Document G2o91Ne81GYbkBMovXEog4gm

Afp'inltd Ttvm TUt }outuni of T/** Atn* firun Vh/mw/ An*Hi/wm Affair,. \\/. tss.,,,, :;.;. nCopyright Jflht, Inj t\oo ruun Mftfo'itl 4%vm uitioti //, /?** Asbestos Exposure and Neoplasia Irving J. ScliknfJ, HID, Jacob Chttrg, MD, anti E. CnyliTTliunnionel, DSc, /Veir York PLAINTIFF'S \i EXHIBIT M26 M Building trades insulation workers have relatively light, intermittent, exposure to asbestos. Of 632 insulation workers, who entered the trade before 1943 and were traced through 1962, forty-five died of rancer of the bin" or pleura, whereas only 6.6 such deaths were expected. Three of the pleural tumors were mesotheliomas; there was also one peritoneal mesothelio ma. Four mesotheliomas in a total of 233 deaths is an exceedingly hi eh incidence for such a rare turnor. In addition, an unex pectedly large number of men died of can cer of the stomach, colon, or rectum (29 compared with 9.4 expected). Other can cers were not increased; 20.5 were expected, 21 occurred. Twelve men died of asbestosis. ALTHOUCH PULMONARY CARCINOMA had AAbeen observed in the earliest studies of asbes tosis, association between the two conditions was first suggested by Lynch and Smith in 193-5.* Ad ditional reports of such association followed. Per haps the most striking data was presented in the annual report of the Cltief Inspector of Factories of Great Britain for 1955. Every death with as bestosis in the files of the Factory' Department, from the first recognition of asbestosis as a disease entity, was studied. Altogether 365 such deaths were recorded (1924-1953). Sixty-five or 17.S" were found to be accompanied by cancer of the lung or pleura. Doll, after renewing the problem and add ing data of his own, concluded that lung cancer was a specific industrial hazard of heavily exposed asbestos workers. Nevertheless, sonic investigators have held that, while these observations might be suggestive, they did not establish an increased incidence of carci noma of the lung in pulmonary asbestosis, and. further, that the association was unproved. The factor of selection was considered a poten tial weakness in evaluating reports of autopsy scries. It was noted that complicated and unusual cases would be more likely to come to autopsy, thus raising the apparent frequency of associated lung neoplasms.4 Further, it was argued that au topsy statistics, which dealt with particular groups of (hose who died, do not reflect total populations of asbestos workers.1 Additional reservations were based on the frequent absence of data regarding Frt/rn flip of Thrr.icic D*M.*a>P, Department of Mnlictne, and tl<* Di'tuftrtii nt of r.itholn*^)*. Mount Sttt.ii KimI l h*rr .1 i>mmI nt*riini: of tfte secttMtu on rmimlufiy urtil din'titn of llu- phew ,im] tli*' Amrrii.kn Cftlh of tt 11 ll.tlt Annual Mntiru* of flu* Ainfru.ni Mrdiuil AtMUiJlitHt, Attuotk M, J,,n )7. exposure, smoking habits, and personal history, on the size of series, and on inadequate histological verification in some eases. Within the last few years a number of additional problems connected with asbestos exposure have appeared, making clarification and resolution of the foregoing statistical uncertainty a matter of con siderable concern. First, there has been greatly increased use of the various types of asbestos (a five-fold increase in world utilization of tin's group of minerals, from 500,000 tons to 2,500,000 tons per year in the last 30 years), as well as a greatly in creased number and variety of industrial applica tions of asbestos (over 3,000 such uses nosv re corded). Second, suspicion has been growing that malignancy associated with asbestos exposure may include neoplasms other than carcinoma of the lung. Thus, a significant relationship lias been claimed between diffuse mesothelioma of the pleura and peritoneum and asbestos exposure.* This communication is concerned with investi* gations undertaken to study the following factors: (I) the incidence of deaths due to pulmonary' car cinoma among a group of workers exposed to as bestos under United States industrial conditions in the past several decades, (2) whether or not such individuals would also be found to have an increased risk of other neoplasms, and (3) whether such risks would be present in an industry other than the asbestos-producing or asbestos-products industries, with which most repot ts in the past have been concerned but which would not nec essarily represent the most important areas of as bestos exposure at this time. Further, it was hoped that study of an industry with asbestos exposure of limited