Silicon Dioxide
<p>The <a href="http://en.wikipedia.org/wiki/Chemical_compound" title="Chemical compound" >chemical compound</a> <b >silicon dioxide</b>, also known as <b >silica</b> (from the <a href="http://en.wikipedia.org/wiki/Latin" title="Latin" >Latin</a><i ><a href="http://en.wikipedia.org/wiki/Silex" title="Silex" >silex</a></i>), is an <a href="http://en.wikipedia.org/wiki/Oxide" title="Oxide" >oxide</a> of <a href="http://en.wikipedia.org/wiki/Silicon" title="Silicon" >silicon</a> with the <a href="http://en.wikipedia.org/wiki/Chemical_formula" title="Chemical formula" >chemical formula</a> <b ><a href="http://en.wikipedia.org/wiki/Silicon" title="Silicon" >Si</a><a href="http://en.wikipedia.org/wiki/Oxygen" title="Oxygen" >O</a><sub >2</sub></b>. It has been known for its hardness since ancient times. Silica is most commonly found in nature as <a href="http://en.wikipedia.org/wiki/Sand" title="Sand" >sand</a> or <a href="http://en.wikipedia.org/wiki/Quartz" title="Quartz" >quartz</a>, as well as in the cell walls of <a href="http://en.wikipedia.org/wiki/Diatoms" title="Diatoms" class="mw-redirect" >diatoms</a>.<sup id="cite_ref-1" class="reference" ><a href="http://en.wikipedia.org/wiki/Silicon_dioxide#cite_note-1" >[2]</a></sup><sup id="cite_ref-2" class="reference" ><a href="http://en.wikipedia.org/wiki/Silicon_dioxide#cite_note-2" >[3]</a></sup></p>
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Silica is a common additive in the production of foods, where it is used primarily as a flow agent in powdered foods, or to absorb water in <a href="http://en.wikipedia.org/wiki/Hygroscopy" title="Hygroscopy" >hygroscopic</a> applications. </p>
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It is the primary component of <a href="http://en.wikipedia.org/wiki/Diatomaceous_earth" title="Diatomaceous earth" >diatomaceous earth</a> which has many uses ranging from filtration to insect control. It is also the primary component of <a href="http://en.wikipedia.org/wiki/Rice_husk_ash" title="Rice husk ash" class="mw-redirect" >rice husk ash</a> which is used, for example, in filtration and cement manufacturing.
Inhaling finely divided crystalline silica dust in very small quantities (OSHA allows 0.1 mg/m<sup >3</sup>) over time can lead to <a href="http://en.wikipedia.org/wiki/Silicosis" title="Silicosis" >silicosis</a>, <a href="http://en.wikipedia.org/wiki/Bronchitis" title="Bronchitis" >bronchitis</a>, or <a href="http://en.wikipedia.org/wiki/Cancer" title="Cancer" >cancer</a>, as the dust becomes lodged in the lungs and continuously irritates them, reducing lung capacities. </p>
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(In the body crystalline silica particles do not dissolve over clinically relevant periods of time.) This effect can create an occupational hazard for people working with <a href="http://en.wikipedia.org/wiki/Sandblasting" title="Sandblasting" class="mw-redirect" >sandblasting</a> equipment, products that contain powdered crystalline silica and so on. </p>
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Children, asthmatics of any age, allergy sufferers, and the elderly (all of whom have reduced lung capacity) can be affected in much less time. Amorphous silica, such as fumed silica is not associated with development of silicosis, but may cause irreversible lung damage in some cases.<sup id="cite_ref-35" class="reference" ><a href="http://en.wikipedia.org/wiki/Silicon_dioxide#cite_note-35" >[36]</a></sup> </p>
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Laws restricting silica exposure <i>with respect to the silicosis hazard </i>specify that they are concerned only with silica that is both crystalline and dust-forming.</p>
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Plant materials with high silica phytolith content, appear to be of importance to grazing animals, from chewing insects to ungulates. Studies have shown
that it accelerates tooth wear, and high levels of silica in plants frequently eaten by herbivores may have developed as a defense mechanism against predation.<sup id="cite_ref-36" class="reference" ><a href="http://en.wikipedia.org/wiki/Silicon_dioxide#cite_note-36" >[37]</a></sup><sup id="cite_ref-37" class="reference" ><a href="http://en.wikipedia.org/wiki/Silicon_dioxide#cite_note-37" >[38]</a></sup></p>
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A study which followed subjects for 15 years found that higher levels of silica in water appeared to decrease the risk of <a href="http://en.wikipedia.org/wiki/Dementia" title="Dementia" >dementia</a>. The study found that with an increase of 10 milligram-per-day of the intake of silica in drinking water, the risk of dementia dropped by 11%.<sup id="cite_ref-38" class="reference" ><a href="http://en.wikipedia.org/wiki/Silicon_dioxide#cite_note-38" >[39]</a></sup>
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