Short-Term Toxicity of ZnO Nanoparticles on Microalgae at Different Initial Nutrient Concentrations

Abstract

The aim of this work was to investigate the combined short-term toxic effect of zinc oxide (ZnO) nanoparticles (NPs) and nitrate concentration of the medium on freshwater microalgae. For this purpose, freshwater microalgae Chlorococcum sp. was cultivated in modified Blue-Green medium (BG-11) containing nitrate concentrations ranging from 0 to 300 mg/L, and exposed to ZnO NPs in different concentrations (0.081 to 810 mg/L) for a period up to 96 h. The experimental results revealed that algal growth was affected by the exposure time, NPs concentrations, and mainly the initial nitrate concentration. Differences in microalgae growth rates were observed. The toxic effect of ZnO NPs was higher on microalgae cultured in modified BG-11 with low and high nitrate concentrations. During the 4-day exposure, the highest growth rates were observed at 24 h at an initial nitrate concentration of 50 mg/L; 1.94 d−1 and 0.22 d−1 for 0 and 810 mg/L ZnO NPs, respectively. Nitrate uptake by algal biomass reached up to 40.1% after 96 h of operation in the control culture with an initial nitrate concentration of 50 mg/L. Finally, the results of this study showed the need for the investigation of ZnO NPs toxicity on microalgae under optimum and stressful nutrient conditions for microalgae growth.

Response and Resilience of Scenedesmus rubescens Microalgae to ZnO Nanoparticles

“…Changes in pH values (Figure 4) were observed in all cultures, and its values increased over time. More precisely, as it has already been observed in previous studies as well, algal growth has been found to increase the pH of the culture medium [26]. This is due to the fact that cells consume diluted CO 2 during photosynthesis at a rate higher than that of the dissolution of gaseous carbon dioxide into the medium.…”

“…In previous studies by our team [17] investigating the toxic effect of ZnO NPs on Scenedesmus rubescens, an increasing tendency in the cell concentration was observed after 48 h. This might be attributed to the adaptation period of S. rubescens to new cultivation conditions. Despite the importance of nitrogen in microalgae proliferation and the fact that nitrates were the unique source of nitrogen in our experiments, nitrate availability was found to affect biomass growth in a non-linear way, as demonstrated by other studies as well [15,24,26]. Extracellular as well as intracellular parameters could be the reason for this phenomenon.…”

“…BG-11 (BlueGreen-11) was chosen as the culture medium for this study, and its composition is described thoroughly in our previous work [26]. In order to investigate the effect of NO 3…”

“…In our previous work, the nitrate content of the growing medium was reported to impact the toxicity of ZnO NPs, upon Chlorococcum sp. growth [26]. The scope of this study was to assess the short-term response of S. rubescens microalga to ZnO NPs, a freshwater genus that has been found to be more robust compared to Chlorococcum sp.…”

Effects of Silver Nanoparticles on the Red Microalga Porphyridium purpureum CNMN-AR-02, Cultivated on Two Nutrient Media

“…The growth process was affected by the concentration of nanoparticles and the initial nitrate content in the cultivation medium. Extreme quantities, meaning both high and low levels of nitrates, have been shown to increase the toxicity of nanoparticles [30]. Growing microalga P. purpureum CNMN-AR-02 in MM1 medium with a nitrate content of 0.17 g/L and the addition of 10 nm AgNPs at a concentration of 10 µM led to a reduction in the amount of biomass of 18.7%.…”