Fibers in lung tissues of mesothelioma cases among miners and millers of the township of asbestos,quebec

Twenty cases of mesothelioma among miners of the township of Asbestos, Quebec, Canada, have been reported. To further explore the mineral characteristics of various fibrous material, we studied the fibrous inorganic content of postmortem lung tissues of 12 of 20 available cases. In each case, we measured concentrations of chrysotile, amosite, crocidolite, tremolite, talc-anthophyllite, and other fibrous minerals. The average diameter, length, and length-to-diameter ratio of each type of fiber were also calculated. For total fibers > 5 μm, we found > 1,000 asbestos fibers per mg tissue (f/mg) in all cases; tremolite was above 1,000 f/mg in 8 cases, chrysotile in 6 cases, crocidolite in 4 cases, and talc anthophyllite in 5 cases. Among cases with asbestos fibers, the tremolite count was highest in 7 cases, chrysotile in 3 cases, and crocidolite in 2 cases. The geometric mean concentrations of fibers ? 5 μm were in the following decreasing order: tremolite > crocidolite > chrysotile > other fibers > talc-anthophyllite > amosite. For total fibers < 5 μm, we found > 1,000 fibers per mg tissue (f/mg) in all cases; tremolite was above 1,000 f/mg in 12 cases, chrysotile in 8 cases, crocidolite in 7 cases, and talc-anthophyllite in 6 cases. Tremolite was highest in 8 cases, chrysotile in 2 cases, and crocidolite and amosite in 2 cases. The geometric mean concentrations of fibers < 5 μm were in the following decreasing order: tremolite > other fibers > chrysotile > crocidolite > talc-anthophyllite > amosite. We conclude, on the basis of the lung burden analyses of 12 mesothelioma cases from the Asbestos township of Quebec, that the imported amphibole (crocidolite and amosite) were the dominant fibers retained in the lung tissue in 2/12 cases. In 10/12 cases, fibers from the mine site (chrysotile and tremolite) were found at highest counts; tremolite was clearly the highest in 6, chrysotile in 2, and 2 cases had about the same counts for tremolite and chrysotile. If a relation of fiber burden-causality of mesothelioma is accepted, mesothelioma would be likely caused by amphibole contamination of the plant in 2/12 cases and by the mineral fibers (tremolite and chrysotile) from the mine site in the 10 other cases.     

Malignant mesothelioma caused by childhood exposure to long-fiber low aspect ratio tremolite

A 41-year-old man was found to have a malignant mesothelioma of the pleura. During childhood in Corsica, he had been exposed at home to chrysotile ore from the Canari mine. Analysis of lung mineral content revealed background levels of chrysotile but an elevated level of tremolite and actinolite asbestos. The latter had a geometric mean length of 3.7 μm, a value considerably longer than we have found for tremolite and actinolite from Quebec chrysotile miners but roughly the same as the mean length of amosite and crocidolite in workers with occupational amphibole exposure. No tremolite or actinolite fibers of length greater than 8 μm microns and width less than 0.25 μm were observed. The mean aspect ratio of the tremolite and actinolite fibers was 7, a value similar to that found in chrysotile miners with mesothelioma but considerably less than the mean aspect ratio of amosite and crocidolite from those with occupational expsoure. These data suggest that long-fiber tremolite is a potential mesothelial carcinogen in humans, and that fiber length is more important than fiber aspect ratio in this regard.     

Cell toxicity, hemolytic action and clastogenic activity of asbestos and its substitutes.

The cell toxicity, hemolytic and clastogenic activity were examined in various kinds of asbestos and some asbestos substitutes with reference to the their mineralogical and physicochemical characteristics. There were thirty-five fibrous and non-fibrous samples including UICC chrysotile, size-selected samples of UICC chrysotile, chrysotile altered by heating and grinding, Yamabe (Japan) chrysotile with long and short fibers, Coalinga (U.S. A.) chrysotile with short fibers, UICC crocidolite, amosite, and 19 non-asbestos samples such as, glass fibers, calcium silicates, sepiolites and some clay minerals. The cell toxicity and the hemolytic and clastogenic activity of asbestos were the strongest for chrysotile among all of the asbestos samples tested, and their strengths varied with fiber length and with the conditions of grinding and heating. These cellular effects of Yamabe chrysotile with long fibers and size-selected UICC chrysotile with long fibers were stronger than those of chrysotile of the same origin but with short fibers. These effects were weaker in chrysotile altered by heating and grinding. Among the asbestos substitutes, the cell toxicity, hemolytic and clastogenic activities of thin glass fibers were more marked than those of thick glass fibers. The four types of sepiolite were strongly hemolytic, but their cell toxicity and clastogenicity varied according to their grade of crystallinity and/or fiber size. These effects of calcium silicates and some clay minerals were generally low but varied with mineral species. In general, the cell toxicity, hemolytic and clastogenic activities of the asbestos substitutes tested here were mild compared with those of asbestos.     

