Effects of aqueous stable fullerene nanocrystal (nC60) on Scenedesmus obliquus: Evaluation of the sub-lethal photosynthetic responses and inhibition mechanism

Understanding sub-lethal effects of nanomaterial may be particularly important to determining ecosystem responses as current levels of nanomaterial release are low compared to levels projected for the future. In this work, the sub-lethal effects of water stable, nanocrystalline fullerenes as C-60 (termed nC(60)) were studied on Scenedesmus obliquus, a globally distributed phytoplankton. Sub-lethal concentration for Scenedesmus obliquus was firstly determined as 0.09 mg L-1 using the standard 72 h exposure tests (OECD Guideline 201). Subsequent sub-lethal experiment of nC(60) on the Scenedesmus obliquus was carried out for 60 d and focused on the photosynthesis processes. The results demonstrate that upon sub-lethal exposure, the photosynthetic products of polysaccharide, soluble protein and total lipid were decreased with exposure time. The photosynthetic pigments of chlorophyll a and chlorophyll b were negatively impacted. Further investigations indicate that the decrements in photosynthetic products and pigments were mainly due to the algal Mg2+ decrement (by 40%) at the sub-lethal concentration (0.09 mg L-1) of nC(60). The decrement in Mg2+ of Scenedesmus obliquus was due to the inhibition of Mg2+-ATPase activity caused by nC(60). Sum up, these results not only describe the sub-lethal effects but also provide the probably mechanism for sub-lethal effects of nC(60) on exposed Scenedesmus obliquus. (C) 2014 Elsevier Ltd. All rights reserved.