Effect of chromium oxide (III) nanoparticles on the production of reactive oxygen species and photosystem II activity in the green alga Chlamydomonas reinhardtii

With the growth of nanotechnology and widespread use of nanomaterials, there is an increasing risk of environmental contamination by nanomaterials. However, the potential implications of such environmental contamination are hard to evaluate since the toxicity of nanomaterials if often not well characterized. The objective of this study was to evaluate the toxicity of a chromium-based nanoparticle, Cr₂O₃-NP, used in a wide diversity of industrial processes and commercial products, on the unicellular green alga Chlamydomonas reinhardtii. The deleterious impacts of Cr₂O₃-NP were characterized using cell density measurements, production of reactive oxygen species (ROS), esterase enzymes activity, and photosystem II electron transport as indicators of toxicity. Cr₂O₃-NP exposure inhibited culture growth and significantly lowered cellular Chlorophyll a content. From cell density measurements, EC50 values of 2.05 ± 0.20 and 1.35 ± 0.06 g L⁻¹ Cr₂O₃-NP were obtained after 24 and 72 h of exposure, respectively. In addition, ROS levels were increased to 160.24 ± 2.47% and 59.91 ± 0.15% of the control value after 24 and 72 h of exposition to 10 g L⁻¹ Cr₂O₃-NP. At 24 h of exposure, the esterase activity increased to 160.24% of control value, revealing a modification of the short-term metabolic response of algae to Cr₂O₃-NP exposure. In conclusion, the metabolism of C. reinhardtii was the most sensitive to Cr₂O₃-NP after 24 h of treatment. - Highlights: • Cr₂O₃ nanoparticles are unstable and form large aggregates in the medium. • EC50 for growth inhibition of C. reinhardtii is 1.35 g L⁻¹ at 72 h. • Cr₂O₃ nanoparticles increase ROS levels at 10 g L⁻¹. • Cr₂O₃ nanoparticles affect photosynthetic electron transport.