extent and intensity would throw some light on the potential problems associated with minimal exposure to asbestos. Materials and Methods Our investigations have been concerned with 1,522 members of the Asbestos Workers Union in the New York metropolitan area, members of New York Local 12 and Newark, NJ, Local 32 of the International Association of Heat and Frost Insu lators and Asbestos Workers. As the full title im plies, these men ate insulation workers. Although the union is considered one of the huildmg-trades unions, its members do insolation work in a va riety of industries, including shipbuilding. Called "luggers" in Great Britain, they arc often desig nated "pipe coverers," "insulators," or "asbestos workers" in this country. The union is one of the oldest in the country. Vol 163, No 1 ASBESTOS ENVOSUnE-SELIKOFF ET AL 23 Thr N'c" York lueal, ;ts the ' Salntnjnder Assnrialion of Boiler and Pipe Fclters." was the first onion of insulation workers in the United States. It amal gamated with oilier locals as the Current Asbestos Workers Union in 1912. The stability of this onion has bpen reflected in the stability of its member ship rolls. "Once a pipecoverer, always a pipecnvcrer" has been of epidemiological importance to ns and has made this groop of men particularly suit able for the study of long-term effects of asbes tos inhalation. Unlike unskilled workers exposed to asbestos inhalation in poorly paid industries, there is little labor turnover among insolation workers. Accurate employment records are main tained by the union, which has also been con cerned with health problems in the industry. The trade was badly hit during the depression; some men had to drop out and very few were added during the 1930's. By the end of 1942 the union rolls consisted mainly of men with consid erable experience, plus a few who joined in 1940, 1941, and 1942. Between 1946 and 1962 union membership increased substantially. Source of Data.--From union records, a list was prepared of every individual who was a member of either of the metropolitan locals on Dec 31, 1942, or who joined between that date and Dec 31, 1962. No one was omitted, whatever his subse quent work history. The 1942 list included 632 men; 890 men joined after 1942. Personal data were obtained from union records, and the work history of each man was detailed, including withdrawal from employment (war ser vice, other employment, retirement, illness). These data gave the baseline for calculation of the onset and duration of exposure. For members who had died, records of the Health and Welfare Fund pro vided date and place of death. Copies of death certificates were obtained on all but one of them. Autopsy protocols, histological specimens, and hos pital records were obtained and reviewed in those deaths, approximately one half, in which the ter minal illness had occurred in a hospital. Statistical Anahjsis.--Previous studies have sug gested that neoplasia associated with asbestosis sel dom occurs until 20 years after first exposure to as bestos dust. Therefore, we decided to limit- the present analysis to men with such an exposure history. Our complete records cover all members of the union (including active and retired mem bers, both dead and alive) during the 20-year period from Jan 1, 1943, through Dec 31, 1962. However, with few exceptions, the only men with a history of 20 years or longer since first exposure to asbestos were the 632 men on the union rolls as of Jan 1, 1943. (The exceptions were a few men who joined the union after Jan 1, 1943, but who had been employed previously as asbestos workers elsewhere.) Of these 632 men, 255 died before Jan 1, 1963. Table 1.--Man-Years of Experience of 632 Asbestos Workers Exposed to Asbestos Dust 20 Years or Longer Yar Ac 35 39 ................... 40 44 ................... . <5 49 .................... 50 54 .................... . 55 59 .................... 60 64 .................... 63-69 ................... 70-74 ................... 75-79 ................... B0 84 ................... 85-r ..................... 10431947 65 0 230.5 339 5 391.5 382.0 2210 139.0 33.0 31.5 5.5 3.5 Totals ............. . 