Document N2rdvNKmjR6aekr2qr737xrmg

m Asbestos Air Pollution Truing J. Selikoff, MD; William <7. Nicholson, PhD; and Arthur M. Longer, PhD, New York Findings ol mesothelioma among individuals living in the vicinity of asbestos plants suggested that asbestos air pollution might occur. Measure* merit ot asbestos (Chrysolite) content ol ambient air In New York City and other locations showed levels of 10 to 50 x 10- gm/cu m, and lungs of New York residents examined at autopsy regu larly showed chrysolite fibrils. Occurrence of asbestos air pollution Is now established. What have not yet been defined, however, are the dimensions of disease hazard which may be associated. Epidemiological considerations sug gest that it is improper to equate the several kinds oi asbestos exposure: direct occupational, indirect occupational, exposure In family cir cumstances, neighborhood contamination, and general community asbestos air pollution. Since most urban air pollution is derived from com mercial and Industrial sources, the asbestos in dustry has both Important ' responsibility and opportunity tor its control. E.[ ARLY in the 1960s, the problem of as bestos disease was disseminated from the occupational area into the general, environ ment. Three germinal observations were re sponsible for this. First, Kiviluoto reported finding 499 cases of parietal pleural calcification among 6,312 residents of a rural county in Finland.1 This came very much as a surprise, since the type of calcification observed had previously been Submitted for publication Feb 9, 1971.; accepted Keb 17, 1972. From Mount Sinai School of Medicine of the City University of New York, New York. Road before the American Medical Association Research Conference on Air Pollution. New Orleans, Oct G, 1970, Reprint requests to Director, Environmental Sdenros Laboratory, Mount Sinai School of Medicine, Fifth Avenue and 100th Street, New York 10029 IDr. Selikcfl). described primarily in asbestos workers,3 usually more than 20 or 30 years after start ing work3; yet the cases were not among asbestos workers, but among farmers and farmers' wives. The asbestos link, however, was there; the county did have an asbestos mine. The natural supposition was that as bestos air pollution from the mine was re sponsible, a presumption that was strength ened when the specific type of asbestos pro duced by the mine (anthophyllite) was found in the air up to 50 km away,4 and asbestos bodies were demonstrated in the lungs of cattle grazing in the nearby fields.1 The same year (1950)-saw a second*wor risome communication. Wagner et al5 re ported 47 cases of pleural mesothelioma in a part of South Africa which was important LlJ for asbestos raining. They noted potential asbestos contact for most of the patients two or more decades before, in many instances merely the result of firing in the general area or of chance contact in a family setting. While pleural mesothelioma had previously been attributed to asbestos exposure, the -strength of this association had not been appreciated. More pertinent was the demon stration that it could result from other than occupational exposure. Amplification soon followed. Newhouse and Thompson7 studied all mesotheliomas at the London Hospital. They confirmed the close association with asbestos, 31 of the 76 subjects having had occupational exposure. They also confirmed the impor tance of nonoccupational contact; of the 45 who had not worked with the material, nine had lived in the households of asbestos workers and 11 had lived, decades before, within one-half mile of an asbestos plant f-u :J O Arch Environ Health--Vol 25, July 1072 mm' I * , v* i I m rr.M JINWi ir-SmSmIg I ' '-.-its* \<Z< 2 ASBESTOS AIR POLLUTION--SELIKOFF ET A L Lieben and Pistawka reported similar find and we would not expect their risk to be - f ings in Pennsylvania.8 duplicated in the general population. But is : What appeared to be a strong link in the part of their risk disseminated, with the - chain of evidence for environmental asbestos dusts from their work? What sort of dose-re- -- disease was the report in 1963 by Thomson et al that asbestos bodies were commonly to be found in the lungs of the general popula tion of Capetown, South Africa. They ex pressed a drop of lung tissue fluid onto a slide, examined it by optical microscopy, and in one quarter of 500 consecutive autop sies, found structures apparently identical sponse curve are we dealing with? Is there a threshold which, once crossed, leads to sen- * ous hazard of neoplasia? An hypothesis could be formulated that such a threshold ~ calls for very little asbestos (since small s amounts may still reflect billions of fibers or>i fibrils, or both), and that asbestos workers.** pass it early in their careers. ' O CO ~ UJ Cj __ I <1 1-19 20-39 40-59 60-79 80+ Total with those seen in asbestos workers' lungs. Such an hypothesis, or some variation of * Fror But these were not asbestos workers; they it, is not inconsistent with observations^*; had been ordinary citizens of this large city. made in the last several years. Neoplasms,.^ CD Thomson and associates concluded that the such as pleural and peritoneal mesotheli- ; Tlllf IBP subjects had inhaled asbestos in the course of their urban living, from the many asbes tos products about them. With knowledge of what exposure to these fibers could do under industrial circumstances as a background, and with the observations of Wagner et al5 as an example, they suggested that we were now faced with a "modem urban hazard" and predicted that asbestos-associated neo plasms would rival cigarette-induced lung oma, occur in excess even among asbestos "^ workers with little or no radiological evi--* dence of asbestosis, suggesting that-expo- 4 sures insufficient to cause asbestosis may'-f. still produce neoplasia. The spread of this-:? separation is not established, but it is appar-^ ent recently that while lower dust levels in if industry may prevent much asbestosis, such tlevels will not necessarily prevent cancer.13 It is not now known how low a threshold -j* O OO O <> iu rn ^ *- o uJ Age <1 1-1 20-3 40-5 60-7 80+ To Sen Male cancer in the future. must be to prevent asbestos-associated neo- ^ o o It should be noted that the prediction of plasms. /. j Fern Thomson and associates9 is an extrapola To tion. It is a wide step from occupational Asbestos in Lungs - - * Fro exposure, with large numbers of asbestos bodies, to