title: Cytotoxicity of ZnO NPs towards fresh water algae Scenedesmus obliquus at low exposure concentrations in UV-C, visible and dark conditions.
abstract: Continuous increase in the usage of ZnO nanoparticles in commercial products has exacerbated the risk of release of these particles into the aquatic environment with possible harmful effects on the biota. In the current study, cytotoxic effects of two types of ZnO nanoparticles, having different initial effective diameters in filtered and sterilized lake water medium [487.5±2.55 nm for ZnO-1 NPs and 616.2±38.5 nm for ZnO-2 NPs] were evaluated towards a dominant freshwater algal isolate Scenedesmus obliquus in UV-C, visible and dark conditions at three exposure concentrations: 0.25, 0.5 and 1 mg/L. The toxic effects were found to be strongly dependent on the initial hydrodynamic particle size in the medium, the exposure concentrations and the irradiation conditions. The loss in viability, LDH release and ROS generation were significantly enhanced in the case of the smaller sized ZnO-1 NPs than in the case of ZnO-2 NPs under comparable test conditions. The toxicity of both types of ZnO NPs was considerably elevated under UV-C irradiation in comparison to that in dark and visible light conditions, the effects being more enhanced in case of ZnO-1 NPs. The size dependent dissolution of the ZnO NPs in the test medium and possible toxicity due to the released Zn(2+) ions was also noted. The surface adsorption of the nanoparticles was substantiated by scanning electron microscopy. The internalization/uptake of the NPs by the algal cells was confirmed by fluorescence microscopy, transmission electron microscopy, and elemental analyses.
authors.affiliation: Centre for Nanobiotechnology, VIT University, Vellore 632014, India.
authors.forename: M
authors.initials: M
authors.lastname: Bhuvaneshwari
authors.affiliation: Centre for Nanobiotechnology, VIT University, Vellore 632014, India.
authors.forename: V
authors.initials: V
authors.lastname: Iswarya
authors.affiliation: Department of Biotechnology, IIT Madras, India.
authors.forename: S
authors.initials: S
authors.lastname: Archanaa
authors.affiliation: Department of Chemical Engineering, M.S. Ramaiah Institute of Technology, Bangalore, India.
authors.forename: G M
authors.initials: GM
authors.lastname: Madhu
authors.affiliation: Department of Biotechnology, IIT Madras, India.
authors.forename: G K Suraish
authors.initials: GKS
authors.lastname: Kumar
authors.affiliation: Department of Chemical Engineering, IIT Madras, India.
authors.forename: R
authors.initials: R
authors.lastname: Nagarajan
authors.affiliation: Centre for Nanobiotechnology, VIT University, Vellore 632014, India.
authors.forename: N
authors.initials: N
authors.lastname: Chandrasekaran
authors.affiliation: Centre for Nanobiotechnology, VIT University, Vellore 632014, India. Electronic address: amit.mookerjea@gmail.com.
authors.forename: Amitava
authors.initials: A
authors.lastname: Mukherjee
mesh_terms: D004305:Dose-Response Relationship, Drug; D005618:Fresh Water; D008027:Light / Q000009:adverse effects*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D010316:Particle Size; D044444:Scenedesmus / Q000187:drug effects* / Q000528:radiation effects*; D014466:Ultraviolet Rays / Q000009:adverse effects*; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000633:toxicity*; D015034:Zinc Oxide / Q000737:chemistry / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; D015034:Zinc Oxide
keywords: Dissolution; Effective particle size; Exposure condition; Internalization; ROS; ZnO NPs