title: Toxicity of nano-TiO2 on algae and the site of reactive oxygen species production.
abstract: Given the extensive use of nanomaterials, they may enter aquatic environments and harm the growth of algae, which are primary producers in an aquatic ecosystem. Thus, the balance of an aquatic ecosystem may be destroyed. In this study, Karenia brevis and Skeletonema costatum were exposed to nano-TiO2 (anatase, average particle size of 5-10 nm, specific surface area of 210±10 m(2) g(-1)) to assess the effects of nano-TiO2 on algae. The findings of transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) and scanning electron microscopy (SEM) demonstrate aggregation of nano-TiO2 in the algal suspension. Nano-TiO2 was also found to be inside algal cells. The growth of the two species of algae was inhibited under nano-TiO2 exposure. The 72 h EC50 values of nano-TiO2 to K. brevis and S. costatum were 10.69 and 7.37 mg L(-1), respectively. TEM showed that the cell membrane of K. brevis was destroyed and its organelles were almost undistinguished under nano-TiO2 exposure. The malondialdehyde (MDA) contents of K. brevis and S. costatum significantly increased compared with those of the control (p<0.05). Meanwhile, superoxide dismutase (SOD) and catalase activities (CAT) of K. brevis and S. costatum changed in different ways. The reactive oxygen species (ROS) levels in both species were significantly higher than those of the control (p<0.05). The site of ROS production and accumulation in K. brevis and S. costatum under nano-TiO2 exposure was explored with the addition of inhibitors of different electron transfer chains. This study indicated that nano-TiO2 in algal suspensions inhibited the growth of K. brevis and S. costatum. This effect was attributed to oxidative stress caused by ROS production inside algal cells. The levels of anti-oxidative enzymes changed, which destroyed the balance between oxidation and anti-oxidation. Thus, algae were damaged by ROS accumulation, resulting in lipid oxidation and inhibited algae growth. The inhibitors of the electron transfer chain showed that the site of ROS production and accumulation in K. brevis cells was the chloroplast.
authors.affiliation: Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, College of Environmental Science and Technology, Ocean University of China, Qingdao 266100, PR China. Electronic address: lifengmin@ouc.edu.cn.
authors.forename: Fengmin
authors.initials: F
authors.lastname: Li
authors.affiliation: Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, College of Environmental Science and Technology, Ocean University of China, Qingdao 266100, PR China.
authors.forename: Zhi
authors.initials: Z
authors.lastname: Liang
authors.affiliation: School of Environment and Natural Resources, Renmin University of China, Beijing 100872, China. Electronic address: zhengxiang7825@sina.com.
authors.forename: Xiang
authors.initials: X
authors.lastname: Zheng
authors.affiliation: Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, College of Environmental Science and Technology, Ocean University of China, Qingdao 266100, PR China.
authors.forename: Wei
authors.initials: W
authors.lastname: Zhao
authors.affiliation: Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, College of Environmental Science and Technology, Ocean University of China, Qingdao 266100, PR China.
authors.forename: Miao
authors.initials: M
authors.lastname: Wu
authors.affiliation: Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, College of Environmental Science and Technology, Ocean University of China, Qingdao 266100, PR China.
authors.forename: Zhenyu
authors.initials: Z
authors.lastname: Wang
mesh_terms: D002462:Cell Membrane / Q000187:drug effects; D017377:Diatoms / Q000187:drug effects* / Q000254:growth & development; D004141:Dinoflagellida / Q000187:drug effects* / Q000254:growth & development; D004789:Enzyme Activation / Q000187:drug effects; D020128:Inhibitory Concentration 50; D008315:Malondialdehyde / Q000378:metabolism; D053768:Metal Nanoparticles / Q000633:toxicity*; D015388:Organelles / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism; D014025:Titanium / Q000633:toxicity*; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D017382:Reactive Oxygen Species; D014874:Water Pollutants, Chemical; C009495:titanium dioxide; D008315:Malondialdehyde; D014025:Titanium; D013482:Superoxide Dismutase
keywords: Algae; Nano; Oxidative stress; ROS; Titanium dioxide