Document pBNqVErapvnzGJMrpLVy8mL2d

2704 ^faligimnt Me* Changing Risk Groups for Malignant Mesothelioma Michael Huncharek, MD, MPH Although malignant mesothelioma is a relatively rare tu mor, its incidence is rising. Much of the increase is attrib utable to widespread exposure to asbestos in past decades in asbestos-related industries. In recent years, it has be come increasingly clear that mesothelioma risk is no longer confined to workers In the asbestos industry. This article reports a variety of recently identified "risk groups" and highlights the need for increased surveil lance of these groups to document the occurrence of as bestos-related malignancy and the institution of mea sures for disease prevention. Cancer 1992; 69:2704-2711. The incidence of mesothelioma, previously a relatively rare tumor, has experienced a well-recognized increase during the last 2 decades. Data from the National Cancer Institute's SEER (Surveillance Epidemiology and End Results) program of population-based regis tries show that the annual age-adjusted incidence for the years 1973 to 1978 versus 1979 to 1980 increased by almost 10% per year (in males).1 Information from Brit ish Columbia indicates that for the year 1982, the inci dence in that Canadian province was nearlv six times higher than it was in period 1969 to 1975.2 Clearly, mesothelioma is becoming an increasinglv common clinical entity. The etiologic link between asbestos and mesotheli oma is well documented. The upsurge in incidence of this tumor closely parallels the widespread commerciallization of asbestos, which is responsible for the major ity of cases. Unfortunately, disease risk is no longer confined to workers in the asbestos industrv. This arti cle highlights recent trends in incidence by discussing some newly recognized risk groups. With increased un derstanding of changes in disease risk, more effective disease prevention strategies can be developed. From the Massachusetts General Hospital, Harvard Medical School, and the Institute for Cancer Epidemiology, Boston, Massa chusetts. ' Address for reprints: Michael Huncharek, MD, MPH, Institute for Cancer Epidemiology, Suite 2513, One Devonshire Place, Boston, MA 02109. Accepted for publication September 1, 1991. Newly Recognized Occupational Risk Groups Brake Mechanics Friction products once constituted one of the major markets in the United States for asbestos, and it is esti mated that approximately 900,000 workers in the Un ites States are or at one time were employed as automo bile mechanics and garage workers. It is uncertain what proportion of these workers regularly service brake lin ings and are, therefore, at risk for asbestos-related meso thelioma. In addition, it is also unclear what the health risks are to coworkers not directly involved ir brake repair. A major problem with epidemiologic studies of this work force is the difficulty in tracing a large, nonunionized group of workers. Estimation of disease risk has been impeded by lack of quantitative data on exposure levels among individuals with long-term exposunHowever, several studies examining this occupations setting show the existence of a potentials leriouhealth hazard. In 1976, investigators at the Mount Sinai S hool Medicine studied asbestos exposure among brake reps' workers in New York city.3 Both clinical examinationand fiber counts produced by various operations m brake maintenance workers were analyzed. Sample taken at a distance of 3 to 5 feet from brake drumduring periods of blowing dust showed fiber oncer, trations of 6.6 to 29.4 fibers/ml, with a mea of D" fibers/ml. In addition, ten samples of brake o urn du-: were analyzed by phase-contrast, optical microscope examination and transmission electron microscopic m animation to determine the percentage of short film-' (i.e., 250 to 500 angstroms X 750 to 3750 angstroms Eighty-three percent of all chrysotile fibers were in m;` category, and almost 20% of the total mass of ;en sam pies was chrysotile (determined by electron d action "Throughout the examination by electron m oscop'. attention was given to the morphology of the .ibers ' majority of fibers showed little alteration in the typischrysotile fiber."3 In an acbS jl* analyzed** made dto jber content** lining maint furred. Airbora jjar to those a jjber concenta brake drums a jO to 20 feet to brake drum die in this fiber and a ^ Regan nosures d< m analyst worker; the re >ng electron m a 55-year-old ure, and car ref reported routri replacement or tos exposure * Analysis ( chrysotile fibe by electron di fibers found w point out that sotile to cause .fence from as used only chr rom chrysoti -iudies.'5 The js disease an mortality data The most mechanic revi i 47-year-old known exposi repair work