The ecotoxicological effects of chromium (III) oxide nanoparticles to Chlorella sp.: perspective from the physiological and transcriptional responses

Extensive application of nanomaterials enlarges its concentrations in the aquatic environments and poses a threat to algae. This study comprehensively analyzed the physiological and transcriptional responses of Chlorella sp. after being exposed to chromium (III) oxide nanoparticles (nCr 2 O 3 ). The nCr 2 O 3 at 0–100 mg/L presented adverse effects on cell growth (96 h EC 50  = 16.3 mg/L), decreasing the photosynthetic pigment concentrations and photosynthetic activity. Moreover, more extracellular polymeric substances (EPS), especially polysaccharides in soluble EPS, were produced in algae cell, which mitigated the damage of nCr 2 O 3 to cells. However, with the increase of nCr 2 O 3 doses, the EPS protective responses were exhausted, accompanied by toxicity in the form of organelle damage and metabolic disturbance. The enhanced acute toxicity was closely related to the physical contact of nCr 2 O 3 with cells, oxidative stress, and genotoxicity. Firstly, large amounts of nCr 2 O 3 aggregated around and were attached to cells, causing physical damage. Then, the intracellular reactive oxygen species and malondialdehyde levels were significantly increased that led to lipid peroxidation, especially at 50–100 mg/L nCr 2 O 3 . Finally, the transcriptomic analysis further revealed that the transcription of ribosome, glutamine, and thiamine metabolism-related genes were impaired under 20 mg/L nCr 2 O 3 , suggesting nCr 2 O 3 inhibited algal cell growth through metabolism, cell defense, and repair, etc. Graphical Abstract