Document k6MaJV05bnL89oLE5JDgboBmB

Chrysotile Biopersistence in the Lungs of Persons in the General Population and Exposed Workers Arthur M. Langer and Robert R Nolan Environmental Sciences Laboratory, Applied Sciences Institute of Brooklyn College, Brooklyn, New York Lung burden analysis was performed on 126 autopsy cases of persons who died in New York City from 1966 through 1968. Of the 126 cases, 107 were probably non-occupationally exposed, judging by occupational history and asbestos body content of lung. Fifty-three of the 107 cases con tained short chrysotile fibers/fibrils, <5 pm in length, present in 3-fold greater amounts than were found in laboratory background controls. The fiber concentrations ranged from 1.8 to 15.7 x 106 f/gm/dry lung tissue, and the proportion of fibers >5 pm in length was only 0.34% of the total chrysotile population found. Other inorganic particles present included fragments of amphiboles. In contrast to these data, the lung parenchyma of persons occupationally exposed to asbestos commonly showed the presence of other fiber types, especially amosite and crocidolite, at very much higher concentrations and greater fiber length. Any chrysotile present would usually be in fiber bundle form, with both fibers and fibrils >5 pm in length. Comparison of the lung fiber content of occupationally exposed persons with that of the general population showed marked qualitative and quantitative differences. Fibers are durable, and are retained in a range of concentrations. Their length and dose, among other factors, which control their biological potential are different in the two populations; the risk factors for chrysotile-induced disease are not the same. -- Environ Health Perspect 102(Suppl 5):235-239 (1994) Key words: chrysotile, crocidolite, durability, retention Durability, Retention, and Biopersistence Biopersistence of inorganic dust in the lung is held to be a requirement for the produc tion of chronic disease. Durability, particle size, and depositional pattern affect the ability of scavenging cells to intercept, phagocytize, and sweep breakdown prod ucts out of the lung parenchyma. If a fiber is not broken down within a phagolysosome, translocation may only decrease lung retention at the expense of accumulation at another tissue site. Persistence in the host is preserved. For mineral Fiber, especially the amphibole asbestos varieties, the mucociliary escalator may save the lung but at the expense of increased risk of malignancy in other organs. Pleural drift and mesothelioma indicate that this is biologically important. Biopersistent, durable, inorganic parti cles may have very low biological activities, causing for example, benign pneumoco nioses. Chest radiographs obtained on workers occupationally exposed to barite (7), tin oxide in the absence of free silica (2), zircon dust (zirconium silicate) in the refractory industry (3), and dust in iron foundries (4) show a profusion of opacities with little or no clinical disease. Chrysotile asbestos is considered to possess low carcinogenic potential because of its inherent instability in a biological host, since it lacks both durability and biopersistence (5). Studies using electron microscopy showed some magnesium loss from the chrysotile structure, detectable only for relatively thin fibers (6,7). By using radiolabeling, chrysotile has been shown to degrade in vivo (8). Electron microscopy studies have also shown what appears to be fibril disaggregation from the fiber bundle, as well as some thinning of the fibril wall, within the phagolysosome Table 1. Asbestos body content of standard aliquots of pulmonary tissues obtained from 3000 persons who died in New York City, 1966--1968a; present study population and case distribution forTEM assay. This paper was presented at the Workshop on Biopersistence of Respirable Synthetic Fibers and Minerals held 7-9 September 1992 in Lyon, France. AML wishes to acknowledge the efforts of col leagues who participated in various portions of this study while at the Mount Sinai School of Medicine: R. Ashley, R. Fuller, A. Mackler, S. Perlowitz, Dr. A. Rohl, I. Rubin and Dr. A. Sastre. Special recognition is due to AML's late colleagues who also collaborated, showing keen interest and often brilliant insight into the