Document em5GJRpLNX9z4gDo8G4ZEnxDq

I DIS!RJB TIOW (ip ;/?nt Mo. of ilbrcs > 25 sized -> MS 2 336 reference samples. uTiTjiTBiiTju mu ii ft rtynriiTMi 4>m \o! si \<* 4B.rr "N-'M. Nx* P.'iRiu.i n Or.-a1 Btiiiifi raw; 4irg *7 SJvO-fHM) Eersamon Journal* Lid r IvV B'a'isl* uKvupAi.xMi&l HjgKnc So;k:j. INHALATION AND INJECTION EXPERIMENTS IN RATS TO TEST THE CARCINOGENICITY OF MMMF H. Mukle.* F. Pott,! B. Bkli.mann,* S. Taxenaka* and U. Zikm+ `Fraunhofer Institut fur Toxtkologte und Aerosoiforschung. Nikolai-Fucbs-Strasse 1, 3000 Hannover ft!. FRO. and +Medizinisches Institut fur Umweilhygiene an dcr Univcrsitat Dusseldorf. Aufm Hennekamp 30. 4000 Dusseldorf. F.R.G. Abstract--In parallel inhalation and intraperitoncal injection li.p.) experiments with rats, the glass fibre JM 104. Tempstran 475. exemplifying a very thin and durable man-made mineral fibre (MMMF). was compared with crocidolite (South Africa! and chrysotile (California. Calidria RG 144). Aerosol concentrations were 2.2 6 mg m Exposures lasted 1 yr. No significant tumour rate was found in the inhalation test nor from an exposure combination of 100 ppm SO- and glass fibres. !n 74% of the animals exposed to crocidolite bronchiolo-alveolar hyperplasia was detected. Intraperiioneal injection of0.5 mg of the three different fibre types showed a tumour rate of 17% for glass fibre J M 104.55% for crocidolite and only 6% for Calidria chrysotile. Calidria chrysotile seems to be much less persistent than other chrysotile samples. The long persistence of JM 104 475 in the lung (half-time of lung clearance about 600 days) and the carcinogenic effects of these fibres after inlraperitoiiea! injection indicate that after inhalation ofthin (< 1 fim). long and durable MMMF the suspicion of a carcinogenic potency of these fibres is still well-founded. INTRODUCTION Various inhalation studies on rats with man-made mineral fibres (MMMF) have not shown any evidence of lung tumours (Lee et al.. 1981; Goldstein el al., 1983; McConnell et al.. 1984; Smith et al.. 1984; Wagner et al., 1984). whereas many injection experiments showed positive results. A review was recently published by Davis (1986). Inhalation of UICC chrysotile (Zimbabwe and Canada) and some other specimens of chrysotile induced malignant and benign lung tumours in 20-40%. Crocidolite and amosite with relatively short fibres caused only relatively low tumour rates (Wagner et al.. 1974; Davis et al.. 1978); long amosite was much more effective (Davis. 1985}.' Various causes may be responsible for these findings, such as the higher fibre concentration of chrysotile used in the different experiments. Moreover, the fibre number for chrysotile can increase inside the body by splitting. It has been supposed that lesions of the bronchial epithelium caused by infections or by inhalation of irritants, e.g. cigarette smoke, enhance the chance of penetration and long-lasting residence of fibres in the bronchial wall. The settling and persistence of fibres in this susceptible tissue might be the precondition for the induction of tumours. This patho-mechanism gives one of the possible explanations for the syncarcinogcnic effect of asbestos and cigarette smoke (Pctt et al.. 1984). In our inhalation experiment with rats, the carcinogenic effects of very thin glass fibres, of crocidolite with a greater length than in the UICC sample, of chrysotile from the Calidria mine in California and of the combination of glass fibres with SO. inhalation have been tested. The design of the inhalation study was based mostly on the results of Wagner et al. .