Differential Oxidative Stress of Octahedral and Cubic Cu₂O Micro/Nanocrystals to Daphnia magna

This study attempts to understand the impact of different shapes of an individual micro/nanomaterial on their biotoxicities to aquatic organisms. Two differently shaped Cu₂O micro/nanocrystals (cubes and octahedrons with side lengths of 900 nm) were exposed to Daphnia magna for 72 h, afterward several antioxidant biomarkers such as reactive oxygen species (ROS), catalase (CAT), total antioxidant capacity (T-AOC), and malondialdehyde (MDA) in D. magna were measured. We demonstrated the differential influences of two crystallographic Cu₂O nanocrystals on the antioxidant process. Specifically, octahedral Cu₂O nanocrystals showed a higher level of oxidative stress, possibly because of its larger surface area and higher reaction activity of the octahedron. The biomarker results further showed that the oxidative stress and antioxidant mechanism process involved three stagesantioxidant response, oxidation inhibition, and antioxidant inactivation. Furthermore, the accumulation of MDA was mainly responsible for the ROS-induced toxicity.