title: Assessing the effects of surface-bound humic acid on the phototoxicity of anatase and rutile TiO₂ nanoparticles in vitro.
abstract: In this study, the cytotoxicity of two different crystal phases of TiO2 nanoparticles, with surface modification by humic acid (HA), to Escherichia coli, was assessed. The physicochemical properties of TiO2 nanoparticles were thoroughly characterized. Three different initial concentrations, namely 50, 100, and 200 ppm, of HA were used for synthesis of HA coated TiO2 nanoparticles (denoted as A/RHA50, A/RHA100, and A/RHA200, respectively). Results indicate that rutile (LC50 (concentration that causes 50% mortality compared the control group)=6.5) was more toxic than anatase (LC50=278.8) under simulated sunlight (SSL) irradiation, possibly due to an extremely narrow band gap. It is noted that HA coating increased the toxicity of anatase, but decreased that of rutile. Additionally, AHA50 and RHA50 had the biggest differences compared to uncoated anatase and rutile with LC50 of 201.9 and 21.6, respectively. We then investigated the formation of reactive oxygen species (ROS) by TiO2 nanoparticles in terms of hydroxyl radicals (·OH) and superoxide anions (O2(·-)). Data suggested that O2(·-) was the main ROS that accounted for the higher toxicity of rutile upon SSL irradiation. We also observed that HA coating decreased the generation of ·OH and O2(·-) on rutile, but increased O2(·-) formation on anatase. Results from TEM analysis also indicated that HA coated rutile tended to be attached to the surface of E. coli more than anatase.
authors.affiliation: Department of Biology, Jackson State University, Jackson, MS, USA.
authors.forename: Xiaojia
authors.initials: X
authors.lastname: He
authors.affiliation: Department of Biological Sciences, Alcorn State University, Lorman, MS, USA.
authors.forename: Sabrieon
authors.initials: S
authors.lastname: Sanders
authors.affiliation: Environmental Science Ph.D. Program, Jackson State University, Jackson, MS, USA.
authors.forename: Winfred G
authors.initials: WG
authors.lastname: Aker
authors.affiliation: Department of Chemistry and Biochemistry, Jackson State University, Jackson, MS, USA.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Lin
authors.affiliation: School of Polymers and High Performance Materials, The University of Southern Mississippi, Hattiesburg, MS, USA.
authors.forename: Jessica
authors.initials: J
authors.lastname: Douglas
authors.affiliation: Department of Biology, Jackson State University, Jackson, MS, USA. Electronic address: hwang@jsums.edu.
authors.forename: Huey-Min
authors.initials: HM
authors.lastname: Hwang
mesh_terms: D004926:Escherichia coli / Q000187:drug effects; D006812:Humic Substances; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D017382:Reactive Oxygen Species; D014025:Titanium / Q000737:chemistry / Q000633:toxicity*
chemical_list: D006812:Humic Substances; D017382:Reactive Oxygen Species; C009495:titanium dioxide; D014025:Titanium
keywords: Crystallinity; Escherichia coli; Humic acid; Surface coating; TiO(2) nanoparticles