community contamination, with, as a rule, far fewer bodies, particularly with little knowledge of a dose-disease response relationship. Also, the particles described had the appearance of those seen in asbestos workers, but some uncertainty existed that % It thus became important to know whether ^ asbestos truly was a common contaminant i of urban dwellers' lungs. The demonstration $ that "asbestos bodies" were to be regularly ^ found at autopsy in many cities of the * cases, except pe young children. The same ex addition to bodies"), tmcoa also readily seei these necessarily had an asbestos core,10 es world18 confirmed the finding of Thomson et pecially since it had been known for 30 al, but did not settle the question. It was v than LOj* found; most of t years that such bodies could be found after not known whether the cores were necessari- > tified, although exposure to other fibers as well.11 ly asbestos, an uncertainty resulting from y ments, glass fib Despite these caveats, the three reports, technical difficulties involved in analyzing v more concerned c 1 t taken together, posed a problem that is now such cores.17 v. very real. Occupational asbestos exposure In recent months, the impasse has been - may be associated with serious risk; for resolved by direct search for asbestos fibers ji bers, less than would be more the asbestos 3 example, among asbestos insulation workers and fibrils.18 Investigation of 3,000 consecu- 4 asbestos used in the New York metropolitan area at this tive autopsies in New York had shown that 4 thin fibers wen time, approximately one in five deaths is "asbestos bodies" were common; optical mi- ^ due to lung cancer, one in ten is due to croscopic examination of 175/t x 1 sq cm of r! mesothelioma, one in ten to gastrointestinal lung tissue in each of these cases, showed ^ ing found in 1 tending to vm number of a=be cancer, and one in ten to asbestosis and cor asbestos bodies in 1,449 (48.3%) (Table 1). V7 The critical pulmonale.1--1* These men have been ex It is likely that, had a greater volume of * examining, m posed to amounts of asbestos surely greater tissue been submitted for study, asbestos ** small portion than those in the surrounding community. bodies would have been found in all the 4 mated at l0- I: Arch Environ Health--Vol 23, July 1972 I BB 0005730 l if ASBESTOS AIR POLLUTION--SEL1KOFF ET AL sir risk to |,Nation. Bui i. tedg^th ilv orl^ OSt'-rc. ith? is thou n leads to s< rn hypotht-i. h a threshold (since snull as of fibers or estos worker- e variation of observationNeoplasm', al mesotheliloriff asbesto' iological e\ig that exiMe bestosis m:<\ pread of this jt it is app.iriust levels in oestosis, such ent cancer.' a threshold sociated :*- now whetlicr eontamin.mi jmonstratioii be regular!) ities of the Thomson et tion. It \m.* renecessuriulting from a analy7ti>t: has b-cn i^eStOS fibers 00 consei n! shown t li.i: ; optical mi' 1 sq cm <*' ses, shov.n! i (Table I r volume 'f Iy, asbestr. i in all the 1^7 :3E' &S Table 1.---Asbestos Bodies in 3,000 Consecutive Autopsies in New York City, 1966 to 1968* Male Feirult Total A9 No. <1 1-19 2/73 0/7 20-39 34/102 40-59 316/606 60-79 5S5/997 80+ 106/186 Total 1.013/1.971 * From Linger et alJ* % 2.8 0.0 33.3 52.1 55.7 57.7 51.4 No. 2/53 4/25 19/58 108/247 220/491 83/155 436/1,029 % 3.8 16.0 32.8 43.7 44.8 53.5 42.4 No. 4/126 4/32 53/160 424/853 775/1.488 189/341 1.449/3,000 % 3.2 12.5 33.1 49.7 52.1 55.4 48.3 . Table 2.--Numbers of Asbestos Bodies* Atbtstoi Bodies 0 1-4 5.14 15+ Total cd cn -- LU CD Zj Ago <1 122 2 2 0 126 1-19 28 4 00 32 20-39 107 53 0 0 160 40-59 429 359 45 20 853 60-79 713 630 105 40 1.488 80+ 152 156 40 3 341 Total 1.551 1.204 192 63 3.000 Sfigg; ^ <r- C_D cr-- Sex Male Female 958 (48.6%) 593 (57.6%) Total 1.551 * From Linger et aL11 802 (40.7%) 392 (38.1%) 1.194 152 (7.7%) 40 (3.9%) 192 59 (3.0%) 4 (0.4%) 63 1.971 (100.0%) 1,029 (100.0%) 3,000 OO o ec 2 uj ~T" <~ O uj --cases, except perhaps the infants and very allowed qualitative analysis,17 with ap F""" J-- Jjoung children. preciation that the unique structure of oo )rThe same examination showed that, in chrysotile allows its specific identification by "addition to coated particles ("asbestos high magnification election microscopy. bodies"), uncoated inorganic fibers were Chrysotile fibers or fibrils, or both, were j: also readily seen (Table 2). Fibers thicker found in every specimen (Fig 1). In four of /ofban-.T.O/i were almost universally to be the 28, background contamination could T found; most of these are as yet still uniden conceivably have been responsible for the tified, although some were diatom frag- findings. In 24 of the 28, the number found - Bents, glass fibers, or phytoliths. We were was greater than background counts could concerned, however, with thinner fi- explain (Table 4). The morphological ap less than 1.0/i in diameter, since these pearance and other characteristics of these be more consistent with chrysotile, -fee. asbestos variety making up 95% of the :**stos used in the United States. Such &La fibers were also commonly present, be- fibers and fibrils are recorded elsewhere.19 It is evident that chrysotile asbestos is a common contaminant of the lungs of New York City residents at this time. Similar " found in 1,038 of the 3,000 cases, and electron microscopic observations have been fending to vary proportionately with the recorded in London,10 where not only was cumber of asbestos bodies (Table 3). chrysotile asbestos found in almost 80% of -The critical information was obtained by cases, but it was noted to be the most com T^nuning, in 28 of the 3,000 cases, a very mon and most abundant of all fibers detected. lBail portion of lung (conservatively esti- The question inherent in the observations ^atd at 10-8) by a technique which of Thomson and associates9 in 1963, "is 'iv Arch Environ Health--Vol 55, July 1972 G J | V? ') DB 0005731 ASBESTOS AIR POLLUTION--SEUKOFF ET AL Table 3.