d 41 years, the 'Afferent autt During his en tod clutch re Tansmission ^bestos expc tod said that ?Take drums working cont Another *ricer was S^-old mak 80cria on ngh vlaljgnant Mesothelioma Risk/Huncharek 2705 fit Groups of the major and it is esti's in the L:n-U as automoicertain wha: ice brake Un related meso:at the ' alth ved i. .ake tudies of this e, nonunionease risk has . on exposure m exposure, occupational daily serious aai School of : brake repair xaminations derations in ed. Sample arake drums i>er concen*an of 15.9 drum dust microscopic loscopic e*' short fibrils angstroms)were in this of ten sartf' cBffra aicroswp)'' fe fibers. A ithe typical In an additional report from Mount Sinai, Rohl et . * ana' red residual dust recovered from brake linings tnj nu ` direct measurements of the free asbestos -,,or co nt of "workroom air" in areas in which brake ,.1jna maintenance and brake shoe installation oc-arred. Airborne asbestos dust concentrations were sim ,r to those cited by Lorimer et al.3 (i.e., mean airborne -her concentrations during compressed air blowing of *rake drums ranged from 2.6 fibers/ml at a distance of pi to 20 fi?et to 16.0 fibers/mi at 3 to 5 feet). Samples of crake d m dust showed that the proportion of chryso,.:e in i s material averaged 3% to 6% (as both free ;iber am; as particulates in pulverized binder). Regarding the health effects resulting from the ex posures described, Langer and McCaughey3 published j:i analysis of a case of mesothelioma in a brake repair .uirker; the report included lung fiber studies, includ:nc electron microscopic examination. The subject was bb-vi -old man who had worked in the used car, .re. an. ar repair business since the age of 19 years. He -eportcs routinely servicing automobiles, including the replacement of brake linings. No other source of asbes:os exposure was found. Analysis of lung tissue showed the presence of chrysotile fibers (no amphibole was found) confirmed by electron diffraction techniques. Ten percent of the libers found were longer than 10 microns. The authors point o : that "Controversy over the potential of chrysotile k cause mesothelioma has continued despite evi dence from asbestos textile fabricators, thought to have used only chrysotile, from workers making brake pads, from chrysotile miners and millers and from animal studies."5 They also state, "The risk of malignant asbes tos disease among these workers seems to be low but mortality data have yet to be thoroughly evaluated."5 The most recent report of mesothelioma in a brake niecha c reviews a pleural mesothelioma occurring in 3 47-year-old male automobile mechanic whose only known exposure to asbestos was from clutch and brake repair work during an 11-year period.6 From age 30 to 41 years, the man worked as a brake mechanic in five different automobile service stations and dealerships. During his employment, he primarily performed brake and clutch repairs, engine overhauls, and automotive hansn- -sion and electrical system repairs. He reported asbesti , exposure from clutches, fly wheels, and brakes and said that he often used compressed air to "blow out brake drums," which he described as creating "dusty "'orking conditions." Another case of mesothelioma in a brake repair "'orker was recently published.7 In this report, a 56>'ear-old male elevator mechanic was noted to have an^ocori on routine physical examination. Subse1uent' right upper quadrant pain and chest discom- fort developed. Medical evaluation with computed tomography showed a right paracervical mass that, on biopsy, was found to be pleural mesothelioma. The pa tient reported working as an elevator mechanic for 30 years. He reported asbestos exposure primarily from elevator brake linings that he routinely cut, fitted, and removed during elevator installation and maintenance. Several recent studies from Scandinavia on this topic also deserve mention. Hansen,8 from the Institute of Community Medicine in Denmark, completed a his torical cohort study examining the mortality of car me chanics from ischemic heart disease and malignant neoplasms. The study cohort was identified using re cords of a nationwide census carried out in Denmark in November 1970. Comparison was made with another cohort of skilled male workers who were not exposed to asbestos or "petrochemical substances." Of 583 ob served deaths, one case of pleural mesothelioma was found. Likewise, Jarvholm and Brisman,9 in a 1988 report used the Swedish Death Register and the census of 1960 to study the occurrence of asbestos-associated tu mors in car mechanics. One hundred eighty-seven deaths attributable to cancer were observed, whereas 154 were expected. Thirty-nine were caused by lung cancer, whereas only 23 were