Spherical nanoparticles may be found in stabilised colloidal SAS suspensions. SAS, including colloidal and surface-treated forms, have widely been used in topical and

oral medicines, food and cosmetics for decades without evidence of adverse human health effects. Standard ecotoxicity and toxicity tests generally demonstrated the biological inertness of SAS, and SAS were considered safe if occupational standards and use recommendations are followed (Becker et al., 2009, ECETOC, 2006, IARC, 1997, Lewinson et al., 1994 and OECD, 2004). Nevertheless a discussion about hazards and risks of “nanosilica” has recently started calling into question the safety of www.selleckchem.com/products/ink128.html SAS materials which are made up of primary particles in the nano-size range (Napierska et al., 2010 and Dekkers et al., 2010). This discussion has prompted this work to investigate whether the mode of action (MOA) or mechanisms of toxicity of so-called “nano-SAS” or “nanosilica” are different from those of the commercial SAS forms. To this end a systematic literature search was undertaken to identify relevant publications. The studies considered in this review were selected according to commonly accepted criteria of relevance, adequacy, reliability and validity (Klimisch et al., 1997 and OECD, 2005). In addition, studies with critical results and

those not yet covered in available authoritative reviews (IARC, 1997 and OECD, 2004) were included. There are three main types of silica (silicon dioxide), which are all found under CAS No. 7631-86-9, i.e., (1) crystalline silica, Bleomycin in vivo (2) amorphous silica (naturally occurring or as a by-product in the form of fused silica or silica fume), and (3) synthetic amorphous silica (SAS), including silica gel, precipitated silica, pyrogenic (fumed) silica and colloidal silica (silica sol). Only the manufactured forms of amorphous silica (SAS) will be dealt with in the following article, i.e., SAS produced by a wet process and described by CAS number 112926-00-8 (includes silica gel, precipitated silica and colloidal silica) and SAS produced by a thermal process described by CAS number 112945-52-5 (pyrogenic

silica). It also includes the surface-treated, hydrophobic SAS types, i.e., silica dimethicone silylate, silica dimethyl silylate and silica silylate (CAS 67762-90-7, 68611-44-9 and 68909-20-6). In general, SAS contains no detectable amounts of crystalline 4-Aminobutyrate aminotransferase silica (detection limits vary between 0.01 and 0.3% by weight, depending on the method used; ECETOC, 2006, pp. 12–14). SAS also contains fewer impurities than biogenic amorphous silica which is obtained from various sources such as the shell wall of phytoplankton or the epidermis of vegetables, or non-biogenic vitreous amorphous silica. SAS can be distinguished from other forms of amorphous silica by its high chemical purity, the finely particulate nature and by characteristics of the particles observable by electron microscopy, e.g., shape, structure, and degree of fusion ( Fig. 1).