Effects of myo-inositol hexakisphosphate, ferrihydrite coating, ionic strength and pH on the transport of TiO2 nanoparticles in quartz sand

Evaluating the fate and transport of nanoparticles (NPs) in the subsurface environment is critical for predicting the potential risks to both of the human health and environmental safety. It is believed that numerous environmental factors conspire to control the transport dynamics of nanoparticles, yet the effects of organic phosphates on nanoparticles transport remain largely unknown. In this work, we quantified the transport process of TiO2 nanoparticle (nTiO(2 )) and their retention patterns in water saturated sand columns under various myo-inositol hexakisphosphate (IHP) or phosphate (Pi) concentrations (0-180 mu M P), ferrihydrite coating fractions (lambda, 0-30%), ionic strengths (1-50 mM KCl), and pH values (4-8). The transport of nTiO(2 ) was enhanced at increased P concentration due to the enhanced colloidal stability. As compared with Pi at the equivalent P level, IHP showed stronger effect on the electrokinetic properties of nTiO(2 ) particles due to its relatively more negative charge and higher adsorption affinity, thereby facilitating the nTiO(2 ) transport (and thus reduced retention) in porous media. At the IHP concentration of 5 mu M, the retention of nTiO(2 ) increased with increasing lambda and ionic strength, while decreased with pH. In addition, the retention profiles of nTiO(2 ) showed a typical hyperexponential pattern for most scenarios mainly due to the unfavorable attachment, and can be well described by a hybrid mathematical model that coupled convection dispersion equations with a two-site kinetic model and DLVO theory. These quantitative estimations revealed the importance of IHP on affecting the transport of nTiO(2 ) typically in phosphorus-enriched environments. It provides new insights into advanced understanding of the co-transport of nanoparticles and phosphorus in natural systems, essential for both nanoparticle exposure and water eutrophication. (C) 2019 Elsevier Ltd. All rights reserved.