Document 7MMx3ELkoeprJQLXMXNx4b65g

Asbsstos health question perplexes experts When asked to comment on research directions before an international con ference on the biological effects of in gested asbestos in Durham, N.C., last month. Dr. Paul F. Holt of Reading University, England, summed up the feeling of the whole conference in his response. The main question, to be in vestigated, he said, is: Does asbestos matter, or doesn't it? Coming after more than 40 years of published research on the biological ef fects of asbestos--research that has been greatly intensified over the past 10 years in the U.S. and abroad--this seems a very preliminary question to still be under investigation. Neverthe less, although asbestos is known to cause severe lung damage and to raise the likelihood of certain cancers devel oping following heavy exposures, the effect of smaller doses on the general population isn't at all clear. It seems very farfetched that asbes tos could be dangerous, Dr. Holt say3, but if it is, then everyone is in very se rious trouble. And indeed they would be. Tt seems likely that asbestos occurs naturally in much of the drinking water in the U.S. Environmental expo sure to it is increased by filtration of certain beverages and pharmaceuticals through asbestos filters. Used exten sively in construction for its fireproof ing qualities, asbestos contaminates the air in most office buildings and stores. An examination of lung sections of people living and working in New York City has shown some fibers in the lungs of every person examined. Simi lar results probably could be found in any ocher urban area in the nation. Clearly, there is a need to determine whether this constant and widespread exposure is hazardous. To help evalu ate the danger associated with asbestos exposure as it is now understood and to examine new directions in research to enable a more complete understanding of the effects of asbestos ingestion and exposure, the National Institute of En vironmental Health Sciences and the Environmental Protection Agency sponsored last month's conference. At tended by some 130 scientists and pub lic health officials from 12 countries, the conference emphasized the limited amount of information available on the effects of low-level, prolonged expo sure. The scientists also pointed out how difficult it is to obtain accurate information on these effects. There are three serious difficulties in determining the effects of asbestos on human health, the conference speakers agreed: The term asbestos itself is mis leading, for it encompasses a whole group of minerals that are distinct from each other in chemical composi tion. particle size, and probably biolog ical effect. Many of these particles are so small that detection is extremely diffi cult and time consuming, placing re straints on the scope of research that can be reasonably undertaken. Perhaps the most serious diffi culty in asbestos research, however, is the very long period between initial ex posure and evidence of biological ef fects. In the case of mesothelioma, an asbestos-induced cancer of the linings of the abdomen and chest, this time period is usually 25 to 35 years. Asbestos is any of several silicate minerals existing in fibrous form. The Federal Register lists six main types of asbestos mineral, each with its own chemical composition. To add further confusion, each of these chemical forms exists in both a fibrous or "asbestiform" variety and in a nonfibrous type that is sometimes considered an asbestos mineral and sometimes not. Chrysotile asbestos is the most dis tinct asbestos form and the one most widely used in industry. A magnesium silicate hydroxide, chrysotile exists in nature as a bundle of very small fibrils, each less than 5 microns in length and about 0.2 micron in diameter. These fi brils are hollow, and their large surface area and relatively high surface charge allow for great adsorption of trace metal ions to these particles. The other asbestos minerals, collec tively referred to as the amphibole minerals, have a significantly larger fiber diameter and are solid fibers. They have sodium, calcium, and iron occurring in their lattice structures, in addition to magnesium and randomly substituted trace metal ions. Although not used as extensively for industrial purposes, the amphibole minerals com monly are found as contaminants of talc, chrysotile, and other widely used minerals. Chrysotile fibrils are too small to be detected by conventional optical mi croscopy. To identify these particles positively, Dr. Arthur M. Langer of Mt. Sinai School of Medicine in New York City explains, a combination of transmission electron microscopy, se lected area diffraction, and micro chemical analysis is needed. Others be lieve that scanning electron micro scopes could be useful in detecting chrysotile in combination with some type of chemical identification, but all agree that the main drawback to any detection technique that requires elec tron microscopy is the time involved for each analysis--about one man-day per sample. Any investigation of the occurrence of asbestos in the general population or in the environment must consequently be very limited in scope. Amphibole asbestos fibers are larger. But they also require sublight micro scopes for careful examination and cannot be positively identified without additional microchemicai or selective area diffraction ana The research workers at the confer ence expressed gTeat hope that ad vances in automated analysis would make more extensive sampling possible by cutting down on the time required for analyzing each sample. Dr. Eugene P. White of Pennsylvania State Uni versity, for example, described a com puterized system for examining small particles using a scanning electron mi croscope that is currently used in his