Document 70OYq95DZbgD84K8wE9b1yQda

'To The Interrelationships of Selected Asbestos Exposure Indices JEREMIAH R. LYNCH, HOWARD E, AYER, and DOUGLAS L. JOHNSON* Bureau of Occupational Safety and Health. Public Health Service, Department of Health Education, and Welfare. 1614 Broadway. Cincinnati, Ohio 45202 ' 0 Based on the assumption that the biological effect of asbestos is related to the concent rat ion of respirable fillers, an index was developed which yields the con centration in numbers of asbestos fibers visible under 430X phase-contrast illumina tion. Data art presented relating this index to overall dustiness as measured by impinger counts and to absolute fiber concentration and distribution as measured by electron microscopy. The relation between count estimates and gravimetric measures of total dust and dbrysotiir asbestos deduced from magnesium analyses are given for gross and respirable samples. These relations are developed for ase in operations in the manufacture of asbestos textile, friction, cement, and insulation products. The most convenient, practical, and direct index of asbestos fiber exposure proved to be the concentration of fibers longer than microns counted on membrane filters at 430 X phase-contrast illumination. Introduction A T THE NEW YORK ACADEMY OF Ta SCIENCES Conference on the Biologi cal Effects of Asbestos in 1965, Gilson5 noted the proliferation of dust sampling methods and appealed for international comparability of dust measurement data to be related to bio logical data. He also observed that, as dust levels are lowered, it becomes more important to use the index that is biologically most ap propriate. At the present time the goal of internation al comparability has been partly achieved by the adoption of the concentration in numbers of fibers longer than 5 microns counted on membrane filter samples at 430X magnifica tion with phase-contrast (PCI illumination as the standard method in both Britain and the United States.14 However, information that would permit evaluation of the biological ap- *U.S. Department of Health. Education, and Welfare. Public Health Service. Reason IX. Federal O&sce Suildme. 50 Fulton Street, San Francisco. California 94302. propriateness of this index is still not com plete. ' It is rarely possible to make an absolute measurement of that characteristic of an air borne dust which is directly responsible for its biological effect. To be practical, measure ment for the purpose of assessing hazard and evaluating control must not only be conven ient and relevant but also permit the use of statistically adequate sampling strategies. To evaluate indices obtained from varying ex posure situations, an examination of the con sistency of their relation to other and absolute measures was undertaken. The large number of methods which might be used to measure exposure to airborne dust containing fibers results from what might be called the "degrees of freedom'" of the dust cloud. In measuring the concentration of a gas in air. there Is only one attribute to be measured, and one accurate method gives the same result as another. With granular dust, however, the attribute could be either num ber or weight, and with fibrous dust, length gives another degree of freedom; furthermore, 598 American Indust , dust of mixed ft t. Because ot this c0uld be as mam ,o the asbestos in ; States Public He; study of the asb< choice was narrov weight methods si the'results of ana pics, this paper pr tiemships between (1 \ exhibit the ei tion. (21 reveal t {3! evaluate the I rived. Imping1" Relation The early epid. were based on the til the beginning sampling in the l this method, since exposure be evalu limit value (TLV cubic foot (mpp< necessary to deve, methods of measur performed in the the results that v years ago had p' might be predicted The ratios show oped from stmult membrane filter s; the fiber counts ec pinger. Equivalen tration that would when the imping; the average, a co the same product are textile for asb< ucts, friction for b ings, and asbestos In all cases the the large number samples are not o' ed from pairs of vironment. each h and not necessaril The impinger resi /fnrruan industrial Hygicnt Association Journal .7 99 ted JOHNSON* irnent of Health. '3202 \ related to the yields the con- ntrasl illutnittaas measured by as measured by metric measures es are given for in operations in products. The re proved to be ibrane filters at ndex is still not com- to make an absolute haracteristic of an aitectlv responsible for itt be practical, measureof assessing' hazard and st not only be convertalso permit the use a ampling strategies. To ned from varying exxamination of the con n to other and absolute ken. f methods which mighi posure to airborne dun ts from what might b< ' freedom" of the dus the concentration of i tly one attribute to b< urate method gives thi r. With granular dust could be either num ith fibrous dust, lengtl ' freedom: furthermore Just of mixed fibers and grains gives yet an- (>thcr- .. . gpr.nisr of this varietv of attributes, tiler*1 could he as many as 100 indices of exposure to the asbestos in a dust cloud. In this United States Public Health Service epidemiological study of asbestos products industry, the choice was narrowed down to the count and w-eieht methods shown in Table I. Based on ^/results of analysis of almost 10.000 sarn ie this paper presents summaries of the rela tionships between these methods in order to ] ! exhibit the effect of product and opera tion. f2 1 reveal the bias of the methods, and ry. evaluate the usefulness of tire indices de rived. Impbger Relationships The early epidemiologic data on asbestos *-ere based on the impinger method and, un til the beginning of the present study, most ampling in the United States was done by this method, since only in this way could the exposure be evaluated against the threshold limit value (TLVi of 5 million particles per cubic foot {mppcf iT5 Consequently, it is necessary to develop ratios between present methods of measurement and impinger counts performed in the traditional manner so that the results that would have been obtained years ago had present methods been used might be predicted. The ratios shown in Table II were devel oped from simultaneous pairs of imptngermembrane filter samples and are expressed as the fiber counts equivalent to 1 mppcf by im pinger. Equivalence means the fiber concen tration that would be found, on the average, when the impinger samples were giving, on the average, a concentration of 1 mppcf in the same product area. The product areas are textile for asbestos spun and woven prod ucts. friction for brake linings and clutch fac ings. and asbestos cement pipe. In all cases the correlation coefficients from the large numbers of pairs of simultaneous samples are not over 0.6. as would be expect ed from pairs of measurements of a real en vironment. each having its own intrinsic error and not necessarily measuring the same thing. The impinger results are counts of all visible Table I Srlected Measures of Fiber Exposure Cmini Trttal m af 1(30 X Tal fiber on MF al 430X PC Fibers >5 nsirroin MF at 430X PC Total fiber on MF by electron rmeroseopc Weigh t Tnlal du<u Rcspirafilr dusi OhrvM>ti1r bv magnesium ' Respirable chrvsntilf by ma^nrkium Table II Impinsrer/Mcmbrane Fiber Count Ratios ffibers/mi for ! mppcfl PnxJurl Trxliir Friction (V Fibers . ----- ------------ ------- ---------------------- -------------- >5 n >10 a 10.3 3.7 4.S* 5.9 1.9* 2-7 1.0 0.7 Number of Fairs 5m 200 too Correlation coeffkreru not sjJtttificani at . particles, most!)' grains with generally less than 20cr fiber. These few fibers seen in the impinger sample are a small fraction of the fibers counted on the membrane filters, since the membrane filter is a more efficient collec tor of fibers and the magnification/illumina tion used results in Improved visibility. In the case of the impinger versus total and >5micron fiber ratios in the pipe plants, the cor relation coefficient was not significantly dif ferent from zero at the 95<T confidence level, and the hypothesis that the measures of ex posure are unrelated cannot be rejected. In this case a usable prediction ratio will prob ably need to be based on ratios calculated for subsets within pipe manufacturing operations. Size and Visibility To appraise the value of an exposure index based on measurement of only a part of the things which may