Is the toxic potential of nanosilver dependent on its size? (Particle and Fibre Toxicology)

Background: Nanosilver is one of the most commonly used engineered nanomaterials (ENMs). In our study we focused on assessing the size-dependence of the toxicity of nanosilver (Ag ENMs), utilising particles of three sizes (50, 80 and 200?nm) synthesized by the same method, with the same chemical composition, charge and coating. Methods: Uptake and localisation (by Transmission Electron Microscopy), cell proliferation (Relative growth activity) and cytotoxic effects (Plating efficiency), inflammatory response (induction of IL-8 and MCP-1 by Enzyme linked immune sorbent assay), DNA damage (strand breaks and oxidised DNA lesions by the Comet assay) were all assessed in human lung carcinoma epithelial cells (A549), and the mutagenic potential of ENMs (Mammalian hprt gene mutation test) was assessed in V79-4 cells as per the OECD protocol. Detailed physico-chemical characterization of the ENMs was performed in water and in biological media as a prerequisite to assessment of their impacts on cells. To study the relationship between the surface area of the ENMs and the number of ENMs with the biological response observed, Ag ENMs concentrations were recalculated from ?g/cm2 to ENMs cm2/cm2 and ENMs/cm2. Results: Studied Ag ENMs are cytotoxic and cytostatic, and induced strand breaks, DNA oxidation, inflammation and gene mutations. Results expressed in mass unit [?g/cm2] suggested that the toxicity of Ag ENMs is size dependent with 50?nm being most toxic. However, re-calculation of Ag ENMs concentrations from mass unit to surface area and number of ENMs per cm2 highlighted that 200?nm Ag ENMs, are the most toxic. Results from hprt gene mutation assay showed that Ag ENMs 200?nm are the most mutagenic irrespective of the concentration unit expressed. Conclusion: We found that the toxicity of Ag ENMs is not always size dependent. Strong cytotoxic and genotoxic effects were observed in cells exposed to Ag ENMs 50?nm, but Ag ENMs 200?nm had the most mutagenic potential. Additionally, we showed that expression of concentrations of ENMs in mass units is not representative. Number of ENMs or surface area of ENMs (per cm2) seem more precise units with which to compare the toxicity of different ENMs.