# Mineral Fibres and Asbestos Bodies in Human Lung Tissue: A Case Study
## 3 Results and Discussion
### Mineral Fibres  
In the solid fraction obtained from ashing of the human lung tissue, both non-coated fibres and fibres coated with ABs were found. A total of 52 mineral fibres were examined, of which 31% were coated. The percentage of fibres with ABs detected in the in vivo animal study ranged between 3.3% and 5.7% [18]. The coating process in the rat lung appears to be less efficient than in the human lungs. One of the reasons could be the fibre overload in rats' lung tissue, a well-known problem of animal testing using the intrapleural/intraperitoneal injection mode [28]. In the examined human lung tissue, SEM-EDX micro-analysis and FFT patterns of non-coated fibres (Figure 2 and Figure S2 in the Supplementary Materials) revealed compositions that are compatible with those of crocidolite (83%) and amosite (7%) (Figure 2d,e). Only one silica-rich fibre, i.e., the metastable product of dissolution of chrysotile mediated by Mg leaching [17], was found (Figure 2f). Identification of coated fibres was difficult since EDX spot analyses were influenced by the presence of ABs. However, the FFT patterns obtained on partially coated fibres (FFT patterns obtained from 10 fibres), combined with STEM-EDX micro-analysis, indicated that crocidolite is probably the main type of coated fibres (Figures S2 and S3 in the Supplementary Materials). Figure 3: (**a**) High-resolution FEG-SEM image of an amosite fibre; (**b**) high-resolution FEG-SEM image of bundles of crocidolite fibres; (**c**) TEM image of a crocidolite fibre with stepped edges; (**d**) TEM image of an individual crocidolite fibre showing characteristic diffraction contours. Figure 2: (**a**) FEG-SEM image of a crocidolite fibre; (**b**) FEG-SEM image of an amosite fibre; (**c**) FEG-SEM image of a silica-rich relict of chrysotile; (**d**) SEM-EDX spectrum of the fibre shown in (**a**); (**e**) SEM-EDX spectrum of the fibre shown in (**b**); (**f**) SEM-EDX spectrum of the fibre shown in (**c**); (**g**) STEM image of an individual crocidolite fibre with columnar habit; (**h**) STEM images of a prismatic individual crocidolite fibre; (**i**) STEM image of a thin crocidolite fibre. SEM and STEM images of non-coated fibres show quite straight individual amphibole fibres or bundles (Figures 2 and 3). Amosite fibres appear as prismatic individual fibres (Figure 3a). Crocidolite appears as felt-like aggregates (Figure 3b). Fibrils splitting from bundles show a long, thin columnar habit (Figures 2g-i and 3b). Amphibole fibres form both straight edges parallel to the fibre axis and irregular edges (Figure 3), whereas the silica-rich fibre habit appears as curved (Figure 2c). Amphibole fibres show both straight and irregular ends (Figure 3c,d). Amosite shows more right-angle truncations across the fibre axis (Figure 3a) than crocidolite, which tends toward more columnar forms (Figure 3b). The fibres occur occasionally together with other particles, which were identified as residues of incomplete ashing (Figure 2a-c). The summary statistics of the geometry of the coated and non-coated fibres are reported in Table 1. The data display a wide range of lengths, with values ranging from 2.17 to 107, but the longer fibres predominate in the population. More than 75% of the fibres were longer than 7.45, and 50% were longer than 19.8. The length of crocidolite fibres varied between 2.17 and 107 (average 17.2), whereas the amosite fibres ranged in length from 19.49 to 76.4 (average 38.5). Although the widths of the fibres ranged overall between 0.06 and 2.82, 75% of the fibres showed a width of less than 0.44. However, all amosite fibres had a width greater than 0.40. According to the WHO guidelines, asbestos fibres of respirable size with relevant biological activity (so-called \"critical\" fibres) are those equal to or longer than 5 and having diameters up to 3, with an aspect ratio \(\geq\)3:1 [14].