title: Nano-silver induces dose-response effects on the nematode Caenorhabditis elegans.
abstract: Toxicity of nano-formulated silver to eukaryotes was assessed by exposing nematodes (Caenorhabditis elegans) to two types of silver nanoparticles (AgNPs): with average primary particle diameters of 1 nm (AgNP1) and 28nm (AgNP28, PVP coated), respectively. Tests were performed with and without presence of Escherichia coli to evaluate how the presence of a food bacterium affects the AgNP toxicity. A pre-exposure experiment was also conducted with nematodes pre-exposed to 0 and 1mgAgNPL(-1), respectively, for 20 h prior to exposure at higher concentrations of AgNP. Both AgNP1 and AgNP28 showed adverse dose-response effects and mortality on C. elegans. LC(50) for AgNP28 was lower than for AgNP1 and, hence, at the present test conditions the PVP-coated AgNP28 was more toxic than AgNP1. Including E. coli in the test medium as a food source increased AgNPs toxicity towards nematodes compared to when bacteria were not present. Pre-exposure to a low-level AgNP1 concentration made the nematodes slightly more sensitive to further exposure at higher concentrations compared to no pre-exposure, indicating that nematodes have no efficient physiological ability to counteract nano-silver toxicity by acclimation. The amount of dissolved Ag(+) was 0.18 to 0.21 mg L(-1) after 20 h at the highest AgNP1 (10 mg L(-1)) and AgNP28 (3 mg L(-1)) doses in the exposure medium, respectively. The upper limit of Ag(+) solubility cannot immediately explain the dose-response-related toxic effects of the AgNP nor the difference between AgNP1 and AgNP28. Higher toxicity of AgNP28 than AgNP1 may be explained by a combination of effects of coating, Ag-solubility and higher uptake rates due to agglomeration into μm-size agglomerates in the exposure medium.
authors.affiliation: Department of Biology, Copenhagen University, Øster Farimagsgade 2D, DK-1353 Copenhagen K, Denmark.
authors.forename: Lea
authors.initials: L
authors.lastname: Ellegaard-Jensen
authors.forename: Keld Alstrup
authors.initials: KA
authors.lastname: Jensen
authors.forename: Anders
authors.initials: A
authors.lastname: Johansen
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000502:physiology; D015386:Hazardous Substances / Q000633:toxicity*; D053768:Metal Nanoparticles / Q000633:toxicity*; D012834:Silver / Q000378:metabolism / Q000633:toxicity*
chemical_list: D015386:Hazardous Substances; D012834:Silver