problem: Drs. Victor Baden, Carl Berkley, E. Cuyler Hammond, Joann Schwartz, and Irving Selikoff. Funding support is acknowledged from USPHS EC-00160; USPHS UI-00440; Career Scientist Award (AML), NIEHS, ES-44812. Address correspondence to Dr. Arthur M. Langer, Environmental Sciences Laboratory, Applied Sciences Institute of Brooklyn College, Brooklyn, NY 11210. Telephone (718) 951-4242, (718) 951-4793. Fax (718) 951-4438. Sex Total cases scanned Male % Female % (% of population) 1971 1029 3000 Number of cases selected from each category for present study (%i 3 From Langer etal. (16). (%) cases by sex Asbestos bodies found in scan Positive cases by sex 0 1-4 5-14 >15 n % (65.7) (34.3) 958 (48.6) 593 (57.6) 802 (40.7) 392 (38.1) 152 (7.7) 40 (3.9) 59 1013 (3.0) 4 436 (0.4) 51.4 42.4 (100.0) 1551 1194 (51.7) (39.8) 192 (6.4) 63 1449 (48.6) (2.1) 32 57 18 19 126 (25.4) (45.2) (14.3) (15.1) (100.0) Environmental Health Perspectives 235 LANGER AND NOLAN Table 2. Occupations of 25 persons whose tissue aliquot contained no asbestos bodies. Age at death9 Sex Principal occupation(s) 45 53 75 46 50 80 79 76 76 68 47 58 83 84 63 56 62 50 68 75 54 80 69 71 50 M Handyman M Bartender M Porter M Factory worker (appliances) F Stock broker F Office secretary F Housewife F Housewife M Dress manufacturer M Presser; tailor M Paint factory M Shipping clerk; messenger M Salesman M Asphalt laborer M Pastry chef M Office clerk; salesman M Porter; elevator operator M Foundry worker M Waiter M Salesman; clerical M Restauranteur M Restaurant worker; porter M Restaurant worker; roofer M Bus driver M Butcher 9 Average age at time of death 64.6 years (13.4). (9,10). Animal studies have shown that chrysotile is effectively eliminated from the lung after exposure by inhalation (11). These data, and more, have led some inves tigators to conclude that "chrysotile disap pears from the lung," i.e., it lacks biopersistence. The implications of such a statement regarding carcinogenicity are obvious. If chrysotile is neither durable nor retained, the likelihood of its exerting a lasting or chronic biological effect is signifi cantly diminished. However, the study of human tissues shows that sometimes, even many years Table 3. Occupations of all 19 persons whose tissue aliquot contained 15 or more asbestos bodies. Number of asbestos bodies Age at death9 Sex Principal occupation(s)6 >99c 63 M Pipecoverer >99 55 M Welder-shipyard >99 65 M Elevator operator6' >99 72 M Plasterer >99 51 M Electrician, shipyard >99 59 M Pipecoverer, insulator 92 73 M Carpenter, shipyard 52 67 M Laborer, shipyard 42 72 M Electrician, shipyard 37 64 M Truck mechanic 35 40 M Painter, shipyard 32 48 M Plumber 29 62 M Plasterer 29 73 M Pipefitter 28 58 M Laborer; carpenter 20 72 M Longshoreman; porter 19 56 M Laborer, construction 17 57 M Laborer, construction; longshoreman 17 64 M Painter 9Average age at time of death 61.6 years (9.4).b New York State death certificates record last employment only if dece dent was still actively working. Certificates frequently state "retired." Most data from interview with next-of-kin. cCount stopped at 99 to comply with program format. 6Last employment as shown on death certificate. No interview was avail able with next-of-kin. All cases are male. after cessation of exposure, chrysotile fiber is encountered in lung tissues, and occa sionally at exceedingly high concentrations. Trace amounts of chrysotile have been reported in lungs of persons in the general population (12), and high concentrations in lungs of some occupationally exposed workers (13). This study explores the phe nomenon of chrysotile persistence in human lungs. Materials and Methods During the years 1966 to 1968, 7 lung specimens, obtained from selected anatom ical sites, were removed from each of 3000 persons who died at one of three hospitals in New York City: Mount Sinai Hospital, Manhattan; Veterans Administration Hospital, the Bronx; and Elmhurst General Hospital, Queens (14). The specimens were collected for a study involving the quantitative determination of asbestos bod ies and uncoated fibers, visible by light microscopy, in the lungs of these people, and its possible bearing on morbidity and mortality. In addition to autopsy protocol, clinical records, occupational histories, and a