title: Submicron and nano formulations of titanium dioxide and zinc oxide stimulate unique cellular toxicological responses in the green microalga Chlamydomonas reinhardtii.
abstract: The work investigates the eco-cytoxicity of submicron and nano TiO₂ and ZnO, arising from the unique interactions of freshwater microalga Chlamydomonas reinhardtii to soluble and undissolved components of the metal oxides. In a freshwater medium, submicron and nano TiO₂ exist as suspended aggregates with no-observable leaching. Submicron and nano ZnO undergo comparable concentration-dependent fractional leaching, and exist as dissolved zinc and aggregates of undissolved ZnO. Cellular internalisation of solid TiO₂ stimulates cellular ROS generation as an early stress response. The cellular redox imbalance was observed for both submicron and nano TiO₂ exposure, despite exhibiting benign effects on the alga proliferation (8-day EC50>100 mg TiO₂/L). Parallel exposure of C. reinhardtii to submicron and nano ZnO saw cellular uptake of both the leached zinc and solid ZnO and resulting in inhibition of the alga growth (8-day EC50≥0.01 mg ZnO/L). Despite the sensitivity, no zinc-induced cellular ROS generation was detected, even at 100 mg ZnO/L exposure. Taken together, the observations confront the generally accepted paradigm of cellular oxidative stress-mediated cytotoxicity of particles. The knowledge of speciation of particles and the corresponding stimulation of unique cellular responses and cytotoxicity is vital for assessment of the environmental implications of these materials.
authors.affiliation: ARC Centre of Excellence for Functional Nanomaterials, School of Chemical Engineering, The University of New South Wales, Sydney, NSW, Australia. c.gunawan@unsw.edu.au
authors.forename: Cindy
authors.initials: C
authors.lastname: Gunawan
authors.forename: Aunchisa
authors.initials: A
authors.lastname: Sirimanoonphan
authors.forename: Wey Yang
authors.initials: WY
authors.lastname: Teoh
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Marquis
authors.forename: Rose
authors.initials: R
authors.lastname: Amal
mesh_terms: D016825:Chlamydomonas reinhardtii / Q000187:drug effects* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D017753:Ecosystem; D005618:Fresh Water; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D008856:Microscopy, Fluorescence; D036103:Nanotechnology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010316:Particle Size; D017382:Reactive Oxygen Species; D013997:Time Factors; D014025:Titanium / Q000737:chemistry / Q000633:toxicity*; D018675:Toxicity Tests; D014874:Water Pollutants, Chemical / Q000633:toxicity; D015034:Zinc Oxide / Q000737:chemistry / Q000633:toxicity*
chemical_list: D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; C009495:titanium dioxide; D014025:Titanium; D015034:Zinc Oxide
keywords: Nanoparticles; Reactive oxygen species; Speciation; Submicron particles; Toxicity