Fate of ZnS:Mn quantum dots in Seine River water and seawater. Ecotoxicological effects on Chlorella Vulgaris microalgae

With the wide use of nanomaterials in our daily life, the potential ecotoxicology effect of nanoparticles (NPs) has attracted more and more attention from researchers. Here, the ZnS:Mn (0.5%, 2.0%, 4.0% and 10% of Mn, in mol) QDs were synthesized using the polyol method, and the toxicity mechanism was investigated by contacting the microalgae Chlorella vulgaris with ZnS:Mn QDs in different culture media (BG11, Seine River water - SRW, synthetic seawater - SSW). The crystalline size of the synthesized QDs was around 1.5 nm, but the particles tended to aggregate since the size of the ZnS:Mn colloids determined by DLS ranged from 300 nm to 700 nm at pH 6 and 8. From a toxicological point of view, all these ZnS:Mn QDs caused a decrease in the photosynthetic activity, cell viability, and intracellular ATP level; moreover, the SOD activity significantly increased in SSW, which evidenced that the ZnS:Mn NPs would expose the algae cell in the oxidative stress environment. Finally, TEM observations of the algae thin sections confirmed the internalization of the ZnS:Mn NPs, which caused the leakage of the cytoplasm.