Document MGO20Kmp0ymOo11L4XXwzpgD9

* J ASBESTOS AND HEALTH IN 1969 r -L* i 5< * *---------------------------------------------------------------'AS I . OEORQE W. WRIGHT A5BE5TOS A>D HEALTH L>' 1969`-5 GEORGE W. WRIGHT Although a group of materials referred to g-nerically by the term `asbestos" hive been known and used, to a smell extent, far back in xatiquity, widespread and abundant use of these Sbers did not begin until the last quarter c-: the nineteenth century, with further augmenition of production during the first half of the twentieth century. There are six distinct varieties <: asbestiform fibrous minerals. .Among some of r.ese, there are striking differences in chemical :-d physical composition (1). Most commonly :-sauced is chrysoule, a member of the serr'tntine family. The amphiboles are subdivided .'..-j crocidolite (blue asbestos), amosite, an* t.'-jnhyllite, tremolite, and actinolite. .All are nlic.tes, crystalline in nature, and characteris tically are divisible into very small fibrils. Chrysoti'u and anthophyllite contain much .iii.'.r amounts of magnesium than either crocidolite or amosite, and the last two contain much more iron than the others. The crystalline structure and surface properties, which may be nt importance in the biologic reaction, are also strikingly different among the varieties of libestos (1). In view of the smt variation of hemical and physical properties, it is most un safe to predict that t(ie bioioyic reactions of one y.inctv of asbestos will be mimicked bv anotlier in terms of cither actual consequences or mech anisms. To interpret the biologic actions of 1 From ihe Department of Mi>licin> St. Luke's tiTrw*inl QaMalaasLofan. ~ ' Presented before the Medical .Session, as part of Section SA. at the annual meeting of the .Amen* can Thoracic Society. Miami Beach, Florida. Mnv :s. I960. asbestos, it is imperative that the chancier of the exposure iu terms of concentration, sixe, and types of fibers be known. This sort of data is scant or often nonexistent at present with respect to exposure of humans. - Pulmonary fibrotit: In 1907, Murray (2) re ported the first cases of diffuse pulmonary fibrosis discovered among a group of persons who had experienced substantial and prolonged exposure to respinble-cixed asbestiform fibers. Subsequently, the term^'asbejtosis^ was applied to this reaction. Traditionally, asbestosis has connoted this kind of reaction and its sequelae with regard to altered pulmonary and cardio vascular function. Recently, the term has been corrupted to include such manifestations ti pleural thickening, pleural plaoues, and even tEe simple presence ofifefeirrugi'nous bodies. Resolution of the use of the word asbestosuTtnust be ob tained to bring clarity to scientific reporting. .. Murray's report revealed the paradox of a life saving aggnt possessing the capacity for human harm. At first, the conditions under which this biologic reaction came about seemed to be re stricted to those created during fabrication, conditions limited to textile manufacturing at that time. In 1930, Merewether and Price (3) demonstrated that asbestosis posed a major threat to the health of workers in the asbestos textile trade. It is now known that in any of tlit several trades in which persons experience pro longed exposure to a high concentration of ropinljlc-sizcd asbestiform fiber, it is probable that some of them ultimately will develop pulmonary fibrosis. In response to the report of Merewether and Auentc.\j Rkviiw ov f!K^pta.\Tnr.T Pt*;\.-c, Vui.vsik ton. ItSHi wr iOi CtOriCE w. WRIGHT I'riee^the fabricators of jcb t ns-i-. .n i :i 1111 n 5 products look aut-cantial measures 10 reduce die concentration 01 airborne fibers m the fac tories. The report 01 layers ami Dreesen (4) in ni.J'J further stimulated tlie introduction of such corrective measures, especially in factories of tiie U..5. and in mines and mills of Canada uhere 95 per cent of the free world's asbestos was produced. Regrettably, substantial numbers of persons exposed to asbestos in their occupa tion have never come under a protective occu pational hygiene program. Emulation applicators and some individual or small business fabrica tor* fall into this category. The preventive efforts that were applied led to considerable improvement iq the factories, mills, and mine environments and a subsequent less ening 01 the occurrence and seventy 0^ puf- monarv nbrosu. Unfortunately, the relaxation of precautions governing occupational health, common under the stresses of World War II, seriously interfered with many health protection programs, including that for the safe use of aibestiform fibers. .Vi a result, the protection of workers using asbestos in mining and milling and especially in factory settings has not been as good as it might otherwise have been. Until quite recently, the threshold limit value (TLV) for environments containing as- bcititorm fibers negested tentatively by Sayers 1 ud breesen (4) m has served ns a guide. Data entirely adequate for the purpose were not available in 1930. and it lias taken yean to recog nize this inadequacy and to obtain the informa tion upon which to base a more meaningful TLV. Fortunately, one of the major users of asbestos in the production of textiles end textile products has pursued for many years a program of en vironmental and population monitoring that now provides a more up-to-date experience (5. 0). Thc.-'O studies demonstrate that pulmo nary fibrosis can lie minimized when adequate protective measures are instituted, and rhat the vnccnrrntion of airborne fibers must be tho focal point of attention even though the tcchnnloi.v nf ieh monitoring may he new, difficult, and expensive. The U. S. Public Health Service, which licetn expensive studies into the problems of n-lrf'-n.* anti health in 1901* together with ,vl)e-frn producers and manufacturers in the rb. and Canada are at this time examining 'I'nlW.v. I, I : IVr-on.M communication. their exp-riciice with population exposure t.