have biological significance, it is necessary to examine how that part re lates to the whole. A count of fibers longer than a stated length as seen through a pre cisely defined optical system may be chosen as an index in order to eliminate as a variable the microscopic system's resolving power. It follows, however, that some fibers that are seen will be below the stated length and others will be below the limit of visibility and will not be seen at all. 600 Table III Tiber Size Distribution >>: f'hA-r of Total Fibers. Op-ra?irtii Lonprr than 5 m I r\i iir FiUftr preparation and raiding bo Spinum*. Iwlslirur.. and Aravin* til friftioiv MUirttf OfinHin*. cuKin*. and drilling Fipf \f ixini; Fnmhirta; Inflation m ti:i 5: 5 Mi\>inK Fitiivhinst 55 5(i Lonjjrr than 25 58 -u i 51 28 A* `K S< ph tith< f-tVtobf?, Table IV Ratio of 9*0 a to 430'a Fiber f.onrrntranum (phase contrast! Op'*afi*sn I *Milr Fifn-r prcparaJHtf? and carding Spinnmis. tvUMms:, and wwiiis Friciioo MiVOi' rutiiiiie:. and dUllth# Fip- M*\me Finibhms* Total 2.11 1.8 J.| !.P j > j Finish^*: j'd Flf* r- 2*5 11 2.3 I.S 1.1 II I.1' I ft 13 2M The proportion?, of > 5-micron and >10niicron fibers of all the fibers visible at 430X PC on membrane filters are shown in Table III. broken down by operation within prod uct area. Despite the fact that the textile op erations and the three mixing operations art1 all cases of secondary dust dispersion (that is. the small dust particles already exist in the bulk material and are being shaken loose'1 whereas grinding and finishing are primary dispersion (that is. the dust is being produced and dispersed simultaneously by mechanical abrasion i, the proportions are quite con sistent. Although mode of dispersion undouhtediy has an effect on the proportion of large particles, this effect apparently has a negligible influence on the number distribu tion of particles in the size range of biological significance- Similarly, the variation in bulk asbestos quality, from the long fiber used in 1 textile to the short fiber used in pipe, has no apparent effect on the count proportions of fibers by length. 4,,i, nfitn Industrial Hygiene Vorwald.'" in his early anii: toxicity of asbestos, sugge lone fibers are more toxic than tj,is possibility has been raised result? of recent investigations possibility undoubtedly influent in England and in the United fi fibers longer than 5 microns, th tinned use of this index is based tjon of visibility variability, reft as well as on the biological imp The ratio of the number of 97QX PC to those seen at 430 same filter is shown in Table 1 suits are based on a relatively of samples, and the confidence quite wide. They do, however, the increase in visibility is rout for fibers longer than 5 miemi fibers. Thus, the critical factor lution at this level of magnifit diameter. A typical 430 X PC In Figure 1 and a 9?(>X PC in I The electron microscope, w; ficiem resolving power- to revea tarv chrysotile fibril, permits nn all duet particles of interest, F veloped a method for the dire dust particles from membrane tron microscope grids, A lari' electron micrographs of samples ferent operations were sized wit tide size analyzer. .Si/e distribu that shown in Figure 3. were i. the statistical parameters in T, important to note that only a lion of the fibers were over length. Even if it is assumed are being counted at 430X PC-. 1/100 of the trite number of fif counted. Further, as was shown 130 \ PC. mar count as few i fiber? > 5-irricrons visible at 97C. total fiber count-- at 430 X PI about twice as hiilr as over -5-i PC uounts : Table IIJ . still inc ite f of the true number of fibf F1Gl'RE ] Chmutile asbestos dust viewed 3t 430 X, phase contrast. Tigs tu ChrvsoiiJr asbestos dust viewed at 9~l! * . 'phaw fiimm;. Since all litrht microscope measure only a small part of t. borne fiber cloud, it is imponu 'itrmbrr-OrtobrT, yrtirriV'"1 Industrial Hygiene Association Journal 601 K IV 1 Iin-I 'i'ntrast) l inuuons Trtlaf Fil-T. *J.I` <nc l.H 11 he ] n l.-J l.ti >5. 2.1 IS 1.1 n !: l.M 11 1 ft 2.1! dust is being produced tncously by mechanical ortions are quite eon. lode of dispersion un -ct on the proportion of effect apparently has a m the number distribu- size range of biological y, the variation in bulk t the long fiber used in oer used in pipe, has no he count proportions of Vorwald.'