Document b2v88D1D96m12MqVq9Q1z9Vk

Asbssios hz m 'r"-b v'-tv zv"t J .kj-i `V uO J ^X l ' { 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. Patti F. Holt of Heading University, England, summed up the feeling of the whole eonterenee in his response. The main t|iiestion to he in vestigated, he said, is: Does asbestos matter, or doesn't it? Coming after more than -10 years of published research on the biological ef fects of asbestos--research that has been greatly intensiiied over the [last 10 years m 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 (loses on the general population isn't at all clear. it seems very farfetched that t;.5C^stos could he dangerous, Dr. Holt sacs, hut if it is, then everyone is in very se rious trouble. And indeed they would he. It seems likely :har 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.moEf ct'tiee buildings and oititVH. *vtl bXctU'J ii, H.l l\Jll ;f iu.:\g Sc-l l > ef people living and working in New York City has shown some fibers or .lie lungs of every person examined, 'bmila r results probably could be found in any other urban area in the na: ion. Cloarlv. 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 cor.terence. At tended bv some 130 scientists and pub lic heaith officials from 12 countries. :he conference emphasized the limited amount of information available on >ht etmets of low-level, prolonged expo sure. The S'ieiuisis al=o pointed out how difficult it is to obtain accurate inlormaiion uii these effects. There are three scious difficulties In determining flic cuccis of asbe.-to., on human health, the conference speakers agree tl: 1 he form asbestnj itrelf is mis leading, for it encompa.vH-.s a whole giotip of mineral that are distinct from each miter in chemical composi tion, pmliele size, and probably biolog ical el feet. o Many of these particles are so small! that detection is extremely dilficult and time consuming, placing re straints on rite, scope of research that can In- reasoimPh undertaken. Perhaps me most serious diffi culty in asbestos research, however, is the very long peiiod dm ween initial ex posure auvl evidence of biological eitects. In the c.ise of mesothelioma, an asbestos-induced cancer of the linings of the abdomen and chest, this time period is usually 2d to 3d years. Asbestos is any of several silicate minerals existing in fibrous form. The Federal nCfiintir lists six main types of asboOos 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 nonf'brous type that is sometimes considered an asbestos mineral and sometimes not. Chryaotile asbestos is the most dis tinct asbestos form and the one most widely used in industry. A magnesium silicate hydroxide, ehrvsciile exists in nature as a bundle of very small fibrils, each less titan 3 micion:; in length and about 0.2 micron in diameter. Those fi brils are hollow, and their large surface area and relatively hi::h surlc.ee charge allow for great adsorption of trace inetal ions to these particles. The other asbestos minerals, collec tively referred to as the amphiboie minerals, have a significantly larger fiber diameter and me :-ni;d fibers. They have sodium, calcium, and iron occuHng in 'heir lattice structures, in addiri.m to i ...gnesium and randomly substituted trace metal ions. Although not used nr. extensively for industrial purposes, the amphiboie mir.eiab com monly are found as contaminants of talc, chrysolite, and ether widely used minerals. Chrvsotile fibrils are too small to be detected by conventional optical mi croscopy. To identify these particles positively. Dr. Arthur M. Larger of Mt. Sinai School of Medicine in New Turk City explains, a combination of transmission electron microscopy, se lected area diffraction, and microchemical analysis is needed, Otlurs be lieve that seaming electron microm(uks could be useful in detecting cUiy.MJtile in combination with some type of chemical identification, but all agree that the main drawback to any detection technique that require-* elec tron micrcscopv 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 ip I he environment must consequently he very limited in scope. Amphiboie asbestos fibers are 1 uger. but they also require rubligiit micro scopes for careful examination and cannot be oositivcdy identified without additional microcbemienl nr '.