expected. Again, one death from pleural mesothelioma was found. Analyses of mesothelioma mortality in the United States, which rely on death certificate data, have a major flaw (i.e., misclassification of pleural tumors as deaths caused by lung cancer or other tumors of the thorax). Because the diagnosis of mesothelioma often can be difficult from a pathologic standpoint, death certificate studies may re sult in gross underestimation of incidence. It is unclear how this problem may have influenced the results of the two reports detailed here. It has been estimated that 20,000 deaths from as bestos-related cancer will occur during the next 40 years among automobile maintenance workers in the United States.10 With the many difficulties faced by epidemiologists studying this work force, it is unclear how accurate this estimate will prove to be. Clearly, what is needed is better information on duration and intensity of exposure to respirable asbestos fibers in this occupational group. Additional study is needed to accu rately determine the incidence of mesothelioma among members of this work force. Railroad Workers The 1960 report by Wagner et al.11 of occupational me sothelioma risk included reports of several workers ex posed to asbestos through employment in the railroad 2706 CANCER June 1, 1992, Volume 69, No. 11 \{alignant M industry. Recently, Schenker et al.12 published the re sults of a large scale study in this occupational group. In a case-control analysis, the authors examined mesothe lioma deaths among current and retired US railroad em ployees. Of 15,059 deaths reported by the Railroad Re tirement Board, death certificates were obtained for 87%, which identified 20 deaths caused by mesotheli oma. Among workers who had worked in jobs with potential asbestos exposure, a significant odds ratio of 7.2 was found (based on a 10:1 matched analysis with railroad workers dying of nonmalignant nonaccident causes). Comparison of groups used in skilled trades (e.g., locomotive repair) with regular exposure to asbes tos, yielded a statistically significant odds ratio of 21.4. A nonsignificant odds ratio of 2.3 was found for workers in occupations with intermittent exposure. Although this study is important in that it reports the existence of a mesothelioma risk among a previ ously unexamined occupational group, these data must be viewed as representing an underestimate of the oc currence of this disease. This is because of the reliance, on death certificate data, which in the case of mesotheli oma, often results in misclassification. Additional support for a high risk of mesothelioma among railroad employees is provided by Mancuso.13 This study explored the occurrence of mesothelioma deaths among machinists in the railroad and other in dustries. Among a cohort of 197 machinists employed at the same railroad before 1935 and observed until 1982, causes of death were identified for 132. Of 29 deaths attributable to cancer, 9 were caused by mesothe lioma. The author comments that based on other data available in the literature "because of the small size of the cohort, it is remarkable to have detected such a large number of mesotheliomas."13 In addition, in 1987, Huncharek and Muscat14 re viewed a series of autopsy-confirmed cases of pleural mesothelioma with documented occupational exposure to asbestos. Of 37 cases reviewed, 4 subjects had been railroad employees. In two instances, specific job titles were unavailable; the other two had been a brake repair worker and a machinist. These data provide additional support for the existence of a mesothelioma hazard in this occupational setting, particularly in light of the death being documented pathologically, rather than re lying on death certificate information. Construction Trades Use of asbestos-containing materials (ACM) is particu larly widespread in building construction, including commercial and noncommercial structures. The US En vironmental Protection Agency (EPA) estimates that ap proximately 733,000 buildings in the United States contain ACM.15 Of particular concern is that thorn an<k of these structures are public and private school builg. ings. Obviously, with such widespread use of ACM in a multitude of capacities in buildings across the country employees in the various construction trades constitute another mesothelioma risk group. Estimates suggest that as many as 7,500,000 con struction workers have been exposed to elevated evek of respirable asbestos in the past.16 These exposures are the result of such activities as installation of metal duct work, ventilation systems, and manual removal of as bestos fireproofing.17 "Bystander exposure" also is thought to play a role because sheet metal workers of ten work in