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Abstract
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.
Highlights
Heavy metals are discharged into aquatic ecosystems from various industries, such as the textile, mining, electroplating, and metallurgical industries
The objective of this study is to determine the synergistic toxicity of nano-TiO2 and Zn2+ on Anabaena sp. using a pulse-amplitude modulated (PAM) fluorometer, a rapid and efficient tool for in vivo studies of photosynthetic activity
As shown in the dynamic light scatting (DLS) results and Scanning electron microscope (SEM) images in Figure 1a, the average diameter of the NPs suspended in BG11 culture medium dramatically increased to approximately 450 to 650 nm
Summary
Heavy metals are discharged into aquatic ecosystems from various industries, such as the textile, mining, electroplating, and metallurgical industries. Heavy metals pose a serious threat to human beings and aquatic ecosystems because of their persistent toxicity, bioaccumulation, and biomagnifications through the food chain. A class of organisms forming the basic nourishment for the food chain, are commonly used as model organisms to study the toxicity of heavy metals [2]. The expansion of nanotechnology has resulted in subsequent increased release of nanoparticles (NPs) into aquatic environments during the cycle of manufacturing, transportation, consumption, and disposal [5]. Among these NPs, nano-sized titanium dioxide (nano-TiO2) is one of the most popular engineered nanomaterials increasingly being incorporated into various consumer products. The negative environmental effects of NPs have drawn significant attention in recent years [6,7,8]
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