High bioconcentration of titanium dioxide nanoparticles in Daphnia magna determined by kinetic approach

摘要

The environmental risk assessments of titanium dioxide nanoparticles (TiO_2 NPs) have drawn wide attention and one of the required critical information is the bioconcentration potentials of these nanoparticles in aquatic organisms. In the present study, the bioconcentration of six commercially available TiO_2 NPs with different sizes and surface properties were quantified in a freshwater cladoceran Daphnia magna using kinetic modeling approach. We first calculated the uptake rate constant (k_u) and depuration rate constant (k_e) of TiO_2 NPs and then employed a first-order kinetic model to predict the bioconcentration factors (BCF) at different TiO_2 NPs concentrations. Both the k_u and k_e of TiO_2 NPs were significantly affected by the exposure concentration and the nano-particle property. The predicted BCF values in D. magna of six TiO_2 NPs ranged from 2.40 × 10~5 L/kg to 1.52 × 10~6 L/kg, and had no clear correlation with the exposure concentration. Large nominal size resulted in a lower BCF of TiO_2 NPs at lower exposure concentration. Higher hydrophobicity and Al(OH)_3 coating also resulted in a higher BCF. All the six TiO_2 NPs in this study were therefore considered very bioaccumulative. More attention should be paid to bioconcentration in the environmental risk assessments of TiO_2 NPs, and the physicochemical properties of TiO_2 NPs should be taken into account.