--Correlation of Inorganic Fibers with Asbestos Bodies in Lungs of 3,000 Consecutive Autopsies in New York City, 1966 to 1968* Percentage of cases showing asbestos bodies in relation to occurrence of thin inorganic fibers Thirr Inorganic Fibers Asbestos Bodies O NO. % 1-4 No. % 5-14 No. % 0 1.168 59.5 332 38.3 35 28.0 1-4 705 35.9 424 49.0 52 41.6 5-14 76 3.8 89 10.3 21 16.8 15+ 13 0.66 20 2.3 17 13.6 Total 1.962 65.4 865 28.8 125 4.1 Percentage of cases showing thin inorganic fibers In relation to occurrence of asbestos bodies Asbsstos Bodies 15+ No. % 16 33.3 13 27.1 6 12.5 13 27.1 48 1.6 Thin Inorganic Fibers 0 No. % 1-4 No. % 5-14 No. % 15+ No. % 0 1,168 75.3 705 59.0 76 39.6 13 20.6 1-4 332 21.4 424 35.5 89 46.3 20 31.7 _ 5-14 35 2.3 52 4.3 21 10.9 -17 27.0 15+ 16 1.0 13 1.1 6 3.1 13 20.6 Total 1.551 51.7 1.194 39.6 192 6.4 63 2.1 * Correlation was done by optical microscopic study, from Longer et al. II - Table 4---Chrysotile in 28 Cases Studied by Electron Microscopy Group No. of Chrysotile Fibers + Fibrils Cases Male Female 1 9 4/28 3 1 2 1050 11/28 5 6 3 51-99 6/28 1 5 4 100-200 4/28 4 0 5 "Blank grids" 201 9 3/28 see 3 ... 0 ... A -CO- * chrysotile asbestos commonly found in the lungs of urban dwellers at this time?" has now been answered, "Yes, unequivocally." Relation of Asbestos Lung Burden to Environmental Asbestos Disease There are few data at this time that would allow judgement of the significance of the asbestos we have found in lung tissue of urban residents. Whether or not the amounts present as the result of other than occupational exposure are associated with frequent risk of disease is not known. In part, this is a reflection of the scarcity of data concerning the asbestos content of lungs in general, including those of asbestos workers. Such data as are available suggest that the amount in lungs of the latter is quite small, ranging from 0.6% to 0.001% of lung weight.2123 It would be expected ta even lower in those not occupationally posed. No information is at hand concerning asbestos content of the lungs among the^ cases of Wagner et al,s or Newhouse aiatj Thompson,7 or those of other cases with environmental disease.23 24 Nor is tberw^ quantitative information concerning the bestos content of the lung in individuals i*^ the general population without stigmata asbestos. This is rather urgently needed^ with age, sex, residence, and occupations^ exposure taken into account. - Studies now in progress in our laboratory^ and elsewhere (F. D. Pooley, PhD, communication [July 1970]) indicate thsfj suitable quantitative techniques for estimat-* ing asbestos lung content will be feasit^- and that fairly accurate estimates, Arch Environ Health--Vol 25, July 1972 V B&C 0.5 F10 lung i I BB 0005732 AL Bodies 356 to 1968* 15-H No. % 16 33.3 13 27.1 6 12.5 13 27.1 48 1.6 .;.'V ' ' -JV.; ; 15+ No. 13 20 17 13 63 It % 20.6 31.7 27.0 20.6 2.1 ;scopy Female 1 6 5 0 __ 0 ... J---m- * \*\ rr,^',t;-rsSf; _ i'Hr $n ~`)E? '- ->: B ll f * it;-.. NOTE: THIS DOCUMENTDID NOTCOMEFROMPPGFILES mid be expected to .(.-'Jr?-;-- 1 ot occupationally &X*T.- hand concerning tfc^fQ ^v"', D a lungs among - 3 oorr NWetnwVhirotnuesAe anrr.k,iiwrs-**-* of other cases wit| 13-s4 Nor is the:' i concerning the a- ______ ng in individuals wi ' ar e, and occupatio aunt. ess in our laboratory ~l?<wley? PhD, oft B2t0 0.5 P A, D, E-G 0.3p 970]) indicate ths- ... hniques for estima'---- ---- ont will be feasibl . estimates, appro* Fig 1.--Association of ehrysotile fibrils and incompletely digested lung tissue. Arrows Indicate "hidden" fibrils in partially digested tissue. Arch Environ Health--Vol 25, July 1972 WtTr-r, #5 6 ASBESTOS AIR POLLUTION--SELIKOFF ET AL mating an order of magnitude, are to be anticipated in the future. Asbestos Air Pollution It is probably an entirely justified concept that the asbestos found in urban dwellers' lungs is derived from the inhalation of air contaminated with these fibers. Very little is known, however, of the conditions of such contamination, and facile assumptions should be avoided at this time. An example of where an "obvious" expla nation might also be inaccurate may be found in the assumptions adopted to explain Kivflnoto's1 observations. It seemed natural to expect that the demonstrable anthophyllite asbestos air pollution from the mine and mill was ecologically related to the equally demonstrable asbestotic pleural calcification in the population living about that point source. It turns out, however, that this may not be the entire explanation, and that inti mate contact with local asbestos-bearing rocks, including those used in building houses, saunas, bams, and the like, might also play a role.23 Indeed, the latter association better ex plains almost identical epidemiological find ings in Bulgaria, where, again, pleural calci fication was found in a rural population. In this district, too, an asbestos mine was being worked, but it was an underground mine and had opened only in 1943, too recently for its discharges to be expected confidently to have had the effect noted2* (the lapsed period between initial exposure and evi dence of pleural calcification is 20, 30,40, or more years). As in Finland, the local field rocks have a high asbestos content and are used for various structures by the farming population, which then may have intimate contact with what is shed from them. More important, perhaps, the soils tilled by these farmers can be demonstrated to have asbes tos fiber (anthophyllite) content. The im portance of this observation was empha sized by the discovery that those farmers working plots without asbestos soil contami nation had little pleural calcification, where as farmers working soil with anthophyllite readily showed the radiological changes.27 It may be that similar explanations will be come available for the finding of endemic pleural calcification in some rural areas of> Czechoslovakia.23-2 At first, it seems somewhat surprising that3 so few data are available concerning the:>J asbestos content of ambient air, especially4 since so much is known regarding the asbes-4 tos content of air within the work placed Perhaps the best explanation is that onca4 the factory gates are passed, a whole new set of technical problems is encountered, and^ sampling procedures, analytical approached and measuring methods useful for industrial^ controls are no longer applicable. Fiber Identification.