Behavior of Titanium Dioxide Nanoparticles in Three Aqueous Media Samples: Agglomeration and Implications for Benthic Deposition

Abstract

Predicting the fate of nanoparticles in aquatic environments requires knowledge of how these materials interact with the organic and inorganic constituents in aqueous media. This work explored the behavior of three types of titanium dioxide nanoparticles (rutile and anatase) in natural seawater, artificial seawater, and Milli-Q water and determined the percent incorporation of the nanoparticles in marine snow, an important hetero-aggregation in the ocean. Dynamic light scattering, zeta potential, field-emission scanning electron microscopy, and inductively coupled plasma mass spectrometry were used to examine the particles over three time intervals (<0.2, 1, and 72 h). Analyses determined that anatase, UV-Titan M212, and Aeroxide P25 nanoparticles had a higher agglomeration potential in natural and artificial seawater than in Milli-Q water. The weighted average diameter (weighted size) of the anatase and P25 agglomerations remained relatively unchanged over time in all three water types. The Titan nanoparticles, however, demonstrated a significant decrease in weighted size at 72 h in natural and artificial seawater, but not in Milli-Q water. This decrease in size was associated with the concentration of resident bacteria. In laboratory experiments, all three titanium dioxide nanoparticles were readily incorporated into marine snow, with incorporation efficiencies increasing over 72 to 120 h, reaching a maximum mean value of 95 % after 168 h. This study emphasizes the importance of using environmentally relevant media to better understand the behavior and fate of nanoparticles, including deposition to the sediments and capture by benthic organisms, in marine environments.