laboratory for analysis of coal mine dust. The most serious deterrent to under standing the biological effect of ingest ed and inhaled asbestos, however, is the long incubation period of certain asbestos-induced effects. Asbestos workers in the shipbuilding industry in the U.K. in the 1930's began to develop statistically high incidences of the pre viously rare cancer form mesothelioma in the late 1950's, more than 20 years after their asbestos exposure. Since that time, many orher cases of the dis ease have been reported in patients who worked with asbestos 25 to 35 years earlier. Dr. Irving J. Selikoff, director of the Environmental Health Sciences Center at Mt. Sinai School of Medicine, pre sented data to the conference from sev eral mortality studies of occupationally exposed asbestos workers in New York and New Jersey. His studies show in creases in interthoracic cancer and mesothelioma more than 20 years after heavy asbestos exposure. In addition, he found that although lung cancer deaths did not appear to be more frequent among nonsmoking asbestos workers than among the gen eral nonsmoking population, they were very much more frequent among smok ing asbestos workers than among other smokers. In one study of 17.SQ0 asbestosinstrlntiim workers, of whom la Ci=N Dec. 10. 1973 X4fS05S l 96 Z0V UC-4150 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 waits 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 0.17* 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 chat is ab sorbed is predominantly the chrysotile 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 Asbestos cement worker wears mask to screen out chrysotile libers be used indiscriminately until conclu sive evidence is available. There is not C >1 yet complete agreement, however, on I jjf^were smokers, there- were five to six search Institute for Occupational Dis what sort of regulation should be im --times the predicted number of deaths eases in -Johannesburg, Republic of plemented. Jfrom lung cancer among the smokers. South Africa, told the conference of a Dr. William Eissnberg of the Food r^A smaller study of insulation workers massive effort by the South African and Drug Administration explains that Oin New York showed 10 times the ex- government to establish the danger of it is not possible for FDA,to run elec .^pected number of deaths caused by asbestos exposure. South Africa mines tron microscopy analyses of all the po lur.; cancer among the workers who both amphibole and chrysotile types of tential sources of asbestos contamina smoked cigarettes. asbestos. The government hopes to tion under its jurisdiction. At present, The question of most concern to conduct mortality studies on all of the analysis by polarized light microscopy public health officials, and the area of workers in these mines since 1953. is used to determine purity of foods most intensive research at present, is Most of the workers come from no and drugs, even though this method the effect of asbestos exposure at inter madic groups living in the desert re probably misses many of the smaller mediate levels and the effect of low- gions of South Africa. They work in the and more easily absorbed asbestos fi level exposure to asbestos in combina mines for brief periods then return to bers that may be present in these ma tion with low levels of other carcino their homes, making them very diffi terials. FDA's main concern, according gens that are often present in the cult to keep track of. Nevertheless, the to Dr. Eisenberg, is with parenteral environment. government hopes to be able to follow drugs rather than with substances that Research on these questions takes a substantial number of these workers enter the body through the gastrointes two directions. The most reliable infor and determine, at the very least, which tinal tract, since relatively small mation on the health hazard of asbes asbestos forms are the most dangerous amounts of ingested asbestos appear to tos to man will come from one of the ones. penetrate the body. Last September research directions, studies of the ef The other direction of current asbes FDA began taking steps to eliminate fect of the mineral on man himself. tos research uses laboratory animals to the use of asbestos filters in the pro Thus, the studies that Dr. Selikoff and study details of the effect of the fibers duction of parenteral drugs. his associates have begun on asbestos on tissues. The drawbacks of making EPA's Gordon Everett calls for stan workers in New York and New Jersey inferences from animal models were re dardization of reporting data so that are being continued and expanded. Dr. peatedly pointed out by speakers at the the necessarily limited amount of data Selikoff points out that there are some conference. Especially in cancer re collected in each study can be usefully cases of mesothelioma in New Jersey search, different animal species often compared with results from other stud that cannot be traced to any asbestos respond substantially differently to the ies. He points out that information on exposure. These are being further in same agent. Consequently, many dif the biological effects of asbestos is very vestigated to see if a cause for them ferent animal models must be used and limited and that the effects of many can be found. Multiple effect correla compared if animal response is to be asbestos substitutes have not been in tions, such as that between cigarette reliably extrapolated to humans. vestigated at all. Before asbestos use is smoking and asbestos fiber inhalation, Animal studies seem to show that al banned, it should be certain that a are being looked for also. though inhaled asbestos can be found safer alternative is availabj^.^ejcgsy Dr. Ian Webster of the National Re in the diaphragm, liver, and the epi Dec. 10. 1973Ci = N 19