Document ZDJKKLGm2E4YaVYwB0k5QEMV

, ... 1 _ _ _ _. . . . . . _ . . _ ' - - - - - - - - - - - - - - - - - -. . . . . . . _ . _ . . , _ _ _ _ _ _ p _ _ . . . _ _ . _ , _ _ . . . . . _ ..... -~-----------...._ _ _ _ - -.. .... - ASBEsros I~TERNAT'IONAL AssocrATroJAN 31980 (Limited by Guaranh:e) 68 GLOUCI~STf:R l'I.ACl-:, LONDON \VrH 3HL, El'\Gl..AND Tclcplwue: 01-1&6 :;;:;-~8/9 Tcleer;um; lntag l..<mdon Tcbc:r~!IB58 lNTA G copies to: Nember Associations Executive Committee Members }f.AP }!embers DMAP Members . .. CAP Members : Chairman of ScAP . : WITH CQ}iPLIMENTS ).-~,D .' ~ -... . .. .~ : . .' . ..,.... .... ,I .-' ! '. . . ... :~ : . ..: Enclosed is a report by Dr. Kevin Browne on the medical evidence presented to the Advisory Committee on Asbestos, whose report was recently published. 1(} December 1979 ,. .. __--~-.,__.,. l>irtclnn: Mr. E. v.on tier Rc~t (B~I:;i,.. n); Dr. R. Gaze; Sir 1.'\cville St:ock (Sct.:r(':l!.r'}'} lleg. no. 39245-f. E.lgl.md llrJ;i\tered ol!ic:e. ;n above .............. ........... '''1~--- ~-......... ----.Aioooo...... f'"0"-,1-0H .. .,_....._,, ,.,._,.,_.,__ _ _ _ _ _ _ ..-- . ~--- FMSI 05573 .' FMSI 05574 ' t} . .. -- --- ---- . ..~- :...: ... .... ~ ........... ;: ..... -~-........ 'I ... - 0 - _ ................. -- .................. _ . . . . . . . . . . . . . . . - . : . ; . . _ _ - - . . - - . . . . . . . . . . . . . . . . . . . . . . . . - - .. . .I ' 7/.' :.:\.:_ --I~,-- ---. . 114 Park Street london W1 Y 4AB Telephone 01-IHl!> 6022 Telex jll,ll1 Telegrams Incorrupt london Reg. no. ~0203C Enwlond Reo;~1~rod olfoce u aboY& Sir Neville Stack, Asbestos International Association, 68, Gloucester Place, LONDON, HlH 3LH 5th December 1979 Dear Sir Neville,~ .' , For ~i-rcula tion to the l'A.AP and to t~e Nember Companies of the AIA I enclose an excellent synopsis produced by Dr. Kevin Browne on the medical evidence presented to the Advisory Committee on Asbestos whose report was recently published in the U.K. I feel that this report cannot be improved upon.. I would only add to Dr. Browne 1 s final paragraph the ~aveat that we are likely to be faced with some of the biological effects of inhalation of asbe~tos dust for many years after the use of asbestos has either been closely controlled or eliminated. So great is the latent period between exposure and disease that many years must elapse before Dr. Brov.ne's expectations nre fulfilled. Yours sincerely, ,' Dr. W.J.. Smither Enc. cc. Dr. Kevin Browne ., ;. ..,. ,......_;~----...-:----- . ':\,::-~::\ ... - ... - -~ ...~ . . . . . . . . , l.,, ,I,,.'( :' ~:;~ ~.::~ .. . } ~.. ' .. ,\ : " t ~. ~ -~'".......... .,...... ............. ....... -t'" , _... .. :.. - - - - - : - - - ... ----- , - ..... - FMSI 05575 FMSl 05576 j ...........- .. ~--....---"''-"'..............,........,_..,.....-.!. ........_ \. '\. \ ~~. "TBE ...............__.. _ ._____....~.........- ........ _ .._,......._........ __...... - - - - - - - - --..-------- ...... -- -- JLL F.FFECTS OF ASBESTOS ON HEAI.Tll" .. The Advisory Con~itee on Asbestos asked Professor Acheson, one of its members, to provide a review of the available scientific evidence on the ill effects of asbestos in man, toeether with n critical corrunentnry. His review appears under the above title and in fact constitutes more than half of the total report. Asbestosis, Mesothelioma and Lung Cancer Asbestosis is defined as fibrosis or scarring of the lungs to such an extent as to interfere with their ability to function normally. Three points are made; firstly that there is a wide range of individual susceptibility, secondly that there is a time lag of several years before any ill effects appear, and thi.rdly, in a proportion of patients asbestosis progresses even if the employee leaves the industry. Mesothelioma is a very rare type of.cancer whichhas been known for more than two hundred years, and which is often very difficult to diagnose with any certainty. While about one person