* in his early animal studies of toxicity of asbestos, suggested that the lot'1'' fibers are more toxic than the short, and thb~ pmsibihty ^afl keen raised again by the results of recent investigations.' While this possibility undoubtedly influenced researchers in England and in the United States to count fibers longer than 5 microns, the present con tinued use of this index is based on the reduc tion of visibility variability, referred to above jjs well as cm the biological implications. The ratio of the number of fibers seen at 970X PC* 10 those seen at 430X PC on the jante filter is shown in Table IV. These re sults are based on a relatively small number 0f samples, and the confidence limits may be quite wide. They do. however, indicate that the increase in visibility is roughly the same for fibers longer than 5 microns as for total fibers, Thus, the critical factor in fiber reso lution at this level of magnification is fiber diameter, A typical 430X PCI field is shown in Figure 1 and a 970X PC in Figure 2. The electron microscope, which has suf ficient resolving power to reveal the elemen tary chrysotile fibril, permits measurement of all dust particles of interest. Fraser1 has de veloped a method for the direct transfer of dust particles from membrane filters to elec tron microscope grids. A large number of electron micrographs of samples from the dif ferent operations were sized with a Zeiss par ticle size analyzer. Size distributions, such as that shown in Figure 3, were used to obtain the statistical parameters in Table V. It is important to note that only a small propor tion of the fibers were over 5-tnicrons in length. Even if it is assumed that all these are being counted at 430 X PC, only 1/25 to 1/100 of the true number of fibers would be counted, Further, as was shown in Table IN'. 430 X PC'- niay count as few as half of the fibers > 5-microns visible at 970 X PC. Even total fiber counts at 430 X PC. which are aboui twice as high as over--5-micron 430 X PC counts [Table III . still include less than lOri of the true number of fibers in the air. Since all light microscope methods can iJe asbestos dusi viewed at measure only a small part of the whole air borne fiber cloud, it is important to consid- Ffoi'RE 3, Fiber length distribution. Table V Fiber Size Distribution (SOOO* electron microscope) Ope ration Count Median Length (jU t TratiliFiber preparation and car-dim; Spiriting:, twjstmg, and weaving Friction Mi aim* Grinding, cutting. and drilling Pip* Mivins Finishing 1.4 1.0 i\9 0.8 0.9 (1.7 fft 2.0 2.0 2.2 2.4 2.3 2.2 >5 n 4 2 2 2 2 1 er the use of electron microscope counts as an exposure index. Certain disadvantages, such as preparation time, equipment cost, and lack of general availability, are obvious. Several other problems should also be considered. Samples of a particle density appropriate for light microscope counting are too sparse for electron microscopy unless a very large num ber of fields are counted. Special techniques are required for random field selection to avoid counter bias. Most important is the occasional presence of large numbers of very small fibers (about 0.1 -micron thick by 1.0micron long1 as seen in Figure 4. Since these' small fibers often occur in groups, it is possi ble that they are airborne as clumps (of respirable size* rather than as single fibers. A number of electron microscope prepara tions of samples previously counted by optical microscopy were made. The counts of longer fibers on electron micrographs did not ap- 602 y* V* |f?