--Under the indus^ trial circumstances, there is usually no prob-^ lem to knowing exactly what is being nwaSs sured, since the materials being used are* either well characterized or can be readily* analyzed. Thus, whatever fibers are seen cam* be confidently labelled as "chrysotile," "cra^g cidolite," "amosite," "fibrous glass,^and^ other types. -isss If these same fibers were to be seen in i random sample, especially if they are smalC^ our confidence disappears. All that can be said is that inorganic fibers are presenfc- Even then, if these fibers were found in very ? large numbers, identification could be readi ly accomplished by such mass techniques as x-ray diffraction. When they occur singly ori randomly scattered in small numbers, these? techniques are no longer applicable; and? readily available alternate approaches, sudu as polarized light microscopy, hardly hav*- the same definitive assurance. While it & true that analytical attack on single fibers, still possible, these approaches (Including; electron microprobe analyses, electron dif? fraction, and electron microscopy) are timms consuming and often restricted by the siar of the particle available for analyses. ri> Particles and Fibers---There has locf been an anomaly in particle counting foe; asbestos threshold levels. In the United. States, a threshold level was proposed in 1938 for occupational exposure to asbestW- based upon experiences necessarily limited to that point30 The recommendation reflect ed the instrumental restrictions of the time* and were based upon counting of "particle. by optical microscopy. It was recognized that such particles could either be fibrous nonfibrous and that the proportion couM vary widely according to the materials us ''53 -Awl Arch Environ Health--Vol 25, July 1972 \ V o oo --- LU O _J *, * rn *-ww ci- " tn < ; o LU O c. :s-;.-p cr, \ - Ah in some rural areas o: at surprising Uu: '.dBj concerning tK ambient air, especiall nvn regarding the asb&. within the work plact `-r-k* xplanation is that ojk> passed, a whole new si ns is encountered, an: S analytical approacht- :ods useful for industry r applicable, -+Jti : bn.--Under the indu> there is usually no prol- ctiy what is being roe iiterials being used an rized or can be readi! (ever fibers are seen & ed as "chrysotile," "err- " "fibrous glass," an: 1>-T- rs were to be seen in: v?- ecially if they are sma: ppears. All that can l. mic fibers are preset, ibers were found in ver dficntion could be reae' * :uch mass technique i( ber^^ y occur singly r in^A.l numbers, the. applicable; ai- smate approaches, sue licroscopy, hardly ha' assurance. While it: attack on single fibers: approaches (indudit analyses, electron d - \ microscopy) are tiro `-3=v-` i restricted by the sr jbH , hie for analyses. bby- >ers.--There has Iro Ct*5K- particle counting t ievels. In tire Uni'.- * level was proposed - bhait- =. nl exposure to asbest , ices necessarily limit- recommendation rcflro ;-& restrictions of the tiro -cifj-y-- : counting of "particle py. It was recocnir ` xr. yjld either be fibrnu? : the proportion tf* S ` :g to the materials w b_ *** F'g 2.--Clay particle with adsorbed chrysotile fi brils, in air sample about construction site (x23,000). Arch Environ Health--Vo! 25. July 1972 NOTE: THISDOCUMENTDID NOTCOMEFROMPPGFILES I BB 0005735 | ASBESTOS AIR POLLUTION--SEUKOFF ET A L Fig 3.--Adsorption of Chrysotila fitwits onto surface of diatom. Fibrils would not be seen by optical microscopy. process studied, or other factors. Since the is quite different chemically, !>t . physically.; Fig 4.--Slnfllr, i!ov/nwlnd of chry ticn of day particlt since not only as fiber and fib presumption is that only the fibers are re structurally, and morphologically.31 Chryso~ [Witential biolo sponsible for the biological effect, such ana tile seems unique in its tendency to physical different with lytical dilution is hardly acceptable at this instability under a number of drcumstaacei.- mass, with diff< time, and current approaches to industrial The chrysotUe "fiber" is not a unit wboia' Thu proportion threshold limit values are based entirely on but is, rather, composed of a large number determined wit) fiber count But even here, the matter is not of individual fibrils, each from 300 to 400 Size.--Thus, so easily disposed of, since the admixture of Angstroms. Under industrial circumstances.' asK-stos air po particles and fibers often includes surface it is recognized that when a population of techniques whic interactions among them. Figures 2 and 3 fibers is counted, "invisible" fibrils are also particles. It is show particles of clay and a diatom collect present,32 but that the optically visible fibers vihich do not i ed near a construction site by one of us reflect, in varying proportions under difftf* 'cope will be e (A.M.L.). By light microscopy these would ent circumstances, the total chrysotile popur ;>dd that high m. be categorized as "particles." Yet, by elec lation, even though there is only one fib copy will be n> tron microscopy, it was found that numer for a very large number of fibrils. Also, wifi* tions of at least ous fibers (fibrils) were attached to the sur proximity to the industrial source, many ably over 40,0C face of the particles (opposite surface fibers are still present, not having been sub copy may be charges). In such circumstances, any biolog jected to influences which could result # occupational asb ical effect of the fibers could be incorrectly their separation into fibrils. mountable inade attributed to particles. The question of size In the ambient air, however, very little S idilution of the ; u and magnification is critical. known about the proportion of fibers 1 In addition U Fiber-Fibril.--Each asbestos fiber variety fibrils. The matter is of some importance fibrils, it has bee of them are qui Arch Environ Health--Vol 25, July 1972 rr. 4 ( | BB 0QQ5736 t -a physic;: IK. Chr\m> nden^ to phy.-ivnl of circumstance*, not a unit v.luilr y( a large numU-r from 300 to ui ial circumstat:'<*. 1 a population o.' s" fibrils are .iIm* :al!y visible filxT* ons under dhTcrI chrysotile popsis only one f:!<T fibiils. Also, ith a I source, m.iny having been rubi could result it: ver, very little i* ion of fibers to ome importa nee. H%M-r- ASBESTOS AIR POLLUTION--SELIKOFF ET AL 9 observed chrysotile fibrils with lengths less than 1,000 A in many instances; when these are enmeshed in sampling debris, not only is high magnification election microscopy nec essary, but visual scanning may be inade quate, and inferior to photographic re cording.17 It may be worth noting that such small particles are at present subject to identifica tion by their morphological characteristics only; structural and microchemical analysis by electron microprobe or electron diffrac * `?v tion study has many difficulties. It may be hoped that instrumental advances will reme dy this situation (greatly improved micro probe definition can be anticipated, for ex ample). Turkevich's "World of Fine Parti cles"35 is surely with us. Quantitation.