in four in this country dies of cancer nowadays, only one in every two thousand dies of mesothelioma. Of these, p(::rliaps four fifths occur in people who have at some stage in their lives been in close contact with asbestos, uhile 'for the remaining one fifth, as with so many cancers, no reason can be found. Because of the long time lag bet.;een first exposure and the appearance of tl1e tumour - forty years is mentioned as an average interval - the incidence of mesothelioma is still rising ( there were about 300 cases in this country in 1977) and the peak is not expected to be reached until the 1980's or perhaps even later. Lung cancer is accepted as occurring more often in asbestos workers tnan in the general population, although as the report states, because lung cancer is so cornmonin the population as a whole, individual cases related to asbestos exposure are almost impossible to recognise with certainty. But the part played by smoking is very important. The question whether a non..:. smoking ashes tos worker is more liable to develop lung cancer than a non-smoker elsew11ere is still not settled. But all the series studied are in agrcement that if there is a risk it is exceedingly STT13ll - one estimate quoted. suggests that a non-smoking worker exposed to 1 fibre/cc of chrysot.ile all his working life ran the same risk as he would if.he smoked three quarters of a cigarette per weel~. For smokers, l1owever, the risk is appreciably increased at the sort of exposure level which prevailed 20 years ago, and estima t.es varying between two and eight tin,es the risk for smoking non-asbestos workers l>re quoted. Crocidolite. Arnosite or Chrysotile In tl1e USA, it Js g"nerally held that there is not much to choose between t.he three types of fibre in terms of their harmful effects, and the report draws attention to this fact. Continued --~--~:-.::-.:.:::-..:.--.-.--.-. -------.:-::--~: :.. ~ ......,..........,......::: ........;..,,..;_, ~ ..... "''~- .. ---.....,:.;: ... : .......::...:::.;_:.:..:.,--- .::~-= ..:;.....:..:..- :~; ::~:-~ ~..,;.': ..__... :.:. --... ~_,_.... _.. _ _.__ FMSI 05577 FMSI 05578 . ... . .. j -.. _.... _............ ------ -. ------ _----,_u_, .. , ..........__ ......,..,... _ ..,.... 0 .......--,;.-----', ~ t' ... .' 2 ..-~.-.---- --~"' --- .. ...... .. In this country, on the otl1er hand, crocidolite has for 10 years Leen rer;arded more ndver!>cly, nnd the report r:ivcs much.nttention to evidence distinguishin~ between the effects of the three types. A t~1hlc sets out mortality .figures from nll the important publif;}ud studies <md relates them to the fibre types usc>d in the industries to which they relate for nshestosis. Profcs5or Acheson interprets them ns SU[~gcsting that chrysotile may be tl1e least harmful, crocidolite the most harmful and amosite in between, but he . points out that differences in the qu~mtity of dust inhaled m?y render these comparisons invalid. On cq~ally uncertain eviderlce the same ranking is given for the relative risk of inducing lung cancer. For mesothelioma, however, the evidence is mu.ch stronger. The first major paper linking asbestos with mesothelioma was b~sed on observations on crocidolite miners in Cape Province. The;crocidolite miners in Uestern Australia also produced a high proportion of m_~sothelioma cases, as did gas mask assemblers both in this country (at Nottingham) and in Canada who worked wi.th crocidolite filters. By contrast a search for mesothelioma cases at the Rhodesian chrysotil~ mines was unsuccessful; the same was true of the Ural mines, and among Canadian chrysotile miners less than one death in a thousand was attributable to mesothelioma. Tn manufacturing also mesothelioma seems rarer among, chrysotile Horb.:rs; a study is quoted of 20,000 T & N workers at Rochdale who entered after 1933, and among whom 10 mesothelioma cases were found - and even here some crocidolite had been used, raising the possibility that