title: Gene transcription patterns and energy reserves in Daphnia magna show no nanoparticle specific toxicity when exposed to ZnO and CuO nanoparticles.
abstract: There is still a lot of contradiction on whether metal ions are solely responsible for the observed toxicity of ZnO and CuO nanoparticles to aquatic species. While most experiments have studied nanoparticle effects at organismal levels (e.g. mortality, reproduction), effects at lower levels of biological organization may clarify the role of metal ions, nanoparticles and nanoparticle aggregates. In this study, the effect of ZnO and CuO nanoparticles was tested at two lower levels: energy reserves and gene transcription and compared with zinc and copper salts. Daphnia magna was exposed during 96h to 10% immobilization concentrations of all chemicals, after which daphnids were sampled for determination of glycogen, lipid and protein concentration and for a differential gene transcription analysis using microarray. The dissolved, nanoparticle and aggregated fraction in the medium was characterized. The results showed that ZnO nanoparticles had largely dissolved directly after addition to the test medium. The CuO nanoparticles mostly formed aggregates, while only a small fraction dissolved. The exposure to zinc (both nano and metal salt) had no effect on the available energy reserves. However, in the copper exposure, the glycogen, lipid and protein concentration in the exposed daphnids was lower than in the unexposed ones. When comparing the nanoparticle (ZnO or CuO) exposed daphnids to the metal salt (zinc or copper salt) exposed daphnids, the microarray results showed no significantly differentially transcribed gene fragments. The results indicate that under the current exposure conditions the toxicity of ZnO and CuO nanoparticles to D. magna is solely caused by toxic metal ions.
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium. Electronic address: nathalieadam12@gmail.com.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Adam
authors.affiliation: Zebrafishlab, Physiology and Biochemistry of Domestic Animals, Department of Veterinary Sciences, University of Antwerp. Universiteitslaan 1, 2610 Wilrijk, Belgium. Electronic address: lucia.vergauwen@uantwerpen.be.
authors.forename: Lucia
authors.initials: L
authors.lastname: Vergauwen
authors.affiliation: Systemic Physiological and Ecotoxicological Research, Department of Biology, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerpen, Belgium. Electronic address: ronny.blust@uantwerpen.be.
authors.forename: Ronny
authors.initials: R
authors.lastname: Blust
authors.affiliation: Zebrafishlab, Physiology and Biochemistry of Domestic Animals, Department of Veterinary Sciences, University of Antwerp. Universiteitslaan 1, 2610 Wilrijk, Belgium. Electronic address: dries.knapen@uantwerpen.be.
authors.forename: Dries
authors.initials: D
authors.lastname: Knapen
mesh_terms: D000818:Animals; D002712:Chlorides / Q000633:toxicity; D003300:Copper / Q000633:toxicity*; D003621:Daphnia / Q000187:drug effects*; D053768:Metal Nanoparticles / Q000633:toxicity*; D014158:Transcription, Genetic / Q000187:drug effects*; D014874:Water Pollutants, Chemical / Q000633:toxicity*; D017967:Zinc Compounds / Q000633:toxicity; D015034:Zinc Oxide / Q000633:toxicity*
chemical_list: D002712:Chlorides; D014874:Water Pollutants, Chemical; D017967:Zinc Compounds; D003300:Copper; C016837:zinc chloride; C029892:cupric chloride; D015034:Zinc Oxide; C030973:cupric oxide
keywords: Aquatic; Caloric content; Differential gene transcription; Metal; Microarray