-.i pultm.n.iry t.btO:is during the past 30 vears will I,.; 0: mu-rest to learn how their fi.-.di.arcompare to those of the United Kingdom. A provisional TLV expressed in concentration of respirable-sized asbestos fibe'rs has been set re cently in the United Kingdom, and a slightly dif ferent value has been established in the U.A. (G, 7 Whether these are proper (or all varieties of a-be.-tp* and all settings in which human ex posure might occur is debatable. There is c-s,-idcrable evidence to suggest that chrvsc.--1* penetrat-s to the deep lung spaces less readily and is cleared from 'he iunz more readily r-n either amosite or crocidoiite (3). Also, chry-aule cau-vs less pulm-- nary fibrosis in expenmer.-jl animals than amosite or crocidolite (9). With regard to the prevention of pulmonary fibrosis, one would conclude in 19<i9 that in many seeing* the measures taken have not been adequate, and there are populations fhat have had little or no protection at alL The knowledge required r<j protect all worker* ia not available at present, and its development is one of the urgent risks ot the immediate future. Neverthe less, an important step has been taken toward further defining the conditions necessary for the prevcnrkti and ultimate abolition of significant pulmonary fibrosis :n persons exposed to as bestos fiber. Rr'-i-croiicnic cinecr: Although in 1333 Lynch :.r. 1 Smith >10) reported bronchogenic cancer in parien*i with asbeitosis, it was cot until ["43 tint the possibility of this second liinlosic a-.fiuonce of a-bstos fiber was seriously raised, when Merewcther (II) demonstrate': brunch'c-mc cancer in 1-3 per cent of autopsies of por-c who had asbcstoiis arising from em ploy iner.* in die t>.~iie trade. Eight years Ire:. Doll 113- r-pirv:-: a frequency of lung car.:*: of rra the r.xpec'ed rate in textile works:- cx|v>-.-i : *r .it Ic-i-' CO years, during the perto i Ix-twryu : nd 1 `S>. This experience ha* beet: confirm- i in the t-xule trade by N'ewhous-i fl3> Entcrhr.- and K-i.drirk (14', and Manets-' and I'.I-Arar t!5>. More recently, .dclikon and co-w'-rk::- 1101 r'-ported a frequency of br-r.- *hc-ni*' '-ukur eizht times that anticipated ir. a sruur of in:'. ."An workers employed :cr more 'h n CO >*..* who utilized a subsrar.'iaj imrtic.n f 'heir time removing old or apply:?.; now in*".'it.on .at contained a*bc*to-i. This ASrBEiTOS A.ND HEALTH IV 1060 160 : r.ci of p pnri: j that .i.i'c.ni'f.rm fibers persona exposed for JO or more years. This indi -i.iy an undetermined _roie in\ tbe augmented cates a heavy and prolonged exposure to asbestos trequency ot bronchogenic cancer in some cate for these two types of worker. Knoxand^ni- gories oi workers. In none ot these categories, sociates (31, in a continuation of the study of -.o"eu;r, has there been a full exposition of other textile workers previously reported by Doll lubstaneca which coexast with asbestos in the (12), allow* that the incidence of lung cancer rnvironment and to which the worker has been decreases with progressively smaller total ex. exposed (5, 6, 17, IS). It is possible, therefore, posurcs to asbestos fibefs. Xewhotue (13). also hat coexisting materials possessing carcino in an asbestos textile population, has shown genic potential might be'implicated. It would be that the occurrence of pulmonary cancer differs prudent to explore this possibility thoroughly markedly with total exposure. She reports no oetore accepting asbestos per se as the carci increase of the incidence of bronchogenic nogenic tactor. cancer in a tow to moderately exposed group, In asoestos textile mills, the exposttre involves whereas m a heavily exposed group the inci primarily two varieties of asbestos, chrysotile and dence was augmented eightfold. Both groups crocidolite. In some factories, oil has been were from the same textile mill and were similar applied to the fibers before final processing. with' respect to duration of exposure and the Moreover, in the process of "opening" the length of time of observation. Enterline and ibers, a strong possibility exists that traces Kendrick (U) demonstrated a stronger rela '>i metals known to ^have carcinogenic in- tionship between lung cancer and employment duences may have been added to the fibers in the asbestos textile trade than exists in the '10-21). less dusty manufacturing of asbestos building Insulation workers have been exposed not products or building materials. In a series of inly to chrysotile and amosite but also, espe studies, Maneuso and El-Attar (13) suggested cially in shipyards, to crocidolite. The nature that cancer risk is lower with lesser exposures >i their work, as they remove old insulation and to asbestqs. From thess observations, the in ipply new in various places, exposes these ference strongly favors a dose relationship be workers to many nonasbestos substances, some tween bronchogenic cancer and whatever effect of which may be hydrocarbons adsorbed onto asbestos fibers may ultimately be *hown to have the asbestos fiber. The exposure history oi in in its causation. sulation workers is seriously Licking as to specific The question of whether'the carcinogenic ~ details of all of the materials that they may role of asbestos is related to the specific kind of have inhaled in addition to asbestos. fiber is more difficult to answer. For this pur Of the numerous questions which could be pose,populations having long-term exposure to po-ed concerning the relationship of asbestos only one variety of fiber are needed. Virtually md bronchogenic cancer, the following three all fabricating processes use more than one are of immediate practical importance: (I) Is variety within the same premises at any one the influence dose-related? (?) Is it related to time or have used more than oue variety at variety of asbestos? (3) Does the relationship various times. Populations restricted to mining evolve cocareinogtnesu? Some evidence bear and milling in the production of aabestos fiber ing upon these questions is now available, but lend themselves best to a study of the effects :n no instance is it complete. of :\ iinclc kind of fiber, and it is to these Data concerning the question of <10-0 rela l<npiil:itinni that one must look for an answer to tionships do exist. The type ot work related the iniluvticc of a single variety of fiber. most strongly to the development of broncho Kiviluoto and Meurman (22) showed that genic cancer has been in the textile and the vxjm.