asbestos-contaminated areas secondary to other related construction work (e.g., boiler removal). Zoloth and Michaels18 analyzed 385 deaths that oc curred between January 1976 and April 1983 cmons; members of a sheet metal workers union in the New York metropolitan area. A proportional mortality analy sis showed elevated proportional mortality ratios (PMR) for lung, colon, and rectal cancer and an in creased incidence of mesothelioma. In 1987, this study was extended to include deaths occurring before Oc tober 1986, resulting in the increase of the study popula tion by 331 subjects. Statistically significant e! vated PMRs were observed for all malignant neoplasrm (PMR = 148) and for cancers of the stomach (PMR = 259) liver (PMR = 260), and lung (PMR = 186). Six deaths attributable to mesothelioma were documented on death certificates. The authors conclude that "the 1.8c of the deaths in this study attributable to mesothelioma (6 of 331) demonstrates that this disease continues to tx an important cause of mortality in this populab n."l! Recent data from Sweden19'20 using the 5 edish Cancer-Environment Registry also documer. ,s in creased mesothelioma risk among workers in the con struction industry. Malker et al.19,20 examined cana-: incidence data from that National Swedish Cancer Re gistry for 1961 and 1979. Thirty-five confirmed cases o: peritoneal mesothelioma were found, 13 cases amoni employees in the construction industry (three of the em ployees were insulators). In addition, textile v rker> painters, and pulp and paper industry workers iowN a nonsignificant elevated risk of peritoneal mesothe lioma. Also suggesting the existence of a mesothelionu risk in this occupational group is a recent report o: pleural mesothelioma in an electrician who did ni': work in a shipyard.21 This patient worked as an electri cian from 1959 until retirement in 1974. He r mrtN working in buildings in which acoustic insulat n "'3? being sprayed. In 1971, he became employed asma'n' tenance electrician at an airport and reported being >n contact with old asbestos insulation and fireprooh11:- material. He 0ften would Althoug vards are ki cancer, the r received littl gccupational Indoor Ashe. knowledge c exposure in environment represent a : particularly buildings. Of all in dcularly diffi and risk ma cause of its \ for acoustic Surveys by i present in a} dal building of 3.6 mill (192,000) of troweled asb talof 1.2 bill mgs contain rhe EPA als US schools tain friable / ties. Unfortu published li rome asbest :>sess expo> f ACM pre 3ut available Few stu -ration of as useful inforn 1-PA report -'tgs.23 Air s ttost seriout Samples we -k)n electro data were o kingdom an The EP/ fcbestos lev ^bic centim '7cc." In a ^EM) meas and Bi flm 0.0 to \lalignant Mesothelioma Risk/Huncharek 2707 lat thousands school buildi of ACM in a i the country, ies constitute 500,000 conlevated levels exposures are of metal duct rmoval of as;ure" also is \i workers ofsecondary to er removal), eaths that oc1983 amone in the New "tality anal -rtality ratios ?r and an m87, this studv ig before Ocstudy ulacant e.^vated iplasms (PMR PMR = 259), 6). Six deaths cumented on hat "the 1.8% mesothelioma antinues to be opulation."lf the Swedish xmments irrs in the conmined cancer sh Cancer Rermed cases of cases among ree of the emxtile workers, deers showed seal mesotbe- mesothelioma ent report ot who did not las an -'"ctri- He * rted isulation w^5 red as a main- wted being in i fireproofinf material. He stated that insulators and other coworkers kiften vould remove asbestos insulation in his presence. / hough electricians who do not work in ship yards ire known to have an increased risk of lung cance.. the risk of mesothelioma in these workers has mceived little attention. Increased surveillance of this occupational group may be justified.22 Indoor Asbestos Exposure .knowledge of the health risks associated with asbestos expos re in the work place has led to concerns that enviri imental (i.e,, nonoccupational) exposure could :epree nt a serious health hazard. These concerns are particularly acute with regard to exposure to ACM in buildings. Of all indoor pollutants, asbestos represents a parucularly difficult problem from a health risk assessment and risk management perspective. This is largely be cause f its widespread use as fireproofing in buildings, vr ac stic control, and as pipe and boiler insulation, surve by the US EPA estimate that friable ACM is preseni in approximately 733,000 public and commer cial buildings in the United States,23 representing 20% uf 3.6 million buildings examined. Five percent 1192,000) of buildings were found to have sprayed or troweled asbestos surfacing material, representing a to tal of 1.2 billion