Table 1.
Summary of currently available nanoparticle size-related toxicity data for selected (eco)toxicological test organisms.
Figure 1.
Electron microscopy images and UV-Vis absorption spectra of the studied citrate-stabilised Ag nanoparticles.
A: TEM photos of the particles; B: SEM photos with EDX mapping; C: UV-Vis absorption spectra (Ag-10 nm 8 mg/L, Ag-20 nm 11 mg/L, Ag-40 nm, Ag-60 nm and Ag-80 nm 5 mg/L in ultrapure (UP) water. Maximum absorption is indicated with a vertical dotted line; wide absorption spectrum indicates polydispersity of the sample.
Figure 2.
Sedimentation of Ag NPs in ultrapure water and in artificial freshwater during 60
Concentrations of Ag NPs were: Ag-10 nm 8 mg/L, Ag-20 nm 11 mg/L, Ag-40 nm, Ag-60 nm and Ag-80 nm 5 mg/L. Decreased absorption of light (420 nm) by Ag particles in artificial freshwater (test medium for D. magna) (dotted line) is due to settling over time. In ultrapure water (solid line) no decrease in absorption was observed.
Table 2.
Physico-chemical characteristics of the studied citrate-stabilised Ag nanoparticles.
Figure 3.
Dissolution (%) of Ag NPs in different test media.
Ultrapure water was used as a solvent to mimic the dissolution in the bacterial and yeast assays, OECD 202 artificial freshwater was used for Daphnia magna assay, algal test medium for Pseudokirchneriella subcapitata and cell culture medium for Balb/3T3 murine fibroblast assay. Dissolved ionic Ag was measured after incubation of 1 mg/L Ag NPs or 0.01 mg/L AgNO3 for 4 hours (ultrapure water), 24 hours (cell culture medium), 48 hours (artificial freshwater) or 72 hours (algal medium), depending on the length of the toxicity assay. The results shown were measured from Ag NPs suspensions and AgNO3 solution after ultracentrifugation. These results were confirmed by single particle (SP)-ICP-MS according to which 1.4% of 10 nm Ag NPs, 1% of 20 nm Ag NPs and 0.5% of 10 nm Ag NPs had been dissolved in ultrapure water.
Table 3.
Nominal, dissolution- and bioavailability-corrected EC50 values (mg Ag/L) of different sized Ag NPs and ionic AgNO3 for various test organisms.
Figure 4.
Dose-response curves and the respective EC50 values of Ag formulations to test organisms and cells.
Upper panel (A–D): dose-response curves; lower panel (E–H): EC50 values. X-axis shows nominal Ag concentrations. * - significantly (p<0.05) different from EC50 value of AgNO3.
Figure 5.
Dissolution-corrected EC50 values of 10–80 nm Ag NPs and AgNO3.
EC50 values presented in Figure 4 (lower panel) were normalized for dissolved Ag (for dissolution, see Figure 3). * - significantly (p<0.05) different from EC50 of AgNO3.
Figure 6.
Response of E. coli sensor to subtoxic concentrations of Ag formulations and bioavailability-corrected EC50 values.
(A) Induction of bioluminescence in Ag-inducible E.coli bioreporter strain by AgNO3 and 10–80 nm Ag NPs. Concentration of different Ag formulations at 2-fold induction is shown; (B) 4-h EC50 of AgNO3 and Ag NPs, corrected for dissolved Ag (see Figure 3) or bioavailable Ag, calculated from bioluminescence induction of Ag bioreporter strain (see panel A).