Document YDLZyMm5O8dp0268LGb01r9y

FILE NAME Household Contact HC DATE 1992 DOC HC027 DOCUMENT DESCRIPTION Journal Article - Changing Risk Groups for Malignant Mesothelioma - NAS 2704 34.70 Mal Changing Risk Groups for Malignant Mesothelioma al and Michael Huncharek MD MPH fibe linu Although malignant mesothelioma is a relatively rare tumor its incidence is rising Much of the increase is attrib- Newly Recognized Occupational Risk Groups utable to widespread exposure to asbestos in past decades in asbestos industries In recent years it has be- Brake Mechanics 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- related malignancy and the institution of mea- sures for disease prevention Cancer 1992 2704 2711 Friction products once constituted one of the major markets in the United States for asbestos and it is estimated that approximately 900,000 workers in the Unites 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- The incidence of mesothelioma previously a relatively rare tumor has experienced a recognized increase during the last 2 decades Data from the National Cancer Institute's SEER Surveillance Epidemiology and End Results program of population registries show that the annual adjusted incidence for the years 1973 to 1978 versus 1979 to 1980 increased by almost 10 per year in males Information from British Columbia indicates that for the year 1982 the incidence in that Canadian province was nearly six times higher than it was in period 1969 to 1975. Clearly mesothelioma is becoming an increasingly 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 majority of cases Unfortunately disease risk is no longer confined to workers in the asbestos industry This article 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 ings and are therefore at risk for asbestos mesothelioma In addition it is also unclear what the health risks are to coworkers not directly involved in brake repair A major problem with epidemiologic studies of this work force is the difficulty in tracing a large nonunion- ized group of workers Estimation of disease risk has been impeded by lack of quantitative data on exposure levels among individuals with long exposure However several studies examining this occupational setting show the existence of a potentially serious health hazard In 1976 investigators at the Mount Sinai School of Medicine studied asbestos exposure among brake repair workers in New York city Both clinical examinations and fiber counts produced by various operations in brake maintenance workers were analyzed Samples taken at a distance of 3 to 5 feet from brake drums during periods of blowing dust showed fiber concentrations of 6.6 to 29.4 fibers with a mean of 15.9 fibers In addition ten samples of brake drum dust were analyzed by contrast optical microscopic examination and transmission electron microscopic ex- amination to determine the percentage of short fibrils From the Massachusetts General Hospital Harvard Medical School and the Institute for Cancer Epidemiology Boston Massa- chusetts angstroms i.e. 250 to 500 angstroms X 750 to 3750 Eighty percent of all chrysotile fibers were in this category and almost 20 of the total mass of ten sam- ples was chrysotile determined by electron diffraction Address for reprints Michael Huncharek MD MPH Institute for Cancer Epidemiology Suite 2513 One Devonshire Place Boston MA 02109 Accepted for publication September , 1991 Throughout the examination by electron microscopy attention was given to the morphology of the fibers A majority of fibers showed little alteration in the typical chrysotile fiber ilar fibe bra 10 bral tile fibe pos an WO ing 5 tire rep rep tos chr by fibe poi soti den use fror stuc tos mor mec a 4 kno rep 41 diff Dui and trar asb and bra wor Wol yea isoc que 1 , Malignant Mesothelioma Risk Huncharek 2705 In an additional report from Mount Sinai Rohl et al analyzed residual dust recovered from brake linings and made direct measurements of the free asbestos fiber content of workroom air in areas in which brake lining maintenance and brake shoe installation oc- curred Airborne asbestos dust concentrations were sim- ilar to those cited by Lorimer et al.i.e. mean airborne fiber concentrations during compressed air blowing of brake drums ranged from 2.6 fibers at a distance of 10 to 20 feet to 16.0 fibers ml at 3 to 5 feet Samples of brake drum dust showed that the proportion of chryso- tile in this material averaged % to % as both free fiber and as particulates in pulverized binder Regarding the health effects resulting from the ex- posures described Langer and McCaugheypublished an analysis of a case of mesothelioma in a brake repair worker the report included lung fiber studies including electron microscopic examination The subject was a year man who had worked in the used car tire and car repair business since the age of 19 years He reported routinely servicing automobiles including the replacement of brake linings No other source of asbes- tos 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 fibers found were longer than 10 microns The authors point out that Controversy over the potential of chrysotile to 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 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 The most recent report of mesothelioma in a brake mechanic reviews a pleural mesothelioma occurring in a year male automobile mechanic whose only known exposure to asbestos was from clutch and brake repair work during an year period 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 transmission and electrical