The TiO2 NPs were semi-spherical, 81% anatase, 19% rutile, and 15-30 nm in size. While the primary size of NPs was in the range from 15 to 30 nm, the NPs tend to quickly aggregate in seawater. [42] To produce 10 g L-1 stock dispersions, 10 mg of NPs were added to 1 ml of filtered (0.2 m Millipore) natural seawater, sonicated for 30 min, vortexed briefly, and diluted to 10 mg L-1 with filtered natural seawater.