it could be responsible for the cases which occurred. The greatest question-mark hangs over amosite. A thorough attempt to find cases of mesothel:i.o;na linked with the Tnmsvaal amosi te mines re~ealed only 4, co;npared with 83 from the Cape crocidoli te mines, a fact which Professor Acheson regards as 'truly remarkable' especially as up to 1951 more amosite than c.rocidolite had been mined. The only strong evidence against amosite comes from Selikoff's study of the New Jersey factory where among men employed during wartime 2% had died of mesothelioma by 1973. The conditions in this factory were known to be extremely bad, and there is a faint possibility that some crocidolite was also used. In most other studies of workers in manufacturing and insulation, exposure l-:as to at least t:"..;ro or all three of the fibres. Selikoff is quoted as saying that only chrysotile was used up to 1930 in the USA and cluring the 30s only a little amosite and almost no crocidolite was imported; on the basis of a further assumption about the greater use of amosite in shipbuilding he has produced figures purporting to show that the risk of mesothelioma is the same whether insulators use amosite or chrysotile. Professor Acheson :i.s clearly reluctant . to take these at their face value. He also raises the possibility, for \.l'hich there is some Sllpport in the various studies, th~ t mixtures of fibres may carry more risk thau ex~osure to one type alone. Fibre Size and Dose Response The fate is discussed of fibres after they have been inhaled. Only fibres shorter than 200,u and thinner than 3p dia1neter are thought to penetrate to the depths of the lungs, and the normal clear;~.nce mechanism of the lungs appenrs to be nble to dispose of fibres shorter than lOp. ..:,.. Continued -------------------- -,-..-........~ ....:.-.....- - .--.t.~ ...........~ ................. - ........ ,. .......,..._.........~, ........ , .... - .............,....._,........_ ....... -- FMSl 05579 FMS\ 05580 '..' . . . . 4 __ , . . _ , , , . o.:J00--.1 - - .......... , ... _ _ ...... h - 0 " " - ' ~ " ' ,,,,..,._ " '' ' ' " . - I. , .. - - .. ~. -~, .. .... r.. : . . ,.... '~ ~ -~ r..!" j'i:;j j',~-i7i'.",.....,..--'*-----..--.. -.- .................. _-........._......--...-.' .- ..........,... - ----.. - ... ~ 6 ... .. .\ _ --........... ...,_.............. !. Tnking si!okin'g first, a,lthough this is tuentioned briefly in connection \Ji't~thth,gl c;tnceX1, its. inflttellcc on the cJeveloptnent of asbestosis is ir,norc<l,m~d the major 'part it plays in the c<~usation of these two dlsca~;c!S is not at nll. given the emphasis it deserves. On the second point, the :thst>nce of' a threshold for the close-response to chry:;oli.lc is tn<ntioned 'within tlw range experienced in industry'. But: this is the one vital issue l-lhich ha.s not been faced; the dust ran~e experienced in the industry in the 50's and 60's, on which the statistics ~f asbestos related disease are based, were probably bet'l-1een 10 and 1,000 times those to be fotjnd in the last 10 yt>a.,rs. It is true that much space was.devoted to dose response and the possibility of a threshold dose, but estimates -were still rnade of alow dose effects based on high dose experience, and real examination. of the evidence for the lungs' capabilities for clenring and the consequences of overloading \Jas passed over .\ ~.