coli bacteria were less sensitive with a growth inhibition of 48 ± 8.5% at 5000 ppm. The presence of light did not significantly increase the toxicity. Increase of the particle size to 930 nm or 60,000 nm did not influence toxicity ( Adams et al., 2006). Silica particles (10–20 nm, purity 99.5%, obtained as dry powder from American Elements, USA), stabilised with a non-toxic dispersant (100 mg Dispex A40/L) did not inhibit oxygen uptake by yeast cells up to

the highest tested concentration of 1000 mg/L; however, some damage of the cell membrane was found 17-AAG datasheet (Garcia-Saucedo et al., 2011). Fumed and porous type SiO2 particles (purchased from Sigma Corp., USA) with specific surface areas of 349.71 and 644.44 m2/g, and primary particle sizes of 7 nm (fumed) and 10 nm

(porous type), respectively PS-341 (aggregate sizes not reported), did not affect DNA integrity (as measured in the Comet assay), nor growth or reproduction parameters in Daphnia magna at the only tested concentration of 1 mg/L. An increase in the mortality rate of D. magna was observed after a 96 h-treatment with fumed material (mortality rate 10 ± 8.16%) and porous type material (15 ± 4.08%; controls 5 ± 4.08%). In larvae of the aquatic midge Chironomus riparius, an increase in mortality was observed after exposure to the porous-type SiO2 particles, but growth indicators were not significantly changed ( Lee et al., 2009). Because of the high variability in the results reported by Lee et al. (2009), and because only one dose level (1 mg/L) was tested and therefore no dose–response relationship

can be established, the relevance of these findings is doubtful. Fujiwara et al. (2008) report a non-linear, but size-dependent growth inhibition of algae (Chlorella kessleri) after a 96 h exposure to suspensions of Na2O stabilised SiO2 nanoparticles (Catalloid; 5, 26 and 78 nm). The pH of the culture medium was adjusted to 7.7. The 96 h-EC50 values were 0.8 ± 0.6%, 7.1 ± 2.8%, and 9.1 ± 4.7% for materials with primary particle sizes of 5, 26 and 78 nm, indicating an overall very low level of toxicity, even after exposure concentrations that by Methocarbamol far exceed current standard testing guideline recommendations. Toxicity was independent of illumination with light. The size of cells increased in the presence of 5 nm particles, and, to a lesser extent in the presence of materials composed of 26 and 78 nm-sized primary particles (as shown by flow cytometry). Coagulation of cells was observed after exposure to the material containing 5 nm particles (1.02%; test conditions not specified further). In a study reported by Ji et al. (2011), SiO2-nanoparticles showed no significant toxicity in Chlorella up to the highest tested concentration of 1000 mg/L. A low level of toxicity was found in the alga Scenedesmus obliquus by Wei et al. (2010), using silica “nano”-particles (primary particle sizes of 10–20 nm, purity 99.