--Under industrial circum stances, there is little difficulty in estimating the quantity of asbestos in a given sample of air. From this, the surface area of the fibers can be estimated or directly measured by nitrogen absorption or other techniques. It -T is even possible to conceive of gravimetric methods, rather , than the more laborious :iyiFta 4.--Single, short fibrils collected 3/16 of mile /'downwind of chrysotile source. Arrow indicates pose "yticn of clay particle. counting of fibers. Quantitation is much more difficult in ambient air samples and, in our experience, only approximations can presently be obtained. t/anoe not only must number be categorized Current Approaches to Asbestos Air Sam V^as fiber and fibril, but the surface area and pling.--With the foregoing factors in mind, /potential biological effect might be quite the absence of published information on as ^./different with the same total chrysotile bestos levels in urban ambient air may be j^aass, with different percentage fibrillation. understood. Few air monitoring agencies l'3he proportion of fibers to fibrils cannot be have had available the technical equipment V*determined without the electron microscope. for the examination of ultranricroscopic as 'ZrT'- Sb*.--Thus, a critical factor in studying bestos fibrils. Moreover, even those fibers ^asbestos air pollution is the utilization of seen by optical microscopy in air samples ^techniques which will measure very small required elaborate techniques (such as elec -^particles. It is unlikely that approaches tron diffraction or microprobe analysis) for pWhich do not include the electron micro- positive identification. ;.-9oope will be effective. Indeed, one might Present approaches to quantitating asbes -;^add that high magnification electron micros- tos levels in ambient air, using ultramicro . jjisepy will be needed, including magnifica- scopic techniques, have sought two objectives. 'vhcns of at least 20,000X (direct), and prob- The first is to obtain a measure of the mass _?ibly over 40,000 X. While optical micros- of asbestos per unit of air volume at various ^jeopy may be suitable as a guide for locations in urban centers and later, for 'occupational asbestos exposure, it has insur- comparative purposes, in more rural areas. 'mountable inadequacies in studying asbestos This would provide a stable estimate, since . pollution of the ambient air. fiber size distributions change as sampling is '- >"In addition to the fine diameter of the undertaken at different distances from as -:fibrils, it has been our experience that many bestos emission sources. Equal numbers of jof them are quite short, as well. We have fibers can represent significantly different .zf.:. ,'AZ* Arch Environ Health -Vol 25. July 1972 CO Lvi c~: }O .r BB 0005737 | 10 ASBESTOS AIR POLLUTION--SELIKOFF ET AL amounts, by weight, of asbestos. Moreover, it is not currently known how strongly bio logical effect is dependent on fiber size. This being so, a measure by mass or weight may be more conservative for the establishment of air quality criteria and standards, since the biological effect of a sample dominated by large fibers may be overestimated. Secondly, fiber size distribution is impor tant At the moment, to obtain such a distri bution at each sampled site is time-consum ing, and the presence of other material and tained by measuring the volume of asbesto*^ per grid square and multiplying by the ap4i propriate density. Figure 4 shows several^ isolated fibrils in an ambient air sample seen by electron microscopy. Usually, onjyd single fibrils, if any, are observed in tbe4 microscopic field. .. However, as one takes samples sources of asbestos, more large fiber bundk*^ are present in the initial sample. As that* are dispersed during sample preparation, obS casionally some groups of fibrils remain ijSf l>f `. t:ce to spray f t.u!:ing from 10% ^irtlt-rs, spandrels, buildings. O were taken b th<- -pray material i ,.f :i.-bestos*containi ,i\, r widespread ax j.rit ticc was of su ,Wv.- York City has .vf- .-tos fireproofing existing transfer and sampling methods may distort the observed fiber distribution. How ever, experiences in current studies suggest that these problems can be overcome, and that complete fiber size distributions will be obtained at selected sites in the near future. Sample Preparation.--In our studies, air samples were collected on membrane filters having an effective pore size of either O.Sfi or 1.2ft. While this pore size is larger than the largest dimension of some asbestos fi brils, it has been found that" the surface charge properties of the filter and the asbes tos, as well as the circuitous path through the filter, allow virtually complete collection of all asbestos material. Both high-volume samplers capable of drawing 40 cu ft/min through an 8 X 10inch filter, and small battery-operated per sonnel monitoring samplers with a capacity of 2 liters/min through 8 sq cm, were found effective in sample collection. Portions of each collected sample were ashed in. an acti vated oxygen asher which oxidized the mem brane filter and all organic or carbonaceous material in the sample.34 The residue, con sisting mostly of fly ash and mineral matter, was dispersed on a microscope slide by grinding in a solution of 1% nitrocellulose in amyl acetate for two to five minutes. Upon evaporation of the amyl acetate, the dispersal was scanned for uniformity by op tical microscopy and a representative area chosen for transfer to an electron micro scope grid for scanning. tact The presence of these bundles, or evex^ localized fibril clumps, gives rise to a vaii*-S tion between samples greater than onef would expect from statistical consideration*^ alone. However, the scanning of many squares serves to average their effect Results of Initial Investigations.