A novel synthetic erionite fibre radiolabelled with (57)Co.

The aim was to produce a radiolabelled fibre suitable for long-term carcinogenesis studies. To this end, we have successfully synthesised erionite fibres by a method adapted to incorporate (57)Co into the crystal framework. Morphologically the fibres are straight, of median length 2.5 microm, with 11% of fibres > 8 microm long, and median width 0.32 microm. These values are comparable to natural Oregon erionite. Autoradiography confirmed that the (57)Co was associated with the fibres themselves. The stability of the radiolabel in vivo was examined by instilling 1 mg of synthetic erionite into the lungs of F-344 rats. About half of the thoracic content of (57)Co was cleared in the first week, and over the following 5 weeks the remainder was cleared slowly with a half-time of 120 days. After 6 weeks the urinary excretion of (57)Co was only 0.054% of the initial lung content per day. This represented fibre dissolution plus any leaching of (57)Co from the fibres. It can be concluded that the (57)Co is bound into the erionite fibres with sufficient stability in vivo for studying their effects in relation to translocation to the pleura.

The effects of heating and devitrification on the structure and biological activity of aluminosilicate refractory ceramic fibres.

Three grades of ceramic fibre have been examined for their composition, structures and biological effect in several in vitro assay systems. The fibres were examined in the 'as-manufactured' state and after heating at 1200 and 1400 degrees C. Devitrification of the fibres at 1200 degrees C probably gave mullite crystals on the surface and caused the formation of the high-temperature form of cristobalite and, in zirconia grade fibres, the high-temperature, tetragonal form of zirconia as well. Further heating changed surface structure and led to zircon production in the zirconia fibres. Heating reduced the affinity of the fibres for the surface of V79-4 cells and lowered fibre toxicity toward these cells and towards macrophage-like cells. These changes in toxicity were not due to a reduction in the fibrous nature of the materials although they did become more brittle and powders prepared from them contained more isometric particles than those from as-manufactured materials. This suggests that the devitrification occurring during the use of these materials in high-temperature environments will not necessarily enhance their adverse biological activities despite the production of one phase of crystalline silica.

Fibrous dust release from asbestos substitutes in friction products.

A small-scale study was carried out on friction and reinforcing materials containing Kevlar and glass fibres. Kevlar, an aramid fibre, and synthetic silicate fibres are being increasingly used in brake pads and shoes for cars and trucks. The fibre levels given out under abrasion in the laboratory were low. As a comparison, a brake pad containing asbestos was also tested and gave high levels of airborne fibres.

Modification of fibrous Oregon erionite and its effects on in vitro activity.

A sample of erionite, a fibrous zeolite, was modified by milling to reduce the number and length of the fibres and by extraction with cyclohexane. The in vitro activities of this mineral were found to depend on the presence of long fibres. The erionite contained fewer of these fibres than the UICC asbestos samples but, unlike these materials, erionite can cause the transformation of C3H 10T1/2 cells. Erionite did not increase the activities of benzo[a]pyrene in this cell transformation assay. The cytotoxic activities of both asbestos and erionite have a similar dependence on the number of long fibres. Extraction with cyclohexane did not affect the activity of erionite.

Airborne asbestos fibre levels in buildings: a summary of UK measurements.

The UK Health and Safety Executive, in conjunction with the Department of the Environment, has carried out a number of surveys of airborne asbestos fibre concentrations in buildings. All samples have been collected on membrane filters and analysed by analytical transmission electron microscopy. Four categories of buildings under normal occupation have been investigated; non-domestic buildings containing sprayed or trowelled asbestos, domestic buildings containing sprayed asbestos or asbestos plaster, buildings with warm air heaters containing asbestos and buildings without asbestos materials. A number of buildings have also been surveyed during and after the removal of asbestos materials. The choice of measurement indices and analytical procedures is reviewed, before measurements are compared in terms of the concentration of asbestos fibres greater than 5 microns long. The decision whether to remove asbestos from occupied buildings is discussed with reference to the associated cost and risk. In the present survey, management of undamaged asbestos appeared preferable to large-scale removal.

Levels of airborne man-made mineral fibres in dwellings in the UK: results of a preliminary survey.

Levels of airborne man-made mineral fibres (MMMF) were measured during the insulation of lofts and after the disturbance of the insulation wools. Transmission electron microscopy was used for the analysis. Generally, the personal samples showed fibre levels of up to 0.7 f/ml, whereas static samples showed fibre levels of 0.05 f/ml in the lofts. Little contamination of living space occurred during these operations.

The in vitro activities of a highly carcinogenic mineral fibre--potassium octatitanate.

The in vitro activities of a highly carcinogenic potassium octatitanate fibre (Fybex) have been investigated. This material caused a low level of in vitro transformation in C3H10T1/2 cells and is thus more active in this assay than the UICC amphibole asbestos samples but less active than fibrous erionite. This ranking is in accord with carcinogenicity in vivo. However Fybex had no detectable activity in an assay for DNA damage based on the S1-nuclease sensitivity of the DNA from exposed cells. In that assay crocidolite asbestos was more active than either of the more carcinogenic dusts. It is suggested that the activities of amphibole asbestos in assays for genetic toxicity may depend on the production of free radicals via a catalytic reaction requiring the presence of transition elements which are either not present or only present at low concentrations in erionite or Fybex. This type of reaction may not be related to in vivo carcinogenicity. The action of fibrous dusts against macrophage-like cells, measured in this instance by the release of arachidonic acid, remains one of the best measures of biological activity.

Size distributions of airborne superfine man-made mineral fibers determined by transmission electron microscopy.

A survey was conducted to determine the size distribution of airborne man-made mineral fibers in three factories using bulk materials which contain many fibers with diameters less than 0.3 micrometers. Personal samples were taken in two of the factories visited. In all the cases a full length and diameter distribution, determined by transmission electron microscopy, are presented. Median diameters ranged from 0.1 to 0.3 micrometers and, as a result, a substantial proportion of the fibers would not be detected using light microscopy or scanning electron microscopy even for fibers longer than 5 micrometers.