-ure diirint the production of nnthophyU itvsnhiinn applications trade*: the worker, in litc in Finland carries with it a threefold to t mo*t instances, has been employed in cither fivefold increased risk of bronchogenic rawer trade for 20 or more years. Mercwcther and iur those in the age group older than 43 years Price (3), and ?eliko(T and associates (21) re with more than 10 years of exposure. At this port an incidence of ndjcsro'd.s (pulmonary time, there are no published data with respect abro-isl in these groups ot SO per cent among to tlir frequency nf bronchotonie cancer in the i 470 u:orcl w. wright erocidolite or amusite production areas of South Africa, the only place in the world where ap preciable amounts of these types of fiber are produced. A verbal report' from South Africa suggests that the frequency is somewhat higher than anticipated in the general population of that country. Data from these regions will be awaited with great interest. In 1958, Braun and Truan (23) reported a study of the frequency of lung cancer in workers of the mines and mills producing only chrysolite in the eastern part of Quebec, Canada. From the data avail able to them at that time, they found no evidence of an augmented frequency of bronchogenic cancer in this group of employees. .Although the period oi. observation was only five years and the group was diluted by short-term exposures, it contained more than 1,700 persons employed longer than 20 years, all of whom had had at least five years of.exposure and 030 of whom were older than 55 yean of age. The data would have been more meaningful if arranged in terms of total exposure and time from beginning of ex posure. Nevertheless, if an excess of lung cancer equivalent to that seen in the settings referred to previously in this paper did actually exist in this population, it seems likely* it would have been found. This same population is now being restudied after a much longer period of observation and in a more adequate way. Vigiiani and associates (24) have found evidencVof an augmented frequency of cancer of the lung and pleura in a group of 23S persona, previously compensated for asbestosis arising from all occupations, who died between 1943 and 1307. In a subgroup of 32 miners exposed ro chrysotile only, there was no augmentation of the rate of cancer of lung and pleura. Al though these studies suggest that chrysotile has little or no carcinogenic influence, more ex tensive and refined epidemiologic data are needed before reaching that conclusion. The possibility that the carcinogenic role of asbestos is solely that of a cocarcinosen is very strong. The data of Selikoff and associates (2-5) are especially pertinent in this regard. In that not a single bronchogenic cancer has been found in an insulation worker who was a nonctcarcttr smoker, even though thc_gxDflflire tu asbwtOS'experienced hv the nonnnnkprt was the same as tlut of those who and did develop lung cancor. ' \Vi l(rr. lVr.otul communication. The considerable variation in the lung cancer incidence between populations of dif fering types of employment may be solely related to dosage, but it may also be the resultof ditiering cocarcinogens. Gross and associates (26) produced a higher than anticipated fre quency of pulmonary cancer in rats exposed to chrysotile. They attributed this variance, .from the experience oi others, to be related to con tamination of the chrysotile fibers by nickel, cobnlt, and chromium caused by the" wear of the metal components of the mill used m' pre paring the fiber for administration to their ani mals. Cr.tlley and associates (19, 20) showed sub stantial amounts of these trace metals in the asbestos fibers used commercially. Miller and as sociates (27) have shown that benzo (a) pyrene plus asbestos augments the yield of pulmo nary tumors produced by benzo (a) pyrene alone. H.mngton and associates (25) raised the possibility that adsorbed hydrocarbons occur ring natively or picked up in storage and handling may play a role in cocarcinogenesis. Aj reviewed in 1969, the role of asbestos in augmenting 'he incidence of bronchogenic can cer appears to be dose-related, may be dependent upon the specific category of fiber, especially in relation to the degree of effect, and appears to be chat of a cccarcmogen. Ihiothtliomi: Subsequent to the earlier rejious linking occupational exposure to asbestos and bronchogenic cancer, there were several suggestions that tumors of the peritoneal and pleural mesothelium might be similarly linked. Interest in this phenomenon remained dormant, however, until Wagner (29), in 1939, reported 20 eases of pleural mesothelioma associated with the Northwest Cape region of South Africa. He suggested that these were related to exposure to erocidolite asbestos because 14 of the persons wore bora or had spent their early youth near Kuruman, where erocidolite production is one of the major industries. This observation prompted an intensive search for ail mesothe liomas in South Airiea. Gilson (30) plotted the number and distribution of the South African cases up to 1062 and demonstrated a striking concentration of cases in the Northwest Cape Although almost none was found to occur elsewhere in South Africa, the inference that the concentration of mesotheliomas coincided with the solo source of erocidolite in South Africa would mu !' warranted. A substantial quantity AaBtSTOs and HEALTH IN 1'JU`J 471 c: crocidolue has been produced for a period of -.r.y