--Am-4 bient air levels were measured at-varioospl sites in New York CityXThese samples we**g taken at selected locations of the sampling^ network of New York City's Department cti. Air Resources. The sites were all located air public buildings distant from any known-' significant source of asbestos. The chrysotile; content of ambient air in the various sa-~ pling locations was as follows: Manhattan,/* 25 to 60, asbestos air level in 10- gm/cu ng Bronx, 25 to 28, asbestos air level in 10* gm/cu m; Brooklyn, 19 to 22, asbestos air level in 10- gm/cu m; Queens, 13 to 23; asbestos air level in 10~ gm/cu m; and Staten Island, 11 to 21, asbestos air tewfcj in lO gm/cu m. While preliminary nature, the samples from Manhattan tendei't to be higher than those from other borough*-;: Lowest values were usually from sites mcdA distant from densely populated busioe*, areas (Staten Island). While amounts ranging from approx mately 10 to 100 X 10" gm/cu m of sam^ pled air may appear to be exceedingly; small quantities of asbestos, it is well k* recall that chrysotile asbestos easily ments into ultimate fibrils 300 to 400 A i*' diameter and often 2,000 A or smaller * Prior to the implf firy's regulations, !<>v.<-r Manhattan ; v(i i.iity of buildin uli.-re spray firepro raining materials w; on which data levels in 10 f -jri- 1. downwind frc -i< ,-ite 2, 45 dow .trs i upwind from c ind from any sc from a.spray u:.v. jnd from any sot Tlte data in New minted by measurem its more rural areas. >.f ,iir in three selt lull, ass: Philadelphia t* *-s I in 10-* gm/cu i level in 10AU. -oiy, Pa, 10 to J" gm/cu m (am fu;i<I in .the air of th " ti-ing this material "Hir-se data, though --Lihiish that, at leas, is a background *n of the ambient '* lusher about const Much more ir <!. however, befc 1** made concern M!,'h contamination During this procedure, those chrysotile length. Thus, 10~ gm of chrysotile asi*** I fiber bundles present are broken into their tos could represent a million fibrils. . *r-F; I Epidemiologic; elementary fibril form. The grid is scanned That Manhattan has higher levels of**?' at 42.000X in an electron microscope. Typ bestos than other boroughs is to be expected Environmental Disc * ;!'l>ostos pollution ically, six grids are prepared of each sample, as greater use of asbestos in building and three 100/t x 100/t squares of each grid struction takes place in that borough. are scanned. The mass of asbestos is ob ing the past ten years, it has been corrOT^ ^ t-ihlished. What ha vcr, are the di a&IQTE: THIS DQArch Environ Health--Vol 25, July jy.'-t CiLFS.. NOT CCTvl -n*nili-P 00 0573 3" Y'T T AL ASBESTOS AIR POLLUTION--SELIKOFF ET AL 11 urzng the volume of asbostn)Ct3ce to spray fireproofing material conandmultiplying by the- ^jning from 10% to 30% asbestos, onto 1 ^ur ^ shows sevfjjfjers, spandrels, and decking of high-rise l rmbient air sample buildings. Often, inadequate precau- " ra'croscoPy. Usually, o^0ns were taken by contractors to contain any' axe observed In spray material and extensive "snowfalls" of asbestos-containing material took place one takes samples r^yer widespread areas of Manhattan. This os, more large fiber bundpjactice was of such obvious concern that e initial sample. As thtb'ew York City has banned the spraying of ring sample preparation, Ggtbestos fireproofing, effective as of Feb 26, .roups of fibrils remain fJJ72 e bundles, or ev> Prior to the implementation of New York Umpf' gives rise to a vari City's regulations, data were obtained in mnpes greater than o: lower Manhattan at various sites in the n s tistical considerafior vicinity of buildings under construction r*e scanning of many gj, where spray fireproofing with asbestos-conivemge their effect. t taming materials was used. During the two vesbgations.--A days on which data were obtained, the as- fvar' best05 levels in 10' gm/cu m were as follows: ity. These samples we ate 1, downwind from a spray source, 45 to oca mns^ of the samplii SO; site 2, 45 downwind from one source or- ityg Department< and upwind from others, 15 to 30; site 3, si es were all located 0 upwind from any source, 20; site 4, down- ,a n__ rom CaUnJJyT AkJnJoOwWI vrind from a spray source, 45; and site 5, ' asbestos. The chrysotiij upwind from any source, 20. air in the various san The data in New York have been supple as follows: Manhatte mented by measurements in other urban and level in 10* gm/cu it in more rural areas. The chrysotile content bes^^air level in 10 ] 22, asbestos a of air in three selected locations was as follows: Philadelphia, 45 to 100, asbestos inf"Queens, 18 to % level in 10~ gm/cu m; Ridgewood, NJ, 20, 1 10~ gm/cu m; ant s&estos level in 10~ gm/cu m; and Port 21, asbestos air lew Allegany. Pa. 10 to 30. asbestos level m Whilea* prelimin--ar-y -" 10~* gm/cu m Campsite fibers were also anhattan tendw found mthe air of this community; a facto- 1 r||m ,0aier ^orou?h; ry using this material was present). y rom sites nur ThSe^dataTThougETnnTTimiteS, serve to populated busuw* establish that, at least in the areas sampled, there is a background of chrysotile contami png from appro*!-, nation of the ambient air and that this may 3 gm/cu m of aim j be higher about construction sites in urban to be exceeding!.', mas. Much more information will be re istos, it is well trj quired, however, before reliable estimates -sbestos easily fra? ' a be made concerning quantitative levels dls 300 to 400 A if | rfsuch contamination. Y0 A or smaller v. of chrysotile fix*1 on fibrils. ; Epidemiological Perspectives higher levels of a.- is to be expa irti. s in building con hat borough. Dufhas been corrunor Environmental Disease.--The occurrence of asbestos pollution of urban air is now established. What has not been defined, however, are the dimensions of disease *hich may be associated with this pollution. Indeed, it is hardly proper to speak of "as bestos air pollution" in general terms. There are different sets of circumstances in which such pollution can occur, varying in inten sity, intimacy, and duration of exposure. Lapsed Period.--A problem common to all types of asbestos air pollution is the long lapsed period between onset of exposure and appearance of disease. In general, this is 20, 30, 40, or more years insofar as neoplasia is concerned. There are variations, of course. It may be that intensity of exposure is one such variable; others could include fiber va riety, fiber size, competitive risk of asbesto- sis,3c cofactors such as cigarette smoking,13 trace elements, and perhaps other concomi tant air pollutants. Defined Populations.