs in causiDg tbc disease is difficult epidemiologic::ally1 and impclllibJe in tbc individual csposec1 to both; nevertheless, both have played their pan--u least in thc: puc. Whether current 1eftls ofdust c:zposure in the c:oal industry will be sllffic:ient to came imponmt c:JiDic:al etreca on the airways remains m be seen, but tbe evidence sugests that this is unlikely. Similar arsumeaa apply to the rdation between exposure- to asbestoa, cigarem:s, and lung cancer. Here the rwo causal facton seem to ~ in a multiplicative IXIlUUll:t. Exposure to asbe:stos probably has a linear relation with the: risk of developing lung CIIICI:r.Lo ll This risk is very high indeed in the heavily =posed. smoker, but the: risks are also substantial in a Smoking, coal, asbestos, lla:rily ezposed non-smola:r. Two forms of ac:tion wouid, tbcref'~ reduce the number of workers at risk oflung cancer: and the lungs reductiOll of asbestos leveJs in the industry and reduction of smokm:g. Cutting the proportion of smokers would have more Over the past 20 years the number of British coalmioers with pncumcx:oniosis bas fallen subsWJ.tially. In pan the fall is due to the fac:t dm fewer men work in the pits, but it is also a respon.o;e to dfcaive meaSures taken co reduce dust levels underground-on the evidence of resc:ard1 showing the association bc:twcen c:xposure to respirable dust and the risks of developing pneumoconiosis.' Some SOO men a yenr are stiii diagnosed as having the dise:lse by the pneumoconiosis medic:al boards, though the average aga at which men show signs of the cWI'erent saages ofthe disc:asc: have been inc:reusing steadily, largely redecting the higher dust levels of earlier years. Asbestosis, the other import:lnt pneumoconiosis in Britain, continues to be: diagnosed by the pneumoconiosis boards in dfea m workers aposed to asbestos than in the: general population. Dust control has been much improved in both indu.'ltri~ ia recent yean, and further improVCCIClltS will be lllllUc in the ~ fu_mre voluntanly and in response to public pressure or ~ .-\5 well as reducing the risks of the specific: pneumo- comoses m the workcn, this wiil also reduce the risk of c:bzoaic bronchitis in miners and lung c:anccr in asb~:~tos ~Yet these latter dise:lllcs will continue to be: a problem m _industry .as well as in the general population so long as ~Je JDc:1rl CO_D.tm,.ue to smoke. An important rcduc:tioa in their "Dee. WUL occur only when the same public: and gtwo:m ~ prcssun: is c=a:rted oa smoking as on du'lt control. Bmmiug tobacco advertising would be a sensible nen seep. about 200 people a year; no decline in incidence has yet been seen, but current Just-control policies in the industry are c:ocpc:c:tcd to proJuce 'uch an effect in the nc:ar future. [n thc:My <l<:..:upational disc:1scs arc: wholly prc:vcnt:tble, but in pr J<:tic.:.: ,,, Inn~ a~ society requires an indu,try's proJu.:ts >urn.: m.:n "cil t'Jil ill ;tnJ even Jic: a' a n:,ult..". t:<'>t in t<.:rtn> of \ J~~ ,'.(. ~ S, WlliLDD WH, Ropn JM. New cluu sma.Urtis (or 1 N . ns ~lli coa!nuacs. Nuni970;2:!7:.W5-7. Coal Boarli. .W.Jiciru tn"fli~ .,_...,1 por 1979./10. Lonli,n: ' , ~onyamnoo.n,a,l .CoTah.IBe tr>i:akrlsi,oI>'!fIal,l..cs,int ik. Rr .\1-.1] ICI~ll;:!lll :137-4. $"'""'""'o;;al Collcze nf t>liyici""' ftm.m .\t~~i~..;.11, :Q7t. ~..J h<.Jir!: "'''" TLlftbri,hcc Well.: , JA , \. '?.' J FMSI 05516 458 lli!ITISH ~IEDICAL JOURNAL VOLt:ME ::1'13 HC\IIand _wv:. Eridcmiology of chronic bron~bitis. In: ScoJJin~; ]G. Cu":'m1ng G, Thurlbcck W~t, cds. S.imnji.: j.>~md.ui~m of rcspi~t.>rY C m.:Jr,;1n~. arell PJ. TLroennddosni:nHccii~a~aUnetatnens.m, 1o9iW81>.c in tbc T;aitcd Klnsdom. Health . r ....t~. t97B;J0:49-54. ' RaBenSn,_~'\ht"aclkacarlmDiOnc, nA.afIinel:d WMaDlr.oCn h r~o1n.i c bronchitis a11d dUSt exposure in cd. lnht.Z&d pGFficla. J. Old Wokinc, Surrer: Unwin,l97l. ' R osm Role JM of , .lt.tdlcld M dust in l.bc D, jac world :ob nc s~al M Rae S 1 i Walkc:r OD, W'alron 'IX"H. A dcvelapmc:Dt o chrOniC btoncbiris ill Bridsh coal millen. Br11rrtl M..ll91l ;30:217-26. z.- me1 Ja~ M. Smolr.inc aaddiabiliqoill.millcn. Sano:a ll. .O.Sbatas aa4 1uas-. aulysh !:I l!MIO~;ii:7c4CI. al -iclcnce ooa lhe u b - ldns i>aUncdaiL 11 c - - 1917;20: 123-31. . 11 1.id4ell O.Asbatosmd pablicWdl. 7'7tclr-198l~:lt1-4.. hyJ'<=ncn~ion, for example, have ~.:n rcpon<.'d in some thou not all indu.~trial studies, and rccorJings of indu~ al noise have-produced incn.-a.scs in dia~tolic blood prcssu and total peripheral resistance lasting longer than the noi Work performance, accident rates, and behavio~ ma also be adver.;ely affected, though confounding faCtors exclude in. real-life studies; and Broadpcnt ci G Jansen suggesting that stcelwor~ wor more domestic disputes than oth~ Reducing noise and even prQViding however, cost money-how m-qch is no cart. but the notes in the background paper accoa_;uPanyin the coasultativi: dbcument suggest large s.ums.0,With . resources more spent on reducing noise could.mcan 1 for other health and Safety mea-;ures. The comm~;ion tains that few if any worken Noise at work will be exposed for long to ly 90 decibels since in praaice the design target ,riu nee o be two or three decibels lower than the limit. J{ also e hasio;es the general requirement to Enorm_ous numbers of people are exposed to potentially ~amagmg le\els of noise at work. In Britain, in manufactUring reduce noise .far as reasonably practicable, and adch that it "will keep the tion under review, and will consi9cr mdust.ty alone about 600 000 work in noise levels a~'C: an whether to"pro ~ome lower value if this seem~ correct in average of 90 decihels-noisy enough to make shouting the light-of fu dc:vc:lopments." The praent proposal, then, necessary for talking to someone scmdiDg at arm's length. could, indeed seen as ..a ~c:nsible first step in legislation." Over 2! million more work in levels over 80 decibels. ~e . Health and Safety Commission bas nowl proposed lepslaaon based on the 1972 voluntary code .of practiceS and the specific regulations