Document N7xNmDGk8vnmQ94wpbRqwOaV

an h e s a m p l in g s t r a t e g y d e c is io n s T made at the tim e of the basic epidemiologic ys- study of an industrial dust hazard ultim ately de ore term ine the m ethods th at will be used to evaluate aal exposures in later regulatory or control situations. Threshold Lim it Values (TLV) are based on a Co. co rrelatio n b etw een h e a lth effects a n d exposures way as m easured by a particular method. Since no )001 m ethod, w ith th e possible exception of electron Measurement microscopy, m easures all of the dust and no two m ethods m easure exactly the same fraction, the ila * of A sbestosirai correlation of exposures w ith health effects should ilth not be expected to be the same w here different m ethods of exposure m easurem ent are used. Al Exposureand though it is possible to establish a transition from 'er one m ethod to another by means of simultaneous companion sampling, the num ber of samples re In- quired is large, m aking this approach difficult. 185: T herefore, th e m ethods used in th e original study are im portant not only because of their contribu .ary JEREM IAH R. LYNCH tion to the success of that study bu t also because Am HOWARD E. AYER succeeding industrial hygiene surveys will be largely committed to the use of those methods. lio- &eh, Threshold Lim it Value for Asbestos ro- T he p resen t T LV fo r asbestos has its origin in : of a linear or "one tim e" epidemiologic study of the 11: asbestos tex tile in d u s try conducted b y D reesen et al.1 in the Nineteen-Thirties. The then avail and irty able impinger m ethod was used to sample the alih dust; all particles, both grains and fibers, w ere counted since few fibers were seen. Dreesen et ro- al. sta te d th at, " . . . if th e d u st concentration in irty asbestos factories could be kept below 5 million :1th, particles p e r cubic foot (m ppcf) new cases of as , bestosis probably would not appear." Elsewhere, mce th ey described this suggested TLV as tentative. The reason for their hesitancy in recommending SON, a definite exposure lim it w as th a t only fo u r of the iro- w orkers studied had been exposed to levels under iiovron 5 m ppcf for o v er 10 years. This is n o t surprising w hen one considers the conditions of these mills a t th at tim e as compared with present conditions (Table I). The incidence of fran k disease was so great th at prior to the beginning of th e study out of a to tal of less th a n 600 em ployees th e plants d ischarged 150 w o rk ers suspected of having as- bestosis. From the Bureau of Disease Prevention and Environ mental Control, National Center for Urban and Industrial Health, Occupational Health Program, U S , Public Health Service (H EW ), Cincinnati, Ohio. Engineering controls have reduced dust con centrations by an order of magnitude over the past 30 years. T he economics of d u st control a re such th at the cost of further im provem ent, if necessary, m ay well equal the cost of all im provem ents made > . l Journal of Occupational Medicine 21 Asbestos Exposure SURVEY O F O PERATIO N Fiber Preparation C a rd in q Spinninq Twisting W eaving ________________ TABLE I_______________ Dust Concentrations -- Asb estos Textile Surveys PENNA. 1934 P H S 1938 W IT H O U T W IT H CONTROL CONTROL M ean Concentration in mpDcf 67.0 31.1 16.2 3.8 19 8 36.0 25.7 7.1 II.1 14.0 6.0 3.3 -- -- 2.1 PU BLIC H EA LT H SERVIC E 1964 2.3 1.2 1.2 1.9 0.8 to date. It is, therefore, necessary for the benefit T his p re se n t p ap er is concerned w ith the first of both the w orker and the industry that precise segm ent only, m easurem ent of exposure. knowledge of the health hazards of asbestos be obtained. Present Epidemiologic Study Im pinger Sampling and Counting Im pinger samples w ere collected routinely in both the baseline surveys and resurveys of the The present epidemiologic study of the asbestos products industry by the U nited States Public H ealth Service has been adequately described present epidemiologic study because only by this sam pling method could dust levels be related to the present TLV, w hich is based on dust concen elsew here,2,3 an d w ill only be sum m arized h ere. The reasons for the study are as follows. tration m easurem ent by impinger. Im pinger sam ples collected sim ultaneously with other sample 1. T h e su b stan tial changes in th e size and te c h types are also used to establish relationships be nology of the industry have created new exposure tw een methods to perm it estimation of past ex situations in need of evaluation. posures in term s of other fractions of the airborne 2. O ver-all red u ctio n s in asbestos d u st levels dust. Since the confidence limits of a dust count now m ake it possible to exam ine the relation of im prove as the num ber of particles counted in asbestos to asbestosis in w orkers w ith long-term creases and only a few fibers are seen in impinger lower level exposures. sam ples the original investigators chose to count all particles and, thus, arrive at a m easure of over 3. T he relatio n sh ip b etw een types and m agni all dustiness. The success of this approach as ap tudes of exposures and the occurrence of lung plied to dust control in that era of massive ex cancer needs to be defined. The study is divided into the following seg posures is evidenced in the im provement in the industry (Table I). However, in m odern asbestos m ents. product