Biopersistences of Man-Made Vitreous Fibers and Crocidolite Fibers in Rat Lungs Following Short-Term Exposures

122

100

The peculiar characteristics of dust toxicity are discussed in relation to the processes taking place at the particle-biological medium interface. Because of surface reactivity, toxicity of solids is not merely predictable from chemical composition and molecular structure, as with water soluble compounds. With particles having the same bulk composition, micromorphology (the thermal and mechanical history of dust and adsorption from the environment) determines the kind and abundance of active surface sites, thus modulating reactivity toward cells and tissues. The quantitative evaluation of doses is discussed in comparisons of dose-response relationships obtained with different materials. Responses related to the surface of the particle are better compared on a per-unit surface than per-unit weight basis. The role of micromorphology, hydrophilicity, and reactive surface cations in determining the pathogenicity of inhaled particles is described with reference to silica and asbestos toxicity. Heating crystalline silica decreases hydrophilicity, with consequent modifications in membranolytic potential, retention, and transport. Transition metal ions exposed at the surface generate free radicals in aqueous suspensions. Continuous redox cycling of iron, with consequent activation-reactivation of the surface sites releasing free radicals, could account for the long-term pathogenicity caused by the inhalation of iron-containing fibers. In various pathogenicities caused by mixed dusts, the contact between components modifies toxicity. Hard metal lung disease is caused by exposure to mixtures of metals and carbides, typically cobalt (Co) and tungsten carbide (WC), but not to single components. Toxicity stems from reactive oxygen species generation in a mechanism involving both Co metal and WC in mutual contact. A relationship between the extent of water adsorption and biopersistence is proposed for vitreous fibers. Modifications of the surface taking place in vivo are described for ferruginous bodies and for the progressive comminution of chrysotile asbestos fibers. Environ Health Perspect 1 05(Suppl 5): 1013-1020 (1997)

Section: State Of the Surface And Biopersistencementioning

confidence: 65%

Surface reactivity in the pathogenic response to particulates.

Fubini

1997

122

100

“…The fibers chosen for this evaluation were MMVF11 (a glasswool), MMVF22 (a slagwool), and RCF1 (a refractory ceramic fiber), all sized to rat-respirable dimensions (11) 10).…”

Section: Methodsmentioning

confidence: 99%

“…Samples were chosen from three of the constituent groups comprising the MMVF family (9): glasswool, slagwool, and refractory ceramic fiber (RCF). In addition, the samples selected were the same as those used in in vivo fiber durability studies reported previously (10) Figure 1. Rate constants (k) for total fiber dissolution at pH 4 and at pH 7.6 (composition) and pH; to obtain an indication of the fiber leaching process under both pH conditions through change in specific fiber chemistry with time; and to document morphological changes to the fibers resulting from the dissolution and leaching processes.…”

Section: Introductionmentioning

confidence: 99%

Dual pH durability studies of man-made vitreous fiber (MMVF).

Bauer¹,

Law²,

Hesterberg³

1994

Dissolution of fibers in the deep lung may involve both extracellular and intracellular mechanisms. This process was modeled in vitro for each environment using an experimental flow-through system to characterize both total dissolution and specific chemical changes for three representative MMVF's: a glasswool, a slagwool, and a refractory ceramic fiber (RCF). Synthetic physiological fluids at pH 4 and at pH 7.6 were used to simulate macrophage intraphagolysosomal, and extracellular environments, respectively. Actual commercial fiber, sized to rat-respirable dimension, having an average fiber diameter of 1 pm and an average length between 15 and 25 pm, was used in the experiments. Fiber dissolution was monitored through change in chemistry of the fluid collected after percolation at a constant rate through a thin bed of sample. There are great differences in total fiber dissolution rates for the different fibers. Slagwool and RCF dissolve more rapidly at pH 4 than at pH 7.6, while the reverse is true for glasswool. Dissolution is sometimes accompanied by a noticeable change in fiber morphology or dimension, and sometimes by no change. There is strong dependency on pH, which affects not only total fiber dissolution, but also the leaching of specific chemical components. This effect is different for each type of fiber, indicating that specific fiber chemistry largely controls whether a fiber dissolves or leaches more rapidly under acidic or neutral conditions. Both total dissolution rates and calculated fiber composition changes are valuable guides to interpreting in vivo behavior of manmade vitreous fibers, and demonstrate the usefulness of in vitro acellular experiments in understanding overall fiber persistence. -Environ Health Perspect 102(Suppl 5): 61-65 (1994)

“…The only reproducible attempt made to correlate biopersistence rather than durability, and biological effect, was in the Geneva inhalation studies (37,38). The existing data show that ceramic fibers are more biopersistent than the glass fibers tested; rockwool is more biopersistent than slagand glasswool and less biopersistent than ceramic fibers.…”

Section: Biopersistencementioning

confidence: 99%

The occupational physician's point of view: the model of man-made vitreous fibers.

Brochard

Pairon²,

Bignon³

1994

This article gives a detailed description of the procedure the occupational physician uses in interpreting the available scientific data to provide useful information for prevention of pulmonary diseases related to man-made mineral fibers, particularly lung cancer and mesothelioma. As it is difficult to reach definite conclusions from human data on the toxicity of specific fibers, an experimental approach is needed. Concerning animal data, we emphasize that adequate inhalation studies are the "gold standard" for extrapolating to humans. However, experiments using intracavitary injection or cells in vitro may represent indicative tests for a possible carcinogenic effect. Such tests should be used to assess the intrinsic carcinogenicity of fibers, but they must be confirmed by adequate inhalation models. Despite the present uncertainties, a proposal is made that could make it possible to classify fibers according to their toxicologic potential, grading them in accordance with physicochemical parameters, in vitro testing, and animal experiments. This procedure may be applicable to nonvitreous fibers and to organic fibers. -Environ Health Perspect 102(Suppl 5):31-36 (1994)