Document bBKZQB52Z8Lm3kmw0EBBNvamo

i Dust-Fiber Relationships in the Quebec Chrysotile Industry Graham William Gibbs, MSc, PhD, Maurice LaChance, Eng, Montreal r Epidemiological studies of Quebec chrysotile miners and millers have related various indices of health to dust expo sure, as measured with the midget lmplnger. The Interpretation of these rela tionships In terms of fiber necessitates the conversion of midget Implnger (par ticle + fiber) counts to membrane filter (fiber) equivalents. An Investigation In In Canada and the United States, for many years routine measure counts derived from the membrane filter technique.*-7*' In North America, ments of airborne concentrations of there are no asbestos standards based asbestos have been made by the on gravimetric or other methods. midget impinger method. In conse Unfortunately, safety standards quence, the few epidemiological stud have little validity unless based on ies that have related health of as epidemiological evidence and, as has bestos workers to dust exposure have, been stated, this evidence has of ne which 87 side-by-side midget Implnger- of necessity, been forced to use con cessity been related to midget im '< membrane filter samples were taken at centrations measured by this tech pinger counts. There might be no se five mines and mills showed that the cor nique. This has been true of surveys rious difficulty in converting dust relation was poor apd no single conver in Quebec of mortality, roentgen- counts to fiber counts if some reason sion factor was justified. Until more de ographic appearance, respiratory able constant relationship were found tailed Information on the relationships between midget Implnger and membrane filter counts can be obtained. It Is recom mended that safety standards, at least In this Industry, should continue to be based on dust counts, for which there Is consid function and symptoms in chrysotile miners and millers,1'* and also of sur veys of production workers in the United States.'-7 Because of its relatively low effi to exist between the two types of measurement. Ayer et al" measured the ratio between the membrane fil ter count and the midget impinger counts for textile plants, and found erable epidemiological support, rather ciency for the collection of fibers, the that ratios differed for different oper than on fiber counta, for which there Is no midget impinger is not ideal for the ations in the same plants and for sim direct evidence. determination of airborne asbestos ilar operations in different plants. fiber concentrations.' This limitation This report describes a preliminary and the belief that fiber is the essen investigation of this problem in the tial cause of disease have led to the Quebec mining and raillingjadustrv. _ recommendation that standards for exposure should be based on fiber Methods | BB 0015787 1 Surveys in August 19*71 and 1972 were Submitted for publication June 8, 1973; ac cepted July 31. conducted at up to nine selected sites in From the Department of Epidemiology and each of five mines and mills of the Quebec i Health, McGill University, Montreal (Dr. Gibba) chrysotile mining and milling industry. A and the Quebec Aabestoa Mining Association, Thetford Mines. Quebec (Mr. LaChanoe). Reprint requests to Department of Epidemiol ogy and Health, McGill University, 3775 Univer total of 87 pairs of membrane filter sam ples and midget impinger samples were collected side-by-side at each location with sity St, Montreal H3A 2B4 (Dr. Gibbs). sampling rates of 2 liter* per minute and Arch Environ Health/Vol 28, Feb 1974 Dust-Fiber Reiatlonahipe/Gibbe A LaChance 89 K V l. v? 2.8 liters per minute, respectively. The fil ter and impinger inlets were both at ap proximately 1.5 meters above the floor. Sampling times ranged from 5 to 30 min utes, and were the same for both methods. The membrane filters were 37-mm plain white (pore size, 0.8p), and the samples were taken with the entire filter exposed. These samples were fixed, mounted with use of the British method," and counted at 500 x magnification with a Zeiss standard binocular WL microscope with phase con trast optics. One observer counted all sam ples; 20 random fields, of area 0.0055 sq mm. were observed, and all libera greater than 5p in length were counted. A fiber was defined as any particle with a length-tobreadth ratio greater than 3:1. The midget impinger method, essentially that ap proved by the Asbestos Textile Institute.1' used isopropyl alcohol, and particles were counted at 100 x magnification with lightfield illumination. These samples were counted by two observers. One observer (M.L.), who had made all previous routine midget impinger surveys of the Quebec mining and milling industry,' counted 51 of the total number of samples, and the other observer (trained by M.L.) counted the remainder. Counts made on the same samples by the two observers were within 15%. Result* A plot of all 87 membrane filter and midget impinger counts is shown in the Figure. As membrane filter sam ples were collected over the same sampling period as the midget im pinger samples, the fiber concentra tions on the filter were not always op timal (2 to 6 fibers per field). This was A plot of membrane filter and midget impinger counts; mpcf represents millions of par ticles per cubic foot. owing to the low ratio of fiber to other particulates in certain processes and the time limit imposed by evapo ration of isopropyl alcohol from the impinger. The linear correlation coef ficient for 56 samples with more than 1 fiber per field was 0.32, and, after a logarithmic transformation of both variables, the correlation, was in creased to 0.45. For 31 samples with less than 1 fiber per field, the linear correlation was very close to zero (-0.03), and the correlation of loga rithmically transformed data was 0.25. The highest