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Selenium nanoparticles (SeNPs) were first designed as nutritional supplements, but they are attractive also for use in diagnostic and therapeutic systems owing to their biocompatibility and protective effects. This study aimed to examine if different SeNPs stabilization strategies affect their (i) antimicrobial activity against bacteria Escherichia coli and Staphylococcus aureus and yeast Saccharomyces cerevisiae and (ii) toxicity to human cells of different biological barriers i.e., skin, oral and intestinal mucosa. For surface stabilization, polyvinylpyrrolidone (PVP), poly-L-lysine (PLL) and polyacrylic acid (PAA) were used rendering neutral, positively and negatively charged SeNPs, respectively. The SeNPs (primary size ~80 nm) showed toxic effects in human cells in vitro and in bacteria S. aureus, but not in E. coli and yeast S. cerevisiae. Toxicity of SeNPs (24 h IC 50 ) ranged from 1.4 to >100 mg Se/L, depending on surface functionalization (PLL > PAA > PVP) and was not caused by ionic Se. At subtoxic concentrations, all SeNPs were taken up by all human cell types, induced oxidative stress response and demonstrated genotoxicity. As the safety profile of SeNPs was dependent not only on target cells (mammalian cells, bacteria, yeast), but also on surface functionalization, these aspects should be considered during development of novel SeNPs-based biomedical products., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study, motivated to fill the knowledge gap on environmental safety of selenium nanoparticles (SeNPs), provides information on the stability and environmental safety of four differently coated SeNPs rendering both positive and negative surface charges. The stability and dissolution behaviour of SeNPs were determined in an aquatic model media of different ionic strength to provide information regarding the environmental fate of SeNPs in different environmental conditions. The environmental safety of SeNPs was evaluated by acute regulatory toxicity tests using Daphina magna and Vibrio fischeri as model organisms. Agglomeration was observed for all studied SeNPs in test media with higher ionic strength caused by the disruption of surface charge leading to electrostatic instability. Toxicity of SeNPs on both aquatic species was dose-dependent and increased with exposure time. The obtained data indicated that all of the tested SeNPs could be classified as harmful to the natural bacteria V. fischeri and harmful to toxic to crustaceans D. magna, but dependent on the coating agent used for SeNPs stabilization. Although SeNPs have attracted great interest for use in biomedicine, this study demonstrated that their ecotoxicological effects should be considered during the design of new of SeNPs-based products., Competing Interests: Declaration of competing interest The authors report no conflict of interests., (Copyright © 2020 Elsevier Ltd. All rights reserved.)