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

Anabaena sp. was used to examine the toxicity of exposure to a nano-TiO(2) suspension, Zn(2+) solution, and mixtures of nano-TiO(2) and Zn(2+) 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-TiO(2) particles exhibited no significant toxicity at concentrations lower than 10.0 mg/L. The 96 h concentration for the 50% maximal effect (EC(50)) of Zn(2+) alone to Anabaena sp. was 0.38 ± 0.004 mg/L. The presence of nano-TiO(2) at low concentrations (<1.0 mg/L) significantly enhanced the toxicity of Zn(2+) and consequently reduced the EC(50) value to 0.29 ± 0.003 mg/L. However, the toxicity of the Zn(2+)/TiO(2) system decreased with increasing nano-TiO(2) concentration because of the substantial adsorption of Zn(2+) by nano-TiO(2). The toxicity curve of the Zn(2+)/TiO(2) system as a function of incremental nano-TiO(2) concentrations was parabolic. The toxicity significantly increased at the initial stage, reached its maximum, and then decreased with increasing nano-TiO(2) concentration. Hydrodynamic sizes, concentration of nano-TiO(2) and Zn(2+) loaded nano-TiO(2) were the main parameters for synergistic toxicity.