title: In vivo retention of ingested Au NPs by Daphnia magna: no evidence for trans-epithelial alimentary uptake.
abstract: In vivo studies with Daphnia magna remain inconclusive as to whether engineered nanoparticles (NPs) are internalized into tissues after ingestion. Here we used a three-pronged approach to study the in vivo retention and efflux kinetics of 20 nm citrate stabilized Au NPs ingested by this key aquatic species. Daphnids were exposed to suspended particles (600 μg L(-1)) for 5 h after which they were depurated for 24 h in clean water containing algae. Light microscopy was used to follow the passage of Au NPs through the gastrointestinal tract, Au body burdens were determined by ICP-MS (inductively coupled plasma mass spectrometry), and transmission electron microscopy (TEM) was used to examine the presence and distribution of Au NPs in tissues. Results revealed that the elimination of Au NPs was bi-phasic. The fast elimination phase lasted<1h and the rate constant at which Au (of Au NPs) was eliminated was 1.12 ± 0.34 h(-1) (±SE) which accounted for ∼75% of the ingested Au. The remaining ∼25% of the ingested Au NPs was eliminated at a 100-fold slower rate. TEM analysis revealed that Au NPs in the midgut were in close proximity to the peritrophic membrane after 1 and 24h of depuration. There were no observations of Au NP uptake at the microvilli. Thus, although Au NPs were retained in the gut lumen, there was no observable internalization into the gut epithelial cells. Similar to carbon nanotubes and CuO NPs, our findings indicate that in daphnids the in vivo retention of Au NPs does not necessarily result in their internalization.
authors.affiliation: Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, England, United Kingdom. Electronic address: frkhan@ruc.dk.
authors.forename: Farhan R
authors.initials: FR
authors.lastname: Khan
authors.affiliation: Imaging and Analysis Centre, Natural History Museum, Cromwell Road, London SW7 5BD, England, United Kingdom.
authors.forename: Gabrielle M
authors.initials: GM
authors.lastname: Kennaway
authors.affiliation: U.S. Geological Survey, 345 Middlefield Road, MS 465, Menlo Park, CA 94025, United States.
authors.forename: Marie-Noële
authors.initials: MN
authors.lastname: Croteau
authors.affiliation: Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, England, United Kingdom.
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Dybowska
authors.affiliation: Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, England, United Kingdom.
authors.forename: Brian D
authors.initials: BD
authors.lastname: Smith
authors.affiliation: Department of Biology & CESAM, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal.
authors.forename: António J A
authors.initials: AJ
authors.lastname: Nogueira
authors.affiliation: Life Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, England, United Kingdom.
authors.forename: Philip S
authors.initials: PS
authors.lastname: Rainbow
authors.affiliation: U.S. Geological Survey, 345 Middlefield Road, MS 465, Menlo Park, CA 94025, United States; John Muir Institute of the Environment, University of California at Davis, Davis, CA, United States.
authors.forename: Samuel N
authors.initials: SN
authors.lastname: Luoma
authors.affiliation: Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, England, United Kingdom; School of Geography Earth & Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, England, United Kingdom.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Valsami-Jones
mesh_terms: D000818:Animals; D003621:Daphnia / Q000378:metabolism*; D004064:Digestive System / Q000378:metabolism; D004435:Eating; D004848:Epithelium / Q000378:metabolism; D006046:Gold / Q000737:chemistry* / Q000493:pharmacokinetics*; D007700:Kinetics; D053768:Metal Nanoparticles; D057705:Transendothelial and Transepithelial Migration
chemical_list: D006046:Gold
keywords: Depuration kinetics; Electron microscopy; Gold nanoparticles; Internalization