1,912.0 19481953 185 0 486 5 324 0 364 0 390 0 34 1.5 181 0 115.5 70.0 18.5 2.0 2,478.0 195310i7 70 291.5 530 0 303 0 316.0 344 0 286 0 137.0 70.5 33 5 8.0 2,336.5 19531062 no 70 0 114.5 502.5 26S 5 255 0 230.0 197.5 75.0 23 5 13.5 2.011.0 Of these 632 men, 339 had been exposed to as bestos dust prior to 1924. In other words, as of Jan 1, 1943, 20 years or longer had elapsed since these 339 men were first exposed. The remaining 293 men reached the 20-years-since-first-exposure point at some time after Jan 1, 1943, and before the end of 1962. The 339 men who were Erst exposed prior to 1924 were counted in each of the 20 years (or up to the time of death of those who died). The 293 who were first exposed in 1924 or later were counted only after they reached the 20-years-sincefirst-exposure point (those who died being dropped at the time of death). When the statistics were completed, we found that we had records covering a total of S,737.5 man-years of experience of men with a history of 20 years or longer since first exposure to asbestos dust. Of the 8,737.5 man-years, 1912.0 were in the fiveyear period 1943-1947; 2.47S.0 were in the period 194S-1952; 2,336.5 were in the period 1953-1957; and 2,011.0 were in the period 195S-1962. Table 1 shows the age distribution of the man-years in each of these five-year periods. Table 2 shows (1) the average age-specific death rates of all US white males during each of these periods, and (2) the average age-specific death rates from cancer of the lung, pleura, mediastinum, and trachea among US white males during each period, as reported by the US National Office of Vital Statistics. The man-years were then multiplied by the cor responding reported US death rates to ascertain the expected number of deaths under the null hypothesis that the death rates of asbestos workers do not differ from death rates of all US white males (both age and date being taken into consid eration). The results arc summarized in Table 3. Results Total Deaths.--During the first five years ( 19431947) only 2S deaths occurred among the asbestos workers, whereas 39.7 deaths would have occurred had their agc-specific death rates been the same as for all US white males during those years (Ta ble 3). In other words, at the start of the study, the asbestos workers had below average death rates. This is by no means surprising Indeed, such I ; PLAINTIFFS j I \ EXHIBIT I | 1539 (2) Ii I Taoia i..--lot;: Jsains ano uaatns rrom Conccr ot tne Lung. Broncnus. Pleura, Mediastinum. ana iracnea per 10,003 White Males per Year* A5# 5T33 '.............. 40 14 .............. 45 40 .............. 50 54' .............. 53 5? ............ 60 64 .............. 65*69 .............. 70 74 ............ 75 79 .............. 83 84 .............. 85+ ............... 1943*1947 Total 36* 55 85 133 195 795 435 634 977 1.453 2.422 Lwof Cancerf ,.T7 1 2 4 5 7 7 6 6 5 3 1918-195Z Total 30 46 73 324 183 781 417 605 915 1.3*53 2.162 Luna Cancer! "*' .... 1 3 5 8 10 11 11 10 8 7 1953-1957 T01.il ~7o 43 72 US' 178 276 lf6 586 878 1.346 2.017 Lung Cancer! *` 1 3 6 10 14 17 16 14 12 9 195819S2 Total *25 42 70 116 178 772 lls 607 866 1.363 2.148 Lnn- Cancart t 1 3 7 11 17 21 21 17 15 11 -De.-th reies ai reoorted annually by the US National Office ol Vital Statistics. A five.ytar average is given here for each period. Average for 1953 1952 is a protection ot 1958-1960. since 195I-1952 rates are not yet available. fDeitn rates include cancer of the lung, bronchus, pleura, mediastinum, and trachea, assigned to international list code No. 47b-f prior to 1943 and to No. 160164 thereafter. ir almost always found in tile first few years of a prospective epidemiological study of this type. The explanation is almost certainly ns follows: The 632 men in this analysis were actively employed ns as bestos workers in 1942. Since disability from illness or other causes precludes employment in a trade of this type, these men were presumably well (or at least not disabled) at the start of the study pe riod. Almost any group so selected as to exclude the ill and disabled has a lower death rate during the ensuing few years than does the general popu lation. since ill and disabled persons have extreme ly high death rates. A selective effect of this type gradually wears off with time and largely disap pears within five to ten years from the time of in itial selection. During the second five-year period (1945-1952) the death rate of the asbestos workers was slight ly higher than the death rate of all US white males, ie, 54 observed deaths compared with 50.S ex pected deaths. In later periods, the death rate of the asbestos workers was proportionately higher. For the'period 1953-1957, there were S3 observed deaths compared with 56.6 expected deaths, and for the period 195S-1932, there were SS observed deaths compared with only 54.4 expected deaths. Table 3.--Observed and Expected Number of Deaths Among 632 Asbestos Workers Exposed to Asbestos Dust 20 Years or Longer Cause of Death f 3943- 1947 Total, all causes .......................... 