Toxic effects of nano-ZnO on marine microalgae Skeletonema costatum: Attention to the accumulation of intracellular Zn

• Nano-ZnO was more toxic than bulk-ZnO on marine microalgae Skeletonema costatum.
• Zn2+ released in medium could not explain different toxic effects between nano-ZnO and bulk-ZnO on microalgae.
• The total Zn content in the cell of microalgae was the dominant toxic mechanism of ZnO.
• Higher intracellular total Zn under nano-ZnO treatment than bulk-ZnO resulted in more toxicity of nano-ZnO on microalgae.
• Nano-ZnO could enter the cell as whole through transmembrane process.

To explore toxic mechanisms of nano-ZnO on marine microalgae, algal growth inhibition test was carried out, and total Zn in the cell and total dissolved Zn in f/2 medium were determined. It was found that nano-ZnO was more toxic than bulk-ZnO on marine microalgae Skeletonema costatum. No matter under nano-ZnO or bulk-ZnO treatment, accumulation of intracellular Zn had a good linear correlation with growth inhibition ratio (IR). The total Zn content in the cell of microalgae was the dominant toxic mechanism of ZnO. Intracellular total Zn could be an indispensable parameter to indicate the toxic effects of nano-ZnO. Higher intracellular total Zn under nano-ZnO treatment than bulk-ZnO resulted in more toxicity of nano-ZnO on microalgae. Compared with Zn2+ released by nano-ZnO into medium, lipid peroxidation (MDA level) injury, aggregation of nano-ZnO and transmembrane process of nano-ZnO also contributed to toxicity of nano-ZnO on Skeletonema costatum. The accumulation of intracellular Zn provides a new insight into toxic mechanisms of nano-ZnO.