Crystalline silica has been classified as a human lung carcinogen. In addition to this, silica is also linked to other serious lung diseases such as Silicosis and Chronic Obstructive Pulmonary Disease.

Permissible Exposure Limit (PEL) set by OSHA 10 milligram of Silica per cubic meter of air by the percent of SiO2 (mg/m3). NIOSH has recommended the PEL 50 micrograms respirable free silica per cubic meter of air (µg/m3) averaged for a work shift of 10 hours/day or 40 hours a week.

OSHA’s Safety and Health Program Management Guidelines for silica can be found at Federal Register 54:3904-3916, January 26, 1989. If you are interested in more details go the following link:

https://www.cdc.gov/niosh/docs/81-123/pdfs/0553.pdf

Dear Colleague Asit Kumar Batabyal,

The response of our colleague Dr. K. Shahzad Baig does not concern the silica dissolved in water (ions that are found in water).

In some regions, and all depends on the tablecloths, the silica concentration can vary between 1 and 5 mg / l. Some mineral waters can contain up to 100 mg / l. To my knowledge, there are no standards for silica dissolved in water.

The silica is not considered toxic as such, but the inhalation of free silica or silica-rich dust (in mines, workshops of sculptors in some trades (grinding on public works or construction sites ) exhibits at least two serious diseases (usually fatal) respectively in the respiratory system and skin and other organs.

Naturally present in the bones, skin and teeth, silica - also known as the Silicon - is a super mineral for health that is often overlooked. For example, in her book Revitalize your hormones, Dr. Theresa Dale emphasizes that the silica acts as a stabilizer in the body, restoring balance between calcium and magnesium, which produces a positive effect on hormone production between other. Furthermore, the silica is also a stabilizer for tissues and membranes.

But above all, the body needs silica to form collagen - the protein that makes our skin remains smooth and supple and our bones are healthy. Collagen gives a youthful appearance to your skin and your nails, and higher quality bone. With age, our body becomes poor in silica, which causes wrinkles, dry skin, bones and more fragile and brittle nails. The collagen that is below the dermis supports the elasticity of the skin - which is largely due to the role of silica. In fact, silica is considered the cornerstone of nature: it keeps the bones and healthier nails, and skin looks younger.

With my best regards

Prof. Bachir ACHOUR

For the case of drinking water the concentration of  silica is not regulated. Sodium silicates may be added to drinking water as a corrosion inhibitor and sequestering agent. According to European Standard EN 1209, the maximum permissible concentration is 15 mg/L (European Committee for Standardization 1997). In the US public water supply, an average of  SiO2 content is 7.1 mg/L.  

 Soluble silicates have a low acute toxicity by the oral route. The average daily intake of silica background exposure via drinking water and diet is in the range of 43 - 107 mg SiO2/day

 http://www.heraproject.com/files/14-f-05 ra%20risk%20assessment%20of%20soluble%20silicates%20final%20draft.pdf

 There are no primary or secondary regulations for general silicates in drinking water http://www.watertechonline.com/contaminant-of-the-month-silica-and-silicates/

From the  above discussions,  we may  conclude that the consumption of excessive amount of dissolved silica has no adverse effects on  health; It is beneficial for health. I am working in a rural tract where the SiO2 content in groundwater samples ranges from 22.92 to 96.7 mg/L.

Thanks to Dr. Bachir Achour and Dr. K. Shahzad Baig for providing valuable information. 

Asit Kumar Batabyal K. Shahzad Baig Bachir Achour this article refers to relation between silica in ground water with the chronic kidney disease which causes kidney failure. this is a very significant issue which needs more investigation.

(study by nizam institute of medical sciences)

https://timesofindia.indiatimes.com/city/hyderabad/chronic-kidney-disease-may-be-5th-leading-cause-of-death-in-india-soon/articleshow/68405308.cms