28 Observed (asbestos workers) *cec:ed (US white mates).... 39.7 Total cancer, jtl sites .................. 13 Observed (asbestos workers) Caoested (US white mates).... 5.7 Cancer of lung and o'eura ......... Observed (asbestos workers) Caoected (US wniie males) .... 6 0.8 Cancer of stomach, colon, and rectum ...................................... Observed (asbestos workers) >oected (US white males).... 4 2.0 Cancer of all other sites com bined ........................................ Observed (asbestos workers) Eeoected (US white males) .... 3 2.9 Asbeitosis .. .. ............................... 0 Observed (asbestos workers) Vcrs 194a- 195319S2 1957 54 85 50.8 56.6 17 26 8.1 13.0 a 13 1.4 2.0 47 2.5 2.6 56 4.2 8.4 14 Total, 1958-' 194319.2 1962 88 255 . 54.4 203.5 39 95 9.7 18 36.5 45 2.4 6.6 14 2.3 29 9.4 7 21 5.0 20.5 7 12 Cancer of the Lung, Pleura, and Trachea.--In each of the four five-year periods, far more deaths from cancer of the lung and pleura occurred among the asbestos workers than would have oc curred had their death rates from these diseases been the same as for all US white males (Table 3). Altogether 45 of the 632 ashestos workers died of cancer of these sites, whereas only 6.6 such deaths would be expected from general US experience. Of these 45 deaths, 42 were recorded as due to bronchogenic carcinoma and 3 to neoplasms of the pleura. The pleural neoplasms were all recorded as mesotheliomas. Thus it was found that the death rate from can cer of the bronchus and pleura was 6.S times as high among these asbestos workers as in the gen eral US white male population (both age and date being taken into consideration). It may be asked whether the high rate of lung cancer among these asbestos workers could pos sibly be attributed to an unusually large proportion of cigarette smokers among them. We cannot an swer this question directly, since we have not yet been able to ascertain the smoking habits of the men who died. However, the following pieces of evidence indicate that unusual smoking habits can not account for the high death rate from lung can cer among these workers: We have interviewed 320 of the 377 surviving members of the 1942 group. Table 4 gives a sum mary of the smoking habits in this group compared with a sample of men drawn from the general population of 1,121 counties in 25 states/ The un ion sample is somewhat inadequate since it does not include the men who died and does not in clude all of the present living members of the union. Nevertheless, it shows that a substantial proportion of ashestos workers never smoked ciga rettes regularly. Certainly the 632 men in our analy sis of death rates were not all heavy cigarette smokers. In the general male population, lung-cancer death rates are about ten times as high among cigarette smokers as among nonsmokers; and the Vol !SS. No 1 ASBESTOS EXrOSUHE--SEUKOFF ITT AL 2S Table 4.--Smoking Habits of 320 Abestos Workers Exposed to Asbestos Dust 20 Years or Longer Compared With Sample of Men From the General Population* 40 49 50 59 0 69 70+ N-?v*r S^roWd ftrgularljr Aibctloi WorfcofS, % 9.3 14.3 20.3 25.S Cintnl Population. % 18 8 19 9 23.6 37.1 Smokad Pipe. Clear. Navar C'SJ'ertat Aibatios WerkarV % 4.6 6.1 10.1 11.8 Ganaral Population, / 7.5 9.9 16 2 23.9 History of Clg.r.lt. Smoking Aibaatot V/orrr, % 86.1 . 79.6 69.7 62.7 Central Population. % 73.7 70.2 60.2 39 0 Sampla of men from general population as reported by Hammond and Carfinhel.7 death rate from king cancer increases greatly with the amount of cigarette smoking.' However, a large proportion of all men in the United States have a history of regular cigarette smoking. From data in a prospective study on smoking,* it may be esti mated that if all men smoked a pack or more of cigarettes a day (ie, if all the nonsmokers, cigar smokers, pipe smokers, and light cigarette smok ers had, instead, been heavy cigarette smokers) the lung-cancer death rate would be approximately 3.4 times as high as it is at this time. From this we may conclude that even if all our asbestos workers had smoked a pack or more of cigarettes a day (and, indeed, from our sample we know they did not), and if exposure to asbestos were of no significance, then their lung cancer death rate would have been about 3.4 times as high as the rate in the general US male popula tion. Clearly, the smoking habits of the asbestos workers cannot account for the fact that their lungcancer death rate was 6.8 times as high as that of white males in the general population. Gastrointestinal Cancer.