*Vvj * SWTMbcr-October , "ii /9 s_t_a_tistotincsailaecroantsioidnesramti.oankse mitabkeifhcitu di.f.f.i.c.l.J.j.t i obtain close agreement bbeettwweeeenn counts ewl within a laboratory, and the differences , ,rican Industrial H,^ Since only the dust 00 the pulmonary air $: Cr adteonuvraseslnt,yrsipagisllrueswhav.htt.eehiec-trerre-eebntvveieseetdtwrrsioett^uthheoseennyyseleasaeasbkrroeeowrwafeaaetcopinigogrprhiu.herrtontsr.pt.m-imnr~Tieageht.tteehhs,ooed-ds{i1^*Ij,ct%^t,. cent examples of this trend are tthine* n- e* wweeiigghhtt TTLi vY*'-s for quartz and bituminous eo^ This reasoning applied to asbestos led to th* collection of many gross and respirable m** jgnificant in pneuincvcx0/rt. a number of w>-- s of respirable-mass *02 devices. A horizon: j^racteristics similar to ^ British Medical Re*) jjjpjrable dust sampling membrane filters on wbj< samples, analysis of which yielded some rel*. jd at 430X PC. A men) tionships between count-and-weight and without the elutriator wa? h,,^,ct,RE 4 Blectrui besti's dusi, w>Kraph d chryunilc as- among-weight methods. CbfysotiJe asbestos and its parent rock. r. pentine. are hydrated magnesium silicate* I s.. , VJ Coiur.r ' >eht Ratios frodun Trutilr Frieiitm Phpr Typ- of r>hcr Count Total >j# >Hj jB Total >5 M >U>v c*'*nn:t<`tr|o Mean ',-r' Pfr tr, 14 J0() '.TlXt S.400 Sit. .WO it.9m 5.SW) 'ctjio.s.3St0nf0fjt GOSettvaonjnadrtra.ofrrdiijc 28 2.9 3.4 containing a relatively constant 25// mag. nesium. Owing to the extremely high sen*;, tivity of the atomic absorption spectrometer for magnesium (0.0! jug/ml for lfc absorp. iionl, it is possible to count asbestos fiber* on one-half of a membrane filter at 430X PC and to analyze the other half for magnesium. In this way. the direct count/weight ratio* shown in Table Vi were obtained. Several difficulties with this method are readily ap parent. Only chrvsotiie asbestos is deter mined: thus, the crocidoiite used in some and the counts from were used to calculate th The finding that 60<7 < microns were able to perj reveals that many of the enough to have falling s file range. Other simult, using a Hexhlet and a s by side, were analyzed f jjfsimn. giving the mu VIII. The 95?r confide mean percent passing are of most of this data. U$< of dust found on these sa with the asbestos bv ma suited in Table IX'. Th. types of asbestos cement pressure pipes is not pear to be greater included in the weight of asbestos. Further, tica) microscopy. Th those obtained by op- all other sources of magnesium, especially the volved in the prepx-u vvhnical difficulties in- nonfibrous parent rock associated with the bestos samples make . and counting of as- chrvsotiie asbestos, interfere directly. impossibie from the o! limitative conclusions appeared that the c.. v.ata obtained, but it Although count data did not exhibit any electron microscope difference between consistent shift fit fiber length distribution was in those fibeiy - | nts and optical counts with product, operation, or mode of disper These small fibers, v 'After than 1-micron, sion, the weight of asbestos, calculated from dominate the elec tux they are present. the magnesium content, gave decreasing fiber if the other technic.-, vroscope count. Even weight in this order: textile, friction, pipe could be overcome, difficult#* mentioned (Table Vis. When the count/weight ratios an electron niicroscoc-. would result, from were used to convert the tentative TLV of 12 be fiber concentru; w vomit method, would fibers (5 ju length's per milliliter to the equiv these very small fibv'x v strongly biased by alent gross weight concentrations of asbestos not indicate that th-. . Present evidence does (based on magnesium determinations', the a dominant role. should be given such gross weight concentrations were 2 mg/m3 for textile. 1 mg/m'1 for friction, and 0.5 mg/ Weight Relationship.. Differences betw-.x ' ounters and certain nvs for pipe. A single value for the weight TLY for all product areas would be equiva lent to a fourfold difference in fiber threshold between textile and pipe plants. the product, total dust I does not vary greatly fcjl J However, the percent d pected in either the to] dust will vary from t[ to product Summary The impinger measu and as the TLV for a non-asbestos dust prese source of error in the e to asbestos. Other cour| are available to count varying degrees of conve ods that cannot differs other dust suffer from tl as the impinger in that centration could differ the same total or resp tion, depending on the method for chrvsotiie v mbcr-OctobfT, }9?q I jljnrriean Industrial Hygiene Association journal 603 make it difficult to >ctween counts even I the differences are oratories. These fac. of counting, led in. weight methods 0f re appropriate. Re. Since only the dust capable