Asbestos concentration and fiber size in lungs of the urban residents]

Asbestos fiber concentrations and fiber size distribution in lung tissues of 53 urban residents (males: 34, female: 19) were analyzed by low temperature ashing-analytical transmission electronmicroscopy. The following findings were obtained. 1. Pulmonary asbestos fibers were found in 51 out of 53 patients. The types of asbestos fibers were chrysotile, amosite, crocidolite, actinolite and tremolite. 2. Thirty-six of 53 patients had no history of occupational asbestos exposure, and their geometric mean concentration of asbestos fibers was 1.67 x 10(6) fibers/g dry lung. Most of these asbestos fibers are probably attributable to general environmental contamination. Thirteen patients who had a history of occupational asbestos exposure showed a geometric mean of their pulmonary asbestos concentrations (5.82 x 10(6) fibers/g dry lung) which was significantly higher than that of patients without occupational asbestos exposure (p less than 0.01). 3. The geometric mean concentration of asbestos fiber in males (2.70 x 10(6)) was higher than in females (1.59 x 10(6)), probably due to a difference in the occupational asbestos exposure between males and females. 4. Regardless of the patient's sex, the geometric mean concentration of asbestos fibers in patients without a history of smoking (male: 4.91 x 10(6), female: 1.78 x 10(6)) was higher than that in patients with a smoking history (male: 2.76 x 10(6), female: 1.37 x 10(6)). The difference, however, was not statistically significant, and no correlation was seen between the concentration of asbestos fibers and smoking history. 5. Although most asbestos fiber utilized in Japan is chrysotile, the geometric mean concentration of chrysotile (0.87 x 10(6)) was almost identical to that of amphibole asbestos fiber (0.90 x 10(6)). 6. Of the asbestos fibers observed, 95% of chrysotile and 85% of amphibole asbestos were less than 5 microns in length and 93% of the total asbestos fibers were too small to be visible by light microscopy.     

Mineral phases and some reexamined characteristics of the international union against cancer standard asbestos samples

Standard asbestos samples to be used for biomedical research were first prepared by the International Union Against Cancer (UICC) in 1966 in the United Kingdom and South Africa. Using modern techniques, X-ray diffractometry, analytical transmission electron microscopy, and thermal analysis, we have now analyzed these UICC samples to determine the mineral compositions (mineral phases) and their respective quantities. UICC chrysotile A (from Zimbabwe) contains 2% fibrous anthophyllite as impurity; chrysotile B (from Canada) does not contain any fibrous impurities, only non-fibrous minerals. UICC amosite and crocidolite are almost pure. UICC anthophyllite has 20–30% talc as impurity. The chemical compositions and fiber size distributions of the UICC asbestos samples have also been determined. The mean widths of the fibers of chrysotile A and B are smaller than those of the amphibole fibers. This agrees well with the earlier results which showed the two chrysotile samples to have a larger respirable fraction than the amphiboles. © 1996 Wiley-Liss, Inc.     

