Document B8GeGw7L1d1k3jqNRzkxY6jKj

In the Forum eoiiBrtSff t pgS-00-00000029^2 Is Short-Fibered Asbestos Dust .; a Biological Hazard? . ;> Paul Gross, WD, Charitaloo, SC . Contrary to the dolarmlnallon L*>al Oio Inasmuch as asbestos fibers smaller development of mesotheliomas. So far finer the quartz' dual. tho greater Its palhogenlcliy; tho palhoganlclty of tho lineal aibraloa dual ha a been shown to bo negligible. It has been the finding ol research labo ralotlea In Germany, England, South Al-/, flea, and Ihe United Stales that sbort-tJ-IJ bered aabeatoa, dual, lo, leaa than 5jt In if length, la Incapable ol causing fibrosis or ? cancer. This finding. In conjunction with 1 the (allure ol different laboratories In tho than Sft tend to remain airborne longer than the larger ones, they have a greater chance of being inhaled. Furthermore, although the anatomy cf the respiratory tract tends to preTent the intrusion into the airspaces of all but a few of the larger suspended particles, this deterrence does not extend to the smallest particles. The latter very readily enter the air- as ability to penetrate into and Lransmigrate across the intact intestinal wall is concerned, once again it would appear that the. subraicronic fibers would be better able to accomplish this feat than would the coarser ' fibers. Originally, the question'-.of the pathogenicity of the short-fibered as- j bestos dust bad relevance only to United Kingdom and In this country lo dl- spaces with the Inspired air. Some of people occupationally exposed to as- } cem abnormalities following prolonged esbesloa feeding lo rala, should lead to the abandonment of the present concept that maintains that mesotheliomas and paslrolnlestlnal cancers arlae Iro.-n tho In gestion ol asbestos dual cl oared from tho lungs. These ncgaltso results should also ctlay the alarm thal has been rslsod si a msult ol the finding of ultra microscopic the short asbestos fibers may settle bestos; but more recently short as-' on the alveolar surface by sediments- bestos fibers have been found in ccr- tion, whereas the smallest fibers, tain beverages and oty water, in behaving almost like gas molecules, ambient community air, and in the contact the alveolar membrane by lungs of city dwellers.*-* Coo- diffusion. sequcntly, the relevance of the above What is the potential of these ex- question must now extend to entire - tremciy fine submicronic fibers to . .urban populations. However, lest un produce disease? Is their potential due alarm be raised by the last state- mineral fibers In certain bererages and greater than that of optically visible ment, it should be pointed out that in drinking walsr. fibers? Is the behavior of submicronic city dwellers no disease has been asbestos fibers as opposed to that of found that could be attributed to the larger fibers similar to that of the fi- presence of submicronic asbestos 6- brogenic effect of very fine quarts bers in the pulmonary tissues. Nci- By short-fibered asbestos dust is meant that which has a fiber dosj as compared with that of the tber has there been documch Is lion of same weight of coarser quarts par- an increase in abdominal caocers in . ``englh of less than S/l Although fi tides?'-* .- the general population, in spite of the bers of this Rise usually constitute a These questions take on added im- fact that in many cities and smaller cry small fraction of the weight of a portancc in view of the commonly communities drinking water has been 'ust. cloud, their numerical prepoo- held hypothesis that mesotheliomas and is now transported in asbestos- . crance over the larger fibers may be of the pleura and peritoneum arise by cement pipes. :anifol<L the transmigration of fibers to the At the International Conference on/ pleura and peritoneum, respectively. I the Biological Effects of Asbestos! Subreic'-rd for publialioa Seyt 11, t573; se?ui Jan 30. 13M. Trers die Dcpirsewol of Palidefy, lit Modi1 U Diversity of Sou Lb C retina, Oiirlritoo.SC. ftrphnt requests lo the Drpsnmrat of PithoU V. llrdiu] Uoivrrsity of South Clrolioa, SO *rr St, Ctrriutot, SC 23101 (Dr. CnuJ In the case of abdominal mesolbcliomas, it is assumed that the asbeslos'-fibcrs cleared from the lungs are swallowed and then migrate through the intact intestinal wall to the peritoneum, there to initiate the \ held in Dresden in 1963, Klostcrkdt-' \ter* found .that both chrysotilc and crocidolile, gTound to an average fi-ber length of less than Sji when in-] . jected intratracheally or intraabdora-j inally, produced no fibrosis. The- 2099 I5 I ! pci--.or.