Synergistic Effects of Nano-Sized Titanium Dioxide and Zinc on the Photosynthetic Capacity and Survival of Anabaena sp.

摘要

Anabaena sp. was used to examine the toxicity of exposure to a nano-TiO2 suspension, Zn²⁺ solution, and mixtures of nano-TiO2 and Zn²⁺ suspensions. Typical chlorophyll fluorescence parameters, including effective quantum yield, photosynthetic efficiency and maximal electron transport rate, were measured by a pulse-amplitude modulated fluorometer. Nano-TiO2 particles exhibited no significant toxicity at concentrations lower than 10.0 mg/L. The 96 h concentration for the 50% maximal effect (EC50) of Zn²⁺ alone to Anabaena sp. was 0.38 ± 0.004 mg/L. The presence of nano-TiO2 at low concentrations (<1.0 mg/L) significantly enhanced the toxicity of Zn²⁺ and consequently reduced the EC50 value to 0.29 ± 0.003 mg/L. However, the toxicity of the Zn²⁺/TiO2 system decreased with increasing nano-TiO2 concentration because of the substantial adsorption of Zn²⁺ by nano-TiO2. The toxicity curve of the Zn²⁺/TiO2 system as a function of incremental nano-TiO2 concentrations was parabolic. The toxicity significantly increased at the initial stage, reached its maximum, and then decreased with increasing nano-TiO2 concentration. Hydrodynamic sizes, concentration of nano-TiO2 and Zn²⁺ loaded nano-TiO2 were the main parameters for synergistic toxicity.