(1974) and of Davis et al. (1978 ). From the studies of Wagner et al. (1974) in which TS6 H Mt'HLr. et a!. a' n; tumours were produced after an exposure of only 1 day. we expected a significant tumour rale following crociciolite and chrysotile inhalation. Mere recent results of : . McConnell et ai. (1984) and Wagner et al. (1984). which were published after the $j beginning of this study, showed lower tumour rates. For comparison with the inhalation study, the carcinogenicity of the three fibre specimens was also determined in intraperitonca! tests. The in vivo persistence of . MMMF was investigated in a parallel study (Bellmans et a!.. 1987, this symposium). ^ :i:j The studies were funded by different sponsors, so partly different fibre types and fibre i--i treatments were used. j-i MATERIALS AND METHODS ii; Origin of dusts Glass wool (Code 104, Tempstran 475) was supplied by Manviile Corn., Denver. Colorado. U.S.A. A detailed description of this very thin and durable fibre is given in the paper by Bellmann et al. (1987). Fibres were shortened by a 50-min treatment in a knife mill. Sufficient amounts of UICC asbestos samples for the inhalation study were not available. Therefore, another crocidolitc sample from South Africa was used which was slightly longer than UICC crocidclite {preparation by Dr Rendall). in accordance with a recommendation in a report from NTOSH (1979). chrysotile from the mine Idria in California. U.S.A. (= CaIidria chrysotile) was used. It was provided as commercially processed powder. NIOSH (1979) characterized this specimen of chrysotile as follows: contaminants included mica (less than 2%). quartz (less than 2%). carbonates (less than 3%), other unidentified mineral (less than 1 %) and hematite. Approximately 1 % of the sample consisted of metallic fragments, probably introduced during mining and processing of the crude asbestos ore. The sample displayed good fibrous structure; no non-fibrous serpentine minerals were detected. The fibres existed in bundles with rounded ends. Bundles ranged from 0.5 to 68 um in width and 1 300 gtn in length. T he material as received was treated in a knife mill for 1 min before it was fed into the aerosol generator. The Calidria chrysotile samples for the inhalation experiment and for the injection study came from different distributors. The material used for the injection study was pre-treated by the producer for manufacturing asbestos paper; this resulted in smaller fibre diameter (see Tables 1 and 3l. For the intraperitoneal test. UICC-chrysotile 3 (Canada) and titanium dioxide (P 25 Degussa) as a granular control dust were used additionally. 1-j ^ :(?; h; jj :.j Tj ;J j . < ; :;1 ' ') .j j .| .i | .| ij `1 Inhalation study The fibre aerosol was generated by a vibrating-bed aerosol generator (Spurny et al.. 1975; Spurny. 1980). The size distribution of the fibres in the exposure box is listed in Table 1. This is different from the distribution of the initial material, because the aerosol generation process favours the aerosolization of thicker fibres. Monthly samples were taken on a N'uclepore filter. The size distribution of about 200 fibres was determined with a scanning electron microscope. The detection limit was 0.05 ,um. Fibres were discharged by a Krvpton-85 source. The fibre aerosoi concentrations are .listed in Table 1. Chrysotile fibres consisted of relatively thick bundles, therefore the j; ,; i' : '. ij 1j )1 :j pected a significant re recent results of published after the y of the three fibre rii'o persistence of 7. this symposium!, ibre tynes and fibre 'iiie Corp., Denver, hie fibre is given in min treatment in a on study were not .