Bioaccumulation and depuration of TiO nanoparticles by zebrafish through dietary exposure: Size- and number concentration-resolved analysis using single-particle ICP-MS.

The bioaccumulation and depuration of TiO nanoparticles (TiONPs) by zebrafish via the dietary exposure following the OECD Test Guideline 305 (OECD TG305) was evaluated using particle size- and number concentration-resolved analysis based on single-particle ICP-MS (spICP-MS). We found that using enzymatic digestion without HO or excessive heating can recover 84.0 ± 4.0% and 94.5 ± 3.5% of TiONP mass and number concentrations from fish tissue, respectively, without altering the size distribution of parent TiONPs. OECD TG305 can allow for the evaluation of bioaccumulation and depuration of TiONPs by fish based on the particle mass and number dose metrics. The toxicokinetic modeling can reasonably describe the mass- and number-based measurement data with the derived absorption efficiency α at ~0.2, depuration rate at ~0.5 d, and kinetic biomagnification factor (BMF) at ~0.007 comparable with available data. The mass concentration- and number concentration-based bioaccumulation metrics including body burdens are correlated for TiONPs that remained nano-sized in vivo and exhibited marginal physicochemical alterations upon uptake by fish. The result indicates that the traditional mass concentration metric may be used to represent the fish bioaccumulation potential for chemically inert NPs like TiO.