Bioaccumulation and biomarker responses of cubic and octahedral Cu₂O micro/nanocrystals in Daphnia magna

Great progress has been made in the controlled fabrication of nanomaterials with given sizes, shapes, and geometries. However, how such changes in structure potentially affect the bioavailability and toxicity of metal nanoparticles to aquatic organisms remains mostly unknown. The present study reports the different behaviors of two types of Cu₂O micro/nanocrystals (micro/nano-Cu₂O) with different shapes (cubic and octahedral) and crystallographies (with exposed surfaces as {100} or {111}). The bioaccumulation, median lethal concentration, and biomarker responses of Daphnia magna exposed to the two micro/nanocrystals are also investigated. The Cu accumulation, production of metallothionein (MT), and inhibition ratio of D. magna increased gradually with increasing micro/nano-Cu₂O concentration. The two crystals showed slight Cu accumulation differences toward D. magna, and their biomarker responses and toxicities to D. magna differed significantly as well. The octahedral Cu₂O micro/nanocrystals were more toxic to D. magna compared with the cubic micro/nanocrystals probably because of the higher surface activities of the {111} facets compared with those of the {100} facets for cuprites. Food ingestion was the main entry pathway of the micro/nanocrystals into organisms, and toxicity was consequently determined based on the dissolution behavior of the micro/nanocrystals in vivo.