system repairs He reported asbestos 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 fort developed Medical evaluation with computed a tomography showed right paracervical mass that on biopsy was found to be pleural mesothelioma The patient 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.from the Institute of Community Medicine in Denmark completed a historical cohort study examining the mortality of car mechanics 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 observed deaths one case of pleural mesothelioma was found Likewise Jarvholm and Brisman in a 1988 report used the Swedish Death Register and the census of 1960 to study the occurrence of associated tumors in car mechanics One hundred eighty deaths attributable to cancer were observed whereas 154 were expected Thirty 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- related cancer will occur during the next 40 years among automobile maintenance workers in the United States 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 accurately determine the incidence of mesothelioma among members of this work force working conditions Another case of mesothelioma in a brake repair worker was recently published In this report a 56- year male elevator mechanic was noted to have an- isocoria on routine physical examination Subse- quently right upper quadrant pain and chest discom- Railroad Workers The 1960 report by Wagner et al 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 industry Recently Schenker et al.12 published the results of a large scale study in this occupational group In a control analysis the authors examined mesothe- contain ACM.15 Of particular concern is that thousands of these structures are public and private school buildings Obviously with such widespread use of ACM in lioma deaths among current and retired US railroad em- multitude of capacities in buildings across the country ployees Of 15,059 deaths reported by the Railroad Re- tirement Board death certificates were obtained for employees in the various construction trades constitute another mesothelioma risk group 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 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 asbestos 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- Estimates suggest that as many as 7,500,000 con- struction workers have been exposed to elevated levels of respirable asbestos in the past These exposures are the result of such activities as installation of metal duct work ventilation systems and manual removal of as- bestos fireproofing Bystander exposure also is thought to play a role because sheet metal workers of- ten work in contaminated areas secondary to other related construction work e.g. boiler removal Zoloth and Michaels analyzed 385 deaths that occurred between January 1976 and April 1983 among members of a sheet metal workers union in the New 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 York metropolitan area A proportional mortality analysis showed elevated proportional mortality ratios PMR for lung colon and rectal cancer and an in- on death certificate data which in the case of mesotheli- creased incidence of mesothelioma In 1987 this study oma often results in misclassification was extended to include deaths occurring before Oc- Additional support for a high risk of mesothelioma among railroad employees is provided by Mancuso 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 tober 1986 resulting in the increase of the study population by 331 subjects Statistically significant elevated PMRs were observed for all malignant neoplasms 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 1982 causes of death were identified for 132. Of 29 death certificates The authors conclude that the 1.8 o me deaths attributable to cancer 9 were caused by mesothe- of the deaths in this study attributable to mesothelioma lioma The author comments that based on other data 6 of 331 demonstrates that this disease continues to be a. population available in the literature because of the small size of b the cohort it is remarkable to have detected such a large number of mesotheliomas In addition in 1987 Huncharek and Muscat,,re- b viewed a series of confirmed cases of pleural an important cause of mortality in this Recent data from Sweden using the Swedish Environment Registry also documents in- creased mesothelioma risk among workers in the con- struction industry Malker et 19.20 examined cancer mesothelioma with documented occupational exposure to asbestos Of 37 cases reviewed 4 subjects had been incidence data from that National Swedish Cancer Re- gistry for 1961 and 1979. Thirty confirmed cases of S railroad employees In two instances specific job titles peritoneal mesothelioma were found 13 cases among were unavailable the other two had been a brake repair employees in the construction industry three of the em- ir ir worker and a machinist These data provide additional ployees were insulators In addition textile workers support for the existence of a mesothelioma hazard in painters and pulp and paper industry workers showed this occupational setting particularly in light of the a nonsignificant elevated risk of peritoneal mesothe- death being documented pathologically rather than re- lioma lying on death certificate information Also suggesting the existence of a mesothelioma risk in this occupational group is a recent report of Construction Trades pleural mesothelioma in an electrician who did not work in a shipyard This patient worked as an electri- f Use of containing materials ACM is particu- cian