Surface Reactivity in the Pathogenic Response to Particulates

Abstract

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.

An observational study of giant cell interstitial pneumonia and lung fibrosis in hard metal lung disease

“…Toxicity stems from reactive oxygen species generation in a mechanism involving both elements in mutual contact. 26 Inhaled cobalt and tungsten carbides may cause lung toxicity even in those who are less sensitive to those elements, which can result in lung fibrosis with GIP features. Qualitative elemental analysis of fibrosing lesions in GIP also demonstrated the presence of miscellaneous elements-Al, Si, Ti, Cr and Fe-in addition to tungsten, cobalt and/or Ta.…”

Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy

“…In addition to fiber length, chemical factors play an important role in fiber durability and biopersistence; fibers with high alkali or alkali earth oxide contents and low contents of Al 2 O 3 , Fe 2 O 3 , TiO 2 tend to have low durability and hence low biopersistence [76]. On the other hand, studies of mineral particles have demonstrated that the toxic and carcinogenic effects are, in some cases, related to the surface area of inhaled particles and their surface activity [77,78]. Particle surface characteristics are considered to be key factors in the generation of free radicals and reactive oxygen species formation and in the development of fibrosis and cancer by quartz (crystallized silica) [77].…”

“…On the other hand, studies of mineral particles have demonstrated that the toxic and carcinogenic effects are, in some cases, related to the surface area of inhaled particles and their surface activity [77,78]. Particle surface characteristics are considered to be key factors in the generation of free radicals and reactive oxygen species formation and in the development of fibrosis and cancer by quartz (crystallized silica) [77]. …”

Assessing the in vitro toxicity of the lunar dust environment using respiratory cells exposed to Al2O3 or SiO2 fine dust particles

“…2). It also contains glass aggregated with nano-scale beads of iron, called nanophase Fe (Heiken et al 1991;Fubini 1997;Taylor 2000;Park et al 2006). SiO 2 makes up 45% of lunar dust particles and is normally found in combination with other minerals and metals (Heiken et al 1991;Pieters et al 2004).…”