that apply to a few industries. The central pro,-isions are that exposure to noise must be reduced ~everth a general obligation to kc:ep noise levels as low as le and below the statutory limit would not jn1luen the poorer or less conscientious firms as powerfully d a lower statutory I~; and once the figure of 90 . is enshrined in legislation we cannot realistically to the lowest level that is "reasonably practicable"-whether / ~y reduction of the actual noise or, failing that, by ear ~ . non-and that no one must be aposcd to ~ thm. 90 any early change. The doc:ument speaks ofthe aippling ts to industries if the regulatiom were very stringent and the likelihood that some would have to close. The social decibels. Is this level too high? / The risks of damage afa:r given exposares are knoWii. qui precisely, largely as a result of the work of Bums d Robinson.3 After a lifetime's exposure to 100 deci. the 2/:document states, 32% of people will have a heari9C hold level o_f SO decibels or more (averaged over 1, 3kHz), and wtth 90 and 80 decibels the proportions will 11~ and 3'o A hc:aring threshold of 50 decibels is at .;hic:h implicatioas of different limits, in terms of direct and indirect costs and benefits, need to be spelt out quite fully in the coming months, so that society can make an informed choice. We need too to hear more of the "strongly held and diifc::riog views" about adoption of 90 decibels as the main aaion le\'C:l, to which the commission refen so laconic:ally. Its final decision to propose 90 decibels must reflect Britain's present c:conoiDic circumstances and a substantially lower limit may not be the DHSS startS to pay disability beneffis this is a considerable level of disability. A hearingt' of 30 decibels or more represems impainDcm of . understandiag of conversation even in low ba ' noise, and is now recognised as such by the Ind ' Injuries Advisory Council.~ A careful look at figure 1 : doc:Dment shows that o~ this basis at least 40% of wo exposed to 90 decibels feasible. But would not 85 decibels, which would nearly treble the number of workers protected by legislation, be preferable ? At the very least, this could be written into the regulations as a "warning level." At all eventS, we hope that many of those in the health professions will send their views to the Health and Safety Commission before: the end of April 1982.t w1Il have some. handicap. Not of this will be due to noise, but the steepness of the ~ at which some 26% are from 90 down to points to the 8s0izdeecoifbetlhs~ problem. Moreover, some . ose in noisy jobs, now more than " m the past, have app !ide amounts of noise in their leisure hours. An estimated ,r2% of the large population of di~co anenders have nois oW; and, though these kinds ofpursuits are unlikely to djOver a working lifetime, such combined exposure sh not/be forgonen. The Heal ancV' Safety Commission says that it selected levels ov dea'bels for mandatory action "to ensure that the effoz(is directed to areas of greatest need." But this would ve ~roteaed. the far greater proportion of workers to n~e ofB0-90 dec::ibels, as figure 2 in the document s : the .proportions suffering damage are smaller but the . olute oumbers could be large. A further point, not dealt rith by the commission, is that the damaging effects of noise are not.necessarily confined to hearing. Other health effects are less certain'; but higher blood pressures and incidences of """Decibels" refers tbroughouc to ciB (A} O\'er an ei;hthour period. 1 Health Uld S.Ccty Commiuiaft. Proruri#rr of ~u..,;., tU - " CDIU- of ~ rcpl;uitiiU arrtl drafr apprMI<d awh of praaiu arrtl pid;mu-.. ,.,._IfLolldon: HMSO, 1981. Ocpanmcnt of Employment. C...U of praaiu ftrr rlwi., IM of ""fJ/oycd.fiWStiiU ro rtaiu. London: H.\oi.SO, 1972. ~- . Bums W, Robinmo 0. H<..rint <DUi nai.r in iruiwtry. London: HMSO Industrial lniurics AdviSOI'"f Council. Occu['QtioruJI dt.J{Mu. London: .w-,HMSO, 1978. (Cmrlo il66.) 1 Bickcrd~ J, Grqory .... A11 ft'aiu4titm of hr.m., rill '" a.rrmd.-n tU tii~&~~~lw.pla. Leeds: Schoot of ContrUcrional Studies. Leeds Polytechnic, 1979 (witb Noise Advisory Council memorandum June 1980). , Gloq O.Po/lunoll ami p<"''l< [twO articles on noiwf. Br llf<ti 1 1980;281 1325-i ana 1404-6. - T Andren~ HanSSOil L, Bliirkmu M, Jonnnn A. :Soise"" a contributory factor tn tbe development of dcvarftl ano:rial pressure. Aa Md .'ic..ruJ 1980;207 :493-8. "B.....thcm 0. HWIWI!"crformance in noise. In: Harris C, cd. Hi>ruJio"''* n"'" ""'""' s- of Health rrorcs manr d~heSparfoebtly_:l.:nmCdooemfdum.iNiss~seiwaotnY.t:o'tr~rkk:DMndIcUrG(rhpr'fCa'WIwIt-ooHffit"lhll","'I'HC' IS~7RnEd:c:hzh:ct1wa7.lrrii1r.t.-i~1g9fl'.<lluup: an m.z.:lunny nouc. London: HMSO, 1981. t Commcnn to: Mr C 0 Ldtc, H<ohh and Sa!ctv E~ecutic Hazard'US Sub.ranccs Oi\'ision, Br:mch HSO 03, ::S Charel Str.;., Lundun N'\t"l 50T ' FMSI 05517 j ! Canadian Medical Association Journal, 1981 (August 1); 125(3): 237-239. ,, ~ ?" IOEH 5525 Y''\ Code 90 81 EDITORIALS Asbestos and -public health F.D.K. LIDDELL, MA, PHD Asbestos workers are known to have an increased risk of pulmonary fibrosis, pulmonary carcinoma and diffuse primary interstitial mesothelial tumours of the pleura and peritoneum. Suspicions about the role of inhaled asbestos in these conditions date back to 1906, 1935 and 1960 respectively, and these suspicions were confirmed in the 1930s, 1960s and 1970s. However, t.he health effects of asbestos are highly complex and only because of recent intensive epidemiologic investigation has synthesis become possible. Most of the epidemiologic evidence is in the first three references;':. clinical implications are discussed by Becklake: although her epidemiology is somewhat outdated. It is now known that the probability of adverse effects from inhaled asbestos depends on the total number of fibres inhaled (a function of both duration of exposure and concentration) and the type of asbestos. Most asbestos used in the Western World is "chrysotile", which is mined mainly in Quebec. The rest is "amphibole" - essentially crocidolite and amosite which is now mined only in South Africa. Although the mechanisms of retention and elimination cf asbestos are not fully understood. on average and where exposures are similar much less chrysotile than amphibole is found iri the lungs post mortem. Thus, amphibole might appear to be the more potentially hazardous agent; indeed, this has been confirmed in many epidemiologic studies. The findings conform to a "fibre gradient", with crocidolite the most hazardous and chrysotile the least. In humans one cannot measure "dose" - that is, how much dust is retained in the target organ. At best, through personal samplers one can measure fibre concentrations in the air. However, in most studies even workplace asbestos levels have not been measured. Perhaps the best epidemiologic investigation was that of a birth cohort of all I 1 379 persons born between 1891 and 1920 who worked in chrysotile production in Quebec;' this study was crucial for the Health and Safety Commission's advisory committee on asbestos in the United Kingdom. The wide range of accumul- From the department of epidemiology and health, McGill University, Montreal Reprint requests to: Dr. F.D.K. Liddell, Department of epidemiology and health. McGill Universitv. 3775 University St.. Montreal. PQ H3A 2B4 ated dust exposure - that is, the summation, job by job, of dust concentrations multiplied by the number of years in the job - allowed a study of the shape of exposure-response relationships; that for lung cancer, in particular, was effectively linear!'7'1 This finding and the results from other studies have provided strong evidence against a threshold or "safe" exposure, despite the hope expressed in an eadier review' that was cited, but not endorsed, by Gloag!" There have been so few studies in which asbestos exposure has been assessed in more refined terms than duration of exposure that it is impossible to estimate exposure-response relationships for each fibre type and each response. However, we can evaluate, using certain reasonable assumptions, the fibre gradient for certain responses. Thus, the fibre gradient is almost certainly steeper for mesothelioma than for other responses.11 'u With lung cancer the gradient remains quite definite; in chrysotile production the risk is only mildly increased;'13 in chrysotile processing the risk may be higher, although the few small studies are difficult to interpret; in pure crocidolite exposure the risk is always much higher; .. and working with amphibole-rich mix- tures carries some of the highest risks."'' The association of asbestos exposure with gastroin- testinal cancer is uncertain; some other etiologic factor may also be involved.11 Evidence concerning laryngeal cancer is even more equivocal,'"" but this cancer is so rare that even if asbestos exposure enhanced the risk the effect on total mortality would undoubtedly be small. Diagnosis of asbestosis is far from standard, if only because no clinical signs are specific and s.ome history of asbestos exposure is required. However, there is some support for the usual "fibre gradient", although rather shallow.' Among asbestos workers cigarette smoking increases the risks of lung and laryngeal cancer but not mesothelioma or gastrointestinal cancer and perhaps not asbestosis. In Quebec the relative risk Clf lung cancer appeared to depend on smoking habits, the slope of the asbestos exposure-response line being steeper for nonsmokers than for smokers; however, in other studies the slopes seemed to differ only slightly! Either way it is clear that exposure to chrysotile in mining and milling at the current control limits is equivalent in carcinogenic potency to smoking about three or four cigarettes a week. CMA JOURNAL/ AUGUST !, 1981/VOL. 125 FMSI 05518 /237 1I} f ~, . (I'~) \. In all asbestos-related diseases there is a long in- posure may occur around demolition sites or when terval between the first exposure and the onset of certain building materials are damaged; if the materials symptoms. Today's cases are attributable to working contain amphibole strict precautionary measures must conditions 30 to 40 years ago. Over the next decade be taken during repair or replacement of building mate- or so more cases will undoubtedly appear, perhaps rials. On the other hand, the hazards during such pro- decades after cessation of exposure. However, since cedures must not be allowed to be worse than those of conditions have generally been improving since about leaving the asbestos in place. No ill effects have yet 1950 we may have already seen the worst of the been demonstrated from the presence of asbestos in pathologic effects of asbestos, despite some question.: drinking water, food or beverages, or in the general able forecasts widely circulated in the United Stales... atmosphere. Indeed, the air pollution around Thetford Cases arising from the current levels of exposure will Mines, PQ was quite severe for many decades, but there not be seen until well into the 21st century. was no evidence that excess asbestos-related mortality Some of "today's cases" are discussed by Finkelstein or morbidity in the local population could be attributed and coworkers in this issue of the Journal (pages 259 to to anything other than occupational exposure. 