J. Catalán, H.K. Lindberg, K.J. Aimonen, H. Wolff, I. Wedin, M. Nuopponen, K.M. Savolainen, H. Norppa
Finnish Institute of Occupational Health,
Keywords: nanotoxicology, genotoxicity, inhalation, nanofibrillated cellulose
Summary:Nanofibrillar cellulose (NFC) is among the most promising innovations in the forest industry. Due to its unique properties, NFC has a wide variety of possible applica-tions. As NFC consists of thin and long fibres with a high aspect ratio and high specific surface area, it is important to investigate the safety of NFC at an early stage of product development. The objective of the present study was to examine the potential genotoxicity of four NFC materials (in gel form; fibril diameter 2-15 nm, length several µm) in comparison with a bulk-sized cellulose material. Multiwalled carbon nanotubes (MWCNTs) served as a comparative fibrous nanomaterial. In vitro genotoxicity was assessed in human bronchial epithelial (BEAS 2B) cells by the single-cell gel elec¬trophoresis (comet) assay (24-h exposure, 9.5-950 µg/ml) to detect DNA strand break¬age and by the cytokinesis-block micronucleus (MN) assay (48-h exposure, 25-1250 µg/ml) to show possible chromosomal damage. For genotoxicity assessment in vivo, the comet assay was performed on lung cells and bronchoalveolar lavage (BAL) fluid cells and the MN assay on bone marrow polychromatic erythrocytes, after single pha¬ryngeal aspiration to female C57BL/6 mice (24-h and 28-d follow up; 10, 40, 80 and 200 µg/mouse). The NFC materials tested did not induce significant DNA strand break¬age or micronuclei in vitro. However, all NFC materials, except one, caused DNA dam¬age in mouse lung or BAL cells, as determined by the comet assay. For one NFC, the effect was dose-dependent in lung cells both 24 h and 28 days after the exposure. The comparative materials, bulk-sized pulp and MWCNTs, were also able to induce DNA damage after 24 h and 28 days. None of the NFCs or comparative materials showed systemic genotoxic properties, as measured by the micronucleus assay in bone mar¬row. The outcome of the in vivo studies was not predicted by the in vitro tests, as none of the NFCs or the bulk-sized pulp were genotoxic in vitro. This suggested that the mechanisms responsible for the effects observed in vivo were not present in the in vitro cell system used. All materials studied were biopersistent in the lungs for at least 28 days, which raises some concern, particularly as there was some increase in DNA damage still at this time point. A longer follow-up would be required to better define the fate of the NFC material in the lungs and the duration of the increased level of DNA damage. The respiratory exposure route used in the present study was chosen to mimic a tentative worst-case-scenario in NFC manufacture, where nanocellulose in liquid may be aerosolized in the atmosphere and inhaled by workers. It is unclear how realistic this kind of exposure could be in up-scaled production of NFC. [Supported by UPM Kymmene Oyj, Stora Enso Oyj, the Finnish Safety and Chemicals Agency, and the European Commission, NANoREG 310584].