complete personal profile was known for each case. Similar studies had been done in urban areas elsewhere (15,16). These studies (17-20) showed a strong correlation between the presence of both asbestos bodies and uncoated light-visible fibers with sex (males greater than females), Table 4. Chrysotile detected among 126 cases studied by TEM. . Exposure categories by number of asbestos bodies found Number of chrysotile ______ 01-45-14^15 fibrils/fibers N xfa N xf N xf counted N xf Total chrysotile Nx106 f/g/dry <9 10-27 >28 Total 5 3.4 10 19.3 17 175.2 32 3188 10 4.3 20 20.0 27 113.4 57 3504 1 1.0 8 15.0 9 94.1 18 970 3 4.7 5 20.0 11 134.5 19 1594 19 <0.58c 43 0.64-1.73 64 >1.79* 126 Chrysotile6 >5 pm 1-5 pm <1 pm N 7 100 3081 (%) N (%) N (%) N (0.22) (3.14) (96.64) 6 151 3347 (0.17) (4.31) (95.52) 11 136 823 (1.13) (14.02) (84.85) 28 463 1103 (%) 0(1.76) (29.05) (69.19) N Total 52 850 8354 9256 9xf = average number of chrysotile fibers/fibrils found among cases (N). b These values were converted from length of the object on the viewing screen, at a particular scan magnifica tion, to pm. c Limit of detection is 0.064 x 106 f/g/dry lung (64,000 fibers). d Range of positive cases, 1.79-15.74 x 106 f/g/dry lung. 236 Environmental Health Perspectives CHRYSOTILE BIOPERSISTENCE Figure 1. Chrysotile recovered from an occupationally exposed worker's lung (A), with fiber displaying characteristic structure (B), and from the lung of a person in the general population (C). Scale in (C) is approximate for (A) as well. The 18 pm2 area represented in (A) is about 1/625th the area of an entire grid opening. Compare this chrysotile concentration with that in (C), with the fibrils shown counted in an opening of 11 236 pm2. The numerical difference of chrysotile con centration is about x 20,000 and a mass difference in excess of x 1 million. These illustrate the opposite outliers of chrysotile exposure. age (prevalence and amounts increased with age), and occupation. The overall asbestos body distribution is given in Table 1. These studies clearly indicated that asbestos bodies, and the accompanying fibers with diameter <1 pm, were not uniformly distributed among the general population, but rather along an exposure continuum, in which most of the group had experienced lit tle or no direct exposure to asbestos. They would provide a reliable tissue burden benchmark for ambient air exposure, against which the chrysotile levels found in persons subjected to workplace exposure to asbestos could be compared. Chrysotile biopersis tence, across a range of exposures, may be explored utilizing this material. It was decided to make a more detailed examination of a number of cases, using transmission electron microscopy (TEM). Bulk tissues from 126 cases were subjected to complete alkaline digestion, from which the particles were recovered by centrifuga tion. Aliquots of the dust suspension were transferred to grid substrates and examined by TEM. Twenty-eight specimens were analyzed with an RCA 3G microscope with a magnification x31,000, and the remain der with a Hitachi HU11E-125 micro scope with a magnification x42,000. The asbestos fiber that was counted was identi fied as chrysotile on the basis of morphol ogy and structure. Amphibole fibers were presumably also present but could not be identified. The study population, selected on the basis of asbestos body content, occupation, and personal history, is shown in Tables 1-4. Results The completed study showed that the general population dying in New York City between 1966-1968 experienced a wide range of exposures (Tables 1-3). The greatest concentrations and highest preva lence of asbestos bodies occurred in males, especially workers in occupations involving asbestos-product use or installation. These included pipe-coverers, shipyard workers, and general construction workers (Table 3). Two plasterers are listed among the occupations (when) plasterers in New York City sprayed asbestos-containing fireproof ing on steel structures during building con struction. Most of the cases were not occupationally exposed. These included women and white-collar workers, who made up an important proportion of the category without asbestos bodies. At least some chrysotile fiber was found in the lungs of 124 of 126 persons in