`'as used which was In accordance with u the mine Idria in d as commercially :rysoti'ie as follows: ). carbonates (less Approximately 1 % during mining and irous structure; no d in bundles with ) ftm in length. The it was fed into the on experiment and terial used for the sbestos' paper; this itraperitoneal test, .sa) as a granular erator (Spurny et losure box is listed terial. because the r fibres. Monthly out 200 fibres was imit was 0.05 um. oneentrations are dies, therefore the Experiments to test the carcinogcnicit) of MMMF 757 fibre number appeared low. Further investigations showed that bundles of Calidria chrysotile split into thinner fibres in the lung. Female Wistar rats (Ivanovas, Kisslegg im Ailgau, F.R.G.. age 12 weeks at start) were exposed, nose only, in tubes which were constructed similarly to those described by Smith et al. (1981). The inhalation box could house up to 60 rats. Exposure lasted 5 h 4 times a week. After each treatment, the animals were put into Makrolon" cages. The total exposure period lasted 1 yr. Because of the high solubility of SO, in water, exposure leads to an impairment of the upper airways. Lamb and Reid (1968) and Reid (1970) exposed rats to 400 ppm for 3 h a day, 5 days per week for up to 6 weeks. Tracheal goblet cells increased in number and size. On the basis of this information, a few hours after the fibre exposure we exposed rats to 100 ppm SO, in a 6 m3 stainless steel exposure box for 5 h, 5 days per week for 1 yr. During exposure animals were housed in wire-mesh cages. Total exposure lasted 1000 h, so the cumulative mass exposure was 3000,2200 and 6000 mghm'3 for glass fibres, crocidolitc and chrysotile. respectively. The numbers of fibres retained in the lungs were measured after low-temperature ashing, by scanning or transmission electron microscopy 6,12 and 24 months after the start of exposure. For chrysotile samples at 24 months a transmission electron microscope was used. Table 2 gives the total numbers of animals in the exposed groups with the numbers sacrificed early for the investigation of fibre retention. Animal numbers in the glass fibre groups were about doubled, because low effects were expected. Injection study Female Wistar rats (from Ivanovas, Kisslegg im Ailgau. F.R.G., aged 5 weeks at start) were treated by means of a single intraperitoneal injection with one of the dusts mentioned, suspended in 1 ml saline (for doses see Table 8). The details of animal housing and examinations are described by Pott et al. (1976,1987). The distributions of the fibre sizes are listed in T able 3. Fibres were sonicated for about 1 tnin. Calidria chrysotile consisted partly offibrils and partly of large bundles, therefore sizing of these fibres was very difficult and resulting numbers and fibre dimensions are not very reliable. RESULTS Inhalation study Table 4(a) shows the numbers of retained fibres after 6, 12 and 24 months of the study. The size distribution of fibres is shown in Table 4(b). Size distribution of chrysotile fibres was investigated by SEM and TEM after 12 months' exposure. Results showed that the SEM was capable of detecting fibre size distribution correctly. At 24 months (1 vr post treatment) fibre splitting was marked for chrysotile. The median fibre diameter decreased from 0.2 to 0.08 fim. The median fibre lengths of glass fibres and crocidoiite were about the same. The gravimetric fibre contents of lungs were calculated from the data ofTables4(a) and (b). These are listed in Table 5. The retained chrysotile mass decreased by a factor of 10 in the 12 months of the post-treatment observation period. For glass fibre and crocidoiite fibre mass was determined additionally by analysing the silicon content oflungs after 12 months1 exposure. The 58 K. Mlhlf t'f a! TaRI-E i Sut rilSiKBUTIONS >.N0 CONCENTRAUONS OF FIRRES IS THE EXPOSURE BOR. FIBRE AN AI VSE5 BY SEM. OHTFCTION | IMIT 0.05 /.m Fibre type 10% < Fibre length l/tm) 50% < Si7c distributions Fibre diameter 90% (/an) 10% 50% 90% < <<< Glass fibres (JM 104 4'5i Croeidolite (South Africa! Chrysotile (Calidriai 5.0 4 8 0.7? 