-ry consisted nnly of j i a macrophage reaction. In contrast,! ; longer fibers of the some asbestos re-1 ' suited in fibrosis in both regions. At the same conference Timbrell and Skidmore* reported the results ob tained in rats and guinea pigs ex posed to equal concentrations (by weight) of short-fibered amosite (90`S of the fibers <4/i long) and long-fi- bered asbestos (15'S of the fibers >4^ long). They concluded, "minimal reac tion has been observed to short fibres but a marked reaction has been ob- 'served to the longer fibres." Id the following year, Webster reported that monkeys inhaling finely ground cxocidolite (fiber length <5p) also showed merely a macrophage reac tion in the lungs. In 1970, Hilseher'ct al* showed the chiysotile or crocido-- lite, when ground to a fiber length of <3ft with a microtome and injected intraabdominally, produced no fi brous adhesions; whereas the same asbestos with greater fiber length did cause dense fibrous adhesions. In 1971, the-Johns-Manville Re search Laboratory prepared for us 'chrysotile asbestos ground to a fiber length of <5jl We injected this dust iatratracheally into 10 rats and were able to confirm that such shoirt-fi- - bered asbestos could induce'no more tban a macrophage reaction (unpub lished study). In 1973 Smith cl al* re ported that hamsters injected in- trapleurally with chrysolite ground to a fiber length of <lji developed no pleural cancer, whereas hamsters in jected " inlrapleurally with longer chrysotile fibers did develop such can cers. Recently Wright (private com munication) disclosed that in his labo ratory short-fibered asbestos injected Iatratracheally also failed-to elicit a fibrotic reaction. M.iroudas ct aJ" have concluded that, "Particles (min eral fibers) smaller than 20p in length induce neither growth in vitro nor . mesothelioma in vivo." *--. Thus, these reports from different laboratories are unanimous in finding asbestos that has an average length of <5(i is devoid of pathogenic poten tial. This included not only the fibro- genic potential*-'-1* but also, the can- ccrogenie potential.'-1* ^ It may be argued that when bestos is ground to a very small fiber ar.J nonsp-rcihcity of such turr.nr size, cither in a ball mill or a hammer- duction in rati is demonstrated in the mill, much of the energy is converted first" of the two above-mentioned pa into heat and the heat may change pers when the authors list a betlcr- the chemical structure of the fibers. than 607i tumor production with mag To continue this argument: since, nesium hydroxide and a 55* tumor strictly speaking, the fibers so altered production with fibrous glass! In con may no longer be asbestos, the bio trast. they reported only a 40W tumor logic "inertness" of such "altered" as production with chrysotile. This lower bestos need not necessarily apply to -tumor production was doubtlessly re fine asbestos dost that has not been lated to a high mortality crused, in heated to a high temperature. turn, by the exceedingly high dosage This argument is rendered void by of materials injected (100 mg). the following facts: ' The employment of unrealistic dos 1_ The short-fibered asbestos of age, of inappropriate routes of ad Hilseher et al* was found to have ministration, and of inappropriate maintained its fibrous structure after animal species (all three "sins" were the grinding proems. committed by the above authors) to 2. Smith ct al* prepared' short-fi- achieve positive results has recent bered asbestos as an aqueous slurry. ly been adequately discussed by Dr. This obviated excessive heat. H. E. Stokinger." . 3. It has been concluded that the When asbestos is ingested, it is the chemical structure of 2sbestos does ullramicroscopically-sized asbestos fi not determine its pathogenicity since bers that are assumed to be respon synthetic chrysotile is devoid of patb- sible for the development of mesothe ogenicity.1* The latter.has the same lioma .by virtue of their alleged chemical and crystalline structure as penetration and transmigration the natural, product. Therefore, the through the intact intestinal wall mere process of grinding with the as The failure of short-fibered asbestos sociated heat production does not ac- to induce mesotheliomas when in count for the lack of pathogenicity of jected intrapleurally'-'* makes the the finely ground asbestos. However, above