Pulmonary responses to silica dust : the influence of crystalline structures and physico-chemical properties

The inhalation of silica crystalline polymorphs leads to the development of pulmonary nodules that vary in extent and in fibrotic content. In this study, a single protocol was used to test different silica samples (i.e., 2 non-crystalline samples: one vitreous silica, one diatomaceous earth , 4 crystalline samples: one pure a-quartz ground in a wet atmosphere, one of the same quartz heated until it becomes oc-cristobalite and 2 cristobalites obtained by heating diatomaceous earth). Wistar rats received a single intra-tracheal injection of alveolar dust and were followed over a period of 3 months. The results were exploited using macroscopic examination (wet lung weight), histological examination and biochemical dosing (hydroxyproline, lipid, and silica content). The results showed that vitreous silica, diatomaceous earth, wet-ground quartz and both types of cristobalites are responsible to a greater or lesser extent for the pulmonary reaction typical of exposure to silica (i.e., nodules ); with different cellular and fibrotic surface areas for each sample. a-cristobalite (obtained from the wet-ground quartz heated to a very high temperature; 1,300 °C) leads to the formation of only small foreign-body granulomas. All crystalline minerals tested caused alveolar lipoproteinosis. It was thus concluded that the crystalline structure plays a less important role than the surface state in the formation of silicotic nodules

Morphological and Chemical Mechanisms of Elongated Mineral Particle Toxicities

Much of our understanding regarding the mechanisms for induction of disease following inhalation of respirable elongated mineral particles (REMP) is based on studies involving the biological effects of asbestos fibers. The factors governing the disease potential of an exposure include duration and frequency of exposures; tissue-specific dose over time; impacts on dose persistence from in vivo REMP dissolution, comminution, and clearance; individual susceptibility; and the mineral type and surface characteristics. The mechanisms associated with asbestos particle toxicity involve two facets for each particle's contribution: (1) the physical features of the inhaled REMP, which include width, length, aspect ratio, and effective surface area available for cell contact; and (2) the surface chemical composition and reactivity of the individual fiber/elongated particle. Studies in cell-free systems and with cultured cells suggest an important way in which REMP from asbestos damage cellular molecules or influence cellular processes. This may involve an unfortunate combination of the ability of REMP to chemically generate potentially damaging reactive oxygen species, through surface iron, and the interaction of the unique surfaces with cell membranes to trigger membrane receptor activation. Together these events appear to lead to a cascade of cellular events, including the production of damaging reactive nitrogen species, which may contribute to the disease process. Thus, there is a need to be more cognizant of the potential impact that the total surface area of REMP contributes to the generation of events resulting in pathological changes in biological systems. The information presented has applicability to inhaled dusts, in general, and specifically to respirable elongated mineral particles

Etude des sites donneurs et accepteurs d’un électron en surface des amiantes

Les propriétés oxydoréductrices des fibres d’amiante sont étudiées par utilisation de la spectroscopie de résonance paramagnétique électronique. La présence de sites à caractère réducteur, est mise en évidence sur deux des supports testés : chrysotile et amosite. L’étude structurale de ces matériaux permet d’associer les centres réducteurs à des groupements hydroxyles et des oxygènes de surface en basse coordination. L’influence de cations paramagnétiques du réseau sur les résultats quantitatifs est discutée