plants, such as asbestos cem ent pipe (A ) . The present exposure of groups of w ork plants, we find ourselves in the anomalous posi ers will be m easured by baseline surveys. Past tion of counting airborne dust known to consist exposures will be obtained from plant or regula m ostly of cem ent against a TLV intended to apply tory agency records; and future exposures from only to asbestos dust. periodic resurveys so as to yield a history of ex The lack of fibers in the im pinger samples was p osure spanning a t least 20 years. not due to the absence of fibers in the air. The (B ) . D eath certificates and, w here available, im pinger, an im paction device, has a collection ef autopsy records will be obtained for those m em ficiency related to the aerodynam ic size of par bers of the exposed group on whom social se cu rity death claims have been filed. From these ticles and is no t efficient for particles w ith falling speeds less th a n th a t of one m icron (i) , unit den data (age and cause) specific death rates will be sity spheres. F u rth e r, the 10X objective, light field, constructed and related to exposure. counting technique used does not resolve par (C ) . More sensitive m easures of health status ticles m uch sm aller than one micron. Laboratory will be obtained from medical examination of a selected sample of the study population. experim ents showed that the im pinger passed fibers and from field sampling it is estim ated that (D ) . T echniques of fu tu re m edical an d e n only ab o u t one o u t of 100 fibers in th e a ir as seen vironm ental evaluation and hazard control will be d e v e lo p e d . in electron m icrographs was seen in the im pinger sam ples. 22 Ja n u a ry 1968 V o lu m e 10 No. 1 Lynch, Ayer Fiber Counts on M embrane Filters It is evident from the preceding that another m ethod is needed if we are to obtain a statistically useful index of airborne fiber concentration. In terest in fibers stems from th e need to m easure TYPE C O U N T T A B LE II Total fibers Fibers ionqer than 5 ft Fibers longer than 10 \i C O N C E N T R A T IO N F IB E R S / C C 50 30 15 th a t factor in the environm ent th at is most rele should fall in this low er range, dust concentra vant to the disease-causing m echanism and will, tions w ould be so n ear the low er practical lim it of therefore, yield a significant correlation between sensitivity for the im pinger that accurate m eas health and exposure. Fibers have long been im urem ents would be impossible. Consequently, the plicated as the causative agent in asbestosis and shift in emphasis in the present study from the m ay be significant in cancer. Tim breH 's4 w o rk im pinger to the m em brane filter m ethod is based showed that because of the peculiar aerodynamic not only on increased relevance, bu t also on the t properties of fibers (i.e. th a t th eir falling speed is dependent on diam eter only w hen aspect ratios greater sensitivity of the latter method. are g reater th an 10) it is possible for m uch larger W eight Methods for Asbestos objects (longer and heavier) to penetrate deep Even though th e ' greater precision of gravi n into the lung in the shape of fibers than in the m etric m ethods over count m ethods is unques e ' shape of grains. This appears to be a most sig tioned, the ability to capitalize on this lessened is nificant biologic property considering th a t the variability is lim ited b y the n atural variability of parent m inerals involved (amphibole and serpen the environment. W hen used as an index of as tine) are not considered biologically active. bestos exposure a m easurem ent of the gross Based on methods developed in G reat Britain," w eight of airborne dust suffers from the same e a m ethod of collecting and counting fibers on problem as im pinger counts. If the relevant factor m em brane filters was developed.6 These fibers is the airborne concentration of respirable fibers, h av e p o re sizes of 0.8 a b u t a re alm ost 100% ef a gross mass m easurem ent yields only an index of e nt ner nt *r- P- X- he :os I pe ist ?ly ficient down to several hundredths of a micron because of surface effects. They are rendered transparent w ith a 1-to-l m ixture of diethyl oxa late and dim ethyl phthlate and counted with a 4 mm. objective (430X) under phase contrast il lum ination. B y exam ining a suitable num ber of fields, it is possible to count enough fibers to m ake a statistically useful estim ate of fibrous dust con centration. In addition, longer duration personal type samples which are not possible with the impinger method may now be used. Some comments on the relationship between the impinger and the m em brane filter w ith respect to the question of sensitivity will reveal a fu rth er lim itation of the impinger method. From large over-all dustiness, w hich includes m uch dust of low er biologic significance, especially in m ixe ldust environments. Size-selective presam pling de vices suitable for long-period respirable mass sampling have been developed. However, airborne dust, even in the respirable fraction, contains m ostly grains, both in num ber and in weight. Some of these grains are particles of the parent rock ad jacent to the asbestos vein, chemically and crystallographically indistinguishable from fibrous asbes tos. O ther particles are grains of process m aterials and of am bient dust. W ith the non-respirable dust excluded by a