subcapitata. In this study, no correlation with the surface area was found. Alumina coated particles showed
lower toxicity than bare particles at concentrations ≥46 mg/L, except at pH 6.0. Addition of organic matter decreased toxicity of both particles. Due to the low surface GDC-0199 cell line charge, alumina coated particles aggregated in test medium and dissolution and nutrient adsorption characteristics were different and phosphate deficiency could have contributed to the higher toxicity of those particles at pH 6.0–6.8 compared to higher pH values. Again, the biocides and dispersant contained in LUDOX® CL-X may have contributed significantly to the toxicity observed and the values reported by van Hoecke et al. (2011) should therefore not be associated with pure SiO2 particles. After injection into the yolk of zebrafish embryos, silica nanowires (55 nm × 2.1 μm) with aspect ratios (i.e., ratio between length and diameter) greater than 1 were found to be highly toxic (LD50 = 110 pg/g embryo) and to cause embryo deformities. Spherical SiO2 particles (particle sizes of 200 and 50 nm, synthesised by the Stöber method) did however not exhibit any toxic or teratogenic activities
at the same concentrations ( Nelson et al., 2010). Treatment of mussel haemocytes with 1, 5 or 10 mg/L SiO2 particles (primary particle size 14 nm, aggregated size in artificial sea water after 1 h 150–1600 nm) did not induce significant cytotoxicity in the neutral red retention (NRR) assay, but stimulated lysozyme release, oxyradical- and NO-production Selumetinib chemical structure (Canesi et al., 2010). Studies have been summarised by the OECD (2004), the ECETOC (2006), the EPA (2011) and Becker et al. (2009). Epidemiology was reviewed, amongst others, by the ECETOC (2006), IARC (1997), Merget et al. (2002) and McLaughlin et al. (1997). Therefore, only the most relevant and more recent studies are described in detail in the following section. either A large number of in vitro studies have examined the uptake of SAS particles at a cellular level. Shapero and co-workers
( Shapero et al., 2011) report time and space resolved uptake studies of 50-, 100 and 300-nm silica particles by A549 human lung epithelial cells. Particles of all sizes were taken up by these cells and found in endosomes of the cells. Also, Yu et al. (2009) found by TEM that SAS particles with average sizes between 30 and 535 nm were all taken up into the cytoplasm of mouse keratinocytes. Similarly, silica particles between 30 and 400 nm were taken up by 3T3-L1 fibroblasts during 24 h of exposure at 50 mg/L and located mostly in vesicles, not in the cell nucleus ( Park et al., 2010a and Park et al., 2010b). Silica particles of different sizes (70, 200, 500 nm) were detected in the cytosol and endosomal compartments of human cervical carcinoma (HeLa) cells; the smaller particles were preferentially localised in lysosomes. No particles were found in mitochondria or nuclei ( Al-Rawi et al., 2011).