The number of modifications of graphene-based nanomaterials is rapidly growing due to their extraordinary electronic, mechanical, optical, and antibacterial properties [1-3]. The environmental safety assessment of new materials required ecotoxicological bioassays with various endpoints [4,5]. In this study, we compared the aquatic toxicity of three types of graphene-based nanoparticles (NPs) (Table 1) in two marine microalgae, namely, Attheya ussuriensis and Porphyridium purpureum. Changes in microalgae cell conditions were measured by flow cytometer CytoFLEX (Beckman Coulter, USA) (Table 2).The one-way ANOVA test was used with GraphPad Prism 8.0.2 (Graph- Pad Software, USA). A value of ≤ 0.05 was considered statistically significant. All the measurements were performed in triplicate after 24 h, 96 h, and 7 days of exposure to the concentrations of NPs of 1, 5, 10, 25, 50, 100, and 200 mg/L. The growth rate test demonstrated no dose and time-dependent toxicity in all the experimental series. Interestingly that all the tested NPs inhibited microalgal growth at the range of concentrations between 1 and 25 mg/L, and further increase of the concentration ether mitigate the toxic influence or stimulate the growth of microalgae. The highest growth inhibition of both microalgae species (up to 25%) was caused by GQDs after 24 and 96 h of exposure at the concentration of 10 mg/L. GNR inhibited the growth of P. purpureum only at the highest concentrations. SWNTs demonstrated dose and time-dependent growth stimulation of A. ussuriensis (4 times after 7 days compared to control) and dose-dependent growth stimulation of P. purpureum (up to 1.5 times). Among the registered biochemical changes, all the NPs caused membrane depolarization of microalgae. However, only SWCNTs caused dose and time-dependent esterase activity inhibition, which can be caused by metal impurities in this sample. This observation correlates with our previous results [6]. All the tested NPs increased ROS generation in P. purpureum cells. In general, graphene-based NPs demonstrated low toxicity in used microalgae and even stimulated their growth. Registered biochemical alterations varied depend on microalgae species and types of NPs.