--It should be recog nized that the different kinds of asbestos air pollution are not limited to well separated O </> ~.Z~ UJ compartments. Exposure to general commu nity asbestos air pollution may be over whelmed by indirect occupational exposure, in the case of a construction workman. Simi larly, the asbestos inhaled by virtue of fami ly contact in the household of an insulation worker could hardly be attributed to the scant asbestos fibnls in the air of a rural community in which that employee hap pened to live. Such permutations are com mon and may be misleading unless identi fied. When considering neighborhood air o pollution about an asbestos plant (30 years ago, since it would be these people with UJ p owhose fate we would now be concerned) it is fr* well to remember that, at least in the 1930s and 1940s, people who worked in a plant tended to Jive near it Thus, the population about a plant being studied would have to be well characterized, to identify those with direct occupational exposure, before the ef fects of neighborhood contamination could be evaluated. Sources and Control Sources for asbestos air pollution can be looked at in two ways. They can be identi fied and measured without reference to ex posed populations. Epidemiological atten tion may then be attracted to these "con tamination sources in search of disease." Alternatively, sources for asbestos air pollu tion can be studied in relation to their po tential for exposure of human populations. Arch Environ Health--Vol 25, July 1972 ASBESTOS AIR POLLUTION--SELIKOFF ET AL At this time, both approaches are ham pered by inadequate information on the relative significance of peak exposures com pared to constant background contamina tion, There is clinical evidence which indi cates that heavy exposures for brief periods (.days, weeks, months), with retention"ot the inhaled fibers for the rest of the individ ual's lifetime, may carry serious disease potential?7 '`rhereforeT intermittent hie peak exposures may carry an unusual risk! especially when adcied to the cumulative retention^ssociatecTTvith background pollu tion over long periods of time. Adequate information is needed concern ing the natural history of asbestos air pollu tion, including persistence, variations with meteorological conditions, and ultimate fate.33 Asbestos fibers, being mineral, may persist in the environment for long periods. It is not known, however, if this is so, or to what extent attrition occurs by a variety of physical processes. We have found amosite asbestos fibers in the settled dust and in the household air, within homes which had been occupied 15 years before by workmen of an amosite factory, Similarly, both settled dust and ambient air in a construction work man's home contained chrysotile fibers at levels beyond those usually observed as background. Neighborhood contamination from factory sources may also be associated with long persistence of the mineral fibers. In preliminary studies, we have found this to be true ot botn superficial son containing Son and settled dust on attic ratters in sucK neighborhoods. It is apparent that informa tion concerning persistence and fate of as bestos air pollution would be important, if only as a background to the evaluation of air levels from current emission sources. Natural Sources of Asbestos Air Pollu tion.--It is likely that some air contamina tion occurs from natural sources. Serpentine rock outcroppings occur in many parts tfc the United States and other countri^. ; >. .i.i and peritonea t.,, m the London at Studies in our laboratories suggest that, ot& an ultramicroscopic level, serpentine vwr-j frequently contains some fibrous mineralj - IJeben J, Fists I ..-hr* exposure. Art r*.: components, which are properly classified aachrysotila. In addition, some outcroppings? > Thomson JG. F l.N-toa as a modei T r.'-St. 1963. contain frank chrysotile veins. Such duyso^i I". Gross P, Crall< tile-containing rocks are widely distribute^ although not necesarily in comn^rrialJ concentrations. Nevertheless, ahrasinn ti,, l-odies: Their no. i J 28:541-542.1 11. William* E: " r.:i:of coal-workers. weathering of such surface formations migh^i be accompanied by release of chrysotile-fir| 12. Sflikofi 1J, Ch rv|.i-tire and neoplas : Selikoff IJ. Ha bers into the surrounding air. --.leisure, smoking a Industrial and Commercial Sources.--Al though natural sources for asbestos air I!.1 1966. 11. Selikoff IJ, Ha i-. experiences of a lution should be considered, it is likely fiwV* they add only an infinitesimal amount faj HA Ced): P < .'ijerrnee on Pnr tt.ioi. Oxford Unive the asbestos air burden in urban areas. I.V Hygiene stand. is derived from commercial and industrial^ sources. Here, emission-source inventories? I- '1 Occup Uyg 11:47 91. Selikoff IJ, Ha r.on-occupationsl can be prepared and would include trar*^* port and storage of raw fiber supplies, maif^ ufacture of the many useful asbestos-con-" -i ir. Amrr j Public . 17. I-nnger AM. S -ls-itos in the lung.i- A Environ Health taming products, transport and end-use efc; these products, their weathering, and ulti-* 14. linger ANt F: llg,lnic fibers, inc i!in|isy: Preliminary mate disposal as waste. In general, the po? / iiiliil Particles am tential for pollution varies with the degree;, of fixation of the fiber in'the product ^ I k I.td. 1971, vol 2, i`.. Lsnger AM, iiivsotile asbestos f Approximately two thirds of the asbestos; ---lxations. Amer Mir used in the United States is used in con^struction products. Ship building and repair^' Jt>. Pooley FD, Ol i*-tis-fioii of asbestc 1>: Proceedings o and waste disposal of asbestos products art*, important areas for study. Spraying of bestos-containing mineral fiber insulation? I'neiitrtocor.iosis. 1 'diversity Press. 197 -M. Sundius N, B\ ""slosis-lungen uni ohas already been mentioned. Factory emifr? sions are an obvious, and controllable, di5?i ' r nsbestosis - korp. " I3.J8. pyfjltenttie J. Km culty. Housekeeping in all asbestos-using far? nt! particle sb cilities may turn out to be a knotty problem! os textile wor and ultimately associated with much asbe^-. tos air pollution. This investigation was supported in part by Fub&: Health Service grants OH 00305 and ES 00353. ' Dr. Lsnger was the recipient of Career Award ES 44812. . J References --.-y cS5 1. Kiviluoto R: Pleural calcification as roentgen ologic sign of nonoccupationat endemic nnthophyllite-asbeetosis. Acta Radiol, suppl 194, pp 1-67, I960. 2. Jacob G. Bohlig H: Roentgenological complica tions in pulmonary asbestrwis. Fortschr Reontgenstr 83:515-525,1955. 3. Selikoff U: The occurrence of pleural calcifica tion among asbestos insulation -workers. Ann NY Acad Sci 132:351-367,1965. 