Size-dependent toxicity of silica nano-particles to Chlorella kessleri

Abstract

SiO₂ nano-particles were found to exhibit size-dependent toxicity toward the alga, Chlorella kessleri. Small SiO₂ nano-particles exhibit stronger toxicity: 50% inhibitory concentrations (IC₅₀) value for 5 nm = 0.8 ± 0.6%, 26 nm = 7.1 ± 2.8%, and 78 nm = 9.1 ± 4.7%. Enlargement of the cell body was observed by flow cytometry, which is due to the presence of structures that obstructed cell division. Optical and transmission microscopes were used to observe coagulated cells with incomplete division. Although the physiological effect of SiO₂ nano-particles was not clear, SiO₂ nano-particles are toxic, at least for algae in aquatic media. Under the transmission electron microscope, several amorphous structures appeared in the cells that were exposed to 5-nm silica nano-particles.

Keywords:

• Silica nano-particles
• Chlorella kessleri
• size-dependent toxicity
• cell structure

Acknowledgments

We thank Professor Hiroko Baba and Assistant Professor Akiko Hayashi, Department of Molecular Neurobiology, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences for their instruction of preparing samples for transmission electron microscopy. This work was supported by a Grant-In-Aids (#18550080) from Japan Ministry of Culture Science and Education.

Notes

*50% inhibitory concentrations. The values are the averages of quadruplicate experiments, and are expressed as weight/volume %