Inhalation carcinogenesis from various forms of asbestos

Rats, rabbits, guinea pigs, gerbils, and mice were exposed to the inhalation of chrysotile, crocidolite, or amosite for 2 years. Mean atmospheric concentrations were 47.9–50.2 mg/m³, but only 0.08–1.82% of the dusts retained fibrous morphology during the dissemination procedure which involved hammer milling. Trace contamination especially by chromium and nickel was also increased. Light microscopic fiber counts per ml chamber air were 54 (chrysotile), 1105 (crocidolite), and 864 (amosite). A fibrogenic response to these dusts was observed in all five animal species, the severity corresponding to the extent of exposure (with reaction to chrysotile frequently very slight). Gerbils developed frequent alveolar proteinosis. Mice developed spontaneous papillary carcinomas in the lungs. Disregarding the latter species, carcinogenic response to asbestos inhalation was restricted to rats and occurred in all three exposure groups. There were 2 lung cancers and 1 pleural mesothelioma after chrysotile inhalation; 4 lung cancers after crocidolite inhalation; and 1 lung cancer and 2 pleural mesotheliomas after amosite inhalation. These cases constituted 7–9% incidence of malignancy among rats with adequate survival record. Hypotheses of asbestos carcinogenesis are reviewed and it is suggested that different etiologic principles may be involved in the causation of lung cancer and of pleural mesothelioma.     

Airborne fibre concentrations and lung burden compared to the tumour response in rats and humans exposed to asbestos

The excess risk of tumours exposed to asbestos were previously compared with the results of rat inhalation experiments. It could be demonstrated that humans at the workplace suffer from a tumour risk at fibre concentrations which are 300 times lower than those needed in the rat inhalation model to produce the same risk. However, the estimation of human risk was based on the study of workers at a chrysotile textile factory, whereas animal experimental results were related to exposure to amphiboles. Since for this comparison the risk of cancer due to exposure to amosite or crocidolite fibres at the workplace is of interest, quantitative exposure-response relationships for lung cancer and mesothelioma for the white workforce of South African amosite and crocidolite mines were discussed. On comparing the risk of lung cancer in this study with the risk of lung cancer for chrysotile textile workers, it can be concluded, that the risk of lung cancer and mesothelioma from crocidolite and amosite was higher than in the chrysotile textile factory.It could be also demonstrated, on the basis of a study of the lung burden of mesothelioma cases and of controls, that a significantly increased odds ratio of about 5 was established at amphibole concentrations of between 0.1 and 0.2 f μg⁻¹ dry lung (WHO fibres longer than 5 μm from TEM analysis). On the other hand, carcinogenic response was observed at a fibre concentration 6000 times higher in animal inhalation experiments with crocidolite asbestos (SEM analysis of WHO fibres). As a result of these findings, it has been concluded that inhalation studies in rats are not sufficiently sensitive for the detection of hazards and risks to humans exposed to man-made fibres.     

The pathological effects of prolonged asbestos ingestion in rats

The effects of prolonged ingestion of amosite, crocidolite, and chrysotile UICC standard reference asbestos samples were examined in groups of laboratory rats. Animals were given over 250 mg per week for periods up to 25 months and were monitored for the remainder of their life span. Animals were examined for evidence of pathological effects and gastrointestinal mucosal cytokinetic disturbances and for signs of penetration and dissemination of fiber. There was no excess of malignant tumors in the experimental groups when compared with control animals, and no gastrointestinal mucosal abnormalities were found. An examination of the cytokinetic status of a subgroup of animals exposed to asbestos similarly showed no evidence of any adverse effects of prolonged ingestion of amosite asbestos fiber. Detailed electron microscopic examination of various tissue residues for the presence of asbestos fibers was also undertaken. No penetration and/or damage to any of the gut tissues was found. Although occasional fibers were found in a variety of tissue residues, there was no evidence of preferential retention of fibers within any specific tissue and no sign of higher fiber burdens in those animals with tumors. It was concluded that there were no significant adverse effects of prolonged asbestos ingestion in healthy laboratory rats. The implications of these findings are discussed in the light of other published work.     

Talc and amosite/crocidolite preferentially deposited in the lungs of nonoccupational female lung cancer cases in urban areas of Japan.