assumption highly question by fitting together some newly de able. Unpublished data from differ rived experimental findings, a theory ent laboratories (David B. Clayson, has recently been formulated regard University of Leeds; L. M. Swio- ing thc'locus of pathogenicity of as-' burne, St- James's Infirmary, Leeds. bestos dust that docs offer a reason England; and John M. G. Davis, In able explanation for this lack of stitute of Occupational Medicine, pathogenicity." . ' Edinburgh) in which rats were fed as There is, however, one laboratory bestos intimately mixed io their food, that reported that short-fibered as indicate complete failure to induce tu bestos is tumorigenic. Pott and mors or any other kind of abnormal Friedrichs" and later, Pott et al" ity by these regimens. (A joint paper maintained that 100 mg of chiysotile describing these investigations from with a fiber length <3/i injected into the different laboratories is in prepa the abdomen of rats caused the devel ration.) opment of cancers. Nearly S0 of the As one example, the following ex tumors were sarcomas-moslly fibro periment may be cited: ten weanling sarcomas. male rats were placed on a finely The character of the tumors pn>- ground basal diet containing 5fl by duced by this technique should have weight of chrysotile asbestos. Five given the authors pause for reflec litter mates were pair-fed with the tion; not only because rats will pro-. same weight of food as the experi- duce fibrosarcomas secondary to in- mental rats had consumed on the pre jeclcd or imbedded materials known, vious day. This regimen was rontin- to be biologically inert, but also be ued for 21 months. At the end of this cause subcutaneous' fibrosarcomas are time, the weight curve of the as- very common spontaneous tumors in ' bestos-fed animals was not signifi- aging rats. An ipdication of the ease eantly different from thatof the pair- 2100 116 Aceh Envi/on Heil;n/Vol 29.'Aug 1924 F03-00-00000029- Short-Fibcfed Asbestos Ouit'G>csi /ill fjnlroli. The ar.ina'.j were killed l>./ lvrsr of proper **/ P*. witS nal wr.i|>-:ip. ,\i Ic.ui i,, ISvj. u!- 21 months after the initiation of the feeding period. At autopsy, no gross IhoAtf from the )p of people of CiaHralon. SowUs Carolina. Am J*4 Jiyf A** J 3JJJ43, 1971 trainicroscopic asbestos paitidu were believed to have fiUrogcnic po abnormality was found in either 4. Crosa P. el ik U>Tnplalr Uox*|ort of fi tential for guinea pigs. group of animals and microscopically no tumor or other gastrointestinal le breuj dull frao list J Orrwp A/#d 15.1&U U9. 1971 5. KloMe/kMLrr TV: EspersmrnlrKr Unlef* Ccoi'.ce \V. Comstock. MD The Johns Hopkins University .- sion ivas observed.1* It is to be noted that in previous studies, the first as- aucKunj^en tlber dir Bedrulvm; dcr fafcrHJn-r fur die Aibrstfibrove ioif UAlenuehunpct Dber die BecirsAuaaonj: der PibooM durtk Pol/- School of Hygiene and Public Health Hagerstown, Md bestotic lung cancer death occurred 16 vinvlp)*rsdin-?Oa*d, In iiVr/utir irri*va/m months after the initiation of the' dust exposure11 and the first asbes- 4t Arberlea: A'on/rrmt, Jfft, Drvdtn. Berlin, Drul*chr* Xeolnlinjlitot fi)r Arbtiumedtun, pp 47-SZ. I jeply that Paul Holt used the same make hammcrmill to commi lolic pleural cancer death in rats oc curred 17 months after the intrapleu ral injection of asbestos dusL>: C. TimKrvll Y. Skidraoec JW: Sifntfinntt of fibre lenjT.h is rptnmrsul uUilsiis, so fiirV /wi# iririii;ra d< Arbo/ri; /Airmotumalr Xn/rrr*a 1944. Drt4t*. Berlin, DcvU6n Z^ nute his asbestos as 1 used.. I fully agree with his statement that a high proportion of-the particles lo which he It is of interest in this connection that the dose of fibers in the intesti tnlinaiiiut fur Arbriumedian, pp liK. 7, Webi'.rr 1: The pathogenesis of ubnlajii, lo Shapiro HA (edt F^trnmpmiotU: ^rorredfepr exposed his guinea pigs was too small to be seen by the light mieroscopc. nal tract of the asbestos-fed rats was pf the filrrMlirml Cr"/rrrvr, Jph* mujkurp. The more important aspect of astronomical compared with the dose of fibers that is likely to be swallowed ISO. Cap? To^o, Oxford Uai*erail/ Proas. 3970, pp 117-119. 6. Hilschrr W, ft *J; Zvaaoetnhlngo Zwi- Holt's statement is tbe long /fcers were present ia the dust cloud. Hav-. daily by a person occupationally ex achro Aabeslose und favertingt- ha(irru*r* _ ing seen his set-up, I was impressed posed to asbestos dust-and he, in turn, would have an astronomically aeAoyrcn S7:15&.fiA7, 1970. 