Document 9JQRNgO2MQ3r6n5Yvx0ZNJ0wL

21S MAKCJ.MU.T R. JIECKLAKE Iv, (lie greater mesothelioma an<l, possibly, canter potential of arnosite in manufacturing processes, compared to mining, could be attrib uted to the smaller particle size for the fiber re leased in a production plant compared to that at the mine head. At the practical level of environmental con trol, regulations proposed for chrysotile in 1068 (223) by the British Occupational Hygiene So ciety were at a level (2 fibers per cm3 aver aged over 3 months) that, it was hoped, would allow no more than 1 per cent risk of disease (specifically, asbestosis) in a 50-year working life. Evidence suggests that this would also re- tluce risk of bronchogenic cancer. At the time, the British Occupational Hygiene Society was uncertain that standards for other fibers should follow "hy analogy." They subsequently pro posed the same standards for arnosite (226). but a standard 10 times more stringent for crocidolite (227) was promulgated by government regulation. Furthermore, because all standards should be regarded as no more than an expres sion of the "best available hypothesis" ol lev els adequate to protect human health, they should always be reviewed in the light of sub sequent evidence. This was done in 1973 for chrysotile, and no change was recommended (228). In the United States, the Occupational Health and Safety Administration (OSHA) pro mulgated a standard of 5 fibers per cm* in 1972, to Ire reduced to 2 fibers per cm* in 1976 (229), and there was a recent proposal to lower further the standard to 0.5 fibers per cm* (230). These standards apply to all fiber types. Research should continue in an attempt to identify more precisely the reasons for betweenfiber differences in biologic elfect, beta vise a better understanding of what determines the biologic responses of this mineral can only re sult in its human use being conducted under conditions that more effectively protect the health of the exposed worker. Fig. 3. [From Schneidcrman (93): reprinted by per mission of publisher.] Dose-response relationship lor cancer of the bronchus and lung. The data shown are those of McDonald (7, p. 189), describing chry sotile asbestos miners (left scale), and those of En terline and associates (82, 83), describing produc tion workers (right scale). In McDonald's data, mor tality was expressed as equivalent average death rates (85, 92) to enable a wilhin-population comparison between men with low and higher dust exposure. The data of Enterlinc and associates were re ported as standardized mortality ratios, which used for comparison the most appropriate gen eral population statistics. Dust exposure in both studies was calculated in similar fashion and ex pressed in million particles per foot*-yesrs (82, 83, 91). The vertical scales are drawn so that an equiva lent average death rate of 20 is equated with a stan dardized mortality ratio of 200 in the top panel and 400 in the bottom panel, which results in both sets of data falling on tlic saute curve. Clinical Implications of the Epidemiologic Findings Facetl with a patient in whom the diagnosis of one of the described diseases has been made, i.e., fibrosis of the lungs and/or pleura, or can cer of the lungs and/or pleura, it may be im portant to establish whether, in this particular case, the disease is asbestos related. If the pa tient is currently known to be exposed, this rarely presents a problem. If not, a systematic history is called for, and. should include all his or Iter previous occupations (including short term jobs, summer jobs, and so on), as well as those of his or her work colleagues and family members. In addition, places of residence should be noted, particularly if the diagnosis is meso thelioma and/or pleural plaques. The discov ery of asbestos fibers, coated or uncoated, in biologic material (sputum or biopsy or surgical material) requires explanation, if not already evident from the history. Establishment of an association with asbestos has importance if atiributahility is questioned (in cases of compensatiou). as well as for other workers if the risk had not previously been recognized. The dose relationship, particularly of fibrosis. ^ to anc an 25 sati tioi san sor. its cal da mt we