Assessing the long-term adverse effects of aluminium nanoparticles on freshwater phytoplankton using isolated-species and microalgal communities

The physicochemical properties of aluminum oxide nanoparticles (Al₂O₃-NPs or AlNPs) allow them to remain suspended in water for extended periods. Despite this, AlNPs are one of the least studied types of metal nanoparticles and pose a significant risk to aquatic ecosystems. Therefore, it is essential to understand the toxic mechanisms of AlNPs on microalgae and cyanobacteria, as they can have adverse effects on the entire aquatic food web. Our research aimed to assess the toxicity of continuous exposure to low environmentally relevant concentrations of AlNPs on the growth rate, photosynthetic activity, oxidative stress (ROS), and microcystin production (MC-LR) in a phytoplanktonic community (PCC) consisting of Scenedesmus armatus and Microcystis aeruginosa. Both single and community cultures were exposed to 1.0 μg mL-1 AlNPs for 28 days. The results showed a significant 20–40% inhibition of S. armatus population growth in both individual and community cultures after 28 days of exposure. In contrast, M. aeruginosa exhibited increased survival and cell division rates when exposed to nanoparticles, both individually and within the community. Additionally, S. armatus showed a substantial reduction in gross photosynthesis (Pg) and net photosynthesis (Pn), with less inhibition in respiration (R) after 28 days of exposure. Conversely, M. aeruginosa demonstrated higher rates of photosynthetic productivity in all three parameters (Pg, Pn, and R). In the PCC, respiration was inhibited from 14 to 28 days, and both Pg and Pn were also inhibited. Both S. armatus and M. aeruginosa showed 28–31% levels of ROS generation, while the phytoplanktonic community exhibited no significant ROS production. Moreover, the production and release of MC-LR decreased by 8–38% in M. aeruginosa compared to the control strain. These findings underscore the importance of monitoring the use and application of nanomaterials to mitigate their potential toxic effects on aquatic ecosystems.