Effects of silica nanoparticles on growth and photosynthetic pigment contentsof Scenedesmus obliquus

To assess the aquatic ecosystem safety for silica (SiO_2) nanoparticles (NPs), the growth inhibition and photosynthetic pigment contents of Scenedesmus obliquus in logarithm growth phase exposed to SiO_2 NPs and SiO_2 bulk particles (BPs) suspensions were measured. SiO_2 NPs with 10-20 nm diameters were found to be toxic. The 20% effective concentration (EC_(20)) values for 72 and 96 hr were 388.1 and 216.5 mg/L, respectively. The contents of chlorophyll decreased significantly under moderate and high concentration (50, 100, and 200 mg/L) of SiO_2 NPs after 96-hour exposure, but the carotenoids did not. SiO_2 BPs were found to be nontoxic up to 200 mg/L. The toxicity of SiO_2 NPs probablely due to their sorption to algal cells surface. The results imply that there is potential harm to aquatic environment in using SiO_2 NPs, and it should deserve special concern.