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fUi ^ **< iVit <r*f 1 Asbestos health question perplexes experts When asked to comment on research small that detection is extremely diffi directions before an international con cult and time consuming, placing re ference on the biological effects of in straints on the scope of research that gested asbestos in Durham, N.C., last can be reasonably undertaken. month. Dr. Paul F. Holt of Reading Perhaps the most serious diffi University, England, summed up the culty in asbestos research, however, is feeling of the whole conference in his the very long period between initial ex response. The main question to be in posure and evidence of biological ef vestigated, he said, is: Does asbestos fects. In the case of mesothelioma, an matter, or doesn't it? asbestos-induced cancer of the linings Coming after more than 40 years of of the abdomen and chest, this time published research on the biological ef period is usually 25 to 35 years. fects of asbestos--research that has Asbestos is any of several silicate been greatly intensified over the past minerals existing in fibrous form. The 10 years in the U.S. and abroad--this Federal Register lists six main types of seems a very preliminary question to asbestos mineral, each with its own stUl be under investigation. Neverthe chemical composition. To add further less, although asbestos is known to confusion, each of these chemical cause severe lung damage and to raise forms exists in both a fibrous or "as- the likelihood of certain cancers devel bestiform" variety and in a nonfibrous oping following heavy exposures, the type that is sometimes considered an effect of smaller doses on the general asbestos mineral and sometimes not. population isn't at all clear. Chrysotile asbestos is the most dis ft seems very farfetched that asbes tinct asbestos form and the one most tos could be dangerous. Dr. Holt says, widely used in industry. A magnesium Chrysotile fibers In lung tissue but if it is, then everyone is in very se silicate hydroxide, chrysotile exists in rious trouble. And indeed they would nature as a bundle of very small fibrils, The research workers at the confer be. It seems likely that asbestos occurs each less than 5 microns in length and ence expressed great hope that ad naturally in much of the drinking about 0.2 micron in diameter. These fi vances in automated analysis would water in the U.S. Environmental expo brils are hollow, and their large surface make more extensive sampling possible sure to it is increased by filtration of area and relatively high surface charge by cutting down on the time required certain beverages and pharmaceuticals allow for great adsorption of trace for analyzing each sample. Dr. Eugene through asbestos filters. Used exten metal ions to these particles. P. White of Pennsylvania State Uni sively in construction for its fireproof The other asbestos minerals, collec versity, for example, described a com ing qualities, asbestos contaminates tively referred to as the amphibole puterized system for examining small the air in most office buildings and minerals, have a significantly larger particles using a scanning electron mi stores. An examination of lung sections fiber diameter and are solid fibers. croscope that is currently used in his of people living and working in New They have sodium, calcium, and iron laboratory for analysis of coal mine York City has shown some fibers in the occurring in their lattice structures, in dust. lungs of every person examined. Simi addition to magnesium and randomly The most serious deterrent to under lar results probably could be found in substituted trace metal ions. Although standing the biological effect of ingest any other urban area in the nation. not used as extensively for industrial ed and inhaled asbestos, however, is Clearly, there is a need to determine purposes, the amphibole minerals com the long incubation period of certain i whether this constant and widespread monly are found as contaminants of asbestos-induced effects. Asbestos i exposure is hazardous. To help evalu talc, chrysotile, and other widely used workers in the shipbuilding industry in ate the danger associated with asbestos minerals. the U.K. in the 1930's began to develop exposure as it is now understood and to Chrysotile fibrils are too small to be statistically high incidences of the pre examine new directions in research to detected by conventional optical mi viously rare cancer form mesothelioma I enable a more complete understanding croscopy. To identify these particles in the late 1950's, more than 20 years of the effects of asbestos ingestion and positively. Dr. Arthur M. Langer of after their asbestos exposure. Since exposure, the National Institute of En Mt. Sinai School of Medicine in New that time, many other cases of the dis vironmental Health Sciences and the York City explains, a combination of ease have been reported in patients Environmental ' Protection Agency transmission electron microscopy, se who worked with asbestos 25 to 35 sponsored last month's conference. At lected area diffraction, and micro years earlier. tended by some 130 scientists and pub chemical analysis is needed. Others be Dr. Irving J. Selikoff, director of the lic health officials from 12 countries, lieve that scanning electron micro Environmental Health Sciences Center the conference emphasized the limited scopes could be useful in detecting at Mt. Sinai School of Medicine, pre amount of information available on the chrysotile in combination with some sented data to the conference from sev effects of low-level, prolonged expo type of chemical identification, but all eral mortality studies of occupationally sure. The scientists also pointed out agree that the main drawback to any exposed asbestos workers in New York how difficult it is to obtain accurate detection technique that requires elec and New Jersey. His studies show in information on these effects. tron microscopy is the time involved creases in interthoracic cancer and There are three serious difficulties in for each analysis--about one man-day mesothelioma more than 20 years after determining the effects of asbestos on per sample. Any investigation of the heavy asbestos exposure. human health, the conference speakers occurrence of asbestos in the general In addition, he found that although agreed: population or in the environment must lung cancer deaths did not appear to The term asbestos itself is mis consequently be very limited in scope. be more frequent among nonsmoking leading, for it encompasses a whole Amphibole asbestos fibers are larger. asbestos workers than among the gen-- group of minerals that are distinct But they also require sublight micro eral nonsmoking population, they were from each other in chemical composi scopes for careful examination and very much more frequent among smok tion, particle size, and probably biolog cannot be positively identified without ing asbestos workers than among other ical effect. additional microchemical or selective smokers. In one study of 17,800 asbes Many of these particles are so area diffraction analysis. tos insulation workers, of whom 9590 18 CSEN Dec. 10. 