from 1959 until retirement in 1974. He reported larly widespread in building construction including working in buildings in which acoustic insulation was ma commercial and noncommercial structures The US En- being sprayed In 1971 he became employed as a main- f vironmental Protection Agency EPA estimates that ap- tenance electrician at an airport and reported being in proximately 733,000 buildings in the United States contact with old asbestos insulation and fireproofing a Malignant Mesothelioma Risk Huncharek 2707 material He stated that insulators and other coworkers presence often would remove asbestos insulation in his Although electricians who do not work in shipyards are known to have an increased risk of lung cancer the risk of mesothelioma in these workers has received little attention Increased surveillance of this occupational group may be justified. Indoor Asbestos Exposure Knowledge of the health risks associated with asbestos exposure in the work place has led to concerns that environmental 1.e. nonoccupational exposure could represent a serious health hazard These concerns are particularly acute with regard to exposure to ACM in buildings Of all indoor pollutants asbestos represents a particularly difficult problem from a health risk assessment and risk management perspective This is largely because of its widespread use as fireproofing in buildings for acoustic control and as pipe and boiler insulation Surveys by the US EPA estimate that friable ACM is present in approximat~ ly733,000 public and commercial buildings in the United States representing 20 of 3.6 million buildings examined Five percent 192,000 of buildings were found to have sprayed or troweled asbestos surfacing material representing a total of 1.2 billion square feet In addition 563,000 buildings contain asbestos in the form of thermal insulation The EPA also conducted a national telephone survey of US schools and found that approximately 35,000 contain friable ACM representing 35 of all school facili- ties Unfortunately little information is available in the published literature evaluating ambient levels of airborne asbestos fibers in buildings In addition data that assess exposure risks given a building's function type of ACM present and condition of these materials are not available Few studies exist that document airborne concen- tration of asbestos fibers in buildings However some useful information is available such as that from 1987 EPA report of 43 containing federal buildings Air sampling was done at sites containing the most seriously damaged ACM within each building Samples were subsequently analyzed using transmission electron microscopic examination In addition data were 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 cubic centimeter cc with an arithmetic mean of 0.006 123 In a related transmission electron microscopy TEM measurement of airborne fibers in US Cana- dian and British school buildings fiber levels ranged from 0.0 to 0.1 cc with an arithmetic mean of 0.03 cc The EPA qualified these findings by stating These data . ... provide an indication of prevalent levels 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 In 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 as Data such that discussed have led some to sug- gest that asbestos exposure in buildings poses an extremely low cancer risk Unfortunately a major limitation of using short air sampling as a basis for risk assessment is that it does not necessarily reflect longterm 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 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 chrysotile asbestos 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 approximately 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 autopsy diag- ceiling material showed 70 amosite asbestos This pa- tient died of mesothelioma 9 months after it was nosed The cause of death was confirmed at 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 finding 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 air sampling cannot evaluate this type of potential hazard Projections of expected disease incidence among building occupants and building maintenance personnel may grossly underestimate such occurrences ? 2708 CANCER June 1 1992 Volume 69 No. 11 Other Risk Groups As mentioned mesothelioma risk was once thought to be limited to industry workers During the last 2 decades it has become increasingly clear that this risk is quite diverse A recent study by Muscat and Wynder highlights this point In a hospital control study an attempt was made to determine the role cigarette smoking plays in the etiology of malignant 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 265 matched control subjects without tobacco conditions were included in the study Table 1 shows the occupations of 68 male patients with mesothelioma and 1 female patient with mesothelioma with probable or likely asbestos exposure As shown 38 patients were employed as maintenance workers including such oc- Table 1. Occupations of 68 Men With Mesothelioma And 1 Woman With Probable or Likely Asbestos Exposure , Occupation No. of yr of asbestos exposure Shipyard workers n = 18 Worker Electrical engineer Maintenance construction Mechanic Welder Metal shipyard worker Construction maintenance workers n = 38 Carpenter Carpenter construction worker Construction worker Construction manager Electrician Electrical engineering technician Gasket winder Insulator Maintenance supervisor worker Painter Plumber pipe layer Plumberpipe sheet metal worker Sheet metal worker Other metal worker Welder Other construction worker Other construction / painter 2 20 39 16 2 2 23 20 25 36 14 38. 