9. Smith TV'E. ct ah Biologic difference* In rr* spom-e U long* and ahon asbestoo fiber*- Am i*d by the high density of the dust con centration (unmeasured!) lo which his greater dose of fibers than the dose of fibers ingested daily by an urban, Hyy Arxr J J2JU62, 197Z 30. blaroudaa KC, et at Fibroblast anehonge is carcinogrncaii bjr fibres L607-S09,- guinea pigs were exposed. The dosage of long-fibered (optically visible) dweller drinking a beverage or water 1571 particles must have been enormous containing mineral fibers. The uniformly negative asbestos 1L C>ou ?, Harlrj P-A Jr: The locus of patho genicity of aabeaiA* dual: A Theory. Arch av>tv* H<cUK 273:0.212. 1971 whereas the dosage of submicronie fi bers (those visible only with the elec feeding results should cast some doubts on the tenability of the con cept that peritoneal mesotheliomas 12. Crou P, Harley P.A Jr. Aabcalaa-ioduerd lolralborario tiuoc reacUoaa. AreA PrlW 1971 11 Poll r. rHrdneha )CH: Tuaorro der Racu tron microscope) must have been as tronomical. Holt's finding of many optically and an increased prevalcoce of gas trointestinal cancers arise in occupa tionally asbestos-exposed people from aach Lp. lojeklioo fiaerfomigtr $Uub*,>'oUr* ' wnjjrnaeAoyirn 59:3lfi, 1971 14.. Pott r, et ah Tuooreo dcr Pattc ch i.p. * Injekiioo voa g-toaWrneo Chrvaolil und Benoo visible fibers in the lung sections of his animals as pictured in his illustra- ` tions and of many asbestos bodies at the ingestion of asbestos fibers cleared from-their lungs. There must,, (a) pyreft. Zb Bai-t JJyf J Abt On> lSS:AS3-469, 19T1 IS. Stokinger HE: Sanity ta irsearOs and teal* test to the plentiful dosage of long fi bers. This undermines his claim tbit of neeessity,:bc some other explana ualioa of earironrccnlal health: Ho* la achiev* "Fine dust particles, too small to be tion! ' Although not an asbestos-feeding a realistic evaluation (in xveo ao<aaodnnUV Scitntt 374:3-6i3, 197L IS. Crosa P, et ah Problems in the pathology seen under tbe light microscope, will produce asbestosis in the guinea pig." study, a recent report purports to demonstrate that the presence of as bestos in the intestinal lumen results of aabcaiosis, to Sbapiro HA (rJV Ns* f*wv*vn\oJta* Pntftil+ft if the J*urmctia*ct Conftrnur, Jokonnr;l*ry. JSO. Cap* Tom; Osford Uoietmily Presa, 1970, pp 12M31 Tbe dcienninant(s) of asbestos tox icity is not known and 1 make no claim to such knowledge. However, in in the penetration of asbestos fibers into the blood stream and organs 17. Crosa P, cl ah Eaperimeelal aabcoloais Tbe development of lung cvneer in rsla tvA pul monary .deposiu of chryaotHe aabenos dust. this article, I point to one aspect ofasbestos dust which is not associated throughout the body, inclusive of the Arxk iTneiron //tilth I3.34hlai, JK7. with pathogenicity. brain." The writers injected (he as 31 Ponufrael KD. Cunnirgham HM: PeneLnlion of aabestos through the digestive tnet of bestos into the stomach by means of a . mu. A*'o(ure 243:152-Sal, 1971 y- By "submicronie" is meant some thing invisible with the light micro syringe and needle, thereby ignoring scope but visible with this electron the probable opening of vessels in the path of the needle track and the pres Rebuttal . * microscope. This generally means a particle<0.2o;i in thickness. Although ence of injection! In looking through "Biological Ef the vast bulk of fibers that have been fects of Asbestos" (Ann tvV Acnd Sci ground lo a length <5? are submi- Relerences 136:37, 1965) 1 find one paper by Holt, cronic, some would be thicker than Mills, and Young that says very small 0.25p and therefore, optically visible. 1. King U.tt tl:Th cltoftef dlffgirnt forms asbestos particles do cause fibrosis in Perhaps, it would be best not to spec of purr silica oa Use lung* of flU. Sr J Afrtf 30.M7.19il 1 HiLei T, k'indsvisur YH: Lursj rtUaUoa of quaru dvst.imsller than ont-half csicofv J 1*4 Hyi 7*'irW 29142-J45. 1947. 1 Crosj P. el *1: Mineral fiber control of bo- oid lur^-i: A eo npari so o of lit couala obtained the guinea pig lung. In the published discussion, no one challenges this re sult; one discussant, Jao Webster from South Africa agrees with it, and Gilson quotes it approvingly in his fi ify "submicroscopic" and speak, only of "short" fibers as defined in the opening sentence of the report. Paul Gross Naples, Fla %l onM Arch Environ HeaUh/Vol 29, Aug 1974 rOS--(30-00000(32944 Snori-Fibe<cd Asbestos Oust/Gross 2101