1.5 5.0 6.0 15.4 4.5 14.0 0.53 0.45 0.80 0.17 0.57 0.46 0.5$ 0.67 1.6 Fibre ivpe Concentrations: means and standard deviations Fibre mass Number of fibres 1 ml " ') (mg m ' '! All fibres Fibres 11 s 5 /uni Glass fibres (JM 104 4"5) Croeidolite (South Africa) Chrysotile (Calidria) 3.0-1.8 5.5 i-1.3 6.0 r 5.9 576 *-473 5011 + 835 541 + 165 555- 139 165- 74 131 r 75 T.ybi e 1 Exposure groups and animal numbers in tips inhalation study Exposure group Number of experimental animals For investigation of For tumour investigation fibre retention Glass fibres Glass fibres + SO, Croeidolite Chrvsotilc (Calidriai SO, Clean air (nose onlc) Clean air (without treatment! Total 108 108 50 50 50 55 50 471 15 15 10 10 10 5 10 69 i able 3. Size distributions of the fibrous ma (trials dsfd in the intra peritoneal tests Fibre type Fibre length i/im) [0-c 50% 90% <<< Per cent > 5 /<m Fibre diameter (gm) 10% 50% 90% <<< Glass fibres* Crocidohle* Chrvsotilc (Calidria)+ L'ICC-chrysotile (Canada)% 1.4 3.5 8.4 0.9 5.1 7J 0.4 1.5 5.9 0 3 0.9 36 28 0.09 0.18 0.40 0.09 0.50 0 56 15 0.05 0.03 0.10 3 0.08 0.11 0.18 'Analysis by SEM. +F;bres exist to some extent as bundles analysis by TEM. _tAecordmg to Timbreul i 19"0i. aN\U5ES3V ? ' ^iatncler *<0" / 'i. ~ 4- ->7 i?'^7 o so '.`-6 !& / ;.,t.ons ' ml `I ;5Jxi.W G2;t ? 13 i " 10 |0 5 |0 Experiment* to test the carcinogenicity of MMMF 759 lABl.t 4. FIBRES (SEMi RETAINED IN LINGS ST VARIOUS TIMES FROM THE SI ART OF THE INHALATION STUDY (a) Number of fibres per i lng. all sizes and. in parenthesis. fibres longer than S ;im Exposure group Glass fibre Glass fibre - SO. Croddolite Chrvsotile 6 Months mean - SD 1831 28 (49x H) 2081 43 <40 11) 403 S4 (66+ 151 398 -134 (39 a. 9) V 4 3 Fibres per lung (106) 12 Months () meaniSD .V 310 + 165 <70 P 261 340+104 (61 25) 557+269 (56+ 3! i 347 - 129 (35 16 j 4 4 3 3 24 Months (iii mean + SD 187+ 32 (25- J| 223-118 (40+ 18! 229 < 82 (52- 2) 223 - 26* (U 7) X 4 4 > 3 (b) Size distribution op fibres retained in lungs after inhalation (FROM S EV1-PHOTOS I Distribution of fibre length l/imi Distribution of fibre diameter fiim) |V Exposure group Glass fibres Glass fibres + SO2 Crocidolite islighlly longer than OUT) Chrvsotile iCahdria I Months 6 12 (i| 24 (iil 6 12 HI 24 (iil 6 12 (i) 24 (iil 0.98 0.86 0.92 0.S2 0.64 0.91 078 0.71 0.96 6 1.0 12 (il 0.9 24" (iil 0.8 50% < 2.7 2.5 1.9 2.4 1.9 "> t 1.3 1.7 2.7 t 2.3 1.5 90% d S.2 8.7 5.8 7.1 73 6.6 7.3 4.9 9.3 5.0 5.1 3.4 Per cent >5 iim 26 23 13 21 17 17 17 10 * 1 10 12 5.! 10% < 0.09 0.08 0.10 0.09 0.08 0.10 0.16 0 15 0 12 0.11 0.11 0.04 50% < 0.23 0.20 0.23 0.22 0.18 0.25 0.26 0.25 0.22 0.19 0.20 0.08 90% < 0.52 0.52 0.49 0.52 0.55 0.55 0.49 0.44 0.43 0.41 0.54 0.12 (il End of exposure: m! 12 months post exposure. *AnaK sis by TEM. T o.:0 S;: 0.03 o.n 0.40 0.36 0 (0 0 IS .; Table 5. F:urf mass rftained in lungs di ring and aftlr inhalation txp'isi'RF -mean and SDl Exposure group Calculated fibre mass per lung (mul Aficr After After 6 months 12 months 24 months Chemically determined mass per lung (mg) 12 month? .V Gloss fibres Glass fibres SO. Crocidoiilc Chrysolite iCalicrial 0.42-0.09 0.40 j; 0.16 0.59-0 16 0 31-0 13 0.561-0.23 0.52 (-0.16 0.67 0 54 0 29-0.12 0.20 -0.05 0.21-0.05 0.39--0 01 0.03-0.03 0 53-0.14 ad. 1 2-0.5 n.d. 4 5 n d. = no: determined. 1 i 1 760 H. VU:hlf ei al. values are also listed in Table 5. At the end of the inhalation period of 12 months the lung burden was about 0.3-1 mg, corresponding to 200-600 million fibres per lung for the three different fibre types. The half-times of fibre clearance during the 12 months after exposure were calculated on the assumption of first order clearance kinetics. The standard error range of the half-time was calculated from the clearance constant k and the standard error , In 2 - flow 7 7 K ( f ^ l 2 taigh In 2 i "* h-sp Results are presented in Table 6. In the inhalation experiment the ciearan.ee half-time of fibres (all sizes) was 300 days for crocidolite and about 600 days for glass fibres. The additional treatment with SO,during the exposure period did not influence