yc-jrs, hundred* of mdes away ui the s-.iieru Transvaal, the same area in uhicii amo;-e and cnrysocile asbestos are produced Ul). investigators in other parts of the world a-'-'e examined the distribution of mesotheuotnas _:d the ircquoncy of mesothelioma in popula. .us occupationally exposed to asbestos, with me result that a strong relationship between ex;osure to asbestos fiber and the presence of i_Tsutheuooia has been indicated. Most of the .uses outside South Africa, where taming and audio? are implicated, have been reported in .a* United Kingdom and, to a lesser degree, in iae l".i. In spite of a thorough search, no mesotheliomas have been found associated, with imthophyilite asbestos production in Finland and few are reported us France (32), -here the subject has probably not been laoroughiy investigated. In the United King-voi, the association has been wish populations insulation workers and asbestos textile manu facturing factories (33). In the U.3., the relaviniiip has been shown predominantly with mjufauon workers (16) and, to a lesser degree, ~.;h textile manufacturing-employees ila). Re nat study of the distribution of mesotheliomas -a Canada will be commented upon later. In most of the studies to date, the question -as been raised as to whether the population a: risk with respeet to mesothelioma is to be isund outside as well as- inside tliertietory or place of work. There has been a plethora of speculation by students of the problem that .::tn has been accepted as fact or interpreted as iucii by iay writers. These dramatic, speculations aave further compounded an already difficult marer for those responsible for public protec* on as well as those responsible for the health :f employees. Controversial or paradoxic issues .bout mesothelioma and asbestos deserve `a more complete discussion than ii possible in this : it *r. Among tne controversial leiHlfH iMflt he relationship of asbestos exposure to meso.henoma of the pleura and peritoneum arc the : 'I'.owing. There is a lively controversy among patholocir'? regarding the requirements for establi-Unq the diagnosis of primary mesothelioma (34). Not only is there a question with respect to he histologic criteria, but even more important, he ucces-uty for establishing by autopsy wheihiT the tumor ii primary or st<-vndary It la apparent that the overwhelming number of c.isva tuns iar oeing related to .'.abestos -\r* diagnosed on the basis oi biopsy alone. Further study will be needed to demonstrate whether mesothelioma is being over or under diagnosed. If one accepts that aouie kind of direct or indirect relationship between asbestos and mesothelioma exists, docs it involve a specific variety of fiber.' The daft from the U.S. and United Kingdom does not lend itself to resolving this quesuou because chrysotile, amosite, and crocidolito are involved in the insulation workers' exposure, and chrysotile plus crocidohte in that of the textile manufacturing employees. If one examines the mining and milling exposures to the specific variety oc fiber, interesting facts emerge. Kiviluoto and Meurman (22) did not find a'single mesothelioma in a large popula tion ot miners and mill workers exposed only to anthoohvtlne. This troun worked for three months or more between the period of 1933 and 1967. Although others have stressed the long period ot time required for mesothelioma development, one would think that if aotbopbyllice by itself, is implicated at least one east would have been found by now in a setting known to cause asbestosis and a somewhat aug mented frequeucy of bronchogenic cancer. In a study of the distribution of mesotheliomas in Canada, McDonald and co-workers (33) were unaote to show excess irequency in the geo graphic area where chrysotile, but no other ianetv ot asbestos, is produced. The South African distribution of mesothe liomas' is unusually interesting. Webster (36) reports that before the end of 1963, 179 cases of mesothelioma were agreed upon as meeting aeecptable criteria. Of these, the history of ex posure was known in 143 patients, and in 24 there was no asbestos exposure. Fifty-one pa tients had been exposed during the mining and milling of crocidohte in the Northwest Cape only. An additional 32 patients with mesothe lioma. not ex(scd occupationally, were as sociated in some way with residence in the Northwest Cape. Sluis-Cremmer (31) has in dicated that about 20 per cent of all erocidolite production in South Africa actually comes from minci located in the Transvaal, a few hundred miles from the Northwest Cape. He also indi cated that although the exposure may have been * mu-what tas intense in these mines than in ii,.... i>i thi` Northwest Cape, it nevertheless was 472c GEORGE W. VRIGHT high. The writer's inquiries confirm this and indicate further that the mines of the Trans-vaal have heen in operation for as many yean u those in the Northwest Cape. The mechanism for obtaining _ data regarding mesothelioma in the Transvaal crocidolite area is identical to that for the Northwest Cape. Because not a single case of mesothelioma has been discovered from the crocidolite mines or surrounding com* munities of the Transvaal, although 51 cases have come from the crocidolite mines and 52 additional cases from the neighboring commu nity in the Northwest Cape producing exactly the same kind of fiber, the contention that crocidolite per se causes mesothelioma becomes difficult to accept. Sluis-Cremmer (31) pointed out this paradox in 1964. Webster (36), in his current report on asbestos exposures in South Africa, likewise calls attention to this disparity. It is of equal interest that only 3 cases of mesothelioma have been reported as originat ing from the Transvaal, these being from the amosite asbestos mines (36). No cases of mesothelioma have been reported from the chrysolite mines of the Transvaal. On the basis of what is known about the number of persons employed, the intensity and duration of exposure, plus lapse rime, one