presam pling device, the asbestos and parent rock fraction can be determ ined by x-ray diffraction or, in the case of chrysotile, by vas num bers of companion im pinger/filter pairs col magnesium analysis. No analytical m ethod has .''he lected in asbestos tex tile m ills an equivalence b e b e e n developed fo r m easu rin g only fibrous asbes ef- tw een the two sam pling m ethods has been ob tos in the presence of particles of associated rocks. -aring tained.7 Thus, when im pinger samples yield, on the average, a concentration near the TLV of 5 A irborne Carcinogens en- mppcf, the fiber concentrations as m easured by A ll of the foregoing has been concerned w ith .id, m em brane filter samples w ould be expected to be exposure m easurem ent for the prevention of as >ar- as show n in Table II. bestosis. A lthough the mechanism of cancer ory A lthough there is no form al TLV applicable to am ong asbestos w o rk e rs is n o t clear, ap p aren tly sed English asbestos textile mills, a goal of 4 fibers airborne asbestos fibers are a factor. Thus, the .hat longer th a n 5 ,u p e r cc. has been m entioned.8 If methods of fiber concentration m easurem ent serve een th e above equivalence is approxim ately valid, this to m easure this fiber factor w ith respect to cancer iger indicates that the TLV by im pinger would be on as well. O ther asbestos contam inants of interest the order of 1 mpccf. If the safe level of exposure are polynuclear arom atic hydrocarbons and cer- o. 1 Journal oj Occupational M edicine 23  <s . Asbestos Exposure tain trace metals, especially nickel, chromium, co balt and manganese. In all of the early plants su r v eyed in th is study, high volum e (30 to 50 cfm) samples on glass fiber filters w ere collected for airborne polynuclear aromatic hydocarbon meas urem ent. Levels in the w ork places w ere not sig nificantly above am bient air pollution levels. However, trace m etal analyses, of similar high volum e sam ples collected on glass fiber and, more recently, m em brane filters, do show significant amounts of nickel, chromium, cobalt and m an ganese and it can be presum ed that past levels w ere higher.8 Since these data are collected w ith ou t exact inform ation on the specific factor to m easure for cancer-risk correlation no conclu sions can be draw n at this time. Selection of a Standard Method A s an outcome of an epidemiologic study, a safe level of exposure should be set in term s of a m eth od of exposure m easurem ent which meets the following criteria in the order given: 1. T he enviro n m en tal factor m easu red should be sufficiently relevant to the disease mechanism to correlate w ith health status even in environ m ents w here exposures to mixed dust occur. 2. T he sensitivity of th e m ethod should be such as to m easure levels well below the TLV. 3. T h e m ethod should lend itself to an appro priate sam pling strategy; e.g., long-period personal sam ples in the case of asbestos. 4. T he expense of conversion from existing m ethods should be reasonable. The im pinger m ethod of m easuring asbestos ex posure does not m eet any of the criteria well with the exception of expense. W eight m ethods would be p referred if th ere w ere an analytical break through. A t present fiber counts on m em brane filters are the best m ethod of estimating exposure as related to the risk of asbestosis and the air borne fiber concentration as a factor in the risk of lung cancer. U.S. Public H ealth Service Cincinnati, Ohio 45202 References: 1. D reesen, W. C.; D alla V alle, J, M.; Edwards, T. I.; M iller, J. M. and Sayers, R. R : A Study of Asbestosis in the Asbestos Textile Industry, Public Health Bulletin No. 241, U.S. Governm ent P rinting Office, W ashington, D.C., 1938. ' 2. Cralley, L . J.: Objectives and G eneral P lan fo r Oc cupational Health Study of the Asbestos Products Industry. Division of Occupational Health, Public Health Service, departm ent of Health, Education and W elfare, 1962. 3. L ynch, J. R.: Asbestos S tudy--Procedures and F in d ings. Trans 27th A n n M eet Am Conf Governmental Indus Hygienists, 1965. 4. Timbrell, V.: The Inhalation of Fibrous Dusts, A n n N Y A cad Sci 132:1, 1965. 5. A ddincley, C. G : Asbestos D ust and its M easurem ent A n n Occupa Hygiene 9:2, 1966. .6. E dwards, G. H. and L ynch, J. R.: T he M ethod Used by the U.S. Public Health Service for Enum eration of Asbestos Dust on Membrane Filters A nn Occupa Hygiene 11:1, 1967. 7. A yer, H. E.; L ynch, J. R. and F annly, J. H.: A Com parison of Impinger and Membrane Filter Techniques for Evaluating Air Samples in Asbestos Plants A nn N Y A cad Sci 132:1, 1965. 8. R oach, S. A.: M easurem ent of A irborne Asbestos D ust by Instrum ents Measuring Different Param eters A nn N Y A cad Sci 132:1, 1965. 9. C ralley, L. J.; K eenan, R. G. and L ynch, J. R.: Exposure to Trace Metals in the Manufacture of As bestos Textile Products. Presented at the American Industrial Hygiene Conference, Chicago, Illinois, 1967. Allergy to W ork Some people are literally allergic to work, according to a report subm itted to an Italian medical conference. The report said that m uscular activity could release an excessive am ount of histam ine, a pow erful chemical stim ulant in the body tissues, to cause rashes and allergies. R euters dispatch from Caramanico, Italy, as quoted in New Y o rk Times, A u g u st 30, 1967. 24 J a n u a ry 1968 V o lu m e 10 No. 1