Acute Toxicity Tests of TEMPO-oxidized Cellulose Nanofiber Using Daphnia magna and Oryzias latipes

Abstract

Abstract Ecotoxicity data on cellulose nanofibers (CNFs) is limited despite their wide application prospects. Herein, acute toxicity tests of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized CNF to Daphnia magna and Oryzias latipes were conducted according to the Organisation for Economic Co-operation and Development (OECD) test guidelines taking the CNF dispersibility during the test into account. To select a suitable test medium, the interaction between the medium components and CNF was first evaluated using five test media with different ion concentrations. The viscosity, zeta potential, and concentration uniformity of TEMPO-CNF changed with increasing ionic concentration. The toxicity test results showed no acute toxicity of TEMPO-CNF to the two species, even at the highest exposure concentrations in this study. Both the median effective concentration (EC50) and median lethal concentration (LC50) were > 100 mg/L. In most cases, the measured CNF concentrations were within 20% of the nominal concentrations and remained largely constant. However, in the D. magna acute toxicity test, the concentration uniformity of TEMPO-CNF tended to decrease when the CNF concentration was low. Our results demonstrate the importance of measuring CNF concentrations during testing. We also found that the ion concentrations in the test solution changed because of the interaction between the medium components and TEMPO-CNF. This finding demonstrates the importance of examining the components of the medium to avoid mistaking the effects of depletion of the medium components on aquatic organisms for the direct effects of TEMPO-CNF on aquatic organisms.