262). They explain that most of their 172 former work- Finally, some adequate substitutes for asbestos do ers certified as having asbestosis had first been exposed not resemble asbestos; however, of the ones that do, "when hygiene cnnditions were considerably worse the better they mimic the properties of asbestos the than they are today"; their general findings support more similar the effects on health are likely to be. earlier results."".. However, specific interpretation is Indeed, in experiments in animals glass fibres with the not easy because the 20 cases in which compensation same dimensions as crocidolite produced biologic was awarded between 1942 and 1969 may well have effects at least as serious as those of the amphibole!' differed from the others for the following reasons: At least 30 years' exposure of a large group of workers change in the criteria of certification during the three would be required to test the effects of any substitute; decades; a wide range of ages at the time of award; even then its safety could not be demonstrated. different types of exposure, particularly to amphibole; Decisions on control limits, on whether to repair or and accepted interactions of these factors. All these replace asbestos after it has been damaged and on sub- factors make Finkelstein and coworkers' discussion stitutes for asbestos, must be based not on emotions especiall) difficult to generalize from. particularly as, stirred by the results of past exposure to clearly exces- for most of the subjects, the period of observation sive doses of asbestos but on the best available scien- following the award was rather short. Furthermore, tific evidence. their Fig. 1 is just another way of presenting the data for "all causes" that appear in their Table Ill; while References there is undoubtedly a "horror story" from the past it is one told twice over and is not two such stories. Nevertheless, one can only agree with the sentiment in their final remark: that hygiene must be maintained so that the future risk of asbestos-related disease is eliminated. No control limit can guarantee absolute safety; limits for industrial exposure are usually derived from findings in workers with low exposures (by the standards of the 1950s). At a factory in Rochdale, Lancashire, England (where chrysotile was used mainly, although crocidolite was probably used substantially, even into the 1960s) no relation was found, among workers who had entered the industry after 1951, between lung cancer and asbestos exposure up to the equivalent of eight respirable fibres per millilitre of air (well above most countries' control limits) for 50 years." In Quebec no excess exposure was detected in those who had worked all their lives with asbestos at concentrations below about 20 fibres per millilitre.' Crocidolite should be subject to much more stringent regulations, including special care in any essential processing or handling. Because amosite is an amphibole and evidence against it is accumulating, it seems sensible for it to be subject to similarly stringent regulations. Asbestos exposure has occurred in nonoccupational settings,1 but it is unlikely that the concentrations can have been high enough for long enough to constitute a serious hazard (except in instances of household contact with asbestos workers). Nonoccupational ex- I. ACHESON ED, GARDNER MJ: The ill-effects of asbestos OD health. In Health and Safet)' Commluion: A.sbsto. FlruJI Rport of th Advi.sory Commill on A.sbstos, vol 2, HMSO, London, Bnll, 1979: 7-83 2. McDoNUD JC, LIDDELL FDK, GIBBS GW. EYSSEN GE. McDONALD AD: Dust exposure and monality in chrysotile mining, 1910.:.75. Br J lnd Md 1980;. 37: 11-24 3. WAGNEr. .R: (ed): BlolortcaJ Eflct of MinNl Flbrs, IARC sci pub! no 30, lnU All"f'CY for Research on Cancer, Lyon, France, 1910 4. BECKLAKE MR: Asbeslos-relllled diseases of the IUDI !Uld olher oraans: their epidemiolocY and implications for clinical practice. Am Rtv Rtplr Di 1976; 114: 187-227 5. Rowt..u<Ds N, GIBBS GW, McDoNALD AD: Asbestos fibres in lhe lunp of chrysotile miners and millers: a ptellminary report'. In WALTON WH, CRITCHLO"'' A (eds): lnhaJtd Part/cl V, Perpmon, Oxford (in press) 6. Health and Safety Commission: A.sbttstos. Final Report ol th Advisory Committtt on Asbtsto, vol I, HMSO, London, Enai, 1979 7. LIDDELL FOK, McDoNALD JC, THOMAS DC: Methods of cohort analysis: appraisal by application to asbestos mining. J R Stat Soc 1977: 140 (series A): 469-491 8. BURY G: Dose-response in case-control studies. J Epidtmlol Com- mun Med 1980: 34: 217-222 9. ZIELHUIS RL: Public Health Rlsk.s of Expourt to A.be>tos. Report of a Working Group of Ex,.rt Prtpared for tht Commlulon of the EuropltJII CommunltiiS, Director-General lor Socilll A./fairs. Health and SaftY Dirtctorate, Perpmon, Oxford, 1977 I0. G LOAG 0 : Asbestos - c:an II be used safely? Br M d J 1981 ; 282: 5S 1-5S3 . II. McDoNALD JC: Asbestos-related disease: an epidemiolotlical review. In WAGNER JC (ed): Biolol{ical E/fecu of Mlnual Flbru, lARC sci pub! no 30, Inti Asency for Research on Cancer, Lyon, France, 1980: S87~1 12. MCDONALD AD. McDoNALD JC, POOLEY FD: Mineral fibre content of mesothelial tumoun in North America. In W.u.TON WH, CUTcH- LOW A (eds): lnhaltd Partlcl V, Perpmon, Oxford (in press) 13. RUBINO GF, PIOLATTO G, NEWHOUSE ML, ScANSETI't G, AaiSINI GA. MUUAY R: Mortality of chrysolile asbestos workers at lhe Balangero Mine. Northern llaly. Br J lnd Mtd 1979; 36: 187-194 . 14. JoNES JSP, PooLEY FD, SAWLE GV, MADEL RJ, HAOOEliWAL A, SMITH l'G, BERRY G, WIGNALL BK: The consequences of exposure to asbestos dust in a wartime ps-IIUI5k factory. In WAGNER IC (ed): Biological Effects of Mlnral Fib.,. !ARC sci pub no 30, Inti Agency for Research on Cancer, Lyon. France, 1980: 637-653 15. MCDoNALD AD, McDONALD JC: Mesothelioma after crocidolite ex posure during gas mask tnanufacture. Environ R~s 1978; 17: 340-346 238 C:VIA JOURNAL/ AUGUST !, !981/VOL. 125 J \ FMSI 05519 '( ? l. 16. Hoaas MST. WooDWARD ST, MUllPHY B. MusK AW, El.DEII JE: The mcidcnce of pneumoconiosis, mesothelioma and otber respiratory cancer in men enaaaed in mining and millina aooidolite in Western Australia. In WAGNER JC (ed): Biological Eflects of Min"al Fibres, IARC sci publ no 30, Inti Aaency for Research on Cancer, Lyon, France, 1980: 6!5-625 17. NEWHOUSE ML: Aobestos in the workplace and the community. Ann Occup Hyg 1973; 16: 97-107 18. SELIKOP!' JJ, HAMMOND EC: Multiple risk !acton in environmental cancer. In FRAUMENI JF Ja (ed): Per~o,.. at High Ri.rk of Cancer: an A.pproGch to Canc~r Etiology and Control. Proceedings of a Conje.,nce, Key BI$CtJyne, FlorlDil, Decemb" 10-12, 1974, Acad Pr, London, Enll, 1975: 467 19. NEWHOUSE ML, GREGORY MM. SHANNON H: E.tioloiY of carcinoma of lhe larynx. In WAONU JC (ed): BiologlctJI Effects of Mineral Fibre. IARC sci publ no 30, Inti Asency for Research on Cancer, Lyon, France, 1980! 