of penetrating jjjto the pulmonary air spaces is biologically significant in pneumoconiosis-producing dis hes, a number of samples were collected by means of respirable-mass size-selective sam pling devices. A horizontal elntriator having characteristics similar to those proposed by Table VII RespirabUity of Textile Fibers by Count Type Fiber Count Total >Sm >10 it St- Fusing Elutriator B4 80 6(1 trend are the new and bituminous coal, n asbestos led to the and respirable mass h yielded some reta in-and-weight and the British Medical Research Council51 for respirable dust sampling was used ahead of membrane filters on which fibers were count ed at 430X PC. A membrane filter sample without the elutriator was taken simultaneous ly, and the counts from the pair of samples were used to calculate the data in Table VII. Table VIII Asbestos Dust Passing an Elutriator Product Textile Insulation. Mtu Weight Pissing 81 29 *4 22 $Y/r Confidence Interval 24-38 21-37 39-49 19-25 i its parent rock, sermagnesium silicates constant 25T mag. xtremely high sensi- orption spectrometer Tnl for 19c absorp- ount asbestos fibers ne filter at 430X PC half for magnesium, count/weight ratios e obtained. Several thod are readily ap> asbestos is deter.iolite used in some pressure pipes is not of asbestos. Further, lesium. especially the associated with the fere directly. The finding that 60% of the fibers over 10 microns were able to penetrate the elutriator reveals that many of the longer fibers are thin enough to have falling speeds in the respira ble range. Other simultaneous sample pairs, using a Hexhlet and a gross dust filter side bv side, were analyzed for asbestos by mag nesium, giving the results shown In Table VIII. The 95^ confidence intervals of the mean percent passing are typical of the range of most of this data. Use of the gross weight of dust found on these same samples, together with the asbestos by magnesium analyses, re sulted in Table IX. The percent asbestos in the product, total dust, and respirable dust does not vary' greatly for the same product. However, the percent of asbestos to be ex pected in either the total or the respirable dust will vary from 5# to 659? from product to product. Table IX Asbestos in Product and Dust Product Shinelc I imitation:** % Asbestos Content Product Total 13ufcl Respirable Dust JS-85 68 64 30-60 22 36 10-30 12 18 10-30 25 28 5-15 4 6 N<M including croeidofitc. including amosite- analysis is not specific or general enough to form the basis for a threshold for asbestos. Conclusions Certain general statements are possible, based on the data presented: did not exhibit any length distribution . or mode of disper ses, calculated from : gave decreasing fiber extile, friction, pipe count/weight ratios tentative TLV of 12 lilliliter to the equivntrations of asbestos determinations', the ions were 2 mg./m* friction, and 0,5 mg/ value for the weight as would be equivance in fiber threshold plants. Summary The impinger measures all types of dust, and as the TLV for asbestos decreases, the non-asbestos dust present becomes a major source of error in the estimation of exposure to asbestos. Other count methods, however, are available to count asbestos fibers, with varying degrees of convenience. Weight meth ods that cannot differentiate asbestos from other dust suffer from the same disadvantage as the impinger in that the asbestos fiber con centration could differ by a factor of 10 for the same total or respirable dust concentra tion, depending on the product area. The method for chrysotile weight by magnesium 1, There is. at present, no practical abso lute method for the routine measurement of exposure to airborne asbestos fibers. The tech nical difficulties of the electron microscope for dust counting make its routine use unfeas ible: when it is used, the results are heavily biased in favor of very small fibers. 2, Each of the methods considered mea sures something different and, therefore, they do not correlate well. Ratios between results by different methods should be used for quali tative prediction only. 3, Each method is strongly influenced by one attribute of the dust cloud. The biologi cally optimum method cannot be selected un- 604 Septcmber-October 19?q less it is known which attribute is biologically most appropriate. 