the study, but it was decided to recognize that there was a background level. This was set at the highest level found on "control" grids, nine fibrils in nine fields (one per field opening of 11,236 pm2 area). In 19 of the lungs studied, the fibril count was <9. Setting the statistical population at approx imately three times this value, at 27 fibrils, there were 64 (30.8%) statistically positive cases out of 126 (Table 4). There are three important caveats: First, the background level observed varied in these two tissue populations so that the highest value, that reported in the 1971 study (12), was used for all cases. Second, some of "the <9 cases" included short fibers, not fibrils, suggesting a "real" expo sure had occurred. Third, four of six cases Volume 102, Supplement 5, October 1994 237 LANGER AND NOLAN with >99 asbestos bodies had almost no chrysotile in their tissues, and the two oth ers had only modest amounts, slightly more than three times the background level. Virtually all the chrysotile in nonoccupationally exposed persons was composed of short fibrils, most <1 pm in length, with the modal class between 0.2 and 0.5 pm (Figure 1C). The asbestos bodies in the occupational group were characteristically amphibole fibers. However, it should be noted that many occupationally exposed workers had lung burdens the chrysotile contents of which indicated intense, pro longed exposure (12,20), being several orders of magnitude higher than the gen eral population. The chrysotile fibers were much longer also (Table 4). Most of the chrysotile fibers/flbrils observed in this study were <5 pm in length. Only 52 of 9256 (0.56%) chrysotiles observed were longer (Table 4). There was a trend, however, which sug gested that the lungs of individuals with, apparently, occupational exposure to asbestos contained more chrysotile, fibers/fibrils > 1 to 5 pm, and > 5 pm in length (Table 4). The quantitation of the chrysotile levels in the 64 positive cases, counting all fibers and fibrils, including those <1 pm in length, gave values between 1.8 and 15.7 X 106 fibers per gram of dry lung tissue. The values for remaining 62 cases ranged from below the detection limit, 0.064 X 106 fibers per gram of dry lung tissue to 1.73 X 106 fibers per gram (Table 4). The highest chrysotile levels found did not correlate with asbestos body content nor with occu pation. The highest "general population" level of chrysotile >5 pm in length, was about 1.7 X 106 fibers/g of dry lung tissue, in an 80-year-old male. His exposure source remains unknown, and his cause of death was coronary heart disease. In this study, amphibole fiber (presum ably, based on morphology and diffraction character) >5 pm in length was restricted to individuals who were occupationally exposed. Discussion and Conclusions The presence of chrysotile in lung tissues indicates durability, retention, and host, biopersistence; and the trace amounts found in the general population are pre dominantly short fibrils. Rare outliers were found. Only in lungs of some heavily exposed workers were high chrysotile con centrations found; in these instances they appeared to be long unaltered fiber. The present study supports the tissue assay guidelines used in our laboratory, which exclude fibrils less than 1 pm in length from analysis, since they appear to repre sent nonoccupational exposure. Chrysotile fiber elimination most certainly occurred in all cases, but in proportions that could only be estimated. Chrysotile asbestos had been detected in the lungs of 50 of 83 persons (60.2%) known to be exposed to asbestos either in their occupation or as bystanders of an exposed occupation or in the households of asbestos workers (13,21). The highest chrysotile exposure was calculated at 7790 X 106 fibers >1 pm in length per gram of dry lung tissue (Figure 1A). The mean value, for all 50 cases, was calculated as 715 X 106 fibers >1 pm in length per gram of dry lung tissue, and the proportion of long fibers in the asbestos varied between 5 and 50%. Analysis of selected fibers showed preservation of both chemistry and struc ture. It would appear, therefore, that in occupational exposure to chrysotile not only are doses higher, but the proportion of long fibers is greater than in the chrysotile to which the general population is exposed. The biological activity of chrysotile may depend on its durability and persis tence, but the influence of the other fac tors--fiber length and dose--clearly affect the asbestos-disease risk (22,23). For this reason, the general population is not at the same risk as those that are occupationally exposed. REFERENCES 1. Pancheri G. Su alcune forme di pneumoconiosi particularmente studiate in Italia. Tio pneumoconiosi e baritosi. Med D Lavoro 41:73-77(1950). 