To analyze the correlation between asbestos lung burden and lung cancer, lungs of 211 female cases with and without lung cancer were examined. Phase-contrast microscopic (PCM) counting of ferruginous (FBs) and uncoated fibers (UFs), which had length longer than 5 microns and aspect ratios greater than 3:1, revealed a significantly higher level of FBs plus UFs in urban lung cancer cases than urban non-lung cancer cases (1380.5 vs. 550.3; p < 0.001). No difference was noted between rural lung cancer and non-lung cancer cases. Analytical electron microscopic studies identified various kinds of mineral fibers with an aspect ratio greater than 3:1 in the lung tissue including chrysotile, actinolite/tremolite, amosite/crocidolite, fibrous talc, mica, silica, iron, wollastonite, chlorite, kaoline, and others. The most frequently detected fibers were thin, short chrysotile fibers, most of which could not be found by PCM, followed by relatively thick, long actinolite/tremolite fibers, fibrous talc, and in a smaller number, amosite/crocidolite of intermediate length and width. Amosite/crocidolite and fibrous talc counts in urban lung cancer cases were greater than those of urban non-lung cancer cases, rural lung cancer, and rural non-lung cancer cases; these findings were consistent with PCM analysis. Therefore, it is suggested that fibers detected in PCM observation may be mainly amosite/crocidolite with some parts fibrous talc and that fibrous talc in urban environments may be another candidate for carcinogenic or cocarcinogenic factors of female lung cancer.     

Comparative toxicities of different forms of asbestos in a cell culture assay

Three forms of Union Internationale Contre le Cancer (UICC) asbestos, amosite, crocidolite, and chrysotile, were assayed for their cytotoxicity (inhibition of colony formation) in cell culture. Using embryonic human intestine-derived (I-407) and adult rat liver-derived (ARL-6) epithelial cells, the order of cytotoxicity was chrysotile > amosite > crocidolite. All three asbestos types were more toxic to I-407 than to ARL-6 cells. Chrysotile, amosite, and crocidolite were also tested for inhibition of colony formation in cultures of mouse colon-derived epithelial-like (MCE-1) cells; these cells were more resistant than the I-407 cells to all three fiber types; although similar to the ARL-6 cells in sensitivity to chrysotile and amosite, the MCE-1 cells were more sensitive to crocidolite then the ARL-6 cells. Leaching of the three asbestos forms for 3 days in sterile deionized water did not appreciably affect the cytotoxicity of I-407 or ARL-6 cells. Leaching in hydrochloric acid, however, greatly decreased the cytotoxicity of chrysotile on these cells and particularly in cultures of ARL-6 cells slightly increased the cytotoxicity of amosite and crocidolite. Leaching in deionized water altered the composition of the asbestos as revealed by release of substantial levels of Mg²⁺ and Ca²⁺ into the leaching fluid. Greater titers of these ions were released during leaching in hydrochloric acid.     

Asbestosis in Experimental Animals

Previous animal experiments with asbestos dusts have been almost entirely confined to chrysotile asbestos. It was, therefore, decided to investigate the effects of mill dusts from the three types of asbestos that are produced commercially in South Africa, namely chrysotile, amosite, and crocidolite. Chrysotile and amosite samples were relatively pure while in contrast the crocidolite dust was found to consist mainly of ironstone and silica and contained less than 10% of asbestos fibre. Guinea-pigs, Vervet monkeys, and rabbits were exposed to these dusts. The results were assessed on histological criteria. It was found that, in all three species of animals, the amosite dust produced more marked lesions than the chrysotile and that these lesions occurred at an earlier period. It was not possible to compare these lesions with those caused by the crocidolite dust, owing to its impure nature. It was noted, however, that this dust caused severe lesions in guinea-pigs and monkeys and that the animals in this group succumbed more readily to respiratory infections.     

Recovery of ingested asbestos fibers from the gastrointestinal lymph in rats

Using the transmission electron microscope, asbestos fibers have been assessed in lymph fluid collected from the thoracic lymph duct in five groups of rats previously exposed to asbestos fibers (by ingestion). Ten rats were gavaged a single dose weighing approximately 20 mg. Five were given pure UICC chrysotile A while another group of five had pure UICC crocidolite. All the rats of the chrysotile group were positive animals with recovery rate values ranging from 6.9 × 10^?7 to 3 × 10^?5 (90% of the fibers being recovered during the first 16 hr following the gavage). The crocidolite group had only three positive animals and lower recovery rate values of 5.7 × 10^?8 to 5.6 × 10^?7. A third group was fed a synthetic diet containing 1%, by weight, chrysotile with a majority of short fibers (90% below 4 μm). Of the 15 rats comprising this group, 13 were positive with maximum daily recovery rates ranging from 2.1 × 10^?7 to 2.1 × 10^?6. A group of eight rats fed the same kind of diet but containing a higher proportion of long fibers, showed only four positive animals, however, they had higher daily recovery rates ranging from 1.9 × 10^?5 to 2.1 × 10^?4. No fibers were encountered in the samples of the two control rats. This study demonstrates the passage of chrysotile and crocidolite fibers across the gastrointestinal wall, with the passage rate being higher for long fibers than short ones.     