would expect far more than 3 cues of mesothelioma if amosite had the same potential u the factor causing mesotheliomas in the Northwest Cape. The dosage and particle site have not been sufficiently different in the Northwest Cape and Transvaal to explain the striking absence or minimal occurrence of mesotheliomas in the Transvaal.. The discovery of such a striking concentra tion of mesotheliomas in the Northwest Cape suggests the need for a thorough study of tie differences between tms region tnaotner areas of. South Africa in terms of possible etiologic factors. That something other than, or in ad dition to/asSestos plivs a role in mesothelioma formation seems inescapable.. The geology and climate of the Northwest Cape differs con siderably from- that of the Transvaal. Trace metals, chemical*, or oils adsorbed onto asbes tos may bo factors. If crocidolite is impli cated, it is likely to be . in the role of a coenreinogen. some additional agent providing the difference between the experience of the North west Cape and the Transvaal. Much more study needs to be made of this aspect. The question of whether there is a tolerable exposure or threshold limit value for asbestos without contracting an enhanced nsk of de veloping mesothelioma has been raised bv the finding of what, on first inquiry, seemed m be minor exposures to the fiber in nonoccupatiooal settings as a background for some of the cases of mesothelioma reported in South Africa (36. and the United Kingdom (33). Although orirnally it had been thought that there were mamsuch examples of mesothelioma developing out side an occupation or occupation-associated en vironment, better and more complete exposure histories reduced this proportion greatly. A? present. SO per cent or more of the mesorETliomas thus studied in the United Kingdom and iHutth Africa have been shown to have an occupational or paraoccupmonai wsdriJiHflb with libestos fiber. The level of this exposure _U_jiibstantial. Most cases occurring outside actual "on the job occupational exposure"'occur through an exposed worker living ou the same premise*, who brings fiber into the home on his clothing, or through contamination of the environment surrounding an industrial opera tion which has cast airborne fiber into--the atmosphere for years and thus exposed person? living or working in such a neighborhood. This was imperially exemplified in the Northwest Cape region of South Africa where roads were made of asbestos-bearing waste rock, where women were employed in hand cobbing ~or in gleaning asbestos fiber from the waste heaps and where >he mill disseminated blue fiber quite widely around its location. There is reason to believe that these various types of exposure have been substantial in the population thus involved during the past 40 years. With respect '0 neighborhood or parnoccupntional exposure to asbestos in the US., it is of interest that Borrow and co-workers (371 called attention to the fact that none of their scries of mesoMiehoma. gleaned from a com munity medical practice, fell into this cate gory of exposure. Is it reasonable to believe that the cases o: mesothelioma in which no occupational or paraoccupational asbestos exposure can be dis-' closed, amounting to less than 'JO per cent o! those reported from the United Kingdom and ^onrii Africa, m" t.ut represent a renmnn tc the casual exponres which might be experi enced bv the public at largef In the United A5BE5T03 A_VO HEALTH IN 1969 473 Slr.cdPBB, 'vhcre 10 intensive search for meso cent of the population exhibited these bodies thelioma has been pursued actively during the I hose structures luve been assumed by many to :iit four years, fewer than 100 cases thus far represent coated asbestos fibers and, therefore, have been discovered in persons who have not to indicate an exposure to the inhalation of as had a known substantial exposure to asbestos bestos fiber, hence a higher risk of developing 13). If one adds to this a portion of the 132 mesothelioma. Several facts militate against ruses about which there was no information, this conclusion. tae number of persons who have not had a The coated fibers found in the lungs of the tiicoverablo substantial exposure, but in whom . mesothelioma has developed, is less than 200. This number is such a minuscule proportion Subiic have not been proved to oe asbestos bers. When they are found in persons who have ex-perienced a heavy expoaure to the in the adult population from which the cases halation of asbestos fiber, it is reasonable to were gleaned that it becomes difficult to en- assume that the bulk of these bodies do rtain the view that the asbestos fibers that represent asbestos fiber. It has been shown, may he m tne air ana respired id a cafuat however, ..that other materials which are fashion by the public at large cose a genuine fibrous in nature trill produce bodies of an c-ircmogenic threat. identical appearance (41). Crallev and as If QQe postulates that there are respirablc- sociates (42) have listed 20 mineral materials r.red fibers of asbestos in the ambient**air .that are fibrous in nature and that may be oreathed by the general public, the strikingly - widely disseminated in the environment ot the ;are occurrence of mesothelioma not related to occupation strongly suggests that there is a olerable level of airborne asbestos fiber which doe* not cause an undue risk of development 'i mesothelioma. The findings of-Xewhouse *13i and McDonald and associates (35), which indicate that a genuine occupational exposure *o asbestos has been tolerated without evileace of an increased risk of developing a general public. Because of the numerous other types of fibers that may, and almost cer tainly do, gain access to, human lungs where they become coated with an iron-protein com plex, Gross and co-workers (43) suggested the term ferruginous bodies for these structures and suggested that they be called asbestos bodies onlv when it is known"*with certainty, mesothelioma, suggest