2. Pendergrass EP, Pryde AW. Benign pneumoconiosis due to tin oxide. J Indust Hyg Toxicol 30:119-123 (1948). 3. Harding HE. The toxicology of zircon. Br J Ind Med 5:75-76 (1948). 4. Vorwald AJ, Pratt PC, Durkan TM, Delahant AB, Bailey DA. Siderosis: A benign pneumoconiosis due to the inhalation of iron dust. Indust Med Surgery 19:170-180 (1950). 5. Beger PJ. Uber die Asbestosiskorperchen. Virchows. Arch Pathol Anat 290:280-353 (1933). 6. Langer AM, Rubin I, Selikoff IJ. Electron microprobe analysis of asbestos bodies. In: Pneumoconiosis. Proceedings of an International Conference, Johannesburg, 1969 (Shapiro HA, ed). Capetown:Oxford University Press, 1970;57--69. 7. Langer AM, Rubin IB, Selikoff IJ, Pooley FD. Chemical characteri zation of uncoated fibres from lungs of asbestos workers by electron microprobe analysis. J Histochem Cytochem 20:735-740 (1972). 8. Morgan A, Holmes A, Gold C. Studies of the solubility of con stituents of chrysotile asbestos in vivo using radioactive tracer tech niques. Environ Res 4:458-464 (1971). 9. Suzuki Y, Churg J. Structure and development of the asbestos body. Am J Pathol 55:79-107 (1969). 10. Suzuki Y. Formation of the asbestos body: A comparative study with three types of asbestos. Environ Res 3:107-118 (1970). 11. Wagner JC, Berry G, Skidmore JW, Timbrell V. The effects of the inhalation of asbestos in rats. Br J Cancer 29:252-269 (1974). 12. Langer AM, Selikoff IJ, Sastre A. Chrysotile asbestos in the lungs of persons in New York City. Arch Environ Health 2: 348-361 (1971). 13. Langer AM, Nolan RP. Fiber type and burden found in parenchy mal tissues of workers occupationally exposed to asbestos in the United States. In: Non-occupational Exposure to Mineral Fibers (Bignon J, Peto J, Saracci R, eds). IARC-WHO Special Publication 90, Lyon:International Agency for Cancer Research, 1989;310-315. 14. Selikoff IJ, Hammond EC. Asbestos bodies in the New York City population in two periods of time. In: Pneumoconiosis, Proceedings of an International Conference, Johannesburg, 1969 (Shapiro HA, ed). Capetown:Oxford University Press, 1970;57--69. 15. Thomson JG, Kaschula ROD, MacDonald RR. Asbestos as a mod ern urban hazard. South Afr Med Jour 7:77-81 (1963). 16. Thomson JG. Asbestos and the urban dweller. NY Acad Sci 132:196-214(1965). 17. Baden V, Schwartz J, Churg J, Selikoff IJ. Demonstrations of asbestos bodies: comparison of available techniques. In: Proceedings of the 2nd International Conference on Biological Effects of Asbestos (Anspach M, Holstein MH, eds). 1968;22-29. 18. Schwartz J, Langer AM. Technique of removal and analysis of sin gle fibrous particles from human lung tissue. Proceedings of the 2nd International Conference on the Biological Effects of Asbestos (H Anspach, H Holstein, eds). 1968;8-12. 19. Berkley C, Langer AM, Sastre A, Arneson A. Electron microprobe analysis of asbestos bodies. In: Proceedings of the 2nd International Conference on the Biological Effects of Asbestos (Anspach M, Holstein H, eds). 1968; 12-22. 20. Langer AM, Baden V, Hammond EC, Selikoff IJ. Inorganic fibers, including chrysotile, in lungs at autopsy: preliminary report. In: 238 Environmental Health Perspectives CHRYSOTILE BIOPERSISTENCE Inhaled Particles, III. Proceedings of the Conference of the British Occupational Hygiene Society, London, Vol 2 (Walton WH, ed). London:Unwin Bros, 1971;683-694. 21. Langer AM, Nolan RP. Fibre types, concentrations, and diseases among persons exposed to asbestos in the United States. (Submitted for publication) 22. Browne K. Asbestos related malignancies and the Cairns Hypothesis. Editorial. Br J Ind Med 48:73-76 (1991). 23. Langer AM, Nolan RP. The properties of chrysotile asbestos as determinants of biological activity. Accompl Oncology 1: 30-51 (1986). Volume 102, Supplement 5, October 1994 239