the half-time of glass fibre clearance. Forchrysotile, the half-time is influenced by fibre splitting (see below) and therefore appears high. Table 6 also lists, for comparison, the corresponding half-time of fibre clearance after intratracheal instillations found in a companion study by Beilmann et al. (1987. this symposium). Table 6. Clearance half-times of fibres after inhalation and. for comparison, after INTRATRACHEAL INSTILLATION IBF.LLMANN Ct III.. 1987). ALL FIBRE-SIZES Fibre type Half-time (days) Fibre inhalation" Intratracheal instillation" Low Mean High Low Mean High Glass fibre (J.Vt 104/475) Glass fibre !JM 104 4751 +SO, Crccidofite (UICC) Crocidolite (slightlv longer than UICC) Chrysotile A (UICC) Chrysotiie iCalidriai 376 597 892 347 573 1642 201 301 603 402 617 1333 539 745 1205 135 185 289 2655* -- 824" --488* `Results of Bellmans et al. (1987). 'Calculated half-times and standard error range. 'Negative values due to increase of fibre number splitting of fibre bundles. The results of histopathologicai examination are given in Table 7. The median life times of the exposure groups were 106-11L weeks. Only the SO,-treated group had a shorter life-time of 99 weeks. The last surviving animals were sacrificed at 140 weeks from the onset of the exposure. Three primary iung tumours were detected: one adenocarcinoma (crocidolite), one squamous cell carcinoma (glass fibres) and one adenoma (glass fibre+ S02). One squamous metaplasia was found after crocidolite inhalation and one after glass fibre inhalation. Septal thickening, which can be caused by interstitial fibrosis and/or interstitial inflammation, was detected in about 30-40% of the animals in al! fibre-exposed groups. The degree of fibrosis appeared to be slight to medium. A high incidence of bronchiolo-alveolar hyperplasia was detected after crocidolite exposure. ' The tracheae of rats sacrificed after 6 months or i yr of exposure to SO, were id of 12 months the in fibres per lung for arlng the 12 months arance kinetics. The ance constant k and iment the clearance ut 600 days for glass iod did not influence is influenced by fibre , for comparison, the uillations found in a OMPARISON, ALTER trachea! instillation* Mean High M5 1205 185 289 -824!' -483* bie 7. The median Iifc,-treated group had a acrificcd at 140 weeks s were detected: one glass fibres) and one ound after crocidolite asis and/or interstitial - in all fibre-exposed . A high incidence of exposure. /-Tjjosure to SO, were F.vperimep.ts to test the carcinogenicity of MM Mr 761 Table " Histopathological changes in the lungs Or rats exposed to various fibres iinhalatiov ' siudy) Exposure group Number of rats examined Septal thicking (inters!, fibrosis, inters!. inflammation) Total l%| Bronchiolo alveolar hyperplasia Totai (%l Squamous metaplasia Median Primary life-time tumour (weeks! Glass fibre Glass fibre 107 41 (38% j 12 (11%) j 1 ISO 110 108 50 (29%) !7*(!6%) 6 ! IA) 106 + SO, Crocidolite Chrysotiie SO, Control (nose 50 !8 (36%) 37"(74%) i 1 (AC) 111 50 21 (42%) 6 (12%) 0 0 109 50 5 110%) 1 12%) 00 99 55 6 (11%) 4 ;7%l 00 108 only-tubes) Control (without 50 !2 (24%) 3 (6%) 00 108 treatment) `Significantly different in /--test from combined control groups. P<() 05. SC: Squamous ceil carcinoma. A: Adenoma. AC' Adenocarcinoma. examined by scanning electron microscopy. Compared with controls, the SO,-exposed rats showed basically a normal respiratory epithelium. Injection study The tumour rates in the injection study are given in Table 8. Incidences after treatment with saline, TiO, and Calidria chrysotiie are low. Table 8. Results of the intra peritoneal test: tumours in the abdominal cavity excluding uterus ' TUMOURS Fibre type Glass fibre (/M 104 475) Crocidolite (South Africa) Chrysotiie (Calidria) Chrssoiiie (Canada l TiO, Saline Number of rats examined 30 32 32 32 32 32 Dose i.p. (mgl 0.5 0.5 0.5 1.0 10 1 ml Tumour rates (%| 17* 55* 6 84* 0 6 Median life-time (weeks) 116 109 116 5! 