687-695 20. SARACCt R: Asbestos and luna cancer: an analysis of the epidemiological evidence on the asbestossmokina interaction. Inti J CGnc~r 1977; 20: 323-331 21. HAMMOND EC, SELltcOFF 1J, SEIDMAN H: Asbestos exposure, ciprette smoking and death rates. Ann NY Acad Sci 1979; 330: 47.3490 22. Pno R: Distorting the epidemiolOJY of cancer: tbe need for a more balanced view. Natur. 1980; 214: 297-3011 23. LIDDELL FD, McDoNALD JC; Radiological findings as predicton of mortality in Quebec asbestos worken. Br I 1nd Med 1980; 37: 257267 24. BERRY G: The prognosis followinl certification with asbestolis in the United Kingdom. In WAOND JC (ed): Blolorlcal Eflects oJ Mineral Fibres, IARC sc:i publ no 30, Inti Aleftcy for Research on Cancer, Lyon, France, 1980: 603-608 25. PTo J : Lung cancer mortality in relation to measured levels in an asbestos textile factory. Ibid: 829-836 26. 8VJtON JC, HODiiSON AA, HOLMIIS S: A dull suney carried out in buildings incorporating asbestos-based materials in tbeir construction. Ann Occup Hyg 1969; 12: 141-145 27. MtLLI!R K.: The in vivo effects of J1us fibres on alveolar macro phage membrane cbaracteriltics. In WAGHBI JC (ed): BlolotJical E/lecu oj Mineral Flbns, IARC sci publ no 30, Inti Agency for Research on Cancer, Lyon, France, 1980: 459-<465 College of Family Physicians of Canada's position on family medicine. certification DONALD I. RICE,* MD I am hesitant to comme on the views expressed in the editorial by Conn and c leagues, of the Canadian Federation of Medical Stude s (CFMS), on family medicine Certification,I given tO risk Of further aggraV,ating the serious level of em onalism that has already developed over the decision the College of Family Physicians of Canada (CFPC) enforce its long-standing policy of limiting practice igibility to sit its certification examination in family family physicians who graduated prior to I one might have anticipated. the undergraduate s ent hody a;; represented by the CF\tS is particular!:- se tive to this issue. I would be less than responsible, however, if I permitted a number of the statements made in Conn and colleagues' editorial to go unchallenged. Since the CFPC and myself, as the college's chief executive officer, appear to be the authors' main focus for attention. I want to share with the readers of the Journal several observations, in the hope that a more balanced perspective may be provided as to what the policy of the CFPC on practice eligibility is all about. The following claims represent the major thrust, as I interpret it, of their editorial. Claim I . The College of General Practice of Canada, now the College of Family Physicians of'Canada, was established by the Canadian Medical Association (CMA) in 1954, and was provided with a mandate as set out in the original objectives of the college. Response: True. The CFPC, like the Royal College of Physicians and Surgeons of Canada, the Canadian Executive director. College of Family Physicians of Canada Reprint requests to: Dr. Donald I. Rice. Executive director. College of Family Physicians of Canada, 4000 Leslie St.. \Villowdale. Ont. M2K 2R9 Cancer Society, the Canadian Council on Hospital Accreditation and a number of other national associations, was established by the CMA. The cFPC is proud of this heritage and co.ntinues its close association with the CMA as an affiliate member. Like other national associations. established by the CMA the CFPC is an independent, autonomous body, incorporated by an act of Parliament, that is free to establish its policies within the framework of its act of incorporation. Claim 2. Over a period of 25 years the CFPC has digressed from its original objectives. which. in the words used by Conn and colleagues, represents a "clear violation of the second proviso set out by the MA in 1954". They provide two examples: (a) the p otion of graduate (residency) training in family med e and (b) involvement in economics and politics. They 'nt out in particular that the CFPC has somehow pe ed a disservice to Canadian medicine and to the Cana an public by creating a two-tier systemcertificated a noncertificated family physicians. Response: T and false. The CFPC takes pride in the knowledge tha 'ts policy has changed significantly since its inception years ago, in response to the changing needs of fam physicians and the Canadian public for the services pr . ided by family doctors. The decision to establish resid cy training programs in family medicine was made b ractising family physicians who, on the basis of eir own experience, acknowledged that a period of un rgraduate training and an internship were inadequat family practice. The CFPC is concerned and involve ith large-E economics and Iarge-P politics within the amework of doing those things necessary to maintain a ttractive practice climate for its members. This inter stopped short of involvement in the nitty gritty of and how much a family physician should be paid a CMA JOURNAL/AUGUST 1. 1981/VOL. 125 FMSI 05520 !NP'Tl 1TF Oft OCCUPA J : AND Eh''' -- W.1!:NTAL HE.0 _. ;,, mTREAL., CANA.J, ThunL~. 1981,36,241-244 5511 Code 0 1 9 90 81 Editorial Asbestos and public health The highly c:omplex health eff=tS of asbestos have possible that chrysotile may not penetrate deeply and been the subject of many symposia and publications that those fibres which are initially retained become over the last two dec:1des. The Health and Safety susceptible to the system of natural elimination Commission's Advisory Committee on Asbestos including dissolution. Amphiboles. on the other hand, produc:d itS final report 1 late in 1979; in a second may penetrate quite deeply. and their relative volume (ofcommissioned papers), there is an excellent indestructibility seems to l.:a.d to retention more or review by Acheson and Gardner of the IllEff'ects of less indefinitely. Whatever the mechanisms. it seems Asbestos on Health.