Toxicity of Ag, CuO and ZnO nanoparticles to selected environmentally relevant test organisms and mammalian cells in vitro: a critical review

Abstract

Nanoparticles (NPs) of copper oxide (CuO), zinc oxide (ZnO) and especially nanosilver are intentionally used to fight the undesirable growth of bacteria, fungi and algae. Release of these NPs from consumer and household products into waste streams and further into the environment may, however, pose threat to the 'non-target' organisms, such as natural microbes and aquatic organisms. This review summarizes the recent research on (eco)toxicity of silver (Ag), CuO and ZnO NPs. Organism-wise it focuses on key test species used for the analysis of ecotoxicological hazard. For comparison, the toxic effects of studied NPs toward mammalian cells in vitro were addressed. Altogether 317 L(E)C50 or minimal inhibitory concentrations (MIC) values were obtained for algae, crustaceans, fish, bacteria, yeast, nematodes, protozoa and mammalian cell lines. As a rule, crustaceans, algae and fish proved most sensitive to the studied NPs. The median L(E)C50 values of Ag NPs, CuO NPs and ZnO NPs (mg/L) were 0.01, 2.1 and 2.3 for crustaceans; 0.36, 2.8 and 0.08 for algae; and 1.36, 100 and 3.0 for fish, respectively. Surprisingly, the NPs were less toxic to bacteria than to aquatic organisms: the median MIC values for bacteria were 7.1, 200 and 500 mg/L for Ag, CuO and ZnO NPs, respectively. In comparison, the respective median L(E)C50 values for mammalian cells were 11.3, 25 and 43 mg/L. Thus, the toxic range of all the three metal-containing NPs to target- and non-target organisms overlaps, indicating that the leaching of biocidal NPs from consumer products should be addressed.

Figures

Fig. 1

Schematic representation of the scope of the current review

Fig. 2

a Annual production volumes of nanomaterials (data are adapted from Piccinno et al. 2012). b–d Fields of application of Ag (b), CuO (c) and ZnO (d) nanoparticles based on the publications indexed by Thomson Reuters ISI Web of Science. Search was done in March 2013. The following search terms were used: ‘silver’ OR ‘CuO’ OR ‘ZnO’ AND ‘nano*’ AND ‘application category’ (indicated in the figure). Numbers next to each application category indicate the number of articles retrieved and their respective percent share. The numerical data are presented in Supplementary Table S1

Fig. 3

a Labels of bulk CuO and nanosized CuO. Note the same CAS number. b 200 mg/L stock suspensions of CuO. c TEM image of nano CuO and bulk CuO. Note 43-fold difference in the SSAs of bulk CuO and nanosized CuO

Fig. 4

Uncoated Ag (50 mg/L), PVP-coated Ag (50 mg/L), uncoated CuO (50 mg/L) and ZnO NPs (200 mg/L) after 0, 2 and 24 h incubation in different (eco)toxicological test environments: 1 deionized water; 2 artificial freshwater for the tests with Daphnia sp. (OECD 202); 3 AFW for Thamnocephalus sp. (Thamnotoxkit F™ 1995); 4 algal growth medium (OECD 201); 5 protozoan mineral test medium (Osterhout’s); 6 yeast extract peptone dextrose medium; 7 bacterial M9 medium supplemented with 0.1 % glucose and 0.5 % amino acids; 8 bacterial LB medium containing tryptone and yeast extract. Detailed composition of test media is given in Käkinen et al. (2011)

Fig. 5

Number and share of individual L(E)C50 or MIC values used to derive the median L(E)C50 or MIC for nanoparticles (a) and metal salts (b). Total number of individual values: 317

Fig. 6

Toxicity of CuO, ZnO and Ag nanoparticles to different organisms. Median L(E)C50 values for all other organisms except bacteria and MIC for bacteria ± minimum and maximum values are presented. Different organisms/cells are shown by respective pictograms and the number on the pictogram indicates the number of L(E)C50 values used to derive the median value. Note the logarithmic scale of x-axis and that L(E)C50 and MIC values of NPs reflect nominal concentrations. The classification to hazard categories is explained in Table 1

Fig. 7

Plots of the median L(E)C50 values of Ag, CuO and ZnO NPs versus the median L(E)C50 values of the respective soluble metal salts to different organism groups. Data are plotted from Table 1

Fig. 8

Variation in individual L(E)C50 or MIC values used to derive the median L(E)C50 or MIC value for mammalian cells in vitro (a) and bacteria (b)

Fig. 9

L(E)C50 values of PVP-coated Ag NPs to mammalian cells versus size of nanoparticles. a All collected data were used; b data from one article (Liu et al. 2010) were used; c data from one article for one cell type were used (Liu et al. 2010)