3 60 38 47 35 36 33 1 54 38 2 30 32 26 38 40 13,31 24 44 11 2 33 41,30 41,30 3,31 3,31 13 15 19.5 40 Data are summaries of patents in Muscat ) Wynder EL Cigarette smoking asbestos exposure and malignant mesothelioma Cancer Res 1991 2263- 2267 Used with permission 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 industries Of particular interest were the cases of mesothelioma in a potter who reported using a kiln with asbestos insulation and a teacher whose exposure was from friable asbestos insulation in a classroom during a year period Both females listed in Table 2 had histo- ries of domestic asbestos exposure Table 3 lists the occupations of 24 male and 16 female patients with mesothelioma and without known or reported asbestos exposure It is unclear how many of these individuals were exposed to respirable fibers because exposure in nonasbestos industry settings often goes unnoticed For this reason it is un- known what proportion of all mesothelioma cases are nonasbestos induced In the discussion section of their article Muscat and Wynder2 comment on a report by Zielhuis et al who reported a female patient with mesothelioma the woman had worked as an ironer in a laundry where deteriorating asbestos cloths were used that contami- nated the surrounding environment Another patient was found to have worked for 5 years as a stagehand This patient reported often being covered with painted asbestos flakes that originated from stage scenery which had been covered with asbestos as a fire retar- dant The medical literature is filled with reports of other patients with mesothelioma attributable to unusual as- bestos exposure For instance Otte et 29 reported three family members who died of mesothelioma sec- ondary to exposure from an asbestos cement product manufactured by family members in their home The family manufactured a material called Rollfix which was used to fix screws in drilled holes Amosite gyp- sum and sand were the major components of the product the material was produced in the basement of the family home for 17 years As the author reports The basement had no ventilation and cleaning was undertaken by the mother No protective equipment was used . . and no special work clothes were used ' .. After production stopped the family stayed in the same residence and no attempts were made to remove asbes- tos from the house The father mother and son all died of malignant mesothelioma they were three of the six family members involved in the manufacturing pro- cess Another report was published by Driscoll et al.30 in 1988. These investigators reported five patients with malignant mesothelioma in a Native American pueblo of 2000 persons In such a small population far fewer cases were expected to occur during a month period Tat Wit Wit -- Mer tic Ar 3 the Si 3 bu 5 ) 2709 Malignant Mesothelioma Risk Huncharek Table 2. Nonasbestos Occupations of 14 Men With Mesothelioma and 2 Women With Mesothelioma With Reported Asbestos Exposure No. of yr of No. of asbestos Occupation patients exposure Men 2 Police officer 1 Teacher 1 Potter Navy ensign 1 Environmental consultant 1 1 Navy machinist 1 Navy service engineer , 1 Stationary engineer 1 Machinist 1 Insurance salesperson 1 Navy seaman 1 Plant manager 1 Supervisor oil company 2 10 2+ 12t 15 6 40 36 31 2 3 2 26 Chrysotile and Mesothelioma discussion of asbestos mesothelioma risk Amunsyt 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- of asbestos accounts for about 95 of the world's ety prodEuacrtliyonwoofrkasbbyestSotsanton et al demonstrated that fiber dimensions are an important determinant of bio- and carcinogenic potential Recent modi- lfoigciactiroenss poofntsheose findings have led some such as Moss- Table 3. Occupations of 24 Men and 16 Women With Mesothelioma With no Asbestos Jobs or Reported Exposures Men Accountant Air traffic controller Air Force Bus driver salesman ironworker Women Bank teller Executive director 1 10 1 5 months * Reported domestic exposure to asbestfosrom classroom ceiling for 2 years and + Reported fnable asbestos crumbling worked in an asbetsos plant for 2 Used a kiln with asbestos insulation Reported asbetos exposure on a Navy ship summanes of patients in Muscat J. Wynder EL Data are mesothelioma Cancer asbestos exposure and malignant Cigarette Res 1991 smoking 51.2263 2267 Used with permission Carpet installer Delivery driver recapper Director of merchandise Health officer Insurance sales n = 2 Inspector steel mill Jewelry manufacturer Lumber business manager News editor Musician telephone coin collector aes April 1984 to September 1985 Additional investigation showed that asbestos was routinely used by Native American craftsman in the production of silver jewelry i.e 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 were cleaned by clapping the boards together or rubbing the working surfaces together This procedure lib- scrubbed erated respirable asbestos fibers In addition this population also experienced asbes- tos exposure through the use of asbestos as a whitening and moccasins that are used agent for buckskin leggings in ceremonial dances These leather items are with cakes of asbestos which often is derived from pipe filter insulation Talcott et al.31 studied a cohort of cigarette workers all males involved in manufacturing asbes- filters from 1951 to 1957. The primary containing crocidolite Of the 33 men in type of asbestos used was the cohort 28 had died as of December 31 1988 versus deaths The