Surface charge controls the fate of Au nanorods in saline estuaries.

This work reports the distribution of negatively charged, gold core nanoparticles in a model marine estuary as a function of time. A single dose of purified polystyrene sulfonate (PSS)-coated gold nanorods was added to a series of three replicate estuarine mesocosms to emulate an abrupt nanoparticle release event to a tidal creek of a Spartina -dominated estuary. The mesocosms contained several phases that were monitored: seawater, natural sediments, mature cordgrass, juvenile northern quahog clam, mud snails, and grass shrimp. Aqueous nanorod concentrations rose rapidly upon initial dosing and then fell to stable levels over the course of approximately 50 h, after which they remained stable for the remainder of the experiment (41 days total). The concentration of nanorods rose in all other phases during the initial phase of the experiment; however, some organisms demonstrated depuration over extended periods of time (100+ h) before removal from the dosed tanks. Clams and biofilm samples were also removed from the contaminated tanks post-exposure to monitor their depuration in pristine seawater. The highest net uptake of gold (mass normalized) occurred in the biofilm phase during the first 24 h, after which it was stable (to the 95% level of confidence) throughout the remainder of the exposure experiment. The results are compared against a previous study of positively charged nanoparticles of the same size to parameterize the role of surface charge in determining nanoparticle fate in complex aquatic environments.