1973 i dermal layer close to the gastrointesti nal tract, ingested asbestos is very poorly absorbed, if at all, through the lining of the stomach and colon. Dr. John M. G. Davis of the Institute of Occupational Medicine, Edinburgh, Scotland, could detect no asbestos passing through the stomach or intesti nal walls of rabbits fed asbestos fibers in his laboratory. However, Dr. R. D. Pontefract of the Canadian Food Re search Laboratories injected an asbes tos sample directly into the stomachs of laboratory animals and was able to detect about 0.1% of his sample in the epiderm. In studies with baboons. Dr. Webster found that very little ingested asbestos penetrates the walls of the stomach and colon and that almost all that does is of the smaller chrysotile type. Studies with inhaled asbestos also show that the fiber that is ab sorbed is predominantly the chrysotile Asbestos cement worker wears mask to screen out chrysolite fibers were smokers, there were five to six times the predicted number of deaths from lung cancer among the smokers. A smaller study of insulation workers in New York showed 10 times the ex pected number of deaths caused by lung cancer among the workers who smoked cigarettes. The question of most concern to public health officials, and the area of .most intensive research at present, is the effect of asbestos exposure at inter mediate levels and the effect of lowlevel exposure to asbestos in combina tion with low levels of other carcino gens that are often present in the environment. Research on these questions takes two directions. The most reliable infor mation. on the health hazard of asbes tos to man will come from one of the research directions, studies of the ef fect of the mineral on man himself. Thus, the studies that Dr. Selikoff and his associates have begun on asbestos workers in New York and New Jersey are being continued and expanded. Dr. Selikoff points out that there are some cases of mesothelioma in New Jersey that cannot be traced to any asbestos exposure. These are being further in vestigated to see if a cause for them can be found. Multiple effect correla tions, sucb as that between cigarette smoking and asbestos fiber inhalation, are being looked for also. Dr. Ian Webster of the National Re search Institute for Occupational Dis eases in Johannesburg, Republic of South Africa, told the conference of a massive effort by the South African government to establish the danger of asbestos exposure. South Africa mines both amphibole and chrysotile types of asbestos. The government hopes to conduct mortality studies on all of the workers in these mines since 1953. Most of the workers come from no madic groups living in the desert re gions of South Africa. They work in the mines for brief periods then return to their homes, making them very diffi cult to keep track of. Nevertheless, the government hopes to be able to follow a substantial number of these workers and determine, at the very least, which asbestos forms are the most dangerous ones. The other direction of current asbes tos research uses laboratory animals to study details of the effect of the fibers on tissues. The drawbacks of making inferences from animal models were re peatedly pointed out by speakers at the conference. Especially in cancer re search, different animal species often respond substantially differently to the same agent. Consequently, many dif ferent animal models must be used and compared if animal response is to be reliably extrapolated to humans. Animal studies seem to show, that al though inhaled asbestos can be found in the diaphragm; liver, and the epi type- \ Conclusive evidence on the effect; of environmental levels of asbestos ' on man, or even reliable estimates of what that level is, will not be available for some time. In the meantime, current asbestos exposure may be causing can cers that will not be detectable until the next century. Thus, representatives of regulatory agencies present at the conference agree with asbestos research workers that asbestos presents too much of a threat to human health to be used indiscriminately until conclu sive evidence is available. There is not yet complete agreement, however, on what sort of regulation should be im plemented. Dr. William Eisenberg of the Food and Drug Administration explains that it is not possible for FDA to run elec tron microscopy analyses of all the po tential sources of asbestos contamina tion under its jurisdiction. At present, analysis by polarized light microscopy is used to determine purity of foods and drugs, even though this method probably misses many of the smaller and more easily absorbed asbestos fi bers that may be present in these ma terials. FDA's main concern, according to Dr. Eisenberg, is with parenteral drugs rather than with substances that enter the body through the gastrointes tinal tract, since relatively small amounts of ingested asbestos appear to penetrate the body. Last September FDA began taking steps to eliminate the use of asbestos filters in the pro duction of parenteral drugs. EPA's Gordon Everett calls for stan dardization of reporting data so that the necessarily limited amount of data collected in each study can be usefully compared with results from other stud ies. He points out that information on the biological effects of asbestos is very limited and that the effects of many asbestos substitutes have not been in vestigated at all. Before asbestos use is banned, it should be certain that a safer alternative is available, he cau tions. 409677 0375 Dec. 1 0. 1973 C&EN 19