that the tolerable level or can be presumed on the basis of known j substantiir/The evidence strongly favors the exposing, that the centre! fiber of the body ts concept that" the casual exposure of the gen in fact asbestos. This would appear to be a far eral public has not exceeded rich a level in more accurate designation and scientific atti the past. tude than to insist on calling oil of these Ferruginons (asbestos) boHiti. In spite of the bodies asbestos bodies whether or not they foregoing considerations, additional develop are known to be sueh. ments have caused some investigators to suggest The literature ^wmim Urnmnnin bodies that an epidemic of mesotheliomas will occur has become quite large, and sweeping infer -mong tiie general public in the near future ences from their presence in the general pop 3S>. This apprehension is based on the finding ulation have been made (38, 44). Without i: Thomson and associates 139*. confirmed by several others, that structures identified as being -igidar to asbestos bodies (commonly seen in persons known to have an intensive exposure to asbestos filers) are found in ii ner cent or more of the adult general public by direct examina tion of lung tissue or of the juices presold from such tissue. The frequency of occurrence of ifiese bodies in the lungs of the general public appar ently depends upon the volume of lung tissue examined and the intensity with which the search is mule, because Utidiian ar.d co-wnrkrra (401 report that in ilieir seri s jlmnat |OQ | r attention to the necessary quantitative and qual itative factors, it has been predicted that the experience of the geocral public with respect to mesothelioma will parallel that which has tints far been disclosed in certain very specific occupational and paraoccupational settinp. A mmilter of facts indicate a great need for cau tion before arriving at such a serious conrltbiun. To transfer the experience of a specific itern pat ional or paraoccupational population to ill.* general public requires evidence that the .Ajvwurr of the public docs, in fact, corre 474 GEORGE V. WBICHT spond to those populations in which an in creased risk of mesothelioma is said to exist. This is especially true now that it has been demonstrated tlue there are some occupational populations in which the exposure to asbestos fiber exceeds many fold that of the general public and in which no evidence of an unusual mesothelioma risk was found (13, 22, 33). What is the present situation in this regard? As indicated in foregoing discussions, conI elusions with regard to the relationship beI tween mesothelioma and asbestos- fiber per se. i even in an occupational setting, are rather un\ certain at this time. The roles of types of fiber, cocaremogenesis, and dosage are so 'far from being clear in these special occupational set* tings as to give little assurance that they can be transferred in any meaningful way to the nonoccupationaJ related or general public popu* latioru. .Although a scant number of ferruginous bodies has been demonstrated in lungs from the general' public, there has been no demon* stration that these are in fact the result of exposure to asbestos fiber rather than to one or more of the many other materials known to be capable of producing ferruginous bodies. At this time, the determination of whether the fibrous core of a ferruginous body is in fact .liber.os is extraordinarily difficult and quite beyond the means of other than the most sophisticated laboratories. In spits of this, the necessary investigation must be done before the contention that all ferruginous bodies in the general public are in fact asbestos fibers can be accepted. Quantitative estimates' indicate that the number of ferruginous bodies found in the lungs of the general -public is a small fraction of the number found in the lungs of those who had been occupationally exposed. If one accepts the contention that ferruginous bodies reflect a*l**sto exposure, one must conclude tint the general public has had far less ex posure than those persons in occupations us-" ing asbestos fiber. That some persons with known occupntiohal exposure to asbestos fiber appear to have hut few ferruginous bodies complicates an interpretation of quantitative measurement of ferruginous bodies. It is clear flint much more comprehensive and rcliabte il.ira with ri'inrd to the dvnnmics and the lu.iiiiitative :>nd qualitative a*pect of fer ruginous bodies is necessary before any meaningtul interpretation of their importance ;or the general public can be made. The finding of ferruginous bodies in a large proportion of the general population lus led to the contention that the augmented use of asbestos in the manufacture of products has greatly increased the degree to which the gen eral public has been exposed to this fiber. This assumption has been based upon the simple statistic of asbestos consumption, w:;h no attention being paid to how the fiber a used nor the degree to which its ultimate fabricated form would lend itself to dissemi nation of fiber among the public (30). Al though it is possible that augmented consump tion of asbestos fiber ted to a greater output of these fibers from factories into the air sur rounding the factory, this does not constitute a generalised public environmental exposure. Tabershaw (45) baa pointed out that asbestos is used for the most part in fabrication of materials that are unlikely to become air borne. It is not widely appreciated that the bulk of the products using asbestos actually bind the fiber firmly in the product, and there is subsequently very little opportunity for re lease of this fiber except by slow wear of the products. The estimated consumption of asbestos fiber in the L.a. has increased from 125.000 horr tons in 191S to 720.000 in 1963: most of the increase occurred after 1940.