Silica toxicity

Some accessory minerals that accompany the inhaled dose of particles may themselves be reactive (such as pyrite, an iron sulfide) and may be able to modify fluid chemistry sufficiently to enhance or diminish particle solubility, or to release redox-active species such as iron. For example, the well-documented decrease in crystalline silica toxicity when combined with other, nonsilica mineral particles (SSDC, 1988) implies that the other mineral particles are reacting chemically with the body fluids and the silica to modify the surface chemistry of the silica that induces ROS generation and cytotoxicity. 

Nash et al. (1966) synthesised another compound, polyvinylpyridinioacetic acid, which has even greater hydrogen bonding capacity than poly-2-vinylpyridine-l-oxide and very efficiently protects macrophages from silica toxicity. This protection was confirmed by Sakabe and Koshi (1967), who also showed that it prevents the increase in acid phosphatase in macrophages following exposure to quartz particles < 2 pm in diameter. However, polybetaine was slightly more active than poly-2-vinylpyridine-1 - oxide. 

PvPNO. Starting in 1958, compounds were found that offset the development of silicotic tissues in animal tissues treated with silicogenic forms of silica. An undisclosed compound 48/80, an organic base, was found effective by Marks et al. (347-349) but too toxic for use in man. They also reported that certain phenazines and a histamine-releasing agent neutralized silica toxicity. The compound 48/80 may simply coat the silica surface. Some protection was observed by polymyxin B and by hexylamine. 

The immobilization of reagents onto sorbents often results in increase of their sensitivity and, in some cases, selectivity, allows to simplify the analysis and to avoid necessity of use of toxic organic solvents. At the same time silicas are characterized by absence of swelling, thenual and chemical stability, rapid achievement of heterogeneous equilibrium. 

SORBTION-X-RAY-FLUORESCENCE DETERMINATION OE TOXIC METALS WITH THEIR PRECONCENTRATION ON COMPLEXING CHEMICAL MODIEIED SILICA... 

Fillers fibreglass, silicas, calcium carbonate, powdered metal pigments some may be absorbed potential primary irritant dust inhalation low toxicity... 

The basis on which the TLVs are set may differ from substance to substance. For some, such as levels for silica dust, a guiding factor is protection against impairment of health. For others, it is the comfort level of the individual, such as freedom from irritation, nuisance, or other forms of stress for example, the TLV for sulfur dioxide is based on irritation and not on toxicity per se. The TLV list is reviewed annually resulting in some revisions in values and some additions to the list. 

Anhydrous hydrogen fluoride and hydrofluoric acid react with substances containing silica and silicon oxide to form silicon tetrafluoridc and fluorosilic acid. SiF, a colorless gas at ambient temperature, is liighly toxic. An equilibrium mixture of SiF in the presence of moisture also contains hydrogen fluoride and hydrofluoric acid. 

As a result of its highly polar character, silica gel is particularly useful in the separation of polarizable materials such as the aromatic hydrocarbons and polynuclear aromatics. It is also useful in the separation of weakly polar solute mixtures such as ethers, esters and in some cases, ketones. The mobile phases that are commonly employed with silica gel are the n-paraffins and mixtures of the n-paraffins with methylene dichloride or chloroform. It should be borne in mind that chloroform is opaque to UV light at 254 nm and thus, if a fixed wavelength UV detector is being used, methylene dichloride might be a better choice. Furthermore, chloroform is considered toxic and requires special methods of waste disposal. Silica gel is strongly deactivated with water and thus, to ensure stable retentive characteristics, the solvent used for the mobile phase should either be completely dry or have a controlled amount of water present. The level of water in the solvent that will have significant effect on solute retention is extremely small. The solubility of water in n-heptane is... 

The products of the photooxidation of naphthylamines adsorbed on particles of silica and alumina were putatively less toxic than their precursors (Hasegawa et al. 1993). 

Miniaturised SEC uses small fused-silica packed-capillary columns (0.32-1 mm i.d., 30-200cm) instead of relatively large metal columns. Miniaturisation puts stringent requirements on the quality of SEC columns. Advantages of ptSEC are (i) much smaller amounts of (toxic, expensive) solvents (ii) smaller samples (iii) better and easier temperature control (iv) increased detector compatibility (e.g. MS) and (v) greatly reduced... 

In a facile and rapid stereoselective, three-component, one-pot reaction, a series of cis-isoquinolonic acids 132 were synthesized using silica supported sulfuric acid to catalyze the reaction between homophthalic anhydride 133 with different aldehydes 134 and amines 135. This three-component cyclocondensation offers a variety of advantages including high yields, easy experimental work-up, and the use an inexpensive, non-toxic, readily available, and recyclable catalyst <06JHC187>. 

---