- ' ' r Yet ~sbestosis has never been recorded with the minimal exposure found in the environment (as would be expected on the no-threshold calculation). There is a strong suggestion from the figures that much of the disease over which there is uncertainty, such as stomach cancer, only arises when there is mas6ive exposure by comparison w~th modern experience. We know too that lung cancer becomes common in another type of sev~re lung fibrosis unconnected with asbestos but implying that at a certain. stage a qualitative change may take place in the body's defences. This is also in keeping with \Jhat we kno~ about the way the body's defences - the immune system - react. The system itself is extremely complex, but the analogy "'ith a rnateri<1l which is stressed to breaking point is still applicable~ With all this in mi~d, .anc bette::- evidence O'f- true d'ose exposure fre,u; e-lectron mir.xo-sc:::pe- st~die-5, ~~~ c:ru reasonably Ehpect'" t"hat"" n10oern control limits will relegate asbestos-related disease altogether to the past. * * * * * * * ........._. __ , ......... _ . . _ ....... _ ..., .. - .._ . . . . . . . . . . ." . - - -... ---~--. . - - . . . . . . . . . . . . . . . . . . . . . , _ _ _ ..,. _ _ _ _ 4 _ _ _ . _ _.,_ .........- . - ............ , . . , . FMSI 05581 ... ... .. .. FMSI 05582 . - ....... -- --.-- ..-- ----- - - ___..'-\ --~ , .' .........................-~-- ............. 5 ......~-------- ............ ...... ..... ......._._..... ... - .. t SirnUttrly a lung cancer risk is considered unlik(~ly in ordinnry . circumstances. 11w mesothelioma risk is dealt with in more dctoil owing to reports wl1ich nrise frorn time to time that it hns occurred followi.ne extremely brief exposure. There nrc 'certainly a small ntJnher of cases attributable to do1nestic exposure dating from the d.1ys \.JhE!n wives h1:ushed the dust off their husb;md 's overalls, and there doE!s seem to have been a higher incidence in the neighbourhood of shipyards, perhaps for the same reason~ But it is concluded caut~ously that with .modern practice no danger exists. Asbestos fibres have also bccn.found in drinking wate~ and manufactured food and drink. The main' c~idence on which any conclusion can be based comes from Duluth~ on the ba1iks of Lake Superior, where the water supply was contaminated with waste asbestos fibres dumped in the lake. No excess of cancer deaths has been found. Similarly, animal experiments in ;.;hich quantities of asbestos were' eaten did not suggest any harmful effect. Conclusion The advisory committee's final recommendations are based closely on the conclusions of Professor Acheson's report, and do not need to be repeated here. But it is worth setting down the basis on which his figure was arrived at. He points out that in the case of occupational exposure in ionising radiation a health standard has been set (5 rcms per year) which, if it was reached annually for 50 years, it was calculated would lead to an increase i~ cancer mortality in the exposed workers from 207. (the "natural" cancer incidence) to 22~. This is a decision which has been made and lo.'hich has been accepted by society in general both in this country and internationally- If asbestos is accepted as a parallel situation, and -if for chrysotile it is accepted that about half the mortality is due to lung cancer and half to asbestos, a 2% excess mortalit:r (as for ionising radiation) \7ould, on the basis of estimates containing "very considerable uncertainties",'result from fibre levels in the range from 5 to 0.4 fibres per cc. And out of this range he suggests lfibre/cc, nearer the lower end, as an acceptable compromise. .. . -~ .. I' I I I I I Comment i l . _Professo~ Acheson's review was, I believe, s~bstantially completed 'nearly two years ago, and there have been a few minor research developments since then. Tremolite is beginning to be regarded with much more suspicion, occurring as it does as a contaminant of some chrysotile mines, and the high proportion of mesothelioma cases in a Turkish villag~ due to a form of zeolite, a naturally occurring non-asbestos mineral fibre, has given further impetus to research on how this type of tumour is caused. Cancer of the larynx is not now considered to be asbestos-related. As far as asbestos in food and drink is concerned, further careful animal studies have produced no ill effects. And finally the electi-on mircoscope is beginning to make a big impact on studies of the type and quantity of asbestos in the lung, and in analysis of environmental exposure. Dut the two asp<!cts of asbestos-relat.ed disease, over which the report is most deficient have not been changed by new evidence. Tl'lt!sc are the influence of smoking anti changes in industrial practice in this country. ..........., -- .... ,. . . . . . . .