Synergistic toxic effect of nano-TiO2 and As(V) on Ceriodaphnia dubia

Due to the active development and application of nanotechnology, engineered nanomaterials (ENMs) are becoming a new class of environmental pollutants that may significantly impact the environment and human health. While many toxicity investigations have been conducted, there is little information about the synergistic effect of ENMs and other toxic compounds in the environment. In order to extend this knowledge, the combined effect of TiO2 nanoparticles (n-TiO2) and As(V) were investigated. High concentrations of As(V) can accumulate on the n-TiO2 surface. Cultured Ceriodaphnia dubia (C. dubia) species were used to examine the synergistic toxic effect through exposure to 1) n-TiO2 suspensions, 2) As(V) solutions, and 3) mixtures of n-TiO2 and As(V) suspensions. Results showed that n-TiO2 alone was not toxic when the concentration was less than 400 mg/L and that the 24-hour median lethal concentration (LC50) of As(V) alone was 3.68 ± 0.22 mg/L. However, in the presence of low concentrations of n-TiO2, the toxicity of As(V) increased significantly. At the same initial As(V) concentration, the toxicity of n-TiO2 first increased, reached a maximum, and then decreased with an increase in n-TiO2 concentration. Hydrodynamic size and sorption capacity were most important parameters for toxicity.

Research highlights
► Nano-TiO2 alone is not toxic to C. Dubia at concentrations less than 400 mg/L.
► As(V) toxicity is enhanced by a low, “safe dose” of nano-TiO2.
► Further increasing nano-TiO2 concentration reduces As(V) toxicity.
► The adsorption of As(V) plays an important role on enhancing/decreasing As(V) toxicity.