Document zQZzN1VxgoGa01aL9KO0jy94R

FILE NAME: Avondale (AVD) DATE: 19: DOC#: AVD DOCUMENT DESCRIPTION::Z:ZZKZ DDZZZ __ ... _.......__.__ .........__._____.-- PLAINTIFF'SEXllll!If ------- UC-2171 Measurement of Asbestos Exposure JEKRMlAH R. LYNCH HOWARD E. AYER T HE SAMPLING made at the time STRATEGY DECISIONS of the basic epidemiologic study of an industrial dust hazard ultimately de- termine the methods that will be used to evaluate exposures in later regulatory or control situations. Thre5hold Linut Values (TLV) are based on a correlation between health effects and exPOSures as measured by a particular method. Since no method, with the possible exception of electron microscopy, measures all of the dust and no ~wo methods measure exactly the same fraction, the correlation of exp;,sures with health effects should not ~ expected to be the same where different methods of exposure measurement are used. Al- though it i5 possible to establish a transition from one method to another by. means of simultaneous companion sanipling, the number of _.samples re- quired is large, making this approach difficult. Therefore, the methods used in the original study are important not only because of their contribu- tion to the success of that study but also because succeeding industrial hygiene surveys will be largely committed to the use of those methods. From the Bureau of Di.,eaae Prevention 4,wl Enolronm~mcl Control. NQtiona! Centet' fo-r Urbo'B ond lndtL.tmal Health, Oce11pational Health P,-ogTam, U.S. Public Health Sttuli!e (HEW}, Ci11cinnat,, Ohio. Threshold Lfm.ft Value !or Asbestos The present TLV for asbestos has its origin in a linear or "one time" epidemiologic study of the asbestos textile industry conducted by Dreesen et al.' in the Nineteen-Thirties. The then available impinger method was used to sampl~ the dust; all particles, both grains and fibers, were counted since few fibers were seen. Dreesen et al. stated that, ", , i the dust concentration in asbestos factories cou)d be kept below 5 million particles per cubic foot (mppcf) new cases oI asbestosis probably would not appear." Elsewhere, they described this suggested n.v as tentative. 'l'be reason for their hesitancy in recommending a definite exposure limit was that only four of the workers studied had been exposed to levels under 5 mppcf for over 10 years. This is not surprising when one considers the conditions of these mills at that time :is compared with present conditions (Table 1). The incidence of frank disease was so great that prior to the beginning of the study out of a total of less than 000 employees the plants discharged 150 workers suspected of having as bestosis. Engin~ring controls have reduced dust con centratious by an order of magnitude over the past 30 years. The economics of dust control are such that the cost of further improvement, if necessary, may well equal the cost of all improvements made Journal oJ Occupational Medicine 21 ucc 006946 AsbeJtos E.1-poJttTfl SURVEY OF OPEIIATION f,ber Preporotion Cordinq Si,ir,ninq lwiJtinQ WaevinQ- TAII.E I Oust Cor,centration1 - A1besto1 Tertile Surveys PENN"- PHS 1938 1934 WITHOUT WITH CONTROL CONTROL Meon Concentrotion ,n mppcf 117.0 31.0 1,.0 JI.I 25.7 3.3 16.2 7.1 3.8 II.I 19.8 14.0 u PUBLIC HEALTH SERVICE 19~ 2.3 1.2 1.2 1.9 0.8 to date. It is, therefore, necessary for the benefit of both the worker and the industry that precise knowledge of the health hazards of asbestos be obtained. Present Epidemiologic Study The present epldemiologic study of the asbestos products industry by the United States Public Health Service has been adequately cfescribed elsewhere,2- and will only be sununarized here. The reasons for the study are as follows. 1. The substantial changes in the size and technology of the industry have created new exposure situations in need of evaluation. 2, Over-all reductions in asoestos dust levels now m:tke it possible to e,camine the relation of asbestos to asbestosis in wc,rkers with long-term lower level exposures. 3. The relationship between types and magnitudes of exposures and the occurrence of lung can~r needs to be defined. The study is divided into the following segments. (A). The present exposure of groups o workers will be measured by baseline surveys. Past exposures will be obtai~ from plant or regula tory agency records; and future exposures from periodic resurveys so as to yield a history of ex posure spanning at least 20 years. (B). Death certificates and, where available, autopsy records will be obtained for those members of the exposed group on whom social security death claims have been filed. 1'"'rom these data (age and cause) specific death rates will he constructed and related to exposure. (C). More sensitive measures of health status will be obtained from medical examin;ition of a selected sample of the study population. (D). Techniquts of future medical and environmental evaluation and ha7..'