authors state that the the 8.3 expected almost entirely at- threefold increase in mortality was tributable to associated diseases ie lung cancer malignant mesothelioma and asbestosis Five of the 28 deaths were attributable to mesothelioma Office administrator Owner of boat business engine repair farmer teacher Real estate sales Retail Stationary engineer Stock clerk bus driver Truck bakery owner Truck terminal manager Vice president fuel company Women Housewife secretary 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 estate agent smoking summaries of patents in Muscat , Wynder EL Cigarette 2263- Data are mesothelioma Cancer Res 1991 asbestos exposure and malignant 2267 Husband is an auto mechanic ere 2710 CANCER June 1 1992 Volume 69 No. 11 man et toadvocate the amphibole hypothesis Mossman et al suggest that chrysotile is of doubtful carcinogenicity whereas the amphiboles are much based on the finding that chrysotile often is present in much smaller quantities in lung tissue than is amphiboles Unfortunately because little is known about the more potent carcinogens and are therefore responsible for most asbestos mesotheliomas Unfortu- biologic properties of asbestos fibers in the human lung it is difficult to interpret these data It has been found nately numerous factors complicate analyses of the that chrysotile is preferentially cleared from the lung 2 pathogenic potential of different fiber types These fac- within the first few weeks of exposure in contrast with tors include the scarcity for study of occupational co- amphiboles although the ultimate fate of the fibers is 3 horts exposed to a single fiber type during considerable unknown i.e. chrysotile may be preferentially cleared time periods Most past exposures have been to mix- to the pleura tures of fibers In addition accurate exposure data often In summary available data support the idea that all are lacking or of questionable quality fiber types are capable of inducing malignancy Al- Nicholsonpoints out that wide variations of risk though crocidolite may be more potent than chrysotile exist among different industrial settings and even it is not unique in its tumorigenic ability With the wide- within a single industry suggesting that fiber type is not spread use of chrysotile in a multitude of products and the parameter responsible for these differences Al- applications it would seem unwise to ignore the poten- though errors in exposure estimates may partially ac- tial health risks of chrysotile count for such discrepancies it is likely that the altering of the asbestos fibers by industrial processing is responsible For instance processing chrysotile may change Conclusion fiber dimensions from the majority being long curly 10 a fibers to narrow straighter ones that are known to be Few commercial products have been as extensively 11 more carcinogenic Thus fiber type becomes far less studied as asbestos and few commodities have gener- important parameter in estimating risk than actual fiber ated as much legal public health and public policy in- dimensions terest as this miracle mineral The use of asbestos Also supporting the belief in chrysotile's carcinoge- fibers dates to ancient times but the health concerns 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- related to its use are a recent phenomenon In 1960 Wagner et al provided the first clear evi- dence of a relationship between asbestos exposure in this case crocidolite and mesothelioma Since then thelioma risk As Nicholson points out the risk of me- sothelioma per fiber exposure in three studies where it hundreds of studies have documented the epidemiologic biologic and clinical charactenstics of this can be estimated directly from exposure and incidence data is identical to that for exposure to 98 chrysotile disease Initially mesothelioma risk was confined primarily to miners millers and workers in asbestos plus % crocidolite 60 chrysotile plus 40 amosite and 100 amosite respectively Moreover in most other studies where the mesothelioma risk cannot be estimated directly the ratio of the number of mesothelioma to excess lung cancers is the same for exposures to predominantly chrysotile to 100 amosite and to mixtures of chrysotile amosite and crocidolite .. ... ... The ratio for 100 crocidolite is about twice as great 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 chrysotile also is complicated by the insistence of some investigators that lung fiber studies of exposed workers 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 populations at risk for having this malignancy continue to expand As pointed out in this article occupational risk is no longer confined to industry workers Likewise nonoccupational hazard exists such as household and occupant exposures Many questions regarding the biologic behavior of mineral fibers remain unanswered e.g. how does asbestos 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 asbestos worldwide particularly now in the Third World the epidemic of mesothelioma may continue well into the 21st century It is hoped that with a greater appre- ciation of the scope of asbestos exposure occurring out- demonstrates that the amphiboles are responsible for side of the industrial setting more effective strategies the majority of lung cancers and mesotheliomas This is for disease prevention can be developed - Malignant Mesothelioma Risk Huncharek 2711 References McDonald JC Health implications of environmental exposure to asbestos Environ Health Perspect 1985 62.319 328 2. 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