* Once the fiber, m the torm of a product, is put into place, it is not released except by gradual wear, which in most examples is minimal. During factory processing, the public at large is not exposed. During the use of certain products, such iinsulation removal aud application, fibers are released and those in the immediate vicinity, workmen and public, may be exposed. This category of product can be thought of a* having fibers that are "loosely bound," in con trast to such products as asbestos cement or floor tile which actually incorporate the fibers and bind them very tightly. The quantity of asbestos fiber used for "looselv bound" product*. including insulation ifirore 1). has increased from 39.000 onlv to 33.000 short ton; between 1920 and 1903* The commercial crude of fiber indicate* the kind of product* in which it will be u-<d. ' l'iind*:u W. F : P<,r*>nal communication. tiBESTOa a.VD HEALTH IX I960 U. S. A. IMPORTS CHRYSOTILE ONLY 475 Ftc. 1. Amount of chtyaotile asbestos (abort lonalujed in the U. S. during 4930 to 1965, according to ihe grade of fiber. Longest fibers are grade 3 and shorten are grade ' bound" products include insulation and- other materials that may release fibers during use, installation, or removal. That most of the augmentation of consump tion of chrvsotile has been in grades 4, 6, and 7 (especially 7) is shown in figure 1. Grade 7 goes predominantly into asphalt and vinyl fioor tile, which usually has a life of 20 to 25 years or more before it is changed, as a result of decoration alterations rather than wear. The bulk of grades 4 and 8 goes into asbestos cement products, especially asbestos cement pipe, in which the replacement time is indefinite--systems now in use are more than 30 years old. Air contamination does not occur from this source. Although there may be some weathering of asbestos cement shingles and siding, the rate of wear is very slow. It can readily be seen that although there has been an augmented utilisation of asbestos fiber, the largest fraction of it has gone into strongly bound products designed to last many years. The wear from these products is alio far less than the total product by the time the ma terial is discarded. Asbeno* forms an essential part of friction materials. Concern has been repressed that the public is exposed to large quantities of asbestos fiber liberated by the wear of automobile brake linings: This !s~~u3awematcd. The amount of asbestos fiber used in friction material ia the US. xnt estimated at 33,000 tons, lea than 5 per cent of the total in 1985.' Studies of the ma terial released during the use of brtkea (45T demonstrated that the high heat of faction destroys the asbestos converting it to an amorphous material no longer having tiie char acteristics of asbestos. Of the total materials removed from brake linings during their use, less than 5 per cent appears u actual asbestos. Hie amount of asbestos fiber released by normal friction material wear must be small indeed. The fibers that might be released from all kinds of wear either become intimately bound with the soil or art captured ia either rain water or in water used for cleansing. Ultimately the fibers are distributed predominantly where water is distributed. A study of river water has shown that asbestos fiber is almost universally present aiTtioiiih in quite small amounts. How 47G - LEGRCE W. WRIGHT TABLE 1 Amount or Commkxci.il Talc Usto rox V cxious . Products in tub U.S. (Short Toss in 1807) ci fibers m the general environment as a rc-i'.t of 'vear.^^^^^bvjou^fror^^jjuj^j^^^ihci, commercial^alc^^rovidM^a^goGjn^jgj^^j t Total U.S. consumption Ceramics yaint Ku'sfing Insecticides Paper Refractories Rubber T`>ilet preparations Other 820,000 220,000 lit,l>00 72,000 iiO, 000 45,000 41,000 31,000 2a, ooo 107,000 least equivalent to that of asbestos for supply-mg rc.-pirabie-sued fibers tint could produce ierru;inons bodies. It is dithcult to conceive of a better way of having fibers inhaled than the use of cosmetic talcum powders, fn this re~;ard, it is ci interest Hint Avril and Chirru^y ~14`.11 lound no ferruginous bodies in lit uion-iie* in France. It is claimed that the . cu-rmetic talcum in France has no fibers.* The Total U.S. consumption of xsliestos in 1004 was extent to which other mineral or vegetable 720,1100 .hort tons. fibers known to be present in the environ > ment of the general public may contribute much of this comes from wear of products and how much from leaching of soil is of course not determined. The concept that asbestos is indestructible is fallacious, and the belie: -that it accumulates on the surface of streets and other places seems ill-founded. to the production of ferruginous bodies is as yet unknown. ; Data have been reported recently by Selikon mid Hammond 50) showing that the frequency oi occurrence oi ferruginous bodies is 'essen tially the sime m lungs~obtamedbv^utosvin than commercial asbestos may lead to {ernijijljus^^bodiea must be considered. Talc is jprm of magnesium silicate that exists in sev eral tornw, has large industrii use, and com* montv is contaminated bv fibrous substances inch as tremolite and even chrysotile. It should be noted that talc production has been shown to cause pulmonary ftbrosts and possibly in fluence the development of bronchogenic can cer (47). .Vs shown in table I, the consumption m commercial talc in the U5. exceeds that tor asbestos. Attention to some of the products made suggests that the opportunities for air borne talc dissemination may have been aug mented to an even greater degree than, has ii-ijestos. Cralley and associates (43), in an assessment of 22 cosmetic talcum powders purchased in the U.S.. found that an average of 20 per cent of the particles were fibers. The? fibers aro fully capable of producing ferruginous bodies in the experimental animal. Tt is pi interest to note that the amount of _ (`bmmorcial talc that ultimately finds its way infn tmlet j>ri'|<arafions is far in excess of tfie amount lir'asTio-ios used in tbe manutarture oi in-ulutinu mari'rlals. Insecticide preparations consume a larger"tonnage than all