Nonfibrous talc

In a study of 20 workers exposed for IQ-36 years to talc described as pure, at levels ranging from 15 to 35mppcf, no evidence of pneumoconiosis was found. In another study that compared the pulmonary function of workers exposed to either fibrous or nonfibrous talc, it was concluded that although the fibrous form was the more pathogenic type, both talcs produced pulmonary fibrosis no data were presented to document the types of talc involved." ... 

A study of 260 workers with 15 or more years of exposure to commercial talc dust (containing not only talc, but also tremolite, antho-phyllite, carbonate dusts, and a small amount of free silica) revealed a 40-fold greater than expected proportional mortality from cancer of the lungs and pleura. In addition, a major cause of death was cor pulmonale, a result of the pneumoconiosis the effects were likely due to the asbestos-form contaminants. The role of nonfibrous talc in these disease states could not be assessed. 

Nonfibrous Reinforcements. Because of the higher costs associated with nonasbestos fibers and the performance requirements needed in replacing asbestos, platy minerals such as mica and talc, and metal powders such as iron and copper, are being used as a portion of the total reinforcement package in NAOs. 

Toxieology. The nonasbestos form of talc, also termed nonfibrous or pure talc, has not been proven to cause the effects produced by exposure to fibrous talc, namely, fibrotic pneumoconiosis and an increased incidence of cancer of the lungs and pleura. 

Nonfibrous reinforcements are also employed as reinforcements and fillers. They result in increased tensile strength and deflecdon temperature, but usually decrease impact resistance. Nonfibrous reinforcements are preferred when fabricating with exceptional flatness. The nonfibrous include mica, glass beads, and minerals such as wollastonite (talc, calcium carbonate, and kaolin are considered fillers). Unlike fibrous reinforcements the nonfibrous reinforcements can be processed by many different technologies. 

Steatite ste-o- tlt n [L steatitis, a precious stone, fr. Gk, fr. steat-y stear] (1758) High purity talc containing maximum allowable proportions of 1.5% CaO, 1.5% Fe203 and 4% AI2O3 as impurities. See Magnesium Silicate, Nonfibrous. 

Uptake ean similarly be increased by exogenous sources of AOS. Brief exposure to whole cigarette smoke, which is a highly concentrated source of AOS and other radicals, and then to a mineral dust suspension produces considerably greater uptake of asbestos, titanium dioxide, fibrous silicon carbide, and talc (51 -53 Fig. 2). The increase in uptake is proportional to the dose of cigarette smoke, and the smoke effect can be inhibited by catalase, superoxide dismutase (which destroys superoxide anion), or deferoxamine (see Fig. 2). The effects of low levels of ozone are similar (Fig. 3), but differ from cigarette smoke in that superoxide dismutase is not protective (126). Smoke also fails to enhance the uptake of nonfibrous silicon carbide or iron oxide (hematite 53) the latter observation is particnlarly interesting because it was recently shown (127) that hematite does not catalyze the formation of AOS. This observation emphasizes the idea that redox-active surface iron, as opposed to compositional iron, is cracial to AOS formation and particle nptake. 

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