Silicon dioxide is the main component of beach sand and is commonly known as quartz in its pure crystalline form. For industrial purposes the amorphous (non-crystalline form) silicon dioxide or silica is of greater importance. Amorphous silica can be found in a range of products including varnishes, glues and paints. It is also used in foods and in dietary supplements sold in drug stores and pharmacies.
Dietary uptake of small amounts of silicon is important for the human body as silicon is one of the ultra-trace elements. Amorphous silicon dioxide is also being used as a food additive (labelled E551) or as a component in medicinal clay whereby it could enter the human body via the gastro-intestinal tract. Dermal uptake of silicon dioxide particles derived from contact with paints, inks or adhesives is highly unlikely. Quartz, the crystalline form of silicon dioxide, can be inhaled as fine dust that is released from underground mining activities when digging for ore, coal and other minerals. Since the overall amount of silica in the environment is very high it is difficult to distinguish between naturally occurring silica and industrially generated silicon dioxide.
Nanoscaled silicon dioxide occurs almost exclusively in its unstructured amorphous form which so far hasn't shown any negative characteristics in all performed experiments from animal to environmental studies. Silicon is an essential ultra-trace element for the human body and silicon dioxide in its amorphous form is considered to be non-hazardous. On the other hand the crystalline version of silicon dioxide is known to be harmful to humans: those who are permanently exposed to quartz dust, e.g. at their work place below ground, carry a high risk for chronic lung diseases (e.g. silicosis) and other pathological changes in the lung.