Abstract
The aim of this work was to investigate the long-term toxic effect of zinc oxide (ZnO) nanoparticles (NPs) on freshwater microalgae, combined with the nutrient consumption in the culture. For this purpose, two common microalgae media (Blue-Green 11, BG-11, and Bold’s Basal Medium, BBM) were used. Scenedesmus rubescens was used as freshwater microalgae model species and was exposed to ZnO NPs at different concentrations (0.081 to 810 mg/L) for a period up to 28 d. The experimental results revealed that microalgae growth was affected by the time of exposure and the NPs concentrations, but mainly the culture medium used. Differences in microalgae growth rates were observed and attributed to the selected culture medium. The toxic effect of ZnO NPs was higher on microalgae cultured in modified BG-11 compared to BBM, despite the fact that S. rubescens exhibited higher growth rate in modified BG-11 without the exposure of ZnO NPs.
Highlights
Nanoparticles (NPs) have always existed in the natural environment[1]
At 810 mg/L zinc oxide (ZnO) NPs, the biomass concentration remained constant at 0.75 g/L after the third day, which was attributed to the concentration of NPs added in the culture (Fig. 1a)
It was observed that the microalgae culture in BBM exhibited tolerance to higher NPs concentrations than culturing in 1/3N BG-11, especially at 8.1 mg/L ZnO NPs
Summary
Nanoparticles (NPs) have always existed in the natural environment (soil, water and atmosphere)[1]. Zhu et al.[13] found that ZnO NPs exhibited higher acute toxicity to zebrafish embryos than TiO2 and Al2O3 NPs. Recent studies[8,9,12,13,14,15,16,17] have shown that ZnO NPs have toxic effects on microalgae, which depend on the species type, exposure time, NPs concentration, and mainly the culture medium. The species type of microalgae (freshwater or marine) define the behavior of NPs and the toxic effects mechanisms since NPs dissolution depend on the aqueous matrix composition (pH, ionic strength, organic matter content, etc.). Scenedesmus rubescens) and marine (Dunaliella tertiolecta and Tetraselmis suesica) microalgae species They reported that the sensitivity of algae to ZnO NPs strongly depended on the species type, the concentration of NPs and the medium www.nature.com/scientificreports/. The Zn ions were more toxic than ZnO NPs for zinc concentrations lower than 50 mg/L, while ZnO NPs exhibited higher toxicity than Zn ions at concentrations greater than 50 mg/L6
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