Toxicity of Silica

Petushkov A, Ndiege N, Salem AK, Larsen SC (2010) Toxicity of silica nanomaterials zeolites, mesoporous siliea, and ammphous silica nanoparticles. Chapter 7. Elsevier, Amsterdam Pillai O, Dhaniknla AB, Panehagnula R (2001) Curr Opin Chem Biol 5(4) 439-446 Pitt WG (2008) Adv Drag Deliv Rev 60 1095-1096... 

Depasse, J. and Warlus, J. 1976. Relation between the toxicity of silica and its affinity for tetraalkylammonium groups. J. Coll. Interfac. Sci. 56 618-21. 

A number of studies [18] submission of information on in vitro and in vivo toxicity of silica nanoparticles - both crystalline and amorphous. Most of the results on the toxicity in vitro is reduced to the analysis of size - and dose-dependent cytotoxicity, increased reactive oxygen species and proinflammatory stimulation. The data obtained from in vivo studies demonstrate nanoparticles induced lung inflammation and fibrosis, emphysema, and granuloma formation. It is therefore important to monitor the content of nano-sized silica in the body. 

Lin W, Huang YW, Zhou XD et al (2006) In vitro toxicity of silica nanoparticles in human lung cancer cells. Toxicol Appl Pharmacol 217 252-259... 

Potential exposure routes for siUca nanowires include the skin and mucosal membranes, as weU as intentional internal exposure for proposed biomedical purposes. The inhalational toxicity of silica and siUca-based materials is weU known and has been extensively reviewed [58-60]. CrystalUne silica, a multidimen-... 

In in vivo studies, the induced toxicity of silica nanomaterials is transient, with the level of apoptosis, neutrophil and macrophage counts andcytokine/chemokine expressions returning to normal between one week and one month of recovery. 

In summary, whilst the toxicity of silica nanomaterials is generally low-and even more so at lower concentrations-a variety of factors which include the nanomaterials size, shape, surface properties, dopants, treatment dose and time, all affect their toxicity to similar degrees. Although such toxicity is a relatively recently investigated topic, and many studies are still at the experimental stages, the above-described factors are crucial for the safe use of silica nanomaterials in a variety of biological applications. 

Size-dependent toxicity of silica nano-particles to Chlorella kessleri. Journal of Environmental Science and Health. Part A, Toxic/Hazardous Substances Environmental Engineering, 43(10), 1157-73. 

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). 

The size of the nanomaterial greatly influences its toxicity particularly as the nanomaterial s size decreases, certain of its parameters changed [3, 11, 118, 119]. Many studies have shown that variations in the size of nanomaterials account for the different toxicity levels between nanosized and micrometer-sized materials [97, 99,100,103], It is known that a reduction in size can increase the rate of uptake and translocation of silica nanomaterials in vitro and in vivo, thereby inducing a more severe and transient toxicity [56]. 

Based on well established silica chemistry, the surface of silica nanomaterials can be modified to introduce a variety of functionalizations [3, 11, 118]. The toxicity of surface-modified nanomaterials is largely determined by their surface functional groups. As an example, Kreuter reported that an apolipoprotein coating on silica nanoparticles aided their endocytosis in brain capillaries through the LDL-receptor [122-124]. Overall, silica nanomaterials are low-toxicity materials, although their toxicity can be altered by surface modifications. 

Dose-dependent toxicity has frequently been observed in the study of nanomaterials [110-116], with increasing doses of silica nanomaterials invariably worsening their toxicity. Both, cell proliferation and viability were greatly hampered at higher doses in in vitro studies [111, 113, 116]. 

The toxicity is not only based on the amount or size of silica nanoparticles, but also on the cell line [95]. Cancer cell lines (A549, MKN-28) had a higher viability and resistance to silica nanoparticles than did normal cell lines (MRC-5, WS1 and CCD-966sk) [111]. Similarly, a previous study showed that A549 cells were more resistant to the treatment of silica nanoparticles than were macrophages [113]. 

The nuisance dust aspect of bauxite is in sharp contrast to the limited industrial situation where lung injury was reported in Canadian workers, who in the 1940s engaged in the manufacture of alumina abrasives in the virtual absence of fume control. Fusing of bauxite at 2000°C gave rise to a fume composed of freshly formed particles of amorphous silica and aluminum oxide. Despite the poor choice of the term—bauxite fume pneumoconiosis—sometimes used to describe the disease, scientific opinion favors the silica component as the probable toxic agent. It should be emphasized that bauxite from some sources may contain small amounts of silica. 

Toxicology. The toxicity of calcium silicate depends on particle size, aspect ratio, and amount of silica and respirable fiber. Synthetic nonfibrous calcium silicate is considered to be a nuisance dust. 

More recently, the importance of silica fume particle size on toxicity has been noted. Specifically, particles of the ultrafine size range may be expected to have higher toxicity compared with particles of larger size. 

---