correlation obtained for these data (0.45) demonstrated an association between the results ob tained by the two methods. However these correlations suggest that for al mines the regression lines are unsat isfactory fot the prediction of fibei counts from impinger counts, as tht improvement in prediction for tht best correlation (0.45) is only 13fJ better than a conversion obtained at random. A 50% improvement of pre diction would require a correlation co efficient of 0.87. If membrane filter and midget im pinger counts were considered by work area (Table), it was clear that the ratios of the two in some mines were of a different order from those in others where the same process was Ratios of Membrane Filter Counts to Midget Impinger Counts' Mine A B C D E All mines Overall Mam 4.5 (281 11.4 (IB) 21.9 (18) 5.9 (11) 1.7 (12) Underground 1.7 (1) 1.7 (1) Open Pit Drill 8.0 (2) 9.1 (21 5.2 (2) Shovel ' 5.4 (2) 2.4 (2) 7.9 (2) 0.6 0.5 (1) m 5.3 46 (7) (7) Dryer end Crusher Dryer 32 (2) 29.8 (2) 1S.9 (2) 2.0 (31 0.4 (2) 9.5 (111 Crusher 2.5 (61 3.7 (4) 12.5 (4) 8.8 m i.i (2) 5.3 (17) Rock Screening 4.9 (5) 29.8 (2) 32.6 (2) 10.4 (2) 0.3 (11 14.2 (12) Mill Fiber Screening 3.5 (51 8.5 (2) 47.4 (2) 4.3 (2) 5.3 (3) 11.0 (14) Bagging 8.1 (3) 6.1 (2) 31.1 (2) 3.8 (3) 4.5 (1) 10.4 (111 Storage 3.3 (2) 20 (2) 22.8 (21 08 (1) 81 (7) * Membrane filter counts were measured in fibers per milliliter; midset impinger counts In millions of particles per cubic foot. Numbers In parentheses are numbers of membrane filter-midget impinger pairs. -------- I BB 0015738 J-------- 70 Arch Environ Health/Vol 28, Feb 1974 Dust-Fiber Reiationships/Gibbs & LaChance 1 1 employed. In addition, ratios varied with stage of production within the same mine and mill. fiber exposure of persons in the Que bec asbestos mining and milling in dustry, or indeed of deciding Whether Arrh Environ Health 24:401-406, 1972. 4. McDonald JC. et al: Respiratory symptoms in chrysotile asbestos mine and mill workers of Quebec, Areh Environ Health 24:358-363, 1972 Conclusion* the dose-response relationships would be better or worse than those ob 5. Gibbs GW, LaChance M: Dust exposure in the chrysotile asbestos mines and mills of Que bec. Arch Environ Health 24:189-197. 1972 Although only 87 pairs of samples tained from particle counts. Until sat 6. Enterline P, Weill H: Asbestoais in asbestoe were collected in this pilot investiga tion, these were sufficient to demon isfactory conversion factors are de rived. it would seem best to base cement workers. Read before the IARC Confer ence on the Biological Effects of Asbestos. Lyon, France. 1972 strate that no single conversion fac standards, at least for mines and 7. Enterline P. De Coufle P, Henderson V: tor could be applied to all mines or to mills, on particle counts, for which Mortality in relation to occupational exposure in the asbestos industry. J Oecup Med 14:897-903, A all work areas within a mine. This re there now exists a reasonable body of 1972. sult coincides with the findings of evidence. A similar argument proba 8. Rendall REG. Van Sittert GCH: The suit 5 A Ayer et al" in textile plants. bly applies equally to all epidemio ability of conventional dust instruments for sampling asbestos dust clouds, in Shapiro HA Thus, the conversion of dust-dis logical studies of asbestos workers in (ed): Pneumoconiosis: Proceedings of the Inter :i ease relationships for the Quebec North America in which exposure has national Conference, Johannesburg. 1369. Cape Town, South Africa. Oxford University Press. mining and milling industry to fiber- been considered. 1970, pp 74-80. disease relationships does not seem possible at the present time. Further This investigation was supported by a grant from the Institute of Occupational and Environ 9. Standard for Asbestoe Duet Concentration for Use with Asbestos Regulations 1963, technical note 13. London. Dept of Employment and Pro ft information on the relationships of the two methods at each site within each plant is required. With adequate mental Health of the Quebec Asbestos Mining Association. H. Hui. BSc, and A. Corsillo carried out the Add surveys and performed the midget im- ductivity, Her Majesty's Factory Inspectorate, 1970. 10. Threshold Limit Values for Substance in Workroom Air Adopted by ACGIHfor 1979. Cin counts of pairs of samples at selected pinger and membrane Alter counts. cinnati, American Conference of Governmental sites, and with assumptions as to the effects that dust control and changes Industrial Hygienists. 1972 p 37. 11. Ayer HE, Lynch JR, Fanney JH: A com parison of impinger and membrane Alter tech in ore have had on impinger-filter counts, dose-response relationships based on fiber exposures could be ex References 1. McDonald JC, et al: Mortality in the chryso- niques for evaluating air samples in asbestos plants. Ann NY Acad Sci 132274-275, 1965. 12 Hygiene standards for chrysotile ssbestos dust, Committee of Hygiene Standards of the amined, and it is possible that safety standards based rationally on fiber tile asbestos mines and mills of Quebec. Arch Environ Health 22:677-686, 1971. 2. Rossi ter CE. et al: Radiographic changes in British Occupational Society. Ann Occup Hyg 11:47-69. 1968. 13. Asbestos Textile Institute Method for De counts could then be established. Without this, there is no way of esti mating with any accuracy the total chrysotile asbestos mine and mill workers of Quebec. Areh Environ Health 24:388-400, 1972. 3. Becklake MR, et al: Lung function in duyaotile asbestos mine and mill workers of Quebec. termining Asbestos Dust Concentration. Ap proved by the Asbestos Textile Institute, Air Hy giene and Manufacturing Committee. Pompton Lakes. NJ, Asbestos Textile Institute. 1963. r ** SI iT HHi A r T'bb & * Arch Environ Health/Vol 28, Feb 1974 't fc Dust-Fiber Relationships/Glbbe A LaChance 71 a*,-it