Asbestos as reference material for fibre-induced cancer

The objective of this paper is to review published data on the carcinogenicity of asbestos fibres with regard to the elucidation of a potential risk originating from exposure to man-made vitreous fibres (MMVF). Steps in the comparison of the two fibre classes are characterization of the fibres, pulmonary deposition, biodurability and biopersistence and a review of the cancer risk from asbestos fibres after inhalation in rats and humans. Various dust samples of chrysotile, crocidolite, and amosite were used as reference materials in studies with experimental animals. These fibres are normally thinner and shorter than MMVF. These differences in dimensions cause differences in the deposition in the airways. In addition, significant dissimilarities exist in the deposition pattern between rats and humans. Data from biopersistence studies show that focusing only on fibres longer than 20 wm and using weighted half-time for a characterization of risk may be misleading. Inhalation experiments with rats need fibre exposure concentrations over 100 times higher to match the lung cancer risk of asbestos workers, and about 1000 times higher to reach the same mesothelioma risk. Also, the striking difference between the low lung burden of amphibole fibres of asbestos workers with mesothelioma and the more than 1000 times higher lung burden of rats with a low mesothelioma risk demonstrates the low sensitivity of the inhalation test model for the carcinogenic potency even of crocidolite fibres. It can be concluded that the rat inhalation model is also not sensitive enough to predict the cancer risk of other fibre types for humans.     

Experimental asbestos carcinogenesis

Laboratory rodents were exposed to one of three mineralogical types of asbestos dust, amosite, crocidolite, or chrysotile. Inhalation exposures were accomplished in chambers where ballmilled specimens of these dusts were disseminated for 4 hours daily, 4 days weekly, at a mean atmospheric concentration of about 48 mg/m³. Additional animals were injected with these dusts intratracheally, intrapleurally, or intraperitoneally. Histopathologic studies showed a fibrotic reaction in all species to all three types of dusts, with amosite provoking the strongest such response especially in guinea pigs. Two pulmonary cancers were produced in rats exposed to the inhalation of crocidolite. Local injection into the pleural or peritoneal cavities caused 5 mesotheliomas in rats after chrysotile treatment and 6 mesotheliomas in rats and rabbits after crocidolite treatment. Guinea pigs and hamsters developed no tumors in this experiment, and with the dose used, there were no tumors in any species in the amosite group.     

Coagulation of human plasma by asbestos fibers

Negatively and positively charged asbestos fibers shorten the partial thromboplastin time of human plasma, indicating coagulation of the plasma. A sample containing short (<5 μm in length) chrysotile fibers is ineffective. Only the negatively charged amphiboles (crocidolite and amosite) are able to activate factor XII (Hageman factor). This particular effect of the amphiboles is enhanced by high-molecular-weight kininogen and leads to kinin formation.     

Effects of asbestos fibers on alveolar macrophage-mediated lymphocyte cytostasis

Prolonged asbestos inhalation results in pulmonary inflammation and fibrosis. Since alveolar macrophages are active in regulation of immune responses in lung and appear to be involved in the pathogenesis of asbestosis, we evaluated the effects of asbestos exposure on the ability of these cells to regulate lymphocyte function. Alveolar macrophages obtained by lung lavage from BALB/C mice were treated in vitro with either UICC amosite or chrysotile asbestos and the effects on lymphocyte cytostasis compared with those of macrophages incubated with latex beads or zymosan. Macrophages (10%) incubated either alone or with latex beads for 48 hr effectively inhibited lymphocyte mitogenesis. However, alveolar macrophages incubated with either amosite or chrysotile asbestos did not demonstrate intact cytostatic activity. Decreased viability of chrysotile asbestos-treated macrophages correlated with loss of cytostatic effects, but alveolar macrophages exposed to amosite remained viable. We conclude, therefore, that exposure of alveolar macrophages to asbestos can result in loss of their ability to down-regulate lymphocyte proliferation, a finding which may be important in the pathogenesis of asbestos-related disease.     

