Investigation of the Effect of Engineered Nano-Titanium Dioxide on Heavy Metals Contamination in Aquatic Environments

Due to strong oxidizing properties, titanium dioxide or titania nanoparticles are widely used in the water and wastewater treatment industry to remove or reduce various contaminants. The extraordinary properties of titania have led to the neglect of its side effects on the environment, especially on the aquatic ecosystems. In this study, different concentrations of titania nanoparticles were used over a period of 96 hours in lab scale to evaluate their impact on the heavy metals distribution in an aqueous media. The sediment samples of Anzali wetland contaminated with heavy metals were applied in all experiments. The results revealed that arsenic (As) was strongly affected by titania nanoparticles and its exchangeable bonds were desorbed from the sediment. Subsequently, 50 ppb titania led to concentration of As in the water column, which increased from 0 to 9 ppb. In addition to As, nickel (Ni) was desorbed from sediment through the separation of its organic bonds. On the other hand, 50 ppb titania reduced the concentrations of manganese (Mn), copper (Cu) and zinc (Zn) in the water column from 42, 32 and 29 ppb to 17.7, 2.87 and 20.9 ppb, respectively. According to the chemical extraction analysis, heavy metals adsorption in the sediment was mainly in the form of exchangeable and sulfide bonds. However, lead (Pb) and cobalt (Co) were not affected by titania and exhibited a conservative behavior.