of the unI'ound kinds of a*bcstos fiber put totether. Hubber, which utilizes a Large amount of com mercial tale, may contribute to the discharge with tUe contention tntt tha augmented use~oi asbestos during the past 33 years has greatly enhanced the exposure of the general pubiic to adx-stos fiber. It also raises the Question of whether the fibers in these ferruginous bodies are in fact asbestos. A similar study in Great Britain failed to demonstrate any ferrugi nous ftodies in lung samples obtained at ne cropsy in 1936 or in lung samples from fe males autopsied in 1946 (51). Although they may have been fewer than now, there surely must have been potent sources for the dissemi nation of both talc and asbestos in Great Britain before 1036 and 1946. The previous findings provide little or no evidence to suggest that an epidemic of niesothelk-nu among the public at Large is to lie expected. In a more positive way. the data from South Africa indicate that during the past five or six years the number of new ca*s of mesothelioma have been rather constant at approximately 20 per year, and in Great Britain tooi^or.ly a moderate increase has been shown. Although ;he study of ferruginous bodies i. of interest, the necessity for the central mre to K' identified and for quantitative d.va tn be obtained in order that more meaningnl conclusions be reached about their import * Aviil. J.: Per*on .1. uiimiinir-.ition. AiBLiTO* AND HEALTH IN l'J0 477 rucgeits 'hat this is an area of study with epidemiologic point of view it is proper to diminishing returns. A direct approach to the consider these findings as evidence of asbestos more easily identifiable naked fibers contained exposure. ic the lung would appear to be a more fruit Long-term implications of pleural plaques are ful avenue of search. Still better would be a a matter of interest. In general, unless the direct approach to the tyres and amounts of thickening of the pleura is extensive, the ef fiber present in the ambient air of the various fects of this patchy thickening on various as environmental locations that are of interest pects of pulmonary function are minimal or with respect to occupational, parnoccupational, absent/ There is no evidence that the presence and general public exposure. Although this pleural plaques connotes anything with re .ould pose the disadvantage of not giving spect to the ultimate development of mesotheinformation with regard to long-term past ex TToma^lB'^rTtwoofthegeographlcareaa posure, there is equally no guarantee that in which the largest concentrations of pleural ferruginous bodies truly represent the complete plaques have been reported, Finland (52) and history of past exposure. The direct approach eiutern Quebec Province,' do . not have a to the study of fiber populations in the ambient demonstrated excessive frequency of mesothe air would have the advantage of telling us lioma. To use the presence of pleural plaques what the conditions are ior the public at pres as a marker of previous asbestos exposure is ent. of limited value, in view of the fact that other Pltural plaqutt: Attention has beer, directed toward another phenomenon said to be the result of past exposure to asbestos fiber. Since the first recognition that prolonged inhalation causes lead TO this Condition and especially in view of the fact that the absence of plaques in no wav connotes the absence of absestoe ex posure. of asbestos fibers might in some persons lead to diffuse pulmonary fibrosis, clinicians have been aware that areas o: thickening of the pieura occur in some such tenons. At times, this thickening is localized hading to the ap pearance of plaques, some f which may be calcified. The pleura effects : znge all the way_ from minimal findings to extrusive and bizarre, irregularly shaped, calcific masses. Pleural plaques with or without calcification are a matter of considerable interist at the present time. Unexpectedly, these manifestations are often absent in persons who have well-developed diffuse pulmonary fibrotis resulting' from pro longed exposure to asbestos fiber, and they may be very extensive in persons with little or no diffuse fibrosis. In fact* rather extensive pleural plaques have been reported aj being ciraraon in large populations not directly ex posed occupationally to asbestos, but living in or near the region where asbestos fiber is being produced or used (52). There are, of course, other causes for pleural plaques and calcifi cation, and, in some instances, it is unwise to ascribe these findings to the inhalation of asbestos fiber. In a geographic area where i-besros fiber is known to be present in con The relationship between asbestos and health of humans, as renewable in 1969, indicates that serious exposures to asbestos fiber can occur in certain occupational and immediately ad jacent environments. Fortunately, the con centration oi asbestos fibers fn "these settings can be controlled. The environment of the in sulation workers Ts more difficult to control than tfte more hxed and permanent environ ment of the factory and associated neighbor- AB tpproximauon of the concentration of respirable-sized asbestos fiber that can be tolerated without the risk of pulmonary* fibrosis has been achieved. There is reason to believe that this concentration will also minimize the risk of pulmonary* malignancy including meso thelioma. Because of the long time lapse as sociated with the development of malignancy, longer periods of observation are desirable ior a final decision on this point. There is reason to believe that the occupational use of asbestos fiber' can achieve tne same degree ot saielV IT rhe use of explosives, radiatiofi, ana beryuiUB. although extensive alterations may be required in the control of production and manufacturing. siderable concentration in the ambient air. there is every reason to Mieve that from an 'tV< khikc M : Ptrson.nl communication. ' Csrtii-r. 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