--Rather to out surprise, the death rate from cancer of the stomach and the death rate from cancer of the colon and rectum were higher among the asbestos workers than would be expected from the rates reported for the US white male population, calculated in the same way as for lung cancer. Twelve deaths from gastric cancer occurred among the asbestos workers, as compared with only 4.3 expected. Seventeen deaths from cancer of the colon and rectum occurred among the asbestos workers, as compared with 5.2 expected. Cancer of All Other Sites.--The combined death rate from cancer of all sites other than lung and pleura, and stomach, colon, and rectum was not increased. Twenty-one such deaths occurred among asbestos workers, as compared with 20.5 expected. Asbestosis.--01 the 255 deaths, 12 were due to asbestosis (pulmonary insufficiency, cor pulmo nale). The lapsed time from first asbestos exposure to death from asbestosis averaged 45.S years, with a i.mge of 32 to 50 years. Comment Ctiicinoina of the Lung.--The results with regard to carcinoma of the lung are clear. Industrial ex posure to asbestos by insulation workers, as stud ied here, results in a marked increase in the inci dence of cancer of the lung, approximately six to seven times the expected incidence; Altogether, 45 (17.6%) of 255 men with more than 20 years elapsed since the onset of exposure died of cancer of the lung or pleura. These data do not give the "incidence of cancer of the lung in asbestosis." They relate to the spe cific conditions of our investigation: to a group of men with only intermittent exposure to materials containing limited amounts (often 2% to 20%) of asbestos under working conditions varying from very dusty, as in extracting old insulation in closed quarters, to those with little dust exposure, as in building construction in open air. Moreover, they relate to the relatively recent past, in a trade with the shorter work week of the strong building trades unions, in an era when industry has been aware of potential asbestos hazard and the working popu lation has had some consciousness of potential risk associated with, dust exposure. These data would not necessarily apply to asbestos exposure in other industries, such as the factory production of asbestos products, the asbestos textile industry, etc, where conditions of employment might be quite different. Our results do not contradict the even higher incidence of lung cancer suggested in other studies they are merely a shade less strik ing. Diffuse Pleural and Peritoneal .1lalignanctj-- Mesothelioma.--Determining die incidence of dif fuse pleural mesothelioma is complicated by the insecurity of its histological verification. While some pathologists will so categorize a high propor tion of diffuse pleural tumors, in the experience of others it is a very rare tumor and may be mim icked by anaplastic peripheral carcinoma of the lung and diffuse fibrosarcoma of the pleura. It is difficult to evaluate completely the published re ports of diffuse pleural mesothelioma in ashestosis in the absence of complete details of each .ease. To the present time, there has been no informa tion concerning the incidence of diffuse pleural mesothelioma in ashestosis, since the published cases arc reported without reference to a total pop ulation in which they occur. Nevertheless, the 6 ASBESTOS EXPOSUItE-SELlKOFF ET AL JAMA, April C, 1904 growing number of reports of ituliviclunl suggests tli.it those tumor'; arc* porlups becoming relatively frequent complications of asbestos ex posure. Cur observations in this series are similarly sug gestive. In three of the 25-5 deaths among the men who hat! worked for 20 years or more, the ex.nnining pathologist considered the death due to dif fuse pleural mesothelioma, and in the two cases in which wc have been able to res iesv the histological material, the histological appearance was that of ten so categorized, and ashestus bodies were pres ent. This incidence of more than 1% of deaths from pleural mesothelioma is strikingly high for a tumor svhich is generally considered to be extreme ly rare. In one case in our series pathological ex amination suggested diffuse peritoneal mesotheli oma. This single experience is too fragmentary for es'aluation. Gastrointestinal Carcinoma.--Isolated instances of gastrointestinal carcinoma in the presence of asbestosis have been known, but there have been no data to indicate that these were more than coinci dental findings. Among the asbestos workers studied here, cancer of the stomach, colon, and rectum was three times as frequent as expected. Tiicse data suggest that there may perhaps be an etiological relationship between industrial asbestos exposure and carcinoma of the gastrointestinal tract. Environmental Asbestos Exposure.