.lrd control will be developed. This present paper is concerned with the first segment only, measurement of exposure. lmpinger Sampling and Counting Jmpinger samples were collected Iroutinely in both the baseline surveys and resurveys of the present epidemiologic study because only by th~ sampling method could dust levels be :related to the present TLV, which is based on dust concentration measurement by impinger. lmpinger samples collected simultaneously with other sample types are also used to establish relationships between methods to permit estimation of past exposures in terms of other fractions of the airborne dust. Since the confidence limits of a dust count improve as the number of particles cowite<i increases and only a few fibers are seen in impinger samples the original investigators chse to count all particles :md, thus, arrive at a measure of overall dustiness. The success of this approach as applied to dust control in that era of massive exposures is evidenced in the improvement in the industry (Table 1). However, in modern asbestos product plants, such as asbestos cement pipe plants, we find ourselves in the anomalous position of counting airborne d.ust known to consist mostly of cement against a TLV intended to apply only to asb~stos dust. The lack of fibers in the impinger samples was not due to the absence of fibers in the air. The impinger, an impaction device, has a collection efficiency related to the aerodynamic size of particles and is not efficient for particles with falling speeds less than that of one micron (/t), unit den s1ty spheres. Further, the lOX objective, light field, counting technique used d~s not resolv~ particles much smaller than one micron. Laboratory experiments showed that the impinger passed fibers and from field sampling it is estimated that only about one out of 100 fibers in the air as seen in electron micrographs was seen m the 1mpmger samples. 22 January 1968 Vufome 10 No. 1 ucc 006947 Lynch, ~yer Fiber Counts on Membrane )filters It is evident from the preceding that another method is needed if we are to obtain a statistically useful index of airborne fiber concentration, In- terest in fibers stems from the need to measure that factor in the environment that is most relevant to th.e disease-causi.ng mi:chanism and will, thel'efore, yield a significant correlation between health- and exposure. Fibers have long been implicated as the causative agent in asbestosis and may be significant in cancer. Timbrell's work showed that becaus@ of the peculiar aerodynamic properties of fibers (i.e. that their falling speed is dependent on d~eter only when a.spect ratios are greater than 10) it is possible for much larger objects (longer and heavier) to penetrate deep into the lung in the shape of fibers than in the shape of grains. This appears to be a most sienificant biologic property considering that the parent minerals involved (amphibole and serpentine) are not considered biologically active. Based on methods developed in Great Britain,5 a method of collecting and counting fibers on membrane niters was developed. These fibers have pore sizes of 0.8 ~ but are almost 100% efficient down to several hundredths of a m.icron because of surface effects. They are rendered transparent with a l-to--1 mixture of diethyl oxa late and dimethyl phthlate and counted with a 4 mm. objective (430X) under phase contrast illumination. By examining a suitable number of fields, it is possible to count enough fibers to make a statistically useful estimate of fibrous dust con centration. In addition, longer duration pers<>naltype samples which are not possible with the impinger method may now be used. Some commcmts on the relationship between the impingei- and the membrane filter with ,:esped to the question of sensitivity will reveal a further limitation 0 the impinger method. From large numbers of companion impinger/filter pairs collected in asbestos textile mills an equivalence between the two sampling methods has been obtained.r Thus, when impinger samples yield, on the average, a concentration near the TLV of 5 mppcf, the fiber concentrations as measured by membrane filtei- samples would be eJtpected to be a11 shown m Table II Although there is no formal TLV applicable to English asbestos textile mills, a goal of 4 fibers longer than 5 ," per cc. has been mentioned.3 If t.he above equ1valct1ce 1s apl)roximdely vr,Jid, this indicates that the TLV by impinger would be on the order of 1 mpcd. If the safe level of exposure TYPE COUNT Total ftbeB Fiber, l<,nqc, ti.an S ll Fiber1 lonQer 1hen IO I' lAtl II CONCENTRATION FlaERS/CC so 30 rs should fall in this lower range, dust concentrations would be so nenr the lowe-r practical limit of sensitivity for the impinger that accurate measurements would he impossible. Consequently, the :shift in emphasis in the present study from the impinger to the membrane filter method is based not only on increased relevance, but also on the greater sensitivity of the latter method. Weight Methods for Asbestos . Even though the greater precision of gravimetric methods over count methbds is unquestioned, the ability to capitalh.e on this lessened variability is limited by the natural variability of the environment. When used as an index of asbestos exposure a measurement of the gross , weight of airborne dust suffers from the same problem as impinger counts. l the relevant !actor is the airborne concentration of respirable fibers, a gross mass measurement yields only an index. 