square feet. In addition, 563,000 build ings o tain asbestos in the form of thermal insulation. The E! v also conducted a national telephone survey of IS schools and found that approximately 35,000 con tain friable ACM, representing 35% of all school facili ties. Unfortunately, little information is available in the published literature evaluating ambient levels of air borne asbestos fibers in buildings. In addition, data that assess exposure risks given a building's function, type ACM present, and condition of these materials are not aw liable. Few studies exist that document airborne concen tration of asbestos fibers in buildings. However, some useful information is available, such as that from a 1987 EPA report of 43 asbestos-containing federal buildIngs.23 Air sampling was done at sites containing the most seriously damaged ACM within each building. Samples were subsequently analyzed using transmisS1n electron microscopic examination. In addition, data w re obtained from 35 buildings in the United Kingdom and Canada. The EPA report indicates that "Prevalent airborne asbestos levels . . . ranged from 0.0 to 0.2 fibers per ^ubic centimeter (cc), with an arithmetic mean of 0.006 /cc."23 in a related transmission electron microscopy JEM) measurement of airborne fibers in US, Canalan, a * 1 British school buildings, fiber levels ranged t0lh 0 to 0.1 f/cc, with an arithmetic mean of 0.03 f/cc.24 The EPA qualified these findings by stating, "These data . . . provide an indication of prevalent lev els which may be found in schools and in nonschool buildings. However, they are insufficient to support generalizations about the total population of buildings or the relative airborne concentrations in schools as contrasted with public and commercial buildings."23 Tn addition, the EPA presents the caveat that main tenance and cleaning activities in such structures can result in elevated airborne asbestos levels, a fact not reflected in air sampling data. Data such as that discussed have led some to sug gest that asbestos exposure in buildings poses an ex tremely low cancer risk. Unfortunately, a major limita tion of using short-term air sampling as a basis for risk assessment is that it does not necessarily reflect long term airborne fiber levels. Sampling generally takes place under "nonroutine" conditions (i.e., under cir cumstances of curtailed activity). Thus, the data do not reflect contamination levels that may occur with rou tine building use. For instance, in a review of several hundred cases of pleural mesothelioma conducted by the author, in 1986 to 1987,14 two cases of pleural mesothelioma in school teachers were found. Both of the teachers were exposed to friable ceiling and pipe insulation during the course of many years. Analysis by an independent labo ratory of the insulation material in both environments showed the presence of predominantly chrvsotile as bestos with, in one case, small amounts of amosite. A study from the United Kingdom reports pleural mesothelioma in a female office worker; the disease re sulted from exposure to amosite in the building of the patient's employment. The ceiling of this building was sprayed with amosite insulating material approxi mately 1 inch thick covered by a layer of paint. This material was in disrepair for some time, causing dust release into the indoor environment. Analysis of the ceiling material showed 70% amosite asbestos. This pa tient died of mesothelioma 9 months after it was diag nosed. The cause of death was confirmed at autopsy.25 In addition to building occupants, another group that must be evaluated for possible health risks is main tenance and repair workers. Oliver et al.26 reported find ing radiographic abnormalities and impaired pulmo nary function associated with asbestos exposure among school custodians. Little information concerning these groups is available, although it is easy to envision how periodic, intense exposure could occur among such workers. Short-term air sampling cannot evaluate this type of potential hazard. Projections of expected dis ease incidence among building occupants and building maintenance personnel may grossly underestimate such occurrences. 2708 CANCER June 1, 1992, Volume 69, No. 11 Malignan Other Risk Groups As mentioned, mesothelioma risk was once thought to be limited to asbestos-industry workers. During the last 2 decades, it has become increasingly clear that this risk is quite diverse. A recent study by Muscat and VVynder27 highlights this point. In a"hospital-based case-control study, an attempt was made to determine the role cigarette smoking plays in the etiology of malig nant mesothelioma and to quantify the risk of asbestos exposure in this malignancy. One hundred five male and 19 female patients with histologically confirmed malignant mesothelioma and 2b5 age-matched control subjects without tobacco-related conditions were in cluded in the study. Table 1 shows the occupations of 68 male patients with mesothelioma and 1 female pa tient with mesothelioma with probable or likely asbes tos exposure. As shown, 38 patients were employed as construction/maintenance workers, including such oc- i able 1. Occupations of 68 Men With Mesothelioma And 1 Woman With Probable or Likely Asbestos Shoot mcta! 