--The recent demonstration, by South African * and British * in vestigators of pleural and peritoneal neoplasms among individuals who had chance environmental exposure to asbestos many years before raises the very important question of possible widespread carcinogenic air pollution. The possibility of en vironmental exposure has long been known. Soon after the initial clarification of nsbestosis as a clinic entity, Hnddow 1U demonstrated asbestos bodies in a man not employed in the industry but living next door to an asbestos factory. This finding was later mirrored in the finding of chronic beryllium dis ease among residents of a community near a beryl lium factory." What is new, however, is an appre ciation of the potential extent of the problem. Thomson and associates ,J have reported the fre quent findings of asbestos bodies in the lungs of urban dwellers. Among 6.312 individuals x-rayed in an area about an asbestos mine in Finland, Kiviluoto 13 found 499 cases of pleural calcification of the type characteristically seen among asbestos workers, without obvious cause. In a comparable area without any asbestos mine, no cases were found among 7,101 persons x-rayed. It should be noted that these were not people who worked in the mine--none did--but, rather, were farmers, housewives, and others who lived in the general location. In one subject who came to autopsy, polarized-light microscopy demonstrated asbestos fibers in the lung. Similarly, the lung of a cow graz ing near the mine also showed the presence of asbestos. A particular variety of environmental exposure may be of even greater concern. Asbestos exposure in industry will not be limited to the particular craft that utilizes the material. The floating fibers do not respect j'ob classifications. Thus, for ex ample, insulation workers undoubtedly share their exposure with their workmates in other trades; intimate contact with asbestos is possible for elec tricians, plumbers, sheet-metal workers, stcamfitters, laborers, carpenters, boiler makers, and fore men; perhaps even the supervising architect should be included. 1 E 100th St, New York 10029 (Dr. SelikofF). This study was supported by the Health Research Coun cil of the City- of New York. Cooperating in this investigation were the executive of ficers of the International Association of Heat anti Frost Insulators and Asbestos Workers. Washington. DC, and the officers and membership of the New York and Newark, NJ, locals of this Union. References 1. Lynch, K.M., and Smith, W.A.: Pulmonary Asbestosis: Carcinoma of Lung in Asbesio-Silicusis, Amcr J Cancer 21.*.f.-(il (May) 1035. 2. Annual Report of Chief Inspector of Fat lories for Year 1935. London: ller Majesty's Stationery Office, 1956, cmntl 8, p 20ti. 3. Dull, lL: Mortality From Lung Cancer in Asbestos Workers, Urit ] Imill Ur .l/ctf 12:31 -SG, 1955. 4. llohlig, H., and Jacob, C.: Ncue Cesichtspunkte iiber den Lungr.ikrebs der Asbcstarheitcr, Dcutsch Med Wschr 81:231-255 (Feb 17) l`j.50. 5. Braun, D.C., and Truan, T.D.: Epidemiological Study of Lung Cancer in Asbestos Miners, AMA Arch Indnstr ffru/rii 17:034-0*5 (Jne) 195S. G Wagner, J.C.; Strggs, C.A.; and Marcli.md, P.: Diffuse Pleural Mesothelioma and Asbestos Exposure in North Western C.ipe Province, Brit J Intltnlr Med 17:200-271, 1'Ji.ll, 7. Hammond, F..C., and Carfiiikcl, L-: Smoking Habits of Mrn and Women, J Sul Cancer hut C7:-lI9-4-I2 (Aug) 1961. 8. Hammond, E.C., and Horn, D.: Smoking and Death Rales: Report on Forty-Four Months of Follow-up of 187,7S3 Men. I. Total Mortality; II. Death Rates by Cause JAMA 166:1159-1172 (March 8); 1294-130S (March 15) 195S. 9. McCaughey, W.T.E.; Wade. O.L-; and Elmes. P.C.: Exposure to Asbestos Dust and Diffuse Pleural Mesothelio mas, Brit Med J 2:1397 (Nov 21) 1962. 10. Haddow, A.C., in Report of Annual Meeting of British Medical Association, Manchester, 1929, Lencet 2:230-231 (Aug 3) 1929. 11. Chesner, C.: Chronic Pulmonary Crariulomatosis in Residents of Community Near Beryllium Plant: Three Autnpsied Cases, Ami Intern Med 32:1()2S-104S (Junr) 1930. 12. Thttntsoti, J.C.; K.isehul.i, H.O.C.; mid M.icDun.ild, n.R.: Asbestos as Modern L'lbjn Hazard, S Afr Med J 37:77-Sl (Jan 19) 1963. 13. Kiviluoto, R.: Pleural Calcification as Roentgenologic Sign of Nnn-Oceup.itiunal Endemic Anthnphyllilc-Asbestosis, Acta diuhol Suppl 194, pp 1-67, 190(1. 2 PLAINTIFF'S [ EXHIBIT { 1539(5)