-. J.,.--~---- ,_. Cont.inued l ,-.,---,_........ ~ FMS\ 05583 . '. FMSI 05584 ! ... . . ..'I-~ ..,.. ,. .,,...,. ~ -- - - _ _______ --.. .......... - .. .... ..... ......... " ....~-------'""'-- .. ..,_,-.~--- -~ ~ ..... ... _,. ..._.... .. . '4 I 'l11e conun<1'lt is made in the r.eport that there has been n trend :.d.ncc the \.'.'lr to mill cltrysotilc to n greater extent: t.l.wn prcvlou!.ily (for all purposes except asbestos cement), thereby pt-oducing fibres with a SHt:tllcr mean cli.'1ructcr, aud tlt<~t if this were continued the t'cduction is risk associated with chrysotilc rtL:'lY be lost. An im.'ll F.xperi'men ts .Animal experiments have been carried out .since before the war in an attempt to shed more light on asbestos effects in man. It has been found possible to prod~ce lung fibrosis, lung cancer nnd mesothelioma in rats by exposing them to inhalation of asbestos dust. The early experiments encountered the same difiiculties of variations in fibre count and fibre size of different samples, and curr~nt experiments are a tternpting to control these. _./ In these animal inhalation studies chrysotile has shah~ itself consistently to be at least as likely as crocidolite to produce asbestosis, lung cancer and mesotheliomas, while amosite consistently coces off best. Davis' conclusion is quoted that for a given average diameter, samples with the highest proportion of fibres >20 pin length are the most dangerous, and it is suggested again that fibre size rather than type may be the decisive factor. But these experiments have all exposed the animals to massive doses (measured in hundreds or thousands of fibres per ml) and have rais_ed more problems than they have answered. Other Cancer Risks There have ever ~he years been s~veral reports of increased mortality in asbestos workers from cancer of the stomach, bo,.;el, larynx 1 ovary and breast and these are listed and discussed in some detail. Again the results of yarious studies are not cons is tent and again it is Selikoff's series in which the important increases in mortality occur. The report concludes that while the information available is sketchy and other explanations for the figures can be given~ a true increase in cancer of the stomach, bowel and larynx remains a possibility in insulation workers exposed to a mixture of fibres; chrysotire miners and manufacturing workers do not appear to run any extra risk, and evidence oe excess risks for other organs is inconsistent. Environmental Exposure Such measurements as have been made suggest that levels of asbestos fibre in the general atmosphere, even in the dust of cities, are very low - less than one thousandth of the current 2 fibre/ml standard for. industrial workers. Higher concentrations maybe expected inside buildings in which asbestos has been used in the construction. Even here, however, in most circumstances fibre levels were almost always less than one hundredth of the current standard. Higher levels were reported where sprayed asbestos was exposed to wear and tear, and further studies are recommended. Asbestos ~ernent, on the other hand, seems to be associated with even less risk of release of fibre to the environment. Heviewing the evidence for actual health damage, the report considers it unlikely that the public is at risk from asbestosis (ltlthough one or two cases of pleural thickening may have.occurred, tltese arc certainly known to occur in areas in Europe where mineral fibre occurs naturallr in Lhe soil). Con tinu,~d : FMSI 05585 c. FMSI 05586 . ' .. . . :- ... ~---........----'"' ~- --~- --~~ ...- - ______......... ....... 4 ............ - .... --'-- : ....... _ _ ...........