ZnO Nanoparticles: Effect of Size on Bacterial Bioluminescence, Seed Germination, Algal Growth, and Gene Mutation

Effect of zinc oxide (ZnO) nanoparticles (NPs) size was evaluated in the context of bacterial bioluminescence, seed germination, gene mutation in bacteria, and algal growth. Different sensitivities and half maximal effective concentration (EC_50s) were observed, showing orders of toxicity: bacterial bioluminescence (0.31-0.40 mg/L) > algal growth (1.08-2.90 mg/L) > seed germination (6.56-9.98 mg/L). Furthermore, size of NPs plays a critical role in toxicity. The mutation ratio decreases with increase in the size of NPs, with 2.4 for 5 nm and 1.1 for 80 nm, at 100 mg/L of ZnO NPs. Effect ZnO particle size differed according to tested assays. Under exposure conditions with large sizes, toxicity of ZnO NPs increased on seed germination, but decreased on algal growth and gene mutation. Toxicity results of algal growth and seed germination showed statistically significant differences (p < 0.05) between 5 and 80 nm ZnO NPs. In the case of bacterial bioluminescence, no significant differences were observed among each of the sizes tested. These findings show that a toxicity evaluation of NPs needs to consider the different effects with respect to particle sizes and tested organisms for an accurate assessment of toxicity.