~ More recently, McDonald's that, on average and where exposures are similar, team has published the latest report of mortaliy in a very large cohort of Quebec miners and millers.~ and the proceedinp of '1 symposium held at the (WHO) International Age-.r.y for Resea"Ch an Canc:u, in co'1siderably less <:hrysotile than amphibole is found in !he lung post mortem.' s If these beliefs are wellfounded, it is clear that, compared with ch~otile, the amphiboles have substantially gre:1ter potential Lyon. in September 1979, have now appeared. At for causing ill effects. the September 1980 British Oc:cupational Hygiene Also important is that, with all asbestos-related Society's Symposium an Inhaled Particles, all but disease, thc:re is a delay, usually of several decades, one of the asbestos papers fitted and helped to fill out between first exposure to respircible fibres and the the pattern. The findings from the last werec:ompletely onset of symptoms. Thus. today's cases are not out of line with anything that has aone before; so attributable to present conditions. but to those of 40 much so that reasonable scientists must await careful or more years ago. Meanwhile new cases can arise evaluation before allowing thi, paper' to inftuence several decades after cessation of exposure. It is also judgement based on scores of well-authenticued clear that it could talc.e up to half a century before reports. With this single exception. matters have there would be any serious possibility of discovering become sufficiently clear that reasonable synthesis whether c:ontrol had been satisfactory and perhaps a seems possible. This editorial dr:1ws freely on many like period before the appearance of a new hanrd. sources but. to keep within reasonable limits. it In no study in man is it possible to measure the dose concentrates largely on mortality in relation to -that is. the amount of dust reaching or better, asbestos exposure, with especial reference to death retained in. the target organ. At best. measurements from lung cancer. Morbidity is given less weight can be made of the fibre concentrations in the air because of rhe areater difficulties of diagnosis and close to that inspired by individual workers. Personal attribution, particularly bearing in mind the intu- samplers are now in use. but in the past only assess- actions with smoking. In view of the recent editorial. d mesotheliomas are reviewed only cursorily. The bulk of the Westem World's asbestos is "chrysotile." a magnestum silicate mined mainly in Quebec; the remainder consisrs of the so-called ments in the general area of the work plac: were possible, and even these have been available in very few studies. With such measurements, linked to work histories, it is possible to assess roughly the exposure experienced by each worker in certain periods. and "amphiboles." ferrous and ferric silicates-almost this may be a reasonably satisfactory index of dose. entirely crocidolite and amosite-both now produced Without such measurements, the only available only in South Africa. Russia produces almost as surrogate is duration of eltposurc; this has been used much chrysotile as the rest of the world. mainly for in most studies, but is obviously less than satisfa..:tory "home" consumption. but no amphibole. and. indeed, of dubious validity. It is now thought that the dimensions of retained If on I) for the difficulties just mentioned, there can fibres in the lung ..are more important in carcino- be no ideal epidemiological study. The best have been genesis rhan their chemical composition, while rhe in occupational settings and that of Quebec chrysotile processes of inhalation. elimination. and retention prod~cticn workers3 has many advantages o\er most. also seem to depend on physical characteristi.;s. ft is A large birth cohort of 10 939 males and +W females Addlftl far reonnc rten~CSla: Profeuor 0 Liddell. O.parcmenc "'' Eou1emaotoo and Heah.h. ~~~Gill Unvnuy, 377:5 L'nivenuy Streel. ~onuul, QIMbec. Conacla HJA ~84. who worked at least a month in the industry, some as early as 1904, was followed to the end ot' !975; only Z~,~of those known to be alive in 1936 were untra~ :!41 FMSI 05521 242 and there had been nearly 4500 deaths. Estimates of been reported, and their findings are all difficult to respirable dust concentrations. job by job. were interpret: they are not incompatible with risks higher obtained to cover the relevant periods of exposure. than in mining and milling. but much less than with and smoking histories were obtained for almost all the amphiboles (e."tcept in reference 5). The risk of men alive in 1950. The data have been analysed by lung cancer in pure c;rocidolite exposure was much different methods. and the results have been consist higher in Nottinaham.11 Eastern Canada. 1' and ent. 10 The inclusion of those with very short employ- Western Australia.19 and some of the. highest risks ment led to a very wide range of accumulated dust were in amphibole-rich miltturcs. :n 21 exposure-the summation. job by job. of dust Gastrointestinal cancers appear to be asbestos- concentration multiplied by years in the job. This associated only in certain circumstances, so that some overcame some of the problems of selection and other aetiological factor may also be involved.t4 survival that arise when a study group is defined in Cancer of the larynx was clearly unrelated to asbestos terms of long employment, or employment at a exposure in Quebec3 and in London, 12 but has been particular time, as has been usual in other studies. associated with asbestos, probably amphibole. in a The advantage of having suc:h a wide range of few other studies. z Fortunately, the tumour is rare exposures is that it allows study of the shape of the and even if there is an enhanced risk from asbestos exposure-response relationship; in Quebec for lung exposure. the absolute effect on total mortality is cancer it was effectively linear.3' 11 Results from undoubtedly small. Diagnosis of asbestosis in life is other studies have tended to support such a relation- so difficult (because even the radiologic:al.signs are not ship12 or one that is possibly "sub-linear"-that is, specific and some history of asbestos exposure is steeper for short ~eriods of exposure and more required) that reliable comparisons between fibre shallow for longer periods. 