Effect of cultivation media on the toxicity of ZnO nanoparticles to freshwater and marine microalgae

• Short-term bioassays were conducted for four algae species in different media.
• The culture medium has significant contribution on the toxic effects of ZnO NPs.
• S. rubescens exhibited quite different behavior depending on culture media.
• D. tertiolecta was the most sensitive organism to ZnO NPs exposure.

The aim of this work was to investigate the effect of zinc oxide nanoparticles (ZnO NPs) on freshwater and marine microalgae cultivated in different media. Freshwater species Chlorococcum sp. and Scenedesmus rubescens were cultivated in modified Blue–Green medium (BG-11) and Bold's Basal Medium (BBM), and marine species Dunaliella tertiolecta, and Tetraselmis suesica, cultured in salt modified BG-11 and f/2 medium. The microalgae species were exposed for 96 h with a daily reading of algal growth rate, to different ZnO NPs concentrations (0.081–810 mg/L). Significant differences were observed on microalgae growth rates, with the marine being more sensitive than the freshwater species, as revealed by their half inhibitory concentration values (IC50). The IC50 values in freshwater species were affected by the culture medium. The lowest IC50 values (<2.57 mg/L) were observed in the marine species. S. rubescens showed the less toxic effect in cultures with modified BG-11, compared to BBM cultures, with IC50 values >810 mg/L and 14.27 mg/L after 96 h exposure time, respectively. ZnO nanoparticles appeared to have toxic effects in all species tested, depended on the species type, the exposure time, the NPs concentration, and mainly the culture medium.

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