Determination of the variability in elemental composition of asbestos fibres by analytical transmission electron microscopy

An investigation was carried out to assess the variability in the elemental composition of asbestos fibres as determined using an energy dispersive X-ray spectrometer (EDS) attached to an analytical transmission electron microscope. UICC reference standards of chrysotile, amosite and crocidolite asbestos were analysed at five locations along the length of each fibre to observe within-and between-fibre variability. A total of 355 analyses were carried out on 71 fibres. No statistically-significant differences were found among the results obtained at the various locations along each fibre.     

Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry

BACKGROUND: As an indicator of occupational, domestic, and environmental exposure, the level and type of asbestos fibers were determined from lung tissue samples of workers and residents who resided in the area of the world's largest asbestos mine at Asbest, Russia. METHODS: Electron microscopy was used to analyze and measure the concentration of asbestos fibers in a series of 47 autopsies at the Asbest Town Hospital. Work histories were obtained from pathology reports and employment records. RESULTS: In 24 chrysotile miners, millers, and product manufacturers, the pulmonary concentrations of retained fibers (over 1 microm in length) were 0. 8-50.6 million f/g for chrysotile, and < 0.1-1.9 million f/g for amphiboles (tremolite and anthophyllite). The concentrations were lower in 23 persons without any known occupational contact with asbestos; 0.1-14.6 million f/g for chrysotile, and < 0.1-0.7 million f/g for amphiboles. On average, 90% of all inorganic fibers were chrysotile, and 5% tremolite/anthophyllite. No amosite or crocidolite fibers were detected in any of the samples. CONCLUSIONS: The mean and range of pulmonary chrysotile concentrations were about the same as reported previously from the Canadian mining and milling industry. In the Russian samples, the mean concentration of tremolite fibers were less by at least one order of magnitude. Occupational contact was the most important source of asbestos exposure.     

An assessment of the fibrogenic potential of very short 4T30 chrysotile by intratracheal instillation in rats

Three groups of five rats each received, respectively, a single intratracheal instillation of saline (control), 5 mg of UICC chrysotile B asbestos, and 5 mg of a preparation of very short chrysotile fibers (4T30, 100% less than 8 micron) isolated by a sedimentation procedure. At various intervals after the treatment (1 to 60 days), assessment of lung morphology was performed on each animal. Although the two types of chrysotile fibers have similar chemical composition, structure, and surface charge, the lung tissue reaction differed considerably. Lungs of animals exposed to UICC chrysotile B showed significant pathological alterations as early as 7 days following treatment. The lesions were localized in and around terminal bronchioles and consisted of inflammatory cells, fibroblasts and collagen deposition which distorted and obstructed small airways. Reaction to very short 4T30 chrysotile fibers was quite distinct. Seven days after treatment, lungs of these animals showed alveolar and interstitial accumulation of inflammatory cells. The alveolitis persisted 60 days after treatment and no fibrosis was apparent. It appears that very short 4T30 chrysotile fibers are much less fibrogenic than UICC chrysotile B and that intratracheal instillations in rats may represent a useful mean of rapidly assessing the fibrogenic potential of various dusts. These observations support the concept that fiber length is an important factor for fibrogenicity of asbestos.     

Clearance and dimensional changes of crocidolite asbestos fibers isolated from lungs of rats following short-term exposure

Previous studies in this laboratory have demonstrated fiber clearance and dimensional changes in chrysotile asbestos using a rat inhalational model of short-term exposure. The purpose of the present study was to determine whether or not similar changes occurred in crocidolite asbestos fibers isolated from the lungs of rats at various intervals after termination of exposure. Fibers were recovered on a membrane filter using a sodium hypochlorite digestion-concentration technique, and the numbers and dimensions of the fibers assessed using scanning electron microscopy. The mass of crocidolite asbestos retained in the lung was then calculated. Of the respirable fraction, 19% was deposited in the lungs, and 25% of this amount was still present 1 month after exposure. These values are similar to the 23% deposition and 19% retention rates for chrysotile determined in our previous study. There was a progressive increase in mean fiber length with time postexposure (P less than 0.05), but no significant changes in the diameter of the population of crocidolite fibers retained in the lung. Thus it appears that the tendency for longer fibers to be retained within lung tissue is a characteristic shared by serpentine and amphibole asbestos fibers, whereas longitudinal splitting with progressive decrease in mean fiber diameter in vivo occurs primarily with the serpentine fibers.