13 Either way, there seems type can only be made where the diagnoses have been no evidence for a threshold or "safe" dose. The made by the same team. Diagnosis of asbestosis at implications of this are important. death is inevitably related to awareness and to lt is difficult to make quantitative comparisons compensation procedures. However, what evidence between the health effects of the dilferent types of there is suggests the same. gradient, if perhaps even asbestos fibre. For many purposes. mixtures of less steep, by fibre type.z amphibole and chrysotile have been found satis- Cigarette smoking is an important factor in lung factory from a commercial point of view, and there c:anc:er and cancer of the larynx, but docs not seem to are very few large groups of workers (other than affect the risk of mesothelioma or of gastrointestinal miners and millers) who have been exposed to a cancer. and perhaps not of asbestosis. In the latest single fibre type. Even were single-fibre studies Quebec data on lung c:anc:er.~the slope of the asbestos possible, differences in selection and management exposure-response line appeared to depend on policies. problems over reference populations. and smoking habits. beina steeper for non-smokers than the almost certain lack of information on dust for definite smokers; other data seem to fit the concentrations. all militate against reliability of multiplicative model better. 23 u However, from the comparison. ln mixed-fibre studies, where groups of Quebec data it is clear, whatever the model. that workers have been distinguished by exposure to a today's control limits for occupational exposure to single fibre, the above factors should be standardised. chrysotile arc equivalent in carcinogenic: potency to However, the classification by fibre type may ha,e very light smoking-that is, only three or four been imperfect (or there may have been contami cigarettes smoked each week. nation), and numbers have tended to be rather small. Bearing in mind the lag period. it is important to The findings from most studies to date appear to consider findings in men with low exposures to support the hypothesis of a "fibre gradient", such chrysotile. In analysis of the Quebec data on lung that crocidolite has much the most severe health cancer up to the end of 1973, it was reportc=d that no effects, and chrysotile the least, with amosite some- excess was detectable (at anything approaching a where in between. This is compatible with the beliefs conventional level of statistical significance) where expressed in the third paragraph of this editorial, and eJtposure was less than a certain amount. based on the the gradient seems to exist with all health hazards. integration over time of a concentration of respirdble For mesothelioma. the gradient is undoubted, and is asbestos dust. This is equivalent to saying that ion almost certainly steeper for this outcome than for any the linear hypothesis and with a Cllnser\'at ive fibre/dust other.u u conversion ratio) in a 50-year working lifetime. in As to lung cancer, the gradient still exists although concentrations below about 20 respirable fibres per it is probably not quite so steep. Chrysotile production millilitre of air (ie 20 f/ml), nocxcess could have been has yielded a comparatively mild excess. 3 14 Only a detected with any confidence. The proposed control handful of small studies in chrysotile processing have limit1 for occupational exposure to asbestos is of a FMSI 05522 .._..___..____________________________________ 243 concentrallon of I f/ml. or one-twentieth that indicated in parentheses above. At Rochdale (where the fibre was mainly chrysotile but where there was probably significant use of crocidolite even into the I960sl. no relationship was found-in those who had entered the industry after 195 !-between lung cancer and exposure up to the equivalent of 8 fiml for .SO years.: Other low e;'(posures have occurred in nonoccupational settings; it is difficult to see how concentrations can have been severe enough for long enough for them to have been a serious hazard in the past. except when: then: was domestic contact with asbestos workers. Over the ne:ott decade or longer, mon: cases of asbestos-related disease will undoubtedly appearbut they will be the result of working conditions 30--<0 years before their appearance. However. conditions have generally been improving for at least two decades. and it is possible that we :lre already over the worst of the pathological effects, despite some questionable forecasts informally, but widely, circulated in. the USA.~ Should any cases arise from today'5 levels of exposure they will not be seen until well into the twenty-first century. The latest UK government regulations limiting occupational exposure to chrysotile to I f/ml from 1981 do not. of course. guamntee absolute safety. Even if it were assumed that there had been no crocidolite at the Rochdale factory, and putting a 'ery gloomy interpretation on the lindiniS then:. 