130 120 "Significantly different in //-lest from combined control groups. 7*<0.05 DISCUSSION ,. _ In the inhalation experiment, no significant tumour.rate was obtained for any of the fibres investigated. First of all, this result was surprising for the positive control crocidoiite for which the carcinogenicity in man is evident, as results by Wagnkr et al. 1 '62 H. Mchle er al. (i960) have shewn. Although Wagner et al. (1974) demonstrated the carcinogenic effect of crocidolite in rats. Davis et al. (1978) established only very low tumour rates after crocidolite inhalation in rats, as in this study. The lung burden of crocidolite in both those studies was about 9 mg after 12 months of exposure. The crocidolite lung I burden in our study was about 1 mg, but Wagner et al. (1974) reported a significant tumour rate for a comparable dust retention. The high rate of bronchioio-alveoiar hyperplasia of 74%, one case of squamous metaplasia and one adenocarcinoma may indicate a tendency of the crocidolite fibres used to induce neoplasms. & 1 In the intraperitoneal test, crocidolite showed a very strong carcinogenic effect. An p 5 injection cf oniy 0.5 mg led to 55% malignant tumours in rats, compared with a tumour rate of 0 6% in controls, in regard to the Caiidria chrysotile which was recommended by NIOSH (1979) as a reference material for chrysotile, we do not know of any carcinogenicity studies. When we started our inhalation experiment, we expected a carcinogenic potency comparable to that of the UICC-chrysotile samples. However, a significant tumour rate was found neither in the inhalation experiment nor after intraperitoneal injection of 0.5 mg. An injection of 1 mg LTCC-chrysotiic. Canada, led to a tumour rate of 84%. Bolton et al. (1984) showed that even an injection of 0.05 mg of this material induced tumours. For Caiidria chrysotile, a considerable decrease of the fibre diameter was observed for fibres retained in lungs compared with fibres in the inhalation chamber. This is due to the higher deposition rate of thicker fibres in the upper airways and splitting of fibres in the lung. There seems to be a considerable difference in persistence between the UICC-chrysotile samples and the Caiidria chrysotile. Bellmann et al., (1987, tnis symposium) found a strong increase in the numbers of very thin UICC chrysotile fibres longer than 5 pm 2 yr after intratracheal instillation. In contrast to these results, the fibre number of Caiidria chrysotile decreased after the exposure period. In Table 6 the fibre clearance after inhalation and intratracheal instillation is compared. Comparable half-times were found for the glass fibre 104 475 and crocidolite, based on all fibres retained in lungs. If the clearance of glass fibres > 5 pm is similarly calculated at 12 and 24 months, the half time after glass fibre treatment is 254 days and 547 days after glass fibre + SO, treatment, respectively. These values are less than the ones for all fibres as listed in Table 6 and also much less than the value of 3500 days for clearance of glass fibre JM 104 475 for fibres >5 pm reported by Bellmann et al. (1987) after intratracheal instillation. The main reasons for these differences are the relatively low number of fibres > 5 pm counted in the inhalation test and the difficulties of sizing fibres exactly. Therefore, in Table 6 the half-times for all fibres arc calculated, which are more reliable. Considering the low tumour rate of crocidolite and Caiidria chrysotile in our inhalation experiment, it is not surprising that the investigated glass fibre showed no significant carcinogenic effects either. After combining SO,-inhalation and glass fibre S? = exposure, tumours could have been expected in the upper