4. The preferred index of asbestos ex posure is fibers longer than 5 microns counted on membrane filters at 43UX phase contrast. The method of counting is convenient and practical, and fibers >5 microns constitute a direct index of asbestos fiber exposure. References 1. Gilson. J. (... Man and AtbrUas. Ann. SSfi, 132: 9 (December 1965 J- A<oA. 2. Gommilier on Hyttiem* Standard*. British Occupational Hyim-nr Socict' Hv^irnr Standards ior Chrysotilc A*- bcMCH- Du*t. Ann. Orcitp. Hrg. //- 4~ (!96fn. 3. Efwvwtes C. H. and j, ll. Lynch: by tfcr t'.S. Puhbr Health Seivirr for % Aftbesto* 0usi on Membrane Filters. Ann. ti9b8s. CuP- Hi Dressrev. W. C . I- M. Dalia Valls, T. 1 j. M- Milue*. and R R Sayjws: A Study of in the Aa!**io* Textile indutrv. Puttie H+JitL***** Hull. 24i n938L *"* (jimmiure on Threshold Limit Values: Thrtsb0U / I'fduft n/ Aitbmnr Cvataminanis, American Cof at Governmental Industrial Hysrienists fl969j n ****** VoftW**U>. peritnenul! Sfrd, 3: 1 /A!SiiH.1tu9Jd5`1,iie. i;s.To.f *M'. P^uitttA*, and" Asbestos-i*. Arch, "P. C'. f` W*. Ind H'\** s* * ** Iff;1- - Ur JKxlibr<>*rnic *!" to Art*,,* Med. Lav*>m 59: 6 U96&I. D- Ax Absolute Method of Sampling antj u t suremetit of Solid Air-Borne Particulates Arch r2` Hvg. Ocrup. Atrd, 8: 412 (November 1953). ** Medical Research CouociL Dum Subcororniitee. Ia<L- trial Fulaionary Diwavr Committee: Recommendation of fhr MHC Paorl* Rcbtm.it to .Scbrttvr SampW u ' mv- of joitii Meeting. London, March 4, 1952. * Received jaimarv 7. tgi*u Radiation Publications The International Commission on Radiation Units and Measurements has recently issued two new reports which are of interest to industrial hygienists dealing with radiation problems. These reports are: ICRU Report 16: Linear Energy Transfer. This report defines the concepts of linear energy transfer and the methods of calculations of distribution of absorbed dose. The applications and limitations of the linear energy transfer concept are also covered. In a series of nine appendices, measurement., range, distribution, dosimetry, and symbols are presented. An extensive bibliography is included. The publication may be purchased for $3.00 per copy. ICRU Report 1": Radiation Dosimetry: Y'-Rays Generated at Potentials of 5 to 150 kv. In this report there are discussions of measurement of energy fluence. spectral distribution, measurements and absorbed dose. This publica tion may be obtained for $2.50 per copy. Address orders or inquiries to ICRU Publications, P.O. Box 4869. Washing ton. D. C. 20008. Proposed Revision The American National Standards Institute is proposing to revise the follow ing standard: Z9.1-1951 Safety Standard for Ventilation and Operation of OpenSurface Tanks. This standard covers the protection of operators from con tact with gases, vapors, mists, or liquids used in. created, related, released or disseminated by open-surface tank operations and the design of ven tilating systems for controlling and removing said gas. vapors, or mist. This guide does not cover protection from fire. Comments relative to the proposed revision of this guide will be welcomed by the Board of Standards Review and the comments should be received by November 24. 1970. Copies of the standard may be purchased from the Ameri can National Standards Institute, Department BSR, 1430 Broadwav. New York. New York 10018. ' HERBERT Department 77 The rat liver of many fort injection of a vat structurally relati on the dose and ganic, inhibit liv affect this eniym action among co those that are m toxic than the p: ln-froducflon I-THE MJCROSOM 1 TEM which appi sponsible for the metal pounds, has been und number of years,'"3 He pact of the operation on the response of mar ' neons chemical compt pletely appreciated, T system is subject to in! duction by various found as air pollutar dustrial chemicals/'''' The effect of fastinc cation of several druc Dixon rt aLS and Ro reported reduced N-d< livers of fasted animal teration in benzene m has been previously re | Ryan/ Thus the imn Thi; sruds was supporrrd Senior Research Grant Gn General Medical Sciences, j to Lav,Tence Roslinski and 1 in this work, 1