The binding of phenanthrene to engineered silver and gold nanoparticles

The steadily rising production and use of engineered nanoparticles (ENP) leads to their entry into the aquatic environment. In addition to the various adverse effects that have been seen for different organisms, ENP are suspected to influence the transport, bioavailability and toxic properties of a range of environmental contaminants that may adsorb to their surface. In this study, the binding properties of the polycyclic aromatic hydrocarbon phenanthrene to stabilized silver and gold ENP were investigated using a novel mass balance based single-equilibrium approach. Only citrate coated gold ENP (AuNP(CIT)) were found to bind phenanthrene. No binding was observed for polyvinylpyrolidone coated silver ENP (AgNP(PVP)) nor citrate coated silver ENP (AgNP(CIT)) suggesting that the properties of the core material have a major influence on binding reactions. A binding coefficient K(b) was defined as the ratio between the concentration of phenanthrene associated to the AuNP(CIT) and that freely dissolved in the exposure medium. Temperature was not seen to significantly influence K(b) within an environmentally relevant range (4-25 °C). The presence of methanol significantly reduced or prevented the formation of the AuNP(CIT)-phenathrene complex. Results suggest that the binding is a low energy physio-sorption, likely associated to a partial displacement or specific arrangement of the citrate capping on the gold core.