respiratory tract if any tumours had occurred. However, the impairment of ciliated airways by SO, was relatively low. therefore these results do not disprove the hypothesis that after impairment of the bronchial epithelium the carcinogenic risk of inhaled fibres is elevated. It is concluded that the low carcinogenic potency which may be associated with thin - and durable MMMF is very difficult to demonstrate in an inhalation study. However, the long persistence of JM 104 475 in the lung and the carcinogenic effects of these i d the carcinogenic y low tumour rates en of crocidoJite in he crocidoiitc lung lorted a significant >ronchiolo-alveolar enocarcinotna may isms. cinogenic effect. An , compared with a rysotilc which w'as i!e. we do not know on experiment, we -chrysotile samples, tion experiment nor E UICC-chrysotiie, lowed that even an didria chrysotile. a es retained in lungs ie higher deposition ie lung. There seems rysotile samples and on) found a strong than 5 um 2 yr after number of Calidria fibre clearance after iblc half-times were s retained in lungs. If 124 months, the halfer glass fibre 4-50, all fibres as listed in arance of glass fibre 7! after intratracheal ively low number of sizing fibres exactly, ich are more reliable, ria chrysotile in our lass fibre showed no lation and glass fibre .piratory tract if any airways by SO, was lypothesis that after of inhaled fibres is ie associated with thin ition study. However, genic effects of these Experiments to test the carcinogenicity of MMMF 763 fibres after intraperitoneal injection indicate that after inhalation of thin (< 1 fim). long and durable MMM F the suspicion of a carcinogenic potency of these fibres is still well founded. Acknowledgement -This study was supported by the Umweltbundesamt. F-E-Nr. 106 06 034 and the Commission of the European Communities. Contract ENV-629-D. REFERENCES Bellmann, 9., Mlhle. H . Pott, F.. Konig. H.. Kioppel. H. and Spcrny, K. 11987) Persistence of man made mineral fibtes (MMMF) and asbestos in rat lungs. Ann. occup. Hyp. 31. 693-709. Bolton. R. e.. Davis. J. M. G.. Mili fr. B.. Donaldson. K.. and Wright, A. 11984) The effect of dose of asbestos on mesothelioma production in the laboratory rat. In Vlth International Pneumoconiosis Conference 1983. Vol. 2. pp. 1028 1046. Bergbau-Bcrufsgenossenschaft. Verlag fur neuc Wissenachaft. Bremerhaven. Davis. J. M.G. (1985 (Review ofanimal experiments, in: Proceedings ofthe Fifth International Colloquium on Dust Measuring Technique ant! Strategy. Johannesburg. S.A.. 29-31 October 1984 (Edited by Baiinach. F-l. pp. 25 38. SAAPAC. Johannesburg. Davis. J. M. G. (1986) A review ofexperimental evidence for the carcinogenicity of man-made vitreous fibres. Sound. J. If'k Environ. Hith 12, suppl. 1. 12-17. Davis, j. m g.. Beckett. S. 7., Bolton, R. E.. Collings. P. and Middleton. A. P. (1978) Mass and number of fibres in the pathogenesis of asbestos-related lung diseases in rats. Br. J. Cancer 37,673- 688. Goldstein, b,, Rendall. R. E.G. and Webster,;. (1983) A comparison oftheellects ofexposure ofbaboons to crocidolite and fibrotLs-giass dusts. Environ. Res. 32, 344-359. I.amb, D. and Reid. L. (1968) Mitotic rates, goblet cell increase, and histochemical changes in mucus in rat bronchial during exposure to sulphur dioxide. J. Path. Bact. 96. 97-111. Lee, K. P.. Barras, C. E.. Griffith. F. D.. Wakitz. R. S. and Lapin, C. A. (1981) Comparative pulmonary responses to inhaled inorganic fibres with asbestos and fiberglass. Environ. Res. 24, 167 191, McConnell. E. E.. Wagner] J. C. Skidviore. J. M. and Moore. J. A. i 1984) A comparative study of the fibrogeme and carcinogenic effects of U1CC Canadian chrysotile B asbestos and glass microfibre (JM 100). In: Biological Effects qf Man-Made Mineral Fibres. Vol. 2. pp. 234-250. 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