50 years continuous exposure to the upper limit allowed by the: regulations would lead to I 25 ~~ excess mortality from lung cancer, or about 012.5 ~.;; O\'erall e:otcess. z Crocidolite is, of course, subject to much more stringent regulations-no more imports and especial care in any necessary processing or handling. As amosite is an amphibole. and as evidence against it is accumulating, it would seem sensible to tre:lt it on the same lines as crocidolite. One reason is that chrystotile c:1n. perhaps with some ingenuity, often be used instead. although there will remain specific problems such as the production of large-diameter pressure pipes. Non-occupational exposures to asbestos mav cominue because: of demolition or damage to certain building materials, particularly those used for insulation where the materials often contained amphiboles. Then: is no doubt that any exposure to respirable asbestos is to b: avoided wherever possible. and strict precautionary measures durng repair or replacement are clearly indic:lted. Nevertheless. great care must be exercised that the hazards during such operations are no worse than those ari~ing "naturaily"-that is. from leaving the asbe:nos in situ. It is also important to note that the peak figure identified in a survey:7 of buildings containing asbestos materials in the UK was only 008 f/ml (one-twelfth of the proposed control limit for occupational exposure); however. it is agreed that more information is required "about asbestos levels in new and old buildings in relation to type and usage of asbestos-containing materials. particularly insulation materials."1 No ill effects have yet been demonstrated of asbestos in drinking water, in food and beverages or in the general atmosphere. Indeed, the pollution of the air around Thetford Mines, by far the dustier of the two mining areas in Quebec. was for many decades quite severe. but then: was no evidence that excess asbestos-related mortality or morbidity in the general population could not be attributed to occupational exposure. A final point must be made about substitutes for asbestos. Some adequate substitutes exist which do not resemble asbestos; where they do. it should be borne in mind that the better a substitute mimics the physical and chemical properties of asbestos the closer the ill esTects on health an: likely to be. Indeed. there is animal evidencell that glass fibre of the same dimensions as crocidolite has biological effects at least as serious as those of the :lmphibole. ft must also be emphasised that at least 30 years' e.~posure of a large group of workers would be required to ..test" any substitute. and even then it would not be possible to demonstrate that it wa.~ ..safe." OOUOt.AS LIDDELL Deparfmnrt of Epiclemiolugy and Health MnJi/1 Uni11ersity, ,'vfontrea/, Quebec, CanadD Refernces He:lith and Safety Commission. AsMstos Volume I: ji11ol reporr !Jf the advisory committee. London: HMSO, 1979. 2 Acheson ED. Gardner MJ. The ill-effects of asbestos on health. In: Haith and Safety Commission. As!wsro.r Volum~ :Z: paf"r.f prepared for th adYisory committ~~- London: HMSO t979: 7-83. 3 McDonald JC. Liddell FDK. Gibbs GW, Eyssen GE. ~eDonald AD. Dust C:OCJ'OSUTC :md mortality in chrysotile mining, 191o-75. lk J !Ire/ Mtd 1980; 3'7: I1-24. 4 Wagner JC Ed. Biological Effer-ts of .Wineral Fibres: Pror:redings a( a Symf"'sium organistd hy lA RC. tlrt French Nario11ol /n.<rimte of Hralrlr and M~clir:al R~search and tht fl.ftdical Research Co11ncil, Prnarth, (j K. lrrld at the lnr~rnariuna/ Agency for Rtsearc/r un Canr:tr. L}'OII. Franct, :Z5-:Z7 Septemher 1979. !ARC Scientific Publication no 30. Lyon: IARC. 19110. ncmcnt JM. ll:arri~ RL. Jr, Symons MJ, Shy C. Estimates of Jt,:-rt:~l"llnse for respiratory can.:1:r among chrysolllc asbestos textile worken. lu: FMSI 05523 ( 244 Walton WH, Crilchlow A c:ds. lnltttkd Particlf's V. O;~~ford: Pet'pmon Pres.,, 1981. 6 Elmes PC. Mesotheliomas. minerals, and man-made mineral fibres. TTrorax 1980~ 35: 561-l. 7 Gibbs GW. ~rsonal communication. 1980. 8 Rowlands N, Gibbs GW, McDonald AD. As~tos fibres in the lunas or c:hrysotile miners and millc:rs: a preliminary repon.ln: Walton WH, Critchlow A c:ds. lnllfllf'd Particlts V. Oxford: Perpmon Pres.,, 1981. 9 Uddell FDK. McDonald JC. Thomas DC. Methods of cohon analysis: appraisal by application to asbestos minina. J R Stat Soc 1977; Series A 140: 469-91. 10 McDonald JC. Liddell FDK. Monality in Canadian miners and millen aposed to chrysotile. Ann NY AC'ad Sci 1979; 330: 1-10. II Berry G. Dose-response in. case-control studies. J Epidtmiol Commun Mtd 1980~ 34:217-22. 12. Henderson VL.. Enterline PE. Asbestos e:'lposure: factors associated with excess cancer and respiratory disease monality. A"" NY Aclld Sci 1979: 330: 117-26. 13 Seidman H. Lilis R. SclikotT IJ. Shon-tcnn asbestos exposureanddelayedcancerrisk.ln: Nicbcras HEed. Pruditlfll of T11ird lnttrmniollfli S)mposillm on Dtttion and Prnrntion of CtllfUF', Ptll't /, Vol 7. New York: MIU'Qil Dekker, 1979: 94~. 14 McDonald JC. Asbestos-related disease: an ~iolotical review. In: Waper JC ed. Biol,;t:oJ Eifts ofMiMrtll Rbrtll: PrtJCftditlfll ofa SymposiUiff orpninrl by /ARC, tlw F~h Nt11ionol fiVIitulf' of Htalth tmd MtdiroJ RtHIIrf'h and the MtdlcoJ Rt:s~h CouiK'il, Pt11flrth, UK. iltld at rht /nttr- llatiollfll Atttlff'yfor Rnnrr-!1 on CaiK'n-,l.yon. Fr(llf('tt, 2S-Z7 Stpt~ /979, IAR.C Scientiftc Publication no 30. Lyon: IARC. 1980:1:587-601. orIS McDonald AD. McDonald JC, Pooley FD. Mineral fibre content mesothelial rumours in North America. In: Wallon WH, Critchlow A eels. /1rha/td Partff'lts V. Oxford: Perpmon Press. 1981. 16 Rubino GF, Piolatto G. Newhouse M L. Scansetti G. Aresini GA Murray R. Mortality of chrysotile <~sbc:stos workers at rhe Balanacro Mine, Nonhern Italy. Br J /ndl Mtd 1979: 36: 187-94. 17 Jones JSP, Smith PG, Pooley FD '' a/. The consequences or UJ!OSUre to asbestos dust in a wanime gas-mask factory. In: Waaner JC ed. BiolotriC"ai Efff'f'ts of Mintr'tll Fibrt:s: Prof'ttdilrtrs of a Sp,_ po:sium orpni:std by lA RC, rlw rrtnC"h Nationt~l /nstitutt of Hf'olth and M~iC'oJ Rf'stardt and tht Mf'diC'al Rf':srt~rC'h Coull('(/, /'t'narth, UK, lrrlcl at tht lntf't'tl4tional Af(t"nC'.I' for Rr~rarrlr nn C"<mrrr, L.l'"" Fratl('f', ZS-27Sr(ltrnthc-r 1979. !ARC Sc:icntiflC !'ublic:uion no 30. Lyon: IARC. 1980"; Z:637-S3. 18 McDonalci AD. McDonald JC. Mesothcliom:a after croc:iciolite exposure durin& gas mask manufacture. EJI\'irolf Rts 1978: 17: 340-6. 19 Hobbs MST, Woodward SO. Murphy B. Musk AW, Elder JE. The incidenca of pneumonoc:Qniosis, . . mesothelioma and other respiratory cancer in men cnaa;ccl in minina and millina crocidolite in Western Australia. 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