Long-term toxicity of ZnO nanoparticles to Scenedesmus rubescens cultivated in different media

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.

Long-Term Toxicity of ZnO Nanoparticles on Scenedesmus rubescens Cultivated in Semi-Batch Mode

“…Finally, in both cases, there was a control flask with medium without NPs. The concentration of 0.081 mg/L ZnO NPs is considered low, and has been previously investigated in short term toxicity tests [13,24].…”

“…It should be mentioned that certain properties of NPs, which might be critical to specific applications, may largely vary depending on the production techniques employed [12]. The effect of NPs on a living organism also depends on the behavior of the NPs in the living environment of organisms [3], the concentration of NPs and the exposure time [13]. The exposure time of microorganisms on NPs is a factor that has not been extensively investigated, despite the fact that NPs in nature will be present for a long period and the organisms will be exposed for a long time.…”

“…Various metal NPs on Scenedesmus sp. have been investigated including Al 2 O 3 , TiO 2 , SiC, ZnO, and CeO 2 [2,10,11,13]. Short-term toxicity tests have shown that even at low concentrations, metal NPs have a negative effect on algal photosynthetic metabolism [10], while at high metal NPs concentrations a lethal damage of the cells may occur.…”

“…On the other hand, a controlled presence of metal NPs in a Scenedesmus sp. culture may have a positive effect on algal growth and lipid content [10,13]. The lipid content of microalgae is an important factor for the choice of suitable algal species for biofuel production.…”

“…The effect of NP toxicity on microalgae in short term and batch mode experiments has been investigated by many researchers. However, recent studies have reported the need to study the behavior of NPs in real environmental conditions, and to relate the long-term exposure conditions as well as the continuous supply of NPs [13,21].…”