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

• nC60 inhibited the growth rate of S. obliquus.
• nC60 at the sub-lethal concentration decreased algal photosynthetic products.
• nC60 at the sub-lethal concentration decreased algal chlorophylls contents.
• nC60 decreased algal chlorophyll center ion Mg2+ content by inhibiting Mg2+ uptake.
• nC60 aggregated to algal surface and partly decreased Mg2+-ATPase activity.

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 C60 (termed nC60) were studied on Scenedesmusobliquus, a globally distributed phytoplankton. Sub-lethal concentration for S. 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 nC60 on the S. 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 nC60. The decrement in Mg2+ of S. obliquus was due to the inhibition of Mg2+-ATPase activity caused by nC60. Sum up, these results not only describe the sub-lethal effects but also provide the probably mechanism for sub-lethal effects of nC60 on exposed S. obliquus.

nC60 particles are adsorbed on algal surface, and block the Mg2+ channels, consequently result in photosynthetic toxicity: decrease the photosynthetic pigment, photosynthetic products and other photosynthetic concerned ions, Mg2+.Figure optionsDownload as PowerPoint slide