4. Laamanen A, Norn L, Raiuiio V: Observa tions on atmospheric air pollution caused by tos. Ann NY Acad Sci 132:240-245, 1965. ^ 5. Wagner JC, Sleggs CA, Marchand P: DiS^ pleural mesothelioma and asbestos exposure North Western Cape Province. Brit J Industr Aft*1 17:250-271.1960. ^ 6. Weiss A; Pleurskrebs bei lungenasbsstose. vivo morpbologiscb gesiehett. Mediiinische 1-.93-94.- 1953. 5' 7. Newhouse ML, Thompson H: Mesothelioma <* In a rccen: - Monitoring c ! third line of Arch Environ Health--Vol 25, July 1972 0005740 'ET AL occur in many parts of other countri,,. >or^2s suggest that. on'c^wel, serpentine \or.is some fibrous miner;,; i are properly classified ii-tion, some outcropping, sotile veins. Such chryvoks are widely distributed, cessarily in commercLil vertheless, abrasion and surface formations mirf:; v release of chrysoti!,' f: nding air. Commercial Sources.--A1 trees for asbestos air j*,;. insidered, it is likely that infinitesimal amount tn den in urban areas. Mia-t tnmercial and industrial ission-source invenforiis nd would include trans raw fiber supplies, manjty useful asbestos-con'-msport and end*u>c of ir weathering, and uhidste. In general, the i> i varies with the di-gnv er i* he product vo A.s of the asbi stn1 is used in ron ship building and n-iuir. of asbestos products an - study. Spraying of a> oineral fiber insulation c.ntioned. Factory enti- . and controllable, diffi in all asbestos-usin'- h to be a knotty problem, iatsd with much n>l*v frf*- '-*VX ASBESTOS Alii POLLUTION--SELIKOFF ET AL 13 * jjeora end peritoneum following exposure to asbes'-Iat in the London area. Brit J Industr Med 22:261y-~sfp, 1965. g Lieben J, Pistawks II: Mesothrlioan and as,ie*tos exposure. Arch Environ Health 14:559-563, 1567. h:< 9. Thomson JG, Kaschula ROC, MacDonald UR: f Asbestos as a modem urban hazard. 5 Afr Med J ' 7:77-81.1963. ^710. Gross P. Gralley LJ, doTieville RTP: AsbesVies bodies: Their nonspecificity. Amer Induslr Hyg S-Aeiae J 28:541-542. 1967. .YriL Williams E: "Curious bodies'' found in the of coal-workers. Lancet 2:541-542,1934. ,*.12. Selikoff IJ, Oiurg J, Hammond EC: Asbestos .^exposure and neoplasia. JAMA 188:22.26, 1964. _y5~- 12. Selikoff IJ, Hammond EC. Churg J: Asbestos '.exposure, smoking and neoplasia. JAMA 204:106- :-J12.1968. ?*fc-J4. Selikoff IJ, Hammond EC, Churg J: Mortali- experiences of asbestos insulation workers, in Shapiro HA fed): Proceeding! of the International 7-Conference on Pneumoeoniotit. Capetown, South Jifdac*, Oxford University Press, 1970. pp 180-186. 15. Hygiene standard for chrysotile asbestos dust. ''-Am Occup Hyg 11:47-49, 1968. Selikoff IJ, Hammond EC: Community effects '.of noo-occupational environmental asbestos expoInsure. Amer J Public Health 58:1658-1666, 1968. - 17. Longer AM, Selikoff TJ, Sastro A: Chrysotile ^awwstos in the lungs of persons in New York City. i`Arch Environ Health 22:348-361,1971. '-*13. Linger AM, Baden V, Hammond EC, et al; JJnorganic fibers, including chrysotile, in lungs at .-autopsy: Preliminary report, in Walton WH (ed): Inhaled Particles and Vapours, IIL London, Unwin * .Bms Ltd. 1971, vol 2, pp 683-694. XT 19. Langer AM, Madder AD: Morphology of ^chrysotile asbestos fibrils: Electron microscopic ob1.servetions. Amer Mineralogist, to be published. -^*20. Pooley FD, Oldham PD, Urn CH, et al: The -detection of asbestos in tissues, in Shapiro HA _^<*d): Proceedings of the International Conference -on Pneumoconiosis. Capetown, South Africa, Oxford ^University Press, 1970, pp 108-116. rif':2L Sundius N, Bydgett A: Der stsubinhsU einer ubeatosis-lungen und die beschaffenbeit der sogenn- :-t*r asbestosis - korpemhen. Arch Getverbrpath 8:26.^ao, 1336 '^,*22. Beattie J, Knox JF: Studies of mineral con-fimt and particle size distribution in the lungs of '.-**bto* textile workers, in Davies CN: Inhaled Particles and Vapours. New York, Pergamon Press, 1961, pp 419-433. 23. Bohlig H, Dabbert AF, Dalquen P. et al: Epidemiology of malignant mesothelioma in Ham burg: A preliminary report. Environ Res 3:365-372, 1970. 24- Borow M, Conston A, Livoroeso LL, et al; Mesothelioma and its association with asbestosis. JAMA 201:587-591, 1967. 25. Raunio V: Occurrence of unusual pleural cal cification in Finland: Studies on atmospheric pollu tion caused by asbestos. Ann Med Intern Fenn 5S (suppl 47): 61, I960. 26. Zolov G, Bourilkov T, Babadjov L: Pleural asbestosis in agricultural workers. Environ Res 1:287-292. 1967. 27. Burilkov T, Michailova L: Asbestos content of the soil and endemic pleural asbestosis. Environ Res 3:443-451,1970. 28. Hromek J: The mass incidence of characteris tic pleural changes in citizens of the western part of the former JiMava region. Rozhl V Tuberh 22:405- 515,1962- 29. Rous V, Sludeny J: Aetiology of plcumL* f A plaques. Thorax 25:270-284, 1970. _ __ ^ 30. Dreessen WC, Dallavslle JM, Edwards TT, \ al: A Study of Asbestosis in the Asbestos Textsif*--' 4 Industry, bulletin 241. Public Health Service, .1938. _ 31. Speil S. Leioeweber JP: Asbestos minerals us modem technology. Envirvn-Res 2:166-208,1969. *-* 32. Lynch-JR, Ayer HE: Measurement of asbeth- tos exposure. J Occup Med 10:21-24, 1968. 33. Turkevich J: The world of fine particle^-., Amer Sci 47:97-119, 1959. 34. Berkley C. Churg J, Selikoff IJ, et al: The.,. detection and localization of mineral fibers in tissue: Ann NY Acad Set 132: 48-63, 1965. ~ ... 35. Spraying of Asbestos Prohibited, local law 49, in Air Pollution Control Code of the City of New York, sec 1403. 2-9. 11 (b). New York City Dept ofl Air Resources, Aug 25,197L * -`" 36. Jacob G, Anspach M: Pulmonary neoplasii ^ among Dresden asbestos workers, Ann NY Acad Set 132:536-543,1965. . ' 37. Selikoff IJ, Bader RA, Bader ME, et al*--Asbestosis and neoplasia. Amer J Med 42:487-496#-'' ' 1967. O 38. Asbestos: The Need for and Feasibility of Air Pollution Controls, Committee on Biological Eflecbf"" of Atmospheric Pollutants. Washington, DC, Na tional Academy of Sciences, 197L f" ^upoorted in part by I 00.305 end ES 0035* Ipierit of Career Awm-1 pollution caused bv 02:240-245, 1965. CA, Marchand P: nXW md asbestos exposure ovince. Brit J Industr Vf^bs bei lungenasbesto**'. r i-.ert Meditinitche 1 A3 r,` onpson H: Mesothelioma r- ' 'sWEF? ERRATUM V' In a recent article by Sherwin and Yuen, "Silicone Fluid for the Metering and Monitoring of Nitrogen Dioxide" (24:331, 1972), the number "5.23 ppm" in the i- y* third line of column 1 on page 331 should read "3.93 NO;,." 4i: I1 n` iI fJ. J BB 0005741 l mm . -a$&: Arch Environ Heallh--Vol 25, July 1972