0 over-all dustiness, whic.-h includes much dust of lower biologic signific,mce, especially in mixeddust environments. Size-selective presampling devices suitable for long-period respirable mass sampling have been developed. However, airborne dust, even in the respirable .fr_!lc~n, C(!ntains mostly grains, both in number and in weight. Some of these grains are particles 0 the parent rock ad. jacent to the ai,be:;tos vein, chemically and crystallographically indistinguishable from fibrous asbes- tos. Other parCles ilre grains of pr<1cess materials and of ambient dust. With the non-respirable dust excluded by a presampling device, the asbestos and parent rock fraction can pe determined by x-ray diffraction or, in the case of chrysotile, by magnesium analysis. No analytical method has been d-eveloped for measuring only fibrous asbestos in the presence of particles of associated rocks. Airborne Carcinogens All of the foregoing has been concerned with exposure measurement ior the prevention of asbestosis. Although the mech~nism of cancer among asl>Pstos workers is not clc?ar, apparently airborne asbestos fibers are a factoT. Thus, the niethods of fiber conc-entration measur~ment serve . to measure this fiber factor with r~spect to cancer as well. Otht>r asbesto~ contaminants of interest are polynuclear aromatic hydrocarbon~ a11d cer Journal o( Occupational Medicine ucc 006948 23 Asbestos Exposure tain trace metals, especially nickel, chromium, co. balt and manganese. In all of the early plants surveyed in this study, high volume (30 to 50 cfm) s.unples on glass fiber filters were collected for airborne po}ynudear aromatic hydocarbon measurement. Levels in the work places were not significantly above ambient air pollution levels. However, trace metal analyses, of similar high volume samples collected on glass .fiber and, more recently, membrane filters, do show significant amounts ol nickel, chrom:.un, cobalt and manganese and it can he presumed that past levels were higher. Since these data are collected without exact information on the 11pecinc a.:tor to measure for cancer-risk correlation no conclusions can be drawn at this time. Selection of a Standard Method As an outcome of an epldemiologic study, a safe level of exp06Ul'e should be set in terms of a method of exposure measurement which meets the following criteria in the order given: 1, The en,ironment.al factor measured should be sufficiently relevant to the disease mechanism to correlate with health status even in environ. ments where exposures to mixed dust occur. Z. The sensitivity of the method should be such as to measure levels well below the TLV. 3. The method should lend itself to an appropriate sampling strategy; e.g., long-period personal samples in the case of asbestos. 4. The expense of conversion from existing methods should be reasonable. The impinger method of measuring asbestos exposure does not meet any of the c:riteria well with the exception of expensi Weignt methods would be preferred if there were an analytical break- through. At present fiber counts on membrane filters are the best method of estimating exposure as related to the risk of asbestosis and the airborne fiber concentration as a factor in the risk of lung cancer. U.S. Pail>Uc 1le11lt1& S~e Cincin114ti, Ohio 4SZOZ Referenc~; 1. Thluu>t, W. C.; DALLA VALLE, J. M.: F.l>WARDS, T. L; MIUD, J. M. and SAn:u, R.R.. A Study of Aabestosls in th~ Asbestos Textile Industry, Public H'taltb Bulletin No. 241, U.S. Government Printina Oflice, Washington. D.C, 1938. 2. CIIALLEY, L. J.: Objectives and ~neral Plan for Occupational Hl!lllth Study of the A s ~ Produca. Industry. Division of Ottupatkmal Health, Public Health Service, Department of Health, E.dueation and Welfare; 1962. 1n,.. 3. LYNCK, J. R.: Asbestoa S t u d y - ~ and F1ndTt'c,,a 21th A"" Meet AM C01lf GCJVem'IM1lcid Ind~, Hwienbu, 1965. ,. TDIIIELL, V.: The Jnhalation of Fibrotl5 Du,ts, An'A NY Aced Sci 132: 1, 1965. 5. ADDlllGLET, C. G.: Asbestos Dust and its Meuuremeo& Ana Occupa Hwietui s:z, 1966. ti. Eow-4Rll6. G. JI. and LYl'ICH, J. R.: The Method Used by the U.S. Public Health Service for Enumeration of Asbestos Dust on Membr;,,ne Filters A'"' Cecup& H~e 11:l, 1967. 7. AYER, H. E.; Lnm,, J. R. and FA-101r.Y, J. H.: A Com parison of Impmger and Membrane Filter Techniques for EvaluMtng Air S:lmples in Asbestos Plants An11 NY Acczd Sci 132: l, l 965. 8. RoAcK, S. A.: Mea.,urement of Airborne Asbeslbs D\lst by lnstrumenta Measuring Different Parametel"$ A1'n NY A.cad Sci l32: 1, 1965. 9. CRAtu:Y, L. J.; KEENAN, R. G. and LY~01, ,1, R.: Exposure f.(1 Trace Metals ui the Manufuture c,l Asbestos Te~lile Products. Presented at the American Industrial Hygiene Conference,- Chicago, Illinois, 1967. Reprinted from Journal of Occupational Medicine l 0:21-2.4, Januaity l 968 Printed in U.S.A. Copyright 24 January 1968 Volume J() No. 1 ucc 006949