Influence of Incubation Conditions on the Nanoparticles Toxicity Based on Seed Germination and Bacterial Bioluminescence.

The effects of the modified incubation conditions of a conventional bioassay on the toxicity of partially soluble nanoparticles (NPs) were evaluated based on the activity of seed germination and bacterial bioluminescence. Different levels of toxicity were observed for seed germination (CuO > ZnO > NiO) and bacterial bioluminescence (ZnO > CuO > NiO). The NP inhibition of seed germination increased strongly under modified incubation conditions: sample volume from 5 mL to 10 mL, shaking from none to 70 rpm, and working vessel from a Petri dish (+/− filter paper) to an Erlenmeyer flask (no filter paper). In the case of seed germination, the toxicity levels of NPs under the modified conditions were 1.26 to 8.49 times higher than the conventional method according to the type of NPs and modified conditions (p-values < 0.05). No significant differences in bacterial bioluminescence were observed between conventional (130 rpm) and modified (160 rpm) conditions. These findings show that for an accurate assessment of partially soluble NPs toxicity in ecosystems, the conventional bioassay method, which is designed for soluble chemicals, needs to be performed under modified conditions because of their insolubility.