Acute toxicity tests of TEMPO-oxidized cellulose nanofiber using Daphnia magna and Oryzias latipes

Abstract

Ecotoxicity data on cellulose nanofibers (CNFs) are limited despite their wide application prospects. Herein, acute toxicity tests of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized CNFs to Daphnia magna and Oryzias latipes were conducted according to the Organisation for Economic Co-operation and Development test guidelines, which consider CNF dispersibility during the test. To select a suitable test medium, the interaction between the medium components and CNFs was first evaluated using five test media with different ion concentrations. The viscosity, zeta potential, and concentration uniformity of TEMPO-CNFs changed with increasing ionic concentration. The toxicity test results showed no acute toxicity of TEMPO-CNFs 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-CNFs tended to decrease when the CNF concentration was low. Our results demonstrate the importance of measuring CNF concentrations during testing and revealed that the ion concentrations in the test solution changed because of the interaction between the medium components and TEMPO-CNFs. This finding demonstrates the importance of examining the components of the medium to avoid mistaking the effects of depleted medium components for the direct effects of TEMPO-CNFs on aquatic organisms.