title: Size matters--The phototoxicity of TiO2 nanomaterials.
abstract: Under solar radiation several titanium dioxide nanoparticles (nano-TiO2) are known to be phototoxic for daphnids. We investigated the influence of primary particle size (10, 25, and 220 nm) and ionic strength (IS) of the test medium on the acute phototoxicity of anatase TiO2 particles to Daphnia magna. The intermediate sized particles (25 nm) showed the highest phototoxicity followed by the 10 nm and 220 nm sized particles (median effective concentrations (EC50): 0.53, 1.28, 3.88 mg/L). Photoactivity was specified by differentiating free OH radicals (therephthalic acid method) and on the other hand surface adsorbed, as well as free OH, electron holes, and O2(-) (electron paramagnetic resonance spectroscopy, EPR). We show that the formation of free OH radicals increased with a decrease in primary particle size (terephthalic acid method), whereas the total measured ROS content was highest at an intermediate particle size of 25 nm, which consequently revealed the highest photoxicity. The photoactivities of the 10 and 220 nm particles as measured by EPR were comparable. We suggest that phototoxicity depends additionally on the particle-daphnia interaction area, which explains the higher photoxicity of the 10 nm particles compared to the 220 nm particles. Thus, phototoxicity is a function of the generation of different ROS and the particle-daphnia interaction area, both depending on particle size. Phototoxicity of the 10 nm and 25 nm sized nanoparticles decreased as IS of the test medium increased (EC50: 2.9 and 1.1 mg/L). In conformity with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory we suggest that the precipitation of nano-TiO2 was more pronounced in high than in low IS medium, causing a lower phototoxicity. In summary, primary particle size and IS of the medium were identified as factors influencing phototoxicity of anatase nano-TiO2 to D. magna.
authors.affiliation: Department of Environmental Biology and Chemodynamics, Institute for Environmental Research, RWTH-Aachen University, Worringerweg 1, 52074 Aachen, Germany. Electronic address: anne.wyrwoll@rwth-aachen.de.
authors.forename: Anne J
authors.initials: AJ
authors.lastname: Wyrwoll
authors.affiliation: Department of Environmental Biology and Chemodynamics, Institute for Environmental Research, RWTH-Aachen University, Worringerweg 1, 52074 Aachen, Germany. Electronic address: Petra.Lautenschlaeger@rwth-aachen.de.
authors.forename: Petra
authors.initials: P
authors.lastname: Lautenschläger
authors.affiliation: Department of Environmental Biology and Chemodynamics, Institute for Environmental Research, RWTH-Aachen University, Worringerweg 1, 52074 Aachen, Germany. Electronic address: Alexander.Bach@rwth-aachen.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Bach
authors.affiliation: Institute for Energy and Environmental Technology e.V., Bliersheimer Str. 58-60, 47229 Duisburg, Germany. Electronic address: Hellack@iuta.de.
authors.forename: Bryan
authors.initials: B
authors.lastname: Hellack
authors.affiliation: Natural History Museum London, Cromwell Road, SW7 5BD London, UK. Electronic address: A.Dybowska@nhm.ac.uk.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Dybowska
authors.affiliation: Institute for Energy and Environmental Technology e.V., Bliersheimer Str. 58-60, 47229 Duisburg, Germany. Electronic address: tky@iuta.de.
authors.forename: Thomas A J
authors.initials: TA
authors.lastname: Kuhlbusch
authors.affiliation: Department of Ecosystem Analysis, Institute for Environmental Research, RWTH-Aachen University, Worringerweg 1, 52074 Aachen, Germany; College of Resources and Environmental Science, Chongqing University, 1 Tiansheng Road, Beibei, Chongqing 400715, China; College of Environmental Science and Engineering and State Key Laboratory of Pollution Control and Resource Reuse, Tongji University, 1239 Siping Road, Shanghai, China; State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, China. Electronic address: Henner.Hollert@bio5.rwth-aachen.de.
authors.forename: Henner
authors.initials: H
authors.lastname: Hollert
authors.affiliation: Department of Environmental Biology and Chemodynamics, Institute for Environmental Research, RWTH-Aachen University, Worringerweg 1, 52074 Aachen, Germany; College of Resources and Environmental Science, Chongqing University, 1 Tiansheng Road, Beibei, Chongqing 400715, China; State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, China. Electronic address: Andreas.Schaeffer@bio5.rwth-aachen.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schäffer
authors.affiliation: Department of Environmental Biology and Chemodynamics, Institute for Environmental Research, RWTH-Aachen University, Worringerweg 1, 52074 Aachen, Germany. Electronic address: Hanna.Maes@bio5.rwth-aachen.de.
authors.forename: Hanna M
authors.initials: HM
authors.lastname: Maes
mesh_terms: D000818:Animals; D003621:Daphnia; D053758:Nanoparticles / Q000032:analysis / Q000633:toxicity*; D010316:Particle Size; D014025:Titanium / Q000032:analysis / Q000633:toxicity*
chemical_list: C009495:titanium dioxide; D014025:Titanium
keywords: Daphnia magna; Phototoxicity; Reactive oxygen species; Solar radiation; TiO(2) nanoparticles