- ._.. - - - - - - .......... _ ...... _ - .... - - -.... - ... - - 3 .. , . Experim:nts in which fihrcs of 'varying chemical structure. . length and diameter were injected into the pleural .space outside the lung in nnima ls showed that the degree to which they were capnhlc of producin{; m:~lign.:m t tumours "'as rcla Led to the proportion of fibre!; in the :.;i:t.e rnnr;e 10-80/J with diar.letcrs Jess tlt:tn 7..5Jl. The curious coincidence by \o.'hich the size r:mge of fibre which is aerodynamically nblc to penetrate to the alveoli, the air sacs where blood is oxygenated, is almost identical with that which will produce malignant tumours when implanted in the pleural cavity outside the lungs in animals .is passed over without comment . But attention is dr.:n.;n to the fact that the nbility to produce mesothelior.Ja in animals extends to fibres with diameters as ~ow as .Olp. The ordinary" light microscope will not detect fibres much smaller than -Jp, so that current methods of counting rn.:Jy not provide n good estimate of the levels of potentially dangerous fibres in the environr.1ent. ofA return is made to this point in discussion Pooley's elect:l::on microscope studies of post-mortem lung tissue of Canadian chrysotile miners. He found tremolite in large quantities in the lungs of men diagnosed in life as suffering from asbestosis, and raised the question whether con.tamina tion by tremoli te or other inorganic fibres may not be responsible for some of the disease attributed to chrysotile (or amosite7). It seems certain that the electton microscope will in future have to play a much larger part in fibre counting. The difficulties in establishing a precise ~elationship between the quantity of fibres inhaled and resultant disease are discussed in detail. Dust counts, which in any case do not go back for very many years, were at first carried out on midget impingers and th,=rr:-,al precipi t.ators before the present membrane f i 1 ter came into use on any scale about 10 years ago and each method gives a different type of result. In addition, methods of counting have changed, so that a dust concentration reported as 2fiml in 1968 would now be reported as between 4 and 10 f/rnl. There is good evidence for each of the three asbestos related diseases that, as common-sense \-'ould suggest, the more dust you inhale the more risk you run . But the question whether there is .e. threshold dose, i.e. a dose below which no risk is incurred, is less readily answered. Professor Acheson believes that the balance of probabilities is against L1ere being a threshold dose in each case. Ho~ever, he qualifies this in the case of asbestosis by adding tha.t he believes there is a simple relationship between dose inhaled and risk within the range experienced in industry. This is a very important qualification to which I will ~eturn later. A large number of studies are listed which provide evidence on dose relationship. Almost all are agreed that the relationship exists, but great discrepancies exist between estimates of the size of the risk incurred at any given dose. It is made clear that the dose response depends not only on the fibre count, but the method by which this is measured, the type of fibre, the presence of contuminc-tnts (such as trernolitc), the amount of cigarette smoking (in the case of asbestosis and lung cancer but not mesotheliom:1) and lastly the diameter range of the fibre .. It has been shown th:1t crocidolite from Cape Province where m:my cases of mesothelion~ have been found, is very fine, the size -.!.. rnnge being 0.09-0.Sp, while Transv;-~al Blue, which seems to h:lVe been responsible for fnr fewer cases, has a size rtmge of 0.2-2.5p. :I Continued ...... :. .......---. ----~--~- ....- ..L........... ---..... - ... ,. -. . :......_...:....:..:~--' . -. ;.,...~~-""--':".!' ~-....... -~..,:..;-_-::-: .~ -~ .-: :~-;:;.: : -: -.:-:-: -:-: ~: -...--:. ::.-1 FMSI 05587 ' - - = - - _m_ i~:Nfi!!Ua<*ll!ll!ll ..~ FMSJ 05588