'worker Othoi nv Welder Other construction worker Other construction/painter cupations as carpenter, painter, electrician, welder, and sheet metal worker. Table 2 lists patients with mesothelioma from the same study who were not employed in asbestos-related industries. Of particular interest were the cases of meso thelioma in a potter, who reported using a kiln with asbestos insulation, and a teacher, whose exposure vas from friable asbestos insulation in a classroom duri >g a 2-vear period. Both females listed in Table 2 had histo ries of domestic asbestos exposure. Table 3 lists the occupations of 24 male and 16 h>. male patients with mesothelioma and without known or self-reported asbestos exposure. It is unclear how manv of these individuals were exposed to respirable fibers because exposure in nonasbestos industry set tings often goes unnoticed. For this reason, it i* un known what proportion of all mesothelioma case air nonasbestos induced. In the discussion section of their article, Muscat ana Wonder' comment on a report by Zielhuis ct al,,2K wfu reported a female patient with mesothelioma; the woman had worked as an ironer in a laundry when deteriorating asbestos cloths were used that contain: nated the surrounding environment. Another p tien: was found to have worked for 5 years as a stage am: I his patient reported often being covered with pwnUv. asbestos flakes that originated from stage scenerv which had been covered with asbestos as a fire retar dnnt. 1 he medical literature is filled with reports of otho patients with mesothelioma attributable to unusual abestos exposure. For instance, Otte ct al.29 rewirtcc three family members who died of mesothelior , sec ondarv to exposure from an asbestos cement p xlm: manufactured by family members in their horn.. Tlx family manufactured a material called "Rollfix," whim er as used to fix screw;, m drilled holes. Amositc, gvr sum, and sand were the ma|or components of the prod net: the material was produced in the basement ot tiv. family home for 17 years. As the author report- ' Th basement had no ventilation and cleaning was ndo taken by the inothei. \o protective equipim used . , . and no special work clothes were ust . After production stopped, the family staved in the sanvresidence and no attenrors were made to remove ashtos from the house. : ne father, mother, and son a died of malignant mesomelioma; they were three of thsix family members involved m the manufacturing pn Another report was published by Driscoll c 12 1988. These investigators reported five patiei - wiC- malignant mesothelioma in a Native American puebk of 2000 persons. In such a small population, far fe'W cases were expected to occur during a 17-month periW Table 2. Is With Me: With Rep Occupatioi Men Police oft Teacher Patter StJtionan. Machinist [n-urance April 198 sen shows \merican cm, "Aslx he intense Tver slag wtv clem ring the u In add expose cent forb ' ceremor ith cakes emulation Talcot 'xirkers g; ' ''contain '.' pc' of ash Me cohort. :;;>' 8.3 e> 'hreefold i Tibutabie cancer, ma nf the 28 d !der, and hom the 3-related of mesodln with sure was during a ad histo id 16 fe t known ear how aspirable stry setit is un cases are iscat and a.,' who >ma; the -y where con' r pa. igehand. t painted scenery, ire retar- i of other usual asreported oma seci product ime. The <," which site, gypthe prodmt of the irts, "The as undernent was ised. . i the same >ve asbesnd son all iree of the uring'"'0' 1 et nlw in lents with an pueblo far fewer nth period Malignant Mesothelioma Risk/Huncharek 2709 Table 2. Nonasbestos-Related Occupations of 14 Men With Mesothelioma and 2 Women With Mesothelioma With eported Asbestos Exposure Occupation No. of patients No. of yr of asbestos exposure Men Police officer Teacher Potter Nav; ensign Envi rmental consultant Nav\ machinist Navy service engineer Stationary engineer Machinist Insurance salesperson Plant manager Super cisor (oil company) 2 1 1 1 1 1 ,1 1 1 1 1 1 2,* 10 1% 1 6 40 36 31 - 2 26 Bank Her Executive director 1 10* 1 Reported domestic exposure to asbestos. t Reported friable asbestos crumbling fro m classroom ce;img for 2 years and tLAMr'kiln MirasheCtosHrsulation"*11" ^^mals:oTp`tients thU.D ' wiSthrpermissi1on8nant ,t T Vender EL HiHarette smoking. %1Q9 1; 51:2263- (April 1984 to September 1985). Additional investiga tion showed that asbestos was routinely used by Native American craftsman in the production of silver jewelry ('f., "Asbestos was used to insulate worktables against the intense heat of brazing torches and molten metal"). Silver slag periodically built up on these boards, which "'ere < caned by clapping the boards together or rub bing t _ working surfaces together. This procedure lib erated respirable asbestos fibers. In addition, this population also experienced asbes tos exposure through the use of asbestos as a whitening ilgent for buckskin leggings and moccasins that are used in ceremonial dances. These leather items are scrubbed ,,vith cakes of asbestos, which often is derived from pipe insula:' >n. T; oft et a/.31 studied a cohort of cigarette filter 'vorke. , (all males) involved in manufacturing asbes tos-containing filters from 1951 to 1957. The primary h'Pe of asbestos used was crocidolite. Of the 33 men in *be cohort, 28 had died as of December 31, 1988, versus *be 8.3 expected deaths. The authors state that the threefold increase in mortality was almost entirely athibutahle to asbestos-associated diseases (i.e., lung Caricer 'malignant mesothelioma, and asbestosis). Five the ; deaths were attributable to mesothelioma. Chrysotile and Mesothelioma Any discussion of asbestos-related mesothelioma risk must consider the controversy regarding what role the asbestos fiber type plays in the etiology of mesotheli oma. This is particularly true because the chrysotile vari ety of asbestos accounts for about 95% of the world's production of asbestos. Early work by Stanton et al,32 demonstrated that fiber dimensions are an important determinant of bio logic response and carcinogenic potential. Recent modi fications of those findings have led some, such as Moss- Table 3. Occupations of 24 Men and 16 Women With Mesothelioma With no Asbestos-Related Jobs or Self-Reported Exposures Men Accountant 4 Air traffic controller (Air Force) Bus driver/salesman/ironworker Carpet installer Delivery driver/tire recapper Director of merchandise Health officer Insurance sales (n = 2) Inspector (steel mill) Jewelry manufacturer Lumber business manager News editor Musician/telephone coin collector Office administrator Owner of boat business/boat engine repair/farmer/rabbi/ teacher Real estate sales Retail Stationary engineer Stock clerk/bus driver Truck driver/bakery owner Truck terminal manager Vice president (fuel company) Housewife/secretarv/machine operator'" Artist Bookkeeper Data entry operator Housewife (n = 3) Housewife/farm worker Housewife/nurse Housewife/secretary Salesperson (n = 2) Secretary Secretary/driver Showroom manager Teacher/real estate agent 2710 CANCER June 1, 1992, Volume 69, No. 11 Malignant man et al.,33 to advocate the "amphibole hypothesis." Mossman et al. suggest that chrysotile is of doubtful carcinogenicity, whereas the amphiboles are much more potent carcinogens and are therefore responsible for most asbestos-related mesotheliomas. Unfortu nately, numerous factors complicate analyses of the pathogenic potential of different fiber types. These fac tors include the scarcity for study of occupational co horts exposed to a single fiber tvpe during considerable time periods. Most past exposures have been to mix tures of fibers. In addition, accurate exposure data often are lacking or of questionable quality. Nicholson34 points out that wide variations of risk exist among different industrial settings and even within a single industry, suggesting that fiber type is not the parameter responsible for these differences. Al though errors in exposure estimates may partially ac count for such discrepancies, it is likely that the altering of the asbestos fibers by industrial processing is respon sible. For instance, processing chrysotile may change fiber dimensions from the majority being long, curly fibers to narrow, straighter ones that are known to be more carcinogenic. Thus, fiber type becomes a far less important parameter in estimating risk than actual fiber dimensions. Also supporting the belief in chrysotile's carcinoge nicity are data of the unit risk for mesothelioma. The unit risk data for mesothelioma closely parallel those found for lung cancer, suggesting that the same factors that affect unit risk for lung cancer also influence meso thelioma risk. As Nicholson points out, "the risk of me sothelioma per fiber exposure in three studies where it can be estimated directly from exposure and incidence data, is identical to that for exposure to 98% chrysotile plus 2% crocidolite, 60% chrysotile plus 40% amosite and TOO % amosite