- elective area diffraction analysis. i Chrysatile fioers in V:ng tissue The research workers at the confer ence e'.piessee! great hope that ad vances >n auiiimated analysis would make mere 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 en'.cope that is curreiuiv used in his laboratory for analysis of coal mine dust. The most serious deterrent to under standing the oioiogjcai effect of ingest ed and inhaled asm--.:,.' however, is the long incubation pcEod of certain asbestos-induced diets. Asbestos workers in the shipbuilding industry in the U K. in the 193U's began to develop statistically high incit'd.ces cf the pre viously rare cancer form mesothelioma in the late 1930's, more than 20 years after their asbestos exposure. .Since that time, many other eases of the dis ease have been reported in patients who worked with asbestos 25 to 35 years <--irher. Dr. Irving J. Seiikoff. director cf the Environmental Health beienees Center at Mt. Sinai School of Medicine, presenit-d data to the eonier'nre !roin sev eral Mortality studies of occupationally exposed asbestos vvurlvr' m New York and New Jersey. Hi- studies show in* crec-Cs m imcrtl.-'i'.'-i ic Mincer and mesothelioma more ih.in 20 years alter heavy .i.-bestos expi-siue. in addition, he louml that although lung cancer deaths dal not appear to be .more frequent among nonsmoking asbe.ui's workers than among the gen eral nonsmoking population, they were very Much more frequent among smok ing asbestos workers than amc-tig other smokers. In one study of 17,J'vit> asbes tos insulation workers, of whom 1)550 da__ CAE if I BB 0016005 J 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 wotkers 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. Selikotf and his associates have ht gun on asbestos workers in New York and New Jef'ev ore being continued and expanded. Dr. Sehkoff points out that there are some cases of mesothelioma iu New Jersev that cannot be traced to any asbestos exposutc. These tire being further in vestigated to see if a muse lor them can bo fuund. Multiple elteet correln tions, such as that between cigarette smoking and asbestos fiber inhalation, arc being looked for also. Dr. Ian Webster of the National lie- search Institute for Occupational Dis eases in Johannesburg, Republic of South Africa, told the confe'Cnce of a massive effort by the South African government to establish the danger of asbestos exposure. South Africa mines both amphihole and chrvsotile typos 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 hope* to be able to follow a substantial number of these workers and determine, at the very least, which asbestos lorins are the most dangerous oties. The other direction of torrent aRie,tos research te-cs laboratory animals to study details of the effect of the fibers on tissues. The drawbacks of making inietences from annual nunt-'- wane re peatedly pointed out by speaker, at the conference Especially in earner re search, diflcuenl animal species often respond substantially dit ercntly to the same agent. Consequent v, many dif ferent animal models mi's be used and compared if animal rmponse 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 lhe epi 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 libers 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 hi., sample in t he epiderm. In studies with baboons. Dr. Webster found that ve y little ingested asbestos penetrates the walls of t be stomach and colon and that almost all that does is of the smaller chry.-otile type. Studies with inhaled asbestos also show that the fiber that is ab sorbed is predominantly the chrvsctile 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 agree mem, however, on what sort of regulation mould be im plemented Dr. William Eisenberg of the Food and Drug Administration explains that it is not possible tor FDA to run elec tron microscopy analyses of all the po tential sources of asbestos contamina tion under its jurisdiction. At present, analysis hv 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 conctrn, according to Dr. KYenberg, is with paretuctal drugs rather than with substances that enter the body through the gastrointes tinal tract, since relatively smell amounts ol ingested asbestos appear to penetrate the body. Last September FDA began taking steps to etimiimte the use o! asbestos tillers in the p<oduct ton of parenteral drugs. F.l'.Vs < lordoii Kxcreti i .tilt foi stan dardize! ion ol repotting data so 'hat the necC'.-saidv limited amount of data collected it; each study can be usefully compand with results from other studies. Ho points out that information on the biological effects ol asbestos i vt. v limited anti that the t Ilia is of nu.uv asbestos substitutes have not been in vestigated at all. Before asbestos use is banned, it should be certain that a safer alternative is available, ho cau tions. j BB 0016006 Dec. 10, 1973 C&EN 19