Biogenic amorphous silica.

Biogenic amorphous silica (BAS) is a natural constituent of living matter (eg, unicellular organisms and crop plants). Diatoms, whose siliceous remains are the geologic precursors to diatomaceous earth, actively process soluble silica into BAS. In some plants, a portion of the BAS exists externally as pointed or irregularly shaped fibers. Although silica-related adverse health effects are usually attributed to crystalline forms, such effects could occur as a result of exposure to BAS at high temperatures (above 800 degrees C), where crystalline silica, a known human toxicant is formed. BAS fibers from food crops can be ingested and lead to adverse health effects due to irritative processes. Airborne BAS fibers from rice can be inhaled during burning or incineration. Fibrous or nonfibrous BAS can adsorb toxic organic compounds and facilitate their entry into the lung. Recommendations for research are suggested to address the issue of potential health effects due to exposure to BAS.