respectively. Moreover, in most other studies where the mesothelioma risk cannot be estimated directly, the ratio of the number of mesotheli oma to excess lung cancers is the same for exposures to predominantly chrysotile, to 100% amosite and to mix tures of chrysotile, amosite and crocidolite. . . . The ratio for 100% crocidolite is about twice as great."34 Animal studies provide additional evidence that all types of asbestos can induce mesothelioma. Inhalation studies reveal that chrysotile is a potent carcinogen. Im plantation of fibers into the pleural cavity of laboratory animals shows that the carcinogenicity of mineral fibers is directly related to their dimensions and not their chemical composition.35-36 The debate over the carcinogenic potential of chry sotile also is complicated by the insistence of some in vestigators that lung fiber studies of exposed workers demonstrates that the amphiboles are responsible for 'he majority of lung cancers and mesotheliomas. This is based on the finding that chrysotile often is present in 'I Referenc much smaller quantities in lung tissue than is amphi boles. Unfortunately, because little is known about the biologic properties of asbestos fibers in the human lung, 1. McDon it is difficult to interpret these data. It has been found that chrysotile is preferentially cleared from the lung within the first few weeks of exposure in contrast - ith amphiboles, although the ultimate fate of the fibe s is unknown (i.e., chrysotile may be preferentially cleared ] | to asbe; 2. Churg / Cancer 3. Lorimei bestos t Sinai 1 b to the pleura).37 In summary, available data support the idea that all fiber types are capable of inducing malignancy. Al though crocidolite mav be more potent than chrysotile, it is not unique in its tumorigenic ability. With the wide I | 4. RohlAr during ! 12:110- 5. Langer worker. 6. Huncha spread use of chrysotile in a multitude of product-- and applications, it would seem unwise to ignore the p :ential health risks of chrvsotile. 7. Huncha lift meci 8. Hansen Scand J Conclusion 9. Jarvholi chanics. j 10. Castlem Few commercial products have been as extensively . DC: La\ 11. Wagner studied as asbestos, and few commodities have gener ated as much legal, public health, and public pol v in 17:260- terest as this "miracle mineral." The use of as estos j 12. Schenkt fibers dates to ancient times, but the health concerns related to its use are a recent phenomenon. workers 13. Mancusi In 1960, Wagner et al.11 provided the first clear evi | railroad dence of a relationship between asbestos exposure (in j 14. Huncha- this case crocidolite) and mesothelioma. Since then, hundreds of studies have documented the epidemio logic, biologic, and clinical characteristics c this disease. Initially, mesothelioma risk was confin- i pri oma: Ini I 15. EPA Stu ings: A F , Protectk J 16. Perkel C marily to miners, millers, and workers in asbestos man ufacturing industries. Subsequently, occupational groups using asbestos products (e.g., insulators, pipe fit ters, and shipyard workers) demonstrated a relatively high incidence of this tumor. Today, it is clear that the Asbestos Envirom 17- Baker EL tion trad populations at risk for having this malignancy continue 489. to expand. As pointed out in this article, occupational risk is no longer confined to asbestos-industry w rkers. Likewise, nonoccupational hazard exists, such as ousehold and building-occupant exposures. Zoloth S The resu 1985; 7:3 19- MalkerF Many questions regarding the biologic behavior ot mineral fibers remain unanswered (e.g., how does as 29:978-9 J- MalkerH bestos cause cancer; how are fibers transported in the human respiratory tract, and what role does fiber type play in pathogenesis). With the widespread use of as bestos worldwide, particularly now in the Third Vorld, the epidemic of mesothelioma may continue v 11 int0 the 21st century.38 It is hoped that, with a greater appre I ciation of the scope of asbestos exposure occurring out side of the industrial setting, more effective strategic for disease prevention can be developed. Vjalignamt Mesothelioma Risk/Huncharek is pi ,nt in n is amphi/n about the mman lung, been found >m the lung ontrast with the fibers is .ally cleared idea that all gnancy. Al a chrysotile, th the wideroducts and e the poten- extensively have gener ic policy inof a Mos :h cc urns st clear evixposure (in 5ince then, epidemioics of this infined prirestos-manccupational jrs, pipe fita relatively ear that the cy continue ccupational :ry workers. :h as house- | behavior of >w does asorted in the s fiber type d use of ashird World, ue we11 ;r>t0 eater e' curring ollt' <e strategies | References M< onald JC. 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